Old high performance engine

[sgtdale]

Just a thought and question.

set up

You have an old hi compression naturally aspirated engine that has a lot of hrs on it and now the compression is low.
When engine was new it of course would need hi octane gas.

question

Now that the compression is low / down, does it still need the same high octane gas or could it be run safely with lower octane gas?

Inquiring minds

 

[timmyboy76]

I dont think so?, only because it still has the same volume(between top of piston and dome) inside the cylinders.
Now if you rejetted it,(smallerpilot/main), than might get away with it,(lower octane).

 

[kustomkarl]

I sold a high compression engine (185psi )from one of my race boats years ago to a buddy of mine that was going to rebuild the tired mill...he installed it and ran it for 2 months while waiting for new parts...he ran it on pump fuel 87 octane with no problems... the compression was at 100 psi when he bought it, and as new it ran only on cam 2 racing fuel or Bp which was 105 octane I think... if memory serves me right. It never did develop any other problems or detonation either with the low compression.

Karl