CRF250R 14.5:1 Vs CRF270R 13.25:1 DYNO

hopefully you have all read the first round of Venom CRF250 build info.... still on 250cc , we built a powerband that was fully 20% more than stock at every point in the rpm band.... endurance engine safety margins used on all choices...and 14.5:1 meant race gas necessary....

next came the Venom 270cc Big Bore kit... we decided to go with pump gas friendly...and since the smaller bore is naturally more detonation resistant than the 450 class machines...we went with a stout, yet safe for pump premium, 13.25:1 compression ratio

it was also appropriate to go with pump gas since this machine will be my personal mount for deep michigan woods riding

i hate to give up 1.25 points of compression.... but adding 20cc's is nice anyways...

a more radical cam than a hot cams stg2 would feed the bigger displacement better on top end, but i love the low and midrange the S2 gives for where i ride...

so here it is....again, more power everywhere... just how i like it


if you havent read the details of the other first generation of mods thread... you should to see what simple / cost effective mods this machine had / has

but here is the dyno graph showing best run of bone stock VS a gang of runs at the end of stock bre 250cc first mod set


That's a great build in both cases - the 270 certainly is not getting what you could if you went more aggressive...but it's gonna be fun and reliable.

do you have any experince with kxf 250s i have a 2010 that has hot cams stage 1 , but i was going to do a 269 with stage 2 cams next. do you think i would have more on top and bottm with the big bore and 2 cams? already have a yosh pipe on.

the kx requires very unique cam timing to make good has a very laid back intake port that IMHO lets a large percentage of intake charge straight out the exhaust during scavenging.

With the right cam degreed correctly - it will produce much more power everywhere. The wrong cam - it hurts it considerably.

Hate to say it - but the HC st1 on that bike is...bad.

Ron posted a lot of info on his build up of that bike in the kx forum. If you look through it you will see he made awesome power - 43 all done up - stk bore.

You would be wiser to spend the money in a "correct" manner with the best cam and spring technology rather than mix and match on that bike. It's truly a finicky engine design - as compared to the hondas which pretty much crank out hp with good head porting, piston, and a host of cams.

thanks, the hc stage 1 has a very good tougue curve i like it but could use just a little more over rev. i spoke to ron but didnt want to spend that much on cams and springs. i ported my last cylinder and most of the work was done on the intake.

thanks, the hc stage 1 has a very good tougue curve i like it but could use just a little more over rev. i spoke to ron but didnt want to spend that much on cams and springs. i ported my last cylinder and most of the work was done on the intake.

And yet you are willing to spend that money on a big bore and ANOTHER cam...

Just do it right, once - and you wont regret it. Sometimes you pay for what you get - and this is certainly that case - I promise you this, the rhc cams and spring kit would make you much more torque and hp than the big bore you are lookin at...

well how was i supose to know,thanks for the info. i get %50 off so it was cheep . 200 compred to over 700 so i gave it a shot. if i do his cam one day im going to do the 269 kit when i need to do the top end.

That's a great build in both cases - the 270 certainly is not getting what you could if you went more aggressive...but it's gonna be fun and reliable.

thank you kind sir :smirk:

i really dont want ...or need...more agressive cam timing for how i will use the bike...

but it really makes me want to try a more radical cam setup to feed the extra cc's.... i would like it on the dyno...but not in the michigan woods...

getting back into the 14.5:1 compression range would be good everywhere on this setup ... it would make more power everywhere...

but then we would be back into race gas dependence....

still....more compression and much more cam would be fun on the dyno rollers

check out the difference from stock to where it is now at 8000 rpm

stock was 24HP.... now it has 31hp...(close to what peak hp was on stock machine, and at 8k rpm :smirk: )

that is a 29% increase in power @ 8000RPM over the stock setup :smirk:

Edited by mixxer

thats a very nice increase

i'm still considering usng a stage 1 cam for tight woods riding with that setup

i have to say i am pretty amazed by the complete lack of performance tech in the dirt bike world.....

i have been an off road dirt biker for more than 30 years and i build LOTS of performance engines for the atv world.... the atv crowd if full tilt boogie into high performance engines....

so lately i decided to push the dirt bike end of things since i'm a dyed in the wool dirt biker.... but nobody in the biggest dirt bike forum in the world seems to have any tech they want to discuss.... or any individuals with dyno runs of their own stuff...

what is up with that??

does everyone just give money blindly to whoever??

do you all only add a pipe and call it good??

does nobody ever dyno tune anything of thier own??

i dont really understand why there is no performance tech discussions in the dirt bike arena

have other reliability biased mods yielded a 29% gain @ 8000 RPM..??

it can't pull at top end until it pulls through upper midrange.... that is why i bias all my mods for full powerband gains... when i have to drop some power in midrange to enhance top end...thats where my interest fades...

I blindly gave my money to Tuf Racing and now I have a screaming crf.

ron and i are friends... we even live close in michigan.... ron is first class all the way...

but thanks for all the excellent tech you have added to the thread..! :smirk:

most of this has been hashed over here over the last 7 years porting cams and big bore kits when Eddy and me started doing them and posting dyno graphs pepole had a good idea whats possible with proper parts.i think the first one was a 2004 with a stage 1 hot cam tim conoly porting a stock piston pump gas and a chm pipe the bike put out 38 hp up from 32 we were amazed @ the time .it seems the 270 kits were always good for about 6 hp @ around 6000 rpm which was huge in the beginning there was a lot of problems with them .With the economy there just isnt that many pepole building 250s they usually end up with a 450 .most of the serious racers have there 250s built just to be able to compete.i think theres more 450s being built .as far as bikes and information vs atvs and information it has to do with the fact that there are so many more atvs than bikes being sold and more shops competeing and bosting there dyno numbers to try to bring in business .

it does seem like the atv world is way more interested in engine building...!

well us quad riders do like our engines lol,. we currently run a 04x bottom end with 280 athena kit and a home ported 07 head stge2 cams and it works quite well. but we are needing an engine built for our next series and we currently have a new ic cube 267 ,and a new 302 ice cube, and a complete rhc 07 head set up,, my question is for the builders on here as we want this one built by the professionals!!!! which kit do you want me to send , will the 302 be the best?? more displacement the better? the 280 works well but gets pulled pretty bad on the long straights by the 300exs that are bored and stroked to who noes what lol. mostly 340cc 380cc range i believe. we also have a rekluse clutch as well to try and prevent stalling.damon is only 100lbs and has a hard time kicking them over <hence the x with the majic button>

we have completed our spring series and our nats arent untill july 1st ,would love to have a fresh pro built rocket for this??

damon won the spring series too!! not bad for his first yr with the bigger quads, but i cant believe how fast he said it dosent make enough on the big straights considering 2.5 months ago he said it was scary fast:)

ron if you guys have time just tell me what you want sent will pull it this weekend and box it up and send it with the head and cam

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