74VETTE

I've recently bought a 74 with the LS4 454 in it. Recent research shows the intake is from 72 judging by the casting number (333841). So out of curiousity I wanted to see if the heads were what one would expect on an LS4. The casting numbers I found were 3931063 GM4T. I did a quick search through a few forums and found that these are from ~69 427 oval port closed chamber.

Now the car runs good, but is not the screamer I would expect a 454 to be. I had always assumed it was a stock setup with low compression and baby cam, so as long as it ran OK I didn't see any point in cracking open the engine, throwing on a new set of aluminum heads, cam, and intake. But now that I've discovered these 427 heads on there, I'm wondering what my options are. Am I a quick cam change away from making a good bit more power? Assuming stock 454 bottom end, is there a way to tell what compression I have now approximately? Or do I need to find out what pistons I have? I appreciate any feedback you can give me.

badrad

It's all a guess without knowing which pistons you have. If it's a stock short block the heads will bump compression up to 9.25:1 and some change. The Vette LS4 cam was smaller than the previous LS5 camshaft. Low compression 454's will still run great depending on how much you want to change, they can take a lot of cam and still be streetable. Bottom 13's to high 12's are easily within reach.

74VETTE

How big of a cam could I safely get away with? I wouldn't mind a little lope but don't want to impact drivability.

Vette5.5

Best way, is really to pull the heads and take some measurements, to get a better idea what's really going on inside there. Always best pulling the engine out to do the work, as far easier to work on, and less likely to mess up an expensive paint job. Once a better idea what's inside, most cam manufacturer tech lines can help with a choice there. Most better ones can give you a part number for a modified catalog grind, to better suit your needs, maybe for a little less overlap.

badrad

Something like Isky's Mega 270/280 grind. It's a real mild lope and wide power band. I prefer to use it for the LS-5 replacement. Most of the decision needs to take into account the trans and rear gear.

74VETTE

I've got a TH400 auto tranny. The speedo suggests my rear is a 3.36 although when I drive upon one of those "SPEED LIMIT IS 45MPH; YOUR SPEED IS nn" stations parked on the side of the road, they show that my speed is just a bit slower than what my speedo shows. So I suspect I have the 3.08 gear in reality.