Continuing in the good porting question thread I am asking all those who siamesed or otherwise shortened their TPI systems...

How short did you go??
did you follow any formula or Ideas and why.

I guess now we know what chrysler thought in the 50s when they said

length of runner X desired rpm for HP peak = 84000

but this seems to give lengths that are too long compared to some of what Ive heard lately and seen of aftermarket intakes (miniram)

just trying to pool the knowlege.
james

 

i have the stock runners
i used no formula
i don't know what to say on the new length of my runner cuz i disrupted the flow of the runer in the middle (since i only siamesed the intake at the part where the runners hook and the runners are not siamesed)
i wish i would have gone farther and would have gone ahead and ported my heads. from what i did i got a great result.
Andrew

 

I took out 2 or so inches in the base and I ported it. Matched the intake to heads and I siamesed the factory runners and ported the factory plenum and MAF with an airfoil and K$N's attached to a modded airbox and Camaro aircleaner lid. With a little cam and some tuning, good tires, luck, exhaust, recent trans and no extra weight, my 305 went 13.99@102 MPH, before the car started showing it's age. That motor long since retired. It worked suprisingly well, considering the only real internal engine mods was a cam, the entire intake was modded stock parts. I went from a 4800 RPM wall to a nice flat powerband up to around 6, power started dropping off around 5. I lost a little low-end torque, but with the 700-R4, I could afford to do that considering I had a better powerband. Some heads would have really helped. But basically, while you're porting, opt for the lesser side if in doubt...you can remove metal, but it's a pain to put it back. only a little is fine. Why not swap to some aluminum L98 heads and a hotter cam while you're at it?

Either way, good luck.

 

I've been researching this topic for quite a while now as it really interests me. I've found a few different formulas so far, but none of them really seem to match up with what really happens in an engine. Right now however I am in the middle of reading a textbook that is devoted to this very subject. I'm still in the beginning stages right now where are the different theories of approximating compressible fluid flow are explained. When I do finally get to the good stuff though, I'll let you know.

Anyway, the basics that I know is that the length of the runner is "tuned" so that the pressure wave created from the intake valve closing travels up the runner and is then reflected back towards the valve once it hits the plenum, but at this point the velocity of the air in the intake tract is toward the plenum, so you really want the wave to travel up and down the runner again once more so that there is now higher pressure on the intake valve and the velocity of the flow is also toward the intake valve. When this condition occurs right as the intake valve opens, it forces more air into the cylinder and therefore increases power.

With our long TPI intakes this condition occurs somewhere around 3750 RPM (+/- 250) and this is evident as that is where the torque peak on dyno graphs. And as we all know, the torque falls of dramatically above and below this resonance point with a TPI.

The reason a Miniram and the LT1 intakes produce such a flat torque curve is that they have more than one resonance point. Since the TPI intake is so long, the next resonance point (another 4 traverses of the runner for the wave) is at a very high RPM. With the short runner design of the Miniram the higher resonance points fall within the usable rev range of an engine, and therefore flatten out the torque curve, which in turn increases HP at higher rpms.

These are the conclusions that I've drawn from my research so far, but I'm no expert..... yet.

------------------
Black 88 GTA L98
261 RWHP, 345 RWTQ
13.406 @ 103.72 MPH
ZZ4 bottom end, Edelbrock 6085 heads, LT4 HOT cam, GMPP 1.6 RR's, ported stock TPI, SLP 1 3/4" headers, no cat, Dynomax cat-back, Stock PROM
E.T.F.A Member #11

 

good stuff guys.
thanks for the replies.

anyone have any data from a truly siamesed tpi system?? (where the intake base and the runners:slp on as&m: are siamesed also)

this seems like the setup that would produce the most interesting results with there being 3 distinct resivoir sizes.
the intake valve to the siamese in the base is your runner,
the siamese to the plenum is your second chamber and the plenum is your .. well plenum.

I wonder if there would be any correlation between this 3 chamber design and carburated dual plane designs. the only difference is that this design has 4 planes (so to speak)

james