Highest CR on 87 octane
#1
08-21-2010 | 11:32 PM
Thread Starter
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Junior Member
Joined: Jul 2010
Posts: 12
From: Vevay,IN
Highest CR on 87 octane
I'm wanting to rebuild my 96 SW1 engine. I've thought about using some 99 rods (5.8) with early model pistons and shaving the piston tops for a lower CR. So what is the highest CR and still be able to run on 87 octane ?
Thanks Rick
Thanks Rick
#5
08-30-2010 | 06:29 PM
Senior Member
Joined: Mar 2010
Posts: 1,912
From: Peoria AZ
At the risk of starting a war, I have seen this particular argument carried out by people carrying around baskets of engine shrapnel to throw at each other who do not agree with their opinions.
Despite multiple technical papers to the contrary and countered by urban legend.
The long rod argument has existed long before there were engine management computors that could retune engines faster than detonation can destroy them. However detuning to run on 87 octane still ends up with degraded performance, excessive engine heat and high exhaust temperatures.
The rule of thumb I like and personally have seen to be affective is stick a decimal point into the octane of the gasoline and build the engine to run with 8.7:1 compression if you are going to run 87 octane.
Anything past that and what you are talking about will be expensive if you are paying for it to be done and in my opinion a waste of time if you are doing it yourself. Any increase in performance, if any, will not be measurable and not worth the expense.
I like my solution a whole bunch better. Run a better grade of gasoline and tune or build for it.
It works, is measurable and is cheaper.
Much of todays engine technology, cylinder head and combustion chamber design, chlinder head materials and quick reaction engine management computors will allow a higher compression engine to run on 87 octane gasoline. If for no other reason than the quick reaction of detonation or ping as it is referred to can retard the timing faster than detonation can damage things.
That is known as detuning.
Detuning a high compression engine to run on lower octane gasolines I have discussed. Being able to run on it and have increased performance are two different things altogether.
Far too many times some one has taken a factory cylinder head engine that back in the day ran on 101 octane (which today if carefully tuned can get away with running on 94 octane because the rating of octane has changed) and upped the compression and crutched the thing to run on available hight test wich in area is 91 octane maximum and then complained about doggy operation, over heating and blowing out of exhaust manifold gaskets due to excessively hot exhuast gas.
I myself have blown up two of them.
It was indeed and expensive lesson to learn. I can now build an engine that can run some compression on 91 octane, but $2000.00 worth of cylinder heads and pistons made out of materials that are getting hard to find is the price to pay.
It is far cheaper for me to build a 9:1 engine or something very close to it that will run on 91 octane (not 87) and tune it to run hard with out damage and a whole lot more fun to drive than something crutched to run on 87 and would not even run on 91 with out crutching.
And I am not about to move where I can by 94 octane gasoline regularly to build more.
I'd like about 15 more hp from my 94 Saturn SC2 on 89 Octane, but it is adequate as it is.
I'd like another 100 out of my fuel injected I6 modified engine on 91 octane, but have not figured out how to get it with out spending a ton of money.
I have about 450HP on 91 octane out of my 390 cu in cast iron V8. It makes me happy.
All, by the way, street and smog leagle. And thats the real trick.
Despite multiple technical papers to the contrary and countered by urban legend.
The long rod argument has existed long before there were engine management computors that could retune engines faster than detonation can destroy them. However detuning to run on 87 octane still ends up with degraded performance, excessive engine heat and high exhaust temperatures.
The rule of thumb I like and personally have seen to be affective is stick a decimal point into the octane of the gasoline and build the engine to run with 8.7:1 compression if you are going to run 87 octane.
Anything past that and what you are talking about will be expensive if you are paying for it to be done and in my opinion a waste of time if you are doing it yourself. Any increase in performance, if any, will not be measurable and not worth the expense.
I like my solution a whole bunch better. Run a better grade of gasoline and tune or build for it.
It works, is measurable and is cheaper.
Much of todays engine technology, cylinder head and combustion chamber design, chlinder head materials and quick reaction engine management computors will allow a higher compression engine to run on 87 octane gasoline. If for no other reason than the quick reaction of detonation or ping as it is referred to can retard the timing faster than detonation can damage things.
That is known as detuning.
Detuning a high compression engine to run on lower octane gasolines I have discussed. Being able to run on it and have increased performance are two different things altogether.
Far too many times some one has taken a factory cylinder head engine that back in the day ran on 101 octane (which today if carefully tuned can get away with running on 94 octane because the rating of octane has changed) and upped the compression and crutched the thing to run on available hight test wich in area is 91 octane maximum and then complained about doggy operation, over heating and blowing out of exhaust manifold gaskets due to excessively hot exhuast gas.
I myself have blown up two of them.
It was indeed and expensive lesson to learn. I can now build an engine that can run some compression on 91 octane, but $2000.00 worth of cylinder heads and pistons made out of materials that are getting hard to find is the price to pay.
It is far cheaper for me to build a 9:1 engine or something very close to it that will run on 91 octane (not 87) and tune it to run hard with out damage and a whole lot more fun to drive than something crutched to run on 87 and would not even run on 91 with out crutching.
And I am not about to move where I can by 94 octane gasoline regularly to build more.
I'd like about 15 more hp from my 94 Saturn SC2 on 89 Octane, but it is adequate as it is.
I'd like another 100 out of my fuel injected I6 modified engine on 91 octane, but have not figured out how to get it with out spending a ton of money.
I have about 450HP on 91 octane out of my 390 cu in cast iron V8. It makes me happy.
All, by the way, street and smog leagle. And thats the real trick.
Last edited by uncljohn; 08-31-2010 at 04:01 PM. Reason: Added information
