Vacuum advance vs Centrifical advance distributors

I'm getting great advice here and I appreciate it. I'd like to hear some thoughts on spark advance. I just finished rebuilding my Dellorto carbs. I noticed that one of them has a vacumn tube (which is plugged currently), presumably to run a vacuum advance. I have a 009 centrifical advance distributor now. I took the points out and installed an electronic unit and it works fine. On one of these forum threads I read that vacuum advance might have some advantages. Any thoughts?

That's what AJ Simms (Mr. Kadron - Lowbugget.com) and other folks say should work the best in theory. I've also read some comments by some people advising against vacuum advance distributors so basically I'm confused too....

Richard, I too had read a lot about the benefits of vacuum advance, mostly on the Aircooled.net. I decided I would try it and bought a Mallory Unilite Dizzy with Vacuum advance from John Connelly at Aircooled.net

The concept of a vacuum advance is to advance your spark when crusing say on the freeway, when your throttle position is quite low (hence, the advance increase due to vacuum). The idea is, when you stomp on it, you lose the vacuum and your advance goes back to you maximum for the Centrifugal side.

So the idea is, you run say 12 degrees to 30 degrees under Centifugal and when you back off the throttle and are crusing (not under heavy acceleration load), your vacuum advance dizzy moves the advance up to say 44 degrees, causing a more complete combustion, supposedly cooler CHT's and better gas mileage.

On my dual 44 IDF's, I never got enough vacuum to raise my advance beyond what was caused by the centrifugal side. Essentially, the vacuum side did nothing. When I asked JC, he said it would loosen up in a thousand miles or so, but I never saw it.

I recently installed Electronic Fuel Injection and my Dual 45 MM Throttle Bodies, when they close, give way too much vacuum and as such I cannot tune the vacuum side down low enough to be useful where my advance gets pulled way over to 45 degrees, way too much for anything other than easy crusing.

All in all, I think I would pass on the Vacuum Dizzy and keep your 009, just my two cents.

Thanks for relating your experience Bill.

I was talking to a friend last night who builds engines for Formula V race cars with considerable success. He says stick with the 009 with the electronic module.

I think I'll leave the vacuum hole plugged up stay with the 009.

Rick

Bill,

THANKS for your post ! The little 009 gets so much bad press, yet it's always worked well for me (I run duals on all the street motors). I never fully understood the function of the vacuum advance distributor until now.

Again, thank you.

TC

Guys, I am glad it helped. The concept of the vacuum advance does seem to have merit it theory, you know really stretching the advance up there when crusing along when the risk of detonation is not a problem, but as I said, I found the actual implementation a little more delicate in actual practice.

My troubles will all be solved when finally I get to my single throttle body EFI setup with a crank triggered EDIS, where my ECU is controlling the spark. My goal is 25% better fuel economy without sacrificing any performance.

For those that keep track of such stuff, I would forego the dual TB EFI setup you may have been considering, I have not found it to be enough better to warrant the expense.

My current install below:

Hi: A centrifical advance can only change the timing based on engine speed. Vacuum advance changes the timing based on engine load. In an ideal world you should be using both to optimize your timing. Most of the vacuum distributors are designed for a stock 1600cc motor with a stock intake manifold. Once the motor is modified with a different cam or dual carbs it will give a very different vacuum profile. The same is true of a centrifiacal advance. If you change the heads, combustion chamber, compression ration, fuel etc you will have changed the rate at which a combustion event burns and need a different centrifical advance curve for optimum efficiency. The only real option is to get rid of your distributor and get a fully programmable ignition system.

So Bill when are you coming completely over to the dark side? You have the EFI when are you going to do the ignition? I think that I will be at the Parts Obsolete Camp out again this year. It is probably the end of June which should give you plenty of time.
Bruce

Bruce,

You must bring Heather or you can't come to PO. LOL.

Bruce

And ... I thought the 009 was designed for an industrial engine with #3 cylinder retarded to burn cooler? That the new Brazilian 009' are inferior to the older German versions? and that to function properly one needed to recurve them with new springs (and no two are factory curved exactly the same)? And of course you have to upgrade to the blue coil (or is the red one hotter?) Is all that 009 Urban Legend?

Wolf, from what I've seen Bosch 009's all work fine. If you check out Gene Berg's instructions for all their carb kits, they recommend the 009 as the distributor of choice for use in VW's because they're specially tailored for them. Back in the old days Bosch blue coils were supposed to be the hot ticket but now they're just standard issue items.

Wolfgang, I think there is probably more urban legend surrounding these engines than anything.

If you are uncertain about the 009, I know for a fact that my Mallory Unilite (the centrifugal part), with the Grey/Grey springs provide a very linear (and hence very swift) advance curve. The Unilite also does not block or jitter at all, period, fineto. At higher RPM, you look at the timing mark through the eyes of your timing light and it looks like a stopped pulley. So if you have doubts about your 009, you probably cannot go wrong with the Mallory Unilite. The bad news is even the Centrifugal Advance Model (the only one I would consider if buying again) of the Unilite Dizzy is really pricey.

Also, all I can say with regard to the 009 is they seem to work pretty darn well, most of the guys that race anything using Type 1 VW power use them. I have always found racers to be the final word, they know what works and will pay largely anything if something works better. I know when I raced, that was my mindset.

Bruce,

Great to hear from you! I could not have gotten this far without your early advice.

My EDIS stuff arrived a week ago (pulley with 36-1 tooth wheel, Coil Pack, EDIS module, spark plug wires, very cool). I am talking to couple of guys about a single TB design for induction. I have found the dual setup less than perfect. The tolerance buildup in my dual TB, hex bar, etc. seems such a travesty, when I have such a precise instrument in my hands in the ECU.

Also, I want that IAC (what a lazy sod, eh?). I have experimented with a few different ideas to get IAC on my dual setup, but it all starts to look like something Rube Goldberg would put together.

One way or the other I will be running EDIS and Crank Fire before early spring (darn holidays, bah humbug!). See you at the campout.

Bill,
what were you running in conjunction with the Mallory Unilite? Did you use their magnacoil and ignition system? I have bought the unilite and was curious as to what you used?

Michael

Michael,

I had an MSD 6L in my IM when I bought it (stock item from Henry). I added a Mallory Blaster Coil (you can see it in the picture above), that was an impulse buy as it looked better in the catalog picture than in real life. I mean a coil is a coil, but it was cheap so I guess I can't complain too much.

Anyway, the Unilite is a nice piece from a quality standpoint and you can actually see a difference with a timing light. Having said that, I am pretty sure you cannot see the difference on a dyno.

Centrifical is the way to go..
Points VS electonic.. depends if you have, or plan to add an Capative / Multiple spark discharge ignition.. :)

Bill: I take it you tried connecting each intake runner together, and then slaping the Map sensor to that line right?? most like with like 3/8-1/2 line/hose??

But it it did look pretty damn good thou :) sad it didn't work out as planed thou.. and is it a Ford EDIS module you are gonna be using?? if so, mount it in a cool location if people haven't warned you yet :)

Kevin,

Good to hear from you. Actually the dual TB setup just has not panned out as I expected. I did Tee the vac's together and the signal is fine to the map. I actually am getting a bunch more top end with WOT than I had with the 36 vents on my IDF's (I am running 45 TB's).

For me, my disappointment is really more a matter of trying to run close to the edge A/F wise. The duals seem to have enough tolerance buildup in the linkage, TB difference, perhaps manifold porting, etc. etc. that I can't get razor sharp (e.g. 14.7:1) and have it run decent at all. If I am down around 11.5-12:1, the car is a beast, but those numbers are more like Turbo numbers, than NA cars. I just can't lean it out without it starting to run poorly in the mid-range. I was hoping to be able to get to the point I could strap a CAT on and pass SMOG. My car is SMOG exempt, but I wanted to clean things up if I could, without sacrificing performance. No way Jose, at least with Duals.

I am thinking a single TB, right sized plenum, and proper individual runners should make the air delivery a little more precise. Then, I am hoping I can actually get things dialed A:F wise.

I got my EDIS stuff the other day (thanks!). I will mount the module in with the ECU (where the boom box once was). I assume the coil packs are impervious to heat?