Well, I was looking at a GM Performance Parts Catalog from 1999, and they have an LT4 crate engine that makes 375HP and 396ft lbs. TQ. The chambers on this particular engine are fast-burning 54.4cc. Valves are 2.00" intake/1.55" exhaust. Compression is 10.8 to 1. What I am trying to find out are the differences between a stock LT4 that makes 330HP and this LT4 crate engine that makes 375HP. Going by the specs , they looked exactly the same to me, so I was wondering if the combustion chamber sizes between a stock LT4 and this one are different. What is the chamber size of stock LT4 heads? Thanks.

 

The crate engine & the production engine are the same. I believe that the crate engines are rated with the gross hp. method vs. the net hp. of the production line engines,& the 330hp rating was a little conservitive. From what I have heard the crate LT4's were actually extra engines left over from the actual production run to be used for warranties etc. UNFORTUNANTLY they are all gone now & not avalible from GM anymore.

 

I know they are not available anymore, but I was looking more into getting the LT4 heads. If they make that much of a horsepower difference, then it would be a good deal. I can get the heads for cheap since my dad is a master mechanic at a GM Performance Parts authorized Chevy dealer. Anyone have these heads on their LT1? If you do, are they worth the money? Thanks.

 

If you have already ported your LT1 heads you won't see much of a difference with LT4 heads, and indeed may lose some power. However if you have the LT4 heads ported....watch out mama!!!!

 

And remember that you have to get the LT4 intake as well to go with the heads.

Other guys on here will no doubt recommend AFR heads or something. However in my opinion the LT4 heads give you a lot to grow with since they flow better than LT1 heads. And if you can get them inexpensively it sounds like a sweet deal.

Check out www.lt4.com for a ton of lt4 related info.

You can still occasionally find a used LT4 engine complete on ebay but it doesn't seem worth it for the HP increase, especially since the top end is mostly where the power is; other differences from the LT1 include an undercut crankshaft and a bit higher compression. There's more, and it is all on that site.