I searched didn't find what I was looking for.
stock 4.0 is 8.8:1 right could I go up to a 9.2 Compression Ratio and run 87 octane or maybe 89. I am planning my stoker build, this is on a renix motor so it has a knock sensor.
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You couldn't find a direct answer because there is two many variables as to whether, "X" compression will ping......
If you live at sea level........and want to run 87, better stick with 8.8 (for a stroker you will have to by a custom piston to keep the compression that low).......unless you put a bigger cam in it..........static compression will not be changed (8.8) but the dynamic compression will be lower by the bigger cam.
If you live at a high altitude......You can get away with more compression and run on 87 (thinner air......less to compress.)
The knock sensor is grate if you make a small mistake in compression ratio, but............you will make more power, with less compression, and no timing retarding, by the knock sensor then you will with higher compression, and the knock sensor retarding the timing, to keep it form Knocking!
With out a knock sensor (HO 4.0L) You have no choose but to run a higher grade of fuel.
the Knock sensor is a +.... but is is only a bandage if you mis the compression.
MY RULE OF THUMB (Have no real world data to back it up but...) is if your at see level, and have a performance cam,.......don't go above 9.4!
If you live at say 7000+ feet You might make it to 9.7--- 10.0 (with a performance cam) with out ping but i don't thing you will be running the 87 octane fuel.
And if you quench # is high,... then the above numbers my need to be a little bit lower.
Flash.
What mods have you done to it?
