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vacuum advance #1226848 05/03/12 07:15 PM 05/03/12 07:15 PM
Joined: Apr 2007 Posts: 905 SD Z zrxkawboy OP super stock
zrxkawboy OP super stock Z Joined: Apr 2007 Posts: 905 SD	The thread on the overheating 67 Belvedere got me thinking, but I didn't want to hijack the thread. This is something I've wondered about from time to time: why do some people not run vacuum advance on street-driven cars? I'm sure no expert, but it seems to me that it would always be beneficial. Any thoughts? It's Swifty! Swifty, you toad sucker!

Re: vacuum advance [Re: zrxkawboy] #1226849 05/03/12 07:20 PM 05/03/12 07:20 PM
Joined: Jun 2006 Posts: 5,163 CT GTX MATT master
GTX MATT master Joined: Jun 2006 Posts: 5,163 CT	Well for one, drag cars don't us mechanical advance so some people plug it thinking that it will give them a performance increase. More likely they re-curved their distributor, or set the timing to get more total advance, or over advanced their timing. Either way some effort has been made to tune the car with a more aggressive timing curve for more power. Then they run into issues at part throttle (usually in high gear on hills) with detonation, so plugging the vacuum advance cures this. I don't like plugging the vacuum advance, it makes a lot of cars (particularly automatics) feel very sluggish under normal driving. But to each their own. Sometimes it may be necessary but I think it often gets plugged when it shouldn't be. Now I need to pin those needles, got to feel that heat Hear my motor screamin while I'm tearin up the street

Re: vacuum advance [Re: GTX MATT] #1226850 05/03/12 09:08 PM 05/03/12 09:08 PM
Joined: Jan 2003 Posts: 2,072 Cambridge, Ontario, Canada C CUDAJAS top fuel
CUDAJAS top fuel C Joined: Jan 2003 Posts: 2,072 Cambridge, Ontario, Canada	I have run my smblk cuda with and with out. My experinace has been varied. With the vac advance hooked up to ported vac (above the throtle blades) the car bucks and jumps under slow crusing speeds and decell. Tried to tune it out but no luck. With the vac advance hooked to constant vac, below thotle bades, the idle smoothed out (increase timing), but under part throtle cruise, highway speed, the car ran incredbibly lean / stinky and 10 - 15 deg hotter than normal. Really not good! Had to stop 45 min into a road trip to disconnect the vac advance. With the vac adacne disconnected, the car runs well, idelas well (choppy but that is the idea).

Re: vacuum advance [Re: zrxkawboy] #1226851 05/03/12 09:14 PM 05/03/12 09:14 PM
Joined: Nov 2007 Posts: 5,337 the house on the left. C cogen80 master
cogen80 master C Joined: Nov 2007 Posts: 5,337 the house on the left.	Quote: The thread on the overheating 67 Belvedere got me thinking, but I didn't want to hijack the thread. This is something I've wondered about from time to time: why do some people not run vacuum advance on street-driven cars? I'm sure no expert, but it seems to me that it would always be beneficial. Any thoughts? because guy are scared to mess with it, don't understand it, or just old and stubborn.

Re: vacuum advance [Re: zrxkawboy] #1226852 05/03/12 09:28 PM 05/03/12 09:28 PM
Joined: Jan 2003 Posts: 24,562 Brookeville, Md Mr.Yuck Not enough dumb comments...yet
Mr.Yuck Not enough dumb comments...yet Joined: Jan 2003 Posts: 24,562 Brookeville, Md	define your "street driven car" it's not really needed for anything but economy. If you have even a mild 440 Lock the sucker in at 38* and be on your way. The MPG different will be minimal at best. However if your junk is advancing up to 50-55* you could hurt something. [IMG]http://i66.tinypic.com/pui5j.jpg[/IMG] Coming soon!!!!

Re: vacuum advance [Re: Mr.Yuck] #1226853 05/04/12 09:44 AM 05/04/12 09:44 AM
Joined: Sep 2006 Posts: 1,139 West Tennessee R rbstroker super stock
rbstroker super stock R Joined: Sep 2006 Posts: 1,139 West Tennessee	In my efforts to make my stroker more streetable, I had a vacuum advance distributor set up by 4 seconds flat. Replaced my non-vacuum tach drive distributor. After swapping and some carb tweaking, I have to say that it is better.

Re: vacuum advance [Re: rbstroker] #1226854 05/04/12 10:31 AM 05/04/12 10:31 AM
Joined: Jun 2008 Posts: 3,916 usa L lewtot184 master
lewtot184 master L Joined: Jun 2008 Posts: 3,916 usa	Quote: In my efforts to make my stroker more streetable, I had a vacuum advance distributor set up by 4 seconds flat. Replaced my non-vacuum tach drive distributor. After swapping and some carb tweaking, I have to say that it is better. i got away from the full centrifugal only distributor for street driving many years ago. a vacuum advance distributor is better for street use. lets the engine burn cleaner.

Re: vacuum advance [Re: lewtot184] #1226855 05/04/12 10:56 AM 05/04/12 10:56 AM
Joined: Feb 2009 Posts: 1,274 Ontario.Canada C can.al pro stock
can.al pro stock C Joined: Feb 2009 Posts: 1,274 Ontario.Canada	..very important feature for street driven cars and your car will run o.k. without it but you're leaving a lot on the table. google "timing and vacuum advance 101".. and you will be without excuse

Re: vacuum advance [Re: can.al] #1226856 05/04/12 11:50 AM 05/04/12 11:50 AM
Joined: Jan 2003 Posts: 27,421 Balt. Md 3 383man Too Many Posts
383man Too Many Posts 3 Joined: Jan 2003 Posts: 27,421 Balt. Md	I guess for me its because I am an old bracket racer from the 70's and under full throttle like drag racing the vacum advance does not work. And I like very fast mech advance as my dist has full advance by 2000 rpm. And it is a race unit without a vacum advance. Right now I have 38 total in very early and it runs great. Never tried a vacum advance but of course I would have to change dist to try it. Ron

Re: vacuum advance [Re: Mr.Yuck] #1226857 05/04/12 12:01 PM 05/04/12 12:01 PM
Joined: Nov 2011 Posts: 2,154 Its a TRAP! DARTH V8Я Oh No!! I just had a moron attack!
DARTH V8Я Oh No!! I just had a moron attack! Joined: Nov 2011 Posts: 2,154 Its a TRAP!	Quote: define your "street driven car" it's not really needed for anything but economy. If you have even a mild 440 Lock the sucker in at 38* and be on your way. The MPG different will be minimal at best. However if your junk is advancing up to 50-55* you could hurt something. Locked out dizzy eh? Guess some people refuse to move ahead 40 years When it takes more than a sweet mullet to prove you rule at the trailer park..

Re: vacuum advance [Re: DARTH V8Я] #1226858 05/04/12 12:08 PM 05/04/12 12:08 PM
Joined: Feb 2005 Posts: 28,312 Cincinnati, Ohio Challenger 1 Too Many Posts
Challenger 1 Too Many Posts Joined: Feb 2005 Posts: 28,312 Cincinnati, Ohio	Quote: Quote: define your "street driven car" it's not really needed for anything but economy. If you have even a mild 440 Lock the sucker in at 38* and be on your way. The MPG different will be minimal at best. However if your junk is advancing up to 50-55* you could hurt something. Locked out dizzy eh? Guess some people refuse to move ahead 40 years Wow yuck, better read up before posting.

Re: vacuum advance [Re: 383man] #1226859 05/04/12 12:52 PM 05/04/12 12:52 PM
Joined: Jun 2008 Posts: 3,916 usa L lewtot184 master
lewtot184 master L Joined: Jun 2008 Posts: 3,916 usa	Quote: I guess for me its because I am an old bracket racer from the 70's and under full throttle like drag racing the vacum advance does not work. And I like very fast mech advance as my dist has full advance by 2000 rpm. And it is a race unit without a vacum advance. Right now I have 38 total in very early and it runs great. Never tried a vacum advance but of course I would have to change dist to try it. Ron in my 65 coronet i use an aggressive centrifugal advance with the vacuum. at first i didn't think it would work but it seems to be a happy set-up. the distributor has a 9 degree plate, full centrifugal is all in at 2200rpm, and a 9 degree vacuum can. i'm sure the engine is burning cleaner with it, especially at cruise, and of course at full throttle the vacuum advance doesn't work.

Re: vacuum advance [Re: lewtot184] #1226860 05/04/12 06:13 PM 05/04/12 06:13 PM
Joined: Apr 2010 Posts: 4,154 bethlehem pa M mikemee1331 master
mikemee1331 master M Joined: Apr 2010 Posts: 4,154 bethlehem pa	i'm also lining up on the 'use it' side. i have played with it both ways and while i won't say my modified 440 6pack setup is a turd without it (how can such awesomeness ever be one) there is a huge difference on the street in 'seat-of-the-pants feel and response.

Re: vacuum advance [Re: mikemee1331] #1226861 05/04/12 06:25 PM 05/04/12 06:25 PM
Joined: Oct 2007 Posts: 288 Birmingham, England M Mick70RR enthusiast
Mick70RR enthusiast M Joined: Oct 2007 Posts: 288 Birmingham, England	I prefer to use vacuum advance for street driving but I limit it to 10/12 degrees. Mechanical is all in by 2500 rpm and vacuum is connected to the manifold. I've ran both ported vacuum and manifold vacuum and had good results with both on different engines. Manifold vacuum suits my current set-up, it idles a lot better with the additional advance so that's what I run. Also tried disconnecting the vacuum advance and my right foot is nearer the carpet when I'm cruising. Last edited by Mick70RR; 05/04/12 06:26 PM. 1970 Road Runner 505 cid MCH CNC ported Stealth heads MP 528 camshaft 4 speed GV overdrive 11.98 @ 117 on street treads

Re: vacuum advance [Re: zrxkawboy] #1226862 05/04/12 07:27 PM 05/04/12 07:27 PM
Joined: Sep 2003 Posts: 1,688 Marlboro, NY, USA R Rick_Ehrenberg top fuel
Rick_Ehrenberg top fuel R Joined: Sep 2003 Posts: 1,688 Marlboro, NY, USA	The bottom line: If you don't have at least 50-55 deg. (total) at lightest throttle / cruise, you're making the Arabs rich and cutting ring / cyl wall life in half! Assuming you have a canister that's marked. say, 8 deg. on the arm (16 crankshaft degrees), you'll be close to dialed in as far as overall advance with the typ. 33-35 deg. (total of initial and mech). You vary the spring pressure on the back of the diaphragm to tune out any detonation. This is not very different than virtually all muscle-era Mopar distributors were stock. Rick

Re: vacuum advance [Re: Rick_Ehrenberg] #1226863 05/04/12 07:42 PM 05/04/12 07:42 PM
Joined: Oct 2007 Posts: 3,893 Oregon hooziewhatsit master
hooziewhatsit master Joined: Oct 2007 Posts: 3,893 Oregon	Quote: The bottom line: If you don't have at least 50-55 deg. (total) at lightest throttle / cruise, you're making the Arabs rich and cutting ring / cyl wall life in half! Assuming you have a canister that's marked. say, 8 deg. on the arm (16 crankshaft degrees), you'll be close to dialed in as far as overall advance with the typ. 33-35 deg. (total of initial and mech). You vary the spring pressure on the back of the diaphragm to tune out any detonation. This is not very different than virtually all muscle-era Mopar distributors were stock. Rick Is there an upper end of too much vac advance? I think I saw 60* on my timing tape the other day I really need to get a mity-vac to test it properly. I don't remember how many degrees it has stamped on the arm. If you ever find yourself in a fair fight, your tactics suck.

Re: vacuum advance [Re: hooziewhatsit] #1226864 05/04/12 07:51 PM 05/04/12 07:51 PM
Joined: Feb 2003 Posts: 21,318 Manitoba, Canada DaytonaTurbo Too Many Posts
DaytonaTurbo Too Many Posts Joined: Feb 2003 Posts: 21,318 Manitoba, Canada	Quote: Is there an upper end of too much vac advance? I think I saw 60* on my timing tape the other day I really need to get a mity-vac to test it properly. I don't remember how many degrees it has stamped on the arm. If you're not getting any detonation while at cruise or a very light acceleration then I'd say you're fine.

Re: vacuum advance [Re: hooziewhatsit] #1226865 05/04/12 07:57 PM 05/04/12 07:57 PM
Joined: Jan 2007 Posts: 7,664 IN A ahy master
ahy master A Joined: Jan 2007 Posts: 7,664 IN	As I understand it, the goal is to light the fire early (advanced) so you get maximum cylinder pressure built up near TDC. The efficiency gain comes from getting the benefit of that pressure for the full power stroke plus higher peak pressure near TDC. With a "fast burn" combustion chamber lighting the fire too early could get max pressure before TDC and really fight the piston going up. Plus it could cause detonation. Slow burn chambers like the 906 can benefit from more advance than the fast burn. On my (sort of) fast burn BB with closed chamber Ed heads I have it set at 50 degrees via EFI. If I could figure out how to do it I'd paste the advance table. Is this optimal? I don't know It would take quite some testing and/or experiments to figure out. I do know it works well. The engine runs well and will get 14 MPG @ 75 MPH or the same on a 2 lane @ 65 MPH with an occacional blast for passing. Not bad for a 496 with 243 @.050 cam.

Re: vacuum advance [Re: DaytonaTurbo] #1226866 05/04/12 08:00 PM 05/04/12 08:00 PM
Joined: Oct 2007 Posts: 3,893 Oregon hooziewhatsit master
hooziewhatsit master Joined: Oct 2007 Posts: 3,893 Oregon	Quote: Quote: Is there an upper end of too much vac advance? I think I saw 60* on my timing tape the other day I really need to get a mity-vac to test it properly. I don't remember how many degrees it has stamped on the arm. If you're not getting any detonation while at cruise or a very light acceleration then I'd say you're fine. Well, I'm not getting any that I can hear over general engine/road/wind/rattle noise If you ever find yourself in a fair fight, your tactics suck.

Re: vacuum advance [Re: ahy] #1226867 05/04/12 08:15 PM 05/04/12 08:15 PM
Joined: Nov 2011 Posts: 2,154 Its a TRAP! DARTH V8Я Oh No!! I just had a moron attack!
DARTH V8Я Oh No!! I just had a moron attack! Joined: Nov 2011 Posts: 2,154 Its a TRAP!	If you have a knock sensor that would be optimal. The computer will give as much advance as possible. Watching my Truck, it'll try and 'hold' 50 degrees at all throttle conditions (cept' for full throttle). I generally never see it go lower then 35 or so even with a very heavy load. When it takes more than a sweet mullet to prove you rule at the trailer park..

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