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Author Topic:   too much compression
hap61
Dirt Roller

Total posts: 11
posted November 18, 2004 03:14 PM  
My cylinder pressure is not to exceed 160lbs per track rules.
My new motor has 49cc heads, has 180lbs per
cylinder. is there anyway i can drop 20lbs
without changing heads or cam ?

need help!
hap61

Istock66
unregistered Total posts: 11
posted November 18, 2004 03:33 PM           send a private message to hap61   Edit/Delete Message   Reply w/QuoteBBBBBB
a compression test like that has nothing to do with the compression ratio, its measuring the leakage or in the cylinder pressure, not volume.

you could put open chamber heads on it and still have the same compression test.


stockcar5
Dirt Forum Champ
Total posts: 578
posted November 18, 2004 03:49 PM  
i hafta disagree ...lower your compression ratio will lower the cylinder pressure if nothing else is changed besides the heads.

also the cam has a TON to do with cylinder pressures. i had a 11 to 1 377 that had 220psi. and i had a 12.5 to 1 355 and that would only get me 190. reason was different cams.

with that said..try advancing or retarding the cam, or play with valve lash (if the cam is solid). but in the end i think a new cam with more overlap will do the trick.

------------------
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hap61
Dirt Roller

Total posts: 11
posted November 18, 2004 03:50 PM  
so how do you reduce engine compression?
i was told larger cc heads or more cam overlap. but want to avoid changing both.
thanks
quote:
Originally posted by hap61:
My cylinder pressure is not to exceed 160lbs per track rules.
My new motor has 49cc heads, has 180lbs per
cylinder. is there anyway i can drop 20lbs
without changing heads or cam ?

need help!
hap61



19J
Dirt Freak

Total posts: 370
posted November 18, 2004 03:56 PM  
Head shim? Or thicker head gasket maybe? Anyone else agree or disagree?

hap61
Dirt Roller

Total posts: 11
posted November 18, 2004 04:36 PM  
Do you think i can lose 20lbs with a gasket or spacer?
Thanks for the feedback.
quote:
Originally posted by hap61:
so how do you reduce engine compression?
i was told larger cc heads or more cam overlap. but want to avoid changing both.
thanks


juliaferrell
Dirt Freak

Total posts: 370
posted November 18, 2004 08:24 PM  
I'd retard the cam a couple degrees. Probably the only way your gonna get twenty without changing the cam out......I don't think lash will get you there.

cobb
Dirt Maniac

Total posts: 131
posted November 19, 2004 07:07 PM  
just drill half inch holes in the pistons

[This message has been edited by cobb (edited November 19, 2004).]

FlyNLoIMCA17
Dirt Forum Champ
Total posts: 753
posted November 19, 2004 10:44 PM  
Ok I have a miracle fix for this...... as usual!!

Cobb.....drilling 1/2" holes in the pistons??? Thats just plain stupid. You should know by now that you will only need 3/8". Dang man your gonna mess him up big time!!

LOL!!!!!!

Eljojo
Dirt Forum Champ
Total posts: 968
posted November 20, 2004 04:31 AM  
Now I see where the term "Cobbed up" comes from!

DirtDogg
Dirt Full Roller

Total posts: 38
posted November 21, 2004 12:06 AM  
you will not lose 20 pounds with out changing one or the other if they are good heads then change the cam with more overlap if the heads are not that good change them .

How often do they check you?
Have you raced the motor yet?
Have you checked it Hot?
We had a Racer we all do but after the race he had his battery cable go through some kind of resister and when they checked his compession the motor turned over so slow that the compression would not read as high. finally got caught when they hooked a battery charger directy to the starter cable.
Do they let you pick the plug to pull?/

b4racing
Dirt Forum Champ
Total posts: 626
posted November 21, 2004 05:06 PM  
put a higher lift cam in at low cranking it will let more presure go by also you can race with the choke in and when they go to test pull the choke shut. Less air in less air out.

pit_boss
Dirt Forum Racer

Total posts: 80
posted November 21, 2004 06:30 PM  
hap,Iam not saying you should cheat or anything, but I would leave it like you have it, run it like it is, and see how it performs against your competition, My guess is you'd be disappointed and wish you had left it. unless your in the top 5 every week they won't check your compression.....

    

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