22 replies to this topic

[rick.spi]

any one know how to fit them... is it a case of a bit of vacuum pipe from the inlet manifold to the gauge (ive got an spi so that would be easily done), or is there more involved...

anyone had experience with them.

ive heard they bounce around like mad, and really look pretty cool lol

thinking of getting matching vacuum, oil pressure and oil temp...

so anyone know about vacuum gauges/ have them fitted???

cheers in advance!

[lrostoke]

I've used the brake servo port on my manifold (non servo car ) , basically just a piece of pipe from the port to the gauge.

[dsgoody]

They do bounce around a fair bit, and a have great amusement factor. I just plumbed mine into the servo line, before the valve thing (not actually sure what its called. Just make sure that you don't have any air leaks as I have had a few times.

[m1tch]

It would help show whats happening with the engine plus it looks cool lol

[dklawson]

I have vacuum gauges on my daily drivers, not for the cool factor but for the fuel factor.

Learn to drive using the vacuum gauge. Try driving in a manor that does NOT allow the needle to bounce wildly around. Also try to drive in a manner that allows you to keep the maximum value on the gauge (with the exception of putting the car in neutral whenever deceleration forces a vacuum reading higher than at idle). If you learn to do these things, if you alter your driving style based on what the gauge is telling you, you will be rewarded with higher gas mileage.

As for how to install them, I don't want to sound like a wet blanket but there have been a couple of lengthy threads on the topic this summer. Please use the Search feature that you'll find at the top right corner of this web page.

[Pooky]

I've got a vacuum gauge and it seems to be overreading. At idle, it sits in the 'Drive' section and at anything like part throttle it buries itself into the 'Poor' section.

I'm using MiniSpares' carb spacers with the vacuum takeoffs on my twin 1 1/4's and the pipe is shared with my Megajolt unit too.

What would cause 'iffy' readings with a vacuum gauge?

[lrostoke]

I've noticed on mine timing not advanced enough makes it read low, plus also tappet clearances if to tight give a low reading.

[Kernal H]

Mine was reading low before I had it rolling roaded. But it's great if you want fuel economy or something to look at. you might be surprised of the difference between 60mph and 70mph in relation to vacuum performance.

[andyapanel]

They are well worth it, if you can interpret them OK. They are excellent for encouraging economy, but can also spot other probs; on my kit car, my vac gauge picked up blocked air bleed tubes on my weber. As far as i can tell, only TIM make them. I would love a Smiths one.

[lrostoke]

http://shop.ebay.co....-All-Categories

[dklawson]

Thanks for the link Irostoke. I had never considered looking on eBay U.K. for the Smiths vacuum gauges. They were never common pieces... even less so over here. When a good one comes up for sale here they will typically sell for around $60.

Certainly there are more sources than just TIM. In my Honda I have an AutoMeter vacuum gauge. In the Mini I've got a VDO. The GT6 had a generic one from R.A.C. (1970s era stuff). Stewart-Warner should also have them. The biggest problem finding them today is they are often combined, dual-purpose instruments sold as "vacuum/boost" gauges for the turbo guys.

Pooky, at idle, a healthy 4-cylinder with a stock cam should be idling with anywhere from 15-20 inches of vacuum. If your gauge is resting in the "normal" or driving range it sounds a bit low. My first thought is that you have a vacuum leak somewhere. However, if that is the cause, don't bother looking for it until you have sorted out all the ignition settings and set the valves as mentioned earlier.

[rick.spi]

cheers for the replys, seems easy to fit so i might go ahead and get one... and there was a smith one on ebay not long ago

and for pooky:

ENGINE STATE VACUUM GAUGE READING INDICATION

Steady idle (800-1200rpm) Gauge steady, 17-22 Normal & healthy

Steady idle (800-1200 rpm) Intermittently drops several needle divisions Sticking valve or broken valve spring

Steady idle (800-1200 rpm) Steady, low reading, 8-14 Small vacuum leak or valve timing off; could have low compression/worn rings (verify with a compression or leakdown test).

Steady idle (800-1200 rpm) Steady, low reading, under 8 Vacuum leak (check brake booster, vacuum lines, etc.)

Idle (800-1200 rpm) Needle drops sharply on a regular rhythm Burnt valve, or a valve with clearance too tight

Idle (800-1200 rpm) Needle drifts up & down, along with rpm drift Mixture off or small vacuum leak

Idle (800-1200rpm) Vacuum gradually drops Excessive exhaust back pressure (plugged muffler or catalytic converter)

Idle (800-1200rpm) Intermittent fluctuation Ignition miss; sticking valve

Idle (800-1200rpm) Steady, above 22 Ignition timing may be too advanced

Open & close throttle quickly Drops to about 2, jumps to about 25 Healthy engine

Open & close throttle quickly Drops to 0, jumps to about 20 May confirm worn rings (especially if idle shows only about
15-20) Verify with a compression or leakdown test.

Edited by rick.spi, 22 July 2009 - 05:20 PM.

[Pooky]

Would the fact that it's twin carbs or there's lots 'using' the low pressure in the intake manifold (vacuum gauge, Megajolt, servo) have any affect?

Thanks for all the advice guys

[dklawson]

Would the fact that it's twin carbs or there's lots 'using' the low pressure in the intake manifold (vacuum gauge, Megajolt, servo) have any affect?

Thanks for all the advice guys

Well... nothing should be "using" the vacuum. The vacuum created by the "sucking in" of the engine should not be allowing airflow in anywhere except through the carb. (i.e. The brake servo will not allow a continuous leak of air into the manifold, nor should any sensor connected to the MegaJolt). Only a leak, or things like weird valve timing or severe wear should cause really low vacuum readings.

See:
http://www.theranger...VacuumLeaks.htm
and
http://www.classictr...cts/vac/uum.htm
and
http://www.centurype...ge-spg-148.html

[daemonchild]

Doug, just so you know: I always book mark your links.
Cheers!