I have the new MSD programmable box in my car, and will be messing with the timing curve shortly. With this unit, you lock the timing on the distributor, and program the curve into the box, so it's basically an electronic way of setting weights and springs.

Specs: 355, stock Edelbrock alum heads, 10.0:1 compression, hydraulic roller cam, 226/234 on a 112, .584 lift, 5-speed manual, 3.90 gears.

I'm thinking a good starting point is 18* at idle, start advance at 1,000 RPM, all at with 34* at 2,500 RPM.

With the 5-speed, I can easily cruise under 2,500 RPM. The distributor itself does not have vacuum advance, but once I get a MAP sensor, I can program a vacuum advance into the box as well.

This is the MSD box I have, if you're not familiar with it. http://www.summitracing.com/parts/msd-6530

 

You are new ground there. The best I can offer is how I got my HEI tuned in. I installed weights to bring in total advance by 2400 with no vacuum advance and 20 degrees base. I jumped in the car along with my distributor wrench, and went for a ride. No ping and is how it still is. 38 degrees total advance and 9.5:1 compression. It just so happens that my highway cruise is at 2400.
Good luck.

 

I run 14 initial and since i run 10 to 1 on iron heads i dont run more than 32 total all in about 3000 rpm. thats what i ran on my 10 to 1 350 this new one i have ready to go we will see.

 

Thanks for the input. I have a feeling the vac advance will be a better tuning aid then the normal curve. With the 5-speed, it probably won't see sub 2,000 RPM speeds very often, except while cruising in 5th. And that's when the vac advance will come into play.

 

Post retracted because of stupidity.

 

Huh? That makes 54 degrees advance.

I hope you're right about your guy because just about every engineer that I've ever talked to had trouble adapting theory to reality.

 

i think he meant 36 all in. I knew I would get this wrong. While I was at his shop he was assembling a Lenco for his son's drag car. Very old school. Hopefully, the motor even runs (doubtful now). You're right the engineering doesn't translate. I should not have listened to him. Never mind.

 

I plan on running 18 base and 18 mechanical, 36 total was best with old combo. With lightest springs on my Mallory magnetic breakerless, all in by 1500 rpm! I just need to find the right allen key to dial back the vacuum advance. Full out, the can puts out nearly 30 degrees.

 

Olds 307 and 403. That sounds too short to run vacuum, as you will have full mechanical and vauum pulling hard on your distributor. I don't even try vacuum as I didn't build this for mileage. I have my mechanical all in at cruise rpm. 2400 and still get 18 MPG. I messed around with vacuum until I was blue in the face, and could never reach a good balance. So if I am sacrificing two MPG, I will remember this the next time I have my foot in the carb. LOL

 

That's what I meant.

 

Does anyone know who carrys and what part number to the 10 degree vac. Adv. Cans. I have read that they where stock units on gm's

 

I am planning 9.6 to 1 with aluminum heads. Should be able to run plenty of timing.

 

Here's a nice write-up on vacuum advances, which includes a list of specs and NAPA numbers of available units.

- Eric

 

eric you da man !!!!! thats a great article. and very good source for those vac. cans