Yamaha TRX850 Enthusiasts Forum

Hi Guys,
Anyone know about thinner head gaskets and what compression can be achieved?
Also has anyone tried just upping the compression to say 11:1 and rejetting (open up breathing of course) to see what effect this has on mid range power (say 4 to 600RPM?

Cheers,
John

Messing with head gaskets on water cooled motors can be risky Redog1, better to go for higher compression pistons (878cc bore kit) or look for horse power gains from carburation changes such as a pair of the marvelous Keihin FCR41`s.
How does 10 horses plus (at the back wheel) grab you? That`s what i got when i fitted mine.
Obviously a larger bore exhaust sytem helps the motor clear its throat better too, the Over and Akrapovic systems have headers over 42mm I/D at the head opening up over their length to the end can or cans:

http://www.overracing.com/shop/YAMAHA-T ... 433SC.html

By the way, ignore the 180 degree crank reference Over should know better seeing as their TRX/TDM based racer was possibly the most talked about of all TRX`s, apart maybe from the Hyperpro Troll:

http://www.carolenash.com/insidebikes/b ... hyper-pro/

Thanks,
I appreciate the improvement better carbs can make, but my experience doing up other bikes has generally shown me that more compression gives the best bang for you bucks, and not just at high revs. Do you think the slight capacity gain from the bore kit is worth it?
I know you can't gain toooo much in compression without cam changes also. JUST thought there might be a slim head gasket kit out there to try.
Will probably go the carbs eventually, but as the bore is in perfect condition, I am not keen throwing away two good pistons to gain compression.

Still, 10hp increase is appealing.

Cheers,

Redog1 wrote:Thanks,
I appreciate the improvement better carbs can make, but my experience doing up other bikes has generally shown me that more compression gives the best bang for you bucks, and not just at high revs. Do you think the slight capacity gain from the bore kit is worth it?
I know you can't gain toooo much in compression without cam changes also. JUST thought there might be a slim head gasket kit out there to try.
Will probably go the carbs eventually, but as the bore is in perfect condition, I am not keen throwing away two good pistons to gain compression.

Still, 10hp increase is appealing.

Cheers,

Skim the head, crazy german upped the comp to 17:1 without any clearence issues (it was not reliable though and blew gaskets all the time) but you should be able to go 13-14 without any problems. And as you say, it´s a very cheap mod!! Think most workshops over here do it for 40€-ish. I´ll be doing it myself soon...

Yep head skims can work well too, although there`s limitations based around the shape of the piston crown.
Where`s Quantime to explain the science behind it when you want him?

Yer i spose a great analogy would be like going to the toilet and having a dump then after having a head skim like going to the toilet and having a dump on an egg cup if not careful I'm sure I saw Prof Juilius Summner Miller do something with an egg about that...

cobbadiggabuddyblooo wrote:Yer i spose a great analogy would be like going to the toilet and having a dump then after having a head skim like going to the toilet and having a dump on an egg cup if not careful I'm sure I saw Prof Juilius Summner Miller do something with an egg about that...

WTF????????