hartsmike

Looking around and yave come acros some nice low milage 350 IROC's. My question is, since even the 350's back in the day werd dogs, how much can I actually build the 350 and still have a streetable car. One, I want to keep the TPI set up as it is factory and I like a factory/non hot rodded car. Two, without putting a high lopey cam in, juat what can I do to increase HP and torque?

MoJoe

iTrader: (5)

It's a engine. It can be built for more HP, just like any other engine.

As for what to do, that depends on your budget and goal.
Exhaust - Regardless of what you do to the engine, the stock exhaust will be a restriction. A proven combo is: Dyno Don's 1 3/4 shorties + Y pipe, add most any after market cat, into a 3" cat-back system.

Heads - any money you put into the factory L98 heads is better spent on a better starting point: iron Vortec heads on the cheap side, to AFR 195s at the $1500 side.

Cam - since you don't want a lopey idle, look for something in the 220* range and .500"+/- lift. The LT4 HOT cam (218*/224*) and other equivalents is as large as you want to go.

Compression - With the cam chosen, you will want to aim for 9.7:1 with iron heads or 10:1 with aluminum heads.

Keeping TPI will limit useable engine RPM, and therefore peak HP numbers, but you will still get great power below that. Look for posts from the SoCal guys; 1989GTATransAm, Kevin91Z, and some of the "long tube runner" threads. They are still managing to get 400+ wheelHP with long tube runners. Try to track down large or siamesed runners: AS&M, SLP, etc. Or, First Fuel Injection, for a "stock TPI style" intake.

hartsmike

Thanks for the input. I would want way more performance than factory but not "hot rod" it. I also read where there is only so much you can do with a TPI. Out of an inexpensive budget, what HP can I realistically get out of a TPI? 350 be to big of a plan?

MoJoe

iTrader: (5)

For what I listed above:
Exhaust $1k.
Heads = $800 - $1500. Possibly +$400 if you need a Vortec intake.
Cam = $250.. fortunately, you already have a roller cammed L98/350, and with a new cam, you reuse the lifters.
Intake = $200-$400 for runners, or $1k for a complete new First system (which can be ordered with a Vortec base).

If you don't want to do this all at once (time and/or budget), do the exhaust first, followed by either the cam + heads, or intake.

Bob88GTA

iTrader: (2)

Speed+Power=$$$$$.

It depends on how fast you wanna go and how much money you have to make it happen!

The 350 is an awesome engine.

hartsmike

Is the TPI actually a restriction? Is it easier or cheaper to just carb?

akanitro

iTrader: (2)

Stick with the TPI. Don't butcher the car up

Blackdog36

iTrader: (3)

I think you have to look at upgrading your car this way. What can I do rather easily that will give a nice performance boost but won't require a lot of ancillary upgrades. There is only so much additional power your stock computer, transmission, exhaust and rear end can handle before you start spending a lot of money.

The stock TPI system was really designed for a 305 v-8. Yes they work on bigger engines but not optimally. Here is what I would look to do for a mild build. I'm sure there are many postings about these items if you search around some more. Here is link to dyno results from a mild 350 TPI build. You may be able to find good deals on used items on forums here, cragslist or ebay.
https://www.thirdgen.org/forums/tpi/...o-results.html

Intake - replace only tube runners with larger diameter units, TPIS big mouth, SLP, AS&M, etc. Replacing manifold is not really worth it. You could port it a little. A lot of people like the siamesed runners since shifts TPI boost powerband up a few hundred rpm. I would try to find used set of any of the above and use those. They all are better than stock. Don't bother with Edelbrock, flow similar to stock.
http://azspeed-marine.com/19latuinru.html

Fuel pressure regulator - get an adjustable unit to bump up pressure a little.

Cam - want to say crane powermax 2032 is most aggressive cam you can use before really needing a computer tune. LT4 hotcam or ZZ4 cam are other options. Similar to intake runners, see what you can find cheap and go with that one.
https://www.thirdgen.org/forums/tpi/...m-350-tpi.html
https://www.thirdgen.org/forums/tpi/...7-tpi-cam.html

Heads - Vortech heads do flow more air than stock but will require a new intake manifold ($400). You might be able to find other used heads that would work with stock 23 degree intake manifold. Option is to have stock heads worked and ported. Anything to get a little better flowing heads would help a lot with cam and intake runner change. Unless you find deal on used vortech heads and TPI style manifold, cost may not be worth switch.
https://www.thirdgen.org/forums/tpi/...nder-head.html

Transmission - stock will be fine. Some people like to add shift kits to help firm up shifts.

Rear end - also will be fine. I'm assuming your Iroc has decent gears (3.00+) and a posi unit. If not, upgrading those would help. Some people like replacing stock cover with aluminum girdle for extra support ($140).

Exhaust - stock exhaust manifolds are restrictive and worth changing out. Dyno Dons are nice units ($570) but I think you would be better suited by a cheaper set. Rest of exhaust might need upgrade especially catalytic converter with a higher flowing unit. Bumping up to a larger pipe diameter to say maybe 3" from cat back to mufflers would help too.

I always thought that the above upgrades would make the 350 TPI engine how GM should have built it. Figure everything out and what it will cost. A few hundred dollar upgrade here and there doesn't seem too bad but start adding up everything and it goes up quick!

VincentZ28

iTrader: (2)

This is your best start. Just only this type of exhaust alone will knock off a second at the track and the mph will be around 102-104. Gut the air box under the air filters. After you do just this you don't need to do anything else. I did it and saw the Dyno results. Also a Magnaflow cat-back would be the best choice.