All I ever hear is how crappy (bascially sums it up) the 500 H.O. motor is when it comes to getting more power out of it. Does anybody know why exactly? What are the internal weak points of the H.O. motor that prevents us from getting much more HP out of it?

Just curious.

Thanks.

 

Dyno tells me I am at 47.5 horse and I still have lots of ideas.

 

You know with my 2000 pre HO, I have thought about this alot. A 4 stroke motor is bascially a car motor, with the right cam/valve hardware, a good exhaust and intake/carb to allow it to pass as much air as possible, is the theory I have been dwelling on. I have heard Aaen makes a hotter cam for these motors, add higher aspect ration rockers and heavier springs. Add a Supertrapp or some other aftermarket pipe and play with the amount of discs, go to a bigger carb and jet it according the amount of discs you are using and how the timing is set. You can smooth out the intake passages of the head, maybe open them up some. Then you can add that clutch kit to take avantage of all this new gotten power. Maybe mill the head down to up the compression ratio, add a lighter forged piston. Now doing all this costs money, is it worth it? Maybe. I can get just as stuck, or crash just as hard with the way it is now. You betcha. I am racing? No.
Why do we do these modifications? Because some of us are MEN and we gotta have more power!! Sorry I am rambling! I have thought about what I would do if the parts were available, but havent justified it enough to try, I could sell my quad, and add the $1500 or so and buy a new/ or slightly used, Prarie, Grizz, 700/600, Rincon, to get me to the power level I would have achieved with the mods. By the way ATV Mag test on the Rincon, I like the manual/auto idea, 2nd in manual would be the perfect tight woods gear for me, down to zero and crank it up to 40. I wish the Sportsmans had 3 gears forward, make low, lower like 0 to 15, and let me shift on the fly! Sorry I am babbling again! I am sure there are mods that can be done with enough money, all parts can be replaces/or upgraded, if cost is not an issue.

Sorry for the length of the post, I am interested in mods that can be performed to these models

Troy

 

I think the 500H.O Motors are very good & dependable never had an engine prob
To get more power ya gotta make breath better you are never gonna get 2 stroke gains that is out of the ?
And 4 stroke mods can be pricey compared to 2 strokes but extra power is there try Trailkings mods he has got the best gains I have seen plus he has benn on the dyno to back them up I think for what he has done would probly cost about 300 the biggest price being the white bros muffler.

 

Aaen does have a lot of stuff, but it is very pricy. They want $175 for a high comp piston, when you can get ia Weisco from Rocky Mtn for around $75-$80 with shipping. Their longer duration cam and porting is what I've been looking at lately, but I never heard of anyone who has done it before. I agree, all the money spent could be $1500 towards a newer faster quad. If I send my head in to get ported, do I have to do anything else to the valves or springs to accomodate? I am also a little bit cautious about doing something to my engine that I cannot change back if I don't like it.

Trailking says he got good gains fromt he White Bros. exhaust, but everyone else I talk to says to go with HPd. If I seem like I'm confused, it's becuase I am. [img]i/expressions/face-icon-small-smile.gif[/img]

 

One reason the HOs don't respond as well to mods is because they already put out 20% more power than the standard 500. You get the rule of diminishing gains at work here...after a certain point, it takes a lot of effort to gain a little.
Another reason is the carb. The CV style carb requires a certain amount of vacuum to open fully. Open up the airbox (for less intake restriction) and the carb doesn't open as much, negating the effect of opening up the airbox.

A different carb is almost mandatory if you want more than very modest gains, a cam & very precice jetting will probably be the cheapest gains for the HO.
Probably more performance can be gained for the first $200 spent might be a clutch kit.

Farmr

 

I will have to disagree about the stock carb. Just about every carb on any stock 4 stroke quad uses the engine vacuum to lift the fuel needle. By opening up the air box you are not changing the amount of vacuum the engine will pull. Same thing with vacuum secondaries on an automotive 4 barrel carb. You still get the same vacuum, but with air box porting you will put more fresh air into the cylinder as well as fuel if your jetting is dialed in. The flatside non vacuum carbs do add power, but dump fuel into the cylinder before the engine is ready for it. The vacuum carb opens the throttle as the engine vacuum increases, thus using fuel as it is needed. As for the best possible exhaust, I am a big fan of White Brothers. It looks and sounds awesome, and stays that way with lots of hard riding. Plus it has great performance gains if used properly! Polaris hired White Bros to make an E-series pipe for the Predator. Down side to that is you can only buy the E-series Predator pipe from the dealer!!! Farmr has a good point. Polaris all ready tweeked another 20% out of the 500HO, so if you want more power you have to get very creative or have deep pockets. My local dealer will port and polish the head for @$420. It will add about another 8HP. That is my next step and should put me around 55 to 56 HP. The price is for me taking them the quad and picking it up. No taking them the head and worrying about putting it all back together. You would not have to change any internals for this mod.

 

I have talked to people who have run their HOs with the airbox opened up, or with the lid removed, and they all swore that even after raising the needle & doing some minor carb fiddling, they couldn't get any noticable power gains. We assumed the carb must not be opening all the way. I suppose it could be that the carb is the biggest restriction in the intake tract (already was running K&Ns).
If that was the case, then you could get the carb bored out, or go up to a bigger one.

Farmr

PS too bad they never made an IRS bike with the 400 engine. Now that one I know how to get more power out of.....

 

Farmr,

It would be cool to find a late model sp500 with a ruined engine for cheap, and retrofit the 400 2-stroke engine into that frame. I too wish they would have come out with one. Surely the idea crossed their minds..........was there a reason other than the phase out of 2-strokes?

Waylan

 

The Trailblazer 400 took the place of the Scrambler 400. It is just as fast. My riding buddy has one. If you take the lid off the air box, you will notice no gains. I experimented for a month with the proper carburation to go with my air box port mod. No one makes a stage 2 kit for the Scrambler 500HO. I worked with an engineer at Dynojet, and many attempts later along with lots of different jets and needles, magic happened. I will explain in detail what to do, but only if you want to know. I am not going to type all of that unless someone is interested.