High Compression Question???

[tdsongster]

What is the downside to running high compression? I know that you will have to run race fuel for 12, 15, 13 etc and that you will need a better rod (carillo for isntance) but aside from that are there any other issues with running such high compression? Will the stock starter for a 400ex have problem starting?

Thanks

[crazyatvn]

Your rod is good as long as you don't go to a big bore like a 440. rod will tend to fail. As long as you don't dip in to the 11:1 range you will be fine with 92-93 octane range. stock starter would be good. Higher compression will produce more heat than stock but not enough to worry about. Thank is all I can think of.

[mojoe2878]

if you go to or past a 12:1 ratio you will need a better rod regardless of if the bore is stock or if its a 440 or bigger. i would actually recommend a stronger rod for anything above a 11:1. if you go 11:1 you will be good with a stock rod IMO. anything past the 12:1 will need a race gas mix or straight race gas.
another problem are blown head gaskets with the higher compresion, this can be greatly reduced by using a flex steel gasket.
you will get more engine heat with the higher compression ratio too but running a race gas mix or straight race gas will help with keeping the temps down.
if you go up to the 13:1 or higher you may need to install a heavy duty type start because it will eventually wear out and have problems turning the engine over with that high of compression. the stock starter was designed for a stock 9.1:1 compression ratio.

[Aceman]

I've also heard you need heavy duty head studs, but I am not sure when that's required.

[RaptorRacrr04]

a guy i ride with has a 12.5 440 kit in his EX..on stock rod. Its been like this for a year and has been ridden very hard, also has a 10k rev box on it and hits it regularly and still running strong. I also know a guy that has 13:1 piston on stock rod and been this way for 2 years and he races.