Has anybody used the 275cc big bore kit from Firefox racing UK?The advertisement is not that clear,the barrels shown looks like new 150 SP but states that MC21 tops are internally cut to accept the bigger bore.

Any help out there.

Thanks in advance

Howzit Harold !
Welcome , I have never seen that kit before . We have two versions of 300CC big bore kits that the guys do here in SA . Neal

Just had a look , that is a nsr150 barrel , we can get 2mm oversize pistons for the standard 250 barrels !

think there's older posts on the fire fox kits saying that whats described is a little suspect! do a seach of the forum??

if you want to go bigger go the TYGA 300 route much better than the suspect 275 one from firefox they changed their name lately from DPS racing

The Tyga kit is very expensive for someone here in south africa. My problem is my barrels. No one can do a proper plating job in this country so I tried out the sleeves. First time out the one sleeve droped about 0.25mm in the barrel and blew the gasket. My problem now is all my ports are to big because I didn't do it myself so I need new ones. It would be best to keep the bike 250cc but were would I get barrels that hasn't seen a grinder?

Depending on which model you have you can buy new 21/28 cylinders here in Australia for $1275 au each or jap 4 have second hand ones for a good price.

I'd be checking out jap 4 performance if I was you.

Andy

We have 3 big bore options ,
Nsr150 option or bore out to 59mm piston or rm125 piston with 2mm oversize . All these have been done locally , only problem is the nikasil guys bum job !

Cool.
Yesterday I bought a MC21 in Durban and the bike would be here in Cape Town about thursday. It is the black one on gumtree for R5000. Would be nice to have one for testing purposes. I am going to try to keep my bike 250cc as far as possible.

malossi do a 180cc kit for the nsr125. if that could be made to fit it would give you 360cc.
the kit uses new barrels and costs about £389 per barrel in the uk.


Last edited by GrantA on Sun Jan 31, 2010 1:15 pm; edited 2 times in total

Harold wrote:Has anybody used the 275cc big bore kit from Firefox racing UK?The advertisement is not that clear,the barrels shown looks like new 150 SP but states that MC21 tops are internally cut to accept the bigger bore.

I mailed them about this kit, ignore the pics they are "just" boring out NSR barrels and fitting bigger pistons.

I remember talking to Andy about it and he reckoned back when Eric Gorr was doing this sort of thing that he reckoned you could go out that far as it cut into the RC valve too much.

The good thing about the 300 kit is it's brand new barrels. They alone are worth 80% of the cost of the kit.
Other than that for what you're spending on either this 275 or 300 motor you could get a better 250 motor built.
_________________
Please do not PM me technical questions, if you can't find it on the Forum start a thread

I can't thank all of you enough. Thanx for all the advice. I will rather save up some money and keep my bike(s) 250cc. Some say you can tune a 250 motor beter than the 300 kit. Ones again thanks for all the effort.
would be great hearing from you guys again.

fontyyy wrote:
I remember talking to Andy about it and he reckoned back when Eric Gorr was doing this sort of thing that he reckoned you could go out that far as it cut into the RC valve too much.

When I spoke to Eric Gorr about this (about 10 years ago! ) I seem to recall he calculated max oversize would be 263cc (without attempting to modify the stroke) before running into port timing issues.

I know someone who persevered with an Eric Gorr oversize, and when it ran it ran strong, but it wasn't reliable. I built an MC18 motor for a friend in the states that had Eric Gorr 250 barrels, and that ran like a scalded cat! It was also reliable... but 250's usually are!
_________________
Andy.
NSR-WORLD.COM

Please keep all responses to Forum posts on the Forum so that others may benefit.

Please DO NOT PM me for technical advice. My time is precious, and you will probably receive a faster response on the Forum anyway.

Check us out on Facebook! Please "like" our page!