Not enough octane? what you guys think?

redfastback said

I agree. No 10.5:1 iron headed engine can run on 89 unless you have severely retarded timing. Do a comp test and get some PSI #'s. That will give you a better idea of your static compression. I bet if you installed an MSD dist, with the 18* bushing, 2 light blue springs, and set your initial at about 16*, and add 91, your gonna run alot harder than you do now.

No it will not feel like nitrous....lol.

Click to expand...

Your statement about compression is far from the truth. I am running a measured 10.6:1 compression with 190-200 psi of cranking pressure on 89 octane and there are others on this forum with similar set ups doing the same.

It's not the static compression that determines the octane need anyway. It's how much cylinder pressure you develop. I get away with 200 psi by virtue of the excellent quench of the magnum head.

The OP very likely has well under 10:1 compression, they were under 10 new from the factory. Also, depending on the over lap in his cam his cranking pressure could very likely be down in the 150 psi range making the use 89 or even 87 octain within reason.

As for timing too much will reduce power just as to little will. The timing needs to be dialed in for the specific combination.