Can anyone tell me what would be the most cost effective way to increase the low end power of my son's predator 90? we mostly trail ride and it could use a little more grunt for crawling over the rough and muddy terrain. not concerned about the top end so much, as we rarely go over 25mph anyways (I'm still a little nervous at times as my 6 year old is fearless!) I work at an automotive engine machine shop and thought about shaving the cyl. head to increase compression, installing boyseen reeds, possibly an fmf pipe, and rejetting.
I'm reluctant to change the airbox other than possibly enlarging the snorkle as we do ride through water/mud. Could just a clutch spring change/kit accomplish what I'm after the way it woke up our 330 trailboss??? Does Wiseco make a better pistion that might
also increase compression/hp??? Thanks, Dan

P.S. I noticed when browsing polaris online parts catalog that the '05's have a new cylinder head but everything else less the transmission with reverse seems the same. Why the new cylinder head?

 

The biggest improvement would be a pipe. Hetricks has a nice pipe. Also think about changing the air box to a K&N or Uni. You will have to rejet the carb and probably change the rollers in the primary clutch to get the most out of the pipe.

 

I would change the gearing. My son also wanted more bottom end grunt, I installed a 40 tooth rear sprocket and new chain and it really helped. Great bang for the buck! I ordered it from Hetrick. The Pred will pick up the front wheels now!

 

I'm going to see how my Sportsman 90 does as we too do a lot of trial riding in mud and rocks. We need to crawl over rocks, etc so to not destroy our machines. I'm already thinking of changing the sproket as I've heard that is a great way to "lower the gearing" on these little wheelers. I like the idea of the 40 sprocket and new chain. Good luck.

 

.


There's basically 2 main ways to lower the ground speed of a Pred-90. These are:


1 - Sprocket changes. For a person with my limited skills, this is a "no brainer / easy" external change solution. Put a bigger sprocket on the rear / smaller sprocket on the front (or both), replace the chain with a longer and possibly better quality and "away you go". With my limited mechanical skills, this one was very easy for me. For details, surf: - Press Here -


2 - Replace your factory rollers. As per Dave from BNC Racing... "replace your rollers (located in the variator - front transmission pulley) with lighter ones in the range of 5-6.5 grams (stock are 9g). The rollers control how much rpm the engine must turn before the transmission "shifts". Think of it as holding your car longer in gear before shifting. The effect is to keep the engine revving higher, up in the power band. This will overcome the negative affect of the smaller sprocket on bottom end power and improve acceleration." Note: I'm sure this method would work great but it means removing the side cover of your transmission and doing to adjusting to its Variator. With a good Service Manual (even with a simular 2 stroke brand/model), you may feel comfortable doing this internal change solution.


To me, it boils down to comfort level of one's Technical skills....


Hope this helps...

.

 

.

To read some really interesting stuff on how to lower a power band, surf: http://www.superflygirl.net/powerband.htm

NOTE: This info was written for motocross bikes but many of its contents does apply to 2 stroke mini-Quads. Pretty interesting stuff that expanded my knowledge of what "can be done".

Hope this helps as well...

.

 

.

Dano38,

If you are thinking about shaving its head to obtain more compression and adding a piston, you might want to consider a Cylinder head upgrade. I found the info within - Press Here - very interesting. Based on its picture and Dyno chart, it appears to dramatically help.

Our '03 Pred-90 has a compression of 120 (confirmed last night). I've been told that increasing its compression up to 150ish (or higher) is a great idea for trail riders. Gives the mini a little more "bottom end punch" without a high reving engine. Some increase up to 180s but to me, this higher compression may put too much stress on its electric starter. Some favor 145/150 compression as an optiminal "balance" range.

For water riding, you may want to consider installing a bigger snorkle pipe. If you do this, you pobably will have to "jet up". If you want to get really fancy (based on your technical skills), you could remove the factory "low position" air box and install a filter under the center hood, or under the gas tank area. For this position, you may have to remove your oil injection tank. Will need some rubber tubing and possible invert carb intake for this trick. Pretty advanced stuff but I read these air filter upgrade works great too. Hopefully, a Performance dealer has such a "bolt on" solution in ther final testing stages??? I'm sure folks like Billy Holt at WRH Racing or Rich at Hetrick Racing could provide you the foundation parts for this Air Filter mod.

For jetting, I've been told the Pred-90 factory carb has a 85 jet. If you do have to "jet up", you'll probably want 3 different size jets to play with. For our modified snorkle, I really should increase jet size from 85 to 90. If you install Racing Pipes, Reeds, better air filter, you'll probably have to jet up to 95 -> 120ish range. It all depends on the pipe you upgrade to and its other air flow mod improvements.

Performance Reeds do help to increase air flow and improve throttle response. We have WRH Performance Reeds in our '03 Pred-90, and am very pleased with them. It does give the engine more throttle response. If you are comfortable with this upgrade, I'd recommend it.

I'm not too sure about your '05 vrs previous '05 Cylinder head change question. I know Billy Holt at WRH Racing is very comfortable with the Pred-90 brand. His son races one. Perhaps he might know why this change was done and if it may impact some of the mods you are thinking of doing. When Billy returns from Texas races, I'm hoping he could help us out with this one. For direct communications, Billy's email is: billy.holt @ wrhracing.com


Hope this helps as well...

.