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Difference between 11.5 and 11.1 cp pistons

13K views 42 replies 15 participants last post by  700craptor 
#1 ·
How big of a difference between the cp 11.5 and the 11.1
Pistons is there? How big of a drop in compression is there?
Is it noticeable in power? The reason I am asking is that I seem
To be having some detonation issues with a brand new 11.5 and
Pump premium 91, and was wondering if it would be worth while changing
To a 11.1 instead. All I can get in town for fuel is 91.
 
#8 ·
We have 93 here how many points will octain booster raise the 91 to? I always thought it was bs never tried I run good Pump fuel :lol: I got it out the pump
 
#10 ·
I always though at 11.5 you should run 93 octane or 91 with a booster additive,if you can get a good one.
 
#11 ·
99.9% of octane boosters dont do a thing but empty your wallet.
 
#12 ·
That's why I never used any if I needed more than pump I either got 100 or 110. It's pretty easy to get here.
 
#14 ·
You should be fine with 11.5 compression. I run a cp 12.1 on pump gas at 1900 ft of elevation. What is the elevation up your way??
 
#18 ·
Well I went with a pcv a tried a couple different maps and am still having detonate issues , I got a hold of some 94 fuel and that helped quite a bit but did nit cure it 100%. It's happening mid rpm range with a load on , not sure what to do. Not sure if the difference in the 11.1 piston would be worth the change out or not. What is stock comp ratio ?
 
#20 ·
Ya Steve I don't know why it's running like this, I got your map in there now and running some 94 and it is a lot better than last week but still not perfect. Would adding one more base gasket be about the same as changing pistons out to the 11.1 ? I am not worried about the cost of an other piston but don't want to go 11.1 if it's not going to make that much of a difference.
 
#23 ·
FYI many CP pistons do have room to have material removed from the dome. For example CP's 105.5mm M1054 has about 60 thousandths that can be removed. You may want to contact CP and see if the Tech piston has that additional meat built into the dome.

Nate
Alba Racing
 
#25 ·
I was just joking for real but if it did grind a hole in it the compression would be lower;) no need to worry about pump gas. I know alot of the builders will take some off the dome to lower the compression if it is needed. But they don't do it with a grinder I'm sure but this is usually with the higher compression pistons(14:1)
 
#27 ·
Hey Nate do you figure .5 is realistic with a double stack base gasket (oem) ? If I can take this piston down to 11 to 1 by double stacking and it cures my pinging then I will know that a new 11.1 should work . Or should I try a super rich map and see what that does?
 
#28 ·
Fuel may help. You shouldnt need more than pump gas at 11.5:1 unless your fuel is poor or you have a lean condition. A base gasket is what about 20 thou thick... I would think you could see about 1/4 of a point lower. Have you tried adding an octane booster to see if that stops the pinging?

Nate
 
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