Actually, how bout this: You find a used KLX that has a poor running engine, perhaps it smokes, and you buy it dirt cheap. You get a 351 kit and make out like a bandit!

There is no way a stockbore can make the power of a 351 - regardless of how a bike is configured, adding a 351 to it creates much more power..

It just that, Turnsleft, in your tiny little signature line, I see over $1500.00 in performance parts.. For some, a lidless setup with an exhaust system and MCM gets all the power they need - and a significant percentage of the power created if one were to add a 351 kit..

 

I know this subject has been beaten to death and this is sort of hijacking a thread, but the big bore subject came up. I haven't really found a definitive answer, either. Is there a huge difference between the 331 and 351. I bought my sf for 2500 with all of the other performance parts already in place. I'm more of a top end rider. I came from racing gncc 125 class and then road racing in the 600 class so I've ridden in the higher rpms. Does the 331 perform better up top due to the smaller piston? Or would I be better to go with the 351?

 

On this engine-go with displacement.

 

Yep go big or go home.

 

And then a 13t front, combined with the mcm mod and a dynojet kit. yall be pumping power wheelies.

 

Yup, I waited 6 months to upgrade to the 351. That was about 5 months 30 days too long... lol

 

You mean like this?
BTW, that's my stockbore + MCM + DGR slipon + lidless carb setup + stock 14 tooth primary..

 

Klxster, the 351 kit was the last thing I did to my KLX. My riding bud has a stock KLX with a 351 and the carb Jetted, and runs way harder than mine did with the pipe and BB carb[pre 351]. Have ran 12, 13, 14 and 15 CS. 12 was good for the tight stuff but mostly I run the 13. I put the 351 on at 4700miles and now has 17500. It is a very good bike.

A little more for my signature line. Michelin Cross AC10s 80/100-21 & 120/90-18, CYCRA pro bend, IMS 3gal tank, rear LED blinkers[thanks to a Fir Tree], OURY road grips, Yamaha bend alu bars and a shifter off my Banshee. FYI the AC10 on the front seems to push a bit I had to move the bars up a bit to move me forward.

 

Absolutely your friends 351 would have run harder than your stockbore. Given any KLX, there is nothing that will enhance power more than adding a 351 BB kit..

But for those that don't want to tear down their engines for a $534 kit, I can get a few more HP and a few less lb ft TRQ with just a carb kit and a full exhaust system, compared to Bills' chart for the 351BB on a stock bike.. Side benefit being, like you, adding a 351 will then bump the power all the way into the upper 20's (28 being the norm) but with a huge increase in the TRQ curve..

 

Yep, I was just saying the 351 is the most bang for your buck[s]. I ran my KLX with the stock bore, open air box[K&N, jetted stock carb], FMF Q4 with power bomb and 12t[&13] from 425miles. I put the BB carb on around 1000 miles. At 4700 miles had the 351 installed. If I was to start over I would start with the 351 and go from there. The bike has 17,500 miles on it now.