Questons about cams, flow, and velocity

On a board to which I suscribe a guy said his ideal cam was 220/230, .600/.600 with a 112 LSA with 1.5 rockers. He didn't gve details about his engine, even though I asked. What would be the ideal scenario to use this cam? What kind of advertised duration would be good to keep this cam barely in the smog legal range? Could this cam work as a flat tappet grind?

Does it matter if a cam has the exact same specs if it is a roller or flat, hyrdraulic or solid?

Instead of more duration on the exhaust valve could you use more lift? Can you use more lift in general since the exhaust valve is typically smaller?

What controls picking the right size valves? Is there a minimum/maximum ratio difference between intake and exhaust valves?

Is it a safe assumption that larger valves require a larger chamber? Is there a way to quantify the intake runner to chamber ratio? Would it matter?

What dimensions are required to determine the maximum lift you can get out of a cylinder head? How would a head/cam work if the cam was set to give you maximum lift up to about 3500 rpm and tapered down to about 75% of that lift by 6000 rpm? Would you need a big or small intake runner? The lift couldn't be bigger at the end than the beginning could it?

Does a lower head angle (23, 20, 18, 15) work better towards a larger or smaller bore? Does the lower head angle allow for higher or lower lift?

If the intake velocity is as important as the flow, how does one compute it? How do you determine how much flow and at what velocity you need it to accomplish x horsepower or torque?

At 100% volumetric effiency are you getting all of the flow you can out of a head, getting as much flow as the velocity will allow, both or neither?

How do you match the intake manifold to the head to get the right flow/velocity?

So many questions.......

On a board to which I suscribe a guy said his ideal cam was 220/230, .600/.600 with a 112 LSA with 1.5 rockers. He didn't gve details about his engine, even though I asked. What would be the ideal scenario to use this cam? What kind of advertised duration would be good to keep this cam barely in the smog legal range? Could this cam work as a flat tappet grind?

Ideal for what motor? How he's going to get .400 lobe lift in that duration is beyond me. Almost no way possible to make that a flat tappet cam unless the journal diameter and lifter diameter are freeking HUGE. Any duration that low with a 112LSA is far from ideal.


Does it matter if a cam has the exact same specs if it is a roller or flat, hyrdraulic or solid?

They usually can't have the same specs due to the lifter differences and limitations.

Instead of more duration on the exhaust valve could you use more lift? Can you use more lift in general since the exhaust valve is typically smaller?

I don't know why that guys cam has more exhaust duration. You can use lift and lobe aggressiveness to get more AREA but it comes at a cost.

What controls picking the right size valves? Is there a minimum/maximum ratio difference between intake and exhaust valves?

For me..... Biggest intake valve I can fit in the heads. Some of the best guys out there say about 53% of the bore size is about as big as you can go. Exhaust valve size depending on the application can differ, I like good exhaust flow on a set of heads that are ment to go in a street motor.

Is it a safe assumption that larger valves require a larger chamber? Is there a way to quantify the intake runner to chamber ratio? Would it matter?

Depends on the chamber shape and design but most times a larger valve will create a larger chamber on something like a 23deg chevy head.

Intake runner to chamber ratio......... never heard of that one before. No correlation.

What dimensions are required to determine the maximum lift you can get out of a cylinder head? How would a head/cam work if the cam was set to give you maximum lift up to about 3500 rpm and tapered down to about 75% of that lift by 6000 rpm? Would you need a big or small intake runner? The lift couldn't be bigger at the end than the beginning could it?

I'm confused.... why would you want less valve opening with more RPM the airflow demands are increased with RPM so you want MORE valve lift and duration.

Max lift is more a variable of the valvetrain than anything.


Does a lower head angle (23, 20, 18, 15) work better towards a larger or smaller bore? Does the lower head angle allow for higher or lower lift?

A canted valve head like a Cleveland or BBC head would work the best on a smaller bore. A BBC is not the best example because those things love big bores to make power with. The problem with them is the high valve angle and the huge chambers, both of those do not play well with a small bore.

Usually a lower head angle comes with motors that are running more lift, but that's due to the fact that the heads really like to flow at higher lifts.


If the intake velocity is as important as the flow, how does one compute it? How do you determine how much flow and at what velocity you need it to accomplish x horsepower or torque?

Well too much velocity is really the problem. Too high of port velocity can choke a motor off. Most guys go way to freaking over board on velocity and small ass ports when it's probably hurting them more than it's helping.

Do a search on MaxRaceSoftware (his screen name) and velocity and you will find a good amount.


At 100% volumetric effiency are you getting all of the flow you can out of a head, getting as much flow as the velocity will allow, both or neither?

Well in the 100% VE range you are getting into intake tuining helping you and exhaust tuining.

How do you match the intake manifold to the head to get the right flow/velocity?

The intake manifold is just a port extension you treat it like part of the cylinder head but I have seen cases were the rules restrict you so much that a larger port on the manifold is a good thing.

The area and the length of the manifold is as important or more important than the flow..... Velocity isin't a huge concern because it never gets to a choke point in a good intake manifold.

Hope that helped some..... Some of these things don't really go together well so it's hard to answer because there is no real connection between the two, or you worry about something else over the problem at hand

Bret

Ideal for what motor?

That is what I am asking... under what circumstances would one want to use this cam?

In the Lingenfelter book he mentions a 219/219 .503/.525 with a 112 LSA cam. Is there really that much difference between the two cams? Doesn't the one above just open a bit farther?

They usually can't have the same specs due to the lifter differences and limitations.

That is understood, but the question still remains since one can only go so large, and one is even more restricted if trying to pass the sniffer. If one is taking emissions into consideration how much more power and torque can one generate from a roller cam than from a flat tappet cam? If the specs end up the same it doesn't seem like it would be worth to spend more money on the roller. I am not stating facts here. I'm trying to think through this and discover what I am missing in my understanding.



I'm confused.... why would you want less valve opening with more RPM the airflow demands are increased with RPM so you want MORE valve lift and duration.

The typical statement is that you lose torque to gain horsepower. I was trying to figure a compromise that allows you to keep the torque and the horsepower. The thought was that with a smaller intake runner you could keep the velocity up at low rpms while the cam/chamber come together better at higher rpm allowing the flow to make the power there.

What is the typical maximum valve lift for a 23 degree head?

If you have high port velocity and corresponding fuel mixture all that is needed is the appropriate spark, right? I thought that was part of the reason for EFI - to accurately match the air/fuel ratio and add spark at the right time. I could see that this could be a challenge with a carb, but I was guessing that EFI takes care of all of that.

Intake runner to chamber ratio came up because I see some heads with the same chamber but a different intake runner size.

Big chamber + big runner = big displacement at high rpm
small chamber + small runner = small displacement at low rpm
small chamber + big runner = ?
big chamber + small runner = ?

Has anyone quantified a relationship of port velocity to power? Is it on a bell curve?

Well in the 100% VE range you are getting into intake tuining helping you and exhaust tuining.

That is why I am trying to understand this stuff so I can accomplish proper intake and exhaust tuning.

I am not really trying to fit any rules class in terms of racing. As long as the engine fits in the car, and passes the hose up the exhaust test I'm cool.

Speaking of which, can a person design an engine around certain emissions numbers? How much is proper fuel/air ratio vs. mass of fuel/air consumed, vs. timing?

Thanks,
Jason

Well I guess this is going to be my easter fun.....

That is what I am asking... under what circumstances would one want to use this cam?

Well it doesn't exsist really, so no point in theorizing on it. If I don't know the application I have no clue what the motor wants. Cams are designed for the motors not motors designed for the cams.


In the Lingenfelter book he mentions a 219/219 .503/.525 with a 112 LSA cam. Is there really that much difference between the two cams? Doesn't the one above just open a bit farther?

Well the big difference that the cam has more exhaust duration and more lift.

No clue on the lobes aggressiveness and the shape of the lobes.


That is understood, but the question still remains since one can only go so large, and one is even more restricted if trying to pass the sniffer. If one is taking emissions into consideration how much more power and torque can one generate from a roller cam than from a flat tappet cam? If the specs end up the same it doesn't seem like it would be worth to spend more money on the roller. I am not stating facts here. I'm trying to think through this and discover what I am missing in my understanding.

A roller will have less overlap for a given duration and LSA to start with, in a situation where you have to meet emissions and make power a roller is the only way to fly. Basically you will walk all over a flat tappet cam in this situation with a roller. Specs might look the same but they are not even close in when you look at the lobe profiles.

http://www.compcams.com/Technical/CurrentCatalog/HTML/18-19.asp

Look at the pictures of the lobes, compare a roller to a flat tappet and you will see the huge difference.

I wouldn't even think of putting a flat tappet cam in a emissions car unless I didn't care what kind of power it makes.



The typical statement is that you lose torque to gain horsepower. I was trying to figure a compromise that allows you to keep the torque and the horsepower. The thought was that with a smaller intake runner you could keep the velocity up at low rpms while the cam/chamber come together better at higher rpm allowing the flow to make the power there.

The chamber doesn't have to do with anything but how fast the fuel gets burned in there, faster burn = lower timing numbers to produce max power.

A bigger chamber just drops your compression ratio.... Where does it's size relate to making power? If you change the compression ratio you will change the power.

http://auto.howstuffworks.com/engine.htm

Try that out for size.... I know it sounds basic but you gotta get why a combustion chamber doesn't have anything to do with RPM before we get into other things.

You want to make the most average power in the RPM band that the motor will run. I don't really think you give up TQ to gain HP in situations you just change the shape of the curve.

BTW a emissions cam is not going to be a big cam which is what you are talking about when you want a cam for the high end.

To me there is a falacy of the small ports and big cams making a street driveable car..... If you ever compared that theory to something like Lloyd is putting out on LT1 stuff you would think he couldn't make any power with the big ports he has and the small cams. The combination makes more power than the small port big cams with just the opposite and they drive AWESOME. Kinda proves that whole thing wrong.


What is the typical maximum valve lift for a 23 degree head?

Depends on the type of cam and application. OEM = .400-.500" lift, Crazy Drag Race stuff = .800, Good Street Performance Motors = .550-.600


If you have high port velocity and corresponding fuel mixture all that is needed is the appropriate spark, right? I thought that was part of the reason for EFI - to accurately match the air/fuel ratio and add spark at the right time. I could see that this could be a challenge with a carb, but I was guessing that EFI takes care of all of that.


EFI is there to gain fuel economy and performance in a emissions friendly application. I don't get how the high port velocity plays into that, high port velocity is not going to help emissions etc....


Intake runner to chamber ratio came up because I see some heads with the same chamber but a different intake runner size.

Big chamber + big runner = big displacement at high rpm
small chamber + small runner = small displacement at low rpm
small chamber + big runner = ?
big chamber + small runner = ?

CHAMBERS ARE A SIZE TO GET CERTAIN COMPRESSION RATIOS!!!! THAT'S IT!!! PERIOD.

There are other reasons for chamber sizes and shapes but you need to get that point first.

If you look at how compression ratios work then you will understand why a bigger motor has a bigger combustion chamber.


Has anyone quantified a relationship of port velocity to power? Is it on a bell curve?

Go do a search on MaxRaceSoftware again..... It's over your head at this point but he's done a ton of work on this.



That is why I am trying to understand this stuff so I can accomplish proper intake and exhaust tuning.

Intake and exhaust tuning has nothing to do with port velocity and chamber sizes it's a whole different ball game. The threads on intake manifolds on advanced tech are pretty in depth on this.


I am not really trying to fit any rules class in terms of racing. As long as the engine fits in the car, and passes the hose up the exhaust test I'm cool.


The emissions test is the hardest part of this.... if you have emissions put a blower on the car it's easier to make power that way.


Speaking of which, can a person design an engine around certain emissions numbers? How much is proper fuel/air ratio vs. mass of fuel/air consumed, vs. timing?


The OEM's do all the time.

Timing is what the motor needs, it will tell you that.

Proper A/F is 14.7:1 or leaner.


Ken and Fred...... I don't know how advanced tech this is, so put it where you see fit, but I don't know where that's going to be.

That is what I am asking... under what circumstances would one want to use this cam?

Let me suggest you make the cam the absolute last part you pick for an engine. You will never design an engine perfecltly around a cam, but its relatively easy to design a cam around a complete engine (shortblock/heads). When I say last I say that exaggeratively, since obviously you want to pick your valvesprings and such after you know what the cam looks like.

Also, agreeing with Bret, that cam doesnt sound right at all, that would be a wicked solid roller, and a pointless one IMO. To get .600" of lift with 1.5 rockers with that little duration seems almost impossible unless it is a solid cam. That doesnt really sound like an ideal cam for any combination except maybe a Wankel :D

In the Lingenfelter book he mentions a 219/219 .503/.525 with a 112 LSA cam. Is there really that much difference between the two cams? Doesn't the one above just open a bit farther?

There could be a hell of a lot more differences than you can see. Valve opening and closing points are extremely important in what a cam does in an engine. The lingenfelter cam speaking basically is just 10* shorter duration on the exhaust side, and about the same on the intake side. And the lift on the lingenfelter sounds more like the correct lift for that duration cam.


The typical statement is that you lose torque to gain horsepower. I was trying to figure a compromise that allows you to keep the torque and the horsepower. The thought was that with a smaller intake runner you could keep the velocity up at low rpms while the cam/chamber come together better at higher rpm allowing the flow to make the power there.

"It is better to make torque at higher RPMs so that you can take advantage of gearing." Very important statement!

Incase you forgot, HP is a function of torque. The higher in the rpm range you make torque the more HP you will have. You can lose torque from your peak torque rpm and still keep gaining HP if the rpms are high enough. No car with an equal amount of torque at 3000 as another car at 6000rpms will win a race. Since 300lb/ft at 3000 comes out to 171hp, while 300 at 6000 comes out to 342hp. And as long as the higher rpm vehicle is geared correctly it will spank the 3000 rpm car.

What is the typical maximum valve lift for a 23 degree head?

Maximum valve lift has little to no correlation to type of heads except how deep you could possibly cut the spring pockets. Max valve lift is mostly determined by PTV (piston to valve) clearance, also spring choice plays a huge part in lift limits.

If you have high port velocity and corresponding fuel mixture all that is needed is the appropriate spark, right? I thought that was part of the reason for EFI - to accurately match the air/fuel ratio and add spark at the right time. I could see that this could be a challenge with a carb, but I was guessing that EFI takes care of all of that.

A lot of velocity doesnt do you any good if there isnt enough air/fuel there to feed the engine at higher rpms. A ton of velocity will do awesome at really low rpms, but velocity and flow are kind of catch 22s when talking in relationship to one another. If someone could design a perfect head it would have a ****load of velocity and flow at all lifts, but the world just doesnt work that way. The only real way to correct velocity problems is to add displacement. If you have a crapload of flow, but not much velocity, sucking more air through the ports will increase velocity, but you then could be short on flow if you increase CI too much. This is why forced induction works so well :D Give the air a bunch of room to go through the head and compress the **** in there and you make power. Have you ever seen the ports on a top fuel head, you could fit your entire fist all the way through them, and theyre only 500ci, but those blowers are supplying enough air for a 14 cylinder engine at 71ci per cylinder, while theyre cylinders are only 62ci.

Dam, I hate typing long responses, cuz guys like Bret can type faster about this stuff than I can :(

Bret...How do you feel about larger combustion chambers flowing better than smaller ones? Not necessarily a wider CC where you can fit bigger valves without shrouding, but just deeper ones. Just use an LT1 for an example, comparing a stock 58cc to a milled to hell 50cc.

Max valve lift is mostly determined by PTV (piston to valve) clearance, also spring choice plays a huge part in lift limits.

Max valve lift happens so far away from the piston it has no effect. Think about that one man. LSA and Duration play a bigger role in P to V than anything.

Spring choice is the main thing that prevents valve lift.

Actually a bigger chamber can hurt flow and help it. The AFR's are a good example of a bigger one helping, the 76cc chamber AFR's flow better than the smaller chamber ones. OTOH a small chamber that unshrouds the valve faster is even better, or a angle milled head. Look at Kaases Engine Masters heads, no chambers in them at all.

As for the velocity thing we could go on all day about that.... someone should find the thread where racerdude and Mindgame talk about it, great thread.

Bret

Max valve lift happens so far away from the piston it has no effect. Think about that one man. LSA and Duration play a bigger role in P to V than anything.

True. But they kind of work hand in hand. Say you want to run a .700 lift cam, but at the duration/lsa desired the valve hits the piston even before max lift obviously, you dont want to change the duration/lsa so dramatically that it screws the cam all up. So you would either have to cut lift down, or more likely cut reliefs in the pistons to accomodate the valve. Only other thing you could do is change the ramp rate of the cam, but most dont really have the ability to screw with that.

I apologize guys. I thought I had come up with some really good questions. I should have read more on the board than I did.

So chamber is only related to compression ratio. Intake runner size helps determine velocity, but too much means a low rpm engine. Low duration high lift cams are unrealistic. Pick the engine first then the cam (I'm still kind of stuck on this one, as the application range gets controlled by this part. The heads and pistons pick the compression ratio and the cam picks the operating range, right?)

I'll go over to the 3rd gen section and try again.

Jason

Your getting real close with that man..... best thing you said so far.

Actually the cam and compression ratio are really tied into each other as well. That's the Dynamic Compression Ratio thing we talk about.

Your operating range will effect the cam, compression and intake port size or quality.


Jon, you're right usually lift goes with duration and LSA but a big rocker arm can change all of that. Look for a view of a engine in action like on the how stuff works link and see where the exhaust valve is closing and the intake valve is opening and where the piston is. That will explain most of it, once you see that you go A HA! in terms of PTV. A earlier IVO and later EVC effect p to v more than anything.

Bret

So chamber is only related to compression ratio. Intake runner size helps determine velocity, but too much means a low rpm engine. Low duration high lift cams are unrealistic. Pick the engine first then the cam (I'm still kind of stuck on this one, as the application range gets controlled by this part. The heads and pistons pick the compression ratio and the cam picks the operating range, right?)



Jason

For the most part yes. But heads have a big part in operating range along with the cam. Biggest reason you pick the cam last is you cannot design a cam without head information. Basically, buy the best heads you can afford, NOT TOO BIG THOUGH, in the SBC case, if you can afford SB2s or another 12* head buy those, then pick a cam. If you can only afford or are limited to 23* heads then those would require a completely different cam to make the combination work correctly. Remember an engines performance is determined by a combination of things, not just the cam, Ill repeat the most important thing to know about engine building, AN ENGINE IS A COMBINATION OF PARTS WORKING TOGETHER.
IE: You could have the sweetest heads, stoutest shortblock, best designed cam, but if youre valvesprings arent picked correctly it wont do crap.

Dang, it happened again.
Bret, I understand that, but changing the rocker arm affects how the cam acts on the valves in other ways besides lift right, I know its minimal, but its there. Also, are you saying that you never run into PTV clearance problems, I know speaking with Joe O. he spoke of running his valves within like .050 of the pistons, I guess this would only ever really be a problem with big crown dome pistons, but it has to be a factor in determining valve lift correct?

Given a 6500 redline, how far down the rpm band can a moderately well prepared engine go before it "runs like a dog"? How does a manual trans affect this?

Jason

running like a dog is relevant to the driver. I know people who thik that a 12 sec. street car is a dog and other's that would crap thier pants in a stock ls1 car.

a manual looses less hp through the drivetrain but requiers more driving skill and stock units are generaly weak. you are also able to keep the engine in a narrower power band so it can bennifit from a more peaky cam.

an auto requires the correct stall and generaly use a wider powerband. diff. cam profiles.

as for the 6500 red line the correct head depends on how many cubes the engine has. and the correct cam depends on the heads and everything else in the engine.

I don't know if you were asking this earlier or not but lift stays the same at all rpm. given the lifter's aren't pumping up diff at diff rpm's

Dang, it happened again.
Bret, I understand that, but changing the rocker arm affects how the cam acts on the valves in other ways besides lift right, I know its minimal, but its there. Also, are you saying that you never run into PTV clearance problems, I know speaking with Joe O. he spoke of running his valves within like .050 of the pistons, I guess this would only ever really be a problem with big crown dome pistons, but it has to be a factor in determining valve lift correct?

Jon,

Yeah you have to have lobes to work with the rocker arms when they are way up there like a 1.8 or higher.

More rocker adds some duration to the cam at .050 but nothing major and the valve action will be faster as well. Also higher loads on the pushrod and lifter from the higher ratio etc.....

You only run into P to V problems when you have early IVO and late EVC events. Tight LSA can do that, and yes I run into those issues. I generally run more lift on cams than Joe O does (from what I have seen).... PTV comes into play a lot on LT1 and LS1 stock bottom motors.

Jason,

You can run a street motor to 6500rpm easy. Idle, drive etc... perfect.

Bret

You only run into P to V problems when you have early IVO and late EVC events. Tight LSA can do that, and yes I run into those issues. I generally run more lift on cams than Joe O does (from what I have seen).... PTV comes into play a lot on LT1 and LS1 stock bottom motors.



Bret

Oh, I was talking about his personal car, I dont know about his forsale cams, mine wasnt anywhere close. Except when I accidentally installed it 38* advanced, then the ITV had a major problem with the piston. :(

Also, Ive been curious about how rocker ratio changes things around in more detail, is there anywhere I can learn more indepth about this?

"Also, Ive been curious about how rocker ratio changes things around in more detail, is there anywhere I can learn more indepth about this?"

What you want to know????

Bret

Well, you said it changes duration slightly @.050. How does it do this, and how does it change with different ratios and such. And also the opening/closing speed increases you say...more in depth?

How do you know what ratio rocker you want. I know we are limited on stud rockers just because of stability, but do you want to run the biggest ratio possible while maintaining stability?

IMO...it doesn't change the duration, as its rated as tappet lift, not valve lift. It will however change the duration of the valve being open .050 because it will take less lobe to lift the valve that far.

Good answer....

The opening and closing speed increases because the valve is moving a larger amount in the same amount of time. Remember duration is measured in degrees but the Webster's definition of duration is that it's a period of TIME!

Cup guys run stupid high ratios.... 2.0:1 etc... You are limited on rocker ratio mostly by the contraints of your valvesprings. If you run it in to coil bind you are screwed.

The other problem is that a spring with 400lbs open with a 1.5 rocker only puts 600lbs on the pushrod and lifter, and a 2.0:1 Rocker puts 800lbs on the same pushrod and lifter. You start really stressing things bad there. You have to worry about that side of the system as well.

Yeah stability is the key, but valve lift kills springs. The less valve lift the less you hurt the springs, more life you get out of them.

Bret

So one might pick a smaller cam, but jack up the lift by changing the ratio. Does this do something a different cam can't do?

Jason

So one might pick a smaller cam, but jack up the lift by changing the ratio. Does this do something a different cam can't do?

Jason

no you could possibly get a differnt cam with the same specs as the prev cam using the higher ratio rocker with a lower ratio rocker it would just have a little more aggerssive profile and tad more lift and duration a .050 but same total duration.

So why would one buy rockers instead of a different cam? Don't the rockers cost more?

Thanks,
Jason

mostly it is to improve on an already exhisting combo. or better an off the shelf cam instead of haveing a custom one ground. also if you find one with the duration you want but would like a little more lift and are going to buy rockers any way. why not?

Look at the pictures of the lobes, compare a roller to a flat tappet and you will see the huge difference.
Bret, (we) both know it is not fair to compare lobes of a roller cam to the lobes of a flat tappet cam. Even having the two cams ground to provide identical valve action would require the roller lobe to appear far more aggresive due to the differences in the shape of the lifter, and how/where the lifter surface makes contact on the lobe of either cam. You threw that in there, just to see whom was paying attention, right? Did I pass? :)

Also, the link to the CC site, displaying the brief tutorial on the differences of the lobe shapes of the different liftered cams is without question, misleading for the reasons given above. CC basically compared apples to oranges. To bad they (CC) didn't display a flat tappet to roller lobe comparo for two cams of identical valve action. Then they would have taught someone something. All they accomplished was to over dramatize the issue.

True.....

The aggressiveness of the average flat tappet cam is not close to a roller, but something like a Cup cam would be right there.

I would actually like to see the physical lobes in cross section like that of a 270deg cup lobe and a solid roller comparison. The valve motion is one thing the lobe shape is another.... the really aggressive flat tappet cams have some huge bearing journals to fit all this in there.

Hey rocker arms always help get some nasty valve motion, which is what we are really worried about here.... just puts big loads on the camshaft and lifter interface on a flat tappet. There are some smart people who have worked that all out though..... Not getting into that! Just imagine.... a 200-260lbs seated pressure on a flat tappet and a 2.0:1 rocker arm! 400-500lbs on the lifter face when you are on the base circle! We aren't talking about Schubeck lifters doing this either. Super Secret $hit basically. Probably using a DLC and some trick cam cores.

Basically the average guy doesn't need to know this stuff, it's just going to confuse them because they will want to do it.

Bret

Jason

I'll steal a quote from Bret here, "look at the whole valvetrain as a system".

Lets say you are starting from scratch and designing for the same actual valve lift but considering doing it 2 different ways. a) with with a smaller cam and a higher ratio rocker. b) with a larger cam and standard ratio rocker. With the right lobes available you could achieve identical actual valve timing events (the comp XE lobes of different lifts allow for close to this)

a) will have the advantage that the lifter and pushrod will only will be undergoing the smaller displacements of the smaller cam and therefore have smaller inertial forces. I.E. the valvetrain will appear slightly lighter. If you use the same springs you will end up with the same spring forces because you have the same actual lift at the valve. Within the limits of whats available off the shelf, you could get away with marginally less spring pressure to control the 'lighter' valvetrain. The drawback is that the higher your ratio the poorer your geometry and you start to have losses there.

b) will have better geometry but the vavletrain will appear to have more mass because the lifter and pushrod are moving further and therefore have larger accellerations/forces. the opposite of a.

In both cases the valve, spring, and retainers undergo the same motion and therefore have the same resultant forces.

Like anything in mechanical design, your making a tradeoff between designs a and b. Remember, i was talking only about theoretical designs here. Sometimes your limited by whats available off the shelf, practical installation, longevity, ect. Either way the performance difference even with totally custom springs available is going to be very small between designs a and b and in practice, but it does explain the general evolutionary trend to higher ratio rockers.

-brent

since the rocker are is just a basic lever the A example will have a greater force on the cam lifters and pushrods because the pushrod is moved closer to the fulcrom point. so that extra force with less mass should be more damaging than a little more mass with a more effecient lever (lower ratio rocker) like Bret said opening force is multiplied with the higher ratio. now which would be harder to move or more damaging. remember just because they have the same opening pressure doesn't mean they have the same pressure on the pushrod lifters or cam. opening pressure is measured where the rocker arms meets the valve then multiplied by the rocker arm.

I didn't even have to say that stuff guys.... Thanks.

One of the biggest problems with larger ratio stuff is deflection.... You can also have more aggressive lobes with less lift and more rocker arm and you will have even more loads in terms of velocity, acceleration, jerk, V^4, V^5, V^6 due to the very aggressive traits of the lobe and the fast action and load mulitplication of the rocker arm.

It can get rather confusing here. The lobe determines a lot, but the rocker is also part of that system.

One of the reasons why the beehives work so well is the lower mass, as Brent said, less mass needs less force to control it. Less force means less deflection and more accurate valvetrain motion.

Bret

From your experience is there a lift point where the tradeoff leans one way or the other? I ask because I just ordered a rotating assembly that has 30cc dished pistons. If I could use 64cc heads and get 0.600" lift with the appropriate safety clearance cool. I haven't picked the heads yet.

So I am picking the cam last.

For flow I need the average for the head between 0.400" and 0.600". Highest average goes to the top of the list.

To get the velocity I have to call the head manufacturer and ask for the runner cross dimensional area? I plug the area into the velocity equation, and that gives me fps or MACH?
The highest velocity without going over .550 MACH goes to the top of the list.

I compare the list for the heads that have the overall best picture of flow and velocity.

Is this right so far?

So far I've figured out that I need 250-270 cfm and a minimcross sectional are of 2.16.

How does the runner length affect this cross sectional area. Do you have to go with a 200+cc runner to get the flow?

I believe you are putting far more prominence in #s, let alone particular #s than necessary.

If the goal has a specific numerical measure and is derived by assembling parts with specific dimensions to generate those specific number how could numbers not be important? How does one compare two products to determine the desired performance/value decision?

I am looking for a workable approach If there's a different one, let me at it.

If the goal has a specific numerical measure and is derived by assembling parts with specific dimensions to generate those specific number how could numbers not be important? How does one compare two products to determine the desired performance/value decision?
And I thot I could post intellectual (well, in my mind anyway) statements. :bow:

I am looking for a workable approach....

I've no problem with that. What I was attempting to state was; any given head flow number isn't 'end of the world' critical. It isn't the #s you get, but the (quality of) flow, in an operating engine environment that really matters. With that stated, if you prefer, attempt to choose a porter with a repitable backround, you'll get #s you'll be pleased with, and can live with.

I think hat is where the wrinkle comes in. From the little that I have observed the porter/machinist is like the drug dealer to the crack addict. I'm trying to stay away as much as possible. I've heard rumors of bills upwards of $1000.00 just to cut on the heads. At that rate I might as well go the the 18* heads with the smallest runner I can get. I would probably be over 500 without much more than matching the intakes and ports.

Even if I did plan extensive use of a head porter it would still make sense to get the as cast heads as close to the numbers as possible.

What this does point out is that maybe what I'm seeking is unrealsitic. It would seem that it shouldn't be so.

Consider:
$1400 heads
$1000 cam with lifters, and rockers,
$1200 rotating assembly
$1000 block prep work
$700 carb and intake
$1000 all the other stuff not mentioned

Edit:
The goal an engine that works best between 2500-6500 and has torque and horsepower peaks of 500 in that range.

Since I am trying to do the assembly myselff I should be right in the ball park of all those crate engines at the same level of output. $2000 more and it would probably make more sense to buy one. I wouldn't learn anything, but I could definitely say I blew a wad on someone elses's brains and folks would go "OOOOOOOO".

I'm new. I know I'm new, but that doesn't mean that I have to start with some funky 300hp 350. The same work and the same parts go into both.

Jason

crate engines . I wouldn't learn anything, but I could definitely say I blew a wad on someone elses's brains and folks would go "OOOOOOOO".

I'm new. I know I'm new, but that doesn't mean that I have to start with some funky 300hp 350. The same work and the same parts go into both.

Jason
:thumb: Youre only gonna learn by doing it.I applaud your approach.whenever you get stuck or cant do it yourself[machining,etc.] theres the pros to help.And the local vets and the guys here with exp.My first 350 was a 300 horser, but that was only for 2 days so we could smog,then it was epoxied bowties and a victor,and a monstrous roller.I learned alot,and the only casualties over 2 years were a cam and a couple pushrods.My buddies that were doing plain jane sbc/sbf learned how to assemble with plastiguage, and never did teardowns for upgrades or maintenance, so didnt really learn precision assembly or any useful tuning/bulding skills.Good luck.

I think hat is where the wrinkle comes in. From the little that I have observed the porter/machinist is like the drug dealer to the crack addict. I'm trying to stay away as much as possible. I've heard rumors of bills upwards of $1000.00 just to cut on the heads. At that rate I might as well go the the 18* heads with the smallest runner I can get. I would probably be over 500 without much more than matching the intakes and ports.

Even if I did plan extensive use of a head porter it would still make sense to get the as cast heads as close to the numbers as possible.

What this does point out is that maybe what I'm seeking is unrealsitic. It would seem that it shouldn't be so.

Consider:
$1400 heads
$1000 cam with lifters, and rockers,
$1200 rotating assembly
$1000 block prep work
$700 carb and intake
$1000 all the other stuff not mentioned

Edit:
The goal an engine that works best between 2500-6500 and has torque and horsepower peaks of 500 in that range.
Jason, if you go with 18° heads then bare ones will run you about $1300 unless you can find a deal. At that point you will have to add seats, guides, valves, springs, etc. They also require offset shaft rockers which are $1000 new and you should use offset lifters which are only available with solid rollers. You're talking about stuff that should make over 600hp if you half-ass the rest of the motor.

That is why I did Not choose to go with 18* heads.

If I were going to spend $1000 on porting on some $1400 heads then it would probably be better to get some $2400 heads to start and leave them alone. That's what I was saying...

500hp is not that hard if you know what you are doing.... The crazy thing is most crate motors are so cheap they are the best way to start for a short block on a SBC or BBC that unless you are going crazy I wouldn't build one. Hell I have a 383 short block in my shop now for a customer that he has about $2000 in with 4 bolt mains and a full Forged Eagle bottom end in. He's actually looking to sell it so right there you have your $2200 bottom end, without any work.

You can either work with a out of the box set of heads to get where you want to go, or get a set of cheap castings and have them ported. Sportsman II's can move some wind if done correctly, Canfield makes some nice cheap castings that kick ass......

Bret

500hp is not that hard if you know what you are doing.... The crazy thing is most crate motors are so cheap they are the best way to start for a short block on a SBC or BBC that unless you are going crazy I wouldn't build one. Hell I have a 383 short block in my shop now for a customer that he has about $2000 in with 4 bolt mains and a full Forged Eagle bottom end in. He's actually looking to sell it so right there you have your $2200 bottom end, without any work.

You can either work with a out of the box set of heads to get where you want to go, or get a set of cheap castings and have them ported. Sportsman II's can move some wind if done correctly, Canfield makes some nice cheap castings that kick ass......

Bret

agreed.

I'll add the vortec head to your list Bret. Bang for the buck, they're probably one of the best out there, not to mention, the aftermarket has plenty of complimentary parts for them.

-Mindgame

Yeah I was going to put that down but nobody really believes you since they are such magazine motor queens.... Hell the aluminum Fast Burns are awesome too... Hollow Stem valves, good chambers, good port volume etc...

Bret

Yeah I was going to put that down but nobody really believes you since they are such magazine motor queens.... Hell the aluminum Fast Burns are awesome too... Hollow Stem valves, good chambers, good port volume etc...

Bret

I know. :)

If they don't believe it then all I can say is... they don't get out to the track quite enough. I know guys running the Vortecs in extremely budgeted strip builds and turning very good times. One guy (local) is in the 9's now with a 385, NA, in a 64 Nova. Using the vortec heads and GM's Victor-like-copy intake manifold. Of course his 60' times are in the low 1.3 region too. ;)

And the FB's... yeah, killer heads for the $.

-Mindgame

Well those 1.3's help the car out prett well getting into the 9's!

Those heads are worth it just in the chambers alone.

Bret

Oh did I also mention, that car is on 10.5 tires. :)

Suspension mods include an underrider bar like Stock Elim. Fords use, subframe connectors and leaf springs, with two extra leaves on the passenger side. Low buck, no nonsense.

-Mindgame

Yeah I was going to put that down but nobody really believes you since they are such magazine motor queens.... Hell the aluminum Fast Burns are awesome too... Hollow Stem valves, good chambers, good port volume etc...

Bret
I agree they would make great heads for a street/ strip 500hp 400, im running a set,and the chambers are awesome, i went REAL lean on my spray tune by accident and it never pinged, just ate a plug.Theyve got my vote.The problem is, i cant find any flow #s for them out of the box.I have a cracked one i scrounged but havent had it flowed yet.I want to step up to a manly solid roller setup, but need to know if i want em ported a bit first, and all the guys i talked to havent seen a set yet.Theres a guy in MI who used to work for EPD[ :cool: ] that gets good #s, but hes the only one ive heard of.Then my dillema of keeping the hollow LT4 valves,and sacrificing a little flow, or going to 2.05s or so,and gaining weight.Ive even got a cracked one so the porter can try four different things to get the best balance of flow.

Damn, i just realized i am continuously semi-hijacking posts here, but the topics always seem relevant when im typing.I apologize and will go haze myself.

It seems that almost all of the heads work if you know what you are doing. The challenge is I don't. To make up for that I've tried to learn through the books and internet (and magazines) what to pick and what to walk by.

Every article or or internet build-up I've seen that has had AFR heads in them for a 383 or bigger has "shown" 500 hp on them. Getting them would be a no-brainer, as my 408 would give me 25 more cubic inches to work with to get there. The challenge is I don't want to wait 2-6 months for them. The next closest I've seen is with Victor jr aluminum heads and a matching single plane intake. Definitely magazine stuff, but may not really be workable because they don't start "making power" until 3500 rpm. Thanks to this website I now know why. I would sure like to know what they are like at part throttle, or if EFI could smooth out the low rpm stuff...

If I run a 64cc chamber that puts me at 11.59:1 combustion. From what I've read that is too much for 91 octane gas even with aluminum pistons. I've read a bit about dynmaic compression ratios and using a lager cam to bleed off some of the compression, but I don't know if that is just compensating for poor design, or just the way this all works. Unless informed otherwise that excludes the fastburns and the vortecs or any other GM head. If I could do it with heads for less than $1000 believe me I would. If the calculator is correct I need a chamber 70cc or bigger to get under 11:1.

It seems that almost all of the heads work if you know what you are doing. The challenge is I don't. To make up for that I've tried to learn through the books and internet (and magazines) what to pick and what to walk by.

Every article or or internet build-up I've seen that has had AFR heads in them for a 383 or bigger has "shown" 500 hp on them. Getting them would be a no-brainer, as my 408 would give me 25 more cubic inches to work with to get there. The challenge is I don't want to wait 2-6 months for them. The next closest I've seen is with Victor jr aluminum heads and a matching single plane intake. Definitely magazine stuff, but may not really be workable because they don't start "making power" until 3500 rpm. Thanks to this website I now know why. I would sure like to know what they are like at part throttle, or if EFI could smooth out the low rpm stuff...

If I run a 64cc chamber that puts me at 11.59:1 combustion. From what I've read that is too much for 91 octane gas even with aluminum pistons. I've read a bit about dynmaic compression ratios and using a lager cam to bleed off some of the compression, but I don't know if that is just compensating for poor design, or just the way this all works. Unless informed otherwise that excludes the fastburns and the vortecs or any other GM head. If I could do it with heads for less than $1000 believe me I would. If the calculator is correct I need a chamber 70cc or bigger to get under 11:1.


Your approaching your compression all wrong.

1. Pick your bore and stroke.
2. Then pick a head(and intake) with flow and port volume to support that bottom end in the rpm range you decided on.
3. Then pick your cam (or pay someone else to, it'll be worth it ;) ) to match the heads, rpm range, cubic inches, and intake you picked.
4. After all that, THEN you can start thinking about milling your heads and or selecting pistons so that your arbitrary static compression ratio gives you a good dynamic compression ratio close to but definitly below 9:1.

So I should pick the pistons last?!

Well I guess I better get the digital camera out to sell these on ebay.

Which is better - small chamber with dish pistons, or larger chamber with flat pistons? I understand the chamber does not make the power, but it affects the compression ratio a lot. With dish pistons can you get more lift out of the chamber? Doesn't that throw the quench away?