kirk_252

So I'm rebuilding my lq4 in my truck and looking for advice. Its stock crank and rods. I had it bored .20 with flat top pistons. I have an Vinci cam "the trucker". But my question is do I run the 317 that are all reworked or my 243 that have about a 1000 miles on them. They both have GM performance valve springs. I all ready bumped the compression up some with the flat tops. Do u thunk the 243 might be to much?

batboy

iTrader: (6)

When you say flattop pistons, you mean no valve reliefs at all? Usually you'll have -3 or -4 valve reliefs which makes a difference in CR. With no relief at all, you'll be at about 11.1 CR with the 243 heads (more like 10.8 with 3cc valve reliefs). The 317 heads will drop CR pretty low unless you have them milled.

Sales2@Texas-speed

iTrader: (5)

Between those two options, for an NA or nitrous combo, I'd go with the 243's!

kirk_252

At what point will premium gas be required? And lq4 pistons have valve reliefs and they have a slight dish also.

Sales2@Texas-speed

iTrader: (5)

There are quite a few variables that go into that number, cam specs, altitude, fuel, and tune just to name a few! Many will draw an imaginary line around 11.3-11.5:1 for static compression and pump gas.