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post #1 of 8 (permalink) Old 01-06-03, 08:40 PM Thread Starter
Chasing 500rwkw
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How is compression raised?

This is probably a dumb question but how is the compression raised in an engine?
I know you can get aftermarket flat top and domed pistons but is there other ways. Is the block skimmed or is it the head only that gets modified?

Thanks guys.

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post #2 of 8 (permalink) Old 01-06-03, 08:49 PM
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Usually only the head. To skim the block the engine will need to be stripped.

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post #3 of 8 (permalink) Old 01-06-03, 08:54 PM Thread Starter
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Thanks for that. I wasnt sure. Now i know.

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post #4 of 8 (permalink) Old 01-07-03, 01:02 AM
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There are five interconnected aspects to compression as measured by ratio.

You will increase your compression ratio by doing any or all of the following; Shaving the Deck of your Block, Shaving the face of your Head, Fitting Flat Top or Raised top Pistons and by increasing the stroke of the crank. Another way is to use thinner than standard Headgaskets, or "O" ringing the Head and block.
"O" Ringing is really only used in extreme applications IE Drag Racing.

You can offset the increase in compression ratio by any of the following, Die grind and reshape the Squish area in your cylinder head (must be done precisely and equally in all cylinders), Increase the Cylinder Bore (don't go mad coz theres only so much meat in the walls), Dished pistons or carefully reshaped pop top pistons. The other method is a bit crude though Mercedes used this on their earlier motors, and thats to add additional head gaskets and Decompression plates.

Without trying to confuse the issue, you can gain a marginal improvement in compression by using "Gapless" Piston rings. These are the same as normal piston rings except that they have an opposing step on each end of the ring which mates up to remove the "gap".

Aiming for a compression ratio of more than 9.5:1 on regular unleaded is very optomystic, although many of the current cars run up to 10.5:1, they have engine management systems with knock sensors which retard the ignition to save it from pinging too loudly.

Hope this helps.
post #5 of 8 (permalink) Old 01-07-03, 03:05 AM Thread Starter
Chasing 500rwkw
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Yes that did help thanks.
The Head and Cam combo that im going for is recommended for use with a 9.5 compression ratio. I'm taking my head head off and giving it to them to do so i imagine they would take care of the new compression ratio this way. Ill probably have to run optimax which is alright cos i use it anyway.

Cheers Guys
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post #6 of 8 (permalink) Old 01-07-03, 05:32 AM
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Static compresion yes another way is forced induction.. Turbo / Supercharge or chemicaly with Nitrous n2o..

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post #7 of 8 (permalink) Old 01-07-03, 03:17 PM
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ebxr8240, I don't think DansEdgli was looking at more than the basic engineering changes to perk up his motor.

I'm not sure that forced or chemical induction will increase compression, but it certainly makes a difference in the "Fun" equation...

The Silver Bullet is back on the road next week can't wait to take it for a blatt up the F3 ...
post #8 of 8 (permalink) Old 01-07-03, 08:35 PM
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you can get your pistons ceramic coated by HPC, that will raise it aswell + a few other bonuses

AU Series 1 I6 Futura, 17" XR Series III Rims, Kings superlow springs and Bilstien shocks, K-MAC adjustable caber kit, xr8 snorkle, BMC Filter, EF a/box lid, custom storm water pipeing, pacemakers, h/flow cat, 2 1/2" zorst mandrel bent, dyno'd @ 117.2kwrw b4 bmc
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