Vacuum Advance Solution?

[cudabob496]

What do you guys think of this idea?

My big block has an MSD 6AL box and MSD ProBillet distributor, but no vacuum advance. I noticed you can buy an MSD timing adjuster that allows you to dial in +/- 15 degrees of timing. So, I can install that, and when crusing, dial in 10 to 15 degrees more advance to have the same effect of vacuum advance, which is better milage and less carbon deposits in the cylinders? When its time to put the hammer down, just dial the knob back to zero, and then I will have my 36 degrees total timing.

http://www.summitracing.com/parts/MSD-8680/

[cageman]

Hmm, you have a big block and want mpg, and you are worried about carbon deposits. I thought this was the performance section, not the joke section.
Carbon deposits, ha. why are you worried about that? carbon builds up due to not getting warm enough, or to rich at idle maybe, I have never seen carbon on something that gets used. The msd box will go out way before you have carbon buildup.

[JVMopar]

Seems like alot of dinking around while driving. Vacuum changes even with engine load not just throttle changes. I'd just put a stock distributor in there that's what I have on my big block with a 6AL. That's just my $0.02

[quietdad]

You can also just get a ProBillet distibuter WITH vacuum advance for the same money. I go for the simple things in life. Once I turn the key, i don't need to think anymore.

[dave5711]

Hey cuda bob, how much cam, compression, and gears are you runnning, and how many cubes?

[cudabob496]

254/258 at .050. solid roller, .625 lift, 10.5:1 comp,3:91 rear, 496 cu in.

[cudabob496]

Originally Posted by JVMopar

Seems like alot of dinking around while driving. Vacuum changes even with engine load not just throttle changes. I'd just put a stock distributor in there that's what I have on my big block with a 6AL. That's just my $0.02

Not really. Think you're gonna race, turn a switch. If not racing, add more advance by returning switch to original position (say 10 degrees more advance). 99% of the time on the street is not spent pedal on the floor with zero vacuum. On my car, weighing 3250 pounds, zero vacuum means warp speed and a trip to jail.

As mentioned in Mopar Action this month, no vacuum advance on a street car means lousy milage, fouled plugs, carbon buildup, and more piston ring wear.

[cageman]

Carbs do the same thing, might as well fuel inject it then with that thinking.

I dont have vacuum advance on anything. I take that back, my 95 ram maybe does, and my 96 neon maybe does, and my 08 patriot maybe does, but my neon doesnt even have a dist, prob the same way with the patriot. all computer controlled.
Thats one of the first things I do to all my old stuff, I get rid of the vacuum advance, weld up the slots so it is like 18 to 20 intitial and advance it to 36. The only motor I have had apart looked like new, so Ill keep doing what Im doing. Only reason I tore it apart was I converted the truck to diesel power, and Im turning the 67 318 block that was in it into a 340.

[DJM]

Cageman when I was worjking at the dealership in Valley in the 70's there were many complains of bogging and poor milage. we recurved the distributor, put a small ball bearing the vac advance hose to look like it was still functioning and let them out the door. It was rare that we had any more complaints but did make a lot of people happy.

[dave5711]

Originally Posted by cudabob496

254/258 at .050. solid roller, .625 lift, 10.5:1 comp,3:91 rear, 496 cu in.

Vacuum advance is going to do absolutely nothing for you man. .02

I run a 242 @ 50 hydro, and don't run a vac adavance. It simply makes no difference. If the curve is right on the distributor, you may even create a surge etc.. Typically, I remove the vac advance from combo's like your's for this reason.

I know there is this horror stroy magazine article out there on this subject, but I really don't think you have anything to worry about here.

[cageman]

I have seen that surge, another reason to get rid of the vacuum advance.
Gotta love magazine articles.

[JVMopar]

Go ahead and dial in that 10 degrees more advance all the time and listen to the ping. You should be running right on the virge of ping anyways without any vacuum advance.

Since your advance would be ported vacuum it would have low vacuum more than just WOT. It would also have low vacuum at idle and low speed operation.

[cudabob496]

I agree with you guys that vacuum advance on a race motor at the strip is a waste, and can create problems. I've been there! Thats why I dumped the vacuum advance originally. But on my motor, just cruising down the street at 2500 rpm, looking for victims, I still think being able to dial in 10 degrees advance would be better for the motor, and I'd get better than the 10 mpg I'm getting. But, if I do it, I'll let you know what happens. I was talking to a Summit guy who put one of these in his motorhome, and he said he loved it! Right now, without vacuum advance, my plugs are a lot darker than they should be for the primary jets I'm using. Vacuum advance may clean them up a little.

[cudabob496]

Originally Posted by JVMopar

Go ahead and dial in that 10 degrees more advance all the time and listen to the ping. You should be running right on the virge of ping anyways without any vacuum advance.

Since your advance would be ported vacuum it would have low vacuum more than just WOT. It would also have low vacuum at idle and low speed operation.

Shouldn't be on the verge of pinging, with reverse dome pistons and zero deck height, 10:5 to one, aluminum heads, and 93 octane.

[cageman]

dish pistons and 10.5 to one, doesnt add up. is that what you call a reverse dome?
so lets say you get 10.1 mpg after you do it, but you beat the bearings out of it, the .1 mpg improvement wont even pay for the doodad after 20 years of daily driving. Then you also chewed the pistons apart detonating every once in a while, and the bearings are beat out of it too, I just dont see the point. Then the accident you get into as your not paying attention to actually driving the car. seems like little gain and alot of pain.

[cudabob496]

Originally Posted by cageman

dish pistons and 10.5 to one, doesnt add up. is that what you call a reverse dome?
so lets say you get 10.1 mpg after you do it, but you beat the bearings out of it, the .1 mpg improvement wont even pay for the doodad after 20 years of daily driving. Then you also chewed the pistons apart detonating every once in a while, and the bearings are beat out of it too, I just dont see the point. Then the accident you get into as your not paying attention to actually driving the car. seems like little gain and alot of pain.

Mopar Action says milage will increase about 3 mpg, so over a year or so the component will probably pay for itself. Accident? The dial will be changed at the light, the same time I flip off the electric fan, and get ready to boogie! Never heard of vacuum advance chewing up pistons, so I wouldn't think electronic vacuum advance would either. Vacuum advace on a big block Mopar adds about 15 degrees advance. I'll start out by adding 10 and see what happens. But I appreciate the heads up, and I will watch for that. Pinging is pretty easy to notice.
PS I think your basic jet pilot in the military has about 250 switches to flip, depending on what he wants to do, so I should be able to handle a couple. Anyway, its an automatic, so its easy to drive.

[cageman]

Fying a plane is no comparison, no one is all of a sudden going to jump out in front of you or cut you off!
If you here it pinging it is to late.
I doubt 3 mpg, thats funny, compared to what, three spark plugs not hooked up to a full 8 on advance. Your deal, could work, but dont expect 3 mpg. I have watched the advance on my 95 ram on the scanner, it works so fast, and it also has a knock sensor, but like I said, it is fuel injected. That is why it gets better mpg than lets say a carbd 318, as the carb is rich a majority of the time.
I have an air fuel meter in my valiant, that thing is a pain in the but, as a good running tune without it it ran fine, but the thing is a po crap in stoich. I just have to many damn cars to fuel inject em all, I doubt any of them will happen. Only way I will ever get decent mpg out of any of them and longevity out of the motors like my 225,000 mile ram has, and it has more life left in it.
What your looking for I dont think is going to happen. But if you have a couple hundred bucks to burn and some spare time, have at it. I know on my race car stuff, most dyno guys dont even want us to have more than 36 degrees total, some will say it might as well be 34 total.
I actually have a couple trucks that have it locked at 36 all the time, sure they start a little hard when warm, but it isnt a big deal to me, it runs good.
My valiant I think is at 23 degrees initial, but it has been so long I cant even remember for sure. I put the light springs in and it is all in by 2000, and I cruise around that. I put a vacuum advance plate in once and it ran no better down the road when I was looking for mpg back when gas was so dang high. Thats on a 273 with a 5 speed with overdrive. I cant forsee 3 mpg on a big block cruising at 2500. Give it a try though, your mind is made up by the help of a salesman.
Speaking of mpg, I want to order an Isky mile a more cam for the 273, Ill have to write that on my board that has things to do all over it.

[cudabob496]

Originally Posted by cageman

Fying a plane is no comparison, no one is all of a sudden going to jump out in front of you or cut you off!
If you here it pinging it is to late.
I doubt 3 mpg, thats funny, compared to what, three spark plugs not hooked up to a full 8 on advance. Your deal, could work, but dont expect 3 mpg. I have watched the advance on my 95 ram on the scanner, it works so fast, and it also has a knock sensor, but like I said, it is fuel injected. That is why it gets better mpg than lets say a carbd 318, as the carb is rich a majority of the time.
I have an air fuel meter in my valiant, that thing is a pain in the but, as a good running tune without it it ran fine, but the thing is a po crap in stoich. I just have to many damn cars to fuel inject em all, I doubt any of them will happen. Only way I will ever get decent mpg out of any of them and longevity out of the motors like my 225,000 mile ram has, and it has more life left in it.
What your looking for I dont think is going to happen. But if you have a couple hundred bucks to burn and some spare time, have at it. I know on my race car stuff, most dyno guys dont even want us to have more than 36 degrees total, some will say it might as well be 34 total.
I actually have a couple trucks that have it locked at 36 all the time, sure they start a little hard when warm, but it isnt a big deal to me, it runs good.
My valiant I think is at 23 degrees initial, but it has been so long I cant even remember for sure. I put the light springs in and it is all in by 2000, and I cruise around that. I put a vacuum advance plate in once and it ran no better down the road when I was looking for mpg back when gas was so dang high. Thats on a 273 with a 5 speed with overdrive. I cant forsee 3 mpg on a big block cruising at 2500. Give it a try though, your mind is made up by the help of a salesman.
Speaking of mpg, I want to order an Isky mile a more cam for the 273, Ill have to write that on my board that has things to do all over it.

Actually, in flying a jet, you can all of a sudden have somone on your tail, and you have 5 seconds to react before you are dead!
Just because you hear pinging, does not mean you have done any major damage. Actually, my mind was made up by many things I have read and know, and the salesmans input was just a small part of it. I have also been talking to the tech folks at MSD. But, cageman, you have some valuable experience, and some good points!

[dave5711]

Originally Posted by cudabob496

I agree with you guys that vacuum advance on a race motor at the strip is a waste, and can create problems. I've been there! Thats why I dumped the vacuum advance originally. .

The surging complaints etc, I was refering too, and saying you don't need vacuum is in reference to your motor on the street.

Tha vacuum advance does nothing at the strip. When I remove vacuum advance, it's because the combo doesn't need it, not because of where it's driven.

[djswwg]

do a test. you say the timing is at 36 total right now and no ping. warm up the engine and advance the timing to 38. drive it at light throttle and see if it pings, bucks,is hard to start (crank over), surges, farts, or anything else you don't like. keep doing this in 2 degree steps until it dosent like it anymore. i doubt you'll be able to advance it to more than 38 or 40. if that's the case, the added economy will be almost negligable. if you can add more than that and the fuel economy increases substantially, your engine is built wrong!-here's why; modern quench style heads (which i presume yours are-probably Eddy#60929 or similiar) are designed to run on today's crappier pump fuel better than the old steel 906's ever could. the less timing you can use to make the same amount of power the better, because you aren't wasting as much of the fuel burn trying to push the piston back down the hole before it reaches the top of the cylinder. if gas completely burned the instant it was sparked we'd all set the timing at 15 after TDC. in the old days with good gas and steel none quench heads the engineers designed lots of timing in at cruise because it was a cheap and easy way to get respectable fuel economy. i seriously doubt if you will ever get much more fuel mileage out of your current combo. and when you think about it, it was built to make power, not for economy. the only way to make more power is burn more fuel. that's why we build 'em the way we do. ie, big cubes, big cams, etc. so try it out, let us know. good luck...........djs

[cudabob496]

Originally Posted by djswwg

do a test. you say the timing is at 36 total right now and no ping. warm up the engine and advance the timing to 38. drive it at light throttle and see if it pings, bucks,is hard to start (crank over), surges, farts, or anything else you don't like. keep doing this in 2 degree steps until it dosent like it anymore. i doubt you'll be able to advance it to more than 38 or 40. if that's the case, the added economy will be almost negligable. if you can add more than that and the fuel economy increases substantially, your engine is built wrong!-here's why; modern quench style heads (which i presume yours are-probably Eddy#60929 or similiar) are designed to run on today's crappier pump fuel better than the old steel 906's ever could. the less timing you can use to make the same amount of power the better, because you aren't wasting as much of the fuel burn trying to push the piston back down the hole before it reaches the top of the cylinder. if gas completely burned the instant it was sparked we'd all set the timing at 15 after TDC. in the old days with good gas and steel none quench heads the engineers designed lots of timing in at cruise because it was a cheap and easy way to get respectable fuel economy. i seriously doubt if you will ever get much more fuel mileage out of your current combo. and when you think about it, it was built to make power, not for economy. the only way to make more power is burn more fuel. that's why we build 'em the way we do. ie, big cubes, big cams, etc. so try it out, let us know. good luck...........djs

I don't think that is correct. Here's why: High performance big block Mopars have had vacuum advance for 50 years! When cruising down the street, vacuum advance sets your total timing to at least 50 degrees before top dead center. When you floor it, and vacuum goes to zero, the vacuum advance goes away, and you are left with initial timing plus mechanical advance for a total of around 36 degrees BTDC. Am I missing something here?
PS I just checked my 1972 service manual, and it calls for vacuum advance on big blocks of 10.5 degrees by 15 inches of vacuum, which is essentially immediatly after startup.

PS I have timing retard feature for startups.

[JVMopar]

Yes and No. There are more factors to think about. Factory air/fuel ratio's were leaned out for emissions. On a molecular level the molecules of air and fuel are spaced farther appart which takes longer to burn than ones that are close together (richer mixture). SO it takes more timing to get the most out of that air/fuel ratio.

Remember that during emissions testing WOT isn't a consideration because it isn't tested so a nice rich mixture can be used. While at part throttle low to moderate low load conditions are where it's tested so those mixtures were leaned out.

What I think he's really getting at is that if you can run more than 40+ degrees of timing without a ping problem then you just simply don't have the optimum compression ratio or cylinder pressure that your current combination and fuel could handle.

You want to have the maximum down force on the piston top to happen at 15 degrees after TDC. With the carb tuned for a constant mixture around 13:1 or slightly leaner you just don't need any more than 36 or so degrees to get the maximum pressure at 15 degrees ATDC. Now lets say your part throttle mixture is 15:1 then you definately want more timing in order to burn all the fuel that's in the cylinder and get the highest force on that piston to occur at the optimum time, and least HC exiting the cylinder.

Just adding more advance won't particularly increase HP.

How I did mine was to adjust it up 2 degrees at a time till it started to ping bad then I retarted the timing 2 degrees. After hooking up the vacuum advance I did the same thing adjusted the vacuum advance till it started to ping under cruise conditions then retarted it just a few degrees.

Of course you could try running a lower octane fuel if you don't have a ping problem already and are running 36 or so total advance. That way you'd save more $ than just few MPG, and you could forget about spending any money on more advance.

[cudabob496]

But isn't it true that vacuum advance on just about all mopar engines adds about 15 degrees advance while you are at part throttle. And at part throttle, your engines has 25 or so inches of vacuum. My 496 is very strong, but still has about 23 inches of vacuum at part throttle (and 10 at idle in gear). I think if people just read this months Mopar Action magazine at the news stand, a lot of questions will be answered.

Like you said, it takes more timing to get the most out of the air/fuel ratio, and thats why vacuum advance adds 15 degrees advanced timing, to make sure there is a more complete burn of fuel, which means better fuel milage due to more power per stroke. I think we are starting to kick a dead horse here.

[cudabob496]

OK gang, I found this tech question at the Mopar Action website:


Tech Question
bob santarsieri, schaumburg, IL, 71 plymouth road runner 440

I have a msd pro billet distributor and msd 6al box. What would be the best setting for the distributor? Right now it is set at 2 heavy silver springs and silver bushing per the instructions. It starts to advance at 1400 and goes to 5500rpm then levels off. What would you suggest. 440ci, 0.040" overbore, 0.474" purple shaft cam, Hedman headers and 3.23 gears. Just street driven. Thanks for your help.

Bob, assuming sufficient octane vs. C.R., you need a curve something close to this:

Under 1400RPM - no advance - set initial at 15 degrees BTDC
2000 - 10 dergees mech (25 total)
2500 - 20 degrees mech (35 total) - all in.

Plus, at LEAST 15 degrees of vacuum advance under light throttle (50 deg. total, 52-55 better).

If it currently doesn't go to full advance until 5500, you're giving up lots of power.

If it currently has less (or no) vacuum advance), you're giving up LOTS of fuel economy and fouling plugs.

Rick

[cudabob496]

Also, here another tech article that has a low compression V8 getting almost 60 degrees total advance with vacuum advance, and a major improvement in fuel economy.

http://www.moparaction.com/Tech/quest/FUEL_STARVED.html

[djswwg]

cudabob496, just re-read and try to understand what JVmopar and i are trying to telling you. it's harder to explain stuff by writing it than speaking it, sorry if i was hard to follow. do you know anyone with a modern design engine like yours with that much advance? i doubt it! your engine sounds like it's built similiar to mine and several others i've done. i'll be amazed beyond belief if you can actually successfully use that much timing (50-55 deg.) with your engine. what is the quench measurement of your engine and what cam are you using?...djs

[cageman]

I wasnt born in 71 when my trucks were new and on the road, but wasnt the fuel high octane back then, then of course you need vacuum advance to completely burn all of that, now adays, the gas is crap and it will burn faster, so less advance is needed to completely burn, and winter gas is way easier than summer.
Those magazines dont do me any good, just advertising is all it is. With the internet, by the time new stuff is out in print, we all know about it allready.

[cudabob496]

Originally Posted by djswwg

cudabob496, just re-read and try to understand what JVmopar and i are trying to telling you. it's harder to explain stuff by writing it than speaking it, sorry if i was hard to follow. do you know anyone with a modern design engine like yours with that much advance? i doubt it! your engine sounds like it's built similiar to mine and several others i've done. i'll be amazed beyond belief if you can actually successfully use that much timing (50-55 deg.) with your engine. what is the quench measurement of your engine and what cam are you using?...djs

Hi, are you saying Rick Ehrenberg (who has an automotive PHd from Detroit), who answered the previous tech question by saying the performance 440 needs 15 degrees vacuum advance, is wrong?

[JVMopar]

I never said he was wrong. The thing your not understanding is that vacuum advance isn't a constant thing. It's always changing based on engine LOAD and throttle angle. That's why you should use the vacuum advance and not just dial in more timing all the time.

Oh by the way JVMopar- Automotive BS Minnesota State University.

[cudabob496]

Originally Posted by JVMopar

I never said he was wrong. The thing your not understanding is that vacuum advance isn't a constant thing. It's always changing based on engine LOAD and throttle angle. That's why you should use the vacuum advance and not just dial in more timing all the time.

Oh by the way JVMopar- Automotive BS Minnesota State University.

But my service manual says that vacuum advance on a big block mopar will always be at 8.5 to 10.5 degrees when above 15 inches of vacuum, and a big block is always above 15 inches of vacuum, unless its floored. I have a pretty radical 496, and it is usually around 20 to 25 inches of vacuum unless I'm really getting on it.

Are you saying that as vacuum goes up past 15 inches, that the vacuum advance will go up correspondingly?