How to use vacuum gauge for FE?

[theholycow]

My Buick is meant to be connected to two vacuum sources, through a modulator device. This guy:
http://www.corvetteactioncenter.com/...m-advance.html
makes a great case for connecting it directly to manifold vacuum.

[22over7]

thc, that's a really interesting article.
I know nothing about American cars, so I have to accept that this guy knows what he's talking about.
The big plus here, is that it's an easy mod to make - and easily changed back if it isn't to your liking (that is a performance orientated site and they have different objectives than we do).

Good luck,
Pete.

[GasSavers_Erik]

My vote is for manifold vacuum advance for fuel economy. The 85-87 Honda CRX HF's were carbed and all used manifold vacuum for advance.

[theholycow]

I'm going to try both the one that I think is ported vacuum (which was previously one of the two simultaneously in use for it) and good manifold vacuum.

I may do some A-B-A if they both drive well but I suspect that ported is going to run badly.

[Porscheman912]

I might be new here, but I have run Vac gauges for years, on my bikes, and muscle cars. The vac gauge needs to be on the manifold, below the butterfly to get the right readings. I know my old 67 Pontiac would idle @ 17, and as soon as you get into it, it would drop. Whether injected or Carbed, it will do the same thing.
Now with your car, it sound like the is a check valve or diaphram where you have it hooked up no. You need to have it hooked direct to the manifold to get the right readings. I use them on my Motorcycles, to make sure the carbs were Sync'ed. Good luck
The FNG

[theholycow]

Good news, everyone!

I moved the distributor advance to ported vacuum and the vacuum gauge to manifold vacuum (as reported in more detail in my spark plug thread).

Now:
- the vacuum gauge works right
- idle is partially better (down to 1000RPM)
- no spark knock!

My driving style was pretty close to good. I need to go easier immediately after shifting gears, and there's a couple hills I maybe should climb in a lower gear.

[FrugalFloyd]

Yahoo!

[Ford Man]

Originally Posted by theholycow

Good news, everyone!

I moved the distributor advance to ported vacuum and the vacuum gauge to manifold vacuum (as reported in more detail in my spark plug thread).

Now:
- the vacuum gauge works right
- idle is partially better (down to 1000RPM)
- no spark knock!

My driving style was pretty close to good. I need to go easier immediately after shifting gears, and there's a couple hills I maybe should climb in a lower gear.

As long as you're not lugging the engine on the hills you'll be more efficient climbing them in the higher gear at lower vacuum readings. I've verified this with the use of the Scan Gauge in my '97 Escort. I've also noticed in my '88 Escort that after I get to highway speed I can back out of the accelerator slightly raising engine vacuum and not losing speed for a pretty good distance.

[22over7]

Congratulations!
I suppose I'll have to add this to my "must try" list.

[theholycow]

Originally Posted by Ford Man

As long as you're not lugging the engine on the hills you'll be more efficient climbing them in the higher gear at lower vacuum readings. I've verified this with the use of the Scan Gauge in my '97 Escort. I've also noticed in my '88 Escort that after I get to highway speed I can back out of the accelerator slightly raising engine vacuum and not losing speed for a pretty good distance.

Thanks, I was going to ask about that...there are situations where I'm not sure whether low RPM at low vacuum and presumably rich mixture is worse than higher RPM with higher vacuum.

Turns out there's also a lot of times when the engine is struggling and bogging and vacuum is marginal, but downshifting makes vacuum drop even more...you gotta really lay into it to get this engine to higher RPM.