Big Block Distributor Question

[HawkX66]

Those of you with a 396/402, what are you running for a vacuum advance can? B26 or B28? I have an 1111498 distributor with a B26, but I've been told I should be looking for a B28 for my spare motor that I'm running. I converted a 1111500 distributor with a Pertronix III, but I need a new a new vacuum can for it.

[L78steve]

The B28 is a low vacuum can. So any solid lifter or rad. cam Chevy should use it.
It will start to pull in at 4 and be all in at 8in Hg.
You want it all in at idle.

[novadude]

Yup. Depends on the cam. If you have a L34 or a mild aftermarket cam, stick with the B26. I don't 100% agree with full manifold source to the can in ALL applications. If the idle circuit in the carb is correct, you don't need a boatload of advance at idle. Also, make sure you are limiting the can to 10-14 deg of timing. Some replacement cans allow a lot more.

I have a 9.6:1 355 with a 217/225 deg @ 0.050 cam on a 108 LSA (104 ICL), and a B26 can works well for me connected to a ported source (no vacuum advance at idle - 12 degrees initial advance). You'll need to give us more info about the 396 if you want better advice on the right can.

[L78steve]

Yup,novadude. The one drawback with full Vac. to the Dist. is when you crank the wheel with P/S and or let out the clutch the RPM drops, so does the Vac advance and you go into a stall or bucking mode.
Without full Vac.(Ported) mode you have a stronger idle and in most cases you can just let out the clutch without feathering the throttle much.

[Plowman]

I like full manifold vacuum to the Vacuum Advance. I don't run any more than 10 deg max Vacuum Advance,depends on cam and stuff. Ported vacuum advance was made for Emissions.

[HawkX66]

Thanks for all the input guys. The engine I'm running is a 1972 402 with truck heads. I have my born with motor stored for now. From what the guy I bought the motor from told me, it has a mild cam and no head work. It's been rebuilt with a/m pistons which I confirmed when I pulled the pan, but I think they're just stock compression replacements. It's real clean and looks good inside, but I'm not expecting that much performance out of it.
I'm running a Holley 3310-3 that I just rebuilt. I was planning on hooking the vacuum advance to a small port on the base plate of the Holley. I'm not quite up on the full ported vacuum vs. manifold vacuum etc. I know enough about advance to be dangerous, but that's about it. I'm planning on making an advance limit block for it though.

Here she is:

[earntaz]

Simple -- hook the vac to a full vac port ... if the engine has a rough idle and you disconnect the vac and it smooths out, you may need to connect to a ported vac source. That is the bottom line. We can beat this horse to hell all day long and opinions are varied. I have connected vac both ways depending on the motor combination. There is no rule one way or another -- try em' both to see what works best on you application. TAZ

[HawkX66]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: earntaz</div><div class="ubbcode-body">Simple -- hook the vac to a full vac port ... if the engine has a rough idle and you disconnect the vac and it smooths out, you may need to connect to a ported vac source. That is the bottom line. We can beat this horse to hell all day long and opinions are varied. I have connected vac both ways depending on the motor combination. There is no rule one way or another -- try em' both to see what works best on you application. TAZ </div></div>
Thanks Taz. That makes sense. Buying the right can was the big question for me. It sounds like opinions are pretty split there too.

[earntaz]

Not a bad looking motor either ...

[HawkX66]

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: earntaz</div><div class="ubbcode-body">Not a bad looking motor either ... </div></div> Thanks Taz. I'm just finishing up going through it. I painted it with Seymour EN48 paint. I'm real happy with how it came out. I still have a few more details to take care of, but I'm just about ready to fire it. I guess she's a bit of a polished turd, but she's my turd...

This is how she started out and ended up: