Let's revisit total timing
Thread Starter
Racer
Joined: Jan 2010
Posts: 348
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From: Lowell MA
Let's revisit total timing
1969 L46 engine. Goal is to have the mechanical advance pegged out by 2800 to 3000 RPMS w/vac disconnected and all in at 36 degrees BTDC.
Received Lars procedure for total timing. Had to remove both distributor weight springs to peg out full mechanical advance at reasonable RPM and locked distributor down when I set it to 36 degrees BTDC. Installed the gold springs from the Mr Gasket 928G kit as suggested and kept the original weights which weigh 6 oz each.
Reved motor and it took close to 3900 RPM to peg out the mechanical advance to 36 degrees BTDC.
Replaced weights with 4oz weights and the total mechanical advance of 36 degrees comes in at 3200 RPM.
There were 2 other sets of springs in the kit but they had fewer coils which would make them stronger.
What would you do to get the total mechanical advance in by 2800 RPM? Lighter weights or springs and where would I get the parts?
J.S.
Received Lars procedure for total timing. Had to remove both distributor weight springs to peg out full mechanical advance at reasonable RPM and locked distributor down when I set it to 36 degrees BTDC. Installed the gold springs from the Mr Gasket 928G kit as suggested and kept the original weights which weigh 6 oz each.
Reved motor and it took close to 3900 RPM to peg out the mechanical advance to 36 degrees BTDC.
Replaced weights with 4oz weights and the total mechanical advance of 36 degrees comes in at 3200 RPM.
There were 2 other sets of springs in the kit but they had fewer coils which would make them stronger.
What would you do to get the total mechanical advance in by 2800 RPM? Lighter weights or springs and where would I get the parts?
J.S.
Team Owner
Joined: Jan 2006
Posts: 37,637
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From: Crossville TN
Just pull on the springs to get a 'feel' for how strong they are. Number of coils doesn't mean anything...the size and material of wire are more important. Use heavier weights and lighter springs to bring mechanical advance in 'sooner' [lower rpm]. Vacuum advance line should be pulled and plugged-off for your testing.
Thread Starter
Racer
Joined: Jan 2010
Posts: 348
Likes: 2
From: Lowell MA
Ok, I know some of you will question my findings but I swapped the weights twice and this is what I observed. The vacuum line is disconnected, used a variable timing light and a digital postal scale to weigh the weights. 6 ounce weights are stock and the 4 ounce weights were given to me and I don't know the manufacturer. Distributor definately pegs out at 36 degrees with no springs attached at a low RPM.
4 ounce weights with the gold springs. Engine had to reach 3200 RPM to reach full mechanical advance.
6 ounce weights with the gold springs. Engine had to reach 3800 to 3900 RPM to reach full mechanical advance.
I also read in different postings that the heavier weight will allow the advance to come in sooner. Placing the 2 weights on top of each other does show a difference in their shape with the 4 ounce having a slightly larger angle. I can only assume the geometric shape of a weight as well as what it weighs can play a roll on the timing curve.
I'll do some online research and purchase a recurve kit. Anyone have any suggestions.
Thanks for your input.
J.S.
4 ounce weights with the gold springs. Engine had to reach 3200 RPM to reach full mechanical advance.
6 ounce weights with the gold springs. Engine had to reach 3800 to 3900 RPM to reach full mechanical advance.
I also read in different postings that the heavier weight will allow the advance to come in sooner. Placing the 2 weights on top of each other does show a difference in their shape with the 4 ounce having a slightly larger angle. I can only assume the geometric shape of a weight as well as what it weighs can play a roll on the timing curve.
I'll do some online research and purchase a recurve kit. Anyone have any suggestions.
Thanks for your input.
J.S.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,118
From: Crossville TN
With the limited information that you have provided, go with the "4 oz weights" with the "gold springs". 3200 rpm is a little 'late' for max power, but it is on the safe side and should still be pretty strong.
P.S. The actual weight of the flyweights isn't the most important factor. What matters is the 'net' weight which is acting on the moment arm distance from the center point of the spindle [which the weight fits over] to the center-of-gravity of the weight itself. The shape of the weight...and how it is distributed...sets up the shape of the timing curve.
P.S. The actual weight of the flyweights isn't the most important factor. What matters is the 'net' weight which is acting on the moment arm distance from the center point of the spindle [which the weight fits over] to the center-of-gravity of the weight itself. The shape of the weight...and how it is distributed...sets up the shape of the timing curve.
Last edited by 7T1vette; Feb 12, 2010 at 11:56 AM.
Race Director
Joined: Apr 2000
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
Well if you have the lightest springs in there and you get 36degs at 3200RPM why do you want 2800 RPM ? Is there some reason for wanting it all in before 3000RPM. I bet you have 32-34 degs. at 3000RPM which is fine for modern heads.
Can you explain why you want 36degs at 2800RPM ? I would just call it a day with closest you can get
Also put some silicone grease under the weights if you haven't already done that
Can you explain why you want 36degs at 2800RPM ? I would just call it a day with closest you can get
Also put some silicone grease under the weights if you haven't already done that
