pickler

Today someone asked me about brake specific fuel consumption in the 4G TL forum when the best 'cruising' speed was being discussed. BSFC is basically the amount of gas your engine burns to give you certain amount of power. When you are accelerating you need to be in your BSFC sweet spot for best efficiency. That is, the engine load and RPM which gives you the most amount of power for the least amount of gas. This is different from MPG. BSFC is important to determine shift points and the amount of throttle needed. Here is a BSFC map of a typical 4-cylinder engine:



^ with that particular engine you get the most horsepower per drop of fuel (sweet-spot) between 1800-3500rpm at 75-90% load. As we know our RDXs have excellent amount of torque in midranges between 3000-5000 rpm. At higher revs the torque takes a nose dive. So this graph from a mercedes supercharged 4-cylinder would be probably more appropriate for our cars (even though it could be totally different):



Now from this graph we can see that the most efficient BSFC for that engine is between 2000-3000rpm at 65-80% engine load.

Now why is all this stuff so important in hypermiling or getting high MPGs? because it helps us with the pulse and glide technique. P&G technique is a very effective hypermiling technique that can greatly decrease your fuel consumption levels. When you "pulse" you are accelerating and whe you 'glide' you are decelerating. For about 1 second of pulse 3-4 seconds of gliding is necessary for optimum results. But how do we know how fast to accelerate? well that's when BSFC comes in. If we look at the second graph and take it as a guide for our cars, we know that we must accelerate at 2000-3000rpm with 65-80% engine load.

anyway, i decided to put this theory to the test with my RDX which many accuse of being a gas guzzler and the results was a bit surprising. First of all i could Not do my best here since it was my first run. subsequent runs were much better i hit about 40mpg after 10 miles of practice, so this is actually a pretty conservative figure (note 6.8L/100km is about 34mpg):


So how can you get 30+ mpg?
1. get scangauge 2 or a similar OBDII reader device which can give you accurate engine load numbers.
2. leave the shifter in D. no need for paddle shifters here. The TCU shifts at optimum RPMS by default.
3. Master the throttle. Learn to apply just enough gas to get to 65-80% engine load but prevent downshifts. Its ok if your car downshifts as long as your RPMs do not venture past 3000.
4. practice makes perfect. Find a deserted road and practice until you can get +30mpg for at least 10 miles straight.

If you can't get a OBDII reader:
My advice: firstly always just give it enough gas in D so that the computer shifts at 3000rpm in first gear, and ~2700rpm at higher gears 3-5. Turbo gauge should not go past 1/3 of boost level. then use pulse and glide. try to drive 'without brakes'. this means anticipate stops and redlights and slow down sooner. turn off engine at long stops and avoid idling at all costs. make sure your tires are pumped up and use low resistance tires like the oem ones. minimize A/C usage.

this method might be cumbersome but its a good way to make those long highway travels more interesting and save you a few bucks at the pump. thanks.

TruckerBomb

I averaged 25.5 on a tank a few weeks ago... wasn't too painfully slow... wasn't too excitingly fun either! lol

DRR98

Wow, 40 mpg? Oh my gosh, that's amazing! Cough...

InfamousJamous

I learned a few tips, thanks!

I'm more interested in going fast so if you have any tips on when to shift for quicker 0-60, 1/4 mile times then I will surely subscribe to that thread.

pickler

lol well your mods suggest that your car is at its full potential. you may want to throw in a downpipe to scavenge more gases from the cylinders. that should make the biggest difference aside from reflash.

with the hondata i would Not shift at sportmode to the new 7200rpm limit. i would just shift at 6800 all gears. that should help you cross 1/4 mi at peak power delivery of ~6000rpm at ~92mph. shifting at +7100rpm will cost you the 1/4 mile but may help you improve 0-60. without hondata i would shift at 6000rpm 2-3 gear.

InfamousJamous

Thanks, I'll play around with the shift points. I do have a downpipe.

markmass

Thanks for posting this. So far I've been keeping the revs low and accelerating softly to avoid the turbo kicking in. I'll use the pulse and glide to try to improve my fuel economy and mileage per tank.

pickler

hey markmass yea its a good technique to try. however you will need a bit of boost to avoid pumping loses. everytime you are accelerating without boost (vaccum) you are not in your B.S.F.C sweet spot. you want 70-80% engine load when accelerating. i say 1/4 to 1/3 boost is ok every time you pulse but no more and make sure rpm are below 2500 when doing this.

koolchaits

Great info, pickler! I will try to remember and use the pulse and glide technique whenever possible, and try to follow the guidelines. Will post the findings, too.

pickler

thats a good idea but if you get tired of P&G you can always just set your cruise control on flat surfaces. 50-60mph is the sweet spot. i have experimented with all the RPMS and speeds. 55mph at ~2000rpm gave me 26mpg on the highway while 80mph just under 3000rpm gave me only 22mpg.

have a look here:
http://ecomodder.com/forum/showthrea...you-15182.html

Lanesky_OH8RDX

I have never seen my average fuel economy go below 9L/100km ever. Driving my RDX from Vancouver to Halifax my best was 9.8 just as i got into Ontario cause the speed limit dropped to 90km/h... I wonder if there is something amiss with the car. I gotta learn this. Hopefully get better tires cause I know that helps too. Stupid no name shite tires.

DRR98

Wanting to squeeze mpg out of an RDX is like being married to a beautiful woman and then limiting love making to try to conserve your energy.

And then bragging to your friends of the astonishingly low number of times you made love.

Put your foot it it! Then tell me how poorly (mpg's) you did, much more interesting.

This is a performance oriented oversized hatch, meant to, well perform. Mpg's not so much.

Not trying to be offensive but wonder why? What is your motivation?

This is leaning into the same turf as the 1st vs 2nd gen issue as to which is a proper RDX.

Mpg vs performance...?

mpetersen22

My guess is that while he enjoys the performance, he doesn't always have to drive it like he stole it. (notice his signature lists the 0-60 time of his RDX)
Hypermile when you don't need the speed. Conserve the gas for when you want to drive fast.

pickler

thanks thats my answer lol. im actually a very spirited driver. lost count of number of civic si drivers i humilated unintentionally at the track.