View Single Post
Old 10-11-2019, 03:34 PM   #13
Patrick L.
Senior Member
Patrick L.'s Avatar
Join Date: May 2010
Location: Upstate NY and western Florida
Posts: 5,204
Default Re: Max Compression Ratio

Originally Posted by Ak Sourdough View Post
Having raced Sprint Cars for 10 years in the 80's, my understanding of alcohol fuel is that it is very easy on the bottom end of an engine. Here's how it was explained to me and seems to be true.

Gasoline burns quickly and makes a big explosion at the top of the cylinder causing big shock loads to the pistons, rods, bearings and crankshaft. All the work and the heat is produced at the top of the cylinder and the combustion gas expands very rapidly, pushes down on the piston, then the explosion is over.

Alcohol burns very slowly in comparison and has a much less powerful explosion at the top of the cylinder when it starts to burn. The advantage comes from the slow burn. Rather than the big bang at the top of the cylinder it burns and expands the gasses all the way down the cylinder making a long powerful push on the piston instead of a jolt and thereby dramatically increases the total force applied to the piston and reduces the shock loading on all the related parts. By burning more slowly, it allows much more compression and more total timing advance than gasoline without causing pre-ignition or detonation. 14 or 15 to 1 compression and 38 to 40 degrees of timing was common in Sprint Car engines at the time.

There are a number of disadvantages too for street use.

Yep, there are disadvantages in alcohol for any use. There are also some advantages.
Patrick L. is offline   Reply With Quote