RM bore kit

[GMX]

Hi,
im intrested in getting a RPM 167 bore and stroke kit for my 2003 rm 125 for that extra kick. I am also intrested in Eric Gorr's bore kit but I beleive they do not create as much horsepower/torque, but is a lot cheaper. I do care about price but which ever creates more power is all that I care about. Eric, could you make my bike run just as much power as a rm 167 kit from rpm? My bike setup is as follows: Bills pipe and shorty silencer, boyesen rad valve, geared down, sometimes use vp c-12. That would mean with a 167 bore and stroke kit I would be close to 50hp out of a 125!

 

[GMX]

...also, what would reliability be like? Im pretty sure it will decrease the life expectancy somewhat but is it to the point that I should be worried of blowing the motor at every race? One more question; would you have to redo the top end more often on a big bore bike then stock?

thanks for any help!

 

[bclapham]

GMX: 50HP out of a full on 250 is asking quite a bit! That said, i think a good direction would be ERic Gorrs 144 bigbore kit. The thing is, if you look on the dynos the 167 wont rev out that good and doesnt have much more power than the 144's etc. a well setup 144 is good for 36-38 HP with a very useable powerband. The other problem that i dont understand with the RPM strokers is how he gets the port timing set up well- since he takes the material from the head to make up for the longer stroke and uses a short reach spark plug and if you read any posts here on port timing you will see that this is the most important factor for engine performance and i cant see how this method of "stealth" stroking gets anywhere near ball park port timing. Also, 167 is a lot to ask from a rm125 considering reliablility and the somtimes suspect rm gearbox and the fact you will be dumping in nearly $2000 and the bike wont be worth much after a season or two- a 60mm piston is a lot for that cylinder to take!

that said, eric can build you 155 kit with 58mm piston and a 2mm stroke for a decent price and i suspect it will be way more reliable than a 167! Eric is using a slightly shorter rod to make up for the longer stroke and keep the port timing well set up, or you can use the stock rod and a 2mm spacer plater under the cylinder (ie the stroker kit is visable). (last time i spoke to him he was building a 2002 rm155 for testing purposes)

the 144's do need a bit more attention than a stock bike but they are reliable and very, very good fun! in addtion, since you arent changing the stroke and port timign excessively both the stock pipes and ignitions work well which isnt allways the case on the stroker. have a look on the forsale forum, i know someone that is selling a bolt on 144 kit;)

if eric gets to read this (ie ever gets his PC hooked up) he has my appolgies for answering on his behalf- but i think i covered everything!:)

 

[GMX]

I know 50HP is alot of power out of almost any small bore engine, I have a 4 cyl 650 street bike that makes 55hp. The RPMs kit must be somewhat reliable since many of the race teams use there kits and all ive heard is good things(both from Gorr and RPM). A stock 167 will create 40hp and with more mods that could be easily close to 50. Im intrested in Erics 155 kit....if it makes MAD POWER! :D I understand that they will need more attention to stock, since this is a race bike it already gets enough of it, hehe. My plan is to get a dynotek ignition in the very near future so I don't know how that effects anything. Thanks very much for the help.....all the choices!!!!

 

[GMX]

Are you the one selling the Bolt on 144 kit? Or are you just selling your bike with it? Oh yeah one more question....does Eric Nikasil plate the cylinder?

 

[marcusgunby]

40 HP is more than i expect a 167 will create(or any 125 based engine)-50hp im afraid isnt even a realistic dream, a CR450f only has about that power, the stoker engines IMO wont produce more peak HP than a 144-probably less in fact due to the reasons bruce said.However it will pull better off the bottom, alot of people dont like the feel of a 167 as its wont rev like a 125, but also wont pull like a 250-i think the best idea is a 144 kit or buy a KTM 200sx.

 

eric uses US chrome to re nicosil the cylinders.

 

[john stu]

167 50hp lol ya right

 

[bclapham]

Originally posted by GMX
Bolt on 144 kit?

yes, here is the link

http://www.dirtrider.net/forums3/showthread.php?threadid=82902

i will also take this opportunity to appolgise to the moderators for breaking a golden rule- please feel free to delete my post if you wish.

 

[bclapham]

on the question of reliability, the big (ie anything AMA) race teams dont use big bores at all, but they use RPM's nicasil plating on stock sized (eg 125 and 250) engines since he is located locally in SoCal where the teams are based. and i expect that any other teams that use the 167 kits in cases where it is legal view those motors as disposable!

as for reliability of Erics/US-chromes plating, i would say that since Eric is the only person from the motorcycle tuning industry to have authored an SAE paper on the topic that he has both the experience and qualifications to build a reliable cylinder. If you want to spend twice as much, check out RPMs, but realise you wont get twice the engine or quality!

in the meantime, if you are looking to get 50HP out of your 125 i suggest you take the engine out of your street bike and see if it will fit!

 

[bclapham]

here is a blast from the past, check out these links

http://www.dirtrider.net/forums3/showthread.php?threadid=5284&highlight=dyno

http://justkdx.dirtrider.net/125dyno.html

 

[GMX]

I rode the 151 bore kit on a 2002 rm and it hauled some serious ass! Who to beleive...you or the dyno? http://www.rpmsbigbore.com/dynorm125.gif

 

[GMX]

I think I might just get Eric to build me a monster machine. Im really intrested in this 155 kit. I think id rather just pay under $1000 than over $2000 for a bike I will probably just end up selling in a few years anyways

 

[marcusgunby]

RPM must have done some serious porting(ie very large exhuast port and very short ring life) to get the 167 to peak at the same revs as the 144-that would take some work IMO.

 

[bclapham]

marcus, clear out your inbox- we need to have a little chat!:p

on the newer rms its easy to build the 2mm stroker and keep the port timing ina good ball park since you can use the 2mm shorter rod from the 97 rm, maybe this is why the rm167 shows a better curve than the yz167- the yz167 doent even look to rev as good as some 250's