I have a 2000 srx that is ported. the head volume is 24.75 CC with the piston TDC. I am calculating this to be a 12.2 compression ratio ( or should I be using the volume from the exhaust port to tdc). How much can I remove from the head and be safe with 91 octane?
Woody255
New member
In my experience, you are NOT safe with pump gas at 12.2:1. I would think 95-98 octane would be close.
YAMMIEGOD3:16
Active member
woody i beg to differ, that compression ratio is plenty safe for pump 93 octane. now with that said it better be 93 octane. 3:16x (yammie tony)
you don't start to build compression until your piston top goes past the top of the exh. port. I would not trim much on the heads if your only going to use 91 octane gas, your asking for detonation problems. There is a BIG difference from 91 octane to 93-94 octane gas. If you have 8dn10 heads they are already smaller chamber then the 8dn-00 heads.
Woody255
New member
Our premium pump gas here is only 91. Cannot buy 93 locally. Would hate to see a guy burn down over insufficient fuel.
YAMMIEGOD3:16
Active member
i use 91 non ethanol in my 2000 srx (tar) sled. my 2002 grass /ice and my 95 800. grass. all comp around what you posted. no issues. 3:16x (yammie tony)
note : not my 79 srx. 50/50 110 and 91. too old to hurt it.
note : not my 79 srx. 50/50 110 and 91. too old to hurt it.
I have some other heads I bought from a racer, I believe will bring the compression ratio up to 12.7. I am wondering if this is safe at 91 with a trail ported motor in which the exhaust ports have been raised?
This machine already comes out of the hole very well. Not sure if more compression is safe or even necessary.
Right now with current set up, I have 110 psi compression.
This machine already comes out of the hole very well. Not sure if more compression is safe or even necessary.
Right now with current set up, I have 110 psi compression.