why remove vacuum advance

[blazer2007]

wha t is the reason for removing the vac advance on the dist.and when you do ,do you change the mechanical advance.It ,s on a 454 450 horse auto

[Pyrotechnic]

Vacuum advance is only required at light cruise condition. Race cars, and I means ones that get driven off the trailer and on to the track...don't spend much time if any at light cruise. They spend most of their time at high RPM where vacuum advance would have no effect anyway.

Don't listen to anyone who tells you that a wild motor on the street doesn't require vacuum advance. On the street, you NEED vacuum advance.

[blazer2007]

ok thanks

[jimfulco]

Vacuum advance tends to make it run smoother and cooler at idle and at very low rpm. This can be good for a race car when not actually on the track racing.

[Marv D]

You don't need vacuum advance on the street with a wild motor
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LOL just pulling Pyrotechnic's chain. I agree 100% Bringing the advance up to 40-45+ under light cruise conditions makes the motor run smoother, and helps promote a more complete, efficient burn. It can show a bad tune up and detonation if your too lean, but that's the tuners fault, not the vacuum advance. If you want to see something cool,,, de-tune a blower motor to 10-12 degrees of advance,,, what a cool sight with all the header tubes glowing orange. That is the same thing that happens (to a lesser extent) with a n/a engine with low advance levels. A incomplete burn pushes burning gases out past the exhaust valve and into the exhaust header/manifold. You don't get the light show, but the underhood heat is there none the less.

As far as race cars,, we usually don't run ANY advance mechanism at all. A distributor with the advance locked out, you set total timing at idle and it hopefully stays there at all rpm's. Just like said,, you are not under any other condition other than WFO for any length of time to make a advance curve necessary. Most race cars launch at 5000ish rpm, and shift in the 7000rpm range. No centrifugal or vacuum advance would have any effect up there so why have it. It would be just one more thing to fail or cause inconsistency.

[Pyrotechnic]

I'll admit, I was about to unleash the fury.

http://cgi.ebay.com/ebaymotors/SBC-C...3A1|240%3A1318

That guy on the other hand, really annoys me.

[Super73]

What about some of the newer Distributors that you set a timing curve via laptop. Are they still using a vacum reference for a MAP reading in the distributor.

[enaberif]

Simply put.

Don't.

I discovered my vac advance was off on my distributor and since hooking it backup and tweaking the system to run with it my gas mileage for driving in town has made a HUGE increase.

[hotrod 80]

I run mechanical advance . Just enough weight to back off for starting . The second it starts it's at full advance .

[scatesracing]

I locked mine and installed a 5300 stall........... That fixed it... lol

[djracer]

I have used Small gm distributers and justed used the magnetic pickup to trigger a 6al with no Advance and it ran great in my 71 truck on the street.

[Marv D]

Originally Posted by Super73

What about some of the newer Distributors that you set a timing curve via laptop. Are they still using a vacum reference for a MAP reading in the distributor.

You mean like the upper end MSD 7530 (series) boxes. I have a 7530T in my Nova and it is pretty cool,, Via laptop you program in 3step settings, advance per 100 rpm's, slew rate, adjust any cylinder anomaly, use the timing as traction control timer. Some very cool stuff but about all I use is the start retard, 3step programs, and a top end retard function. The box is just too darn smart for me. I can get in there and make a mess of the program in a heartbeat.

[Pyrotechnic]

The new MSD 6530 Programmable 6AL-2 has an option to run a MAP sensor and is laptop programmable.

I like the simplicity of the original 6A boxes though. Simple in design and they work well. A completely toasted box can be sent to MSD and rebuilt for cheap. Can't imagine that these new digital boxes are that easy to fix.

[djracer]

Originally Posted by Marv D

You mean like the upper end MSD 7530 (series) boxes. I have a 7530T in my Nova and it is pretty cool,, Via laptop you program in 3step settings, advance per 100 rpm's, slew rate, adjust any cylinder anomaly, use the timing as traction control timer. Some very cool stuff but about all I use is the start retard, 3step programs, and a top end retard function. The box is just too darn smart for me. I can get in there and make a mess of the program in a heartbeat.

I'm in the same boat. I have the 75301 and it has data acquisition. You should try programming with the handheld controller. Its a real pain in the butt.

[Super73]

There was an article in either a Hot Rod or Car Craft over the last few months A/B'ing 3 different distributors that are all programable. One of them seemed very nice. I think it was programable in like 100rpm incraments and you could put any amount of timing at each point.

What I think would be nice is to have a distributor that is programable based on RPM and MAP similar to how all the new EFI stuff is done. Use the vacum input for MAP. It would also be nice if the control box had an input feed for a knock retard senor that you could screw in to a head some where. Also maybe an input for an Intake Air Temp and Cololant temp. Set your timing, if you see some KR pull some out in that area. This would allow you to really nail a street tune. Have a multiplier to reduce timing if you reach a certain IAT or CT.

I can see a company doing it at some point..


With the mounting technology of todays electronic components and how cheap they are, I doubt these companies would want to repair the PCB if something went out on them. But they might offer a replacement PCB..