Terminal F/E; What's yours?!
 

After playing around with my VAFC for a little bit (fine tuning Vtec engagement) I decided to find out what my terminal fuel economy would be using a very simple method... Given that my car runs at 2700 Rpms during cruising speed, I tested the unloaded engine (vehicle stopped, trans in neutral) for fuel consumption in gph and netted approx 45mpg terminal F/E

70mph / 1.55gph = 45mpg

This would be the resultant mpg my Acura would make at a constant 70mpg, flat road, with no rolling resistance, air resistance, or drivetrain losses. Obviously this on its own does relatively no good, but it does allow for a realization of expectations, and will help guide you with the use of EOC, DWL, P&G, DFCO, aero mods, etc. in order to help achieve your goals

So my question is, what's yours?

Does this men your car used 1.55 gph at 2700 rpm, not moving, warmed up, with all accessories switched off? I think that's what you're saying.

If so, try this calculation. Turn the math around and divide gallons by miles. That will tell you how much fuel is being consumed per distance, JUST to keep the engine turning. That is, not considering any useful output from it.

Now compare that number to your actual usual gallons per mile at that cruising speed. For my car, I found a surprisingly high percentage of fuel was used just to spin the mechanicals.

Now, if only you could cover distance without rotating your engine quite so many times. You'd save all that fuel.

Voila. The reason why many of us are big fans of coasting, with the engine idling in neutral or off as appropriate. Every revolution of the engine eliminated is fuel saved. You're better off at 2/3 or 3/4 throttle part time and engine "on vacation" the rest of the time, than you would be driving in a reasonable gear at whatever throttle position would work at that speed.

Using that technique, your terminal mpg isn't terminal at all because you can cover distance on highly reduced fuel use or none at all.

unrealistic of real-world driving conditions.

2700 RPM while not moving is a significantly different situation compared to 2700 RPM while accelerating in any gear, 2700 RPM while holding a speed in any gear and 2700 RPM while engine braking in any gear.

the load placed upon the engine is different in all of those situations.

Yes, that is exactly what I did, netting a Terminal F/E of approx 45mpg at 70mph.


Yes, I understand all this, hence "Terminal."

My point in this thread is that by calculating your completely unloaded engine F/E at a given RPM, is that you CAN NOT exceed (nor by any chance meet) said MPG without the addition of other methods for extending fuel economy.


Was my original post really that hard to understand?

Interesting idea.

I think for me, a more usable figure would be to run it in gear, drive wheels off the ground, at "cruising speed", & see what THAT figure is. (we can actually get "miles covered" that way, too). I know that adds in the drivetrain drag, but how do we realistically reduce that? If you're going to say thin or synthetic oil, etc, etc, ok good. But (to me, again), maybe THAT's the way to test the synthetic oil, etc, etc. - wheels jacked up, running at cruising speed in gear. To me, that removes the aerodynamic and "real life" road variables (wind, grade, traffic, etc), but still leaves in the "real world" drivetrain & wheels turning.

What do you all think of that?

Or am I out in "left field"?

Not at all in left field!... That would be a great way to include the drivetrain losses in the calculation. Unfortunately though, running with the wheels off the ground creates a whole mess on its own... No matter how balanced your tires may be, they will not rotate at such a high rate of speed without excessive hop, as every forgiving tolerance becomes less loaded (bearings, CV's, etc.) If you've ever seen a HMMWV walk itself off of jack stands, you'll know how dangerous this can be!!! O.o

Utilizing a dyno would mitigate these dynamics, but unfortunately we don't all have one in our garage!

So you're cruising at 70? You could save quite a bit if you slowed that down.:turtle:

nbleak21's original post here shares an interesting idea. I and others have gone off on various (interesting?) tangents. That said, nbleak21 deserves credit for the idea.

Whoa! Yeah, "walking off the jackstands" certainly wouldn't be good - especially if you weren't prepared for it. :o

Hmmm... before I go out & do it, I guess I'd better come up with some "safetys"!!

Thanks! :thumbup:

Yessir! Ideally I would gain a few MPG dropping my speed, but most of my commute is interstate, and slow lane speeds avg 65-70mph travelling with the flow of traffic, so generally I find a semi to get some limited draft off of (I don't do the tailgate drafting!)

If you drive 60 or 65 you will find the others that are going that speed.

Also, just ask yourself if those 70 mph people are paying for the gas you need to drive at that speed. I don't think so.

Driving 60mph, I can't stay in lean burn under up hill loads, netting me sometimes as little as 20mpg vs 65-70 where I only drop to a min. 28mpg. Traveling the interstate, I generally pass only 2-3 vehicles (speed limit is 70) in my 60mi commute. Usually those are semi trucks struggling to get up hills, which is the last thing I want to be behind.

Here's mine:

Honda B18B1 engine, B16A transmission (very short)

Idle, 800rpm
0.23G/H

Neutral, 3900rpm
~1.05G/H

70MPH, 3900rpm
~2.2G/H

So even running at 3900rpm I could achieve a theoretical 67MPG at 70mph. Looks like there's a lot of room for improvement aerodynamically in my car.

I once posted to someone on some forum that my first gen 2002 Insight used the same amount of fuel going 40 MPH as his V8 pickup truck did idling. Not sure he got the drift of my meaning. It also looks like you need twice as much fuel to maintain 70 MPH as the engine uses running at the same RPM with no load.

Best testament to higher overall final drive ratio I think I have seen.

I think the last car I owned that revved that high at that speed was an 82 280ZX Turbo with an automatic tranny. Needed a 5 speed badly with a 3.54 rear axle ratio and a .75 OD 5th.

regards
Mech

Crazy thing is, this is a 5 speed. The transmission was originally mated with an engine with a redline of 8200rpm and 2 cam profiles. The gear ratios were close to allow that engine to stay in the upper cam profile (engages at 5400rpm) when accelerating. At all reasonable highway speeds it was still able to cruise in the lower cam profile.

The new engine has a larger displacement (due to much longer stroke), redlines at 6800 and has a very simple head, so this tranny isn't really suited for it. I should've replaced the transmission when I had the engine dropped in but I didn't know much about cars at the time.

nbleak21,
Ahh, Lean Burn Honda powered cars. I spent quite a bit of time figuring mine out.

Mine had a requirement of about 63 mph or better (in fifth gear) for lean burn. That was a minimum of about 2300-2400 rpm. Interstate upgrades would defeat lean burn due to speed lost while climbing.

I use a ScanGauge to monitor engine status: Lean Burn status, load, temperatures. Do you have one?

And I discovered - after 2.5 years of lean burn frustration - that 2 ounces of Marvel Mystery Oil per ten gallons gas enables lean burn down to about 1900 rpm, or about 45-46 mph in fifth gear in my car.

It takes most of a tank before you start seeing clear improvement. After 3-4 tanks you will likely have low speed lean burn available as long as the other engine parameters are within range. I'd recommend 4 oz per ten gallons the first time, that's the recommendation on the bottle. After that you can go down to two oz per ten gallons.

If you're thinking this can't make sense, do a search on this site for marvel mystery oil and read the posts by the other Honda lean burn owners who have tested it. Try 2-3 tanks.

I am actually artificially forcing Lean Burn on a non-lean burn engine (F22b1) using a VAFC. How I've done this:
-Vtec Engagement has been dropped down to 2250rpms
-TPS < 16% (relative) at 2200-2950rpms is adjusted to 50% fuel reduction

I also use the Torque App (for android devices) to monitor my parameters.

I did recently pick up a couple bottles of MMO and I plan to run some through it as well.



Ecky, Thanks for your post as well... quite a difference in the no-load GPH for two honda engines!

Sadly, Toyota was making cars that revved that high up till 2005. Celica/MR2 Spyder equipped C56 transmissions do exactly what Ecky's car is doing, and they do so with a long stroke 1ZZ-FE too (HIGH friction at high rpm, BSFC goes up dramatically after 3500). Needless to say, I am content to cruise at 55mph while everyone blasts past me. I'd guess that 2/3 minimum of the fuel is going towards spinning the engine alone, afterall I can roll around with only 22% load on the engine in 5th at 25mph, and idle is 18%.

Ecky's transmission has it good, he has an 8200rpm rev limit and he uses less than half of it at 70mph on the highway! My 6700rpm rev limit is half used up at 70mph.

The old engine that was meant to go with this transmission was oversquare (81:77) but my new engine has a much longer stroke with the same bore (81:89). It's not as long as the 1ZZ-FE's but I still notice a very significant drop in gas mileage after 45mph (2500rpm).

Going from 45 (2500rpm) to 55 (3000rpm) results in a cruising gas mileage drop from 48 to 38 - that's almost a perfectly linear drop, 21% less FE at 22% higher speed. From 55 to 65mph I go from 38 to 32, which is an 18% drop at 19% higher speed. My gas mileage remains around 48 from 45mph down to about 20mph.

Swapping out my transmission for one from an Integra LS would allow me to go ~21% faster at the same RPM in 5th, or cruise at the same speed with 17.5% lower RPM. Another way of looking at it, I could do 56mph at the same RPM I run now at 45mph.

Lets see, 2.2/1.9*2700/2042*65/70*(120+459/70+459)*45 mpg = 74 mpg at 70 mph

relative displacement * relative RPM * relative speed * relative intake temperature= relative * mpg = relative terminal mpg

I know they make an F/ H2B conversion kit, but I wonder if they make a b2H /F kit... That would drop your final ratio even more!

.68 gal/hr @ 2400 rpm @ 76 mph = 111 mpg

I think that's about the same as my car. Might've been a very slight downhill grade, but 26.x mph (1500rpm ish) was 55mpg, 45mph (2500rpm) is like 48, 55mph (3000rpm) is like 38, and 70mph (3800ish) was like 30? 32? something like that.

Swapping out my transmission for the base Corolla transmission would get me about 10% lower final drive and 10% lower 5th gear for ~20% less revs at the same speed. Getting a 6 speed C60 would either get me ~5% higher revs (Lotus Elise has the same ratio for 6 as my 5, but they have bigger tires so their highway rpms are actually something like 2% lower!), or it would have the 6th gear that gives 10% less revs, but C60s run 2000 dollars or something like that. My standards for quietness and comfort have dropped to the point where I would be extremely happy to have just the 5th gear changed and be able to do 55mph at 2700rpm instead of 3000. Pretty big difference in noise.

If a girl complains about the noise, gonna order a new gearset immediately, :D Until then, I'll just try to think about all the gas I'm saving on 25mph roads by being able to use 1500rpm instead of 1800 and try to forget the extra gas that's disappearing on the highway >_>

Nice! The 1ZZ idles at 0.22 gal/hr I think, about 680rpm. Unfortunately, 70mph=3800rpm so I'm guessing 3800rpm no load would be well over 1 gal/hr.

The other day, I jacked up the rear wheels on the Jimmy and gave it a shot. Interestingly, cruise control wouldn't work. Maybe it has some sort of "smart" programming that knows the front wheels aren't turning - or that there's no load on the engine. (the ABS light came on eventually, so that's why I'm wondering if it "knew" the front wheels weren't turning).

So, very carefully with the foot throttle, I kept it at 50 mph for 2 minutes and got an average "trip" MPG on the ScanGauge of 48.2. I also noted it was at 1550 RPM.

I then did one at 2000 RPM (which the BSFC chart showed to be more efficient), and that one worked out to 65 mph and with one minute on the ScanGauge got 49.5 MPG.

Then I tried it in 3rd gear at 2800 RPM, the best RPM for BSFC. (I was afraid to spin the wheels that fast in overdrive, although I didn't notice anything (vibrations) to make me worried it was trying to hop off the jackstands). Of course, in 3rd gear, I was covering less "miles", so it was only 34.9 MPG.

I noticed the temperature was climbing during all of this, so I went back to 50 mph in top gear and did another one. This time, it came out at 52.8 MPG after running the "trip" on the ScanGauge for 1 minute.

About this time, the neighbor came over & asked if I was having "car trouble", so I figured I'd better quit this "horsing around" before someone else got curious/concerned.

After that, I went ahead and changed my oil & put Mobil-1 synthetic, 5-20 in it. Up until this time, I'd always ran Pennsoil 10-30, or maybe 5-30. So when I get the chance, I'll have to jack it up again and try the experiment again & see if there are any changes.

For the sake of safety, in case it "hopped off" the jackstands at 50 or 60 mph, I was parallel parked on the street in front of my driveway, facing down the street with no cars in front of me for several houses.... and I was IN the driver's seat while it was in gear. So I told myself if any mishap occurred, I could probably hit the brakes & stop it before anything "bad" happened.