Buddy of mine as the same LT1 set up as I have in my 3rdgen. If he where to add in the LT4 heads& intake(complete). How much more HP are we looking at?

 

With an LT4 intake/heads, Hot Cam, 1.6 rockers with valve spring, you should be able to get around or over 400HP.

 

The upgrade is not worth it. You can port the stock heads and go with a better cam than the hot cam and come out way faster and cheaper.

 

Yup. Looking back, I would not have done it the way I did. With that said though, I've got somewhere between 345 and 370 at the wheels depending on which calculator you use, but over Christmas break I will be getting it dyno'd to know for sure.

A better way would be to get the stock heads ported, get 1.6 rockers, something like a CC306 or GM847 cam, Comp R lifters, 58mm TB, 30# injectors, and LT4 timing set, and run low 12's to high 11's, and spend less or close to the same amount of money, and be much faster.

 

Get the heads, intake, 1.6 roller rockers and a bigger cam. Only way the conversion is viable. The 425 hp they advertise was done using a $3000 aftermarket EFI system. With a CC305 or CC306 and the LT4 heads and intake and big cam like a gm847 or CC306, your practically gauranteed a 375rwhp number with a good tune.