Need some help setting vacuum advance

[Finoke]

When I got my convertible the previous owner said it had a bigger than stock cam causing poor idle. He just lived with it.

I found it to be running rich and fouling the plugs. I finally gave it a good tune up and it needed way more initial timing.

I reset the timing. At idle I get the best vacuum at 13.5 inches so I backed off a hair to 13 inches which put me at 23 degs advance.  Then I limited the mechanical advance to 38 degrees.

The car really woke up and runs much better. The plugs look good when I pulled a couple to check. It starts fine both hot and cold. No pinging on the road.

Now to my question. I read on how to set the vacuum advance. My book recommended running the vacuum gauge inside the car and noting the vacuum on the road under load at 2600 rpm then setting the advance in the garage with a vacuum pump. I'm not set up to do all that.

Can I just run it up to 2600 rpm and set the vacuum advance without load. My book says b/rb should be set to 56 degrees total mechanical plus vacuum.

Thanks
Tom

[HP_Cuda]

Lots of folks run it up to 2500 rpm and set the advance.

No problems.

[dodj]

While not quite the answer you might be looking for, I just dialed the vac advance almost completely out of my car. Think I have it limited to about 3*. (Allen key adjustment in the diaphragm housing). I could not get the car to cruise well at 60mph with the vac advance moving total advance up over 40*. Seemed to want to surge and ping.

[HP_Cuda]

Max advance should be 36 degrees, some get away with 38.

[dodj]

Max advance should be 36 degrees, some get away with 38.

I hear ya. But if you have any vac advance it goes a lot higher.

[Finoke]

Thanks Guys. Good comments. Mopar performance recommends 38 deg mechanical advance for b/rb with iron heads. I will sneak up on the vacuum advance. Maybe add 5 degs at a time and test drive. I will report back 

[dodj]

I will sneak up on the vacuum advance. Maybe add 5 degs at a time and test drive. I will report back 

You will have to adjust your initial each time. 

[1 Wild R/T]

Big Blocks generally like 35-36 total mechanical and an additional 18-20 in the vacuum advance for a total of 53-56 total advance...

[Chlngrcrzy]

Big Blocks generally like 35-36 total mechanical and an additional 18-20 in the vacuum advance for a total of 53-56 total advance...

I didn't think you could go that high with the total advance?

[1 Wild R/T]

You can't go that high on mechanical advance, when your cruising under a light throttle & vacuum is high more timing will help fuel mileage... But when you hit the throttle vacuum falls & the vacuum controlled advance falls out...

Mechanical advance is tied to RPMs & the total needs to be limited around 35-36  maybe even 38 degrees....

[Topcat]

Buy the plate and weaker springs that go with it and be done!   

This will set up your mechanical advance to how your engine needs.

http://www.4secondsflat.com/Mopar%20Mechanical%20timing%20limiter%20plate.htm

[Finoke]

Buy the plate and weaker springs that go with it and be done!   

This will set up your mechanical advance to how your engine needs.

http://www.4secondsflat.com/Mopar%20Mechanical%20timing%20limiter%20plate.htm

I bought the plate and when I took my distributor apart I found I didn't need it. The distributor I have is adjustable but the previous owner never adjusted it. He either didn't know it was adjustable or didn't know that it would help his situation. So I made the adjustment using the measurement I took on the plate I bought and applying it to the adjustabliity of my distributor. It worked perfect the first time.

[Finoke]

You can't go that high on mechanical advance, when your cruising under a light throttle & vacuum is high more timing will help fuel mileage... But when you hit the throttle vacuum falls & the vacuum controlled advance falls out...

Mechanical advance is tied to RPMs & the total needs to be limited around 35-36  maybe even 38 degrees....

I always heard that the reason for vacuum advance was for gas milage. Well stated. Thank you. And yes, hitting the throttle drops vacuum. I guess dumping a lot of high vapor pressure gas into a hot engine causes an increase in pressure and a decrease in vacuum.

[HP_Cuda]

 

A bunch of folks don't run vac advance (I don't) cause I really don't care about fuel consumption.

Vac advance really shines at highway speeds.

[Finoke]

A bunch of folks don't run vac advance (I don't) cause I really don't care about fuel consumption.

Vac advance really shines at highway speeds.

That's good to know. At least I can take it out when I want and then make sure I get the vac advance set up before any long trips.