HP/RPM max for stock crank/rod?

[gasguzzler]

I'm looking at going to a ported head and large cam for flat track racing my 426 combo. Has anyone broken a rod or crank from too much rpm or horsepower? I'm suspecting this will be a mid 40 horse engine turning up in the 9000+ rpm range.

Any opinions or experience on the largest cams offered for these quads? I'm eyeing up the biggest web cam they offer.

Thank you!

[thebig450es]

What compression are you running? you dont want to go with too big of a cam without enough compression

[gasguzzler]

I'm currently around 11:1, I may kick it up to 12.5 - 13:1, might try it with my current set-up first. It will have a ported head that will flow very well.

[tri5ron]

Your rod and crank should be able to take it,...
but the headbolts, (and their respective threads), wont.

Don't go cutting corners on a build like that.
Do it right the first time, and have the GTT studs installed, (if you don't already have them).


If you choose to ignore this advise,...
do us all a favor.
Get an accurate tach installed, and aim your gopro at the tach.


I'd like to see the video, and hear just what it sounds like,...

when it blows.

[gasguzzler]

It's already got the HD Studs, TC racing cam, valve springs, and lectron carb. It is currently faster than a stock 08 450ER with a rider at least 40 lbs. lighter than me without the ported head.

[thebig450es]

With what you have already and if you get some cooling mods ie...spal fan, second cooler and bigger oil tank. Id say shoot for the sky for compression. I have zero heat issues with mine and i wish i went into the 14 to 15:1. But the engine is only as good as the weakest part where at extreme mods you need to watch the rod and parts like that. correct me if im wrong but most 400's stop making good power at like 7500rpm

[gasguzzler]

With a stock cam, yes, the 400EX is done by 7,500. With your stroker engine you may be done there too due to your accelerated piston speeds. If you look at CT Racing's 440 big bore engine combo, it's still making good power up to around 9,000 rpm and it sounds like they aren't using the biggest cam available.

How is the Sparks adv. timing key working with your higher compression, big bore engine? I'm looking at installing one of those along with a programmable ignition system.

Thanks!