Fuel Economy Discussion: Short gearing VS longer gearing
03-21-2006, 11:42 PM
#1
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Fuel Economy Discussion: Short gearing VS longer gearing
I have seen so many posts lately where people assume a short geared transmission results in less fuel efficiency compared to a longer geared transmission. Example, putting a LS 5th gear in an ITR transmission in an effort to get better fuel economy.
Lets examine what really happens when you change the gearing.
The following table is the injector duty cycle for a stock GSR. Lets say you are cruising at 4000rpms and are in the fourth load column (from previous datalogging I am generally in the fourth column on a flat highway). Notice that the duty cycle here is 15%
Now lets change the gear ratio so that at the same vehicle speed and same stretch of road, the engine speed increases 1000rpms. If the only thing that changed was engine speed, then yes, fuel economy will suffer, injector duty cycle in the same column increases by 4%...However, when you change your gearing, it takes less throttle effort to maintain speed. So lets take a look at 5000rpms in the previous load column; 14%. Now the engine is using less fuel!
From personal experience, my fuel economy increased when I switched from the 4.40 final drive, to the ATS 4.929, by roughly 20-25 miles per tank.
Common sense would confirm this as well. How would your fuel economy compare if you were going 30mph up a slight incline in 5th gear versus 3rd gear? Third gear would have drastically higher RPM's, but would require much less throttle input, and the result would be that 3rd gear will offer considerably better gas mileage.
Now there are exceptions to every rule and driving habits play the biggest role in fuel economy, but holding everything constant, simply changing gearing to a shorter gearset will only increase fuel efficiency. Conversely, there are limits to how much gearing is too much. I'm not saying you should cruise around at 8000rpms all day, but the relatively small change from gearing (~500-1000rpms, depending on how big of a change) will not detrimentally affect your gas mileage.
There are possible downsides to shorter gearing. Some people are sensitive to the sound of their car at a higher cruising RPM. Some motors have oil consumption problems and a 1000 RPM increase will compound this affect to a certain extent. I'm sure there are other downsides, but those are the two I can think of.
Now that I have triggered this topic...DISCUSS!
Lets examine what really happens when you change the gearing.
The following table is the injector duty cycle for a stock GSR. Lets say you are cruising at 4000rpms and are in the fourth load column (from previous datalogging I am generally in the fourth column on a flat highway). Notice that the duty cycle here is 15%
Now lets change the gear ratio so that at the same vehicle speed and same stretch of road, the engine speed increases 1000rpms. If the only thing that changed was engine speed, then yes, fuel economy will suffer, injector duty cycle in the same column increases by 4%...However, when you change your gearing, it takes less throttle effort to maintain speed. So lets take a look at 5000rpms in the previous load column; 14%. Now the engine is using less fuel!
From personal experience, my fuel economy increased when I switched from the 4.40 final drive, to the ATS 4.929, by roughly 20-25 miles per tank.
Common sense would confirm this as well. How would your fuel economy compare if you were going 30mph up a slight incline in 5th gear versus 3rd gear? Third gear would have drastically higher RPM's, but would require much less throttle input, and the result would be that 3rd gear will offer considerably better gas mileage.
Now there are exceptions to every rule and driving habits play the biggest role in fuel economy, but holding everything constant, simply changing gearing to a shorter gearset will only increase fuel efficiency. Conversely, there are limits to how much gearing is too much. I'm not saying you should cruise around at 8000rpms all day, but the relatively small change from gearing (~500-1000rpms, depending on how big of a change) will not detrimentally affect your gas mileage.
There are possible downsides to shorter gearing. Some people are sensitive to the sound of their car at a higher cruising RPM. Some motors have oil consumption problems and a 1000 RPM increase will compound this affect to a certain extent. I'm sure there are other downsides, but those are the two I can think of.
Now that I have triggered this topic...DISCUSS!
03-22-2006, 04:19 AM
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Re: Fuel Economy Discussion: Short gearing VS longer gearing (92TypeR)
As a general principle, isn't it true that Otto cycle motors perform at their maximum efficiency while at the maximum torque the motor produces?
03-22-2006, 06:20 AM
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Re: Fuel Economy Discussion: Short gearing VS longer gearing (92TypeR)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 92TypeR »</TD></TR><TR><TD CLASS="quote">However, when you change your gearing, it takes less throttle effort to maintain speed. </TD></TR></TABLE>
The entire analysis is based on this assumption, and I wonder whether or not it is accurate. Can you provide any support for this statement?
The entire analysis is based on this assumption, and I wonder whether or not it is accurate. Can you provide any support for this statement?
03-22-2006, 06:39 AM
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Re: Fuel Economy Discussion: Short gearing VS longer gearing (George Knighton)
iirc, Jim McFarland held that BSFC was typically highest near peak tq.
consider that while lugging the car in 5th gear at WOT, the pistons don't have to pull as hard to draw air past a smaller orfice (throttle plate). you're going to accelerate from, say, 40-60mph more slowly than you would in 3rd gear, but it's because even at WOT in 5th you can't burn as much fuel as you can in 3rd. your higher gear isn't allowing the engine to turn as many rpm, so even if you dump more fuel per cycle, running fewer rpm will still likely be better on gas, because you've reduced the load of pulling the air past the throttle.
also, take some A/F readings at speed in each gear using the stock ECU program. at 50mph in 5th the engine runs leaner than at 50mph in 3rd (= conditions).
to get the best mileage apply the least amount of tq necessary to do the work, and make less work (at the throttle, and with less friction at lower rpm).
if you do mostly city driving (stop and go), or lots of accelerating, using shorter gears should save gas, since you can get up to speed and upshift to a more fuel-efficient gear sooner. but, once you're at speed, you want to maintain it in the highest gear possible to reduce the frictional load. at this point, although you'll have a lower throttle position, the pistons moving more slowly have more time to draw air past the plate, so it's not so bad.
consider that while lugging the car in 5th gear at WOT, the pistons don't have to pull as hard to draw air past a smaller orfice (throttle plate). you're going to accelerate from, say, 40-60mph more slowly than you would in 3rd gear, but it's because even at WOT in 5th you can't burn as much fuel as you can in 3rd. your higher gear isn't allowing the engine to turn as many rpm, so even if you dump more fuel per cycle, running fewer rpm will still likely be better on gas, because you've reduced the load of pulling the air past the throttle.
also, take some A/F readings at speed in each gear using the stock ECU program. at 50mph in 5th the engine runs leaner than at 50mph in 3rd (= conditions).
to get the best mileage apply the least amount of tq necessary to do the work, and make less work (at the throttle, and with less friction at lower rpm).
if you do mostly city driving (stop and go), or lots of accelerating, using shorter gears should save gas, since you can get up to speed and upshift to a more fuel-efficient gear sooner. but, once you're at speed, you want to maintain it in the highest gear possible to reduce the frictional load. at this point, although you'll have a lower throttle position, the pistons moving more slowly have more time to draw air past the plate, so it's not so bad.
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03-22-2006, 07:14 AM
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Re: Fuel Economy Discussion: Short gearing VS longer gearing (slofu)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by slofu »</TD></TR><TR><TD CLASS="quote">using shorter gears should save gas, since you can get up to speed and upshift to a more fuel-efficient gear sooner.</TD></TR></TABLE>
Nope. If you "get up to speed sooner" and then coast at your cruising speed, you are using more gas per mile than accelerating at a slower rate up to your cruising speed.
It's the same thing as changing your shift points with a given gearset. You can "get up to speed sooner" by keeping it in lower gears and letting it rev higher, but you will use more gas doing so than you would by upshifting as soon as you can and keeping the revs down.
Nope. If you "get up to speed sooner" and then coast at your cruising speed, you are using more gas per mile than accelerating at a slower rate up to your cruising speed.
It's the same thing as changing your shift points with a given gearset. You can "get up to speed sooner" by keeping it in lower gears and letting it rev higher, but you will use more gas doing so than you would by upshifting as soon as you can and keeping the revs down.
03-22-2006, 08:29 AM
#10
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correct me if Im wrong, but if you are running a HIGHER RPM, isnt your motor turning more revolutions, thus your injectors are FIRING MORE over a certain amount of time? as compared to running less RPM when its firing less because of less revolutions, therefore actually firing less fuel over a similar amount of time? not sure if I explained it right.
03-22-2006, 09:02 AM
#13
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Re: (RTW DC2R)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RTW DC2R »</TD></TR><TR><TD CLASS="quote">correct me if Im wrong, but if you are running a HIGHER RPM, isnt your motor turning more revolutions, thus your injectors are FIRING MORE over a certain amount of time?</TD></TR></TABLE>
This is true, but my reasoning still holds true within a certain range.
For example, lets use the table above as a guide.
Assume 100% duty cycle is 1oz of fuel for this argument...
4th load column:
@ 4000rpms one injector would be fireing 2000 times that minute.
(2000 * ( 15% * 1oz) ) = 300oz of fuel
3rd load column:
@ 4496rpms one injector would be fireing 2248 times that minute.
(2248 * ( 12% * 1oz) ) = 269.8oz of fuel
Running about 500rpms higher in the previous load column will consume less fuel. This change in RPM's is roughly the same as the change in RPM's when switching from the USDM 4.40 final drive to the ATS 4.929 final drive.
But at the same time, running 1000rpms higher in the previous load column, will consume more fuel. Perhaps I should have chosen the 4496 rpm cell as my original argument
@ 5000rpms one injector would be fireing 2500 times that minute.
(2500 * ( 14% * 1oz) ) = 350oz of fuel.
However, looking at a 1000rpm increase at the same vehicle speed is a crazy increase in gearing. I don't even know if the Cusco 5.01 FD will change RPM's that much.
So there are limits to this gearing arguemnt, but if you take the limit of gearing as the 4.929 and the base as the 4.40, the argument still holds true
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nsxtasy »</TD></TR><TR><TD CLASS="quote">The entire analysis is based on this assumption, and I wonder whether or not it is accurate. Can you provide any support for this statement?
</TD></TR></TABLE>
Only from personal experience. If I could take a stock ITR and hook up the OBD2 port and measure throttle position with the stock 4.40 FD compared to the 4.929 FD, I am 99.9% positive that the throttle position with the 4.929 will be less.
I almost have to coast with my 4.929 on flat highways because the car wants to accelerate. Back when I commuted with the R, my commute would consist of 40 miles round trip, mostly on the highway. My fuel economy increased when I installed the 4.929 considerably. Enough to notice it every tank. It has been a while since the car was stock, but I remember it was always a struggle with the 4.40 to get near 300miles before the light came on. With the ATS I had no problems getting past 300, and I remember the few times that I went past 330 on a full tank.
I understand that comparing mileage per tank is not a precise measureing tool, but it gives us an idea of what is happening.
Lets keep this going
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RTW DC2R »</TD></TR><TR><TD CLASS="quote">another point, why do automatic cars have overdrive? isnt that so it drops the RPMs to increase gas mileage?</TD></TR></TABLE>
Don't automatics generally have worse fuel economy than their manual counterparts?
This is true, but my reasoning still holds true within a certain range.
For example, lets use the table above as a guide.
Assume 100% duty cycle is 1oz of fuel for this argument...
4th load column:
@ 4000rpms one injector would be fireing 2000 times that minute.
(2000 * ( 15% * 1oz) ) = 300oz of fuel
3rd load column:
@ 4496rpms one injector would be fireing 2248 times that minute.
(2248 * ( 12% * 1oz) ) = 269.8oz of fuel
Running about 500rpms higher in the previous load column will consume less fuel. This change in RPM's is roughly the same as the change in RPM's when switching from the USDM 4.40 final drive to the ATS 4.929 final drive.
But at the same time, running 1000rpms higher in the previous load column, will consume more fuel. Perhaps I should have chosen the 4496 rpm cell as my original argument
@ 5000rpms one injector would be fireing 2500 times that minute.
(2500 * ( 14% * 1oz) ) = 350oz of fuel.
However, looking at a 1000rpm increase at the same vehicle speed is a crazy increase in gearing. I don't even know if the Cusco 5.01 FD will change RPM's that much.
So there are limits to this gearing arguemnt, but if you take the limit of gearing as the 4.929 and the base as the 4.40, the argument still holds true
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nsxtasy »</TD></TR><TR><TD CLASS="quote">The entire analysis is based on this assumption, and I wonder whether or not it is accurate. Can you provide any support for this statement?
</TD></TR></TABLE>
Only from personal experience. If I could take a stock ITR and hook up the OBD2 port and measure throttle position with the stock 4.40 FD compared to the 4.929 FD, I am 99.9% positive that the throttle position with the 4.929 will be less.
I almost have to coast with my 4.929 on flat highways because the car wants to accelerate. Back when I commuted with the R, my commute would consist of 40 miles round trip, mostly on the highway. My fuel economy increased when I installed the 4.929 considerably. Enough to notice it every tank. It has been a while since the car was stock, but I remember it was always a struggle with the 4.40 to get near 300miles before the light came on. With the ATS I had no problems getting past 300, and I remember the few times that I went past 330 on a full tank.
I understand that comparing mileage per tank is not a precise measureing tool, but it gives us an idea of what is happening.
Lets keep this going
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RTW DC2R »</TD></TR><TR><TD CLASS="quote">another point, why do automatic cars have overdrive? isnt that so it drops the RPMs to increase gas mileage?</TD></TR></TABLE>
Don't automatics generally have worse fuel economy than their manual counterparts?
03-22-2006, 09:12 AM
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^^^
To add to the dicussion and going with you points think of it in this way.
A LS has a 4.266 final drive, but the ITR has a 4.4 and the JDM ITR 4.785. We all know that trying to cruise at 65-70 miles on the highway is a LS requires more throttle than a ITR or JDM ITR, but yet if you look up the MPG ratings for all integra's it's the same.
To add to the dicussion and going with you points think of it in this way.
A LS has a 4.266 final drive, but the ITR has a 4.4 and the JDM ITR 4.785. We all know that trying to cruise at 65-70 miles on the highway is a LS requires more throttle than a ITR or JDM ITR, but yet if you look up the MPG ratings for all integra's it's the same.
03-22-2006, 09:24 AM
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Re: (92TypeR)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 92TypeR »</TD></TR><TR><TD CLASS="quote">
Don't automatics generally have worse fuel economy than their manual counterparts? </TD></TR></TABLE>
I do not know and was not implying. Im dont think we are comparing which is more fuel efficient. Im speaking within respect to automatic trans gearing itself. Overdrive, as far as Im lead to believe, is used to get better gas mileage and it is done so by using longer gears. Im curious why that would be the case (assuming I am under the right impression) if longer gearing has negative effect on gas mileage (as you said).
Again, please correct me if my impressions about overdrive are incorrect because I am assuming based on what I know.
I think its one of those things where it can go either way "within a certain range", or "depending on..." etc
Don't automatics generally have worse fuel economy than their manual counterparts? </TD></TR></TABLE>
I do not know and was not implying. Im dont think we are comparing which is more fuel efficient. Im speaking within respect to automatic trans gearing itself. Overdrive, as far as Im lead to believe, is used to get better gas mileage and it is done so by using longer gears. Im curious why that would be the case (assuming I am under the right impression) if longer gearing has negative effect on gas mileage (as you said).
Again, please correct me if my impressions about overdrive are incorrect because I am assuming based on what I know.
I think its one of those things where it can go either way "within a certain range", or "depending on..." etc
03-22-2006, 09:26 AM
#17
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Re: (wildoutwhitegsr)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by wildoutwhitegsr »</TD></TR><TR><TD CLASS="quote">^^^
but yet if you look up the MPG ratings for all integra's it's the same.
Integra ITR 25 MPG City / 30 MPG Highway
Integra LS 25 MPG City / 30 MPG Highway
Integra GSR 25 MPG City / 31 MPG Highway
All 5spd</TD></TR></TABLE>
Yeah but those are manufacturers advertised ratings. Which many times range from not accurate to downright bogus. IIRC also, I thought I heard Honda was included in the manufacturing groups recently probed about their advertised MPG ratings as compared to their Actual results.
but yet if you look up the MPG ratings for all integra's it's the same.
Integra ITR 25 MPG City / 30 MPG Highway
Integra LS 25 MPG City / 30 MPG Highway
Integra GSR 25 MPG City / 31 MPG Highway
All 5spd</TD></TR></TABLE>
Yeah but those are manufacturers advertised ratings. Which many times range from not accurate to downright bogus. IIRC also, I thought I heard Honda was included in the manufacturing groups recently probed about their advertised MPG ratings as compared to their Actual results.
03-22-2006, 09:34 AM
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Re: Fuel Economy Discussion: Short gearing VS longer gearing (92TypeR)
This might also explain why I get better gas mileage towing in 3rd gear in my truck as opposed to 4th gear. The RPM's are higher but my throttle % is much less. All that I know for sure, my R gets crappy gas mileage. I get about 200 miles per tank city/highway and I get about 3 30 minute HPDE sessions per tank of gas.
03-22-2006, 09:35 AM
#20
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Re: (wildoutwhitegsr)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by wildoutwhitegsr »</TD></TR><TR><TD CLASS="quote">Ok I'll put it this way. If on average the ITR can get 350 mile per tank.
You'd think that the ls would get 500 miles per tank, but it's the same at 350.</TD></TR></TABLE>
I dont know if you can really compare two different cars. too many other factors involved.
You'd think that the ls would get 500 miles per tank, but it's the same at 350.</TD></TR></TABLE>
I dont know if you can really compare two different cars. too many other factors involved.
03-22-2006, 09:38 AM
#21
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Re: (wildoutwhitegsr)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by wildoutwhitegsr »</TD></TR><TR><TD CLASS="quote">Ok I'll put it this way. If on average the ITR can get 350 mile per tank.
You'd think that the ls would get 500 miles per tank, but it's the same at 350.</TD></TR></TABLE>
Actually In my personal experience I've gotten at least between 400 to 420 miles per tank in my 94 LS. And my R when in stock form used to get close to 400 miles per tank.
You'd think that the ls would get 500 miles per tank, but it's the same at 350.</TD></TR></TABLE>
Actually In my personal experience I've gotten at least between 400 to 420 miles per tank in my 94 LS. And my R when in stock form used to get close to 400 miles per tank.
03-22-2006, 09:40 AM
#22
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Re: (RTW DC2R)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by RTW DC2R »</TD></TR><TR><TD CLASS="quote">I think its one of those things where it can go either way "within a certain range", or "depending on..." etc </TD></TR></TABLE>
Agreed. That is why it is hard to say 100% either way. You can take data from one range and it will have the opposite result as data in another range.
In addition to economy, I would also imagine the lower cruising RPM's in overdrive has in-part to due with comfort.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 1GreyTeg »</TD></TR><TR><TD CLASS="quote">Yeah but those are manufacturers advertised ratings. Which many times range from not accurate to downright bogus. IIRC also, I thought I heard Honda was included in the manufacturing groups recently probed about their advertised MPG ratings as compared to their Actual results.</TD></TR></TABLE>
I agree here as well. I did not want to bring EPA ratings into the argument because the politics and systems at which the EPA determine the ratings is definitely screwed
I would like to hear from other members who have switched from a 4.40 FD to the 4.929, or even the 4.785.
Agreed. That is why it is hard to say 100% either way. You can take data from one range and it will have the opposite result as data in another range.
In addition to economy, I would also imagine the lower cruising RPM's in overdrive has in-part to due with comfort.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 1GreyTeg »</TD></TR><TR><TD CLASS="quote">Yeah but those are manufacturers advertised ratings. Which many times range from not accurate to downright bogus. IIRC also, I thought I heard Honda was included in the manufacturing groups recently probed about their advertised MPG ratings as compared to their Actual results.</TD></TR></TABLE>
I agree here as well. I did not want to bring EPA ratings into the argument because the politics and systems at which the EPA determine the ratings is definitely screwed
I would like to hear from other members who have switched from a 4.40 FD to the 4.929, or even the 4.785.
03-22-2006, 09:41 AM
#23
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Re: Fuel Economy Discussion: Short gearing VS longer gearing (Bradstard)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Bradstard »</TD></TR><TR><TD CLASS="quote"> All that I know for sure, my R gets crappy gas mileage. I get about 200 miles per tank city/highway and I get about 3 30 minute HPDE sessions per tank of gas.</TD></TR></TABLE>
You're lucky. Depending on the track I can range between 2 to 3 sessions before I need to refuel now. I carry two to three 5 gallon fuel cans now. I got sick of running out and either having to drive to town on R comps to refuel before lunch or to suck it up and pay between $7 and $9 per gallon of 100 octane at the track
Fuel jugs = my second best track equipment investment by far
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 92TypeR »</TD></TR><TR><TD CLASS="quote">
I would like to hear from other members who have switched from a 4.40 FD to the 4.929, or even the 4.785.
</TD></TR></TABLE>
I'm a 4.929 guy here as almost everyone already knows.
You're lucky. Depending on the track I can range between 2 to 3 sessions before I need to refuel now. I carry two to three 5 gallon fuel cans now. I got sick of running out and either having to drive to town on R comps to refuel before lunch or to suck it up and pay between $7 and $9 per gallon of 100 octane at the track
Fuel jugs = my second best track equipment investment by far
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 92TypeR »</TD></TR><TR><TD CLASS="quote">
I would like to hear from other members who have switched from a 4.40 FD to the 4.929, or even the 4.785.
</TD></TR></TABLE>
I'm a 4.929 guy here as almost everyone already knows.
03-22-2006, 09:46 AM
#24
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Re: (1GreyTeg)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Aquafina »</TD></TR><TR><TD CLASS="quote">Stock I has a 3.722 final drive.</TD></TR></TABLE>
I assume that's for some other car, not an ITR, since the USM ITR has a 4.400 final drive.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 92TypeR »</TD></TR><TR><TD CLASS="quote">Only from personal experience. If I could take a stock ITR and hook up the OBD2 port and measure throttle position with the stock 4.40 FD compared to the 4.929 FD, I am 99.9% positive that the throttle position with the 4.929 will be less.
I almost have to coast with my 4.929 on flat highways because the car wants to accelerate.</TD></TR></TABLE>
I don't think that's right. In my experience, the car "wants to accelerate" and requires less throttle when the gearing is TALLER. Try it on your car. Go at a constant speed and try driving in different gears. I think you'll find that the car requires less throttle in the HIGHER (taller) gears than it does in the LOWER (shorter) gears.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 92TypeR »</TD></TR><TR><TD CLASS="quote">Don't automatics generally have worse fuel economy than their manual counterparts? </TD></TR></TABLE>
It really depends on the car. Some cars have better fuel economy with the automatics, others with the manuals.
I assume that's for some other car, not an ITR, since the USM ITR has a 4.400 final drive.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 92TypeR »</TD></TR><TR><TD CLASS="quote">Only from personal experience. If I could take a stock ITR and hook up the OBD2 port and measure throttle position with the stock 4.40 FD compared to the 4.929 FD, I am 99.9% positive that the throttle position with the 4.929 will be less.
I almost have to coast with my 4.929 on flat highways because the car wants to accelerate.</TD></TR></TABLE>
I don't think that's right. In my experience, the car "wants to accelerate" and requires less throttle when the gearing is TALLER. Try it on your car. Go at a constant speed and try driving in different gears. I think you'll find that the car requires less throttle in the HIGHER (taller) gears than it does in the LOWER (shorter) gears.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by 92TypeR »</TD></TR><TR><TD CLASS="quote">Don't automatics generally have worse fuel economy than their manual counterparts? </TD></TR></TABLE>
It really depends on the car. Some cars have better fuel economy with the automatics, others with the manuals.
03-22-2006, 10:12 AM
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Re: (nsxtasy)
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by nsxtasy »</TD></TR><TR><TD CLASS="quote">I don't think that's right. In my experience, the car "wants to accelerate" and requires less throttle when the gearing is TALLER. Try it on your car. Go at a constant speed and try driving in different gears. I think you'll find that the car requires less throttle in the HIGHER (taller) gears than it does in the LOWER (shorter) gears.
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That is some what true. Even though the lower gear is in fact shorter and requires more gas to keep moving, the difference is that your closer to redline.
Try cruising close to redline in any car in any gear and it's the same. More throttle is needed.
Now if you keep everything the same except the final drive, 4.4 compared to 4.785 and cruise at 3500rpm the 4.785 requires less throttle.
Now if we compare the differences between the 4.4 at 3500rpm and the ats 4.9 at 4000rpm we would need a datalogged fuel map to confirm the differences before and after
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That is some what true. Even though the lower gear is in fact shorter and requires more gas to keep moving, the difference is that your closer to redline.
Try cruising close to redline in any car in any gear and it's the same. More throttle is needed.
Now if you keep everything the same except the final drive, 4.4 compared to 4.785 and cruise at 3500rpm the 4.785 requires less throttle.
Now if we compare the differences between the 4.4 at 3500rpm and the ats 4.9 at 4000rpm we would need a datalogged fuel map to confirm the differences before and after