Timing question !!!
Thread Starter
Racer
Joined: Mar 2005
Posts: 471
Likes: 1
From: Hometown The best
Timing question !!!
I just got my new engine build running and trying to get things sorted out. The engine seems to like a lot of timing ... 16 to 18 degrees at idle and 40 or more at 3000 rpm. It could go higher but I'm afraid to try any higher because I know it shouldn't that high. It has no power with the timing set at 12 degrees at idle and 36 degrees at 3000. Any ideas why it likes so much timing. Could the dizzy be off a tooth? How many degrees would a tooth be worth?
Burning Brakes
Joined: Sep 2008
Posts: 805
Likes: 5
From: Naperville Illinois
Have you verified that your vacuum advance is working? Timing (for me) is one of those things where you have to go step by step and keep track of where you are, particularly if you are changing the curve. Follow the instructions here
http://forums.corvetteforum.com/c3-t...long-post.html
and you'll get it. My vacuum advance was bad...replacing it and setting my timing correctly really woke up my 68 SB--runs much cooler too. I don't have any experience with a slipped distributor gear, but you can buy a TDC tool for 15 bucks and check your marks pretty easily. Good luck!
http://forums.corvetteforum.com/c3-t...long-post.html
and you'll get it. My vacuum advance was bad...replacing it and setting my timing correctly really woke up my 68 SB--runs much cooler too. I don't have any experience with a slipped distributor gear, but you can buy a TDC tool for 15 bucks and check your marks pretty easily. Good luck!
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
Is timing "40 degrees or more" with or without the vacuum advance hooked up? It should be much more with vacuum advance (50+). But, you should set timing with the vacuum can disconnected and the line plugged off to prevent leakage. We need to understand exactly what process you went through to get the readings you describe.
Thread Starter
Racer
Joined: Mar 2005
Posts: 471
Likes: 1
From: Hometown The best
Vacuum advance disconnected and plugged. As I stated, setting the advance any lower and it has no power at all. It should not have to be this high. I could go higher but afraid of detonation as I don't have baffles in my sidepipes yet and it would be difficult to hear the pinging. I'm wondering if the dizzy is off a tooth.
Drifting
Joined: Aug 2005
Posts: 1,682
Likes: 3
From: League City TX
The disrtibutor being off a tooth doesnt affect anything but the position of the housing.
It does not change timing requirements.
If you have put a larger cam than stock in your motor, its not unusual for it to like more initial advance.
When you add more initial advance, you need to shorten up the mechanical advance so that you can keep from getting too much total advance.
If your engine likes 16 initial, the shorten up the mechanical to add 20 degrees more.
If you have fast burn combustion chambers then you may need to limit it even more.
It does not change timing requirements.
If you have put a larger cam than stock in your motor, its not unusual for it to like more initial advance.
When you add more initial advance, you need to shorten up the mechanical advance so that you can keep from getting too much total advance.
If your engine likes 16 initial, the shorten up the mechanical to add 20 degrees more.
If you have fast burn combustion chambers then you may need to limit it even more.
Melting Slicks
Joined: Dec 2009
Posts: 3,225
Likes: 654
From: Thunder Bay
Having the distributor off a tooth won't make any difference to the timing. You can install the distributor anywhere you want. It only affects where the vacuum advance canister points. Confirm that the timing marks are accurate by determinng top dead centre with a TDC finder. Sounds like your marks are off.
Thread Starter
Racer
Joined: Mar 2005
Posts: 471
Likes: 1
From: Hometown The best
OK lets rule out the tooth off theory. The timing marks are corect. It is a larger cam , 234/244 @ 50 w/488/510 lift and we degreed the cam with a degree wheel. So how do you set initial timing at 16 degrees and keep total timing at 36
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Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
You can't maintain 'initial timing' before altering the distributor setting to set maximum mechanical advance, and end up with initial timing being at the same spot...unless you are just really lucky. The only reason to set 'initial timing' is so that the car will run well enough to continue with the re-curving procedure. The important steps are to: 1) set the max mechanical timing (34-36 degrees) so that it will not advance any more after 3000 rpm (because of mechanical advance, anyway), 2) drop the engine speed to idle so that you can record what idle timing is without vacuum advance, then 3) add back the vacuum advance to check/record it at idle and at 3000 so you know what the combined 'total' advance is.
After all of that, the idle without vacuum should be 12-18 degrees and the combined maximum should be less than 52 degrees. If those parameters are not met, you can vary the dizzy weights/springs and/or change the vacuum can to one with a different advance schedule to make all work as intended.
After all of that, the idle without vacuum should be 12-18 degrees and the combined maximum should be less than 52 degrees. If those parameters are not met, you can vary the dizzy weights/springs and/or change the vacuum can to one with a different advance schedule to make all work as intended.
