Intake manifold runner lenght vs cam duration?

I saw this in an old HOTROD and was wondering what you guys thought about this. I think they basically said that with longer runner length less duration was needed bcuz of the decrease in the ability of the intake to flow well relative to the heads? Is there a direct corrilation between the two?

Thanks
Jeremy

There is no set rule really.

One thing that is interesting is to look at the 2 F-body motors.

LT1 3" runner
LS1 8" tappered runner

Now the best HR cams for the best average power up to 6500 are completely different for these two engines, and alot of it has to do with the intakes. The LS1 does have better heads, but don't worry about that here.

A LT1 can use a much smaller cam because the runners don't help to make any TQ for the motor. Where a LS1 can run a ton of cam and it still makes midrange TQ that's on par with a 383 LT1 due to the intake manifold.

So I would say that a LT1 with it's shorter runners needs less cam than a LS1 with it's longer runners.

But this is all a oversimplification of the complex system of a engine.

Bret

What about something like the TPI vs Stealth Ram? Would the same apply there since they are both avaliable for the sbc?

The big diff between the TPI and the Stealth Ram is that the the TPI is too long and the Stealth Ram is just about right.

A TPI is alot like a 5.0L EFI intake where the intake runners are too long to make any decent power over 5500 without a ton of cam.

The Stealth Ram has nice length runners, more like a single plane intake so it will use more cam than a LT1 intake and still make great midrange.


Bret

Can you put a big cam in a TPI and make hp without lossing lowend? I just dont see guys running much larger then a LPE 219 cam in even a 383 TPI.

The cam still does dictate what's going on, and with the long runners on a TPI you are really fighting them to try and make HP with a big cam, so the LPE cam is probably as big as what will work in the low RPM range those motors work in.

Bret

I was doing some more reading on the old Adv look at Hotcam. I got to wondering how intake runner lenght effects how well a small cam would work with a good heads and intake? Mostly I am working on building a 351w right now(yea I know I'm asking for Ford advice on a Chevy mb:o) with TFS TW heads and TFS 351(13.4" runners) intake. I was looking for a cheap cam to make good power, and was wondering how well a zz3 sized cam would work on the longer runner intakes? I can get a Crower cam that specs out at 202/211 112LSA .506/.528 w/ 1.6s, for dirt cheap. Bigger and better things will come, but I am just trying to get it together as cheap as possible and still go as quickly as I can. I hope to be running some 12s.

That Crower is WAY to small to make any HP with the TFS intake and heads on a brand X-- been there.Now Crower makes some B****** cam's for a 351 or bigger so call them ask for Dave he's the MAN to fix you up.

You didn't give flow # but have them ready if you call Crower.


Total system air flow and RPM's will tell you what cam to run.Port length helps to shape the air to get it into the cyl.
Correct length intake ports along with cross section area (to a point you cain't go overboard) , help an LT-1 over a stock intake.

Well, it was either that of the FMS X cam(224/224 112 .542/.542). I am just looking to get the motor together as cheap as possible. A new cam is not in the budget right now. Just looking for a cam that will send me down the track in respecable time.

The 224 cam would be better.Not my choice ----but its a budget thing.

One of the biggest mistakes you see people making is in not properly matching components.

Take the example of the TPI intake and a large cam. One is designed to make low end torque and the other, to make high-end hp/tq. Kinda like putting chocolate and pickles together.... although I'm sure some people like that kinda thing.;)

-Mindgame

Boy thats a REAL bad Combo ugh--poooe
Yea some people think if it's got a nasty chop--it's GOT to be fast.

Originally posted by Mindgame
One of the biggest mistakes you see people making is in not properly matching components.

I think you are being conservative, MG. IMO, THE biggest mistake.

Take the example of the TPI intake and a large cam. One is designed to make low end torque and the other, to make high-end hp/tq. Kinda like putting chocolate and pickles together.... although I'm sure some people like that kinda thing.;)

-Mindgame

Chocolate covered pickles with a nice Riesling Ice Wine. Mmmmm.

I've learned that New Yorkers have rather peculiar tastes in things. Thought it was just them NYC folks but I guess it spreads northwards. :lol:

I bet Bret likes chocolate covered pickles too doesn't he?

:)

-Mindgame

Originally posted by Mindgame


I bet Bret likes chocolate covered pickles too doesn't he?

:)

-Mindgame

He's an omnivore when it come to eating/drinking and thinking. Truth be told, he's a dry red Aussie wine kind of guy. He's come up with some great, economical wine finds. (He probably won't appreciate this post.)

He's never developed a taste for Scotch like his old man, however. We all can't be perfect. :)


Back to topic:

As far as the 351 with the long runners, some decent simulations could of course come up with a custom cam, but then plugging in the currently available stuff that's close could be useful.

Are you married to the long runners? If another intake/fuel delivery system is a possibility in your plan, there's power to be made. Think out of the box. Some $10 Aussie Shiraz beats some $20 CA reds for some of us.

"So many (cams, wines, women),...so little time."

Choose one or more...

"D" all of the above.

Originally posted by OldSStroker
As far as the 351 with the long runners, some decent simulations could of course come up with a custom cam, but then plugging in the currently available stuff that's close could be useful.

Are you married to the long runners? If another intake/fuel delivery system is a possibility in your plan, there's power to be made. Think out of the box. Some $10 Aussie Shiraz beats some $20 CA reds for some of us.

"So many (cams, wines, women),...so little time."

Choose one or more...

Not to the long runners, but efi yes. It was either that intake for the new box intake for the 302 and 351s. I just need something that I can drive everyday in traffic and go lay down some nice times at the track.

Originally posted by mastrdrver
Not to the long runners, but efi yes. It was either that intake for the new box intake for the 302 and 351s. I just need something that I can drive everyday in traffic and go lay down some nice times at the track.

How about Edelbrock's Performer RPM Pro-Flo EFI #3541 ?

Single plane which looks like a cross between a Vic Jr. and a Super Vic, 1000 cfm TB, etc. It's a bolt on. About $2600 (Summit).



Summit EDL-3541 (http://store.summitracing.com/default.asp?target=esearch.asp&N=100&Ntk=PartSearch&Ntt=edl-3541)

$2600! Kind of kills the budget thing.

I was thinking more along the lines of EDL-2945 (http://store.summitracing.com/default.asp?target=esearch.asp&N=100&Ntk=PartSearch&Ntt=EDL-2945+&x=19&y=14) or the new TFS Box top intake(it is in the new Summit, but can't find it on the web). The TFS intake reminds me of the Holley Stealth Ram for the sbc.

Are the 5.0/351 intakes as much as a restriction as the TPI intakes?

Use the Single Plane EFI intake from Edelbrock and a Elbow with a 75-90mm Ford style TB and you are good to go.

That's what I would do with a 7,000 or higher RPM motor.

Bret

BTW Wine, Beer, and some good Vodka, Gin or Tequlia for me.

Use the Single Plane EFI intake from Edelbrock and a Elbow with a 75-90mm Ford style TB and you are good to go.

That's what I would do with a 7,000 or higher RPM motor.

Bret

Originally posted by SStrokerAce
Use the Single Plane EFI intake from Edelbrock and a Elbow with a 75-90mm Ford style TB and you are good to go.

That's what I would do with a 7,000 or higher RPM motor.

Bret

I guess that is something I forgot to mention. This motor will not be turned more then 6500. This car wil turn into my daily driver as much as possible, therefore I don't want to have to run a lot of gear if I can get around it.

I disagree with the "long runners and big cam don't match" theory. Here's why:

How does ram tuning occur?

During the intake stroke, the intake valve is open and air is flowing through the runner, port, and valve into the cylinder. About 1/2 way down the stroke, the air reaches max velocity (piston speed is high and valve is near max lift). Then, the piston decelerates, stops, and starts travelling up on the compression stroke. HOWEVER, the intake valve remains open for as much as 1/3 of the compression stroke (do the math). Your favorite Hot Cam closes the intake valve 68 degrees (!!!) after the compression stroke begins. This is because the air in the runner wants to remain in motion (Newton's 1st law). The inertia of the air in the runner still carries it into the cylinder even though the piston is rising.

Now, consider this: ram tuning is more pronounced in longer, smaller runners because both mass and velocity are greater. So, if you close the intake valve early (small cam), you are taking away its ability to use ram-tuning to fill the cylinder during the compression stroke.

So, a longer runner favors a larger cam. Think it doesn't work? The TPI stock eliminator cars have totally stock TPI runners, but cams that are 260+ deg at .050. Mid 11's aren't too shabby for stock heads, compression, intake, TPI.

Consider the LT1, which is basically the opposite. A short runner doesn't allow much ram tuning so, according to my logic, you need to close the intake valve early by using a small cam to trap in as much as possible since ram tuning won't help fill the cylinder during the compression stroke. Now unless something has changed recently, the quickest stock head, intake, short block LT1 belongs to Frank95Z, who has run somewhere in the 11.50 range with the little Crane 210/224 cam.

Mike

Mike, you're forgetting that the length of the intake runners affects the rpm at which they tune properly. A longer intake runner tunes best at a lower rpm than a shorter runner, given no changes to taper or runner diameter. A smaller cam also "tunes" best at a lower rpm, so matching the 2 is the best approach if you want to make the highest power in a specific rpm range.

What engineermike said makes since to me. Isn't the most important part of ram tuning the 3rd or 4th return wave? Isn't that where all the power is made? This would also support the reason of why the fast 5.0 guys run, what would be considered, a very large cam on a 302.

94bird, you are regurgitating the same generalizations that have been passed around for years. Please carefully re-read my explanation.

Mike

Originally posted by engineermike
How does ram tuning occur?

During the intake stroke, the intake valve is open and air is flowing through the runner, port, and valve into the cylinder. About 1/2 way down the stroke, the air reaches max velocity (piston speed is high and valve is near max lift). Then, the piston decelerates, stops, and starts travelling up on the compression stroke. HOWEVER, the intake valve remains open for as much as 1/3 of the compression stroke (do the math). Your favorite Hot Cam closes the intake valve 68 degrees (!!!) after the compression stroke begins. This is because the air in the runner wants to remain in motion (Newton's 1st law). The inertia of the air in the runner still carries it into the cylinder even though the piston is rising.

Now, consider this: ram tuning is more pronounced in longer, smaller runners because both mass and velocity are greater. So, if you close the intake valve early (small cam), you are taking away its ability to use ram-tuning to fill the cylinder during the compression stroke.

Not necesarily.

You're leaving out the important stuff. That being the runner length and the effect of runner length on wave tuning (when those waves arrive and which wave will arrive at a given rpm).

If you go back to the original point in this thread, it was about choosing a manifold that tuned at the appropriate rpm for a given engine size and camshaft duration. If you are building an engine to turn lots of rpm and your intake doesn't produce strong return waves at that higher rpm, then the combination isn't going to work real well.
Also, if that wave isn't anywhere near the end of the port and the piston is rising up the cylinder (more pressure in cylinder than depression at the intake port), you will probably succeed in pushing the charge back into the plenum.

This happens at specific rpm ranges regardless (camshaft out of tune with intake/exhaust), but the runner length dictates when those waves arrive and all the studies I've seen show that longer runners tune at lower rpms. That's counterproductive to choosing a cam with long duration, designed to make high rpm horsepower.

David Vizard has published quite a bit of data on this. One test in particular comparing manifolds of just 1" length difference showed the same trend. The longer runner moved the torque peak ~200rpm lower and lost HP up top in comparison to the short runner intake. This was in a 7800rpm engine and here we're talking a change of just 1".

So, a longer runner favors a larger cam. Think it doesn't work? The TPI stock eliminator cars have totally stock TPI runners, but cams that are 260+ deg at .050. Mid 11's aren't too shabby for stock heads, compression, intake, TPI.

I don't think it's a mater of working or not.... it just doesn't work as well. And on your point, there are LT1 powered cars going low 10's with similar setups and of course a better cylinder head.

Consider the LT1, which is basically the opposite. A short runner doesn't allow much ram tuning so, according to my logic, you need to close the intake valve early by using a small cam to trap in as much as possible since ram tuning won't help fill the cylinder during the compression stroke. Now unless something has changed recently, the quickest stock head, intake, short block LT1 belongs to Frank95Z, who has run somewhere in the 11.50 range with the little Crane 210/224 cam.

Back to your Stock Eliminator example... the fastest of those guys is running close to 10.3 with a cam that most likely closes the intake valve alot later than the Crane 210/224.

By my logic, you need to close the intake valve at the correct time based on the tuning rpm of the engine. You would need an advanced simulation program to do so, preferably with an exact model of the intake and exhaust system. Then you would look at pressure waves vs crank angle and determine when that optimum closing point should occur. Needless to say, that would depend a great deal on the runner cross section, taper and most importantly... back to the runner length.

I'd venture to say that based on data by Vizard and others, that an engine outfitted with a TPI type intake and a camshaft designed to turn 7500rpm, would be down on quite a bit of horsepower and high rpm torque in comparison to that same setup and say, an Edelbrock Victor Jr.

Then look at some OEM's using manifolds that change between two different length runners on the fly. One designed to tune at low rpms (the long one) and the other to tune at the high rpms. They know what's going on.

-Mindgame

Originally posted by Mindgame
Not necesarily.

You're leaving out the important stuff. That being the runner length and the effect of runner length on wave tuning (when those waves arrive and which wave will arrive at a given rpm).

My explanation was refering to the first, and strongest wave. Each subsequent wave will be weaker and less consequential.

Originally posted by Mindgame
David Vizard has published quite a bit of data on this. One test in particular comparing manifolds of just 1" length difference showed the same trend. The longer runner moved the torque peak ~200rpm lower and lost HP up top in comparison to the short runner intake. This was in a 7800rpm engine and here we're talking a change of just 1".

I'm not doubting that longer runners make more low-end. I agree with that 100%. I'm just saying that a long runner intake will make more power with a large cam than a small one.

Originally posted by Mindgame
By my logic, you need to close the intake valve at the correct time based on the tuning rpm of the engine. You would need an advanced simulation program to do so, preferably with an exact model of the intake and exhaust system. Then you would look at pressure waves vs crank angle and determine when that optimum closing point should occur. Needless to say, that would depend a great deal on the runner cross section, taper and most importantly... back to the runner length.

It is true that a well matched, designed, and engineered combination will produce the best results but, again, long duration cams aren't counter-productive to power when combined with long runners.

Originally posted by Mindgame
I'd venture to say that based on data by Vizard and others, that an engine outfitted with a TPI type intake and a camshaft designed to turn 7500rpm, would be down on quite a bit of horsepower and high rpm torque in comparison to that same setup and say, an Edelbrock Victor Jr.].

Once again, I'm not disagreeing with that. But, the engine outfitted with a TPI intake and a 7500 rpm camshaft would make more power than a 4500 rpm camshaft even though the 4500 rpm camshaft is better "matched" to the characteristics of the intake runner.

Mike

Originally posted by engineermike
But, the engine outfitted with a TPI intake and a 7500 rpm camshaft would make more power than a 4500 rpm camshaft even though the 4500 rpm camshaft is better "matched" to the characteristics of the intake runner.

I wholeheartedly disagree. A mismatch of that magnitude would result in an engine that wasn't good at anything. I stand by my previous post until you show me dyno results to back up your theory. For now it makes no sense to me.

The only sense I could make of your statement is that you mean from 4000-4500 rpm a larger camshaft will make more power than a smaller one. I guess I say, "So what?" With my smaller camshaft I'll be long gone before the other guy gets into his powerband of a super wide 500 rpm. Now, if you tell me your argument is specifically tailored to drag racers who launch at 4500 rpm, immediately shift to 2nd gear, and then row through 5 gears before the 1/4 mile is done, again, "So what?" The only reason to build a combination like this is if the rules limit you to a combination, such as an intake manifold, that is not ideal. How does that back up your argument that a long runner intake manifold goes with a long duration camshaft?

Originally posted by 94bird
How does that back up your argument that a long runner intake manifold goes with a long duration camshaft?

Because it makes more power.

Again, referring to Stock Eliminator TPI motors, a cam of 260+ deg duration would normally make power to 7500, but in a TPI motor, the hp peak would probably drop to ~6000 and shift at 6800. The large cam extends the rpm limit of the TPI.

Originally posted by 94bird
The only reason to build a combination like this is if the rules limit you to a combination

This may come as a shock to you, but EVERY form of racing has rules that REQUIRE a non-optimal combination of some form.

NASCAR engines have flat tappet cams.

Group B Rally cars have intake restrictors.

SUPR motors have non-ported heads.

Renegade motors run 26 psi boost with no intercoolers.

Etc. . .

If you're starting from scratch and building a street/strip motor, then, obviously, the best results would not come from TPI. But the point remains that "mis-matching" a large cam to long runners still makes the most power.

Mike

Originally posted by engineermike
Because it makes more power.


Need I say "So what?" again? What you're saying boils down to, if rules limit you to an inferior head, intake manifold, etc then to make the best of it use all the duration you can because you're going to need it. That induction system restriction is so great that you need much more duration to have a hope and a prayer of making any power at a higher rpm. Of course when doing this you're going to be narrowing your power band so tremendously don't even try to use it for anything but the drag strip.

That is a very weak argument and is not one that would apply to many of us at all on this board.

The basics still apply Mike. A longer runner intake manifold does not go with a longer duration camshaft when you're developing a matched combination. The minute you throw rules limitations into the mix you're throwing out the "matched combination" portion of the above statement and you're building a combination that is only "optimized" for a certain rule set. With that limitation you simply can not say such a generic statement as a longer duration camshaft works better with a long runner intake manifold because it makes more power. You better qualify that statement very carefully.

For my parting comment, ever heard of "area under the curve"? Show me dyno results, as I asked Mike.

94bird, I don't want to get into a p!ssing contest here, which happens way too often on bulletin boards.

To say that "large cams will perform poorly with long runners" is false. To say that "large cams with long runners will produce an extremely narrow powerband" is also false. Conversely, to say that "large cams and long runners produce the optimum combination" is also false, but not as bad as most people think.

According to your logic, my own combo is badly mis-matched. A stroker, as everyone knows, makes alot of low-end but isn't great on top. A centrifugal supercharger, as everyone also knows, makes alot of top-end, but not much down low. This must be a TERRIBLE combination, eh? My torque peak is way down at 3800 rpm but hp occurs at 6300 rpm. Narrow powerband? Don't think so.

I think that most board members here are pursuing maximum power. Perhaps you are the exception to that.

Mike

Mike, as you can obviously tell I don't agree with much you're saying here. I could dissect your last comments also, but I don't think this discussion is going anywhere. I'm sure you mean well, but I'm afraid you're misleading a lot of people on this board.

So what exactly is your point here Mike?

If you're trying to buck a theory that has so much data behind it, then you really need to show your "proofs".

The only specific examples you've brought up are the TPIS vs something more akin to the LT1 intake atop an engine built for 7500 rpm. The long intake is a loser there, sorry. That intake was not designed to tune at those rpms.

Need more specifics for your point. I'm not disagreeing that a 4" runner may not be better than a 6" runner in an application turning 7k or better. We need to find the ideal tuning length and 6" may be it, but the trend is the trend and the data doesn't lie. The real question here is in finding the optimum length....

Originally posted by engineermike
According to your logic, my own combo is badly mis-matched. A stroker, as everyone knows, makes alot of low-end but isn't great on top.

Too generalized.

You should see the dyno chart for my 383.... makes great top end power but the cylinder head/cam/intake are setup to do just that.

Originally posted by engineermike
To say that "large cams will perform poorly with long runners" is false.

Yes, poorer than using the right runner length, which gets shorter as cam duration increases. More on that in a moment...

Originally posted by engineermike
To say that "large cams with long runners will produce an extremely narrow powerband" is also false.

Not necessarily so false... Using a longer runner than optimal lowers the rpm at which VE peaks. It will peak somewhere around peak torque, which in turn lowers the rpm at which peak HP will be realized. The air speed through the intake is already very high and it's only a matter of time before they become too high to produce higher rpm HP. Not my theory, just regurgitating Vizard and others... but isn't that what learning is about though. :)

Conversely, to say that "large cams and long runners produce the optimum combination" is also false, but not as bad as most people think.

Ou examples have revolved around the TPI long runner intake vs something more along the lines of a LT1 intake. Even if you take one of the good TPI's (not factory), at 7000 rpm or so, you are giving up a bunch of HP to produce a lower Torque peak. The whole goal behind a cam that will produce high rpm hp, is to push that rpm range higher. Torque peak goes higher as well, as it should. Using a long runner with this goal in mind just seems counterintuitive to me.

In Vizard's book How to Build Horsepower Vol II, he outlines an empirical formula for approximating runner length. It is based around factors like "effective cam duration", speed of sound at intake charge temps, rpm and the order of the positive pressure wave we are looking to utilize. Formula looks like this...

L = ((720 - ECD) x 0.25V x 2) / (RPM x RV) - 0.5D

L = total runner length
ECD = effective cam duration
V = speed of sound (ft/sec)
RV = order of wave
D = diameter of runner

The trend is obviously clear. For any given order of wave used, longer duration requires a shorter length runner for proper utilization of that wave.

If the long runner were beneficial at high rpm, with larger camshaft durations, we would be seeing more long runner intakes on race cars. Instead, they get used mostly on heavy sedans with mild camshaft duration like the BMW M5. They have their place but I'd bet my house that one of those TPI Stock Eliminator cars would turn better times with a shorter runner and a camshaft of similar duration, utilizing valve events better suited to the intake design.

-Mindgame

You guys keep pounding on and reiterating the same points that I don't disagree with.

Long runners make low end power: I AGREE!

Short runners make more top end power: I AGREE!

Very long runners with a large cam is not optimized: I AGREE!

My point is that a long duration cam with very long runners will make more power than a short duration, "matched" cam. Anyone disagree??? This is proven by data in the Stock Eliminator class that I keep refering to, especially in the TPI and Dodge Magnum 360 engines.

And. . . perhaps the long runner, big cam combo isn't so bad.

How about this: Let's build a short stroke, large bore motor using a 3" stroke and 4.155" bore. That gives us 325 cid that should make good top end. Let's "match" some large valve, large port heads to it, to also get great top end. While we're at it, add a Victor Jr. intake and a 27X @ .050" cam. Is this not a "matched" combination? You'd end up with a motor with great hp that does nothing until 5000 rpm. Add a centrifugal blower and the torque peak will come at 7500. Maybe it's not so great after all.

How about the other end of the spectrum. A stock Magnum 360. Long runners, "matched" short duration cam, small ports. Again, a very well "matched" combination, right? Except for the fact that it's a total turd. . .

A certain amount of "mis-match" is beneficial to get a good spread in power. Big cam + stroker, short stroke + roots blower, small cam + centrifugal blower, etc. . . all make good combinations but would be considered mis-matched. Mindgame, your combination is "mis-matched" also, with a stroker crank + big heads/cam. I bet the stroke gives it the low-end it otherwise would have lost from the cam.

Mike

OK Mike, let me first point out that your assumption that stroking an engine is only done to increase the low end torque is false. I held my tongue when you originally mentioned it, but you just keep on saying it.

It's true that for the same cubic inches a larger bore engine can use a larger valve since the larger bore will shroud the valves less. It's also true that a shorter stroke engine will have less piston speed at a given rpm. A shorter stroke engine also gives the opportunity to run a longer rod. However, if you chose not to take advantage of those opportunities, and built the larger bore / short stroke engine for a lower rpm range, you could make VERY comparable power / torque curves.

Your big cam / long runner intake manifold theory is equally as flawed. Mindgame and I both have asked you many times for dyno sheets (proof) of your theory and you won't produce them. You see, when you have a theory that bucks a generally accepted theory based on physics and dyno / racing experience you should provide proof of your theory if you expect it to be accepted. That's just the way it works. Where's the beef?

I don't claim to know much on this subject, but I am having to agree with Mike on some things. I am building a 351 with a long runner intake. I have talked to a few guys that have something similar and are running low 11s with 3300+lbs race weight. One guy I talked to had FTI spec out his cam and his best run was 11.4s with 3405 race weight. He says it is his daily and said that his cam specs are in the neighborhood of 240/245 on a 112. I would think a cam of this size would be mismatched, but the only problem is that this cam was speced out by FTI, not some shelf cam.

Just a thought.

Originally posted by 94bird
OK Mike, let me first point out that your assumption that stroking an engine is only done to increase the low end torque is false. I held my tongue when you originally mentioned it, but you just keep on saying it.

I've seen back-to-back dyno tests of a 383 versus a 355, same cam, heads, intake, everything. The 383 made 38 ftlb more torque at low rpm, but only 5 hp more up top. At very high rpm, the 355 actually made more hp and torque.

Originally posted by 94bird
Your big cam / long runner intake manifold theory is equally as flawed. Mindgame and I both have asked you many times for dyno sheets (proof) of your theory and you won't produce them. You see, when you have a theory that bucks a generally accepted theory based on physics and dyno / racing experience you should provide proof of your theory if you expect it to be accepted. That's just the way it works. Where's the beef?

As I keep saying, THE PROOF IS IN THE STOCK ELIMINATOR CLASS!!!

If their engines are so horribly mis-matched, you should call them up and let them know that they need smaller cams that are better matched to the TPI and Magnum long runner intakes so they can start running some good numbers. I'm sure they'll really appreciate your input.

Mike

mike in this 355/383 test they used the same cam and top end, and they also used the exact same camshaft. lets think about that for a second, few problems with a test like that. the optimal valve timing for a 383 is a touch different than the ones for a 355. also cylinder head cross sectional area also needs ot be increased for the larger motor since the longer stroke creates higher piston velocities. runner length should probably also change a little bit because the 383 can take advantage of more camshaft. i mean even given the same static compression the 383 can still handle more cam to make the exact same dcr.

given all that you've just proved everyone elses point. that the better matched engine will make more power. the 383 made more torque yeah thats exactly right given the same ivc the effective stroke is longer. do tpi motors make more power with a huge camshaft well yeah if it can move the air in and out at the rpms its meant to be run in but thats as simple as same tq at higher rpm = more hp. at the same time though put a proper intake on it like a super victor or some other manifold for high rpm use and i bet it stomps the tpi into the ground. i think what everyone is trying to say is its more important to build the right engine as best you can, not crutch some horrible intake choice. because lets face it how many of the questions here or on any board are for stock eliminator engines?

Originally posted by engineermike
I've seen back-to-back dyno tests of a 383 versus a 355, same cam, heads, intake, everything. The 383 made 38 ftlb more torque at low rpm, but only 5 hp more up top. At very high rpm, the 355 actually made more hp and torque.

The Edelbrock 350 and 383 packages are about the best comparisons you could hope to make. Same cylinder head, intake and very similar cam specs.

383
460 lbs-ft and 436 hp @5500 rpm

350
407 lbs-ft and 410 hp @6500 rpm

http://www.superchevy-web.com/tech/0310sc_edelbrock/

Sure, turn the 350 to 7000 rpm and it makes more hp than the 383 but it's a moot point cause the 383 can turn more revs too.

As I keep saying, THE PROOF IS IN THE STOCK ELIMINATOR CLASS!!!

And the 4th gen f-body SE cars are going quite a bit quicker with similar cams and shorter runners, better suited to those rpms.

If their engines are so horribly mis-matched, you should call them up and let them know that they need smaller cams that are better matched to the TPI and Magnum long runner intakes so they can start running some good numbers. I'm sure they'll really appreciate your input.

Mike

They are concerned with turning rpm, cause they need hp to win races. They're limited to the architecture of the factory, so they just work with what they've got. The truth be known, alot of those guys would probably run a shorter length manifold if they could.

I think a better measure of the subject would come in comparing classes where there are no limitation on intake design.

-Mindgame

You guys are seriously not getting what I'm saying. You still reiterate points that I have not and will not disagree with.

I'll quote myself so I don't have to type this again.

Maybe you'll read and pay attention this time:

Originally posted by engineermike
You guys keep pounding on and reiterating the same points that I don't disagree with.

Long runners make low end power: I AGREE!

Short runners make more top end power: I AGREE!

Very long runners with a large cam is not optimized: I AGREE!

My point is that a long duration cam with very long runners will make more power than a short duration, "matched" cam. Anyone disagree??? This is proven by data in the Stock Eliminator class that I keep refering to, especially in the TPI and Dodge Magnum 360 engines.


I hate pointing out the obvious, but the Edelbrock 383 made 58 ftlb more at 2500, but only 7 ftlb more at 6500 rpm. How is that much difference from the dyno test I saw? I'm sorry, was someone trying to disprove my statement that strokers are biased towards low-end?

And here's a big shocker for everyone, I AGREE that replacing a
TPI intake with a shorter runner will make more power. But, then again, that's true regardless of cam size. . .

Mike

After a few posts, it is agreed that you more or less agree with the rest of them. But no matter how many examples you give of guys running big cams for racing, this guy wants a daily drivable combo. Not a lopey ass cam that makes 5 more horses at a higher rpm than another smaller cam.

I would have to agree with what Bret has suggested for you to do. If you cannot afford it, then I would try and stay within the optimal camshaft area. As I can say I've experienced in several of my cars before.. running too much cam may lead to a little more power.. but in a car below 6500rpm that needs to be daily driven.
The benefits of that few extra peak hp on a daily driver ain't worth it. I know from experience, unfortunately :)

Good Luck,
Josh

Originally posted by dist0rtion_69
I would have to agree with what Bret has suggested for you to do. If you cannot afford it, then I would try and stay within the optimal camshaft area.

The problem with the intake he suggested is the fact that I will not be turning 7000+ rpms, like he suggested with that intake. Taking that into consideration, I would be more inclined to run something with a little more runner. Maybe like the Victor Jr 5.8, 12.5" runners, but can move enough air for the topend.

True.. I meant the solution more in general though.. I'd much rather see you change the intake out to match your combo if you plan on using a larger cam. You'll be much happier with the car. I have learned this from personal experience. Running a manifold designed with low end torque still might make more power with a larger cam than a smaller cam. I don't think thats really the issue. The issue is.. you could make more/the same power with the proper intake manifold with a smaller cam and have better overall drivability as well as make the power at a lower rpm.

But if your like me.. you don't always have the money to redo the whole combo. So its not a bad idea to go ahead and do the cam you will want in the future, and you can always upgrade the intake manifold later. I ran a 240/246 with a performer rpm and vortec heads for the longest before this latest upgrade to afrs and a victor jr :) hehe. Needless to say it was more bark than bite but it still pulled harder than the 230/236 cam that was in it before.. It still benefitted from more duration, despite the low rpm manifold design. To say that an upgrade woke the motor up though would be an understatement :)

Good Luck with whatever it is you decide to do,
Josh

Mike,

You've backed out of many of the over-generalized statements you made at the beginning of this thread. To the point that it has become difficult understanding just WHAT your point here has been.
We went through IVC and tuning using your Hot Cam example and according to you... "tuning for the first wave". Which btw, would make for a very impractical runner length. So, I presented Mr Vizard's formula which doesn't agree with your reasoning.

Like any successful debate, a point is made, then a counter point is made to hold the other position. Nothing personal, we're all just trying to let each other know WHY we hold the opinions we do. Been pretty civil too.

From what I've digested so far, your only point worth standing on is..... a larger cam in an engine with very long intake runners will make more power?

I might agree with that to a degree. If peak power is your only measure of engine performance. I believe the hp falloff after peak torque would be rather quick to say the least.

The original TPI manifold, originally designed for the 305 ci motor but used on both the 305 and 350, is a good example. Made prodigious torque even on the L98 350 ci engine but really fell on its face with attempts to turn higher rpm.

Either way, in light of this conversation, comments like, "I think that most board members here are pursuing maximum power. Perhaps you are the exception to that", don't seem to coincide with your point. Which is.... larger camshafts make more power, even if not properly matched to the engine architecture.

Peak power... maybe, but not near optimal in any case.

Don't feel this conversation is going anywhere fast. :)

mastdriver,

If you can't afford on of the intakes mentioned then that takes care of that. You'll have to explore your other options.

As for your example... a friends car running 11's, that's commendable. Don't measure what is perhaps closer to "optimum" with track ET's. Your friend may never know that another intake could bump his times considerably and may never even care as long as he can show 11 second time slips to his friends. Point being, the cars that you should look at are those going the fastest within a set of rules.
For the mustang crowd, you have the supercharged guys going really fast with stock "type" intakes. Alot of the choice is going to come down to transmission and gearing but for the NA crowd... most of them have switched over to short runner tunnel ram type intakes or carb-type single planes.

Good luck.

-Mindgame

I think one thing that people are over looking are the LSx cars. Most of these cars are closing in on the 240 duration numbers and are still in the 10s! Now, I know that the intake on the LSx cars are a much better design compared to the 5.0 guys, but those are some large duration numbers for a 15" runner.

Originally posted by mastrdrver
I think one thing that people are over looking are the LSx cars. Most of these cars are closing in on the 240 duration numbers and are still in the 10s! Now, I know that the intake on the LSx cars are a much better design compared to the 5.0 guys, but those are some large duration numbers for a 15" runner.

I read 13"?? (haven't seen anything official) with a good deal of runner taper... that makes for a shorter effective runner length. Either way, the LS1 isn't needing alot of rpm to make good numbers with the smaller cams... it has a great cylinder head. There are 230-ish cammed cars running in the 10's without much trouble.
I don't feel that 240 is as much duration as some would like to think. I'm running a mid 240 duration cam in my 383. Idles well enough and I've turned a couple of high 9-second passes. Runners are about 4" long although I was told, "6 inches with a gradual taper would be ideal". The 4" LT4 runners (spacer underneath) have almost no taper to speak of but they seem to be working ok for me.

-Mindgame

A friend's FoxBody is a 351W that runs 126mph with a Performer RPM intake, 248/252 @.050 , roughly .590 lift @3350 pounds. The car isn't loud inside, the AC blows ice cold at idle, and the factory vacuum brakes work perfect with no canister. The heads only flowed 255cfm, the compression is a tad over 11:1 and it runs on 93 unleaded.

Kinda sounds mismatched, but the thing hauls with a best of 10.9 on a 1.6x 60' and he can drive it anywhere with the TKO 5speed with OD and 4.11 rear gears.

The RPM intake had some of the divider removed for future N20 use, but it picked up 2mph over a Victor Jr.

Another buddy picked up 2 tenths and 2mph from the Victor Jr. to the Performer RPM in the low 11's with his 420ci SBC powered Vega.

Just my useless $.02

Originally posted by Mindgame
I read 13"?? (haven't seen anything official) with a good deal of runner taper... that makes for a shorter effective runner length. Either way, the LS1 isn't needing alot of rpm to make good numbers with the smaller cams... it has a great cylinder head. There are 230-ish cammed cars running in the 10's without much trouble.
I don't feel that 240 is as much duration as some would like to think. I'm running a mid 240 duration cam in my 383. Idles well enough and I've turned a couple of high 9-second passes. Runners are about 4" long although I was told, "6 inches with a gradual taper would be ideal". The 4" LT4 runners (spacer underneath) have almost no taper to speak of but they seem to be working ok for me.

-Mindgame

I'm saying 11.5-12" on a LS1 but the cross sectional is BIG. Then again so is the head.

Yeah a 220-230 cam in a LS1 stock bottom end is pretty dam good if you don't want to turn RPM with it. Which on a stock bottom keeping it below 6,800 is a great idea.

A LS1 almost always has very aggressive camshafts in terms of ramp and .200 duration vs. .050 duration. They also have a pretty light valve and a big base circle and cam journal.

The problem that I see with LS1's is the DCR vs. P to V clearance. You can't mill the heads, or put too much valve in them, or run too much cam so you are pretty dam stuck with a stock bottom if you don't want to flycut the bastards. Then again a built bottom with some compression and cam can REALLY sing with the heads and runner length of a LS1.

Hot Rod has a nice test of the LS1 vs. the GMPP LS1 single plane, and you can see how extra runner length makes hp, even though it flows like dump.

Bret