I have an 87 IROC with a 305 TPI motor and want to upgrade the heads to a set of Corvette L98 heads I bought. I'm hoping someone who has done this conversion can help me with a few questions I have. What is the best set of gaskets to use? Since I have the motor apart I also want to upgrade the cam. I was thinking of using the production LT4 cam that GMPP offers. Please let me know what you think and any problems I might encounter with this installation. If you have upgraded to these heads, What kind proformance increase did have?

Thanks to all that respond.

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1987 Camaro IROC-Z
305 TPI / T5
1969 Camaro with '96 vortec truck engine

 

You better use a small shot of NOS or something because your compression will fall to like 8:1. You might want to consider new pistons. Tru the 350 heqads will flow better, but I dont know if the 305 with stock intake will be able to use it. I think you will hurt yourself from dropping compression. Get the heads and have then gone over nicely. Then buyt a good cam to match the port work. From there start building a 350 for best results.

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86 Trans Am 355 TPI Rebuilt 700R4 with Corvette servo, modified valve body, and a B&M Torque Converter (2000 rpm stall w/ lock up), 87 350 block bored .30 with new crank, bearings, rings, and magnafluxed rods. Reworked 305 heads with 3-angle valve job. Added in the rebuild was an SLP TPI cam, BBK 58mm Throttle Body,SVO 24# injectors,MSD 6A, Hypertech Power Coil, 1.5 Crane roller tipped rocker arms, SLP Intake Runners and Port matching in upper intake including fully ported plenum, TPIS adjustable fuel pressure regulator @ 46psi, Hooker shorty style headers w/ Thermotech heat wrapping, Custom 3” exhaust with Flowmaster muffler and chrome quad tips, Hypertech Thermomaster Computer chip, K&N open element cone filter on modified MAF per TPIS specs, MSD Wires, removal of A/C hardware and a 1LE firewall cover installed. Also there has been a PST front suspension kit with Hotchkis strut tower brace
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Kills:
95 Talon TSI, 96 Probe GT, 91 T/A L98, 89 RS, 86 Mustang GT, 88 Mustang LX 5.0, 92 Thunderbird V8. couple or ricers that I think were Civics or Preludes not sure what year, 95 Celica GT-S, 94 Chevy 1/4 ton 350, one of those NASCAR F150's ..... **** on Monkie
SOON TO BE A SUPER CHARGED TURBO WITH NOS ON A 500000 CU. IN engine

 

I do not think these heads will change the compression of the engine due to the fact that they have the same 58cc chambers as the 305 heads.

 

You shuld have no problem running those heads on your motor, and your compression will not change. These heads are good as they come, but a little port work will wake them up. you will need to modify your intake base to accept the angled center bolts of the Vette heads, and tap into the exhaust crossover to run a stainless steel line from the exhaust manifold or header to it to retain the EGR. The LT4 cam may be a little too agressive for a 305TPI. Even a significantly modded 305TPI will have a hard time with that cam. I would stick with something with no more than .475" lift, and around 215 for duration. The lowest level SLP cam is a good one to get, or find one similar. hope this helps you

89 Transam GTA, a few bolt ons

 

He said LT4 cam, not LT4 hot cam. The LT4 cam can work OK in a 305 TPI, its a lot better than stock but not its still a fairly mild cam. It's a little better than a stock LT1 cam.

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91 Trans Am WS6
Bright White
5.0 TPI auto
Flowmaster 3" 2 chamber catback
Trans Go shiftkit
2000 stall converter

Built on Wednesday

 

I have Corvette aluminum heads on my 305 TPI. This with a Crane 2032 (214/220 dur at 50) with 1.6 rockers yields a valve lift of 482/496. I normally run a supercharger and/or nitrous, but for the sake of evaluating this mod, I ran the car naturally aspirated to the tune of a 0.8 second improvement.

These heads have a 58cc combustion chamber volume, identical to the stock 305 heads. Therefore, compression ratio will remain the same. However, because these heads are aluminum which dissipates heat much quicker, compression ratio can be raised about 1/2 point with no other changes required.

Also, there are no heat riser passageways on these heads but not to worry. I installed everything (including EGR) as though these heads do have passageways. I have to go through a mandatory yearly emissions check which includes a visual and tailpipe sniffer (idle and at load). My results are as clean as with my stock heads with a heat riser. Also, I have set no codes in the two years I've used these heads.

The last issue is the fact that the center two intake manifold bolt holes on each side of these heads are drilled to accept the pre-1987 manifold (the angle is different). The simplest fix is to have four additional holes drilled into the manifold at the same angle as the remaining bolt holes. If you have a TPIS Big Mouth or Edelbrock base, it is drilled to accept both angles.

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Willie

Supercharged 1987 305 IROC-Z, Daily-Driver, Emissions-Legal.
12.57 @ 111 mph.
12.04 @ 114 mph (50-hp nitrous).
http://members.optushome.com/au/downunder1/rides/willie/willie.html

1987 "20th Anniversary Commemorative Edition" Z28 Convertible -- Super Chevy Show Class Winner, 1998.

My custom front marker lamp assemblies:
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[This message has been edited by Willie (edited January 05, 2001).]

 

Thank you for those who have responded. When you installed these heads, Did you just use regular 305 felpro head gaskets or what else is avalible? I read in the GMPP book that you should use a gasket with a stainless steel fire ring with these heads. Did you use them? How much of a problem is the EGR hook up with these heads? I have the have the car emissions tested this year and want to pass. what is the best or easiest way to hook it up and work?

Some of the mods on my car right now are a Hypertech thermomaster chip, MSD coil, ACCEL distributor module, 1.6 ratio rocker arms, and K&N filters.