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| | | | Joined: Jul 2008 Posts: 13 Wrench Fetcher | | Wrench Fetcher Joined: Jul 2008 Posts: 13 | Hello all,
I have a 51 Chevy 3100 with a 235 in it. Last week I converted it to a HEI ignition from a 78 Nova. It runs great but I have a question about the mechanical advance.
We tested the points distributor in a Sun distributor tester, it had 30 degrees of advance. The HEI only has 20 degrees. From what I read this is correct. But do you just run the engine without the extra timing? Or do you advance the initial 10 degrees from the ball bearing in the flywheel?
Or do you just leave it with 20 degrees?
Some people say I suffer from insanity, in reality, I enjoy every minute of it!
| | | | | Joined: Feb 2004 Posts: 29,826 Kettle Custodian (pot stirrer) | | Kettle Custodian (pot stirrer) Joined: Feb 2004 Posts: 29,826 | What is the part number of your point-type distributor? 1951 was the last year for distributors with anywhere from 33-39 crankshaft degrees of centrifugal advance, depending on the distributor part number, plus another 10 or so from the vacuum advance at light-throttle cruise.
In 52, the centrifugal advance dropped to 16 1/2 to 19 1/2 depending on part number plus another 9-11 from the vacuum unit.
If your HEI is getting 20 crankshaft degrees of centrifugal plus 10 or more vacuum advance, I'd leave it as is, or use a delay-flash timing light to set the max centrifugal to about 25 crankshaft degrees or so at 2500 RPM. The vacuum should add 10-12 degrees to that at light throttle cruise for better gas mileage.
Several years of dyno testing of a lot of different engines has shown me that one degree of over-advance robs as much power as 5 degrees of retard from the optimum setting at full throttle, so it's best to err on the side of "not enough advance".
Jerry
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| | | | | Joined: Jul 2008 Posts: 13 Wrench Fetcher | | Wrench Fetcher Joined: Jul 2008 Posts: 13 | Thanks for the reply HL. I'll have to get the part number off the distributor. It's at my friends house with the SUN machine, so it might be a while.
Leaving it alone sounds like the trick to doing this conversion from what I am reading now.
Some people say I suffer from insanity, in reality, I enjoy every minute of it!
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