MinionII

I know the stock TPI intake makes tons of low end, but what exactly is the effect of putting siamezed runners on? That effectively shortens the runners does it not? Does it have a durastic effect on where the car makes power?

school me

Also, what is the stock intake runner length from the begining of the runner at the plenum to the cylinder head port? How much do these intakes flow? I tried a search to no avail.

thanks

BTS88IROC

Yes it does shorten the runner length. Which helps the engine breath up top some, but if you are looking for top end then it would probably be best to switch to a different intake setup such as LT1, miniram, hsr or something of the sorts.

Here is a great thread on porting the intake. https://www.thirdgen.org/techbb2/sho...g+stock+intake

MinionII

So does siamezing the runners change the bottom end on the butt-meter? I geuss the runners are still the same length to the engine, just bigger at the top for less restriction.


So how long from the runner entrance to the intake port on the cylinder head?

thanks

fisherbody86

I remember hearing that from plenum to intake valve was 17-17.5". If you want top end horsepower but want to keep your tpi, you could get a set of slp runners and siamese them. This extends the plenum into the runner, shortening runner lenght, and moving the power band higher into the revs. You will definatly feel a seat-of-the-pants difference in power, a lot less low end grunt, and a good amount of more high end.

MinionII

What is the average cross section of the runners? I thought they were longer...I have a mustang, and my intake plenum to valve length is just over 20" I think. I though the 305TPI would have more low end torque than a ford 302. Has anyone driven both a stock 305TPI and 302HO? I geuss they would both have to be standards to get a good feel, which makes more on the bottom?


For the people who hate longer posts:

Runner length stock TPI intake plenum to valve=???

Low torque of 305TPI 5spd same or better than Ford 302HO 5spd?

thanks

rob231

lingenfelter said the tpi runners are something like 21in. and the ls1's are like 13in. and the lt1's are about 3in.

MinionII

3 inch runners on the LT1? Wow! And they still make bottom end? How is the intake tuned?

Some one explain this one to me.

smithtc

iTrader: (5)

http://www.grapeaperacing.com/GrapeA...ehelmholtz.cfm

http://www.grapeaperacing.com/GrapeA...ntaketuned.cfm

Just some info that may be of interest courtesy of www.grapeaperacing.com

Happy reading...

MinionII

Do the TPI manifolds have a divider in the plenum? They do have dual bore TB's don't they?

Excuse my ignorance

MinionII

TTT


anyone?

thanks

BTS88IROC

You are correct, they are a dual bore TB and the plenum does have a divider in the middle.

MinionII

What exactly does 'ported plenum' refer to on a stock TPI intake?


I read the above links, and it looks like the stock TPI intake is a really good piece! The ports are all tuned equal length, plus the 4cyl per plenum lets the 'Helmholtz resonator' theory work...


"3 inch runners on the LT1? Wow! And they still make bottom end? How is the intake tuned?

Some one explain this one to me." - again I apoligize for my child-level knowledge of chevy motors, but you only learn if you ask

MinionII

can anyone help me out o the above post?

Kingtal0n

ok porting the plenum is where you basically remove all the restrictive areas on around and inside the plenum itself. thats the top piece of the stock TPI, which bolts to the runners, which bolt to the actual intake which bolts to the motor. the injectors and fuel rails are below the plenum. the plenum is where the throttle body is bolted to also.

the major restrictions in the plenum are where the TB bolts up, and where the runners bolt up. there is a lot of extra metal inside the thing. I have a video of myself porting it, its being hosted by a friend right now.

the runner length of the LS1 is actually only 15" as opposed to the LT1 3" and the LS1 still makes more peak power in stock trim. this goes to show you that its not just the intake runners that make power, but the combo as a whole. the whole resononance theory applies to all intakes, even carbed intakes, although to a much lesser degree than dry flow runner intakes like the TPI LT1 LS1 type which do not flow fuel just air.

TPI has great idle-midrange because of its long runners... everyone knows that. but its not a "great piece" for people who like to drag race because as everyone knows or should know horsepower wins the race, and TPI intakes just dont have enough "FLOW" to make the kind of horsepower needed to keep a car in a decent powerband for the length of the track. Even the ZR-1 Had twin runners per cylinder, where the second set would open when the car needed extra flow. if the TPI intakes was like that we could have our great midrange then when we wanted to go fast it would open up for more flow.

point is, its great for daily drivers and stoplight racing. its good for smallish cams and fuel economy, and its good for throttle response and drivability. its NOT good for high Peak HP numbers.

The Lt1 can make bottom end because it still has a relativelly small cam and decent heads, so even though its not making its "resonance" its still able to partially fill the cylinders through the RPM range, like any other car with a single plane would do. while its not "cramming" the air into past the valves it still flows enough to make some decent numbers. now throw a head/cam capable of making some serious HP and the intake shines up top where it counts. but then your back to the old days with big ports low velocities around town and crap fuel economy and drivability. not a street car i would think.

it just depends on what you want and how much of it you want, oh and how fast can you afford to go? a procharged Stealth Rammed motor with some great heads can push the 800-900 horsepower easilly on pump gas, and still retain A/C and fuel economy. but now your talking $$$ flow.

MinionII

Are the stock TPI intake runners all equal? Or are there any weak runners? Like with my mustang, the 1 and 5 runners suck because they neck around to clear stuff and are a couple inches longer than the rest.

Has anyone ever seen a degrade in performance with a plenum port? It seems the plenum volume is selected intentionally for the intended powerband of the motor...

You don't take out the plenum divider when you port, right? That would screw with the 'Helmholtz resonator', being that the theory works best with 4 or less runners per plenum...

thanks very much for that informative reply. my sponge-like brain has sucked it in.


EDIT: Also, do the TPI motors have a '180 degree' crank?

MinionII

gimme more!

TransamGTA350

iTrader: (2)

The plenum is not actually divided. There is a small divider behind the throttle body to straighten the flow thru the twin throttle blades, but inly for about 0.5". The rest of the upper plenum is completely open, so all 8 runners feed off of the same plenum.

In calculating the resonant frequency, the runner length includes the intake port in the cylinder head. The stock TPI runners are about 1.5" diameter, and 21" sounds about right for length give or take a little. I have never actually measured it.

The calculation for the resonant frequency or RPM has really only 3 variables:

Runner Length(Longer=Lower RPM)
Runner Cross Sectional Area(Larger=Higher RPM)
Plenum Volume(Larger=Lower RPM)

All 3 variable affect the result equally.

Camshaft duration also will affect the resonance. It does slightly affect the peak resonance RPM, but it affects the broadness of the resonance more. For example, a longer intake duration will reduce the "peaking" affect right around the resonant RPM. This means that the power peak will not drop off as abruptly as the RPM's increase. It will also move the resonant RPM slightly higher.


I worked on this theory for my senior project in college.

MinionII

you wouldn't want to post or email your whole paper on it would you?

3.1EyeCandy

iTrader: (3)

1) All TPI Runners are the same length/diameter.
2) One of the main reasons people port the plenum is because of the poor mold quality of the alluminum plenum. Most of what is done is "cleaning up" the plenum, rather than truly hogging it out. The ridge that is cleared near the throttle body openings is what is considered "hogging out", and this just increases the plenum volume while giving the air less turbulence. Everything is to be gained from porting the plenum....and likewise nothing to lose.

It's odd to be explaining this to a Mustang guy - but everybody's got to learn sometime Who knows....maybe we'll convert you

Jim85IROC

iTrader: (2)

Total Lengths from Plenum to Valve Seat:
Stock TPI = 25.375 in.
ACCEL Hi-Flow components = 25.375 in.
ACCEL Super Ram components = 21.125 in.
Edelbrock Performer RPM = 12.125 in.
Edelbrock Victor Jr. = 11.625 in.

courtesy of the IROC Homepage.

http://iroc.fbody.com/intake.html

TransamGTA350

iTrader: (2)

I'd rather not post the paper, but I can email it to anyone who is interested. I should talk to a moderator about writing a tech article about it.

I was thinking about the siamesing of the runners. It does not affect the plenum volume, but does affect the average runner cross-sectional area. Increasing the plenum volume will lower the peak RPM according to the helmholtz equation. Increasing the runner area will raise the resonant RPM, and as we all know, the siamesed runners do in fact raise the operating range of the engine.

My email is JSenatro@hartford.edu for whoever would like a copy of the paper

Jim85IROC

iTrader: (2)

I think the effect of the plenum volume on RPM is dwarfed by the effect created by runner length and diameter. Take the Super Ram for example. The plenum volume is substantially larger, yet that system is capable of much higher rpm thanks to the short runners. Holley stealth ram is another system with a plenum volume that's larger than the TPI (though only by a small amount), yet can support much higher rpms.

MinionII

You wouldn't happen to have further info on that project would you? I read the paper...has the intake been fabbed?

TransamGTA350

iTrader: (2)

The intake is still in the process of being built. Most of the parts have been manufactured, and are just waiting for final assembly. Once it is built, it will be installed on last year's Formula SAE vehicle and the fuel injection system will be tuned using a chassis dyno, then compared to the previous dyno runs.

As far as the plenum volume on the Super Ram, I would suspect that it is not all that much differenct than the stock TPI. Since I don't have one, I can't say for sure, but if someone would like to measure, that would be nice. From the looks of it, the Super Ram seems to be a little lower profile, and it's shaped somewhat like an "S". You are right in that the runners are shorter, but about 4". Also, they are 1.75" diameter, compared to the stock 1.5". So even if the plenum is in fact larger, which it may be, the runners are both shorter and have a larger cross-section, so that will overcome the plenum volume change.

But it is important to understand that all 3 variable will affect the result equally.

Kingtal0n

well im really curious about exhaust and intake resonance / scavenging.

Everyone knows that exhaust can be tuned to pull intake charge in, bigger less restrictive exhaust helps at low rpms to yoink in fresh air, much like long runners ram it in at low rpms.

So say on a street driven LT1 with those short runners you could tune the exhaust to help at low Rpms, then just play the runner length and cam/head combo to pull in air at high rpms.

Or even tune the exhaust AND the short runners for high rpm, so when you hit 4-6,000 you not only have the runners ramming in air you have the exhaust scavenging max to pull in a damn near 100% VE...

i think its possible. Or you could just bite the $3500 procharger bullet and have 150+ VE% all the time

MinionII

...getting rid of some inaccurate info...