How can one tell the difference between the two besides looking at the intake manifold? I bought my engine from a local guy here who told me it was a LT4 straight out of a Vette. My optispark dicided to poop itself today so I asked him what year optispark should I get, he said get the one from 94, the one with the small shaft. This pussled me because I couldnt understand why a LT4 engine which was made only in 96 for the vette would use a older style optispark. I had my doubts about the guy, this was the icing on the cake. Now I want to find out what motor I really have.

 

Pull a valve cover. If it doesn't have the GM branded aluminum roller rockers, it's not an LT4. It should also have the ovate wire springs, not regular round wire springs. Also, the LT4 had 7/16" rocker studs, if memory serves. You could measure these. If it has the LT4 parts, I suppose the heads could still be LT1 heads with retrofitted LT4 parts. The heads have the same casting number, AFAIK. If you have an LT1 head around, you could pull the intake manifold and look at the intake ports, they are 0.100" higher on the LT4. Hard to see without a comparison. The bottom end can be verified only by pulling the pan. The LT4 will have 4-bolt mains and the crank is different with undercut and rolled fillets. You could also pull the timing cover - the LT4 timing chain and sprockets are different. The cam sprocket on the LT4 is solid, it is webbed on the LT1. The chain is a roller on the LT4 but not on the LT1.

Rich

 

The heads are 190 AFR heads so I'm not sure if I'll be able to use them to figure it out. The timing cover seems to be like the next viable option to look at. Thanks.

 

Well, the differences in the short block aren't too significant, unless you have a woody for 4-bolt mains. They don't make any hp, that's for sure.

Rich

 

and the 'Vette LT1's were also four bolt mains

As Rich stated, the big advantage to the LT4 was the heads. If you've replaced them, it doesn't matter whether the engine was originally an LT4 or LT1, it's now an LTx with different heads.

One quick and easy way to tell if the engine is a '95 or earlier is too look for the CPS in the timing cover. If it's the original timing cover and doesn't have provisions for the CPS, it wasn't an OBD2 engine, and therefore wasn't an LT4.

None of this matters what it "was". Your engine would have exactly the same performance it does now whether it started as an LT1 or LT4.

 

Good points fellas, great info. It's more or less the fact that if he lied about it what else has he, would he lie about. Your mechanic imho should be like familly, almost like a brother but closer. If you cant trust him who can you trust.

 

I completely understand. For some reason I trust mechanics as much as I trust used car salesmen though

This is why it's a very good idea to educate yourself as well as possible. Then people can't screw you as easily. People will try to get away with as much as they can... don't let 'em.

 

LT1 vs. LT4
Google is your friend.

 

No it's not but thanks.