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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?
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.
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.
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