BBCSwap

What is the max HP you can get out of the stock TPI air intake? I know I read it somewhere but I can't find it.

Vader

Presuming this is a naturally-aspirated application, the stock TPI will support less power than a stock LT1 intake. On a 350 (L98) the common HP numbers are around 240 at the wheels. The LT1 can easily do 340 in stock form, but of course the cam profiles are substantially different to take maximum advantage of each. There are TPIs on 383s and 400 SBCs which have varying numbers.

Coincidentally, both (in stock form) used 48mm throttle body bores. Also, the factory GMPP crate engine RamJet 502 also used the 48mm throttle body and produced 502HP at the crank with 565 ft/lb, so despite other opinions, it may not be as restrictive to a TPI as some might profess. Even though a larger TB may support more RPM and can help in some other installations, a stock TPI doesn't do so well at higher RPM regardless of the holes in front. Greater limitations can be found elsewhere.

AlkyIROC

I can't say for everyone else but when I first bought my car, it had an old school 383 with a carb on a single plane manifold going through that filter assembly. Going back into my logs from the first time I raced it, my first day of racing only got me a 15.0 on a timeslip and I could feel the engine choking. I yanked off that intake system and threw on a 14" open filter on top of the car. The next day, I ran a 14.2 so for me, that air intake system was very restrictive. I was also spinning the engine to 6800 RPM. Camshaft easily supported that RPM.

BBCSwap

I will be putting aluminum heads & TB on my 350 this summerish. I won't be turning those rpm's so it might be ok??? Thanks for the info.

skinny z

I don't think it can be said with any certainty unless there were some dyno tests involved. Scientifically, the limitation would be the pipe diameter before the throttle body. And this is taking into consideration that the twin filter elements have enough capacity to support the given HP target.
That said, I DO know what a modified version will support thanks to Chad Speier.
https://www.thirdgen.org/forums/fabr...ir-intake.html

skinny z

I don't suppose there are any pictures of that arrangement from back in the day?
It's something I've been contemplating however the design is a little off the wall. Especially if a carb hat isn't wanted but rather a blocked off 14" filter case with the filters located in the traditional TPI air box in front of the rad.

SbFormula

I tell you a way to find out. It worked for me.

I assume you have a SD TPI system from '91

You datalog a few WOT passes with no air intake tube, just open throttle body (baseline). You don't have to go fast, as long as you are at WOT and rev to max RPM. Then you do the same with the air intake on. If you see lower MAP value (specially at higher RPM), you have restriction. Make sure you do the test the same day with the same ambient barometric pressure (initial MAP value with key on engine off).

You can, if you want to be more accurate, do multiple tests each time taking air intake components out. That will tell what restriction each component is causing.

BBCSwap

I've read that before and read it again today. So if I understand Chad correctly the stock air intake will flow "718@28" which is a bit more than my predicted engine will be capable of at the rpm I will run, 6,000 Max. I was thinking of getting an air cleaner off a truck with a big snorkel on it and hook it up to the stock one. I know I would have to lower the height of it. And then you could run the 2 square air filters or the 12" one for the truck air cleaner. The 12" one would be 2-3" depending on how the shortening turned out.

AlkyIROC

That was before digital cameras. Previous owner fabricated a hat to fit over the carb that used all the rest of the OEM ductwork from the original filter system for a TPI engine. Looked nice but not very good for performance. Basically it looked like one of the aluminum hats you can now buy when you're forcing turbo air into a carb. This one was fabricated from the inner part of an air cleaner assy.

z 28 jari

iTrader: (1)

Link: https://www.eecis.udel.edu/~davis/z2...no/dyno060502/

SbFormula

I ran my own test on a GMP SP383 Stroker with FIRST TPI intake (835cfm, 71mm, monoblade - year 2012). I had the SLP CAI. Anyone can run that simple test on their set-up, no need for dyno. The more vacuum at WOT the more HP is robbed.

Test was run at sea level with atmospheric pressure at 102.2kpa. 400HP engine.

The numbers are at 5900rpm

Baseline = With complete SLP Cold Air Intake with K&N filter = 96kpa = 1.83inHg vacuum = Delta of +1.1inHg
1 = With open throttle body = 99.7kpa = 0.73inHg vacuum
2 = With SLP Cold Air Intake tube only = 98.2kpa = 1.18inHg vacuum = Delta of +0.45inHg
3 = With SLP Cold Air Intake tube + box, no filter = 96.3kp = 1.74inHg vacuum = Delta of +1.01inHg
5 = Custom 4in Specter Air Intake with cone filter = 99.7kpa = 0.73inHg vacuum (maybe 3.5" would have been enough, but did not want to take a chance considering the price of these things!)

Like the above link article, the K&N filter was not a big contributor of air restriction (+0.09in/Hg). The airbox and air tube were responsible for 92% of restriction pre throttle body.

I don't know if 0.73inHg at WOT 5900RPM is within range, but it sounds acceptable. The vacuum is created post throttle body.

Now how does all this translate into HP? That's when you need the dyno. Probably not much at the wheel.