[hal101]

hey just started mixing fuel for my 455 .040 over #12 heads

have been running on race gas 100 - 110 octane

now i need to run on pump gas so one ounce of additive to 6 gal of 87 ottane
= 96 octane

so i put in the first 6 gal NEVER pinged/rattled/detonated that i herd

but when i turned it off it ran on for about 3 or 4 sec

is that a sign of detonation that i cant hear or nothing to worried about?

[cdrookie]

what additive are you using that turns 87 into 96?

[hal101]

Originally Posted by cdrookie

what additive are you using that turns 87 into 96?

http://bndautomotive.com/aces-formul...oline-formula/

[Schurkey]

Originally Posted by hal101

http://bndautomotive.com/aces-formul...oline-formula/

ACES IV also has 5 times the synthetic lead byproduct that produces a copious upper cylinder lubricant that reduces cylinder/bore wear by 600% and valve recession by 360%

According to WHO? Tested HOW?

I don't trust these folks any farther than I can throw them.

[Blued and Painted]

Those are good 1/4 times for the 2.56 gear. Must have quite the top end charge.
What cam with the hi compression iron head 455.

Run on is pretty common. The question for me is, does detonation occure before or after the normal idle ignition timing.

[PunchT37]

A run on problem usually means you are at the bottom of your octane requirement, provided your operating temps, idle speed, and mixture are ok from the start.

[dhcarguy]

How much is this stuff??? must be expensive, they won't tell you on the site.

[hal101]

Originally Posted by Schurkey

According to WHO? Tested HOW?

I don't trust these folks any farther than I can throw them.

give him a call and im sure he will tell you

the fact that im running on 87 octane and his additive and not hearing any nock or ping tells me it is working

[hal101]

Originally Posted by Blued and Painted

Those are good 1/4 times for the 2.56 gear. Must have quite the top end charge.
What cam with the hi compression iron head 455.

Run on is pretty common. The question for me is, does detonation occure before or after the normal idle ignition timing.

it is the old faithful cam from sd perf

i dont hear any detonation at all my only prob is the run on after i turn the key off

im just asking is the run on some indication of detonation that i cant hear?

[hal101]

Originally Posted by PunchT37

A run on problem usually means you are at the bottom of your octane requirement, provided your operating temps, idle speed, and mixture are ok from the start.

ok so i will move up to 1 oz to 6 gal of 93 octane which = 102 octane and see if it goes away

[PunchT37]

Originally Posted by hal101

ok so i will move up to 1 oz to 6 gal of 93 octane which = 102 octane and see if it goes away

Won`t hurt to try. Timing has no effect as the spark is off while this is happening. So, it`s out of the picture. The fuel can`t take the heat in the chamber without lighting off by itself. That`s why they called it "dieseling" back in the day.

[hal101]

Originally Posted by dhcarguy

How much is this stuff??? must be expensive, they won't tell you on the site.

i dont remember the price i bought 1 gal and i think with shipping and measuring device it was about $300. now that treets 770 gal of gas

i could be wrong but that is what i remember

[gtofreek]

Originally Posted by Blued and Painted

Those are good 1/4 times for the 2.56 gear. Must have quite the top end charge.
What cam with the hi compression iron head 455.

Run on is pretty common. The question for me is, does detonation occure before or after the normal idle ignition timing.

Detonation and pre-ignition are two totally separate things. Detonation occurs after the spark when all the fuel has not been burned by the time max cylinder pressure is reached[usually around 14° ATDC]. At that point, if the octane is too low, whatever un-burned fuel that is left in the chamber, detonates from the pressure, much light a bomb. The trick is too burn all the fuel before max cylinder pressure occurs. If you can do that, then you will not have detonation. This is where small, shallow fast burn chambers really help. Big chambers take more time to burn all the fuel. Detonation starts in the farthest points of the chamber from the spark plug. Usually on the other side of the exhaust valve.

Pre-ignition occurs during the intake stroke, long before ignition. If there is a really hot spot in the chamber, it can light off the a/f mixture as it enters the chamber, while the piston is on it's way down the cylinder. Now, with the a/f burning, the piston starts it's way up the cylinder, compressing the a/f while it's burning. Now the heat and pressure becomes so extreme that it melts the top of the piston, and the pressure blows a hole in it. If an engine pre-ignites, it won't run more that a few revolutions before the piston melts down. This can occur in less than a second. Think about this, at 2000 rpm, the piston is dealing with combustion over 16 times per second.

[gtofreek]

To answer the OP question, the run on is because the cylinders are hot enough to ignite the A/F as it is still entering the cylinders. This happens with high compression. It can be overcome by shutting the engine off in gear.

[PunchT37]

Originally Posted by gtofreek

Big chambers take more time to burn all the fuel. Detonation starts in the farthest points of the chamber from the spark plug. Usually on the other side of the exhaust valve.

Correct. And larger bore engines. That`s why one can get away with less octane, more compression, leaner mixtures, etc, on a Pontiac 350 vs a 455. Especially a modern fast burn chamber aluminum headed 350.

[Kenth]

I have found that nozzle drip caused by a to lean idle circuit and too far opened throttle blades are the main issues for run on turning ignition off.

[Formulajones]

Originally Posted by Kenth

I have found that nozzle drip caused by a to lean idle circuit and too far opened throttle blades are the main issues for run on turning ignition off.

Yep, that's why quite a few cars from this era had idle solenoids or dash pots, that would kick up the idle with the key on, and back off the throttle arm when you turned the key off...so no more run on when shut down. A lot of people confused this with AC, but that's not what it was for. Then show them cars without AC and solenoids and they scratch their heads.

I see this quite a bit with cars that have large cams, and the idle circuits of the carb aren't tuned correctly for the combination, so they struggle to idle, and people kick up the idle speed to compensate, moving the throttle blades passed the idle transition slot. Basically making the car idle off the main jet (nozzle drip) Then complain of poor gas mileage and all the other issues associated with a poorly tuned carb.

[Navy Horn 16]

Originally Posted by hal101

i dont remember the price i bought 1 gal and i think with shipping and measuring device it was about $300. now that treets 770 gal of gas

i could be wrong but that is what i remember

Why not just buy 100LL and mix it at 30%. WAY cheaper.

I don't trust additives at all. You don't really know what they are putting in it, and all you know it is that is making your gas less volatile.

[hal101]

Originally Posted by Kenth

I have found that nozzle drip caused by a to lean idle circuit and too far opened throttle blades are the main issues for run on turning ignition off.

this may be true but it dose not do it with high octane

[Formulajones]

Originally Posted by hal101

this may be true but it dose not do it with high octane

That's because the higher octane is harder to ignite. The issue of unburned fuel is still there, it's just that the higher octane masks it because it's not as sensitive to the heat in the combustion chamber.

Hence the reason why higher octane cures detonation, as well as heat soak and vapor lock, and generally also requires more ignition lead for best performance. It's slow burning.