questions on my 92 Z-28

[joes407]

i recently purchased some aluminum corvette heads that i thought came off an 87 -92 vette. come to find out the heads came off an 85 corvette and my TPI base plate is different. i got the 85 base plate but im curious about how good these heads will perform for me as the 85 vettes had bad horsepower ratings. my bottom end is an L98 block with LT1 crank,rods, pistons and a 502/510 lift cam. i was using the 305 heads that came on my mototr before i put the 350 in and the car ran mid 13's. looking for opinions on if i made a good decision buying these heads or should i have left well enough alone? the new heads are D ported aluminum and im still using the tuned port with a larger throttle body and larger intake runners.

[rolling thunder]

Well first off nothing out of the 80s really had good hp numbers unfortunetly. However that is not because of the heads the heads were very good by factory standards and with alittle port work even do fairly well agains some of the after market heads. Now is it the best head out there no. The problem with any factory head is that it is in fact a factory head designed with other things in mind becides performance and useing 20 year old technology. However concidering the cost ide say its the best value around for a street car.

[joes407]

well, got it done. not sure how happy i am yet. the car seems to be breathing better and is definitely louder. not sure how much gain i actually got though. honestly besides the sound and throttle response it feels about the same. i think i was hoping for a more noticeable increase.

[rolling thunder]

Well thats the catch is matching parts to perform in the same range. Now i dont know what your cam specs are but with alittle over a half inch lift I imagin its got a pretty healthy abount of duration and overlap to it meaing its designed to perform well in the high RPMs while killing low end torque. So no matter what heads intake what ever you decide to put on that motor is only going to help if it too is designed to run in the high RPMs. The catch is the TPI system is designed to work in the low RPMs the opposite of what the cam wants to do. Even with porting and larger runners the still die out at around 4500 rpms maby alittle more with some additional work. So with the new heads i suspect you would pick up a decent amount of high end hp even some low end grunt if not for the TPI/big cam set up. So the next question im sure you want to know what can you do to get some real noticeable gains? Well you have to eather put a smaller cam in that will work nicely with the TPI set up or change over to another type of intake. I suggest if you want to change the intake go with a holly stealth ram manifold as you can use your old electronics and sensors ect and it can be done for around $500. Also you have had the comp retuned for all the changes youve made right? If your running one of the later speed decity typ TPI set up i know its even more critical it be retuned for max benifit as changing the flow rate changes alot with how it calculated how much fuel is needed.

[joes407]

yea im using a superchips style chip. unfortunately they no longer program e prom chips as they consider them old and out dated so even though im local to them they wont reprogram their own product. having more trouble at low rpms rather than at wide open throttle. my iac seems to not be working so im hoping with replacing that that i will get a more reliable idle. i know im gonna have some serious lope from the cam but with my iac messed up im having to use the butterflies to adjust my idle. ive done away with the smog pump and egr altogether.

[rolling thunder]

Yea as expected a big cam will kill off low end torque and have a rough idle depending on how big the cam really is will require serious tuneing to compensate. Its not so much you will have troubles with the high RPMs as far as running condition is concerend its more like thes cars hp curves tend to flatline above 4500 and then drop off quickly. So yea its not so much the quality of idle thats of concern (thats to be expected with a big cam) its the fact that the parts youve selected dont really like to work together and will not yield good hp or torque numbers. Also as far as the removeing the air pump and the egr valve is concerned without dissableing them in the computer that will throw off your air fuel ratio because the computer compensates for them. For example when the air system is running its injecting air into the exhaust and because of that the o2 sensor will be reading a lean mixture. Now this isnt a problem because the comp knows that it should expect this because the air pump is running. However once you take the air pump out the computer still thinks it there and is still expecting the o2 sensor to run lean. Ofcourse because there is no air pump there will be no added air and the computer will think your running rich and will lean out the fuel untill it sees the expected lean reading. There are many other companies that program chips but i think without getting it retuned and having the EGR and air system dissabled i dont know how well you could get the car to run even with everything else functioning 100%.

[joes407]

actually i wish it would lean out some. the thing runs brutally rich. i never considered the fact that those emissions are also in the program. i never get a check engine light though. i think for daily driving it actually ran a bit better with the 305 heads but i didnt get as much lope out of the cam. ill be playing with it for awhile and swapping in/out some sensors till im happy. if i have to i might break down and get a new chip somewhere or have the whole computer reprogrammed.

[rolling thunder]

Yea thats the one thing i dont like about fuel injection you change one thing you change everything. Its nice that the computers have the ability to "learn" but they can only make so much adjustment from there base settings. Ide deffinetly look into the retune i bet it will be the best mod dollar for dollar yet since they can tune the computer based on the cams specs the new heads ect. You can also probably have them turn the emmissions controls off when they burn the new chip. Regardless though good luck and hope u get her straitened out.