im looking to build a tpi engine off the summit 355 kit. not sure what to do with the heads. il like to use stock ones from a vette if possible. maybe a 3 angle job. i figure 24lb injectors, slp runners, port the upper and lower plenum and 58mm tb.

id like to use a power adder. supercharging is to much $$ for this project, dont like n2o but i was thinking a small turbo and custom headers. something for like 6-10psi max
i figure that shoudnt exceed the 24lb injectors. just dont know how to rig something like that up. any thoughts/comments/better ideas to what i wana run is welcome. thanks

 

58mm is to agressive of a throttle body in my taste. 52mm is more like it for a 355. As for all that wacky turbo stuff, consintrate on getting a basic motor set up and getting it to run correctly. That will occupy all your time and decrease the size of your wallet.

 

The 58mm won't hurt, but it won't help either. 52mm is fine. Actually, depending on who you talk to, the OE 48mm should support well over 300 HP, but let's not argue over opinions....I'd go with a 52mm.

Can you buy, install and tune a turbo cheaper than a blower??? I honestly don't know. I agree that I'd get the motor running first, and then worry about the power adder.

....and I might look into the holley stealth ram unless you're one of the die-hard LTR guys like me!!!! You'll make more power for less money!

 

the 52 is fine with me. i said no to the stealthram cause of price. sure 300 something for the intake. but you need the holley rails and holley this and that and whatnot it all adds up. ebay tpi unit with custom home porting lot cheaper and not much of a difference. i miss my gtp hence the reason for a turbo. dont know much about them so looking for any help. mainly junkyard setups. i want to stay low on cost.

 

Your new TPI motor will make your old turbo car seem like a dog if you set it up correctly. Make sure you research cams and heads.

 

if i ever have a tpi motor that makes my supercharged gtp seem like a dog gm will go back to using tpi

 

I would buy the 58 mm TB. Why settle on a smaller one, when we all know youll upgrade at a later date anyway....why pay twice. I had a 52 mm because a certain EFI outfit said it would be fine. They know we are H.P. junkies, and will return at a later date to spend more $$$$. Buy the 58, and be done with it...Tom

 

Be careful, to much air can be a bad thing to... especially on smaller motors like 350's. He will lose all his bottom end.

 

stick with the stock 48mm TB its plenty sufficient, yeah 52mm and 58mm may not hurt but it aint doing any good so ur better of spending the 300 bux on something nessisary.

its easy to tell on a MAP car if ur TB is too small, at WOT ur KPA should be 100, in the higher rpms if the KPA drops in the 90s or lower its because the TB isnt letting in enough air to feed the engine. the stock tpi plenum is a hell of a lot more restrictive then anything else, its about half the size it should be to sufficiently support a 305. the stock plenum is big enough to feed a 2.2L engine...

 

I would agree on that statement with a 305, but a healthy 350 can handle the additional air. If it were a 305, porting the plenum alone would increase the cfms enough. Im just saying that when we go fast, then we want to go faster, thats all. But you have brought up a good point. Thanks ...Tom

 

A 52mm TB w/o an airfoil will flow 849CFM. It takes about 1.3CFM to make 1HP, so, the 52mm TB should flow enough air to make about 692HP at the flywheel. With an NA setup, he will not come close to 692HP. Even with an SC or turbo, 692HP would be about the limit anyway for a street car with some resembles (sp) of drivibility.

The entire setup should be thought thru, heads, cam, exhaust, intake, ECM,,,,,etc. I'm not good at matching components, so a proven setup that makes good HP should be your best guide. So who has a great running 350 or 355 and what is the complete setup?

 

whats a "healthy" 350? i have a friend with an Lt1 caprice that makes around 380hp, and his TB is barely to small, the KPA starts to drop after his peak hp rpm.

the problem with the plenum is not flow, plenums dont flow air, they hold volume. a stock TPI plenum meets the requirements for a 2.2L engine, and barely. an engine needs a plenum that can displace one to one and a half times the displacement of the engine. a 5.0L needs a plenum that can hold a minimum of 5 liters of fluid and a max of 7.5L. a 5.7 would need a 5.7L to 8.6L. a stock TPI plenum for 89-92 which has a larger volume because of the lack of cast for the egr port between the throttle body bores holds 2.25L of fluid.

in other words it really doesnt matter if u put a 70mm TB on it, its a bottle neck, like running aftermarket runners with a stock base.

DOC has made an extremely valid point also a 52mm TB can flow 849cfm. a stock TPI setup flows around 200cfm.

 

I strongly agree with the thirdgenner above who said to get the 355 to run NA as well as you can get it. Then, decide if you want a turbo or SC. FWIW: I'd pick an SC.

Another point: the 24#/hr injectors are an excellent choice for the 355 NA motor. Just buy a good AFPR to get the right fuel at WOT. However, these 24s will not be enough injector for a turbo or SC.

Another point: if you are sure that you are going to go turbo, then you might think about the compession ratio up front, like 9.0:1 as opposed to 10.5:1.