I have a HEI with a AR28 vaccum can. How much advance will this give me?

 

The AR28 can supplies 10 degrees of distributor advance@ 9-12 "HG. It starts coming in at between 3-6 "HG of vacuum.

Be aware that the listed 10 degrees of distributor advance is 1/2 (half) of crank degrees so based on what your timing light sees it's actually 20degrees of advance.

 

Is that going to be ok for a total advance of 36 degrees? I am running the gold springs from mr. Gasket. What should I shoot for for initial timing then?

 

I don't know because I don't know how much mechanical advance your distributor has.

What is the total timing when it's all in when you have the vacuum advance disconected and hose plugged?
Whatever that number is you want a can that will add enough vacuum advance to bring the total timing PLUS vacuum advance to between 50-52 degrees.
If your total timing is at 36 degrees than the AR28 that supplies 20 additional degrees of advance will be too much and you will end up with a total plus vacuum advance of 56 degrees.

 

So should I change out my can for one that is lower or should I set total timing at 32 instead of 36?

 

what is your timing set at now? What is your total timing and your initial timing?
Keep in mind that if you bump up your total timing you are also increasing your initial timing. If your motor os completely stock you can go up a little bit on your initial timing but I don't like to go up too much on it on a stock motor. I prefer having an initial timing around 12 degrees and the total timing of 36 degrees than having the correct can to add another 16 degrees.
Motors that are modified, have bigger cams, etc seem to like higher initial timing settings but on a stock motor you don't want to go too much, again usually around 12-14º or so.
If you bump up total timing to 36º it's better for performance but keep an eye on where your initial falls and if it goes too high you will have to change the mechanical curve in the unit to increase the amount of mechanical advance so that you can stay with an initial timing around the 12-14º range and still achieve the 36º total timing.
Once you do that, than you can select a vacuum can that gives you another 16º of advance ( 8º advance spec on the can) such as the AR15 or AR31 can.

If you don't want to deal with that and are willing to sacrifice a bit of performance, than set total timing to 32º and use the AR28 can since that is what you already - no fuss, no mess, you will be done. Set total timing at 32º and go out and drive and enjoy the car.

 

Its a 290hp GM crate engine. I believe the cam is a 222/222 spec. So its a mild performance cam so 12 - 14 would be ok right?

 

yes, 12 - 14º initial would be fine. If it's a performance cam than 16º initial may be fine also. You will know if your initial timing it too high if the car gets difficult to start, especially when it's higher temps.
I don't pretend to know a thing about cams so the specs you supplied really tell me nothing (I haven't had to learn much about cams yet) so I'm not sure how mild or radical that particular cam is.

If you can set total timing at 36º and keep initial timing in that range you will be fine and just pick up the different vacuum can.

 

Set your total to 36 and swap out that vacuum advance control unit with part number VC1838 (stamped "AR12"). The AR12 will give you 14 degrees of vacuum advance, thus limiting your total combined timing (total mechanical plus vacuum) to 50 degrees. You want this total combined number to be less than 54 (preferably less than 52) to avoid the car "bucking" and "jerking" when cruising at elevated rpm and light throttle. The AR 12 will allow you to keep your 36 total for good power without getting into the "jerking zone" during cruise.

 

lars
what manufacterer is your part #1838 vacuum can?
thanks

 

NAPA. But I believe CarQuest and Autozone use the same number with a different letter prefix. All the "cans" are manufactured by Dana Engine Contols.