paging lars - timing rehash
09-11-2003, 10:46 AM
#1
Le Mans Master
Thread Starter
paging lars - timing rehash
I've got a friend with a 69...we just installed a 454 in the car - its an older engine running about 12:1 CR a Schnieder cam of about 240deg. duration , single plane intake with holley - headers and duals.
We just took the distributor to a local shoppe to get it dialed in and the guys there refused to put more than 20 degrees into the distributor.
What advance should be built into this distributor - the car is driven only to cruises and the strip - it is not a daily driver.
I got the paper on small block timing but nothing on big block timing and advance patterns.
Yours and anyone elses help is greatly appreciated.
We just took the distributor to a local shoppe to get it dialed in and the guys there refused to put more than 20 degrees into the distributor.
What advance should be built into this distributor - the car is driven only to cruises and the strip - it is not a daily driver.
I got the paper on small block timing but nothing on big block timing and advance patterns.
Yours and anyone elses help is greatly appreciated.
09-11-2003, 11:33 AM
#2
Le Mans Master
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Location: Chattanooga TN
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St. Jude Donor '08-'09
Re: paging lars - timing rehash (fauxrs)
Find out what the max total timing is for a BBC. For a SBC it's about 36-38 degrees. Set it to that first, then see where the initial timing comes to. Tune your distributor from there. I tried setting the initial, then going the other direction, and it did not work at all.
Good luck. :cheers:
Good luck. :cheers:
09-11-2003, 11:35 AM
#3
Tech Contributor
Member Since: Aug 1999
Location: At my Bar drinking and wrenching in Lafayette Colorado
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Re: paging lars - timing rehash (fauxrs)
fauxrs -
20 degrees centrifugal advance in the distributor should be more than enough - if I were you, I'd actually run less than that.
Keep in mind that the total timing at WOT is centrifugal PLUS the initial timing. Your max total timing at WOT should not exceed 36-38 degrees. If centrifugal advance is 20, that means you're limited to 16-18 initial advance (36 minus 20 is 16). Most big blocks with a bit of a cam are going to want to idle with at least 25 degrees of initial advance if not more. You're going to have to make up the dfference between 16 and 25 with vacuum advance hooked up to manifold vacuum.
Here's a suggestion for you: When you get the distributor back, drop it in the motor and get it fired up. With the distributor hooked up to the vac advance and everything operational, simply start rotating the distributor slowly back and forth and find the spot that produces the best quality idle. Not neccessarily the FASTEST idle, but the BEST idle. You may have to play with the idle speed and mixture screws while you're doing this. Once you have found the "sweet spot" that produces the best idle, yank the vacuum hose off the distributor and use your timing light to see where your initial timing ended up. The amount of centrifugal advance you put into the distributor should be the difference between this number and 36. Once you have determined this number, and if this number is different from what you received from the distributor shop, send the dstributor out to me and I'll curve it to your specs (if it's a point-style distributor). I have a Sun distributor machine, so I can give you whatever curve you need.
20 degrees centrifugal advance in the distributor should be more than enough - if I were you, I'd actually run less than that.
Keep in mind that the total timing at WOT is centrifugal PLUS the initial timing. Your max total timing at WOT should not exceed 36-38 degrees. If centrifugal advance is 20, that means you're limited to 16-18 initial advance (36 minus 20 is 16). Most big blocks with a bit of a cam are going to want to idle with at least 25 degrees of initial advance if not more. You're going to have to make up the dfference between 16 and 25 with vacuum advance hooked up to manifold vacuum.
Here's a suggestion for you: When you get the distributor back, drop it in the motor and get it fired up. With the distributor hooked up to the vac advance and everything operational, simply start rotating the distributor slowly back and forth and find the spot that produces the best quality idle. Not neccessarily the FASTEST idle, but the BEST idle. You may have to play with the idle speed and mixture screws while you're doing this. Once you have found the "sweet spot" that produces the best idle, yank the vacuum hose off the distributor and use your timing light to see where your initial timing ended up. The amount of centrifugal advance you put into the distributor should be the difference between this number and 36. Once you have determined this number, and if this number is different from what you received from the distributor shop, send the dstributor out to me and I'll curve it to your specs (if it's a point-style distributor). I have a Sun distributor machine, so I can give you whatever curve you need.
