Promax Six Pack Metering Block no Vacuum Advance?

[Hellcat]

Hello all! I had my six pack carbs for my 440 rebuilt by Promax. I had them install their metering block for the center carb not realizing that it doesn't have a vacuum advance port like the original metering block has. Their point was that the vacuum advance would add too much advance and the engine would run much better without it. This is contrary to what I have always thought. It is a street driven car and I was under the impression that you always want to have vacuum advance for a street car. I understand no vacuum advance for race applications since you are full throttle or nothing....generally speaking. I am thinking about installing the original metering block back onto the center carb so I have vacuum advance again, but I wanted to see what the forum thought first. Is there any reason that I would NOT want vacuum advance on a street driven car?

Currently the engine is running without vacuum advance. I have a miss at idle that I'm trying to work out so it has been difficult to tune it, but the timing is set at (going off memory) 17 degrees at idle. The total timing is around 32 degrees and it's all in before 3,000 RPM. The engine seems to like the advance....except when hot starting as you can imagine, it fights itself a little bit before turning over. The throttle response is very quick.

I am using the mopar performance electronic ignition upgrade kit with the orange box. The motor is in a '70 Barracuda. Also the cam is a Comp Cams hydraulic roller XR274HR-10. It has plenty of valve lift 0.538/0.534 intake/exhaust, but the duration isn't overly aggressive for the street 274/282 intake/exhaust, 224/230 intake/exhaust @ 0.050" lift.

 

[Cuda_mark]

Hi Hellcat. I am running the Promax metering block on my center carb as well (512 stroker, 6 pack setup). I am by no means an expert but I think vacuum advance only comes into play at idle or highway cruising when you have substantially intake manifold vacuum. That's why the Promax setup doesn't use it. I've had good luck with my setup...the only thing I had to do is change the vacuum secondary springs in my outter carbs to the stiffest spring holley makes. They were opening way too quickly.

 

[Adam]

Ported vacuum only supplies vacuum at part throttle. The advance you get from the vacuum canister on the dist, helps with economy or cruising. It does nothing at full throttle because the engine vac is very low.

With your cam and intended usage of the car I think you would prefer an operation Vac/Adv. You should try it and you can always swap it back, but first I would bump up the total timing to 34 degrees and lighten the springs so its all in by 2500 rpms. This is easy to check with a tach and timing light that has a built in timing dial. Dial 34 on the timing light and rev it up, while watching the marks on the balancer. Check it at 2000, 2500, 3000... this will tell you your total timing and when it is all in. (you probably already know how to do this, but I included it for others who read this thread that might not know).

 

[moper]

Honestly, I install the Pro Max plates in the outboards and use the factory block in the center. IMO, you should be using the advance, right up to the point where it cannot be utilized because of the cam (performance level). You sacrifice gas mileage and driveability at every throttle position but idle and wide open without it.