3x2 vacuum can with full time vacuum

[Mike R.]

I have read the archives and it looks like the B20/26 VAC is recommended for BB (L89) The current VAC is a 201 which isn't doing much at idle.

Is the B20/36 the best fit for a L89 automatic with full time vacuum?

[Rich G.]

Re: 3x2 vacuum can with full time vacuum

As per Duke who just helped me on a different engine, the B20 or B26 will be all in at 12.5 inches of vacuum. According to Duke, that would be appropriate for a motor that had an idle vacuum of 14.5 inches. Check your idle vacuum and find a can that is all in at 2 inches less than that.

Rich

[Richard M.]

Re: 3x2 vacuum can with full time vacuum

Mike, I used the Napa VC1765 B26 can on the '67 L71 3x2 I redid a few months ago. Yes the 2" rule worked for me and the B26 was the correct choice. I used full time vacuum. There's much info starting at around post#22 in this thread.

https://www.forums.ncrs.org/showthre...83918&uid=6112

Post#30 has some test results on the MS163, MS201, and the Napa B20 advance cans.

Rich

[Timothy B.]

Re: 3x2 vacuum can with full time vacuum

My experence is that full manifold vacuum advance is good for tuning high performance engines. Be careful that you don't give the motor to much timing at idle to where the throttle plates are closed down to far for the idle rpm the engine is happy with.

Distributors and carburetors kind of work together but the distributor tuning is first, 12* to 15* vacuum advance is all that's needed. The lower performance engines like the 300hp only need 4 to 10* inital timing along with the vacuum advance to provide approx 20* total idle timing. If the throttle plates are closed down to far because of to efficent idle timing, after the emulsion screws are adjusted the mixture may go lean when the plates are opened.

It's a balancing act and this is my observation so be careful with to much idle timing.

[Mike R.]

Re: 3x2 vacuum can with full time vacuum

Thanks to all. I will buy the VC1765 B26 can and give that a try.

Mike

[Duke W.]

Re: 3x2 vacuum can with full time vacuum

I'm not sure. The B20/26 is a good match for L71/89 with a MANUAL transmission that pulls about 14" at 900. However, with an auto the idle speed/vacuum will likely be lower. Measure your idle vacuum in Drive and use the Two-Inch Rule.

If the B20/26 doesn't meet The Rule, use the B28.

Duke