I am going to get a new 383 built for my 89 iroc. The engine is rated at 423hp and i want to set up my tpi system to actually make that kind of power. I finally got my wifes ok on this so im gonna go all out on this thing. I do live in California though and have to pass emissions so a miniram is out of the question (i think). I am going to upgrade the plenum, runners and tpi base. My question is would the street ram be a good choice for a 400+ hp 383. I will have an afpr, afr190 heads, new injectors, and a custom chip. I was trying to decide between the street ram because its smog legal, or a combo of as&m runners, ported stock plenum, and tpis big mouth manifold. I would also like to hear if i am forgetting anything that i might also need for this thing. My car is totally stock right now. Thanks

 

I would go with the aftermarket runners, base, and ported plenum. Your using AFR 190 heads. At .500 lift these heads are going to flow 260 cfm on the intake side. The aftermarket runners will flow 275 cfm. That's a pretty good match. I see no reason
to use a street ram. The extra cfm you would gain from a street ram you would end up loosing at the heads. Your going to need a 58mm throttle body. TPIS and AS&M both make 58mm throttle bodies with the airfoil made into the design. I suggest investing in some headers and a good free flowing exhaust system also. There are several different companies that make emmesion legal headers and exhaust systems. Hope I've helped.

 

From what i hear, you can also still port to some extent on the aftermarket manifolds and runners to make them flow even more.

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89 IROC-Z 350 TPI

-Flowmaster Catback
-Performance Resource Chip
-700R4 (Rebuilt) Too much done to actually list
-K&N Airfilters
-Ported Plenum
-2.77 Gears (not much to brag about but eh, its there)
-MSD 8.5 mm plug wires
-Problems every other day with the car (probably not a mod, but to me it sure makes a difference)

 

Go for accel or edelbrock base, AS&M siamesed runnners, port the plenum and get a 58 mm TB. Put on some headers and a free flowing exhaust system.

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GTA -89:Free flow muffler,dual 3" HF cats, Edelbrock headers, Vette heads, 1.52 RR 7/16, ZZ-9 cam, Big Mouth, AS&M LTR, !plenum, 52 TB, MSD 6AL, TPIS level V prom, Superior shift-kit and all the minor mods. and more to come!
http://www.itv.se/tacs/members_cars/m279/m279.html (Swedish Trans Am Club)

 

Thanks for the info guys. I am planning to get slp headers. I will also go with the aftermarket base and as&m runners. I dont know where to get the siameesed runners as they arent listed in the catalog anymore. I am very interested in them if I can get them. Would I have to do any special porting or use special gaskets for the siameesed runners? Also, what size headers would you recommend for a 383?
Thanks again for all this info, its great having a board dedicated just to the kind of car that I drive.