Help reading C1 Dyno Sheet
Thread Starter
Team Owner
Joined: Aug 2007
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Army
Help reading C1 Dyno Sheet
I'm confused by the dyno parameters on my car (attached). The timing is indicated at 43.5 degrees. This is with a dual-point, mechanical-only, stock distributor (before I added a Pertronix distributor with vacuum advance).
Is this initial timing ? or 'all-in' ? Lars and others state that about 38 degrees is optimal 'all in' timing for a SBC so this figure seems high for 'all in' and WAY high for initial.
The cars initial (no vacuum) is currently at 14 degrees...which is (I'm told) about where you want it with a cam of less than 240deg duration (my cam is 228)...
What am I missing ?
Is this initial timing ? or 'all-in' ? Lars and others state that about 38 degrees is optimal 'all in' timing for a SBC so this figure seems high for 'all in' and WAY high for initial.
The cars initial (no vacuum) is currently at 14 degrees...which is (I'm told) about where you want it with a cam of less than 240deg duration (my cam is 228)...
What am I missing ?
Last edited by Frankie the Fink; Oct 30, 2009 at 10:12 AM.
Drifting
Joined: Oct 2008
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From: Rochester Hills Michigan
My Motor's Manual says your 283/270 should have a 1110891, which has 28 degrees centrifugal advance. Ititial lead should be 7, for a total of 35. (The 283/290 1110914 has 22 with 14 initial for 36 total.)
Typo maybe? Your lash looks wrong too...
Typo maybe? Your lash looks wrong too...
Thread Starter
Team Owner
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Army
Thanks mash.... I have the ST-12 and '61 Passenger Car Manual. This engine has a slightly hotter cam than stock so the tune-up specs change. I could never leave a stop light with the stock idle speed and timing. The lash IS set to stock specs right now (ignore those items int he dyno sheet).
My question is that I don't know how the 43.5 deg relates to the dyno run done in '04...
My question is that I don't know how the 43.5 deg relates to the dyno run done in '04...
Safety Car
Joined: Mar 2009
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From: Corpus Christi, TX
The 43.5 degrees is where the dyno operator had the timing set "all in" at maximum mechanical advance.
That's probably a bit high. Even these antique heads don't do much better when you go over 36 to 38 degrees total timing.
That's probably a bit high. Even these antique heads don't do much better when you go over 36 to 38 degrees total timing.
Last edited by Avispa; Oct 30, 2009 at 11:03 AM.
Thread Starter
Team Owner
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Army
I've recurved things and this figure is at 38.5 degrees now; all in at 2900 RPM.. Don't know why they had it up so high for the dyno run..
Thread Starter
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Army
Already done when I replaced the stock distrib with a vaccum advance Pertronix distributor!
Race Director
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I suspect he set teh timing to maximize teh Tq and HP.
But....
Never set your timing on the dyno, as it will be too advanced for normal use, backing off to factory spec is the recommended default.
We detuned my EFI timing map after we got highest reading; once peak was achieved, we backed off 2-3 degrees; we lost 10-15 HP and 10 ft-lb, but as the dyno guy said, your engine will thank you for it.
Doug
But....
Never set your timing on the dyno, as it will be too advanced for normal use, backing off to factory spec is the recommended default.
We detuned my EFI timing map after we got highest reading; once peak was achieved, we backed off 2-3 degrees; we lost 10-15 HP and 10 ft-lb, but as the dyno guy said, your engine will thank you for it.
Doug
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Safety Car
Joined: Mar 2009
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From: Corpus Christi, TX
I don't guess there's any way to "map" a distributor the way you map the fuel and timing of a microprocessor powertrain control module with your laptop. All you can do is change weights, springs, bushings, and if they can still be found, put on one of those advance limit kits Crane Cams used to make.
Drifting
Joined: Oct 2008
Posts: 1,936
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From: Rochester Hills Michigan
The ST-12 has the initial lead at 12 for the 60-61 270, but 7 for the 58-59 270. Looks like both have the 1110891 distributor with 28 mechanical. So the factory bumped the total to 40 for your engine? Maybe that dyno number does make sense.
I don't understand why you wouldn't run the dyno spark advance (based on max. power I assume) unless you get detonation on premium fuel...then it makes sense to back it down. I figure that's what you're getting from the dyno tune: max. power setting. But it's been 42 years since I ran my '59 on a dyno!
I don't understand why you wouldn't run the dyno spark advance (based on max. power I assume) unless you get detonation on premium fuel...then it makes sense to back it down. I figure that's what you're getting from the dyno tune: max. power setting. But it's been 42 years since I ran my '59 on a dyno!
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From: At my Bar drinking and wrenching in Lafayette Colorado
I'm confused by the dyno parameters on my car (attached). The timing is indicated at 43.5 degrees. This is with a dual-point, mechanical-only, stock distributor (before I added a Pertronix distributor with vacuum advance).
Is this initial timing ? or 'all-in' ? Lars and others state that about 38 degrees is optimal 'all in' timing for a SBC so this figure seems high for 'all in' and WAY high for initial.
The cars initial (no vacuum) is currently at 14 degrees...which is (I'm told) about where you want it with a cam of less than 240deg duration (my cam is 228)...
What am I missing ?
Is this initial timing ? or 'all-in' ? Lars and others state that about 38 degrees is optimal 'all in' timing for a SBC so this figure seems high for 'all in' and WAY high for initial.
The cars initial (no vacuum) is currently at 14 degrees...which is (I'm told) about where you want it with a cam of less than 240deg duration (my cam is 228)...
What am I missing ?
I've done a lot of dyno testing and tuning, and I've never seen a Chevy develop peak power with total timing advanced beyond 38 degrees, even on the dyno. Typically, 36 degrees is optimum total timing. You need to shorten your advance curve so you can run about 14-16 degrees initial timing and 36 total. The specs and rationale are outlined in the timing papers that me, Duke, and John put together some time ago - e-mail me if you don't have a copy.
Lars
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