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Doug Steinel's Avatar
 
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reducing CR

If one has a p/c set that has a CR of 10.5, can they get that CR under the magic number 10 by adding copper gasket at base of cylinders? Don't want to have to twin plug it.
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Old 03-13-2005, 03:56 AM
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Do a search on squish band and you'll see why it's not a good idea.
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Old 03-13-2005, 05:26 AM
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what is magic about 10:1? Is that the point at which 93 octane pump gas will no longer cut it without twin pluging?
Justin
Old 03-13-2005, 05:32 AM
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If they are Mahle or factory "10.5:1" the actual measured compression is quite a bit lower. You might be under 10.1:1 already. That said, I thought that (true) 9.8:1CR on 94 octane was about the limit.
-Chris
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Old 03-13-2005, 05:55 AM
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You can have the small end bushing of your rods "offset" to lower CR a little.
Old 03-13-2005, 11:05 AM
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Quote:
Originally posted by 125shifter
Do a search on squish band and you'll see why it's not a good idea.
+1

Machining a little off the top of the piston dome would be a better way to go than trying to move the piston down. Thats assuming there is enough metal there to do so.

It would also help the flame propagation problem in a single plug application too.
Old 03-13-2005, 01:19 PM
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Quote:
Originally posted by ChrisBennet
If they are Mahle or factory "10.5:1" the actual measured compression is quite a bit lower. You might be under 10.1:1 already. That said, I thought that (true) 9.8:1CR on 94 octane was about the limit.
-Chris
Hi Chris:

You said it, sir,..... 9.8:1 IS the limit for 93-94 octane fuels with single ignition.

The thing that people MUST remember is that detonation thresholds are not static; they change with outside air temps, humidity, and cylinder head temperatures.

Without closed-loop knock-sensing, we are forced to set CR's on the low side when using pump gasolines to prevent buying multiple sets of pistons & cylinders.

Big-bore engines are far more sensitive than small-bore ones as well (except for the 2.0's which are quite fussy)
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Old 03-13-2005, 07:37 PM
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How about applying a ceramic coating to the top of the piston domes? I have a discussion going on this subject right now, it should help with detonation. If coating the piston domes helps with detonation, then can a lower octane fuel (91-92) be used?????? Thoughts please.

Best Regards,

Alex
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Old 03-15-2005, 06:35 AM
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Add some closed loop knock sensing if you don't have it and want to push the limits.

http://jandssafeguard.com
Old 03-15-2005, 02:16 PM
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Set the proper deck height with base gaskets to insure the engine has usable horizontal dimensions and contour the piston dome to the compression you desire.
That said: adding base gasket will work. One note : try to use as few base gaskets as possible. One .040 instead of four .010 and so on. If Pelican doesn't sell them, we sell the oversided base gaskets on our web site.

Quote Doug Steinel

"Don't want to have to twin plug it."

Please, everyone wants twin plug, "IF THE PRICE IS RIGHT!!!"
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Old 03-16-2005, 04:52 AM
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