R&T: Heavy foot + short shifting = +20% MPG - Page 3

El Sid · 07-17-2008, 01:30 PM

When Smokey Yunick wrote about his Adiabatic engine in the old Car and Driver magazine, he was using the Chrysler 2.2 turbo engine with high compression and an intake that had a carburetor upstream of the turbo. With the high heat transfer he had a fully vaporized fuel mixture and would run very lean. Blew up lots of engines.

In the article Smokey also said the key to better economy was high throttle openings and engine loading.
In the carburetor, the accelerator pump squirted in extra fuel to compensate for the lean mixture that would result from just opening the butterfly. Then, as the air velocity increases, the vacuum would draw fuel. Anyway, the idea was to have tall gears and large throttle openings as a matter of driving protocol to save fuel. I can see how it worked back in the day of carburetors.

Quicksilver · 07-17-2008, 01:34 PM

Quote:

Originally Posted by El Sid

It is wrong.

Yes, the engine may be at it's most efficient power/fuel point, but to say that the engine as air pump burns less fuel at 4000 rpm when at 2000 it is using roughly half as much air and therefore fuel is just wrong.
The term roughly is due to the volumetric efficiency reaches a maximum at some point - say for a N/A DOHC 92% @ 4000 and only 88% @2000, but if there is less air our modern FI will portion to fuel accordingly.

Better percentage at torque peak - less fuel at lower rpm.

El Sid

I guarantee it! Have you driven very far in 5th gear at 2000 RPM? Let's make the point more clearly...how about doing 40 in 5th gear at 1600 rpm or 35mph in 5th at 1400...are you still going to claim better gas mileage at 30 in 5th at 1200 RPM?
Try it in the real world...Honda's cruise control won't even work at those speeds, because they don't want damage done to their engines...
-Quick

The Rookie · 07-18-2008, 09:39 PM

Sorry, I have the efficiency maps for all the engines we produce, and what you say is rubbish, whether you think you can 'guarentee' it or not! Lugging an engine too slowly may not be the best way forward (usually OK straight and level, not on grades or with headwind), but that's different to getting better FE at 5000rpm to 2500rpm! Most gasooline engines are most efficient at 1500-2000rpm. Besides as many smaller engine have variable cam timing these days, its not even set to the eak torue setting at part load cruise, its usually set to the max power setting to make the pump 'inefficient' so it reducves pumping losses past the throttle as the throttle has to be further open to compensate!

Simon

El Sid · 07-18-2008, 10:12 PM

I thought it was funny - real world - I'm in cruising in 2nd or 3rd at those speeds. How is it clearer to have a 200 rpm difference? Is the low speed to discount the effect of wind resistance? To make our point/observation - you will have better fuel economy at 45 mph in 5th gear than 45 mph in 3rd. Are you not closer to the torque peak in 3rd gear?

Yes, I would think that lower vehicle speeds and lower engine speeds would yield lower gasoline comsumption.

I did set the cruise today at 1500 in 5th - works well to keep out of trouble if the copper is behind you.

Quicksilver · 07-18-2008, 11:06 PM

Quote:

Originally Posted by El Sid

I thought it was funny - real world - I'm in cruising in 2nd or 3rd at those speeds. How is it clearer to have a 200 rpm difference? Is the low speed to discount the effect of wind resistance? To make our point/observation - you will have better fuel economy at 45 mph in 5th gear than 45 mph in 3rd. Are you not closer to the torque peak in 3rd gear?

Yes, I would think that lower vehicle speeds and lower engine speeds would yield lower gasoline comsumption.

I did set the cruise today at 1500 in 5th - works well to keep out of trouble if the copper is behind you.

El Sid-
Well, I guess if you can go through a tank of gas at 1500 rpms in 5th and accurately measure your gas mileage, I'll believe you and recant all I've claimed...until then I'll still guarantee it! An S2000 at 1500 won't even activate cruise control. The engine was not designed either by torque, valve train, nor gears to run at such low engine speeds for longer than it takes to get to 2nd gear.
And I'll even bet that, using the cruise control, the further you get into your torque curve in your 45 mph in 3rd versus 4th, versus 5th, that you use less gas in third!
Rookie-
Show me your engine maps and relate them to the engine's torque curve and I'll believe you...
-Quick

El Sid · 07-18-2008, 11:51 PM

It really doesn't have anything to do with the torque curve.

The engine is effectively an air pump - it pumps air through the cylinders and the fuel is metered by computer to be stokiometric.

The more air pumped, the more fuel is metered.

More air pumped at 4000 than at 2000.

Nothing to do with the torque curve.

jbleee · 07-19-2008, 12:20 AM

okay besides all the bickering i guess the cliff notes might be that lugging your engine is not the best for good mpg and that the raw egg on the brakes and gas pedals is the most logical for the best mpg.

jbleee · 07-19-2008, 12:24 AM

Quote:

Coasting in gear requires gas. No gas equals deceleration/engine braking. Most engines are tuned to accept large fuel volume variations...you tune one to idle efficiently and your Audi would win by coasting while idling...
-Quick

I have always had a question about this...

So for better mpg...coasting is better than Neutral correct?
Also you say no gas is used for engine braking/downshifting. does that mean you have to just downshift with no rev match?
So no gas is used there, but what if you rev match by blipping the throttle

jbleee · 07-19-2008, 12:26 AM

Also-
what if i set my cruise control to 55MPH on the freeway.
Is that better than maitaining 55MPH with my real right foot? if i pretend there is an egg on it will that be better than the computer's movements or is the computer perfect

adc · 07-19-2008, 07:21 AM

Quote:

Originally Posted by The Rookie

Most gasooline engines are most efficient at 1500-2000rpm. n

Back in the old days (of carburetors. I believe running low rpms and low power. The engines I believe were very inefficient bc of the lower pressures on the suction stroke (Throttle almost closed). They were way more efficient at WOT. That is not to say they didn't suck more gas at WOT lol.

Has new technology changed this somewhat?

Again another pitch for very very low displacement engines to keep air flow higher and reduce sucking losses.

I find that keeping my rpm 2000 or lower even during shift points (auto) and driving usually about 1600 or so in town gets me 28 mpg. The problem is it is harder on bearings. I have done a Used Oil Analysis (UOA) on the subie and its way better than my UOA on my 01 Sentra 2.0 SR20DE.

thefoos · 07-19-2008, 09:52 AM

Quote:

Originally Posted by El Sid

It really doesn't have anything to do with the torque curve.

The engine is effectively an air pump - it pumps air through the cylinders and the fuel is metered by computer to be stokiometric.

The more air pumped, the more fuel is metered.

More air pumped at 4000 than at 2000.

Nothing to do with the torque curve.

Your torque curve DOES matter for fuel economy. You get your lowest fuel consumption at the rpm of your highest torque. You should accelerate in that rpm band. I wish I could find a specific fuel consumption graph.

Also, I just quickly scanned this thread, but I didn't see it mentioned. As long as your AFR's stay at schoic, this works. Once you start getting into the enriched areas, this doesn't work.

I have found that I get best acceleration economy boosting under 5 psi, 30-40% throttle, keeping the motor between 2500-4000 rpm.

thefoos · 07-19-2008, 10:03 AM

Quote:

Originally Posted by adc

Back in the old days (of carburetors. I believe running low rpms and low power. The engines I believe were very inefficient bc of the lower pressures on the suction stroke (Throttle almost closed). They were way more efficient at WOT. That is not to say they didn't suck more gas at WOT lol.

Has new technology changed this somewhat?

Again another pitch for very very low displacement engines to keep air flow higher and reduce sucking losses.

I find that keeping my rpm 2000 or lower even during shift points (auto) and driving usually about 1600 or so in town gets me 28 mpg. The problem is it is harder on bearings. I have done a Used Oil Analysis (UOA) on the subie and its way better than my UOA on my 01 Sentra 2.0 SR20DE.

Engines are most efficient at peak torque rpm

That is why old stock V8's are most efficient at low rpm. They are cammed/tuned for low rpm torque

etiennelau · 07-19-2008, 03:11 PM

Quote:

Originally Posted by thefoos

Engines are most efficient at peak torque rpm

That is why old stock V8's are most efficient at low rpm. They are cammed/tuned for low rpm torque

Most Efficient has nothing to do with fuel economy. The engine may be breathing most efficiently at say 4000 rpm. However FE means least amount of fuel used. IE gal/hour or liters/hour.

Any engine management system today will always try to keep A/F ratio to 14:1. Therefore if you accelerate at WOT or even 1/2 WOT you are using a large amount of fuel far more than saying driving with an egg on the dash method(grannie driving).

I have a scangauge on my vehicle. If I accelerate at even 1/2WOT I am consuming rate of at least 4-5 gal/hour. However if I grannie the gas pedal I am consuming at 1.5 to 2 gal/hour.

The Rookie · 07-19-2008, 10:34 PM

The proper measure of fuel economy is the energy generated referenaced to the fuel used, most the worl use grams of fuel burnt per Kw generated per hour.....

I have tested cars at a steady 30/40/50 etc, and 30 was the most economical and that was at about 1500rpm with a 1.4 litre engine (that just happes to be the car we were testing).

Peak torque is just where (there or there abouts) it can pump most air per cycle, efficient as an air pump, not necesarily for economy!

Simon

thefoos · 07-20-2008, 06:00 AM

^^Where is the peak torque on that motor?

I'm not really interested in agruing. These facts about economy have been established a long time ago by IC design engineers. I wish I could find a brake fuel consumption curve out on the internet. The only ones I have are in text books. If you looked at one, you would note that fuel consumption is a parabolic relationship to rpm, with the lowest point of the curve equal to the rpm that peak torque is at.

It is about efficiency. that is what this thread is about anyhow. The more efficient the engine is, the less fuel is used. You guys are over simplifying engine dynamics and boiling it down to rpm's = bad (frictional losses). There are a bunch more variables at work here.

07-18-2008, 09:39 PM	#33 (permalink)
The Rookie Simply the best Contributing Member Join Date: Mar 2006 Location: Warwickshire, UK Posts: 4,453 Gallery: 0 iTrader: 1 / 100%	Sorry, I have the efficiency maps for all the engines we produce, and what you say is rubbish, whether you think you can 'guarentee' it or not! Lugging an engine too slowly may not be the best way forward (usually OK straight and level, not on grades or with headwind), but that's different to getting better FE at 5000rpm to 2500rpm! Most gasooline engines are most efficient at 1500-2000rpm. Besides as many smaller engine have variable cam timing these days, its not even set to the eak torue setting at part load cruise, its usually set to the max power setting to make the pump 'inefficient' so it reducves pumping losses past the throttle as the throttle has to be further open to compensate! Simon __________________ 98 S-turbo, next mod decat D/P and hybrid turbo!

07-19-2008, 12:20 AM	#37 (permalink)
jbleee Oh I wish I were a POST HO too!! Join Date: Jan 2006 Location: Lake Oswego, OR....Eugene for college Posts: 1,138 Gallery: 0 iTrader: 1 / 100%	okay besides all the bickering i guess the cliff notes might be that lugging your engine is not the best for good mpg and that the raw egg on the brakes and gas pedals is the most logical for the best mpg. __________________ -Jeff 04 forester x mt gold

07-19-2008, 12:26 AM	#39 (permalink)
jbleee Oh I wish I were a POST HO too!! Join Date: Jan 2006 Location: Lake Oswego, OR....Eugene for college Posts: 1,138 Gallery: 0 iTrader: 1 / 100%	Also- what if i set my cruise control to 55MPH on the freeway. Is that better than maitaining 55MPH with my real right foot? if i pretend there is an egg on it will that be better than the computer's movements or is the computer perfect __________________ -Jeff 04 forester x mt gold

07-19-2008, 10:34 PM	#44 (permalink)
The Rookie Simply the best Contributing Member Join Date: Mar 2006 Location: Warwickshire, UK Posts: 4,453 Gallery: 0 iTrader: 1 / 100%	The proper measure of fuel economy is the energy generated referenaced to the fuel used, most the worl use grams of fuel burnt per Kw generated per hour..... I have tested cars at a steady 30/40/50 etc, and 30 was the most economical and that was at about 1500rpm with a 1.4 litre engine (that just happes to be the car we were testing). Peak torque is just where (there or there abouts) it can pump most air per cycle, efficient as an air pump, not necesarily for economy! Simon __________________ 98 S-turbo, next mod decat D/P and hybrid turbo!

07-20-2008, 06:00 AM	#45 (permalink)
thefoos Join Date: Jan 2007 Location: Granger, IN Posts: 684 Gallery: 0 iTrader: 6 / 100%	^^Where is the peak torque on that motor? I'm not really interested in agruing. These facts about economy have been established a long time ago by IC design engineers. I wish I could find a brake fuel consumption curve out on the internet. The only ones I have are in text books. If you looked at one, you would note that fuel consumption is a parabolic relationship to rpm, with the lowest point of the curve equal to the rpm that peak torque is at. It is about efficiency. that is what this thread is about anyhow. The more efficient the engine is, the less fuel is used. You guys are over simplifying engine dynamics and boiling it down to rpm's = bad (frictional losses). There are a bunch more variables at work here. __________________ Scott 04 MT FXT STG 2 5 spd 02 WRX STG 2 5 spd

07-17-2008, 01:30 PM	#31 (permalink)
El Sid Join Date: Dec 2007 Location: West Palm Beach, Florida Posts: 494 Gallery: 1 iTrader: 0 / 0%	When Smokey Yunick wrote about his Adiabatic engine in the old Car and Driver magazine, he was using the Chrysler 2.2 turbo engine with high compression and an intake that had a carburetor upstream of the turbo. With the high heat transfer he had a fully vaporized fuel mixture and would run very lean. Blew up lots of engines. In the article Smokey also said the key to better economy was high throttle openings and engine loading. In the carburetor, the accelerator pump squirted in extra fuel to compensate for the lean mixture that would result from just opening the butterfly. Then, as the air velocity increases, the vacuum would draw fuel. Anyway, the idea was to have tall gears and large throttle openings as a matter of driving protocol to save fuel. I can see how it worked back in the day of carburetors.

07-18-2008, 10:12 PM	#34 (permalink)
El Sid Join Date: Dec 2007 Location: West Palm Beach, Florida Posts: 494 Gallery: 1 iTrader: 0 / 0%	I thought it was funny - real world - I'm in cruising in 2nd or 3rd at those speeds. How is it clearer to have a 200 rpm difference? Is the low speed to discount the effect of wind resistance? To make our point/observation - you will have better fuel economy at 45 mph in 5th gear than 45 mph in 3rd. Are you not closer to the torque peak in 3rd gear? Yes, I would think that lower vehicle speeds and lower engine speeds would yield lower gasoline comsumption. I did set the cruise today at 1500 in 5th - works well to keep out of trouble if the copper is behind you.

07-18-2008, 11:51 PM	#36 (permalink)
El Sid Join Date: Dec 2007 Location: West Palm Beach, Florida Posts: 494 Gallery: 1 iTrader: 0 / 0%	It really doesn't have anything to do with the torque curve. The engine is effectively an air pump - it pumps air through the cylinders and the fuel is metered by computer to be stokiometric. The more air pumped, the more fuel is metered. More air pumped at 4000 than at 2000. Nothing to do with the torque curve.

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