Is 40degrees total advance too much?
Thread Starter
Team Owner
Joined: Feb 2003
Posts: 30,183
Likes: 313
From: Lake Norman NC
Is 40degrees total advance too much?
I started out this morning with 36 degrees, ran it for about 30minutes, ran great, then i let it cool..come back out to start it, and its hard to start..had alittle backfire through the carb. I then got it to run, set the timing at 40 degrees @3000rpm..ran great, and pulled like crazy. Came home, let it cool...start it back up, and it fired right up. I just didn't know if 40 was too much, when idealy everyone goes with 36.
Race Director
Joined: Sep 1999
Posts: 11,361
Likes: 383
From: Plano TX
40 degrees is too much and you proabably have some detonation at WOT. Note that you can have detonation without hearing it, especially if oyu have a loud exhaust.
If the car runs better @ 40 dgr, that means that the mechanical advance is overadvancing. You need to limit the mech advance by shortening the slots. best way is to fill them in with a welder. After the slots are shortened you can get the proper advance at low rpm that you liked without overadvancing at high rpm.
If the car runs better @ 40 dgr, that means that the mechanical advance is overadvancing. You need to limit the mech advance by shortening the slots. best way is to fill them in with a welder. After the slots are shortened you can get the proper advance at low rpm that you liked without overadvancing at high rpm.
Melting Slicks
Joined: Feb 2001
Posts: 3,330
Likes: 13
From: Europe , Luxembourg
Hi
At 3000 RPM, did you have the vacuum advance disconnected ?
Only with it disconnected, you set timing to 36 deg, so only on the mechanical advance.
With the vacuum advance connected at 3000 RPM, you can well have much more than 36 advance all together, actually up to 52 mechanical + vacuum at certain RPM. Only at very high RPM, the vacuum will let go again.
Günther
At 3000 RPM, did you have the vacuum advance disconnected ?
Only with it disconnected, you set timing to 36 deg, so only on the mechanical advance.
With the vacuum advance connected at 3000 RPM, you can well have much more than 36 advance all together, actually up to 52 mechanical + vacuum at certain RPM. Only at very high RPM, the vacuum will let go again.
Günther
Race Director
Joined: Nov 2000
Posts: 11,872
Likes: 12
From: Waterloo ontario Canada
Originally Posted by WESCH
Hi
At 3000 RPM, did you have the vacuum advance disconnected ?
Only with it disconnected, you set timing to 36 deg, so only on the mechanical advance.
With the vacuum advance connected at 3000 RPM, you can well have much more than 36 advance all together, actually up to 52 mechanical + vacuum at certain RPM. Only at very high RPM, the vacuum will let go again.
Günther
At 3000 RPM, did you have the vacuum advance disconnected ?
Only with it disconnected, you set timing to 36 deg, so only on the mechanical advance.
With the vacuum advance connected at 3000 RPM, you can well have much more than 36 advance all together, actually up to 52 mechanical + vacuum at certain RPM. Only at very high RPM, the vacuum will let go again.
Günther
That said I run no vacuum and run 43 degrees at 3000 but use a timing computer to pull timming out as I build boost.
I like to run as much advance as I can get away with.
Hard starting is often caused by poor advance weights that don't return to zero when the motor is shut off.
I run a fixed distributor and MSD timming master to add the curve. It is more consistent then and take 20 degrees out for starting.
Thread Starter
Team Owner
Joined: Feb 2003
Posts: 30,183
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From: Lake Norman NC
I'm running full mechanical advance..no vacuum advance on the distributor. I know i can't hear detonation, because I'm basically def with the sidepipes, but wouldn't i be able to feel it? I know its overadvancing, but 40 vs. 36, I like the 40 better. so, Norval, are you saying 40 @ 3000rpm full mechanical advance and no vacuum is ok?
Pro
Joined: Sep 2002
Posts: 690
Likes: 1
From: near Memphis TN
You don't like 40 at 3,000 RPM better, what you like is the quicker curve or more advance at idle, part throttle, and low RPM. You got that when you advanced your distributor but in turn you gave yourself move total advance than is normal.
This is the problem - when you floor it and get over 3,000 RPM on a warm day (or any day for that matter) and hit that 40 degree timing mark you will damage your engine. You also lose horsepower.
Also - are you sure it's not advancing even more after 3,000 RPM?
This is the problem - when you floor it and get over 3,000 RPM on a warm day (or any day for that matter) and hit that 40 degree timing mark you will damage your engine. You also lose horsepower.
Also - are you sure it's not advancing even more after 3,000 RPM?
Thread Starter
Team Owner
Joined: Feb 2003
Posts: 30,183
Likes: 313
From: Lake Norman NC
i'll play with the timing some more tomorrow. I'm not sure but I remember checking the 36 at 3500rpm and it was still there, while at 40, I don't think I bothered checking the timing after 3000rpm..I was in a hurry. Thanks for the help.
Team Owner
Joined: Jul 2001
Posts: 182,997
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From: Lakeland, FL
Cruise-In IV-V-VI-VII-VIII Veteran
St. Jude Donor '03, '06, '17
I ran 38 degrees on my 383 and the timing on my 406 is set to 36 degrees.. I used to run 40 degrees on the 383 initially, but I got better performance at 38 degrees...
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Burning Brakes
Joined: Feb 2004
Posts: 958
Likes: 1
From: In the Beautiful Shenandoah Valley of VA
You might also want to verify that the balancer hub hasn't slipped around a bit on you. This could trick you into thinking that you have more advance than you actually have....
Also, on most street engines (Norval's blown big-block is likely an exception) you would find it a benefit to run vacuum advance. It makes for a much snappier throttle response at part throttle.
Steve
Also, on most street engines (Norval's blown big-block is likely an exception) you would find it a benefit to run vacuum advance. It makes for a much snappier throttle response at part throttle.
Steve
Pro
Joined: Jun 2001
Posts: 672
Likes: 0
From: Quebec
Originally Posted by Steve's74
....
Also, on most street engines (Norval's blown big-block is likely an exception) you would find it a benefit to run vacuum advance. It makes for a much snappier throttle response at part throttle.
Steve
Also, on most street engines (Norval's blown big-block is likely an exception) you would find it a benefit to run vacuum advance. It makes for a much snappier throttle response at part throttle.
Steve
Even so if Norval make 13 Mpg if I remember correctly.Stephan
Racer
Joined: Jul 2002
Posts: 275
Likes: 13
From: South Bend, Indiana
36 degrees isn't the magic number for all smallblocks. Only your dyno knows for sure. My cammed L48 low compression loved 40 degrees (degreed). My 11 to 1 406 preferred 38 with an 8 degree drop when the nitrous kicked in.
