Lars, the Crane Adjustable Vacuum Advance has two adjustments. The port set screw adjusts the rate of vacuum timing change as engine vacuum changes and they give you a plate that can be set to limit the travel of the vac can rod to adjust the amout of vac advance. I have not seen the Accel unit but the Crane unit does not look stock. It looks like an old Ford unit.
here is a link http://www.cranecams.com/master/vacuum.htm

 

The Accel unit looks stock and according to the install sheet it alters the needed vacuum at the same time the advance amount is changed - but for me that's a moot point - I pull vacuum from the manifold and always have enough to open the can at idle. I used to run mechanical only, and now view manifold ported adjustable vacuum advance as a way to make the curve streetable.

 

joe & magic -
Thanks for the info on the two aftermarket units - sounds like they can be used successfully if you know what you're doing and understand the tuning parameters - you guys clearly understand the concepts, and can make good use of the tunability of the adjustable units.

But as we know, most people out there using these units really don't understand the tuning concepts, and tend to get themselves in trouble - they're much better off with a good-performing fixed unit that's matched to their engine requirements. Here is a typical example of the type of tech questions I usually receive regarding the adjustable units:

"Hey Lars - I got me one of them there adjustable vacuum units, and I got it tee'd into my PCV hose. I cranked that little screw all the way in until it bottomed out, and then I backed it out until it fell out. Now my engine don't idle right, and the car jerks around like a freakin' bucking bronco on the hiway. What should I do?"

I think you can imagine what I usually recommend....
:lol:

 

Lars, can you give us a break down on the HEI curve units? I run an HEI in my 62' and I would like to get the timing just right. You have always been very helpful and I know it is a lot of work to get this info but you always seem to have the answers. Thanks

 

"But as we know, most people out there using these units really don't understand the tuning concepts, and tend to get themselves in trouble - they're much better off with a good-performing fixed unit that's matched to their engine requirements. Here is a typical example of the type of tech questions I usually receive regarding the adjustable units:"

Boy do you have that right. Too many people are putzing around with these cars who never skun a knuckle or busted a finger nail before they got their dream car. Alot of us started with some form of GM hand me down, added a 4 Speed or a V-8 or God help me a Straight Axel. We graduated the school of hard knocks while rebuilding it, then moved onto a muscle car. We scattered every possible part over the road, replacing 10 bolt rears with 12 bolts, M22s for M21s, 454s or 427's in place of 396's and on and on. Finally we got the Vette we always wanted as a kid.

Trouble is that likely that Vette (like mine was) has been corrupted and perverted along the 35 years of its life by Bubba and his friends. Unwinding that life of cross threaded bolts, "correct" parts, "incorrect" parts, offshore cheapie replacements parts and on and on is a real chore even when you know what you are doing. I recall guys on the forum with solid lifters riding on hydraulic cam shafts and other such bastardizations. Infinately adjustable things like these Accel Cans, CenterForce Clutches and many other such hot rod goodie parts from the aftermarket are very dangerous in the hands of the inexperienced.

It is a good thing the forum has guys like you who have broad general backgrounds and specialty areas like this advance curve stuff.

 

Torch -
Yes, I can provide all the HEI specs as well - it will take me a little time to compile this, but I'll be glad to post it up as soon as I get it put together. Give me a day or two and I'll give you a complete list with specs.

TheO -
Hi!! Thanks for the post - always good hearing from you!!

 

Lars, thanks I'll be looking forward to the info. You always have been a lot of help, as well as Duke and John Z.

 

I just re-wrote my entire vacuum advance paper shown partially in my post above. The new version has all the HEI vacuum advance part numbers, specs, and applications as well - took me all freakin' night and a bottle of nice wine to cross reference and research the stuff out. Since the "tabs" in the MS Word-formatted paper don't transfer well to a post here, please drop me an e-mail request for the paper to:
V8FastCars@msn.com
and I'll e-mail the paper out to you in Word format as an attachment to an e-mail.