Thread: Ignition Timing
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Old 04-12-2021, 03:10 PM   #2
SeventyOne
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Join Date: Mar 2007
Location: Oakland, Ca
Posts: 1,359
Re: Ignition Timing

Quote:
Originally Posted by Classics Fan View Post
This is my first foray into distributor recurving. I have a GM HEI on original 350 with Edelbrock Performer intake and RV cam, rebuilt .030 with 9.0:1 pistons and original heads. Ported vacuum advance that comes in with bare tip-in of the throttle. The engine ran well but was sluggish. I replaced the OEM center plate, weights and springs with Mr. Gasket parts. The smallest (black) springs are way too light, coming in at 900 RPM. The next size up (silver) work much better, coming in at 1650 RPM BUT I can only get 10 degrees mechanical advance at 2250 RPM. Initial advance is16 degrees so total all-in is only 26 degrees. The curve diagram from the Mr. Gasket kit seems to show the weight/spring combo only allowing 12 degrees or so. If I advance initial much more than 16, it is hard to turn over. Any thoughts or ideas how to get total timing up to between 34 and 36 degrees? By the way, it runs better than ever as it sits now.
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Why do you say the Black springs are too light? To me that curve seems to be what you need for a stockish build. You'd have 16 initial timing and ~20 mechanical advance. Depending on what RPM this maxes out at (hopefully you get around 36* at 3000rpm.)

If you get pinging drop your initial timing to 14 and total advance will be 34. You can also mix/match the springs. IE one black and one silver to get somewhere in the middle between the two curves.

Lastly I'd hook your distributor up to full manifold vacuum. It will help immensely with the sluggishness you are experiencing and the engine will run cooler. Not to mention you can lower the initial to help with starting but still get the advanced timing right away to be more in the right torque range.
You may need an adjustable vacuum canister to dial in how much max timing the vacuum can adds at cruise. Run as much timing as you can during cruise without inducing pinging.

One more thing. I ran a Progression Ignition HEI for awhile and it was super awesome to be able to set my own timing tables from my phone (connected with bluetooth) without having to mess with any springs or weights at all. It's pricier that a standard HEI unit but so worth it.

https://progressionignition.com/
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