How much compression

Discussion specific to the 1995 - 2006 KDX200 (H Series) and 1995 - 2005 KDX220R (A Series) models sold in the USA
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Jaguar
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Re: How much compression

Post by Jaguar »

"The H seems more responsive and snappy in the upper RPM range, while the E bike has a smooth and harder pull from the bottom. That would indicate the opposite of what these numbers are showing, yes? "

That sounds right to me. Higher compression is more advantageous for mid range power.
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Julien D
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Re: How much compression

Post by Julien D »

All else being equal, the higher compression in the H model engine should give it stronger pull from low range up to 6k RPM (when the kips activates). In my experience, it does not. The E engine will walk all over the H until getting into the very top end of the RPM range. That's just personal experience of mine from riding both. YMMV.
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Re: How much compression

Post by C George »

Great collection of bikes !!
200 PSI ,,,, WOW ,, Thats an awesome top end for a KDX.
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Re: How much compression

Post by C George »

Julien D wrote:All else being equal, the higher compression in the H model engine should give it stronger pull from low range up to 6k RPM (when the kips activates). In my experience, it does not. The E engine will walk all over the H until getting into the very top end of the RPM range. That's just personal experience of mine from riding both. YMMV.

The E model has the higher compression .

And I believe it would pull so much better than an H below 6000 rpms.
05 KDX-220R / 06 KDX-225R / Maxima 927 / Millenium Tech / Ron Black / PC , FMF / Many 220 engine mods / 40 + yrs. of riding dirt bikes 🤟🤟
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C George
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Re: How much compression

Post by C George »

Has anybody ever measured how they got the extra compression ?
Is the head that much different ? Cylinder shorter ? Thats quite a difference in numbers.
05 KDX-220R / 06 KDX-225R / Maxima 927 / Millenium Tech / Ron Black / PC , FMF / Many 220 engine mods / 40 + yrs. of riding dirt bikes 🤟🤟
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Julien D
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Re: How much compression

Post by Julien D »

C George wrote:
Julien D wrote:All else being equal, the higher compression in the H model engine should give it stronger pull from low range up to 6k RPM (when the kips activates). In my experience, it does not. The E engine will walk all over the H until getting into the very top end of the RPM range. That's just personal experience of mine from riding both. YMMV.

The E model has the higher compression .

And I believe it would pull so much better than an H below 6000 rpms.

The E model has a higher "usable range" as stated in the manual, however, it has a lower compression ratio. At least for the "low speed" rating. This is obviously conflicting information.
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C George
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Re: How much compression

Post by C George »

I may be wrong but I believe the compression psi number higher on the E is what you feel.

Compression ratio's are confusing and very hard to really measure on a two stroke.

What they'll push for pressure out the plug hole seems to be key.

But ,,, I've been wrong before. :? :?
05 KDX-220R / 06 KDX-225R / Maxima 927 / Millenium Tech / Ron Black / PC , FMF / Many 220 engine mods / 40 + yrs. of riding dirt bikes 🤟🤟
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Julien D
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Re: How much compression

Post by Julien D »

No, I agree with you. In my experience the E will test at a higher PSI, and that would explain the gain in low end power. After a replate/rebuild my E was at about 170 PSI. I just question the published numbers as far as compression ratios.
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Re: How much compression

Post by C George »

I'm in the middle of a new 220 top end for my son's 200 and am sending the head off to RB.

To get 190 -200 psi of compression , I asked for a "race gas " head.

But as I've commented before , I have no problem blending in AV Gas to have a TRUE 95 octane fuel.

A conventional 220 head reworked should make 170-175 psi.
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