Noobie LT4 questions

[Copernicus]

Hello all, never found a chance to introduce myself but thought I might as well Just bought my 1996 Z28 which I absolutely love and added it to our stable of cars we currently play with.

I did have a question though and it was the LT1 - LT4 conversion does provide more power and seems great but what impact does it have on SMOGability? I live in the San Francisco Bay Area and passing Smog with the DMV is quite important out here and pretty darn tricky. Does anyone have any suggestions on whether the LT4 mod is something we Californians can get away with or is this just for our friends not on the West Coast

[raroZ28]

I don't think it affects smog at all. It's a GM part that came on a select 96-97 vettes and f-bodies. It's just heads and a cam, you don't remove any emissions putting it on. Just better flowing heads, aggressive cam, and a better intake.

[Injuneer]

Depends how close they look on the "visual". The LT4 was never used in a 96 F-Body (only in a few 97's), so technically its a modification. Externally the heads and intake are very difficult to visually detect, assuming you removed the red powder coat from the intake manifold. They could look at the casting number on the heads and find it doesn't match what is supposed to be in the car.

And, it will increase emissions. The LT1->LT4 conversion does NOT use the LT4 cam that was certified for the 96 Corvettes and 97 F-Bodys. It uses the LT4 HOT cam, which is not certified for road use. With a good tune, the LT4 HOT cam will pass rolling emissions in most states, but I'm not sure about CA.

There are other ways to increase HP, without making it visible. You could get a moderate cost head port and polish on your LT1 heads, and they would flow as well or better than the LT4 head (at least in their unmolested condition). Throw the HOT cam in with those and a good tune, or maybe even go a step more aggressive on the cam, and you will make as much or more HP than the LT4 conversion kit, at equal or less cost.

The ads for the LT4 conversion promise "425HP"... but that is a little misleading. That is based on an engine dyno test done by MORE Perfomance in maybe 1998 or so. In addition to the LT4 conversion parts, they used long tube headers, larger injectors, a larger throttle body and a few other parts. And they failed to mention that they were using a $3,000+ aftermarket engine management system for the tuning.