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.......

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.


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

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.

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.

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.

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.


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.


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 *** 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.


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

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

 

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?

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.



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?

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.....

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.

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.

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/Cu...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 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.


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


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....

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.

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.


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.

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.

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.

 

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

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.


"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.

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.

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 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 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

 

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

 

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

 

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

 

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?