Best vacuum advance for stock 1970 L48

[Rich D.]

Hi, folks. I know this subject has been covered extensively in other threads, but I'm still not sure I have my answer, so here goes.

Which currently available vacuum advance control would be the best match for my 1970 L48?

My car's TCS system is intact and completely functional, and I drive the car frequently.

Right now I'm running a repro vac adv. that's supposed to deliver 12 deg @ 12".

At this writing, I haven't checked/verified the cent. advance, but I plan to get it as close to stock specs as possible when I change the advance.

Thanks.

[Joe L.]

Re: Best vacuum advance for stock 1970 L48

Hi, folks. I know this subject has been covered extensively in other threads, but I'm still not sure I have my answer, so here goes.

Which currently available vacuum advance control would be the best match for my 1970 L48?

My car's TCS system is intact and completely functional, and I drive the car frequently.

Right now I'm running a repro vac adv. that's supposed to deliver 12 deg @ 12".

At this writing, I haven't checked/verified the cent. advance, but I plan to get it as close to stock specs as possible when I change the advance.

Thanks.

Rich------


The original vacuum control for your application was the GM #1115357. This vacuum control has the following specs:

7"-9" Hg to start the plunger

20-21 crankshaft degrees advance @ 16-18" Hg vacuum

I don't recommend using this vacuum control, though. So, what would I use? Well, considering that you want to maintain the TCS system and, perhaps, original ported vacuum signal, I really don't know what I'd use. Maybe Duke will have some ideas.

[Duke W.]

Re: Best vacuum advance for stock 1970 L48

If you wish to retain the OE ported vacuum advance/TCS the OE specs are fine.

My recommendation is that you convert to full time vacuum advance and bypass the TCS.

In this case my recommendation depends on whether the trans is manual or auto.

I have stated my recommendations for various OE non-emission controlled engines many times, including within the last week or so, and my recommendations are valid for emission controlled engines that are converted to full time vacuum advance. Use the recommendation for the antecedent non-emission controlled engine. The non-emission controlled antecedent for all base 350 engines to '79 is the 327/300.

Duke

[Rich D.]

Re: Best vacuum advance for stock 1970 L48

Joe and Duke: First of all, thanks for the quick responses. I guess I should have mentioned that the trans is manual. Also, the engine is stock, with the exception of being .030 overbored.

I would like to maintain the stock TCS (it cost me enough money and aggravation locating all the components years ago, plus I'm not an NCRS member for no reason ). If I want to do this, which of the currently available vac adv. cans would be closest to stock?

Like I said, I currently run the 12 deg @ 12" can, and have no idea what the cent. adv. curve looks like. I run premium pump unleaded, and get minor pinging only if I lug it through 3rd and 4th gears (which I know I shouldn't do anyway).

Maybe I should just leave well-enough alone??

[Patrick H.]

Re: Best vacuum advance for stock 1970 L48

Rich,

I have converted my 71 distributor to Duke's recommendation of "1965 SHP specs" by having Bill Clupper rebuild and recurve it. I switched vacuum advance as well to the one recommended by Duke, and it runs VERY well. I usually run with the TCS system bypassed, but it's easy enough to plug in the original configuration vacuum lines and use the TCS for judging should I ever require. I also have a couple of original vacuum advance cans to use for judging if needed. The original advance springs are set aside in case I'd ever need them.

So, you can have a better operating 71 and have an operating TCS system - when you want to.

Patrick

[Rich D.]

Re: Best vacuum advance for stock 1970 L48

Thanks for all the input, gentlemen. After further consideration, I figure its just best to leave things as they are for now and concentrate on finishing my other suspension/drivetrain/interior jobs.