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Exactly what is the benefit of a high comp piston

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I am about due to change the piston in my 09, what are the gains from using a High comp piston like 13:1 or 13.5:1. What make of piston is considered the best.

I have the Kawasaki remapping tool but would not know what IG or FI adjustments should be used with a high comp piston.

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I am about due to change the piston in my 09, what are the gains from using a High comp piston like 13:1 or 13.5:1. What make of piston is considered the best.

I have the Kawasaki remapping tool but would not know what IG or FI adjustments should be used with a high comp piston.

The advantage to higher compression is twofold. First, by compressing air/fuel mix to a greater degree, there is an increased amount of potential energy available from the fuel. And, because the volume in the combustion chamber can now be expanded to 13.5 times its fully compressed size, instead of only 13.0 times, so the burning fuel will be able to push the piston farther in the first half of the stroke than with the lower compression ratio, again, delivering more energy from the same amount of fuel.

The other benefit is that since the expansion of the piston as it goes down is increased by the same amount as the compression when it goes up, the intake pulse is stronger. Higher compression engines perform better at low speeds than lower compression ones, and can tolerate more aggressive cam timing without running really ragged down low.

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Having a high compression piston improves the overall performance. Having a stronger forged piston allows you to not worry about going into screaming RPM's. It also makes the compression better allowing the bike to start in fewer kicks and can sometime even higher performance. The best piston in my opinion is easily made by wiseco and they outlast any brand so when its time to replace, buy a wiseco high compression piston, and it will be well worth the money.

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Thanks, is higher octain fuel required with a 13.5:1 compression ratio, and does the ignition timing need to be changed, more advance.

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its all spot on so far but there are downsides to HC pistons too.. 12.5:1 isnt exactly low compression..

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For supermoto I guess you cannot have too much HP, ever.

For off road, a HC piston just makes no sense what so ever, IMO.

For MX, I assume there is benefit for just a handful of riders world wide. This might start a debate, but I'm keen to learn what I'm missing here ...

How many people can honestly say they found a jump on an MX track which a stock KX450F engine wont let them clear? I mean easily, when traction is at least fair, on a relatively short approach, in the right gear.

How many people think they need more HP to holeshot in their class? Seriously, isn't it more about the rider technique and mindset, tire choice, rear shock setup, EFI/CDI map, and anything else impacting TRACTION. A fast kid on a 250F will smoke me every time.

How many people need more HP to solve their cornering speed problems?

How many people agree that a HC piston which is 10% heavier puts a lot of extra load on the rod and crank? Maybe HC owners say they dont need to rev the engine hard, but at times I think that's impossible to avoid.

I've done nearly 300 hrs on std comp pistons. Just 35 on the OEM piston the rest on light weight Wisecos. I often hit the rev limiter a few times per ride to keep the nose up, and it sounds sweet and smooth. Hopefully my bottom end is good for another couple of hundred hrs. Who knows! But with a high comp piston, I'd just have to split the cases as per the manual, and no way do I have time or money for that.

And to top it off with a HC piston you have to be mindful about fuel quality.

WANTED: Flywheel weight. I want to smooth out my engine to be more like the newer EFI engines. PM me if you have one to go.

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Numroe, that all makes a lot of sense. It seems the Wisco stock piston is the choice of the lot of riders rather than oem piston, sounds like the way to go.

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the weight is part of it, the fact that there is literally more compression makes it harder on bearings and i guess rings too..

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For supermoto I guess you cannot have too much HP, ever.

For off road, a HC piston just makes no sense what so ever, IMO.

For MX, I assume there is benefit for just a handful of riders world wide. This might start a debate, but I'm keen to learn what I'm missing here ...

How many people can honestly say they found a jump on an MX track which a stock KX450F engine wont let them clear? I mean easily, when traction is at least fair, on a relatively short approach, in the right gear.

How many people think they need more HP to holeshot in their class? Seriously, isn't it more about the rider technique and mindset, tire choice, rear shock setup, EFI/CDI map, and anything else impacting TRACTION. A fast kid on a 250F will smoke me every time.

How many people need more HP to solve their cornering speed problems?

How many people agree that a HC piston which is 10% heavier puts a lot of extra load on the rod and crank? Maybe HC owners say they dont need to rev the engine hard, but at times I think that's impossible to avoid.

I've done nearly 300 hrs on std comp pistons. Just 35 on the OEM piston the rest on light weight Wisecos. I often hit the rev limiter a few times per ride to keep the nose up, and it sounds sweet and smooth. Hopefully my bottom end is good for another couple of hundred hrs. Who knows! But with a high comp piston, I'd just have to split the cases as per the manual, and no way do I have time or money for that.

And to top it off with a HC piston you have to be mindful about fuel quality.

WANTED: Flywheel weight. I want to smooth out my engine to be more like the newer EFI engines. PM me if you have one to go.

You are definitely entitled to your opinion. Remember his post and what he is asking.

If you are getting 300 hours out of your main bearings then I can understand why you don't have a need or want for more power. That tells me you are not in the upper rpms very often.

As far as the benefits of the HC piston go, have you every lugged your way out of a turn a gear too high and think to yourself I wish I had just a little more grunt now. With the HC piston you can have it. On a stock bike it is just about the equivalent of going up a tooth or two on the rear sprocket in terms of how the pull will feel.

Can you understand why the off road guys would want it now.

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More power = more fun cannot be argued against. But I think a HC piston loses out when considering fun versus cost over time. Which for me is the bottom line, since my ride fun is not spread over multiple bikes.

True I dont rev it hard often, and true I dont lug the engine much or ever. When I think of lugging I mean low revs, and so low that the engine takes a while to raise revs against the load. I usually change rear sprockets so I can ride 90% of any track in 3rd. I also have a Vortex CDI so I can move the power around and control the response.

Can you understand why the off road guys would want it now.
No, not really. I still dont think adding more power and response is a solution for avoiding correct (lower) gearing and perhaps adding some flywheel weight or changing the ignition/fuel map to control the response.

In Australia the offroad pro racing is highly competitive and I've read a few stories about 450F pros going faster with less power and response, and I assume they are fussy about gear ratios and selection.

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No, not really. I still dont think adding more power and response is a solution for avoiding correct (lower) gearing and perhaps adding some flywheel weight or changing the ignition/fuel map to control the response.

In Australia the offroad pro racing is highly competitive and I've read a few stories about 450F pros going faster with less power and response, and I assume they are fussy about gear ratios and selection.

Understood and agreed. But don't knock it until you try it.

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No way high-comp is good for off-road racing. runs too hot 12:1 or 12.5:1 is already plenty high, n they already run plenty hot.

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No way high-comp is good for off-road racing. runs too hot 12:1 or 12.5:1 is already plenty high, n they already run plenty hot.

Are you speculating or do you have actual operating temp. numbers to back this up?

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im not speculating ive built high-comp motors in several applications.. 13.5.1 drag motors for cars/trucks, etc. I know how it works..

it WILL run hotter.

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im not speculating ive built high-comp motors in several applications.. 13.5.1 drag motors for cars/trucks, etc. I know how it works..

it WILL run hotter.

Yup. Hotter. Bigger radiators to compensate.

All performance upgrades have a trade off.

The most common trade off is engine life.

Second is increased heat.

Third is usability: are you converting a all around bike to 'track only' bike?

In my opinion, HP upgrades come in last, after suspension and ergo upgrades.

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Yup. Hotter. Bigger radiators to compensate.

All performance upgrades have a trade off.

The most common trade off is engine life.

Second is increased heat.

Third is usability: are you converting a all around bike to 'track only' bike?

In my opinion, HP upgrades come in last, after suspension and ergo upgrades.

I agree totally. When your talking about racing these 450s in harescrambles (which ive done quite a few here in PA and its pretty brutal at times.)

These bikes are already at a disadvantage with pumping out heat, and 12:1 compression OEM compression isnt exactly LOW in the first place, its a high-comp race motor right from the factory. Racing this bike in the woods with the OEM piston would still benefit from Fluidyne rads and a boysen impeller/cover. I couldnt imagine wanting to run a 13.5:1 piston in the woods, you would need to do the rads and boysen just to bring it back near stock temps, which get too high at times..

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I agree, the more HP the more heat. Just because it blows out a little coolant doesn't mean it is over heating. Again, you don't really know actual temperature differences before and after a piston upgrade to HC. Remember you are holding 50 to 60 HP between your legs not hidden behind a fire wall and hood, of course it is going to feel hot. With out actually measuring temperature you are just speculating. (guessing) Although it may be an educated guess, still speculation.

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