There have been all kinds of posts about vacuum and vacuum leaks...my question is do you ever put a vacuum gauge on an RX-7 to actually measure what the vacuum is? I remember as a kid we used to set our engine timing with a vacuum gauge to max out the vacuum reading. Is the actual vacuum reading of any use to rotary owners?

 

I find that my vacuum gauge is probably the most useful gauge on the car. You can easily tell an engine's general health by how much vacuum it pulls (a good non-ported engine should pull 17" or so at idle), and driving under the highest vacuum reading is a great way to save fuel...Yes, you can also tell if you have a vacuum leak...

 

Well, I'll go ahead & ask then...

How does one effectively use a vacuum gauge for driving at optimum efficiency? I expect it provides information along the lines of "Downshift, you idiot!" when running high throttle settings at low RPM, but what specifically is one looking for?

-=Russ=-

 

Pretty much anyone that has a boost gauge, has a vacuum gauge. Majority of them read both boost and vacuum. I personally do pay attention to them.

 

You can use a combination of the A/F gauge and your vacuum gauge to save gas. It's fairly easy actually. Drive in the gear highest gear that keeps you under about 4K on the tach and with the highest vacuum reading (more vacuum). You should also keep the ECU in closed loop, which you can easily find by looking at the A/F gauge (it should rapidly bounce between full lean and full rich).

 

Hm. I suppose I'll be adding gauges to my car soon.

-=Russ=-

 

Update to the vacuum question. I went home and put a vacuum gauge on my '91 N/A. At idle the reading was a steady 17". For older piston engines this would be a bit light and might indicate a leak or retarded timing. But, based on Aaron's message, I guess for a rotary it's OK. So no vacuum leaks for me.

 

When I cracked an apex seal a few months back, I could see the vacuum pulse as the bad rotor faces went by the intake.
My J-spec idles at 16".

 

I use it to assist tuning the fuel and timing.

Mine idles around 1000RPM, decent street port w/no aux port actuation (all open), S5, pulls 20inHg @ idle.

 

Or you could just follow the cheesy shift light in S4 cars which will illuminate @ 2600 rpm under light throttle