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Richard Jemison
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7,190 Posts
Discussion Starter #304
SETTING IGNITION TIMING FOR RACE MOTORS

Much has been expressed on how to set timing in various ways.
But having some ignition issues with the coupe and switching out the Crane Hi6 system to a newer 6440 version and still having a high rpm eratic miss I removed the Autolite iridium extended tip race plugs, and found no fault there.

I was joined at lunch by Donnie Culberson who has been a high performance store owner for 40 years, and now builds extremely high dollar race engines. He knows his schitt!
Discussing my "ignition?" misfire I received some really valuable information on cam timing and what and how to insure it is truly "right on". As well as determining if plugs are "right" for the engine, both heat range and design. He had suggested a couple of years ago the Autolite plugs I`ve been using in both Racecars and in the hotted up Montreal engine that originally was in the coupe. And really had no problems with any of them but have pushed the rev limits well into 8K plus on both race motors and the Autolites showed evidence of ceramic and ground electrode damage.

At Atlanta with a similar high RPM eratic occurring miss I switched out the Autolites for total cold Bosch Dome plugs sold in the 90`s for Nascar aluminum heads. Problem was solved with the plug change.

Donnie stated most extreme race engine owners had pretty much gone over to NGK race plugs. But they were easier to read as to heat range. As well the ground electrode strap was easy to determine if timing was correct by the location of the "hot spot" on the strap.

Basically here`s what I was told..
With any plug to see if heat range is correct you read the height of the hot area inside the plugs opening, relative to the number of threads above the bottom. With common plugs like Autolite, Champion (rarely used by racers due to failures) etc, the hot area should be about 2 threads above the bottom.
With NGK plugs only about 1 thread. This is about material (alloy) used in the case.

The ground electrode`s alloy commonly failed before heat and detonation caused piston melting.
The same electrode can indicate if timing is dead on for during race pressures and temps.
Looking at the electrode picturing it as a curve attached to the bottom ring of the plug housing, sweeping up and over the center electrode. If the bluish "hot spot" is close to the bottom ring your ignition timing is too advanced. If the "hot spot is near the end of the electrode then your timing is too retarded. The blue area should be at the center of the electrode if timing is correct for the build and use.

To be able to see this evidence on the plugs you have to do an immediate ignition cut after the loaded run. Easy for a drag racer that`s cutting off the engine as the chute stops the car and it`s towed back to the paddock. Hard for road racers as there are only a few tracks where you can cut off the engine and coast to the pit in road. But sometimes if it`s a brief run, a spray cleaning with brake clean will remove rich fluff so you can see the heat coloration inside the plug and on the electrode.

I learned something about sparks and now have to consider his question to me re: intake valve float. Commonly that`s not a damaging situation but it will screw up a power stroke or several. I use a PSI valve spring on the intake side that is not as stiff as the ISKY springs on the exhaust side. Maybe I didn`t shim it enough but installed seat pressure was 105 lbs. But they have had several run cycles. I wish I had had this conversation earlier as the engine was just put back into position, and to remove the cam cover the engine has to come forward about 8". And I had it off checking (and advancing) the intake cam, lash and compression.

Now I`ve got something else to worry about!:unsure:
 

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Premium Member
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13,494 Posts
That post is one of the reasons why the ABB is a great source of knowledge. Thanks.
I had never thought about it before but it is easier to do a plug chop on a street car than on a race car. You should get some tags and a muffler for your race cars.
 

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Richard Jemison
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7,190 Posts
Discussion Starter #306
Well I`ve got my old Belize tag, but that might add cost to the driving award!

As for muffler I just eliminated the straight through muffler BECAUSE you said the car sounded like a Miata!
 

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If you use a turbo Corvair muffler, they sound more like a GTA. They are straight through, with a "big-enough" in & out tube.
 
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