Vacuum

[Bosheff]

How much vacuum should a healthy, stock FL/FLH pan or shovel produce at idle?....bosheff

[NightShift]

Dear Bosheff,
Is idle 1000 RPM? You got a tach? Where are you tapping in at and how you doing it? The manifold or the breather or the breather gear or your wallet?
Really curious what your trying but I only got good vacuum numbers for the last one,

Sorry,

[Bosheff]

Just a thought I been hung up on fer a while. A vacuum guage is probably one of the best and least expensive diagnostic tools ever devised for monitoring the condition of internal engine components. There isn't to much a vacuum guage won't tell ya if ya know how to read it. Why not on an H-D mill? Most automotive internal combustion engines have basic perimeters, give or take, to give ya a starting point to work from, when using a vacuum guage to do diagnostic troubleshooting. Ya gotta have a baseline to start from, so that's where my original question came from. I would think the best place to source the vacuum would be the intake manifold. A small nipple should suffice. Am I thinkin rationally, or is my head up my butt?....bosheff

[NightShift]

Dear Bosheff,
Your right the first thing to do is ask about a base line. But anybody whos done such things was either playing with a monster motor or burnt up from the air leak or both.
LOTS of old manifolds got drilled for gauges like this.

MTRPEAKR.jpg (57.81 KiB) Viewed 1238 times

Where did cars hook up?

[Bosheff]

Upon further thought, as I remember the early Evolutions engine had what was called a V.O.E.S. (vacuum operated electronic switch), for retarding the timing to help eliminate pre ignition. These switches were in fact adjustable. I guess I'll have to dig up some of my old reference material as it should have the specs where these switches operated, therefore giving me some idea as to the answer of my original question. Vacuum guages are also quite useful in manitoring engine mileage and were even installed in some autos as an option to tell drivers when they were gettin good or bad fuel mileage. Nice vacuum guage, Shifty. And I thought I had some over the hill tools....bosheff

[51Hog]

Bosheff--
Never heard of the mileage indicator application before.
I assume that the heavier the foot, (More Load) the less vacuum indicated, and the poorer the mileage?
I still get confused trying to remember the different needle indications while hooked up to an auto engine. Still need to use my cheat sheet.
Dale

[fourthgear]

I think you will find that multible cyl. V-8 & V 6 type motors & the like, will have a much cleaner vacuum reading @ idle to go by . The HD motor will be all over the place @ idle & may not be useful for diagnostics.
Give it a try ,maybe you will have better luck than I did many ,many years ago .

I know the VOES was for fuel shut off until you got engine vacuum to open the fuel valve ,so the " E " part must be for like you said , timing .

You will show vacuum , this I know ,but useful , not sure .

[FlatHeadSix]

wow, this topic is a real time-machine, it instantly took me back to the sixties.

Every auto parts store and mail order outfit like J.C. Whitney (Warshanski? Warshafski?, jump in here Rick and tell me the name of that place on south Archer Ave) sold an under dash add-on vacuum guage. They usually were advertised as a Mileage Meter with Red, Amber, and Green zones to indicate when you were getting the best gas mileage, just like the picture Cotten posted above, the higher the vacuum reading was the better your fuel economy was. We all thought they were cool and installed one. They usually connected to a fitting already present on the intake manifold intended for vacuum wipers or distributor advance, you just added a "T" and hooked it up. If they were good for anything at all they made you more aware of how far you had your foot into the carb, they just taught you not to "floor" it because the wider the throttle plate was open the less vacuum you had, and it bottomed out in the "Red" zone. Nobody cared back then anyway, gas was two-bits a gallon. When you were smoking those bias-ply tires with that 327 you weren't too concerned about fuel economy.

I think the best application for a vacuum guage was for setting the idle air adjustment, you could watch the vacuum guage while turning the idle needle in or out and set it for max vacuum. A "perfect" vacuum is measured as 30" of mercury, most of those guages had dual scales: psi and inches of mercury, but the objective was to get as much vacuum as you could.

I'm really not helping much here, just rambling a bit, but I would have to agree that trying to use a vacuum meter on a 2 cylinder engine would not be quite as effective as using it for the same purpose on a multiple cylinder engine.

mike

[duoglide58]

I remember renting a U-Haul truck in the early 80's that had a vacuum gauge as an economy gauge. If I recall it had a large amber light that lit up when you were driving under high vacuum conditions. It was the first time that I drove a vehicle equiped with such a guage.
Besides not having a place to hook up the vacuum gauge, I have always assumed that the vac on a V-twin would have too much swing in it to be useful.
Doug

[Bosheff]

I whole heartedly agree with everybody that posted. I had a buddy that had a 77 Chevy Impala 2 dr hardtop (the only year and model to have a squared off rear window), and his came from the factory with the vacuum gauge, though it had a different name on the option sheet. It was part of the speedo face. I guess a bit more investigation is needed. Theory is theory. Quite possibly a waste of time, hopefully useful....bosheff

[55PAN]

Mike,

You were close on JC Whitney's old name, it was Warshawsky. Back when I was a teenager I went there to buy some "cool" parts for the Honda 350 I had then.
As far as the vacuum gauge goes I have an old one in my '67 Chevelle.

Bruce

[Bosheff]

67 Chevelles, bias ply tires, J.C. Whitney, 327's, Warshawsky, quarter a gallon gasorine. Don't forget the $2 whores, the 5 cent cigar, ma and pa beer stores, and the $350 ride em home pretty much stock panheads. Life weren't all bad back then....bosheff

[Panacea]

As I recall the VOES switch prevents the ignition from fully advancing until pre set vacuum level is reached. It's supposed to help prevent pinging. I'm sure everyone was wondering....Mike

[FlatHeadSix]

Bosheff--
I assume that the heavier the foot, (More Load) the less vacuum indicated, and the poorer the mileage?
Dale

That's exactly how they worked Dale, when you had your foot in it the vacuum went to zero, bottomed out in the "red" zone, when you were coasting downhill with your foot completely off the pedal it maxed out at 30" in the "green" zone.

All my old Studebakers all had TriCo vacuum windshield wipers and they worked just like a vacuum guage, when you were going uphill the wipers would slow to a crawl (or stop completely), when you took your foot off the gas they would FLY! Electric wiper motors were one of the best automotive inventions that ever hit the market.

Bosheff is right, those vacuum guages are a great diagnostic tool and they used to include one in all the high-dollar Sun Tune-Up kits along with an analog Tach/Dwell meter. They would tell you in a hurry if you had a burnt intake valve or manifold leak. And, as I mentioned earlier, you could precision tune the idle air mixture by reading the guage as you adjusted the needle.

sorry, went back in time there again for a minute....

mike

[FlatHeadSix]

Don't forget the $2 whores

I would put those in the same category as a $2 steak, they were usually pretty tough!

mike