Ported versus straight vacuum???

-
dustoff440

dustoff440

Well-Known Member
Joined
Apr 15, 2009
Messages
1,991
Reaction score
24
Location
central fl
The thermoquad I have is off of a lean burn 400. It has no ported vacuum for the vacuum advance. This is for a mild 360 Magnum(stock except for 340 exhaust manifolds, a knock off air gap, a small cam Intake 276 exhaust 286, Intake lift 496 Exhaust 512 Intake 112 centerline.

I went with more duration and lift on the exhaust as I have stocker exhaust manifolds and also at one point am going to put a 150 shot of giggle gas.I will be running a slant 6 converter (around 1900 stall) and 3.23's.

My question are there any advantages/disadvantages to running straight vacuum off of the intake manifold? I know that at wide open throttle there will be no vacuum pulling on the plunger, but will I have too much advance at partial throttle? I know that I can run it without any vacuum to the plunger but I would like to get as much gas mileage as possible as this will be my daily driver and also am thinking that gas will go to 4-5 bucks a gallon.
 
As soon as you step on the gas from idle your vacuum will drop. This will cause your advance to retard & probably make the engine stumble.
 
Problem I had with straight vacuum is the amount of advance is not consistent at idle. With ported it stops sucking at idle so the amount of advance is always the say allowing a more consistent idle. With staight vacumm it tending to "land" at different idle speeds because the vacumm would keep the advance stuck at differing amounts.
 
You don't need a vacuum advance if you recurve the dizzy. Any Hi-po engine don't run vacuum advance mechanisms.
 
cjh,Yes you are correct, however I'm trying to set it up to get as good gas mileage as possible. Correct me if I'm wrong but I was under the impression that using a vacuum advance helped out in the mileage department. I fear that it won't be that long until gas shoots back up to $4 a gallon and I want to use the Dart as a daily driver.
 
340SFAstback, I'm with you on what you said but wouldn't that be a different scenario with a stock cam that idles smooth and has fairly constant vacuum.(If gas prices skyrocket I would consider reinstalling the stock cam)
 
The vacuum advance can help as far as gas mileage is concerned but I think the only way you're going to get it to work is to switch to a carb that can supply ported vacuum.
 
I would say for now, run without it. I am a big proponent of running a vacuum advance if at all possible. What I'd suggest is you try to locate an earlier Tquad that and rob the baseplate. Set up your ignition curve as you would normally, and when you get the other baseplate, run it. Also, the lean burn carbs are rather lean... So you may want to keep your eyes open anyway for something earlier if for no other reason than tuning parts.
 
moper said:
I would say for now, run without it. I am a big proponent of running a vacuum advance if at all possible. What I'd suggest is you try to locate an earlier Tquad that and rob the baseplate. Set up your ignition curve as you would normally, and when you get the other baseplate, run it. Also, the lean burn carbs are rather lean... So you may want to keep your eyes open anyway for something earlier if for no other reason than tuning parts.
Click to expand...

At this point I'm thinking that my 850 is going to be making a trip to Demon Sizzlers after reading his posts. I want to get the car completely put together with everything else is broken in and dialed in where I can get good spark plug readings and readings from an air fuel gauge then send it to him to install a vacuum port(which apparently can be done but is tricky) and rejet and perform a few other mods to make it just right...in a high state of tune and getting good gas mileage. Basically it is a stock 360 Mag with a knock off air gap and a small cam. Unfortunately it will have to wait till income tax check time. LOL
 
You must log in or register to reply here.
-

Back
Top