We are running 12.1:1 compression on my 383 stroker. To relieve some of this extreme pressure we are changing to a solid roller cam so we can run more duration. Will this be ok for 93 octane pump gas? If it is borderline or too much, can I compensate by backing out some timing with LT1 edit? The CC measurments were taken using a FeL-PRo standard LT1 head gasket. Are there thicker gaskets available? Im a little nervous that here in South Florida where it gets hot I may run into some detonation problems on 93 octane =(

 

You should be ok with more cam.

On the side note, don't add gasket thickness to reduce the likely hood of detonation, because it's more likely to cause it then to help it.

Smokey Yunick found this out years ago. Make sure you have a .040 to .050 quench area (gasket thickness + how far the piston is in the hole) That is going to prevent the detonation more than the slightly lower compression ratio.

With a big cam you can easily run 12:1, but make sure you go to good gas stations. You always have a Knock sensor if you run into problems. The reverse cool on a LT1 motor is definately going to help keep everything cool.

Bret

 

I know it's been beaten to death but it's still a good point to understand......

Tripin,
Do a search for "dynamic compression ratio". You're at least gonna get an understanding of what matters when talking static compression and how it relates to the intake valve closing event of the camshaft.
Bret knows this, he just didn't want to say the "DCR" word as it's been thrown around alot here in this forum. Still good to understand.

-Mindgame

 

One thing that no one has mentioned is that solid lifter cams tend to act slightly smaller WRT to cylinder pressure… then similar duration hydraulic cams, you'll likely have to add 6* or more on both lobes just to get similar cylinder pressures so you'll need a much larger solid cam.

As far as what will be OK, quench, chamber and piston design have at least as much of an effect as compression and valve timing (taken together as DCR), so you're asking a somewhat loaded question

 

Well we are going with a pretty big solid cam, duration is somewhere in the 250 range.

The pistons are forged flat top JE racing pistons that have been custom ground between the valve reliefs and the combustion chambers on the heads have been smoothed out and polished. They look just like any racing type heads.

Thanks for the info guys, my engine builder said there wouldnt be a problem but I just wanted to get some feedback from you guys and see if anyone had a similar setup/compression ratio and how it worked out. We can still lower the CR a little by resessing the valves into the the heads a little. Hes an expert and has been building performance/racing engines for over 15 years.

 

Yeah, you can lower compression a bit by lowering the seats but that's the wrong approach in my opinion cause you hurt flow.

With a cam as large as the one you're suggesting and the IVC that usually comes with a cam on that scale, you shouldn't have a problem with 12:1.

-Mindgame

 

For that exact reason we do not want to resess the valves into the heads. I belive we will be ok with the steps and care we took with the combustion chambers and valve reliefs and also that big fat solid roller cam. Iguess we will find out on the dynometer!

 

What piston rings are you running on this 12:1 stroker?

 

3mm oil rings
and custom fitted rings

there are a total of 4 rings on each piston including the oil ring. I dont remember the name brand, I can check tomorrow but they are top of the line. I didnt spare any cost in building this motor.
We went with 3mm oil rings to reduce friction and free up a few more ponies.

the only negative side with the 3mm oil rings is I have to find a way to get a vacuum in the crankcase. I ditched the EGR and crank case venilation system.

Oh BTW got the specs on my cam today =)
Solid roller billit cam
its a .580 lift on intake .588 lift on exhaust
254 intake duration and 264 exhaust duration
110 Lobe seperation

hehehehe