Compression changes on a new engine

[norcal ex]

I just build a flat top engine. when i first tested the compression it came out to 205. i sent the domes to protec and said i wanted them to be 190 and the squish increased .02 . when i got them they were still around 205psi. I broke in the engine today and the compression is now 215!!!! is it normal for the engine to increase from 190-215? i dont think they really lowered the compression to 190.

 

[Matt_E]

The rings seat after a tank or two, so compression would go up. But you should probably call up Protec about them domes.

 

[SkiDaddy]

My big bore went from 160 to 168, if that helps any. (I have big ports :biggrin.

 

[norcal ex]

i know it goes up, but i wouldnt think it would go up 25psi? that is a lot!

 

[norcal ex]

My big bore went from 160 to 168, if that helps any. (I have big ports :biggrin.

That seems more like it!

 

[kx454]

I just build a flat top engine. when i first tested the compression it came out to 205. i sent the domes to protec and said i wanted them to be 190 and the squish increased .02 . when i got them they were still around 205psi. I broke in the engine today and the compression is now 215!!!! is it normal for the engine to increase from 190-215? i dont think they really lowered the compression to 190.

were they ever at 190? cause from what your saying they started at 205 and went to 215? my ski last year went from 147 to 158ish after it was broke in. maybe i am just reading your post wrong haha.

 

[norcal ex]

were they ever at 190? cause from what your saying they started at 205 and went to 215? my ski last year went from 147 to 158ish after it was broke in. maybe i am just reading your post wrong haha.

I never read it at 190. thats what it was suppose to be changed to tho...

 

[ANT]

did you get your 205 reading when the motor was cold or hot? you have to warm it up to get the right reading if you already didn't.

 

[ATS_Scott]

I just discovered the same thing. I expected compression to come up after break-in but not as much as it did. I did a compression test of a fresh built 701 in a ported 6m6 cylinder with that silly ocean pro swirl head, and got about 165 or so. One cylinder was about 15psi lower than the other. I had not even run it yet so I wasn't worried. Fast forward to 2 tanks of fuel later and compression is 215 in both cylinders. Both tests were done cold with throttle open. I WAS running on 93 pump... I guess I need to drop compression or add racegas.