Hank

A friend is putting a barn find hot rod 69 vette big block back together and he inherited a 70's looking mallory distributor without vacuum advance. The mallory distributor cap has the wires attached semi-permanently, it does look kind of cool in an old school racing way.

He has had the engine rebuilt (and trans, and recored radiator, etc. etc.) and is trying to figure out what to do with the ignition. My advice was to swap out the old mallory for an MSD unit with vacuum advance. But I don't have any experience with running a non vacuum advance car on the street.

What do you guys think? are there other alternatives (like adding a vacuum can to the mallory?). I wish I had a pic to post of the thing, I might be able to swing that later on if useful.

Gerry

1snake

Very good advice. Better gas mileage, throttle response and a cooler running motor is what he has to gain.

Jim

Frankie the Fink

I don't think mating a vacuum can to a mechanical distrib is a good idea. A total swap out is probably best. Vacuum advance will give you better mileage, cooler running and basically 'comes off' when you floor it so you are pure mechanical anyway at full throttle. There is no real downside to adding it (and I did!).

DARN...Snake beat me to the punch..

jim lockwood

The advice so far is good: If you've got the option of having vacuum advance connected, by all means do so.

However, not having it isn't fatal.

Many Vettes left the factory without provisions for vacuum advance and they run just fine. My FI '60 is a great example; it runs well and is pleasant to drive.

In the case of the subject car, I'd try it and see what happens. You can always find a way to install a distributor with a vacuum can if need be.

Jim

Oriondriver

Lars taught us in our "Tuning for beer" session to listen to the car, smell the car, feel the car..." it will tell you whether your setup wants it or not...

magicv8

Many years ago I drove a dual quad Mopar with dual points and no vacuum advance on the street every day
for 4 years with no problems.

That was waaay before I was converted to the church of the bow tie.

66since71

You need vacuum advance for part throttle, light load conditions. Sure it will run, but conditions will be far from optimum. In many cases you could be up to 10 or 15 degrees retarded from optimum.

Advance that is fixed based on engine speed alone is for high load applications, like race cars and airplanes.

Harry

1snake

I don't remember anyone saying that a mechanical advance only dist. wouldn't work. It's just that motors with a vacuum advance dist. run much better.

Jim

GCD1962

Besides the FI engines, the 62-63, 340-HP engines had mechanical advance duel point distributors which ran great on the street.

1snake

Yes, and my 100% original 1960 270HP 283 has the original machanical advance only dist. and it runs fine BUT it would still run better with a vacuum unit. Ask Frank. Damn this is frustrating.

Jim

PinkVetteLady

You don't have to have vacuum advance and I ran my car like that for many years. To be honest I liked it that way with no ill problems. It wouldn't get hot in traffic, it wouldn't detonate, it wasn't any less fuel efficient. Lots of people will tell you that you have to have vac advance for the engine to be happy on the street.. Sorry but you can run it with no problems.

midyearvette

calm down now jim......i dont think we want another vac vs. non thread to start.....you better go grab the shot glass and relax a bit.....

1snake

I think you're right. I guess if people really want to know the truth, they can read the many articles written by John H. and Lars regarding this subject. Maybe GM really screwed up using vacuum advance on the Z-28's and LS-6's. Can you imagine how fast they would have been without it?

JIm

landshark 454

I run a couple of built big blocks with no vacuum advance. I run a tight advance curve in them and more timing from a vacuum advance would cause them to ping under light load.

Vacuum advance does nothing for heavy throttle running, and I am more interested in having the cars run strongest under full throttle. A vacuum advance that can be adjusted could possibly work, but I am not worried about light throttle operation or fuel mileage.

Ironcross

Yep...

square on all 4 corners, believe it gentlemen, ....regardless of what your told...thats the way it was. Dual points and no VC can.

,

AZDoug

Are you telling me that GM and Ford and Chrysler wasted hundreds of millions of dollars putting on vacuum advance cans that served no purpose?

No better gas mileage, no better part throttle response, no better low speed drivability?

Damn, you shoulda been Grand Poobah of the automobile engineering world!

Doug

Ironcross

I`m not telling you anything you dont want to believe...Boots Mallory`s performance distributors were dual point distributors without a VC can. The hot tip setup before electronic ignition. GM did the same with there high performance engines, the millions were probably spent on the low performance engines. There was no overheating or bad driving manners and FI Vettes got 20+ MPG with stiff 4.11 gears. I would have expected that you were aware of this. But in your apparent excitement you missed that it was never said you couldn`t use one, merely you could effectively not use one......Maybe you should get involved with some hands on drag racing...

And I thank you for the Grand whatever thing. Many bestows but that ones a first.......

have some on me, ......I make great popcorn too

mechron

NO, NEVER. i will explain why tomorrow.

obx2323

As you can tell this is a 50/50 split. Me, full MSD ign. with mechanical advance. Played with my curve and initial advance by seat of the pants and it's very peppy at any point of the rpm range. Runs very cool just idling too, but then again I am a long way from OEM with my 350 on all set-ups. I'm not the most gifted mechanically so I have sought advise to a few mechanics/builders and I have found each has their own preference that works and the end result is the same but getting there is different.

GCD1962

Not saying that's not what you experienced, but with the later model 340 Dist, not necessarily true due to a much better advance curve. For many years the 340 Dist was the performance distributor of choice.