What matters most is compression ratio and timing. At a higher CR, there is a higher risk of the gas pre-igniting while the piston is still moving upward. Not good! Higher compression engines need higher octane gas, simply because it takes longer to ignite.I was wondering about the different grades of gas and was wondering if it was okay that I have always but unleaded 87 octane in my tank? Any of this matter? I think this is a 90's engine block, if that matters.
answered perfectly.What matters most is compression ratio and timing. At a higher CR, there is a higher risk of the gas pre-igniting while the piston is still moving upward. Not good! Higher compression engines need higher octane gas, simply because it takes longer to ignite.
When the gas ignites before it is supposed to, called preignition or detonation, it makes a certain knocking sound.lost me with that last one. sorry.
Hey Pete ,Luke, what you are describing is called run on or diesel img. It's from unburned hot carbon causing fuel to ignite without a spark. Not real good for the engine. One near term solution is to use a higher grade fuel. At least a mid grade. So called regular was 89 octane years ago, now at 87 the old engines don't like it. You may be able to get some help from different spark plugs, but for myself, I run 92 or higher in mine.
Thanks Pete I'll keep in touch !Luke, not to hijack the thread, but I'd start with what's easy. The carb, especially if it's been sitting for a few years. Intake gaskets would be unlikely to cause run on. You may want to go to a shop that specializes in dialing in cars. I use Carb Connection in Kirkland, Wa, but since it's about 3000 miles +\- from you that probably isn't an option. I've slowly learned that as much as I enjoy fixing things myself, sometimes I'm just better off taking it to the right shop. Often times the shop will tell me what I can/need to do myself then have them put the final touch on it. PM me with your progress.