XR200 piston in an 85 200x???

[barnett468]

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without the rated compression i would need the dome volume.

[barnett468]

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having the dome volume would be easier because i have to work backwards to calculate it with just the compression rating but no big deal either way.

[mayhem17]

It didn't list the compression it was supposed to be rated at sadly. Just stated mm compression height.

[oscarmayer]

ok guys look here is the dummy version.
stock 200x is 9.2:1
stock 200s is 9.0:1
stock xr200 is 10:1.
drop in a xr200 into a 200x or s and you get 10.1:1 due to volume chamber differences and smaller squish because it is .5mm larger.

in a nut shell, about 1 hp gain on a stock trike.

[barnett468]

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So what will the theoretical compression be with the shorter compression height?

Ok, Scootertrash, here's the answer . . Sorry it took me so long.

Since the compression of the XR200 piston is not mentioned, based on photos of a 10.25 compression piston for the arc200x, I guestimated that the xr piston with the raised dome is 1.3 cc which would give the atc200x 10.50 compression IF the piston pin was in the correct location . . I have verified two different ways that the XR200 pin on the piston in question is 3 mm lower than the ATC200X pin.

Anyway, long story short, accounting for the guestimated dome size, pin location and .5 mm bigger bore of that XR piston, it will in fact LOWER the compression of the atc200x from the factory number of 9.6, all the way down to 7.4, lol.

Now, even if when I gave the XR200 piston a dome that would provide 11.0 compression in the ATC200X if the pin height were correct, it would still only provide 7.66 compression with its shorter compression height and .5 mm bigger diameter.


SUMMATION

Installing the XR200 raised dome piston in question, will in fact, lower the compression of a stock ATC200X by basically 2 points, which will result in significantly lower power, however, on the positive side, it costs around $100.00 less than the correct piston, the bike will no longer smoke from ring blowby, you will easily be able to start it with your hand if your leg is too tired, it will be safer to ride due to the greatly reduced power level, AND you can run kerosene in it instead of expensive gasoline.
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[Scootertrash]

No prob on the time.....

I ain't got the smarts to figure it out so I defer to those who can. I know that the head work that will be done on my Harley has chamber cc, cylinder height, piston dome, milling the heads, base gasket thickness and head gasket thickness figgered in to come to a targeted corrected compression. Waaayyy over my head. That's why it's going to someone with 30 years experience.

[barnett468]

No prob on the time.....

I ain't got the smarts to figure it out so I defer to those who can. I know that the head work that will be done on my Harley has chamber cc, cylinder height, piston dome, milling the heads, base gasket thickness and head gasket thickness figgered in to come to a targeted corrected compression. Waaayyy over my head. That's why it's going to someone with 30 years experience.

There are compression calculators that are helpful too . . You can change the different numbers to see the effects . . The complicated thing is determining actual running or dynamic compression.

Here’s a calculator you can mess with.

http://wallaceracing.com/cr_test2.php


So, a Harley huh…very cool . . What kind is it?

I had a 1974 full dresser AMF FLH and it was fun . . I bought it because my girlfriend liked Harley’s, plus it kept me from going fast on the street, lol . . A friend of mine at Kawi was a friend of Jerry branch of Harley fame so he had him port the head on our 250 Mojave that I tried to race . . He actually worked on Elvis's 125 when Elvis was young, lol.

[Scootertrash]

85 Low Rider. First year of the evo motor in the Low Rider, still a 4 speed tranny, but belt drive. I bought it new, she's my baby. Planning on a Geezer Glide in the next 5 years, this is/will be my hot rod.

[oscarmayer]

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Ok, Scootertrash, here's the answer . . Sorry it took me so long.

Since the compression of the XR200 piston is not mentioned, based on photos of a 10.25 compression piston for the arc200x, I guestimated that the xr piston with the raised dome is 1.3 cc which would give the atc200x 10.50 compression IF the piston pin was in the correct location . . I have verified two different ways that the XR200 pin on the piston in question is 3 mm lower than the ATC200X pin.

Anyway, long story short, accounting for the guestimated dome size, pin location and .5 mm bigger bore of that XR piston, it will in fact LOWER the compression of the atc200x from the factory number of 9.6, all the way down to 7.4, lol.

Now, even if when I gave the XR200 piston a dome that would provide 11.0 compression in the ATC200X if the pin height were correct, it would still only provide 7.66 compression with its shorter compression height and .5 mm bigger diameter.


SUMMATION

Installing the XR200 raised dome piston in question, will in fact, lower the compression of a stock ATC200X by basically 2 points, which will result in significantly lower power, however, on the positive side, it costs around $100.00 less than the correct piston, the bike will no longer smoke from ring blowby, you will easily be able to start it with your hand if your leg is too tired, it will be safer to ride due to the greatly reduced power level, AND you can run kerosene in it instead of expensive gasoline.
.

The XR200 is slightly larger cc head due to the stock piston being .5mm larger than stock 200x. It also has higher compression piston to deck height is exactly the same. So you will gain a tiny bit of performance over 200x piston setup not to mention the cc of the head on the 200x is again slightly smaller resulting in a tiny bi more compression. The gains are minor. Only about 1 hp or so on a stock 200x.
Bigger gains can be had by dropping in a Better cam, larger carb and better exhaust. Do that with the xr200 piston and you can expect 3-4 hp gain over all as it allows the motor to breath better and run more solid. It will also give more torque and a better mid range.


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[barnett468]

The XR200 is slightly larger cc head due to the stock piston being .5mm larger than stock 200x. It also has higher compression piston to deck height is exactly the same. So you will gain a tiny bit of performance over 200x piston setup not to mention the cc of the head on the 200x is again slightly smaller resulting in a tiny bi more compression. The gains are minor. Only about 1 hp or so on a stock 200x.
Bigger gains can be had by dropping in a Better cam, larger carb and better exhaust. Do that with the xr200 piston and you can expect 3-4 hp gain over all as it allows the motor to breath better and run more solid. It will also give more torque and a better mid range.

oscarmayer, thanks for the info, however, unfortunately, according to the actual numbers, your info is somehow inaccurate as far as what amount of compression the piston in question will provide in an ATC200X, so my guess is that you probably just had a number wrong somewhere . . It’s easy to do, I have done it before more than once, but fortunately, I have always caught it because I always double check my numbers and sometimes even triple check them.

When using all the correct data, your numbers will come out similar to mine . . They have no choice . . The math is simple and the math has never lied to me before and I have been using the same math when building engines etc for the last 40 years . . If it had, “The Tecate . . The Most Powerful 3 Wheeler On Earth.” Would not have been the most powerful 3 wheeler on earth, plus my race bike would not have hole shot Jimmy White and several other pros at a couple of races, and I certainly would not have beaten him and the rest of the competition at Saddleback like I did etc . . Also,our Kawi 165 mph Road Race bikes would not have gone 165 mph if the numbers lied.

If you do check the numbers and find an error in my calculation, please feel free to post all the numbers you used so I can see where my error was, however I actually checked the numbers and did the calcs 4 times from scratch to insure it was correct in case there were any questions about the results.
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