Both being ported equally, which would make the most HP? I am looking into doing a big motor for all types of riding (except mud), but really looking for upper rpm HP..
Thanks,

 

500 all the way! A strong 440 puts out about 42hp, a stock CR 500 engine puts out about 57hp. I have heard of 500s with pipes, reeds, jetting and filters putting out close to 70hp. I have seen a few 500s in 250R frames and one in a 400ex frame.Both of which were scary fast. The 440 would not even come close to keeping up with a 500 anyhwere. It would be like comparing a 300ex to a 414 Banshee

 

There are numerous big bore kits for a 400. Go to sparksracing.com and ctracing.com. They have a variety of kits with explanations. Four stroke tech also makes a 500 kit too. IF you want just go with a yzf426 or a yz400f. They are both fast too.

 

If it is for your R just get the PSI 425 kit, even has a powervalve.

 

I think he means a 250R built to 400cc's. He said"400R Stroker". I have seen a few FTZ 400's using the Pilot Top End. One interesting thing to note is that the guy in WI I seen who raced one went back to his CR500 powered quad. I didn't talk to him on this matter but jumping to conclusions I would think the 500 was a bit faster. One thing to think about is VIBRATION though. The 500 would be absolutely ruthless.

 

Thanks for all the responses dudes.

I am talking 2 stroke here (sorry I should have been more precise).

The CR500 making 57HP stock.. what year motor is that? Should the 500 be a 90's & up model? Whats a good year for CR500's?

Also if these 500's vibrate, dont they vibrate in the CR chassis's too?

Does anybody have the PSI website? Thanks for all the help dudes!

 

my dads friend has a FTZ 400R running on alchohol. He's never been beat. Not once. puts out around 90hp. very pricey though.

 

I know a guy who custom built his own 500. Your not going to get upper rpm power so much as rip your arms out grunt! I won't ride it!

I believe it dyno'd at 100+ HP!

If you email me, I can put you in touch. I dont know if he has email.