Hey, I have a GMPP LM1 block/heads that have the stock .45" thick gaskets now and an 8.5:1 CR. I'm wanting to do a cam swamp and replace the head gaskets with some that are .15" thick...hoping the bump the CR up to 9.0:1 or so. Will I have enough piston to valve clearance? Do you think I'll see 9.0?

The cam I'm going with is the Comp Magnum cam (#270H) with a .470 lift. Will these hold up to the stock springs. I know you usually replace them with a cam swamp, but the engine is new and I'd hate to replace something that's new and might be fine.

Thanks for the help,
Matt

 

Valve to piston clearnce is not an issue in a dish piston SBC motor until about .700" of lift, as long as the timing chain doesn't break.

Don't put steel-shim head gaskets in your motor, unless you just really enjoy swapping them out all the time. They are highly prone to failure. The performance loss of blown ones far outweighs the benefits of the very slightly higher compression.

Your car will go faster with a XE268 than with the older 270 design. The stock springs are inadequate for the .390"/410" POS that's in it now, let alone anything that actually opens the valves. Get a set of 981 springs along with the cam.

 

Dude... I would honestly get different pistons, heh... 8.5:1 is anemic. I am going with 10.3:1 on my motor... I really don't forsee you making a lot of power with that compression ratio. Are you planning on a forced induction setup? Your cam sounds pretty good but I believe that you should get the new springs just to be sure. Those are the ones I have on my motor now, you don't need to worry about valve to piston clearance, you need to worry about spring bind. :rockon:

 

Alright, thanks for the quick responses. I was also concitering the High Energy 268H too. The car is a daily driver/weekend racer so a little less lift is fine. If they are so phrone to failure than there is no question that I wont be swamping in those gaskets, I dont want my only car to be down becouse of a blown head gasket. I dont need real high compression.

Also, what would you say the next step is with this engine? I was thinking Vortec heads and a new Vortec Edelbrock intake...I've never done engine internals so I'd like to leave the pistons alone if I could. I'm not looking to make huge power with this engine nor am I planning on a forced induction setup. I'm looking for a very steetable mid-13 second car and I will never run any nitrous on it either (cheatin' juice).

Thanks,
Matt