I would have done a search if this has been talked about before, but of course that feature is broken right now. Sorry if this has been beaten to death before or anything..

Anyway, generally speaking, a bigger intake port and large cam will usually equal big power in the upper RPM range (N/A anyway) right.. but it's generally accepted that it's not the greatest setup for a street car, even if it's raced.. but I don't exactly know why. Low end torque might not be AS good, but what does it matter if you are running a 3000+ stall torque converter and low end doesn't especially matter?

But, what about on a blown application? For instance, a centrifugal blower setup, like a Vortech or Procharger. What will a 215cc intake runner do compared to a 190 or 195cc? I've read that the larger runners have less velocity at low rpms and lifts. Of course I've read a lot of talk of "area under the curve" and how you are at max lift once, but see mid-lift twice per revolution, and the smaller heads might not make the most peak CFM, but might flow more to .300" or .400" lift. Ok, but again, does that matter as much when you're stuffing air down the engine's throat with a blower? All I can see is the potential for more air to get into the engine, and more power as a result.

And, does intake runner length play any kind of part in this? With FI for example.. will a LTR setup make that much less power than a short runner intake, assuming the flow potential is the same between the two, the only difference being runner length? For example, take the Stealthram and compare it to an LT1 intake. The Stealthram is considered a short runner intake but still has longer runners than the LT1 intake, it's more like a Tunnel Ram design.. and also has that huge box on top. The short runner in the LT1 design seems like it would give the air more of a direct shot into the engine and possibly even a less chance of the air getting turbulent, but that's just my own speculation, I have no idea really.

Wow, that became a loaded question. Ok, I'll shorten it.. what are the disadvantages (and advantages?) to running a large intake port setup on the street.... and does intake runner length also play a part in the equation on a blown application? You don't see many people making big power with LTR setups compared to the numbers of people with Super Rams, Stealthrams, and Minirams.

 

The short answer is the same rules apply with a boosted setup in manifolds and heads. Bigger better flowing intake ports still tend to make more top end while smaller ports will make for the best driver (although properly tuned fuel injection tends to mitigate some of the adverse affects of a larger runners and the big cams that go with them).

Manifold runner length should be tuned for the rpm range you will run. The size (diameter) of the runners are dependant on the engines displacement. People with centrifical superchargers on long tube runner engines usually will pick up some additional useable RPM range if they are not getting into valve float. This is primarily due to the boost curve of the centrifical supercharger.

The reason people with long tube runners arent making as much power as people with shorter runners is because of the nature of "power". Power is torque x rpm.
Add the word "Horse" and just apply a constant of (I think) 5250 or maybe its 5200. I'm sure someone will correct me, I dont feel like looking it up... in any event horse power is the same equation as power but you divide the result by 5250. In other words power and horse power are proportinal.

Sooo if you have three motors all making 400 ft/lbs of torque at different rpms the power levels vary greatly... for example 5000 rpm with a highly modified TPI long tube runner setup is going to make 381 hp. Now lets say you take another motor with a super ram and make the same torque at 6000 rpm which is possible due to its shorter runners you will see 457 hp... now lets say you make a screamer of a motor with an edelbrock Victor Jr type intake... it could even be multi-point. Spin it to 7000 rpm and the 400 ft/lbs of torque will bring over 530 hp.

If anything the runner length becomes more important to tune to the correct rpm range as you make big power... IE lets say you double the power level with about 22# of turbocharged boost... your long tube runner 5000 rpm TPI setup will now be down 300 hp to the 7000 rpm motor that is making a massive 1000+ hp. Dont get me wrong, 730 hp is plenty fast in a perfectly driveable street car any way you look at it... just try to get it to hook, lol.

So the shorter runner will put the peak power at a higher RPM and peak power will pick up if the other components like the heads and cam will feed the engine with the air it needs to support more power.

If you want a good book that will realy drive home the effects of runner lengths on power and rpm ranges pick up 5.0L Ford Dyno Tests by Richard Holdener. ISBN 1-884089-45-3 The book discusses the results of a couple thousand dyno tests with different combinations of parts.

 

Sorry but thats totally wrong.

A pound is a force. (lb) And torque is lbs X ft. That is a measure of work (but since this isnt physics is just a static amount of force)

and horsepower is (lb/ft) X seconds. which is work over a period of time (sec). S

Just wanted to clarify that part of your post.

 

Alright, you split a hairs and you are right... the 5252 constant that I didnt want to look up has the 2 x pi (distance of one crankshaft rotation at one foot from center) part of the equation built into it without which RPM is not a valid distance / time component needed to solve the equation. To-shey.

The equation showing all of the constants w/o breaking them down is:

HP = torque x rpm x 2 x pi / 33000

the 2xpi/33000 is where the 5252 comes from.

For those interested I took the trouble to look it up and the 33000 which is watts draft horses power... it lifted 180 pounds 181 feet in one minute. That equates to lifting 32580 pounds - 1 foot in 1 minute... that he rounded to 33000, or one horse power.

In any event the doesnt change the point of the whole thing which was that if the same work is done in half the time you observe twice as much power. Or if you have the same ft/lbs at twice the rpm you have twice the horse power... so an engine that is built to to make torque at a higher rpm will make more power than one that makes the same torque at a lower rpm and long runner intakes are built to maximize torque at lower rpms thus do not build as much torque in the upper rpms thus are not as good for making a high power number as a shorter runner intake.

 

Thanks for the information!

 

Correct me if I’m wrong, but I’m not really sure that any of this answered the original question.

Yes, for the most part the ports behave similarly NA as boosted. VE is VE, you do not move a larger volume of air just because you have more boost, you move the same volume but the boost makes that volume of air denser, and since what makes power is combining air with fuel, and you’ve got more air to combine, that makes more power.

A boosted engine will usually not work any better with larger ports then the same combination would NA. If putting heads/intake with larger ports doesn’t work on the engine NA, then it won’t work on that same engine with boost.

Flow dynamics are very complicated (even more so when you consider that port shape and flow can effect combustion quality so which can make or loose you power also), but for a greatly oversimplified view of why small ports are better once you’ve got sufficient flow for the engine is based on how port cross section (not volume as most believe) effects that same flow. Basically, once at the point where the flow is sufficient to feed the engine, increasing the port cross section does not net you anything, but it does increase the mass of air that you have to move when the valve opens and as mass goes up you will need to use more energy to move that air or it will move slower (at some rpms that could mean a loss of power if you never accelerate that mass of air enough to fully fill the cylinder). If you keep port cross section low while maintaining sufficient flow then the air will not only better fill the chamber, but some of the energy of the flow can be used to create swirl in the chamber (promoting a more homogeneous mixture, which will burn more efficiently) as opposed to being used up just to get the air there.

Although we’re talking about a quantity of air, which would imply that the volume is important, the reason that I’m specifying that the cross section is important is 2 fold. First, the port/runner length could be significantly different changing the volume without changing the velocity in the port, and second, in some designs boundary layer, turbulence and other effects might make parts of the ports basically irrelevant to the airflow, such as if you’ve got too steep a short side radius and you end up with flow separation or a bad manifold to head entry angle (TPI) with similar effects.

Now the flow necessary to feed the engine is probably not as high as many think or would like you to believe (big heads = big $$$), ex, you really only need a port that flows about 200cfm to feed an NA, 400hp V8 (there are some builders that would suggest much less then that, but I haven’t been able to confirm if what they ‘leak’ out is accurate or exaggerated, some have published #’s that imply that much greater engine efficiencies are possible with good port and chamber designs meaning that you don’t need nearly the flow or even VE to make the same power), and assuming that your VE never goes above 100%, you can do it by 5300rpm on a 350. Now this is the difference between some of those that really know, the Lingenfelter’s, Sherman’s, Vizard’s… (and other less well known names, seems like the ones that really work miracles are also just about unknown by the average enthusiast) and the typical engine builder out there. The typical engine builder will get the best total flowing parts that they can afford (or justify) for the build, and then choose valve timings that will get them to where they need to make the power, where those that really know will choose parts that flow appropriately to the power that they’re looking to produce and optimize the whole thing for them, giving them a broader power band, a more efficient engine combination, something that is more fun to drive, better gas mileage and better HP/$ spent (and more area under the curve ).

Look at the Engine Masters challenge during the last few issues of PHR. You’ll notice that the top three (especially second place) used significantly smaller heads then the rest (the second place used a set of out of the box fast burn heads, smaller/less flow then what most of the build ups on this board use), milder cams…, and well, the rest weren’t even that close in their scores. You think that they know something that most of the rest of us don’t?