Advanced Timing ?????
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Instructor
Joined: Apr 2004
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From: HOMOSASSA FL
Advanced Timing ?????
Happy New Year Everyone!!! Is it worth doing advanced timing on a 1970 Corvette 350/300 auto with all NOS ignition components except for the points witch are Breakerless Ignition? I don’t know if they did advanced timing back in 1970. I have heard different options on the subject from mechanics. Mostly due to the types of fuel being used today, unlike the fuel they used in 1970. Advanced timing could cause issues in the engine due to knocking. Which I would think you would just dial the the timing down until the knocking went away. I’m using Shell 93 octane in the Corvette... One of the last items on the Shake Down Restoration List....Any suggestions Droop
Race Director
Joined: May 2006
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when you say "advanced timing" do you mean simply advancing the initial timing a couple of degrees or having the distributor recurved so that you have a total of 36 degrees mechanical at about 2,800 rpm and the vacuum advance is also modified to limit it to about 10 degrees.
Tech Contributor
Joined: Jun 2004
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From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
I don't know what "advanced timing" means. I'd just time the engine (and modify the distributor advance curve) to give the correct timing that the engine wants. Every engine and driven location is slightly different, and will take a different timing curve to optimize idle quality, power, and fuel economy.
Instructor
Joined: May 2016
Posts: 178
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From: Vermont
Droop: Advanced timing goes back to the 50's-60's when young hot rodders thought that if 32 degrees was good, then 36 degrees was better. It also, sometimes, felt faster because the timing was advanced so much that the car was a dog off the line, then once the rpm's caught-up with the advanced timing the car would respond with a little kick in the seat.
HOWEVER, we now know differently. The car's optimum performance will be recognized when all tuning factors are considered. I always rely on a chassis dyno for these settings. The old saying " The Dyno Doesn't Lie " is the only way to know if the tuning is correct.
HOWEVER, we now know differently. The car's optimum performance will be recognized when all tuning factors are considered. I always rely on a chassis dyno for these settings. The old saying " The Dyno Doesn't Lie " is the only way to know if the tuning is correct.
Thread Starter
Instructor
Joined: Apr 2004
Posts: 221
Likes: 24
From: HOMOSASSA FL
when you say "advanced timing" do you mean simply advancing the initial timing a couple of degrees or having the distributor recurved so that you have a total of 36 degrees mechanical at about 2,800 rpm and the vacuum advance is also modified to limit it to about 10 degrees.
Thread Starter
Instructor
Joined: Apr 2004
Posts: 221
Likes: 24
From: HOMOSASSA FL
Droop: Advanced timing goes back to the 50's-60's when young hot rodders thought that if 32 degrees was good, then 36 degrees was better. It also, sometimes, felt faster because the timing was advanced so much that the car was a dog off the line, then once the rpm's caught-up with the advanced timing the car would respond with a little kick in the seat.
HOWEVER, we now know differently. The car's optimum performance will be recognized when all tuning factors are considered. I always rely on a chassis dyno for these settings. The old saying " The Dyno Doesn't Lie " is the only way to know if the tuning is correct.
HOWEVER, we now know differently. The car's optimum performance will be recognized when all tuning factors are considered. I always rely on a chassis dyno for these settings. The old saying " The Dyno Doesn't Lie " is the only way to know if the tuning is correct.
Race Director
Joined: May 2006
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each distributor for a given engine was given a different curve. The curves are in the factory Chasis Service Manual for the particular year. They did not do 'total timing' at the factory as you described above. You can also go to this site and look up the particular year you want and scroll through the document for the distributor information section.
https://gmheritagecenter.com/gm-heri...tion-kits.html
https://gmheritagecenter.com/gm-heri...tion-kits.html
Last edited by MelWff; Jan 2, 2017 at 06:08 PM.
Thread Starter
Instructor
Joined: Apr 2004
Posts: 221
Likes: 24
From: HOMOSASSA FL
each distributor for a given engine was given a different curve. The curves are in the factory Chasis Service Manual for the particular year. They did not do 'total timing' at the factory as you described above. You can also go to this site and look up the particular year you want and scroll through the document for the distributor information section.
https://gmheritagecenter.com/gm-heri...tion-kits.html
https://gmheritagecenter.com/gm-heri...tion-kits.html
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Melting Slicks
Joined: May 2009
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2024 C3 of the Year Finalist - Unmodified
If you look at the tune up information sticker on the firewall, the factory suggested setting your initial timing at around 4-6 degrees BTDC. Of course they did...they were providing a 5 year/50k mile warranty. At that retarded setting, the engine could not make the maximum advertised horsepower. When I set my total timing at 36, I go back and check my initial and it is around 16. I could go higher but why? The engine doesn't make the death rattle and I am not into racing. Back in the day, before going to the drag strip, we just loosened the distributor clamp and kept rotating it until the engine rattled under heavy load at low rpm. Then we retarded it slightly and tightened the bolt. We had no idea what the "advanced timing" number was and could not have cared less.
Thread Starter
Instructor
Joined: Apr 2004
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From: HOMOSASSA FL
If you look at the tune up information sticker on the firewall, the factory suggested setting your initial timing at around 4-6 degrees BTDC. Of course they did...they were providing a 5 year/50k mile warranty. At that retarded setting, the engine could not make the maximum advertised horsepower. When I set my total timing at 36, I go back and check my initial and it is around 16. I could go higher but why? The engine doesn't make the death rattle and I am not into racing. Back in the day, before going to the drag strip, we just loosened the distributor clamp and kept rotating it until the engine rattled under heavy load at low rpm. Then we retarded it slightly and tightened the bolt. We had no idea what the "advanced timing" number was and could not have cared less.
Tech Contributor
Joined: Jun 2004
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From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
If you look at the tune up information sticker on the firewall, the factory suggested setting your initial timing at around 4-6 degrees BTDC. Of course they did...they were providing a 5 year/50k mile warranty. At that retarded setting, the engine could not make the maximum advertised horsepower. When I set my total timing at 36, I go back and check my initial and it is around 16. I could go higher but why? The engine doesn't make the death rattle and I am not into racing. Back in the day, before going to the drag strip, we just loosened the distributor clamp and kept rotating it until the engine rattled under heavy load at low rpm. Then we retarded it slightly and tightened the bolt. We had no idea what the "advanced timing" number was and could not have cared less.
An engine operated in hot, dense Death Valley type conditions is more likely to grenade itself than an engine driven in lower air density, higher humidity Denver type areas.
Melting Slicks
Joined: May 2009
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2024 C3 of the Year Finalist - Unmodified
Yes the car runs better at 36 degrees. It dynoed at 408 hp running at 34 degrees. I could probably run 38 degrees because I mix C12 race fuel at 108 octane along with 90 octane non-ethanol.
Last edited by Faster Rat; Jan 3, 2017 at 11:34 AM.
Tech Contributor
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From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
I have mine set at 15 or 16 initial. My stock distributor springs give me about 20 or 21 degrees of centrifugal (mechanical) advance. This gives me a total of 36 degrees advance at around 3200 rpm. The vacuum advance is of course disconnected and plugged when checking the timing. A correct, functioning vacuum advance helps the idle and part throttle condition. I also went back to ported vacuum (above the carburetor plate) instead of running pure intake manifold vacuum. My Comp cam gives me sufficient vacuum to operate those systems that run off engine vacuum.
Yes the car runs better at 36 degrees. It dynoed at 408 hp running at 34 degrees. I could probably run 38 degrees because I mix C12 race fuel at 108 octane along with 90 octane non-ethanol.
Yes the car runs better at 36 degrees. It dynoed at 408 hp running at 34 degrees. I could probably run 38 degrees because I mix C12 race fuel at 108 octane along with 90 octane non-ethanol.
Le Mans Master
Joined: Oct 2005
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From: Glen Allen, VA
I set up the timing curve on my 79 to 34 degrees total, that's what it likes best, but changed the springs to get it to come in by 2500rpm. It was the singe biggest improvement to how my car ran, like night and day difference. To boot, it was less than $10 as I recall for a Mr Gasket spring and weight kit.
Melting Slicks
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2024 C3 of the Year Finalist - Unmodified
Because that is factory correct and the car actually seems to run better...believe it or not. Having access to one of these, along with somebody who knows what they are doing, really helped. We also changed the vacuum canister. He suggested going back to ported.
Tech Contributor
Joined: Jun 2004
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From: I tend to be leery of any guy who doesn't own a chainsaw or a handgun.
A Sun machine is nice to have (mine is a 506), but it can't tell you what timing or curve the engine actually wants.
Racer
Joined: Mar 2016
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From: Melbourne Victoria
I'd be interested to know more of what it actually does apart from being some sort of dizzy tester?
Last edited by Corvetteoz; Jan 3, 2017 at 10:46 PM.
Thread Starter
Instructor
Joined: Apr 2004
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From: HOMOSASSA FL
Fast, You have some wonderful toys.....I’m going to have the distributor checked out and set up to optimize the timing curve. I have order the spring kit already. What is the ratio for the fuel mixture in the tank? I would like to get away from the ethanol fuel if possible. Droop
Thread Starter
Instructor
Joined: Apr 2004
Posts: 221
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From: HOMOSASSA FL
69, My 350/300 auto, once in a while will stall out at a stop. This is why I’m looking at everything. Fuel, fuel mixture, vacuum, and timing. I’m the only owner. The Corvette started to stall out once they started changing the fuels around 1977. I could run Low Lead 100 avgas and problems went away. But the flight line fuelers won’t sell it to you. Trying to get the correct formula being mechanical, fuel, vacuum or all of the above...Please tell me if I’m on the write path of the Yellow Brick Road...Droop