Gentlemen,

I've been foraging through a few papers here at school looking for a means of calculating inertial effects in intake manifolds. What I am primarily concerned with at this point is a method of calculating the engine speed where the inertial effect is at its maximum. Many of the papers I've read talk around this subject but never spell out the actual formula. The same goes for calculating maximum pulsation effect in the exhaust as the goal is to synchronize the positive pressure intake with the negative pressure in the exhaust. Much is said on the subject but again, no numbers or variables. Anyone with experiance in this area? Any information is appreciated.

Martin Loew

 

i've thought about it and all i figured was that there dad to be some intense math to figure this out. i mean, every intake is designed differently, everything from the bends, to the friction of air against the metal(be it warm/hot aluminum/iron ported/nonported) you get the idea

 

The effective diameters and lengths of the intake and exhaust have alot to do with where this is happening in the RPM band.

You can see upwards of 6psi of faux "boost" when you use intake and exhaust tuning to your advantage.

(I phrase it this way because my understanding of this subject and that of most engine physics is not from the Engineering standpoint, or the physics standpoint. I speak about this in laymans terms because that's how I understand it, how I learned it and how I relay it back to people, so ME's bare with me.)

LT1 intakes are horrible at creating this extra "boost" in the intake tract. The runners are too short and are to big in effective diameter (because if they were not they would flow even worse) LS1 intakes are even better at it but also don't flow extra ordinarily well either. Now the funny thing is that the LT1 guys say that the LT1 makes more TQ down low, the LS1 with it's longer runner lengths most likely makes more tuning pressure down low (or makes less negative tuning pressure) and helps make more TQ and higher VE in the lower rpm's due to the longer length. The LS1 feels like a higher RPM engine because the heads flow so dam well and the intake tuning pressures in the mid and high range are so much greater that the LS1's feel like they pull harder up top. I have seen the effects of intake runner sizing and tuing effects on a manually operated engine dyno and when the tuning pressure is growing the engine will run right way from the operator because it picks up tuning effects "faux boost" so fast and makes a gain in TQ so fast that you can't manually compensate for the TQ gain fast enough. (by loading down the engine with more water flow) I would love to know what that feels like in a car, alot like N2O I would guess.

I guess this is the answer to your question. The only way to take this information and use it is to work on the dyno, flowbench and with highly elaborate computer programs to find what works or what might work and try it.

Again, if you ever see one of my engine combos, and you notice 1 7/8" headers, A single plane, a 850/950cfm Holley and it pulls like a raped ape down low and when it comes on it's scary (I can't do this with a LT1 and a stock intake.) you'll think WTF how can you do this with these "high rpm" parts. That's the beauty of tuning and knowing how to use it for engine building. (BTW just because it looks like a Super Vic doesn't mean it's a out of the box one, I've put 80-100hours into a intake just to move the TQ peak down and keep the same HP level, it's alot of work.)

It's a good subject. It's not like, picking out a set of heads or what cam is going to work for me, but a really in depth area and one that will net you race car like VE's. It also has alot to do with the other parts associated with it, heads, cams etc.

Here is some stuff by Vizzard about this: (w/ a Rod/stroke article)http://www.mercurycapri.com/technica...intake/pt.html
http://www.geocities.com/MotorCity/T...92/vizard.html

Bret

 

Try a book: The Scientific Design of Intake and Exhaust Systems by Phillip H. Smith and Dr. John C. Morrison.

http://www.bentleypublishers.com/pro...309&subject=24

I also saw it at Barnes & Noble.

 

Why don't we have that?

 

I'm assuming you're looking for a mathematical model and that this is a project more in theory than anything else?

You need a few key pieces of information to develop a good model. One, you need to know the intake valve closure point. Two, you need to calculate or arrive at a mean inlet valve flow coefficient. Three, you need to know the intake pipe effective length.
The basic calculation is not terriblly complicated. I can send you a few papers I have on the subject if you're interested or I can point you to a few SAE papers on the subject. Just shoot me an e-mail if you're interested.

Take care

 

I can give you a little info which I have from a SAE book of mine called, Introduction to Internal combustion engines. This book was suggested to me in my Combustion engines class in university.
The book says there are two ways of considering a tuned induction system, one is as an organ pipe and the other is as a Helmholtz resonator.

For a simple helmholtz resonator, which is a volume of air with a pipe attached to it. The resonant frequency is
fh=(c/(2*pi))*(sqrt(A/l*V)), answer comes out in Hz.
c=speed of sound m/s
A=pipe cross sectional area m^2
l=pipe length m
V=resonator volume m^3

the organ pipe model formula is
fp=c/(4*L), Hz with the same variables as from the other one.

with the resonant frequency you can get RPM from f=RPM/120 for a four stroke engine.

I imagine you could use these to model and optimize a simple one cylinder manifold for a specific RPM. I have an example where they model a 4 cylinder engine, but would have to scan it since it would be way too much equation writing. If you really want, I could probably scan it in a week at my brothers place.