on the link
Lars: Vacuum Advance
Thread Starter
Racer
Joined: Apr 2001
Posts: 395
Likes: 0
From: Shoreline WA
Lars: Vacuum Advance
Lars,
I am in the process of rebuilding a tach drive distributor for my 71. The vacuum advance that was on there is stamped "437 15". I can't find my copy of your vacuum advance paper to look it up. I do have a "B 26" I could us in its place.
What would you recommed? I believe I have a NAPA "VC 680" installed in my existing distributor.
Also I noticed the advance posts on the plate attached to the points cam are worn. It is stamped "718 CCW" Do you know if these are available from NAPA? Suggested part number?
Thanks,
Mike
I am in the process of rebuilding a tach drive distributor for my 71. The vacuum advance that was on there is stamped "437 15". I can't find my copy of your vacuum advance paper to look it up. I do have a "B 26" I could us in its place.
What would you recommed? I believe I have a NAPA "VC 680" installed in my existing distributor.
Also I noticed the advance posts on the plate attached to the points cam are worn. It is stamped "718 CCW" Do you know if these are available from NAPA? Suggested part number?
Thanks,
Mike
Melting Slicks
Joined: Jun 2003
Posts: 2,802
Likes: 241
From: Niles, MI
Tech Contributor
Joined: Aug 1999
Posts: 14,365
Likes: 6,345
From: At my Bar drinking and wrenching in Lafayette Colorado
Mike -
The cam plate is not available from any source that I am aware of. I have replacement posts if you have the ability to un-braze your existing posts and re-braze the cam plate with my new ones. Let me know.
The choice of vacuum advance control unit depends on the camshaft in the engine and the vacuum level you pull at idle. For mild-cammed engines following close to stock specs, I recommend using the VC680 (stamped B1). This unit pulls in 16 crankshaft degrees of advance at 16 to 18 inches of vacuum. If you have an engine/cam combo that pulls a bit less than that much vacuum, use the VC1810 (stamped B28). This unit will pull in its full range of advance below 10 inches of vacuum. A mid-range unit that is very popular with aftermarket distributor manufactuirers for use with mildly hopped-up street engines is the VC1808 (stamped B26). This unit also pulls in 16 degrees of advance, and does so at 11 inches - a nice performance unit. The B26 is a great all-around performance unit, so I would use it if I were you (depending, of course, on your cam).
The cam plate is not available from any source that I am aware of. I have replacement posts if you have the ability to un-braze your existing posts and re-braze the cam plate with my new ones. Let me know.
The choice of vacuum advance control unit depends on the camshaft in the engine and the vacuum level you pull at idle. For mild-cammed engines following close to stock specs, I recommend using the VC680 (stamped B1). This unit pulls in 16 crankshaft degrees of advance at 16 to 18 inches of vacuum. If you have an engine/cam combo that pulls a bit less than that much vacuum, use the VC1810 (stamped B28). This unit will pull in its full range of advance below 10 inches of vacuum. A mid-range unit that is very popular with aftermarket distributor manufactuirers for use with mildly hopped-up street engines is the VC1808 (stamped B26). This unit also pulls in 16 degrees of advance, and does so at 11 inches - a nice performance unit. The B26 is a great all-around performance unit, so I would use it if I were you (depending, of course, on your cam).
Melting Slicks
Joined: Dec 2000
Posts: 2,198
Likes: 2
From: Eastern Connecticut
I wanted to resurrect this thread to ask Lars his recommendation for "fast-burn" heads. My guess from articles I have read on vortec heads is to reduce the max mechanical advance from 36* to 34* and max with vacuum from 52* to 50* That means keep the same vacuum can and just turn the distributor back 2 degrees. What do you think? Joe
Tech Contributor
Joined: Aug 1999
Posts: 14,365
Likes: 6,345
From: At my Bar drinking and wrenching in Lafayette Colorado
The fast-burn heads seem to produce best power between 32 and 34 total, and max combined total with vacuum advance pulled in along with the full mechanical should be about 50. You can get there by simply backing off the timing, but this also reduces your initial. If you have a bit of a cam, you're going to want to keep a bit of initial timing in it to obtain a good idle and snappy off-idle throttle response, which means you may have to shorten the advance curve in order to keep an adequate amount of initial timing while limiting the total to 32-34.
Team Owner
Joined: Sep 2003
Posts: 88,393
Likes: 2
From: eville in
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Corvette ZR1X Will Be Pacing the Indy 500, And Could Probably Race, Too!
Verdad Gallardo
Top 10 Corvettes Coming to Mecum Indy 2026!
Brett Foote
Top 10 C9 Corvette MUST-HAVES to Fix These C8 Generation Flaws!
Michael S. Palmer
10 Revolutionary 'Corvette Firsts' Most People Don't Know
Joe Kucinski
5 Reasons to Upgrade to an LS6-Powered Corvette; 5 Reasons to Stay LT2
Michael S. Palmer
2027 Corvette vs The World: Every C8 vs Its Closest Competitor
Joe Kucinski
10 Most Common Corvette Problems of the Last 20 Years!
Joe Kucinski
5 MOST and 5 LEAST Popular Corvette Model Years in History!
Joe Kucinski
2027 Corvette Buyer's Guide: Everything You Need to Know!
Joe Kucinski
Tech Contributor
Joined: Aug 1999
Posts: 14,365
Likes: 6,345
From: At my Bar drinking and wrenching in Lafayette Colorado
Wow - that posting of the article really sucks - the formatting for the tables is all jumbled. If anyone wants a "real" copy of the article, be sure to drop me an e-mail request and I'll send you an MSWord version that is usable and readable.
Lars
V8FastCars@msn.com
Lars
V8FastCars@msn.com
