BrettZ28

I just recently acquired a 1986 Z28 with a 305 TPI. I am an ASE Certified Technician, and I'm looking for some advice on Horsepower and Performance and whether or not to build a 305 or a 350 TPI. The 350 I have is a 1971 350 4-bolt main engine out of an Impala with 041 heads. I already know what is required to convert the 305 injection unit over to a 350, my question is how much HP can you get from 305 and $ vs. $ am I better to rebuild the 305 or rebuild a 350 w/ TPI? Has anyone done either of these before? Thanks guys!

soul strife

Wow! it's been awhile since I've messed with TPI so my dollars are not accuret any more. I know that the 350 is a much better basis. I remember the crank and cam would swap out of both but the 305 can not be bored enough to make it a 350.
I'd go with the 350, stroke/bore it to a 383 and go with it. You will need a new intake. I remeber the intakes being really restrictive on the tpi's.

89TramsAmGTA

By all means use the 350. GM used the same TPI for both units. I'm still running TPI although modified and my best is 12.71 @107+ in the quarter mile. This is with the heavy GTA TransAm with all options.

BrettZ28

What maching have you done? What camshaft, etc. I am looking for info to make this a true screamer 400+ HP! Or at least as much as I can, if you know what I mean. Any details into what will work best would be greatly appreciated, Thanks again.

twocamaros

usin tpi u will never get 400hp

89TramsAmGTA

Well I have dyno'd 330RWHP with the 700R4 transmission with a 3600 Yank stall converter and a 350 motor. Fixing to go a lot higher with my next round of mods. I think that 400HP ceiling has been broken and will soon be smashed.

Here are the basics to my current build. Trickflow heads, ZZ9 cam, 1.6 roller rockers, siamesed SLP runners, ported stock plenum, 58mm throttle body, Extruded Honed Edelbrock manifold, Kieth Black hypereutectic pistons with 10:1 compression ratio, SLP 1 5/8" Tri-Y headers, 3.5" Mufflex exhaust and a custom cold air intake. I would not go with the ZZ9 cam as it is "old school" with slow ramp rates and long advertised duration which screws up the dynamic compression for only 212 degrees on the intake. Much better cams on the market these days. The ZZ9 cam is mainly what is holding me back with the current build.

Next round of mods will be 10.7: compression, Dart Pro 1 200cc heads custom ported, 1 3/4" custom headers, COMP XFI 218 cam with heavy duty valve train parts. Then the little engine assembly tricks for more horsepower.

FASTFATBOY

I have read in MANY articles the 305 TPI setup is NOT the same as a 350 TPI, it is smaller, flows less.


I would not waste my time with the TPI setup it is rpm limited, I would put a Stealthram on it.


David

Domster_ss

Holley makes a replacement intake that will give you an extra 80RWHP with the 350 and 65RWHP 305. Additional upgrades needed; headers, high flow cats and exhaust. Thats about 100-105 flywheel Hp for 350 and 90-95 flywheel HP. That takes the 305 from 235HP to 325-330HP. So Holley claims I personally would go through www.tpis.com they have the tpis down. They know their ****.

LesPaulGoth

Correct, alot of people have that misconception. They say you will get an increase in 80hp, but thats compared at 5500rpm, where the TPI unit would make say, 200hp, the HSR will make 280hp. At peak, you are talking 20, maybe 30 horse. Still, it is a valuable investment, as peak horsepower is not everything, yet, another common misconception. I'll be going with one this summer =)

89TramsAmGTA

To FastFatBoy. Please link me to any article that says there are two different size GM TPI units. One for the 350 and one for the 305. I have seen both on and off cars and there is no difference. There are minor changes over the years but that is it.

91Z-28

Go with the 350 and spend the 530$ on the Holley Stealth Ram while you are at it. If you put a decent cam in it the gains over the stock manifold would be significant.

BrettZ28

http://tpiparts.net/305_tpi_to_350_tpi_conversion
here is a good link for doing conversions from a 305 to 350

2fbodies2NV

AFAIK the only difference between the 305 and 350 TPI intakes themselves are the injectors.

rudyt5000

go with the 350. TPI is good for stop light racing but really looses all its power in the long run. Holley Stealth ram is one of the best you can get..but there are other intakes you can use such as Lt1/mini ram intake with mods to fit. Or go carb

67ProStreet502

The TPI is under-estimated all the time. Top end HP isn't all there is to look for. Shift points don't have to be 6000 rpm. TPI's like lower shift points like 4500-5000. 5250 the stock TPI is peaked out. If my IROC's body wasn't rusting apart I'd have it in the low 12s once my ProStreet is done, and that with using the 305. Say it can't be done? Look in the stock class record books. Unported, unmolested, intake and heads running 12's. And the 350 and 305 intakes are the same, I have one of each. It would be cheaper to run Holley's new intake setup, but I'm not one to conform. TPI base manifolds can still be bought but for high $$. It's up to you what you want, but 400hp is alot to ask for with a stock TPI intake. Look for some siamiesed runners. I ported and lightly polished a set of slp's with good results. But to make the big power you'll need a bigger base too.

FYI Hot Rod did a feature on a third Gen Formula 350 running 10's on the juice, 11's on motor with stock shortblock and accels top with TPIS's big mouth. I'll dig for some cam specs.