MRFUSION
New member
Hi there guys, heres one for you Gurus out there, I need some advice. I just finished building my 980 big bore engine based of the SRX crankshaft and case. I am running 82mm pistons with the stock srx stroke, with 33cc domes installed my squish is pretty good at 46thou. Now I installed this engine in the chassis and have not run it yet, from my calculations the uncorrected compression ratio is 10.9:1. when I pulled this baby over I am showing approx 190psi cranking compression. I do realize that the rings are oiled from assembly and it is not broken in yet either. I run a 944 engine for the last 3 years and its comp ratio was 10.6:1 and compression was 165psi, I run this on premium fuel at altitude with no problems. I could see having more compression on this new engine because of the longer stroke, Im wondering based off the comp ratio if I can still get away with premium fuel? Thanx for any info guys. Shad
well, in my opinion, NO. with .046" squish on a 980, thats pretty tight, gonna take some octane to keep from detonating right there alone. Ign. timing will alos play a key role in the fuel used, a bigger engine wants more timing. Unless your operating this thing at 10,000 ft elevation? The other engine must have alot more squish clearnce?
it would also matter as to the width of the squishband, and the angle of it.
it would also matter as to the width of the squishband, and the angle of it.
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MRFUSION
New member
I will be running the sx 700 cdi so I should get more timing from that. My 944 engine actually had a tighter squish of 44thou. From what I understand the more narrow the squish the less chance of detonation. The squish was from the solder test and measured 1.19mm so I loosly converted it to 46thou. I was just amazed with the compression, I have a smaller set of domes of 31.8ccs I can get carved out if needed. Thanx again for your help. Shad