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..
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.
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.
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.
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.
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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.
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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.
[...]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.
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Last edited by tasdrouille; 03-31-2008 at 08:52 AM.
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...
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.
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..
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.
I think the goal is to never operate at light loads.
To add to what Metro has already said... For highest thermal efficiency - that statement is true... But engines are over sized for that sort of driving. If I operated my engine at peak load all the time, two things would happen
1. I'd get a helluva lot of speeding tickets
2. I'd drastically reduce the operating hours of my engine
It is because the drive train is so big that lower thermal efficiency (lower brake specific fuel consumption) can lead to lower specific fuel consumption.
If I had a 20hp engine in there - it'd be much easier to operate at peak load all the time and maintain a legal speed But, operating a 20hp engine near 20hp for it's entire life will reduce it's service life. The gentleman from wrightspeed motors claimed that your typical car has about a 5,000 engine life. But, that's because these engine live at lower rpm and at low loads for most of their lives....
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you guys are killing me with these abbreviations..
BSFC ? doesn't take that much more to type it out, stop being lazy..
Hypermilers like abbreviations I don't know why - but it has allowed the term CODFISH to exist Goofy
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Challenge me, or correct me, but don't ask me to die quietly.
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 15mpg to 20mpg using a few tricks I posted on my fuel log on CustomTacos..
Fixed it
Here and reporting for duty. Just ordered the Vacuum gauge.
FE??? I concur with Chris D. Too many abbreviations
If lower vacuum is seen for a given speed then you know the WAI is working as pumping losses are being reduced.
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I think the goal is to never operate at light loads.
So I'm so confused right now, I thought that you want high vacuum for better efficiency, not to lower the vacuum. And I also thought that you want to lessen the load, which is where weight-reduction and driving slower to make aerodynamic drag lower come in.
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Yea.. I drive a Jeep and I'm on a fuel economy site, but you just wouldn't understand... "It's a Jeep thing!" *Jeep Wave*
in regard to the efficiency of a WOT(wide open throttle) sweep, i am of the opinion, that the most efficiency throttle opening should be vacuum controlled (or ECU) like the secondaries on the old quadajet carb. especially on carb engines.
Fly by vacuum or fly by wire.
The pedal would allow the throttle to open if there was a little vacuum present(high velocity). refering back to post 4. the part where i want the engine to "catchup" with the throttle opening.
I am thinking that all the BSFC(brake specfic fuel comsumption, i think) curves are based on a controlled sweep or even steady state points.
So i am suspicious that a WOT sweep is the most efficient.
Another way of saying it is, the most throttle it will take without getting into fuel enrichment.(old term but still programmed in many fuel maps) In a previous life, i ran an engine test cell and what i observed (although i was not testing for it specifically) was, that, as the engine vacuum dropped to zero in of Hg, opening the throttle all the way up to WOT did not increase the efficiency. (Some engines went into enrichment at 5 in of Hg.) As engine management advanced in the 90's this became less of an issue because the ECU was doing this "feathering" for you. But for a carb'd engine, i don't think you want to get too far ahead of the engine RPM. Now with VVT variable valve timing, lean burn, high swirl HS, fly by wire and all the rest the ECU is able to dial in much closer to the optimal mixture. On the new engines the exhaust temperature would peak when the ECU found the best mixture for each RPM. What is the best way to determine if the ECU is keeping up with the sweep rate?, i don't know. Wide band o2? If it stays in closed loop and vacuum is close to zero? But i think i am close to optimal if i can just see a little vacuum left on the gage as i sweep. BTW.by the way. The highest ex. temp. i ever recorded was 1850 F on a modular truck engine with aluminum heads
So to make a long story short, i couldn't say that a WOT sweep is the best for most engines. Nor would i say that WAI is best for most engines. I think it depends on how technically advanced or retarded the engine management system is.
Last edited by diesel_john; 04-01-2008 at 01:45 AM.
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.
Sorry for getting a bit impractical...I just didn't want everyone to get the idea vacuum in and of itself is a good thing. I think too many questions are best answered with, "It depends...".
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Originally Posted by trebuchet03
To add to what Metro has already said... For highest thermal efficiency - that statement is true... But engines are over sized for that sort of driving. If I operated my engine at peak load all the time, two things would happen
1. I'd get a helluva lot of speeding tickets
2. I'd drastically reduce the operating hours of my engine
It is because the drive train is so big that lower thermal efficiency (lower brake specific fuel consumption) can lead to lower specific fuel consumption.
If I had a 20hp engine in there - it'd be much easier to operate at peak load all the time and maintain a legal speed But, operating a 20hp engine near 20hp for it's entire life will reduce it's service life. The gentleman from wrightspeed motors claimed that your typical car has about a 5,000 engine life. But, that's because these engine live at lower rpm and at low loads for most of their lives....
Very true points. I was thinking about doing the opposite of driving at the engine's peak efficiency...lower the peak efficiency to suit a particular driving style. I think that is the idea of the WAI, lean burn, EGR, etc. and definately applicable by more mechanically inclined members of this forum. Just another (tough) potential avenue for fuel economy...
As far as engine longevity, I would think some technology could help. SiC ceramic coatings on F1 engines are used to lower friction, increase cylinder wall hardness, and increase engine longevity. Supposedly, honing the bores is nearly as tough as cutting diamonds... Ofcourse, this is getting a bit fanciful...but not impossible.
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Hypermilers like abbreviations I don't know why - but it has allowed the term CODFISH to exist Goofy
Reminds me of the military.
Hmm, maybe we should name this the S.W.O.R.D.F.I.S.H. - the Super Wombat ORgan Dynamo for InFormatIon Subsystem's Headquarters.
Nothing like a good backronym...I wonder if the military has a whole department dedicated to that field.
I may be wrong but I think diesel cars cruise control works so much better than gassers. (More torque) Uphill at highway speeds the RPM does not change much from flat road.
Here is an example of where you want that gauge to read during a regular cruise..........
I do not use my gauge during accel only when at cruising speed. From there, I use the gauge to maintain 10-15 on the gauge. If I see the needle dropping below 10, then I am going up a hill or giving too much throttle. The readings from a manual vacuum gauge are instant and will help you control throttle output and save gas just like a Scangauge would.
. 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.
Goofy 
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