vaccum vs non vacuum advance distributor

[69shelbycoupe 11]

For the last 10 years I have only raced and modified efi mustangs so I am new to old carb and dist setups. I have a 351c that will be a weekend street/strip, car shows, and occasional drive to work car. It has the 2barrel heads on it with the 4 barrel valves. I have a weiand x-cellerator intake and a 750 carb on it. The cam is around 244 dur and 560 lift. I don't want points dist but also don't want to spend $300 on a elec billet dist. Any suggestions on what to get and wether or not vaccum or non vaccum. I don't know the difference in the two. I also don't know how the whole ignition setup is. If I get an elec dist will it eliminate the ign box on the fenderwell? I am confused if you couldn't tell on how or what to do with the ignition. Thanks

[69RavenConv 286]

Given that you don't want to spend a lot on a fancy dizzy, the most cost effective solution is a stock vacuum advance distributor with a Pertronix module. You can also mate a 5.0L EFI intake to a 351C and go with an EFI setup if you want but you need some minor machine shop help to do it.

[69shelbycoupe 11]

I want to go with a carb. I know about the pertronix. If I added that to a stock dist does that eliminate the module on the firewall? Just wire the dist to a coil and that is it or no?

[69RavenConv 286]

Yep, the Pertronix doesn't need any external module. You just need to bring 12V to the dizzy to power it.

[69shelbycoupe 11]

Could you give me an idea about the whole vacuum vs non vacuum benefits or whatever the case may be. I've also seen people with vaccum advance dist and they don't have the vaccum advance hooked up. How does that work? thanks

[69RavenConv 286]

Well, you could start a religious war when it comes to ignition timing, but in real simple terms (I'm no expert) here goes. Vacuum advances the timing at light load & idle conditions. This can improve fuel economy and engine responsiveness.

 

At heavy load or wide-open-throttle, vacuum drops and vacuum timing is retarded. In these situations, the mechanical advance takes over because the mechanical weights and springs operate based on RPMs.

 

Technically, you don't need vacuum advance but you will likely lose fuel economy and responsiveness without it. For a street car, I would keep both vacuum and mechanical mechanisms. However, many drag racers don't use vacuum because they are at full throttle all the time anyway and don't benefit from it.

[bigperm2 10]

69 raven pretty much hit the nail on the head. For drag racing, vacuum advance is really not necessary since you have the car floored the whole time (no vacuum.) I think you should give vacuum advance a shot, especially since most factory distributors have the vacuum can on them. Just be sure to hook the vacuum line to ported vacuum. The purpose of the vacuum advance is to give more advance for low cylinder pressure (vacuum) to compensate for a slower burning mixture. It is true that it really is an economy feature and not really a performance issue.

 

As for the pertronix, they usually are used for a points replacement. So if your distributor is a duraspark dizzy, it might take a little more work to get the pertronix in there. For the most part, the guts of 60s-80s v8 distributors interchange regardless of engine size, so you can bolt in the points "stuff" in your duraspark dizzy.

 

The duraspark setup is IMO a great system. If you don't want to use or figure out how to wire up the module, you can always replace the module with an msd box.

[69shelbycoupe 11]

Well I may just bite the big one and buy a pertronix billet distributor. I hear that there are two different size shafts in the cleveland. Pertronix doesn't state what size dist shafts theirs are. I don't even know which one mine is.

[LoneWolf2U 136]

Just use the point replacing module in your dist, simple 2 wires to coil and resistor wire bypass.

[69shelbycoupe 11]

well, the dist I have is an aftermarket one I got for free that is an accell duel point wich I don't want. Pertronix told me they don't have an ignitor to fit that dist

[LoneWolf2U 136]

Same dist I am using in my 351c.

full mech advance, drive it on the street and going to do some track runs.

My build is Old School except the full roller rockers, which they hadn't made yet when I was in school building up these cars.

 

Points are cheap easy and i carry a set in the bag in the trunk on road trips.

Never have to worry that the local parts store will have electronics when they fail.

 

Go to napa and get a stock replacement and put a pertronics in it under a 100.00

Edited January 16, 2010 by Mach1Rider

[69shelbycoupe 11]

cool, I have stud mount roller rockers as well with my setup. I am particular or weird (whatever you want to call it) but I would like to get a dist without the vacuum advance. I don't think I need it plus it looks cleaner without that big horn looking thing sticking out the front of the distributor haha

[69cobraman 10]

A friend of mine put the Petronix billet distributor in his 351 cleveland and everything looked fine. When he went to put the base of the air cleaner on it hit the dist.. Come to find out the dist. is taller than the stock one. That I would pass this on.

[69shelbycoupe 11]

was that with a stock profile intake or an aftermarket so that the carb sits higher? I have the weiand x-cellerator intake