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Author Topic: Ignition Timing  (Read 1357 times)
jdv69z
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69 RS Z/28 52E


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« on: August 30, 2013, 07:56:20 AM »

I have a friend trying to sort out the motor on his 70 nova. Has trouble getting the car to start, and seems to be fouling as lot of plugs. He is telling me the initial timing is set at 25 degrees. So his total timing would be in the 45 degree range? (No vacuum advance being used) Motor is setup with cam for the 3000-700 RPM range from what I understand. To me that's for drag racing. Do these numbers so right for drag setup cars? That's a lot more initial advance than I've ever used. I'm thinking he has a racing setup and it's not very friendly for the street use he's trying to use it for. Thanks for any insight.
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Jimmy V.
JohnZ
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« Reply #1 on: August 30, 2013, 10:20:07 AM »

I have a friend trying to sort out the motor on his 70 nova. Has trouble getting the car to start, and seems to be fouling as lot of plugs. He is telling me the initial timing is set at 25 degrees.  Do these numbers so right for drag setup cars? That's a lot more initial advance than I've ever used. I'm thinking he has a racing setup and it's not very friendly for the street use he's trying to use it for. Thanks for any insight.

You are correct - he's trying to make a "race" setup street-driveable, and it's not going to happen with a big cam, 25 degrees initial timing, unknown centrifugal advance, no vacuum advance, too-cold plugs, and too many other unknown details to help with a diagnosis. SB? BB? Carb? Distributor? Heads? Cam specs? Compression?
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cook_dw
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« Reply #2 on: August 30, 2013, 10:23:23 AM »

He is running too much timing.  Inital can be whatever but the total (I would think) would be in the 35-38 range.  If he sets his total timing to say 35 degrees and then checks the timing at idle that will give you what the mechanical advance is in the distributor.  If he is running 45 at total and is inital is 25 then that means his mechanical advance is 20 degrees.  Seems to me like it needs more mechanical advance and the timing retarded.  But it is hard to say for sure what is truly needed cause you would need to factor in cam and where it was degreed in as well as engine size and specs.  

Just curious but has he made sure he is not 180 degrees out on the distributor?  Do the headers or manifolds glow red?

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Darrell Cook

1967 LeMans Blue SS/RS L35 clone
1968 Rallye Green SS L78 - unrestored original
1968 Matador Red Z28
cook_dw
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« Reply #3 on: August 30, 2013, 10:23:46 AM »

John beat me to it.. Grin
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Darrell Cook

1967 LeMans Blue SS/RS L35 clone
1968 Rallye Green SS L78 - unrestored original
1968 Matador Red Z28
jdv69z
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« Reply #4 on: August 30, 2013, 10:48:06 AM »

Thanks, very helpful insight.
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Jimmy V.
janobyte
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« Reply #5 on: August 30, 2013, 10:51:54 AM »

Cook ,you are right on and made me delete my post !  Grin  From mild built to drag race only 38 degrees total , on our SBC's always proved best.(per dyno/time slips) I'm not going to spec it out, but our race engine is locked out at 38 degrees, and we have no starting issues. Remember you are always building a "package"
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cook_dw
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« Reply #6 on: August 30, 2013, 11:56:54 AM »

Also he needs to run a vacuum advance if he is going to drive it on the street.  It is dumb to run without one.  I have read several posts on ported vs manifold vacuum as well.  I can make either one work.  But the best for driveability would be manifold.

Cook ,you are right on and made me delete my post !  Grin 
       Grin


Lol yeah this was just fresh on my mind since I was just dealing with the same thing on a car I was tuning last weekend.   Wink
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Darrell Cook

1967 LeMans Blue SS/RS L35 clone
1968 Rallye Green SS L78 - unrestored original
1968 Matador Red Z28
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