Vacuum At Idle

[60K T/A]

Where do I check the vaccum at. I want to make sure I have the right power valve in my center carb.

[MEK-Dangerfield]

You can use the vacuum advance line.


  Mike

[Chryco Psycho]

actually no , you need to hook onto the PCV hose , the vacumm advance line works opposite & should have zero vacuum at idle

[moper]

what CP said. Any manifold vaccum source. Also, mak sure you test it in gear, at hot idle. It's irrelevant if its in park and your car's an auto...

[vinb]

How about the little fitting line that comes off the power brake booster hose on the intake...

[60K T/A]

what CP said. Any manifold vaccum source. Also, mak sure you test it in gear, at hot idle. It's irrelevant if its in park and your car's an auto...

Its manual trans.

[Chryco Psycho]

the booster is manifold vacuum as well , so yes it will work

[67Vette427]

The pcv hose is pretty big (3/8" of 5/16") which is pretty big for most vacuum guages. Plus the car will die out pretty fast if you don't have a good fitting. Your carb/intake should have a fitting ( a small one ) with manifold vacuum. From what I remember there are two or three vacuum sources: Manifold, ported and venturi. I don't think Mopar ever used venturi but they did use ported for the vaccum advance on the distributor. Ported should be 0 at idle where a manifold source should be 5 psi or higher depending on the cam and the motors condition. My Hemi car runs 5 psi at idle and I had to change the springs in the carbs because it was so low do it wouldn't richen up at idle. Most non-performance cars run around 10 psi. Its normal to lose vacuum upon acceleration but it should return with the rpm becomes more even.

[Chryco Psycho]

my vacuum guage has a cone adapter to fit snugly into a 3/8 hose

[AMXguy]

OK after a long talk with Doug at FBO he assures me that Mopar performance distributor MUST be hooked up to a vacuum port with FULL vaccum at idle, a manifold connection is fine. I've always thought that you used the carb port with no vac at idle, this is wrong according to him .

 with a 440 six pack running a cam slightly more than an original six pack cam what should the vacuum be at idle and criuse speed?  I'm getting 11 in. at idle and 17in. at criuse. I just put the new manifold on and I'm trying to figure out if I may have a leak, seems a little low? I can cover the center carb a little bit with my hand and get a slight rise in the engine speed but I'm told that could be from sucking through the outboards? I don't know

[Chryco Psycho]

WTH.... if you connect the dist vac line to manifold vacuum the engine will have full advance at idle retarding with rpm working effective against the mechanical advance causing the advance to be eliminated , this will result in porr power milage & overheating to boot ...sounds like Great advice 
 the vacuum readings so OK depending what cam you have , covering the center carb & having RPM rise could be a mixture adjustment on the outboard carbs or center carb

[dodge freak 2]

Is that the same place as 4sec flat ?

If so run away fast. On a A body forum me and this BJR poster got in to it after he posted how his 318 motor in like a 3300 lb  car--forgot what type, it was like 2 years ago-could run the quarter mile in the 10 second range with a pair of those high swirl 302 heads that he did some magic porting too.

Yeah, right. I told him I believe it when I see him on the speed channel because theres no way a 318 with those 302 smog heads could run 140 mph in the quarter in a stock weight car.

So far, I have not see him on TV or even in hot rod mag. 

[AMXguy]

I forgot to add I'm at over 3000 feet elevation too, so it sounds as if I'm OK. thanks
 
 Chryco I'm not going to argue with you because I'm sure you've forgotten more than I know but maybe his idea works ok if the distributor is curved for it? I don't know but after arguing with him he made it quite clear that the way he sets them is you give it about 16 degrees initial, hook your vac advance up to the manifold for a total of about 34. then as you crack the throttle your vac drops putting you back to your 16,  then the mechanical takes over until you level off and the vac kicks back in. maybe it's just a different way of getting the same place?

[Chryco Psycho]

Same Guy , he has a quick A body but with years to sort out your own car it is not hard to go fast , much harder to make a customer car run fast without the time to sort every detail out completely

[Chryco Psycho]

so most cars do not idle well with 34* timing , & hitting the throttle & having the timing back off makes not much sense either then waiting for the mechanical advance to pull the timing back up to 34* then having both rpm & vacuum as you lift on the throttle so now you have 50* how could this help ?