yz 85 pipe? any advice

[n2dirt2]

2009 yz 85 stock but with vforce3 and shorty silencer. Son races MX and short tight tracks, we are looking to get a little more bottem end out of the corners and such. Son doesn't ride wide open all the time. Has anyone done any testing / trial and error and found a pipe they like? Thanks! :cool:

 

[plynn41]

I've got the same issue so I'm interested in the responses. My son has an '03 YZ85 with an FMF "Fatty", but it's very pipey, and he doesn't ride on the pipe very much. It was probably not the best choice for him out of the 85s. I'm willing to spend a few bucks to fatten up the power curve if it can be done though.

 

[2stroker144]

a buddy of mine has an 06 yz85, with an sst pipe and it has decent bottom....but you can only get so much bottom out of something that doesnt have a power valve... get a kx 85 :)

 

[IndyMX]

I installed Boyesen Pro Series dual stage reeds in my stock reed cage on my YZ85, and that seemed to smooth the power a bit. It wasn't so quick to try to loop out, and the hit was mellowed quite a bit.

 

[JGrossijr]

I tried 3 pipes back to back on a practice day. FMF SST, R&D cone pipe, and a stock pipe. The engine was stock except for VForce3 reeds and an FMF silencer. The stock pipe was best, particularly for bottom end. Compression is the easiest and most cost effective way to help low rpm power, but top end pull will be sacrificed. Check out http://phatheadracing.com/detail.aspx?ID=7 Use the Y02 dome for a good bottom end improvement with minimal top end power loss.

 

[helio lucas]

yes, it will add bottom end and midrange. but will make the transition off\on the pipe very much faster, snapier and dangerous... also for mx might need high octane fuel.
porting will move the power around. big bore wil add power where you like!

 

[JGrossijr]

yes, it will add bottom end and midrange. but will make the transition off\on the pipe very much faster, snapier and dangerous... also for mx might need high octane fuel.
porting will move the power around. big bore wil add power where you like!

The first half of this response is dead on. But the part about "dangerous" is interesting to say the least. You won't need any more than 91 octane with the Y01 or Y02 dome. Porting is a risky & irreversible modification. Big bore adds a little power throughout the entire rpm range and smooths out the hit a little, but is much more expensive. You need to bore the cylinder, replate the cylinder, use a more expensive and harder to find piston, more expensive and harder to find ring, modify the head to match the new bore, and every rebuild from that point forward will be more expensive. Up front cost will be around $500. The Phat head option is $150, adjustable, and completely reversible. Seems like a simple choice to me if your goal is to have a little better torque coming out of the corners for a rider that doesn't ride in the upper rpm range.

 

[helio lucas]

my point in "danger" is that the engine will hit very hard. easy to loose traction and dificult to control.
here is the proof
this stupid guy that almost landed on the rear fender was on a bad day. the track was with mud just before the jump... in a slow lap the damn rear tire spin on the mud and grip on the base of the jump... i felt like superman... :yikes:

about porting, just taking 1mm from the base of cilynder will improve the bottom end. and is reversible. and is cheaper than the complete phat head... i pay 10 euros... at the same time you can raise the compression ratio.

but what do i know?!? :cool:

wait... this guy knows better than me... 102873839 times...
http://www.eric-gorr.com/model tuning tips.pdf

 

[Patman]

I always find it amusing that the first thing people think they need to do is add mpower to a bike. Why not spend a little time learning to understand how the bike you bought really delivers it's power and then accept the fact that if it's not enough you might just need a bigger bike because there is not a lot left on the table with most bikes. Sure internal mods are not as cool looking as a nice new pipe but usually offer the most bang for the buck. As pointed out by helio lucas the mods in Eric's book are based on years of experience and knowledge by the best tuner out there. Buy the book, learn what you really need and not so much want, make a plan, follow the plan.

 

[JGrossijr]

...about porting, just taking 1mm from the base of cilynder will improve the bottom end.

This modification will indeed improve bottom end torque. It does not meet the standard definition of porting though. It's also critical to make sure you can afford to loose .039" (1 mm) piston to head clearance or you are going to end up with a dissapointing and expensive experience. 10 Euro ($14) to get a cylinder base machined & replace the gaskets? I don't think so.
I have done the Eric Gore big bore kit with the machined cylinder base on a KX 65. I spent about $400 on the package. I was happy with it, and agree that Eric Gorr knows what he is doing. Later on I added the Phathead. There is no question that the Phathead had more of an effect on bottom end improvement, which resulted in LESS of a power hit.
In response to Patman: I completely understand your point, but n2dirt2 asked about improving bottom end, not overall power. In most cases improving bottom end results in reducing top end (less peak power & overrev), and a lot of kids are faster this way because the bike is easier for them to ride. Improvements through the corners are worth a lot.
The YZ is a great bike, but it is a little more challenging to ride on short tight tracks than bikes with power valves. I understand the objective.

 

[n2dirt2]

Thanks for all the great advice guys. I think I will look into the fathead and go from there. Does anyone know if there is a thiner base gasket for the yz 85?