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Old 05-28-2010, 09:07 PM
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Pinging Or Dieseling

Man, I can't win.. Trying to get my 355 tuned. It's about 10.5:1, with Dart Iron heads, Lunati Voodoo cam and a 750 vac secondary on an RPM Air Gap intake and Mallory HEI with adjustable advance. I started initial timing, (vac advance unplugged) at around 12 BTDC and it pinged on acceleration, not hard just 1/2 or so, so I started bringing it back 2 degrees at a time and now I'm at 4 BTDC and now it keeps running (diesels) and still slightly pings and backfires through the exhaust and carb.. Total advance is around 35 and I can't seem to adjust it with the adjuster in the can. It does seem to run a little rich, but ***?? Any ideas?

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Old 05-28-2010, 09:47 PM
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Need a library of information before anyone can help.
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Old 05-28-2010, 10:18 PM
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Quote:
Originally Posted by 19nova69
... I started bringing it back 2 degrees at a time and now I'm at 4 BTDC and
now it keeps running (diesels) and still slightly pings and backfires through the
exhaust and carb.. Total advance is around 35 and I can't seem to adjust it
with the adjuster in the can. It does seem to run a little rich, but ***?? Any
ideas?
Dieseling normally means the carb. butterflies are open too far at idle. I would
bring the initial back up to 10 degrees BTDC and limit the total to 32 - 34.
You might find it needs more than 10 degrees at idle, and or less total.
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Old 05-28-2010, 11:54 PM
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Quote:
Originally Posted by 19nova69
Man, I can't win.. Trying to get my 355 tuned. It's about 10.5:1, with Dart Iron heads, Lunati Voodoo cam and a 750 vac secondary on an RPM Air Gap intake and Mallory HEI with adjustable advance. I started initial timing, (vac advance unplugged) at around 12 BTDC and it pinged on acceleration, not hard just 1/2 or so, so I started bringing it back 2 degrees at a time and now I'm at 4 BTDC and now it keeps running (diesels) and still slightly pings and backfires through the exhaust and carb.. Total advance is around 35 and I can't seem to adjust it with the adjuster in the can. It does seem to run a little rich, but ***?? Any ideas?
Is there any better quality of fuel available?
Why so high on the static compression ratio?
What's the piston deck height?
What thickness gasket?
Did you measure your squish on trial assembly?
What's the fuel pressure at the carb inlet?
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Old 05-28-2010, 11:56 PM
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Plugs too hot of a heat range, deposits glowing on the plugs from break-in, too high of an idle speed, hook the vacuum advance to a manifold vacuum source if it's not already then lower the idle speed w/the curb idle screw to close up the primary side of the carb. Hopefully there's nothing in the combustion chamber causing a hot spot- it will act as a glow plug and cause dieseling. Be sure there's no vacuum leaks, might want to use a vacuum gage on it.

All else fails, shut it off in gear will sometimes keep it from running on.

If the timing tab/damper line may be off, you can DETERMINE TDC then MAKE A TEMPORARY TIMING TAPE to use to double check the timing light, if you don't already have a degreed damper.

G/L
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Old 05-29-2010, 08:12 AM
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10.5 cr sbc needs a cam with an advertised duration over 292 degrees to run pump gas (93 octane). what size voodoo cam are you using?

sounds like you will need to get an adjustable distributor so you can limit the total advance to stop the ping while still running enough timing to stop the diesel.

Other solutions would include using a bigger cam, aluminum heads, or lower compression.

just my take on the limited information.

dieseling is caused by too much fuel left in the chamber after shut down. This is typically caused by the throttle blades open past the idle slots during idle which causes a very rich idle. more ignition timing allows the engine to run a leaner mixture at idle and increases the idle speed so the throttle blades can be closed.

and of course, ping is normally caused by too much cylinder pressure for the octane of the fuel. A bigger cam with a later intake closing point will reduce cylinder pressure.
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Old 05-29-2010, 04:31 PM
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I'm running the 276/284 duration Voodoo cam. I messed with this all day, I got the dieseling to go away by advancing the timing a little more, I'm at 10 BTDC at idle now and it goes up to about 24 at higher RPMs, but I cannot for the life of me get the pinging to stop. I have the adjustment on the vac advance all the closed right now and it still pings. If I accelerate slowly it's fine, but once I get into the throttle to get the secondaries opening it starts to ping like crazy, or when it upshifts and is under a load it pings.. Could this be a carb issue? If so what?? It's a Holley 750 vac secondary..

Last edited by 19nova69; 05-29-2010 at 04:43 PM.
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Old 05-29-2010, 09:32 PM
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Quote:
Originally Posted by 19nova69
I'm running the 276/284 duration Voodoo cam. I messed with this all day, I got the dieseling to go away by advancing the timing a little more, I'm at 10 BTDC at idle now and it goes up to about 24 at higher RPMs, but I cannot for the life of me get the pinging to stop. I have the adjustment on the vac advance all the closed right now and it still pings. If I accelerate slowly it's fine, but once I get into the throttle to get the secondaries opening it starts to ping like crazy, or when it upshifts and is under a load it pings.. Could this be a carb issue? If so what?? It's a Holley 750 vac secondary..
You didn't say what fuel you were using. With that compression, you need 93 or higher. If you are running 93, mix in a few gallons of 110 octane and see if that helps. Also, don't allow it to ping. You'll be replacing some pistons before long.
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Old 05-29-2010, 11:04 PM
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The distributor advance curve is all messed up.

The the 276voodoo cam you are running you need to recurve the distributor.
The cam wants about 18 to 24 or so deg at idle but only 32 to 34 at Max advance.
shorten/ limit the length of the advance curve to allow the increased base idle timing without excessive max advance at high rpm.

The mech advance curve travel needs to be shorteed from stock (20-22deg) to around 14 -16degrees.

get the mechn advance sorted out and then readjust the carb.
The throttles will be closed a lot more at idle preventing run on.

then when you get that right, you want around 10-12deg of vacuum advance at highway part throttle cruise. (limit the vacuum advance to around 10-12deg.)
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Old 05-30-2010, 12:46 AM
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Quote:
Originally Posted by 19nova69
I'm running the 276/284 duration Voodoo cam. I messed with this all day, I got the dieseling to go away by advancing the timing a little more, I'm at 10 BTDC at idle now and it goes up to about 24 at higher RPMs, but I cannot for the life of me get the pinging to stop. I have the adjustment on the vac advance all the closed right now and it still pings. If I accelerate slowly it's fine, but once I get into the throttle to get the secondaries opening it starts to ping like crazy, or when it upshifts and is under a load it pings.. Could this be a carb issue? If so what?? It's a Holley 750 vac secondary..
I'm guessing this isn't a daily driver. With that CR you are going to need to fuel it w/a mix that includes some race gas or tune it to run on E85.

Depending on how much fuel you go through and the availability of E85 fuel in your area should make the decision a little easier.

The timing advice you got from FB88 should be followed- here are a few P/N's, etc. to help you dial things in:

The ACCEL 31035 is an adjustable vacuum advance can for GM HEI that allows infinite adjustment to BOTH the amount and rate of advance. Comes w/instructions and tool.

To limit the amount of advance w/an OEM or some adjustable (for tip-in only- NOT total advance applied) cans like the Crane can, you will need to physically limit the vac can's travel w/a VACUUM ADVANCE LIMITER PLATE- Crane #99619-1: 99619-1 INSTRUCTIONS.

Another kit for adjustable vacuum advance is ADJUSTABLE VACUUM ADVANCE CAN KIT- Crane #99600-1: 99600-1 INSTRUCTIONS.

To verify your timing marks are correct: DETERMINING TDC

If your damper doesn't have the degrees on it and if you don't have a dial back timing light, you can easily make a temporary timing tape. Use it to permanently mark the damper w/the total timing: MAKE A TIMING TAPE.
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Old 05-30-2010, 06:45 AM
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I'm running 93 and also added a can of octane booster to no avail.
My Mallory HEI has an adjustable can, so I guess I just need to put in the limiter plate. I'm surprised that cam wants that much advance but I'll try it..
Thanks guys, I hope this works..

Last edited by 19nova69; 05-30-2010 at 06:54 AM.
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Old 05-30-2010, 06:53 AM
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Quote:
Originally Posted by F-BIRD'88
The distributor advance curve is all messed up.

The the 276voodoo cam you are running you need to recurve the distributor.
The cam wants about 18 to 24 or so deg at idle but only 32 to 34 at Max advance.
shorten/ limit the length of the advance curve to allow the increased base idle timing without excessive max advance at high rpm.

The mech advance curve travel needs to be shorteed from stock (20-22deg) to around 14 -16degrees.

get the mechn advance sorted out and then readjust the carb.
The throttles will be closed a lot more at idle preventing run on.

then when you get that right, you want around 10-12deg of vacuum advance at highway part throttle cruise. (limit the vacuum advance to around 10-12deg.)

Getting to that 18-24 at idle, is that with vac advance unhooked or with the vac line on it? I have the advance curve adjusted as much as I can go right now with the can, so I will try the limiter to see if that helps.. Thanks
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Old 05-30-2010, 07:04 AM
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reset the butterflies

Pull the carb, back the idle speed all the way back , close the butterfles then hold it up to the light, and look thru for daylight around the bores. baclfiring can cause problems with seating the butterflies. loosen the screws, tap the butterflies with the plastic handle of the screwdriver while holding them closed then tighten and recheck. If that doesn,t solve the diesing problem get an idle speed solenoid, A lot were used on fords in the 70.s.. the solenoid is wired to the run side of the ignition and the idle speed is adjusted with the engine running. when you turn the key off the butterfles close completely and that usally solves the problem.
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Old 05-30-2010, 08:02 AM
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the root of the problem is you are running too much compression for that cam.

drop the cr to 9.5:1 or install a bigger cam. That much cr needs a cam around the size of a compcam 292H. But that cam would also require a 3000 stall and 4.11 gears.

aluminum head would help but may not be enough.

maybe a set of aluminum heads and a 280H compcam would do the trick.

bigger chambers would also do it. if you are using 64cc heads then a set of 72's should drop the cr to 9.6.
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Old 05-30-2010, 11:03 AM
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Quote:
Originally Posted by 19nova69
Getting to that 18-24 at idle, is that with vac advance unhooked or with the vac line on it? I have the advance curve adjusted as much as I can go right now with the can, so I will try the limiter to see if that helps.. Thanks
Initial timing is set with the vacuum advance unhooked and the line to the carb plugged.
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