I'm thinking about building an LQ4 (possibly LQ9) with high compression to use
E 85 exclusively. I've read where E 85 can support 13 and 14 to 1 compression, perhaps even higher. Without changing the stock pistons, how high can I go compressionwise with a cam that has a lift of approx. .540? Even if I could go like 13/1, I wonder if the stock pistons would stand up. All comments and suggestions welcomed.

 

I assume you're asking about lift for piston-to-valve clearance. I don't know about that, but I know that it is supposed to be better to fight knock and improve combustion with smaller chambers versus domed pistons.
Another consideration with cams is the more duration a cam has, the more tolerant of compression it is as far as detonation goes. A good example would be an engine that has had its displacement increased (and compression) and kept the same cam. This motor would be more prone to knock at high load and low to medium rpm than when it had stock displacement (and compression). A way to remedy that would be to change to a longer duration cam. It will lower cylinder pressure at these engine speeds and reduce the tendency to knock. The pressure will increase at higher rpm, which is OK because there is less time for knock to occur, all else being equal.
Make sure that you tell your cam tech that you are trying for as much compression as possible.

 

Thanks for the reply Mike. The cam I'm thinking about is the Comp cam 269HR, 114 CL, .216 I duration, lift .525 and .220 E duration, lift .532.
I've read a lot of this forum and really not any info I've found about E 85 and very high compression ratios of around 13 and 14:1. I'm guessing there's a reason because E 85 is getting more common. Cheap racing fuel! Guys, join in and tell me something I don't know. It shouldn't be that hard.

 

I don't think that cam fits my description, for whatever my advise is worth. Why did you pick it? What is the overlap? Did you call Comp?

 

Thanks again Mike. That cam looked good to me from a DD standpoint. I was considering it before our conversation tonight. I'm looking on Comp's website and don't see the overlap spec. hmmm

 

Isnt E85 about 100 octane? I think if it were me I would be much more comfortable in the 11:1-12:1 range, but then again I play it safe

 

You can build so much power without going super high compression and more flow intake wise and exhaust wise. The really high compression guys are running monster power applications. Why are you feeling the need to go really high compression right away?
Just curious?

 

I've read several places that E 85 octane is 105. The blend could go as low as E 70 in the winter, making its octane around 102 if a calculated it correctly.

 

I don't need to, I simply thought of it as very cheap horsepower, nearly free. Assuming everything stays together and that's one of my questions.

 

There is no such thing as cheap horsepower. The cheapest thing i can think of would be a nice cam, springs,rods, longtubes, tune, and a decent stall. Like most of us do. In general its an abc123 type deal with our motors and our trucks, our motors eat up those mods with a mass gain in HP. If you want more HP go with N2o on top of that. Or in general if you want cheap horse power just go with n2o. Without touching the bottem end. There is a reason so many build in that direction rather then high compression.