calculated compression ratio changes due to adding MCR
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Road Warrior
Joined: Jun 2009
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From: NYC
calculated compression ratio changes due to adding MCR
After sending out some extra heads for MCR, noticed the MCR's have a pretty deep cavity behind the small hole. Measured it and it was 3 cc's. Went to the big boyz calculator and ran the numbers before and after the 3 cc change and got 10.14:1 before MCR volume change, and 9.85:1 after the 3 cc additional chamber volume due to adding the MCRs. I measured the volume of the MCR's while installed with the MCR's in the engine run position.
So basically, it looks like if you go with .030 head gaskets to get more compression (.025 maybe) but have MCR's put in, you're back to where you were from a chamber side perspective due to the additional chamber volume (aprox 3 cc's in my case).
I understand how MCR's work, and the real benifet is the venting of the chamber pressure while the MCR's are in the open position. But here is another factor to consider when planning engine work.
So basically, it looks like if you go with .030 head gaskets to get more compression (.025 maybe) but have MCR's put in, you're back to where you were from a chamber side perspective due to the additional chamber volume (aprox 3 cc's in my case).
I understand how MCR's work, and the real benifet is the venting of the chamber pressure while the MCR's are in the open position. But here is another factor to consider when planning engine work.
Road Captain
Joined: Nov 2010
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From: Roads of Idaho
Yes, extreme. Good job!!!
We should all be so direct at over killing a solution to a problem!!
Outstanding HDF Member
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From: earth
Post a pic, from your description I just can't visualize how adding compression releases effectively increased chamber volume by 3 cc. How exactly did you come up with the increased volume; math or an actual burette measurement?.
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Road Warrior
Joined: Jun 2009
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From: NYC
I measure the added volume by using a syringe and injecting oil into the chamber of the MCR while the MCR is in the engine run position. I was able to get 3 cc's into the chamber. Of course, the heads are off and I can inject the fluid directly. So you want me to post a picture of a syringe inserted into the MCR hole, with the heads upside down on a table?
HDF Community Team
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From: san antonio
If the machine work for the compression releases was done right and machined for the compression releases that were used, there is no way there would be a 3cc void under the compression release.
A boss is machined into the cylinder head, normally near the spark plug boss and very similar. A hole is drilled into the boss just a hair deeper than the threaded portion of the compresion release; about 2mm, just enough for the release valve to lock in the open position when the release is installed in the threaded hole. The release hole is drilled from the bottom of the boss into the combustion chamber; about 1mm in diameter. Do the math; not anywhere near 3ccs.
Not saying that speakerfritz's measurement's are off but 3ccs is not consitent with the mechanics of installing compression releases. I have never seen a compression calculator that allows for loss of compression due to compression releases; just doesn't add up, 3ccs is a lot when calculating compression.
A boss is machined into the cylinder head, normally near the spark plug boss and very similar. A hole is drilled into the boss just a hair deeper than the threaded portion of the compresion release; about 2mm, just enough for the release valve to lock in the open position when the release is installed in the threaded hole. The release hole is drilled from the bottom of the boss into the combustion chamber; about 1mm in diameter. Do the math; not anywhere near 3ccs.
Not saying that speakerfritz's measurement's are off but 3ccs is not consitent with the mechanics of installing compression releases. I have never seen a compression calculator that allows for loss of compression due to compression releases; just doesn't add up, 3ccs is a lot when calculating compression.
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Outstanding HDF Member
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From: earth
I measure the added volume by using a syringe and injecting oil into the chamber of the MCR while the MCR is in the engine run position. I was able to get 3 cc's into the chamber. Of course, the heads are off and I can inject the fluid directly. So you want me to post a picture of a syringe inserted into the MCR hole, with the heads upside down on a table?
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Road Master
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Last edited by 131tman; Oct 3, 2011 at 07:20 AM.
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