BB Timing Question
Thread Starter
Melting Slicks
Joined: Mar 2004
Posts: 3,472
Likes: 18
From: Lake Ozark, MO
BB Timing Question
BB 454 with XE274 Cam
Got the engine running again with new cam. Initial timing is set a 20 degrees with vacuum disconnected. When I plug in the vacuum advance (non ported) I get about 39 degrees of advance. Is this too high? If too high, how can I correct it? As far a distributor springs, I'm running one soft and one intermidiate.
At 20 degrees I'm getting a little backfire through the carb if the car doesn't start right away. If I retard the timing should that get rid of the backfire?
Got the engine running again with new cam. Initial timing is set a 20 degrees with vacuum disconnected. When I plug in the vacuum advance (non ported) I get about 39 degrees of advance. Is this too high? If too high, how can I correct it? As far a distributor springs, I'm running one soft and one intermidiate.
At 20 degrees I'm getting a little backfire through the carb if the car doesn't start right away. If I retard the timing should that get rid of the backfire?
Melting Slicks
Joined: Jun 2001
Posts: 2,340
Likes: 2
From: Moro IL
If I remember right, you should see about a max of 50 degrees btdc with the vacuum advance applied, and a mechanical advance between 32-36 by 2500 rpm (depends on compression and variables such as cam timing). Your initial timing isn't really relevant except for starting purposes, I've actually seen some BBC's start with some really high initial settings, especially one 73 BB in our vette club. If you need some help I'm pretty local, just PM me and let me know.
Pat Kunz
Pat Kunz
Safety Car
Joined: Oct 2000
Posts: 4,282
Likes: 172
From: Lake Wylie, South Carolina
I have an XS-282 and I have my timing set @ 18* initial and all mechanical in @ 3k. I am running an MSD distributor with one light and one medium spring with the large stop bushing installed. The car runs great and pulls hard throughout the rpm range but idles pretty high and I have problems with run on after the car gets up to temperature and I shut it off. I solved this problem by backing down to 15* initial but with the springs that put me all in up around 3500 and I noticed a significant reduction in power higher up in the rpm range. I still need to hook up my vaccum can for the advance so that might be part of the problem.
BR
BR
East bound and down...
Joined: Dec 2004
Posts: 987
Likes: 3
From: Jonesboro Arkansas
20 deg. intial is a little bit on the high side of what most people run, but it is not unreasonable. My 496 with a XE 284, and 10 to 1 CR seemed happiest at 16 deg initial, 36 deg mech (all in by 2900), and about 52 deg total with the vac can hooked up. I would think that at 20 deg initial your car would be hard to turn over. You must have an aftermarket starter because my beefed up factory one didn't want to crank easily at 18-19 deg intial.
Thread Starter
Melting Slicks
Joined: Mar 2004
Posts: 3,472
Likes: 18
From: Lake Ozark, MO
Thanks LS-Five
Thanks for the input...I'm pretty close according to what you run. At 2500, I was getting 50 total, so that is in line with what you have. I think I'll crank the idle up a little and reduce the initial a few degrees. I do have a mini reduction starter and it doesn't like 20 degress much either
Thanks for the input...I'm pretty close according to what you run. At 2500, I was getting 50 total, so that is in line with what you have. I think I'll crank the idle up a little and reduce the initial a few degrees. I do have a mini reduction starter and it doesn't like 20 degress much either
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Safety Car
Joined: Aug 2000
Posts: 3,909
Likes: 26
From: Clymer PA
With my 468 I don't run a vacuum advance. I have my distributor set for 38 degrees total timing all in by 3000RPMs. Most people will check it at 2500RPMs but I check it at 3000RPMs just to make sure it isn't trying to advance anymore.
