Octane Question
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From: Culpeper, Virginia
Octane Question
I have a kinda dumb question.
I run high test (93) in my truck. Linc 74' 460. Not moded by me or too my knowledge before me.
I have had a guy mention that maybe I should be running regular gas to help a rich condition I'm experienceing on startups. She smells a little rich during driving, but I suspected it stinks cause she has no cat.
If I were to dump some 87 in her, what would I need to consider checking?
Timing? Re-gap plugs?
Thanks,
Blair
I run high test (93) in my truck. Linc 74' 460. Not moded by me or too my knowledge before me.
I have had a guy mention that maybe I should be running regular gas to help a rich condition I'm experienceing on startups. She smells a little rich during driving, but I suspected it stinks cause she has no cat.
If I were to dump some 87 in her, what would I need to consider checking?
Timing? Re-gap plugs?
Thanks,
Blair
Post Fiend
Joined: Jul 2003
Posts: 11,945
Likes: 3
From: Spokane, WA
I don't remember if that's the high compression engine or not but either way, switching to a lower octane gas won't affect how rich it's running. Octane ratings are a measure of how much the fuel can be compressed before it detonates. Higher octane means you can run it in higher compression engines without detonation or pinging whereas a low octane gas in a high compression engine will "go off" before the spark plug ignites the mixture. It does absolutely no good (except to oil companies) to run high octane in a low compression motor. I'm sure someone will post up and tell us which yours is but I'm pretty certain it's the smog controlled low compression beast in which case 87 octane will do just fine.
As far as it running rich, that's in the carburation so some adjustments need to be made there.
EDIT Higher octane will also allow you to run more advanced timing than lower octane, so if you've got some serious advance on the ignition timing this would be a good reason to run high octane fuel. However timing that is so far advanced is not common (or a really good idea) on a street driven vehicle.
As far as it running rich, that's in the carburation so some adjustments need to be made there.
EDIT Higher octane will also allow you to run more advanced timing than lower octane, so if you've got some serious advance on the ignition timing this would be a good reason to run high octane fuel. However timing that is so far advanced is not common (or a really good idea) on a street driven vehicle.
Last edited by ivanribic; Jan 10, 2006 at 03:47 PM.
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It is a waste of money to pump a higher octane into a vehicle that has an engine that doesn't require it.
I suspect an 8:1 compression engine to run fine on 87*
Just re-time the engine once the new gasoline is getting to the carb.
I suspect an 8:1 compression engine to run fine on 87*
Just re-time the engine once the new gasoline is getting to the carb.
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Joined: Dec 2001
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From: Louisville,Ky.
In 73, they dropped the compression to around 8.5 to 1 so it should run fine on 87 octane as long as the timing isn't advanced too far. Just swap over to 87 octane. As long as no detonation is present, it should be fine. If it starts pinging, back the timing back a little bit.
It will smell rich with no cats.
Did you ever get the air cleaner situation straightened out?
It will smell rich with no cats.
Did you ever get the air cleaner situation straightened out?
Cargo Master
Joined: Apr 2001
Posts: 2,364
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From: Eustis FL
A stock 74 460 will not be very prone to ping, nor are any 460's in good tune, unless they are modified with 1969-1971 heads (D0VE C, C9VE, CJ, etc) which will raise compression. Even just adding the Thunderjet heads only raises compression to about 9.3:1, which may still burn 87 octane fine. With these quench style heads, you may even run as high as 10:1 (piston swap)without the extra octane, but it's all dependant on ignition timing (as mentioned), your ign. system, etc. You may run Duraspark II or aftermarket if you are still on points; That will ensure a hotter spark and better burn.
If you are running rich with a good stock Ford carb, it may be because (a)emissions equipment disabled or modified (b) you are at a higher altitude than what that engine (carb) was calibrated for, or (c) the carb adjustments are out of spec.
If its an aftermarket carb, it may need to be calibrated with jets and metering rods, springs.
If you just suspect rich, just check the color of your plugs. If they are black and sooty, then yes, your suspicions are right. Exhaust through a cat. smells different than through a cat.-free exhaust, so that may be what you smell.
Hope this helps you out.
Mark
If you are running rich with a good stock Ford carb, it may be because (a)emissions equipment disabled or modified (b) you are at a higher altitude than what that engine (carb) was calibrated for, or (c) the carb adjustments are out of spec.
If its an aftermarket carb, it may need to be calibrated with jets and metering rods, springs.
If you just suspect rich, just check the color of your plugs. If they are black and sooty, then yes, your suspicions are right. Exhaust through a cat. smells different than through a cat.-free exhaust, so that may be what you smell.
Hope this helps you out.
Mark
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From: Culpeper, Virginia
Thanks Mark,
I'll make it a point to pull a plug soon. It's a easy thing to do.
Running a aftermarket Holley 750, vac sec, elec choke, off the shelf special from Auto Zone.
Running a what I believe is stock ign system, new coil and plugs, wires, cap, rotor, but off the shelf replacement parts is what I got.
I'll pull the plug tonight.
I'll make it a point to pull a plug soon. It's a easy thing to do.
Running a aftermarket Holley 750, vac sec, elec choke, off the shelf special from Auto Zone.
Running a what I believe is stock ign system, new coil and plugs, wires, cap, rotor, but off the shelf replacement parts is what I got.
I'll pull the plug tonight.
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Cargo Master
Joined: Apr 2001
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From: Eustis FL
Depending on where you are at, your carb will need to be calibrated and adjusted. Most carbs 'off the shelf' and calibrated for sea level operation. With my Edebrock, I have gone 3 stages lean with my cruise mode jetting, and one stage lean on my power mode, because my truck is at 3000 feet. (probably won't be there for long!)
I don't run Holleys because of the fact they can be so much more difficult to tune than Edelbrock. They can deliver better power when tuned just right, but I just haven't opened that can yet...
Consult Holleys manual or their website for tuning instructions on your particular carb, and see what can be done from there.
Mark
I don't run Holleys because of the fact they can be so much more difficult to tune than Edelbrock. They can deliver better power when tuned just right, but I just haven't opened that can yet...
Consult Holleys manual or their website for tuning instructions on your particular carb, and see what can be done from there.
Mark
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Posting Guru
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From: Culpeper, Virginia
Thanks again for the input. I run mine at around 500 feet above see level with some various other altitudes but nothing high.
I'll have to look into their website and see what I can dig up.
Thanks again,
Blair
I'll have to look into their website and see what I can dig up.
Thanks again,
Blair
Post Fiend
Joined: Jul 2003
Posts: 11,945
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From: Spokane, WA
For a stock 460 with a Holley 750 you may have to jet it down slightly. When you get a chance to look at the plugs post up in the fuel delivery forum. There's some guys in there that really know their Holleys can they can give you suggestions on how to fine tune it.
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From: Culpeper, Virginia
Got some pics.....
I took some pics of my #1 and #5 plugs.....
[IMG]
[/IMG]
I took a shot of the carb looking down the venturi's.....
[IMG]
[/IMG]
[IMG]
[/IMG]
Might be hard to tell from the picks, but I got some serious blackening happening in them venturi's.
Post up some input fellas. I have put more miles on this truck since October than the last 3 years put together. I'm going to use this as a tow rig for my Jeep outings, I'd love to get this in the best shape I can.
Thanks,
Blair
[IMG]
[/IMG] I took a shot of the carb looking down the venturi's.....
[IMG]
[/IMG] [IMG]
[/IMG] Might be hard to tell from the picks, but I got some serious blackening happening in them venturi's.
Post up some input fellas. I have put more miles on this truck since October than the last 3 years put together. I'm going to use this as a tow rig for my Jeep outings, I'd love to get this in the best shape I can.
Thanks,
Blair
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