craig442

1965 442, all stock - except using msd ready to run distributer (no box). Where on the stock carb does the vacuum advance get connected to? Typically it gets connected to a ported connection (above base plate) so it does not advance the timing at idle, but the stock carb only has two ports, both on the base plate(which have manifold vacuum. None of the diagrams in the assembly manual or service manual show this connection. Any help would be appreciated.

joe_padavano

The use of ported vacuum for distributor advance is an early emissions control measure that started in the mid-60. For best economy and power, you want the distributor connected directly to manifold vacuum, which is what Olds did in 1965. Any port on the intake or carb that provides full manifold vacuum at idle is fine. You can even tee off the line that goes to the AT vacuum modulator.

craig442

Thanks Joe - The engine builder said the following - The factory may have done that...but it goes against every thing any engine tuner knowns....it pulls the advance out ....when it's needed the most ...under load and acceleration...thats when you need ign advance as engine speed increases....not at idle....it also makes mechanical advance virtually useless...because it's "all in" at idle....so it's up to you...look proper....or run proper....@

joe_padavano

That's possibly the most uninformed statement about ignition advance that I've ever read.

Vacuum advance at idle both improves gas mileage and helps lower engine temps when driving in stop and go traffic. It is unrelated to mechanical advance. As soon as you open the throttle, vacuum (and thus vacuum advance) drops off. As soon as engine RPMs increase, mechanical advance takes over. At wide open throttle, there is no vacuum advance, no matter where you have it connected. Mechanical advance (and initial timing) is the only thing controlling the advance curve at that point.

Do not confuse the optimum spark timing for a dedicated drag car with what you want for a street driven car. This is a mistake that many people make. Obviously, initial timing will depend on how much vac advance you get at idle, since too much initial timing coupled with an aggressive vacuum advance can lead to pinging at part throttle. The plugs neither know nor care if the advance comes from initial timing or from the vac advance can - they only care when the spark is fired. You can play with initial timing and vac advance curve (if you have an adjustable vac advance can) to optimize the curve for your engine, driving conditions, and selected fuel grade.

oldcutlass

These are a good read, although for a Chevy the principle is the same:
http://www.corvette-restoration.com/.../Timing101.pdf

http://www.corvette-restoration.com/...ine_Timing.pdf

joe_padavano

^^^Excellent info! Thanks for the links.

Firewalker

Yes, good article and as they pointed out the emissions ported vacuum runs worse and heats up the motor more, than full or manifold vacuum. And ported was strictly for emission laws.

For better snap off a dead stop, at the light manifold vacuum works, as well as more mileage and cooler engines. The reason there is it is putting more advance in, and doesn't cause problems is because that changes a second or so later, as the Vac drops back from the opening of the blades as the vac bleeds off. Most cannister today from the parts stores are adjustable. Ping at cruise, and you adjust the canister backing its timing down some, by turning the allen head screw in the vacuum line tube on it, so "total" becomes a little less. Turned the other way and you get more total timing for more power, and cooler, and maybe more mileage.

Race only are a totally different animal and situation. Though today, with programmable boxes even they can have this added timing advantage without worrying.

cutlassefi

I disagree with most everything here. I've learned a lot about ignition timing and it's effects from Efi tuning.
In my opinion the ONLY reason to use manifold vacuum is to potentially alleviate hard starting at elevated static idle timing settings.
With manifold vacuum, the mechanical is advancing while the vacuum is retarding in most scenarios. That makes for a stagnant curve.
The ideal curve is the best/highest timing at idle and full throttle as well as everywhere in between. Run the most initial you can, with an optimum total. Then use an adjustable vacuum advance pot to tune the midrange/light throttle.

I read the link provided, and I have to say I'm not sure why anybody would believe the same guy who murdered John Lennon😉, or who starts a sentence "Referring back".😉

Jmo.

Firewalker

A little story. A younger friend of mine who became a mechanic came down from the higher altitude town he was living in in an old Ford pickup. He came to see his parents and friends including me and it was summer.

He told me his truck was running hot and pinging just running around here and I asked where he had his Vac advance canister hooked up to. He of course said ported. I said change it to manifold vac.

This totally went against all he was told and did as a mechanic, but he did it anyway knowing who I was over several years, so he changed it and left. 30 minutes later he came back excited, because the overheating was gone, and the pinging, and it ran better than it ever had he said. It was just a stock in tune ford pickup, set the factory way for emissions.

Got back 20 years or more and I had a 69 Camaro L78 new from the factory and the beginning of "emission controls.. With 11 to 1 forged pistons and solid lifter cam, big port heads, and aluminum intake and 780 Holley, and all from the factory it was extremely fast.

But I knew it had more, so I went to a Pro Stock racers house 60 miles away I knew and asked him about it. I told him what the factory stock initial on it was, and he said that is way retarded for those engines. We bumped it up about 7 degrees, and it unleashed a ton of torque more and welded up the new M22 4 speed, from the extra gain. It then chewed up 3 more all on warranty. Then it tore up a stock TH400, then a B&M street strip TH400, and finally a better B&M was sent tome, after talking to me and was rebuilt with a manual valve body, and what they call their funny car clutches and sprag. It was a brute that lasted and set the tires on fire, at full power at speed on all the shifts. Off the throttle shifting you coulnd't even feel it shift. Very very nice. I was 22 by then.

Brute force......not emission stuff, though some if doesn't hurt a thing performance wise.

oldcutlass

Not 100% familiar with the EFI systems other than speaking with a Holley rep. Doesn't an EFI system use an internal timing plot with the distributor used basically as a triggering device. I bet if you look at the timing curves in memory you'll see cruise timing on average in the mid 50's range and wot in the 34-38 range. Initial is whatever you set it to.

cutlassefi

So what you're saying is it was wrong from the factory? Sorry but I don't believe that for a minute.
A common easy mod for early 90's 5.0 mustangs was to advance the timing 8-10* from the factory setting. But they didn't overheat if you didn't. Something else going on there.

craig442

All great replies, but keep in mind my 65 442 does not have ported vacuum on the stock carb, so the factory used manifold vacuum.

So this means GM did it wrong in their hey day?

oldcutlass

No, just use the manifold vacuum.

acavagnaro

Nothing of any real importance to add. Just wanted to take a minute and thank most of the guys who provided information in this thread. After reading it and the links above, I decided to have a better look at the way I plumbed my own set up a few years ago. I measured my manifold vacuum and mapped the vacuum advance canister (applied vacuum vs. % open) and switched from ported over to manifold vacuum.
I was surprised that the tone of the exhaust actually changed slightly at part load. It was a little deeper and the off-idle response was slightly better.


Great information. Thanks again.

Firewalker

Glad you tried it to find out whats best for yourself and the truth and it worked, as it always seems to. The only time ported might be a better idea is in winter if you live in a really cold and nasty part of the country. It should make the engine a little hotter and a little faster. A tad less responsiveness and torque, also might help driving in the snow and ice, or when it is wet outside.

I don't see much cold or wet conditions here, and while I might not change that for winter I usually will change my choke settings, for summer versus winter.