Any advice for driving by vacuum guage? video

[Chris D.]

I made a little video of whats I do when driving by vacuum guage..

Could anyone give me some fine tuning pointer tips for driving with this instrumentation?
also, can someone define what driving with load means?
Im not sure if I understand that one..

yes, I want a sg, but money permitting..

heres the video.. opinions please..
If I get some killer tips, i'll make a new video..
I just want to help others that want to save..

www.youtube.com/watch?v=MBYVZLRyQjk

[bhazard]

The shadow generally holds 10-15 inches of vac at cruise, depending. 18 seems really good. My engines do 18-20 at idle. Of course, every engine varies, especially ones that are 20 years old and turbocharged.

[LostCause]

Awesome video...I hope we get more driving technique videos put up on this site.

Vacuum gauges are a tricky subject for me. High vacuum indicates low throttle load which should mean low fuel consumption, but engine's operate at their lowest efficiency under low load...trying for high vacuum seems like rooting for the bad guy.

I think the gauge would be very helpful in determining the value of a WAI (warm air intake). A WAI will lower charge density, causing a decrease in power, forcing a wider throttle opening. If lower vacuum is seen for a given speed then you know the WAI is working as pumping losses are being reduced. Other mods like opening up the air box might be quantified also.

I'm not sure how load is calculated, but I believe it has something to do with torque. Essentially, it represents the force being placed on the engine. Engine's operate at a higher efficiency when producing high torque, so driving with load seeks to maximize the time the engine is in this band.

- LostCause

[diesel_john]

i have a mileage computer but still use a vacuum gage when i am adjusting the pedal because vacuum is more instantaneous. i can see how fast i am moving the pedal on the vacuum gage. And i can go right to the vacuum that i know will sustain my speed. Also when i am driving up and down hills i can see when i am going over the top better. by driving constant vacuum i can speed up going down the hills and let off going up. i can also do things like avoid downshifts and fuel enrichment. i try not to ever go to zero vacuum. because that means i have the throttle open further than the engine can take. by always showing some vacuum i can gage how fast the engine is responding.

[MetroMPG]

Originally Posted by Chris D.

can someone define what driving with load means?

DWL is essentially keeping the vacuum needle stationary, and adjusting your throttle to accomplish this. That means you'd be letting up going up hill and permitting your speed to drop & gradually regaining it on the down grade as you give it more pedal. It's the exact opposite of what your cruise control was doing, which is why you can outperform it.

yes, I want a sg, but money permitting..

You spent more on your new tonneau than a used SG would cost. Guess which one I would have recommended as the best way to improve your overall MPG?

Just buggin' ya. The vac gauge will help with your DWL.

Originally Posted by LostCause

High vacuum indicates low throttle load which should mean low fuel consumption, but engine's operate at their lowest efficiency under low load...trying for high vacuum seems like rooting for the bad guy.

That's a mixed up perception that I see often. High vacuum at cruise is definitely the good guy.

There's a difference between lowest fuel consumption and best engine efficiency. With a typical engine at light loads, you'll probably get your best MPG well outside of your engine's best efficiency (BSFC) area.

[tasdrouille]

Originally Posted by MetroMPG

[...]High vacuum at cruise is definitely the good guy.

There's a difference between lowest fuel consumption and best engine efficiency. With a typical engine at light loads, you'll probably get your best MPG well outside of your engine's best efficiency (BSFC) area.

Exactly!

Chapter 2 of this pdf is quite interesting. The distance specific fuel consumption map on page 14 is particularly relevant to steady state FE.

BSFC is most usefull to know when accelerating, but when crusing on the highway it's DSFC you should be concerned about.

[LostCause]

Originally Posted by MetroMPG

That's a mixed up perception that I see often. High vacuum at cruise is definitely the good guy.

There's a difference between lowest fuel consumption and best engine efficiency. With a typical engine at light loads, you'll probably get your best MPG well outside of your engine's best efficiency (BSFC) area.

I think the goal is to never operate at light loads.

I like analogies, so here's one about a business.... During busy times (acceleration) a business operates efficiently by working its vast group of employees hard. During low times (cruise) it works efficienctly be cutting its workforce and working the remaining team hard...not by spreading the meager workload.

A small engine operating at its BSFC and sized perfectly for cruise will outperform an oversized engine running high vacuum.

The reason I stand behind this notion is that you can see the automotive industry heading that way...small "undersized" engines that use turbochargers, electric assist motors (aka hybrids), turbocompounding (scania diesels), ethanol injection (MIT research), or just plain neutering (Metro Xfi, CRX HF) to gain fuel economy.

Why does Honda use lean burn, why did BMW try to replace the throttle body with VVT, and what is the value of a WAI? I think vacuum is a pure loss that serves nothing more than an indicator of engine load. I'm willing to be convinced, though...

- LostCause

[MetroMPG]

Originally Posted by LostCause

I think the goal is to never operate at light loads.

True enough. A smaller engine or P&G would improve his MPG, no doubt.

But let's keep this in context. Chris was just asking for advice on what to do with his current setup, at cruise, (my interpretation) to achieve the best efficiency.

[Chris D.]

Heres another spin, I had almost 250 miles and only used 1/3 of the tank..

I found a rig that had a steady rate of speed and followed him for a solid 50+ miles..
I was going for a record till he branched off and the directions called for going into the mountains..

Which is better when going up mountains?
I know economy really goes out the window on this one, but I figure I'd throw this out there..

higher rpm's with high vac #'s or lower rpm's with lower vac #'s?

I just had to ignore the vac guage because it was a bit painfull watch lol

I still pulled just shy of 30mpg when I filled up.. I even went offroading a bit with my truck club.. I have quite a few 4x4 guys in my club shooting for FE reguardless of their trucks setup, one guy (not on here yet0 went from 16mpg to 20mpg using a few tricks I posted on my fuel log on CustomTacos..

As for that tonneau cover, most definatly costing me more than a used GS, but at the same time, this is something I've had in my head to do for a few years..


I'll jump on a group buy on XrunnerUnderground.com (another Tacoma site)
I want the X guage version..

I dont use cruise control as much anymore unless its a nice flat curface or if I have a case of the leg cramps

As for Bhazzard's Shadow ES 2.5 turbo, If I'm able to pull 28mpg out of my Shelby GLHS that was boosted upto a consistant 12.3 in the quarter mile, you could definatly get 25mpg all day long..

If you hook the vac line from the wastegate to the intake, your sitting at no more than 7psi.. I used this technique for break in period..

I was BIG into the 2.2/2.5 cars..

30hp for 12 bucks!

you guys are killing me with these abbreviations..
BSFC ? doesn't take that much more to type it out, stop being lazy..

[bhazard]

I think the main problem with the shadows mpg right now is that it has a bent strut from the PO smacking a curb, the camber and alignment are pretty well off at this point and you have to hold the wheel cockeyed to go straight. Gonna pick up a pair of new struts tomorrow and hopefully get it aligned sometime soon after. We just got 26.3 mpg on a fillup though, but hoping to improve on that. The non overdrive trans doesnt help too much but its still not too bad considering. We got 30 mpg driving 60-70mph to WV in early Feb.

Ive also redone every single vacuum line in the car and simplified the vac system. Ive currently got a homemade manual boost controller on it, though it rarely even sees the boost at this point.