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Deleting vacuum advance???

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reelknots

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Discussion starter · #1 ·
I just dropped off my distributor to get rebuilt and the shop said the advance was way out of wack and unstable. He showed it to me on his Sun machine. Anyway, he said he was going to eliminate the vacuum advance, have 14 degrees initial timing and 36 degrees total all in at 2800. Does this sound like the correct path to take for a street machine used for general cruising?
Thanks for your comments
Steve
 
#2 ·
Key words, street machine and general cruising.
You need vacuum advance, period.
I wonder if the shop even knows how to 'set up' a vacuum advance unit... if it's that out of whack, get a replacement can...
 
#3 ·
reelknots said:
I just dropped off my distributor to get rebuilt and the shop said the advance was way out of wack and unstable. He showed it to me on his Sun machine. Anyway, he said he was going to eliminate the vacuum advance, have 14 degrees initial timing and 36 degrees total all in at 2800. Does this sound like the correct path to take for a street machine used for general cruising?
Thanks for your comments
Steve
Click to expand...
This sounds more like a performance curve at wot blasts.Light load,lean cruise may like has high as 50* btdc.Stick with the vacuum advance for a street cruiser.
 
#4 ·
reelknots said:
I just dropped off my distributor to get rebuilt and the shop said the advance was way out of wack and unstable. He showed it to me on his Sun machine. Anyway, he said he was going to eliminate the vacuum advance, have 14 degrees initial timing and 36 degrees total all in at 2800. Does this sound like the correct path to take for a street machine used for general cruising?
Thanks for your comments
Steve
Click to expand...
That is the curve i have in my 68 pick up with a 468, roller cam, dart heads etc. It has a msd set up with no vac advance, i drive it in the summer on the street as a daily non rainy day machine and have no issues with it at all, but i understand the need for a vac advance and why some would recommend it, fuel mileage being a big one, for me a 12;1, roller cam'ed, dart headed 468, 3500 stall and 3.73 gear fuel mileage isn't a issue. but if i was running a mild small block i wouldn't be without a vac advance
 
#5 ·
Most if not all street cars which have to idle or cruise, need vacuum advance. You'll get better off-idle perfromance, a cooler running engine, and better mileage. As fatblock above says, VA will ensure the total timing (vacuum + mechanical) gets to 50 degrees and higher at cruise which is what your engine needs at cruise.

As a side, if you suffer from dieseling, VA to a manifold vacuum source will eliminate dieseling since the primary throttle blades are more closed at idle.
 
#6 ·
Steve,
I have got to chime in with the others and say you need a vacuum advance on the street. I personally cannot believe that someone who sets up distributors would tell you otherwise unless all they do is WOT drag race engines.
 
Discussion starter · #7 ·
Thanks for all your comments. You all seem to agree for me to keep the vacuum advance. I called my mechanic to discuss keeping the vacuum advance but was told that he's done 1000's of distributors this way and no one ever brought it back to have the vacuum re-installed. My dilema is that I used this guy 39 years ago to help me build up my 69 z-28 into a low 12 second car....he used to race also and he still has a very good reputation in this area. I really trust this guy...( but I haven't seen him in 38 years or so),but I also have a lot of respect for the opinions given to me on this site. I guess if it doesn't work out, I can take it somewhere else to have the vacuum re-installed. I don't want to buy a new distributor since this is the original that came with the car.
Thanks
Steve
 
#8 ·
A very big ditto to the above
I just dropped off my distributor to get rebuilt and the shop said the advance was way out of wack and unstable. He showed it to me on his Sun machine. Anyway, he said he was going to eliminate the vacuum advance,
Click to expand...
This is very confusing to the extent of BS
1/ The VA has nothing to do with and unstable advance..
2/ just replace the VA if it is in the wrong vac and/or deg range
3/The only things that cause an unstable curve are
a.. worn counter weight bushes
b.. worn shaft and bushes
c.. bottom gears not shimmed..they rearly wear enough to cause unstable.


I just dropped off my distributor to get rebuilt
Click to expand...
And ALL of the list above is what is involved in "rebuilding " anyway.

Or I will put another way
Im not known for my dipolomatic attitude when the chips are down...I call it blunt.
If I was dropping mine off, got that sort of BS, I look the guy in the eye..tell him hes talking out a hole and its not his mouth, cut the crap and tell me straight up exactly what is there and what is wrong....And believe me I really do so....but have to be polite in the forms..mods get upset lol
 
#9 ·
I am calling BS here.
Vacuum advance does not become "unstable". I would say that your distributor is worn (pins, bushings, and weights). If your vacuum can is not working, then replace it. Your car will run fine without it, but at cruise (part throttle, light load) you will lose economy and you MIGHT have problems with hot starts (maybe). He should be able to put a curve in your distributor based on your cam specs, and driving style. If you street drive, keep the vacuum can.
I run my car without a vacuum can on the street, but I mostly race and my engine is very radical.
This is all opinion from my own experience. Take it for what it is worth.
 
#14 ·
Why do yopu think it needs rebuilding...
The basics are simple as Smitz mentions above
(pins, bushings, and weights).
Click to expand...
Weights dont tend to wear
pins can wear even if bushes have been word for a few decades, and even so a new set of bushes will fix and last a few yrs.
If the pins are warn there will most likelt be wear in the main shaft and bushes...And it is the shaft that normally wears....the shaft pins etc all come as a single part...
Do not touch the main shaft bushes un less you REALY know what you are doing...they are sintered...check out a couple old threads on that subject.

A worn shft/bushes shows up with a timing light at constant rpms with the timeing wandering around +/- a few degrees...and you will feel the play/slop inside.

The VA simple check, suck on it real hard and see if it holds the vac.
A full check is a small vac pump...those ones ppl blead brakes also fo this...they have a vac gauge on it
put your finger on the actuating shaft and note the amount of vac needed to start moving the shaft and the amount needed when it stops moving...compare with the specs for that part #
If both of the above is ok you can assume 95+% the amount of degrees will be right.
If u want to check that, hold the engine rpms at consatant speed...say 1200
Pull a vac with the pump..the crank degrees will increase..and so will the rpms...keep rpms constant...and pull full vac..note the crank degrees at the start and crank degrees at the end

Be carefull when comparing to part # specs....they could be in cam degrees...these are 1/2 crank degrees.
 
#15 ·
just to add my 2 cents...

For a street perfomance cruiser, you want something in the vicinity of:
18 degrees initial
18 mechanical, all in at 3600 (NOT 2800!!!)

And a vacuum advance that will supply 12 to 16 degrees of additional advance at your cruise vacuum (which will probably be 16" or more) without deploying at idle (probably 10-14 degrees)

What your guy is suggesting was standard practice "back in the day" when we had 100 octane leaded premium and didn't care if our cars got 6 mpg and idled so rich that no one could stand behind it at the A & W.

We know better now. Thru proper tuning, we can have our cake and eat it too.
 
Discussion starter · #16 ·
Let me clarify my original post. I'm going thru this car part by part because I've found that somebody in it's past took too many short cuts. I have a hesitation problem so I started by taking the distributor to the guy who used to do work on my 69Z 38 years ago. He could still be using 70's thinking for all I know. Anyway, he put the distrib on his Sun and showed me how the mech advance was jumping all over...pushing on the point mounting plate made it worse. I kind of expected something wrong since my timing mark jumped around when I was trying to tune the engine.
Anyway, rather than show any disrespect for this fellow, I'd rather try the distributor the way he sets it up without vacuum and then either take it back to him to put the vacuum back on (which he agreed to do if I don't like the way it is) or find someone else to set it up. I'm going to pull the engine and trans soon for some maint so this is a good test to see if he's still got it. At his and my age, no one is as sharp as they use to be....
Thank you very much for all your commments...and showing me how important a vacuum advance can be. I'll come back to you all next week to let you know how the car runs.

Steve
 
Discussion starter · #17 ·
#18 ·
reelknots said:
Thanks for all your comments. You all seem to agree for me to keep the vacuum advance. I called my mechanic to discuss keeping the vacuum advance but was told that he's done 1000's of distributors this way and no one ever brought it back to have the vacuum re-installed. My dilema is that I used this guy 39 years ago to help me build up my 69 z-28 into a low 12 second car....he used to race also and he still has a very good reputation in this area. I really trust this guy...( but I haven't seen him in 38 years or so),but I also have a lot of respect for the opinions given to me on this site. I guess if it doesn't work out, I can take it somewhere else to have the vacuum re-installed. I don't want to buy a new distributor since this is the original that came with the car.
Thanks
Steve
Click to expand...
What the shop is telling you is 100% correct. It will run without a VA, but if you want to get the best overall performance and best MPG, YOU MUST RUN A VA!!!! There is no ifs ands or butts. The guy is probably seeing you bring him a dizzy for a Camaro thinking it's a weekend warrior or a track blaster. Did you absolutely tell him this was a cruiser? If you did, then I would pick up your dizzy and go somewhere else. Anyone who tells you not to run a VA on a cruiser is crazy. Yes it will run and yes it will idle, but if you want the best off idle performance, the best idle quality and the best mileage on the highway, then you MUST have a VA installed, PERIOD!!!!!!!!!!
 
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Discussion starter · #19 ·
67CamaroRS/SS said:
What the shop is telling you is 100% correct. It will run without a VA, but if you want to get the best overall performance and best MPG, YOU MUST RUN A VA!!!! There is no ifs ands or butts. The guy is probably seeing you bring him a dizzy for a Camaro thinking it's a weekend warrior or a track blaster. Did you absolutely tell him this was a cruiser? If you did, then I would pick up your dizzy and go somewhere else. Anyone who tells you not to run a VA on a cruiser is crazy. Yes it will run and yes it will idle, but if you want the best off idle performance, the best idle quality and the best mileage on the highway, then you MUST have a VA installed, PERIOD!!!!!!!!!!
Click to expand...
Thanks, Charlie. I agree with you and the rest of the posts on this subject and I WILL have vacuum advance when I resurrect the engine in the spring. for now, I just want to see if my hesitation problem improves before I rip it down....AND... I don't want to upset this 'old' friend of mine. This is more important to me than mpg for now. Call me lame but that's how I am. You can spell and pronounce "Reelknots" many ways.
 
#20 ·
I understand not upsetting your friend, but if you are spending money and not getting something fixed that you most likely will in the future... who is being upset?
I would have no problem telling my friend they were nuts if they were doing something to my car or telling me something to do that shouldn't be done, just something to consider.
 
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