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  #31 (permalink)  
Old 01-31-2004, 11:24 AM
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Well,I disagree. I do agree if you run to retarded and force your motor to accelerate out of whack your going to create heat though.

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  #32 (permalink)  
Old 01-31-2004, 12:04 PM
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http://hotrodders.com/t23169-15--vac...dvance--2.html

dmorris1200 stated the only good reason I have ever heard of as to why ported vacuum should be used. He likes the retarded timing at idle because it gives his idle more lump like it had a bigger cam. He doesn't have heating issues and once he comes off idle, the vacuum can pulls in the timing to gain his performance back. Although I try to clean up the idle as much as possible, there are quite a few that post on the board looking for the big cam sound. Fuel mileage wasn't mentioned, and for some, it isn't an issue for the typical weekend car. I put a 100 miles a day on mine and mileage IS an issue.

I switched from ported, to manifold vacuum and picked up 2 1/2 MPG on my small block S-10. I also lowered my extended freeway running temps by 10 deg. I have made as many as 16 drag strip passes, back to back, on a 90* day without overheating. Any heat I make during the run, is gone by the time I get to the end of the return road. With ported vacuum, heat soak between runs was an issue. 5 or 6 runs was all I could get because of extended cool down times between runs.

rifraf, If you are getting surges from fluctuating timing caused by the vacuum advance, you need a can that is all in at a lower vacuum reading. The big cam motors that have low vacuum, can't run a stock vacuum can. Get one that reaches max advance with a vacuum reading that is lower than your idle manifold reading. My motor pulls 19 1/2 inches at idle, and my advance is all in by 17.

84_sportcoupe, If you are having trouble getting enough mechanical advance, or if you have too much, you can alter the stops in the distributor. File the slot longer for more advance, or weld it up for less.
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  #33 (permalink)  
Old 01-31-2004, 12:27 PM
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I feel as if Ive spent 2 hours watching my dog chase his tail. I cant take anymore.
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Old 09-16-2013, 06:42 PM
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Vacuum advance and starting

Just had an issue not being able to start 1406 Edelbrock, moved vacuum advance to ported from full and it started right up. Th advance had been switched after a carb kit, go figure, I had huge detonation at cruise and total loss of engine before . Have now put in billet HEI unit and I guess will keep vacuum advance hooked up to ported side of distrib, manifold is used up by brakes and tranny.
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  #35 (permalink)  
Old 09-17-2013, 12:45 AM
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With my limited experiences with vacuum advance, my distributors always had 20 degrees of mechanical advance, so I would run 14 degrees at idle, and get 34 total by 3000 rpms...I ran vacuum advance on ported bc with the holley throttle plates barely exposing the transition slot(which is how they are supposed to be set up) if I hooked up vacuum advance to manifold vacuum it would raise the idle too high so in turn I would have to close the throttle plates on the primaries to bring the idle down and would create an off idle stumble and the thought that the transition slot was not set up how my carb company and pros set them up...if u have to use manifold vacuum to get your car to idle I feel like you have the incorrect mechanical advance set up in your distributor and using manifold vacuum is solving that problem...vacuum advance IMO should only be used for when you are cruising. Using manifold vacuum to clean up the idle is by no means incorrect but I just feel that having the mechanical advance right for the engine to idle is the better way to do it...just my two cents lol
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  #36 (permalink)  
Old 09-17-2013, 05:47 AM
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I ran 32 locked on my 8 to 1 blown 496. Got tired of starter kick back. Changed to VA distributor. Now have 16 init and 34 total at 2500rpm. Manifold vacuum brings idle timing up to 30 and total to 48. At wot vacuum drops off and it retards to 34. Works great, starts easy and runs cool.
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Old 09-17-2013, 06:00 AM
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Thanks for input, as background, I played with these cars 45+ years ago as a teenager. Not that familiar with HEI distrib and carb harmonies but I am learning fast the hard way. For timing, when the new billlet HEi unit was installed it was set at base to get me home, I have now sorted out some other factors, ie. cam has 4*of advance built into it, the mild cam will idle a little rougher, that's OK as long as it doesn't stumble and misfire from the gate. I'm hearing heat stories on ported advance and such and this car does seem to heat up quickly, having carb and distrib tuned tomorrow, hopefully it sorts itself out. New car want to drive it.
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  #38 (permalink)  
Old 09-17-2013, 07:03 AM
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Quote:
Originally Posted by 6T7EH View Post
Just had an issue not being able to start 1406 Edelbrock, moved vacuum advance to ported from full and it started right up. Th advance had been switched after a carb kit, go figure, I had huge detonation at cruise and total loss of engine before . Have now put in billet HEI unit and I guess will keep vacuum advance hooked up to ported side of distrib, manifold is used up by brakes and tranny.
Bull. Strictly an unrelated incident. Hooking your advance to the "wrong" port will NOT prevent an engine from starting. Plus, you should run full manifold vacuum on your advance anyway.
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  #39 (permalink)  
Old 09-17-2013, 07:14 AM
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At the risk of being redundant this is how I learned about timing.
http://www.lbfun.com/warehouse/tech_...ance_Specs.pdf
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  #40 (permalink)  
Old 09-17-2013, 05:45 PM
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Sounds like something from the US Department of Redundancy Department!
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  #41 (permalink)  
Old 09-17-2013, 06:42 PM
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Yea.....I had to get my secret clearance before I could post it! LOL
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  #42 (permalink)  
Old 09-18-2013, 02:57 PM
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Quote:
Originally Posted by malducci View Post

What about the Harry high-school non-vacuum advance polished billet "whizbang" distributors you see in the Summit and Jeg's catalogs? They're JUNK on a street-driven car, but some people keep buying them because they're "race car" parts, so they must be "good for my car" - they're NOT. "Race cars" run at wide-open throttle, rich mixture, full load, and high rpm all the time, so they don't need a system (vacuum advance) to deal with the full range of driving conditions encountered in street operation. Anyone driving a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling, throttle response, engine efficiency, and fuel economy, probably because they don't understand what vacuum advance is, how it works, and what it's for - there are lots of long-time experienced "mechanics" who don't understand the principles and operation of vacuum advance either, so they're not alone.

Vacuum advance calibrations are different between stock engines and modified engines, especially if you have a lot of cam and have relatively low manifold vacuum at idle. Most stock vacuum advance cans aren’t fully-deployed until they see about 15” Hg. Manifold vacuum, so those cans don’t work very well on a modified engine; with less than 15” Hg. at a rough idle, the stock can will “dither” in and out in response to the rapidly-changing manifold vacuum, constantly varying the amount of vacuum advance, which creates an unstable idle. Modified engines with more cam that generate less than 15” Hg. of vacuum at idle need a vacuum advance can that’s fully-deployed at least 1”, preferably 2” of vacuum less than idle vacuum level so idle advance is solid and stable; the Echlin #VC-1810 advance can (about $10 at NAPA) provides the same amount of advance as the stock can (15 degrees), but is fully-deployed at only 8” of vacuum, so there is no variation in idle timing even with a stout cam.

For peak engine performance, driveability, idle cooling and efficiency in a street-driven car, you need vacuum advance, connected to full manifold vacuum. Absolutely. Positively. Don't ask Summit or Jeg's about it – they don’t understand it, they're on commission, and they want to sell "race car" parts.
That whizbang you are writing about is BS. I have been running a whizbang non-vacuum advance dis. for over 30 years on my 307 and 350 and never had any problem at all. I had excellent throttle response, I like smoking up my tires when I hammer the gas pedal, and never overheated, and gas mileage, who gives a dam when I'm running 4:10 gears and a 3500 stall converter. I never did like vacuum advance. You're worry about gas, get a rice burner. Before safety inspection was introduced it passed emission. Still running that whizbang on my 406sbc, today.
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  #43 (permalink)  
Old 09-18-2013, 03:13 PM
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Originally Posted by lg1969 View Post
That whizbang you are writing about is BS. I have been running a whizbang non-vacuum advance dis. for over 30 years on my 307 and 350 and never had any problem at all. I had excellent throttle response, I like smoking up my tires when I hammer the gas pedal, and never overheated, and gas mileage, who gives a dam when I'm running 4:10 gears and a 3500 stall converter. I never did like vacuum advance. You're worry about gas, get a rice burner. Before safety inspection was introduced it passed emission. Still running that whizbang on my 406sbc, today.
you can talk all you want about how you've been doing it wrong for years... but he's still right.

The spark timing needs to be altered according to engine load/manifold pressure. The vacuum advance cans leave a lot to be desired but they're a hell of a lot better than nothing.
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  #44 (permalink)  
Old 09-18-2013, 03:27 PM
How fast is fast enough?
 
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Originally Posted by rifraf View Post
I feel as if Ive spent 2 hours watching my dog chase his tail. I cant take anymore.
With all due respect,

Just about everything you posted in this thread is wrong. Time to sit down, ***************

Last edited by 68NovaSS; 09-18-2013 at 08:53 PM. Reason: Abusive
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  #45 (permalink)  
Old 09-18-2013, 04:02 PM
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With all due respect,

Just about everything you posted in this thread is wrong. Time to sit down, ****************
X2
Sadly, everyone is an expert on the forums.

Last edited by 68NovaSS; 09-18-2013 at 08:54 PM.
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