High Compression?

[Bigbadwhitey]

Ive been trying to research build ideas, and with all the variables im looking at, im curious as to what the negative effects of high compression (say 11.5:1) would be? Assuming a stock crank and rods but new pistons?

[proace4]

thats not really that high... still run pump gas and it leaves you plently of options for actually everything. lol what are your plans for the build?

i'm about to put my new heads on and with impala gaskets i should be right at 11.5 and from what loyd told me... i'll be just fine!

[Speed Inc.]

11.5 is not high

as far as anything negative about 11.5 ??? I see nothing wrong there and just spec your combo accordingly. I run 12.4:1 and can get away on 93 if I chose, but I still mix 93/100 NA just to be safe.

[Bigbadwhitey]

The car is not going to be a track car, as there isnt a track around here for miles
Id be going with either a LE or AI top end (Also confused as to where to go with that). So pump gas is a must (canadian gas prices suckas it is) and be streetable. What do you think i could get away with and still be safe?

[Nocturnal Z]

My old combo I was running was 11.8 to 1, I ran on 91 octane and had zero knock retard.

[gregrob]

11.5 is fine. Static compression only tells half the story as well. DCR is another big factor in the way the car's going to run, react to timing in the tune, octane requirements, etc.

If you have 11.5 SCR and a big donkey dick cam killing the DCR you'll have no problem at all on pump gas. 11.5 SCR and a cam that pushes DCR to 9 or above and you would have probably have to start watching the tuneup much closer as it would narrow your tuning window quit a bit.

[Bigbadwhitey]

static compression ration being calculated without any rotation in the bottom end? Just the standard calculations?

[gregrob]

Not sure what you mean but SCR and DCR are both calculated and neither have anything to do with the "rotation" of the bottom end.

DCR doesn't change when the engine spins faster, etc, ever. It stays the same.

You can calculate SCR by knowing the piston relief size, bore, stroke, head chamber size, hg thickness, etc etc. It's a function of how much air can physically fit in the cylinder.

DCR is different because it is dependant heavily upon the valve events.

[Bigbadwhitey]

Sorry, thats what i was looking for, thanks. So and SCR of 11.5:1 isnt going to be harmful at all?

Depending on the cam im looking at (.22x/.23x .56x/.56x 111lsa?) is there any way to calculate DCR to tell how this si going to effect driveability?

*on a side note, has anyone used the federal mogul rebuild kits? in wondering if their headgaskets will hold up to more than 11.0:1*

[gregrob]

If you can get me the .006 duration numbers on that cam and the rest of the specs for your setup I can calculate SCR and DCR for you.