how much octane?
2nd Gear Member
Joined: Sep 2009
Posts: 205
From: colorado
most engines now a days with the newer fuels can run 91 octane in a 10.5:1-11.5:1 comp deal easy with the right tune and be just fine. 9.0:1-10.0:1 and below can run 87 octane. I have run my 13:1 comp BBC on 93 in a pinch but backed off the timing and stepped up the jets two sizes to keep more fuel to cool it. The trick is not to run too much timing and not to lean it out too much. On the n20 and pump gas I have run a 75 shot and 91 octane in my 4.0L on the stock tune but I am at 6300ft elevation. The stock tune is setup to run on fuel as low as 85 octane so you can get away with it but would not recommend it for too long.
6th Gear Member
Joined: Dec 2003
Posts: 8,872
From: cape giradeau,mo
It really depends from one engine to another
My old 306 9.5 with 18* initial timing ran on 87 lasted 10 yrs
My cj5 with a 1970 350 did not like timing above 10* initial and ran great with 89 but not 87
My 408 11.5 38*total got away with 87 but I went e-85
My 435 runs on cob webbs and dust
My 1993 z28 will only run on 91-93 octane and it's stock the spark knock goes crazy with anything less and shuts up with 93 and I'm going with e-85 tune very soon
So to answer your question that pertains to YOUR car run timing till your car pings or knocks back off 2* and run the fuel that was in your tank so I advise starting with 87
Not one person can say what your car will run on or not but the most common norm is you can run less octane but be smart about it
My old 306 9.5 with 18* initial timing ran on 87 lasted 10 yrs
My cj5 with a 1970 350 did not like timing above 10* initial and ran great with 89 but not 87
My 408 11.5 38*total got away with 87 but I went e-85
My 435 runs on cob webbs and dust
My 1993 z28 will only run on 91-93 octane and it's stock the spark knock goes crazy with anything less and shuts up with 93 and I'm going with e-85 tune very soon
So to answer your question that pertains to YOUR car run timing till your car pings or knocks back off 2* and run the fuel that was in your tank so I advise starting with 87
Not one person can say what your car will run on or not but the most common norm is you can run less octane but be smart about it
2nd Gear Member
Joined: Sep 2009
Posts: 205
From: colorado
It really depends from one engine to another
My old 306 9.5 with 18* initial timing ran on 87 lasted 10 yrs
My cj5 with a 1970 350 did not like timing above 10* initial and ran great with 89 but not 87
My 408 11.5 38*total got away with 87 but I went e-85
My 435 runs on cob webbs and dust
My 1993 z28 will only run on 91-93 octane and it's stock the spark knock goes crazy with anything less and shuts up with 93 and I'm going with e-85 tune very soon
So to answer your question that pertains to YOUR car run timing till your car pings or knocks back off 2* and run the fuel that was in your tank so I advise starting with 87
Not one person can say what your car will run on or not but the most common norm is you can run less octane but be smart about it
My old 306 9.5 with 18* initial timing ran on 87 lasted 10 yrs
My cj5 with a 1970 350 did not like timing above 10* initial and ran great with 89 but not 87
My 408 11.5 38*total got away with 87 but I went e-85
My 435 runs on cob webbs and dust
My 1993 z28 will only run on 91-93 octane and it's stock the spark knock goes crazy with anything less and shuts up with 93 and I'm going with e-85 tune very soon
So to answer your question that pertains to YOUR car run timing till your car pings or knocks back off 2* and run the fuel that was in your tank so I advise starting with 87
Not one person can say what your car will run on or not but the most common norm is you can run less octane but be smart about it
6th Gear Member
Joined: Dec 2003
Posts: 8,872
From: cape giradeau,mo
Well my 408 had 200 psi and alot of people think they have a 11.1 motor when they actually have less it happens
And yes cam has alot to do with it and how fast and efficient there heads flow too
But
And yes cam has alot to do with it and how fast and efficient there heads flow too
But
Banned
Joined: Dec 2005
Posts: 22,374
From: Lil' Rhody
6th Gear Member
Joined: Dec 2003
Posts: 8,872
From: cape giradeau,mo
You know I'm beginning to hate my phone lol
My "but" was going to refer to but a blanket style cam can't manipulate static/dynamic compression unless you get really lucky somebody has to know there stuff in order to design something to compensate let alone offset the octane demands and fuel quality
Besides an old foxbody 5.0 has been ran in the ringer so many times I think it can be justified that octane percentage means sqawt on a stock motor
My "but" was going to refer to but a blanket style cam can't manipulate static/dynamic compression unless you get really lucky somebody has to know there stuff in order to design something to compensate let alone offset the octane demands and fuel quality
Besides an old foxbody 5.0 has been ran in the ringer so many times I think it can be justified that octane percentage means sqawt on a stock motor
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