high octane or regular?
Senior User
Joined: Aug 2004
Posts: 327
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From: Los Angeles
Originally Posted by Dan Tenn
...we got an exta 30 h.p. with the 91 vs. 110 for a total of 610 h.p. Don't waste your money on higher grades unless you need it.
Dan
Dan
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Joined: Feb 2005
Posts: 3,952
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From: Upper Left Coast
Yes you're quite correct. Rather high octane fuel may be required to prevent PRE-IGNITION. Newer engines use knock sensors to adjust timing to prevent detonation when lower octane fuel is used.
Given two identical engines, one with say, 7.5:1 compression and another with say, 10.5:1 compression, The engine with 10.5:1 will produce more HP than the one with lower compression. (running on the same fuel ) If the fuel is low octane, the lower compression engine will run and produce a given amount of HP. The one with higher compression will produce more HP up to the point where detonation begins to take place. Then the HP will fall off and the engine will start to be damaged.(burned pistons, etc.) by the way the lower comp engine will produce no more HP on the higher octane fuel.
One of the reasons that diesels are more efficient is the compression. The other reason is that diesel fuel has more energy per pound/gallon than gasoline. (Kerosene also has more energy per gal/lb than gasoline too) A good way to prove this is to run gasoline in a jet engine and compare it to running Kerosene (JET-A1, etc) Jet A produces more thrust than gasoline.
I'm not sure that I believe that tetraethyl lead prevents valve seat erosion. I have seen older engines run THOUSANDS of miles on propane with NO ill effects on the valves. Last time I checked, propane is lead free.
I also ran my 292 powered 57 Ford on lead free "plant gas" (natural gasoline) for many years with no ill effects.
It pinged like you wouldn't believe (if you stepped on it!)because there was no lead in it too. (the price was right!)
cheers,
RIck
Given two identical engines, one with say, 7.5:1 compression and another with say, 10.5:1 compression, The engine with 10.5:1 will produce more HP than the one with lower compression. (running on the same fuel ) If the fuel is low octane, the lower compression engine will run and produce a given amount of HP. The one with higher compression will produce more HP up to the point where detonation begins to take place. Then the HP will fall off and the engine will start to be damaged.(burned pistons, etc.) by the way the lower comp engine will produce no more HP on the higher octane fuel.
One of the reasons that diesels are more efficient is the compression. The other reason is that diesel fuel has more energy per pound/gallon than gasoline. (Kerosene also has more energy per gal/lb than gasoline too) A good way to prove this is to run gasoline in a jet engine and compare it to running Kerosene (JET-A1, etc) Jet A produces more thrust than gasoline.
I'm not sure that I believe that tetraethyl lead prevents valve seat erosion. I have seen older engines run THOUSANDS of miles on propane with NO ill effects on the valves. Last time I checked, propane is lead free.
I also ran my 292 powered 57 Ford on lead free "plant gas" (natural gasoline) for many years with no ill effects.
It pinged like you wouldn't believe (if you stepped on it!)because there was no lead in it too. (the price was right!)
cheers,
RIck
Originally Posted by Dan Tenn
The only reason to run high octane gas is to prevent pre-detonation, or engine knock. If you think its better or makes more power in an engine that does not require it, you are mistaken. I have dyno sheets from the last engine build I did. It was 542 ci. C$#@vy. We broke the engine in on the dyno and adjusted timing etc. with full 110 race gas. After a few pulls, we slowly started mixing in 91 octane amoco gas until we reached 100% with no knock. We knew this was going to be border-line, but wanted to see the results. Guess what, we got an exta 30 h.p. with the 91 vs. 110 for a total of 610 h.p. Don't waste your money on higher grades unless you need it.
Dan
Dan
