SuzukiSavage.com - Vacumn Gage or Tach ?

Routy

Serious Thumper

Offline

SuzukiSavage.com
Rocks!

Posts: 2280
Winston Oregon
Gender: male

Vacumn Gage or Tach ?
03/17/10 at 07:29:03

My complaint,.....not being able to tell which gear I'm in at higher speeds.
I was going to Tach-o-meter it, but coming from the petcock thread,..I'm now wondering if a vacumn gage wouldn't give the same info,...and maybe much more valuable info.
To me its a matter of knowing how hard the engine is working as to what gear I want to be in while cruising. Judgeing from the value of a vacumn gage on my motor home when driving in the mountains, I really think this mite be the way to go. If I start seeing less than 5 inches of vacumn, its time to grab another gear....period ! If I see 12-15 on the gage, there is no reason not to take her up a gear.

Ever wonder why most pipes turn blue ? Jetting, maybe, but do ya think driving to a vacumn gage would lessen the "blue pipe syndrome" ?

Any comments....ok.

Back to top

Rich
'07 S40 Blvd stocker, except drilled OEM exhaust and white spacer mod...1/2 (.055)

IP Logged

skatnbnc Serious Thumper Offline Spinning Pink Posts: 1286 New Bern NC Gender:	Re: Vacumn Gage or Tach ? Reply #1 - 03/17/10 at 12:18:41 I agree with the issue, because I cannot hear when to change gears once I am on the highway. Vac guage sounds interesting.
Back to top	2006 LS650, HD pipe, Tkat fork brace, elkhide handgrips, badge-free zone, gel seat w/riser, silverblue, the one in FRONT of you, flying the Kings Colours IP Logged

Boule’tard Serious Thumper ModSquad Offline Master of the Obvious Posts: 1620 Austin TX Gender:	Re: Vacumn Gage or Tach ? Reply #2 - 03/17/10 at 12:55:34 Some guy on here rigged up his neutral light to come on when the bike is in 5th gear. I usually just go by sound.. if it's a loud enough BrraaAAAP! time to shift.
Back to top	That which can be destroyed by the truth should be. - P.C. Hodgell IP Logged

Oldnewguy Senior Member Offline thumpin' along! Posts: 369 Upstate NY Gender:	Re: Vacumn Gage or Tach ? Reply #3 - 03/17/10 at 12:57:13 Not much difference between 4th and 5th, about 300 rpm, but the idea sounds interesting. I had a vacuum gauge on my car back in the 50's. It was also supposed to help you drive so that you got better gas mileage. Post it up if you find out more.
Back to top	'96 with Voyager kit, White spacer mod, K&N air filter, HD muffler, solo seat/back rest, hard saddle bags and trunk. IP Logged

Moofed

Full Member
Alliance Member

Offline

...and the engine
just gleams...

Posts: 148
Bloomington, Indiana
Gender: male

Re: Vacumn Gage or Tach ?
Reply #4 - 03/17/10 at 13:42:55

Seems pretty helpful for diagnostics: http://www.secondchancegarage.com/public/186.cfm

Lots of other good info on that site too. My question is would our thumper engine make the needle jump around alot? I mean, a 4+ cylinder engine has a cylinder doing the intake stroke at any given time, right? We do not. I guess another way to ask is, does the petcock diaphragm hold open steadily or does it oscillate open and shut?

Back to top

IP Logged

Charon

Serious Thumper

Offline

Posts: 1811
Harvard, NE
Gender: male

Re: Vacumn Gage or Tach ?
Reply #5 - 03/17/10 at 15:30:49

I have used vacuum gauges on several cars over the years. Last was on a pickup with a 318 V-8. The vacuum gauge needle will jump around even on a V-8, unless you put a "restrictor" in the tube between the manifold and the gauge. The restrictor can be an old carb jet, if you can find a suitable one. I used a small clamp to pinch the tube, and adjusted it until it seemed to work. A large hole makes the gauge jumpy; a hole too small makes it respond too slowly to be useful. Another option might be several feet of small-bore tube, perhaps coiled under the gas tank. The vacuum gauge works nicely for adjusting the idle mixture - adjust for maximum vacuum (minimum manifold pressure).

As far as using it to save gas, I'm not so sure. Keeping vacuum high very simply means not opening the throttle as far - which reduces power. If you drive at highway speed in third gear, the engine will spin quite fast but the throttle will not be far open and the vacuum will be high. Trouble is, maximum engine efficiency happens with a wide-open throttle where intake pumping losses are least. That's why overdrives work - they hold engine speed lower and require larger throttle openings.

Back to top

Eschew obfuscation.

IP Logged

Oldnewguy Senior Member Offline thumpin' along! Posts: 369 Upstate NY Gender:	Re: Vacumn Gage or Tach ? Reply #6 - 03/17/10 at 15:44:10 If I remember right the gauge was used to tell you if you had your foot in it a little too much. The needle would red line. If you accelerated slower it would stay in the green. I am going back 50 years, so I may be "all wet"
Back to top	'96 with Voyager kit, White spacer mod, K&N air filter, HD muffler, solo seat/back rest, hard saddle bags and trunk. IP Logged

Serowbot

YaBB Moderator
ModSquad

Offline

OK.... so what's the
speed of dark?

Posts: 28668
Tucson Az
Gender: male

Re: Vacumn Gage or Tach ?
Reply #7 - 03/17/10 at 16:17:31

Charon wrote on 03/17/10 at 15:30:49:

Trouble is, maximum engine efficiency happens with a wide-open throttle where intake pumping losses are least. That's why overdrives work - they hold engine speed lower and require larger throttle openings.

not sure about that last part.... Undecided

I used to use vacuum gauges in all my cars,... very useful for getting the best gas mileage,,... not so good for a gear indicator...
It would require identical conditions every time to give a repeatable reading.
That includes, headwinds, air density, etc.,...

I try for sixth gear all the time,....
it keeps me humble... Huh

My Geo Metro has a "time to shift" indicator" light... don't know what makes that thing work... I guess it might be vacuum, but it's only good for achieving maximum gas mileage... that's why I haven't installed a vac gauge in this car...

Back to top

Ludicrous Speed !... ... Huh

...

IP Logged

Routy

Serious Thumper

Offline

SuzukiSavage.com
Rocks!

Posts: 2280
Winston Oregon
Gender: male

Re: Vacumn Gage or Tach ?
Reply #8 - 03/17/10 at 16:26:06

Quote:
My question is would our thumper engine make the needle jump around alot?
---------------------------------------
Thats a good question,....I sure never thought about that. But its too late now,...as I thought it was such a great idea, I ran down to Napa, and of course they had every gage imaginable except a simple vacuum gage. But they'll have one at 7am.
And I already fabed the mount from 12ga ss and have it mounted on the bike. I even had a "T" to fit in the vacuum line,.....unless the gage line isn't the same size, then I'll need a reducer "T".
If it works like I hope it will, it saves me buyin a tach, I'll be tickled. I only want to know how hard the motor is working at speed, and that is what a vacuum gage does best. If it is too irratic to be usable, then I blew 30 bucks.
I'll keep posted here,..... maybe even a pic if I'm impressed w/ it Grin

Back to top

Rich
'07 S40 Blvd stocker, except drilled OEM exhaust and white spacer mod...1/2 (.055)

IP Logged

Serowbot

YaBB Moderator
ModSquad

Offline

OK.... so what's the
speed of dark?

Posts: 28668
Tucson Az
Gender: male

Re: Vacumn Gage or Tach ?
Reply #9 - 03/17/10 at 16:27:41

Quote:

My question is would our thumper engine make the needle jump around alot?

I'm guessing a super big yup at low RPM's, steadily decreasing as you increase speed... a reducer jet, like what Charon was talking about would help with that...

Charon Quote:

unless you put a "restrictor" in the tube between the manifold and the gauge. The restrictor can be an old carb jet, if you can find a suitable one.

Useful info, even if it don't work as a shift indicator...
Good luck... Wink

Back to top

Ludicrous Speed !... ... Huh

...

IP Logged

bill67 Serious Thumper Offline old tired Posts: 8517 genoa city wisconsin Gender:	Re: Vacumn Gage or Tach ? Reply #10 - 03/17/10 at 17:13:22 My first car 1949 Chevy had one.You had to have your windshield wipers going to use it,.JOKE if your windshield wipers were going and you step on the gas to much they who stop were ever they were. They were vacuum powered from you engine.Some old timers here will remember that.
Back to top	william h krumpen IP Logged

Routy Serious Thumper Offline SuzukiSavage.com Rocks! Posts: 2280 Winston Oregon Gender:	Re: Vacumn Gage or Tach ? Reply #11 - 03/17/10 at 20:10:38 Hey Bill, I'm not near as old as you, but my first car....55 Ford was superiour to your Chev, in that it had a "double action" fuel/Vacuum pump to keep the wipers going when the pedal was to the medal ! But then, I know you knew that
Back to top	Rich '07 S40 Blvd stocker, except drilled OEM exhaust and white spacer mod...1/2 (.055) IP Logged

Charon

Serious Thumper

Offline

Posts: 1811
Harvard, NE
Gender: male

Re: Vacumn Gage or Tach ?
Reply #12 - 03/17/10 at 20:29:08

My '52 Chevy had vacuum wipers, too. Later on I had a '66 Ford Bronco with vacuum wipers, one on each side. It also had the double diaphragm fuel pump. When you stepped on the throttle the engine vacuum went away, and the wipers would move one "pulse" at a time as the fuel pump diaphragm pulled vacuum. But when you went down a hill, the vacuum wipers really worked well. I used to tell people it had enough power to move the vehicle, or run the wipers, but not both at the same time.

My pickup with the 318 also had an after-market cruise control. Like many cruise controls it used vacuum to open the throttle servo. I found that it needed three inches of vacuum. If I went up a mountain grade, I could watch the cruise "work." It would open the throttle and the vacuum would drop. When the vacuum got down to three inches, the cruise couldn't pull the throttle any harder, and the truck would start to lose speed. I could step on the throttle and maintain speed, depending on how steep the hill was, but the cruise only worked down to three inches.

Back to top

Eschew obfuscation.

IP Logged

Routy

Serious Thumper

Offline

SuzukiSavage.com
Rocks!

Posts: 2280
Winston Oregon
Gender: male

Re: Vacumn Gage or Tach ?
Reply #13 - 03/17/10 at 20:30:23

Charon wrote on 03/17/10 at 15:30:49:

The vacuum gauge needle will jump around even on a V-8, unless you put a "restrictor" in the tube between the manifold and the gauge.

maximum engine efficiency happens with a wide-open throttle where intake pumping losses are least. That's why overdrives work - they hold engine speed lower and require larger throttle openings.

I have used more than a couple Vacuum gauges in past years, and they were all restricted w/ just a little bitty hole in them, and none have ever pulsated on a v-8. I'm only hoping it won't be much more on this thumper.

I'm not sure you fully understand how an overdrive can...but doesn't always give better mileage. A WOT w/ low manifold Vacuum doesn't give better mileage. Lower rpm's while still holding a reasonable manifold vacuum does.

Back to top

Rich
'07 S40 Blvd stocker, except drilled OEM exhaust and white spacer mod...1/2 (.055)

IP Logged

jabman Senior Member Offline Posts: 411 England Gender:	Re: Vacumn Gage or Tach ? Reply #14 - 03/18/10 at 05:14:13 i just fitted one to my vac hose it flicks from nothing to full so fast the needle is a blur more work is needed here it looks
Back to top	93" savage, 177.5 main, 52.5 w/holes 3 turns out , middle circlip, 6" k&n round filter, Dyna muffler, TKAT brace IP Logged