HEI Dist Vacuum Advance question

[franko72]

I finally installed my HEI Dist. I dont think that the vac, advance is working all the way. before I installed the dist. I put my mouth on the vac, advance port where the vac. hose is attached . I sucked on the port but it never seemed to hold pressure to my lip. When I removed the old points dist. I tried the same test and the old points dist. and it held pressure on my lip and did not leak off.Where can I buy a new vac. advance unit?about how much $ does one cost? also how do I go about getting the counter weights to change the curve for better throttle response out of the hole.Its a 402 BB if that matters.It really does start better and runs much smoother, just doesnt seem to have the get up and go when RPM's advance from a stand still position.

[mnunn454]

Originally Posted by franko72

Where can I buy a new vac. advance unit?about how much $ does one cost?

I bought mine from a speed shop for about $25 to $28 as I recall. It was "adjustable" and comes with a little "sawtooth" disk that you use to limit the amount of vac advance travel. That part was probably the most valuable part of the upgrade because by adjusting it I can limit the amount of "retard" that occurs when I tromp the pedal. In other words, it doesn't retard the timing any more than necessary when smashing the throttle.

Originally Posted by franko72

also how do I go about getting the counter weights to change the curve for better throttle response out of the hole.Its a 402 BB if that matters.It really does start better and runs much smoother, just doesnt seem to have the get up and go when RPM's advance from a stand still position.

Second part first, BBCs and SBC's are the same w/r/t the distrib, although they like different advance and total timing settings.

Short answer to part 1: exchange the spring/weights to bring the ignition in at an earlier RPM.

Longer Answer part 1: When you buy the $15 to $25 spring/flywheel advance kit, there's usually a graph in the kit that represents several different curves possible. Springs are usiually color coded. Light springs/heavy weights bring the advance in quicker. Strong springs/light weights bring it in later. I've always had to play with mine to get it where I want it. (This can be lots of fun in the summertime, hanging over a hot engine blistering your elbows and fingers on everything under the hood while you relocate the little spring or snap ring that flew off to parts unknown.). The combo I liked best on my 396 and also on my 454 is one weak and one medium spring with the stock GM flyweights.

Smart people like you (not me) usually pay a speed shop about $100 to "dial in" or "recurve" the distributor's weights and springs to give them the amount of advance they want at any given RPM. Also, some fancy aftermarket distributors will let you set this curve electronically. Once that's set, all you have to do is reinstall the distrib and set the initial/base timing, then go for a cool ride with blisterless fingers.

If this kind of stuff interests you, I've got a neat .PDF article that I pulled off a Pontiac website that goes into much more detail. PM me w/your email address and I'll send it to you.

[ChevLoRay]

The HEI on my truck was in it when I bought it almost 8 years ago. It did okay for about 5 of those years. During that time, I read that a Corvette vacuum advance was a good one to use, so I arbitrarily changed mine when I determined the old one wasn't working to my way of thinking.

No problems for a couple of years, then I started having problems. Didn't know it was the distributor, though. What would happen is that when I let off on the gas, it would die. It would fire back up, then run fine. It was an intermittent event. I was concerned that it was anything but the distributor. I finally decided it was bad, and bought an ACCEL that is essentially a re-man. Problem solved, but what had happened? Found that the breaker plate of the HEI would move when it was supposed to do so, but the wire from the reluctor had a break in it that would open at times, depending on how much the plate moved.

I had priced reman distributors from Auto Zone, O'Reilly's and Advance, as well as NAPA. NAPA was a little bit more, but the other three actually used the same part number and their pricing was within a couple bucks of each other. The ACCEL distributor was less than $20 more money. I'm happy with my choice.

[mnunn454]

Here's the article I referred to above.

Enjoy.

Mike

http://www.boyleworks.com/ta400/psp/distcurve.html