speedzer

Okay, a friend just told me a technique about going full throttle while shifting early to save gas. For example, I nail the throttle and shift at 3000 rpms as oppose to applying 50% throttle and still shifting at 3000 rpms.

One, wouldn't this damage the engine in the long run?
two, can I do this in an automatic TSX?
and lastly, does this really save fuel?

any car gurus out there want to chime in

Stapler

That sounds a bit silly, though I have never tried it.
But if you do that on a carburated car you are dumping gas in, no way it would get you better millage, on modern fuel injected cars they may not just dump the gas in, but i'm shure they would certainly put in more at full throttle.

The best millage I get is just doing the old "pretend there is a egg under the gass pedal" method. Easing on to the gas pedal and never flooring it. I don't think you can do much more than that.

Edr0e

How can that be possible if gas is combusted at a higher rate at wide open throttle.

Lower the rpm's the less gas you are burning.

Nothing more annoying then someone who pulses the gas pedal every 30 seconds. Gives me a headache.Maybe you are one of them. I could not for the life of me explain this phenomena to my mother who drives like total crap so I just told her to WOT the damn car. lol

Maximized

He must of read MT or R&T. They had an article on this.

SteVTEC

The following is the Brake Specific Fuel Consumption map for a Toyota 1MZ-FE 3.0L DOHC V6, in grams of fuel used per kilowatt-hour of energy produced (g/kW-hr). Lower number is better. Most internal combustion engines have BSFC maps that look about like this.




Efficiency favors relatively high loads because gas burns most efficiently at relatively high pressure. On a throttled gasoline engine, this does mean fairly heavy throttle since otherwise there is only very low pressure in the engine. One of the big reasons that diesels are so much more efficient is because they're unthrottled and always operate with high excess air ratios (high cylinder pressure) whether it's idling or at WOT.

Efficiency also favors lower RPM, and this one is easy. Friction in the engine rises exponentially with increasing RPM, so the lower you can keep the revs the more efficiently the engine will operate.

The net result is that if you do use heavier throttle while also keeping the engine at lower RPMs, you should be able to improve your mileage a tad depending on your specific drive cycle (YMMV). In fact one of the reasons that gasoline ICE's are so inefficient in automobiles is because of the fact that most of the time they're just cruising along and very lightly loaded. Efficiency is horrible in that state of operation with gas engines, but not with diesels which continue to have very good efficiency over a much wider range of RPMs and loads.

The kicker though is that your TSX has electronic throttle control. It's actually already doing a lot of this for you and the added efficiency from techniques like this is built into the car. Everybody loves their extra power nowadays, but one of the big reasons that efficiency has also been maintained or improved is because of electronic throttling. Works wonders for optimizing shift schedules and improving fuel efficiency while not pissing off owners who would feel like their car was lagging big time and complain if you did the same thing with a conventional throttle.

subinf

I remember reading something about it also in one of those magazines. At the time I was only driving my mustang and that fucking thing never gets good mileage so I give the article the time of day.

Edr0e

Can someone explain this further?























Great, back to the good ole lead foot and higher insurance premiums !!!

Edr0e

Thanks, makes sense to me now. So basically more throttle/gas and less rpm. Sounds fun.

SteVTEC

From the BSFC map, 100 N-m of torque at 4000 rpm and 200 N-m of torque at 2000 rpm will both produce the same exact amount of power, about 56 hp after converting.

100 N-m x 4000 rpm = 56 hp and 300 g/kW-hr
200 N-m x 2000 rpm = 56 hp and 240 g/kW-hr

It's far more efficient to produce 56 hp at near-WOT and 2000 rpm than it is to produce the same 56 hp at 4000 rpm and only about 1/3rd throttle. The reason being is that friction is a lot lower at 2000 rpm so you have much less energy loss due to friction. The other reason is the higher pressure that the fuel is combusting under, which again allows for much more efficient combustion than at lower pressure.

This theory of operation is why GM can get 29 mpg out of their LS1 V8 engines. They run just above idle on the highway and as a result have very low friction. And at 60-70 mph they only have about 70 hp available. So average load on the engine ends up being a lot heavier which is more efficient and that's where the 29 mpg comes from. The same theory is behind the 1-4 skip-shift feature which was common on a lot of their cars. If you're not accelerating hard, 2 and 3 are blocked and 4th is what you get. Lower RPM and higher load = better efficiency, and GM delivers you a powerful vehicle that gets decent fuel mileage. Ditto on variable displacement engines. Different way to accomplish the same thing.

Edr0e

2200 rpms is when you should shift eh?

Edr0e

So this applies to engines with throttles only?

SteVTEC

Depends on your vehicle and its gearing. I looked in the owners manual for my 5spd Maxima (cable throttle) the last time gas prices hit $3/gal and laughed at the absurdly low shift point suggestions. The shift points had you shifting at about 2200-2300 rpm, and landing at about 1800 rpm (90% peak torque). I gave it a whirl and sure enough I did seem to manage better city mileage. I don't do nearly enough city driving to be scientific though. 90% of my driving is done on the highway going 75 mph where I'm running lightly loaded in the 3000 rpm range with crap efficiency and there's not a darn thing I can do about it.

SakiGT

I think this is correct. Normal "nice" driving my car gets 20mpg.

When I was hauling ass EVERYwhere for the DSM meet I helped out with I averaged 22mpg