Lower RPM at high speeds?

[alkemyst]

Originally posted by: yelo333
It is my hunch that all of these are automatics. I recall a thread on standardshift (but can't find it ATM) about people complaining about their high cruising RPM. The examples given there pointed to the fact that manual's are simply geared shorter to make them feel like they have more pep. An auto can just downshift when it needs to; a manual depends on you, hence the reason why they gear them like they do.

As an example, my '07 MT civic runs in the 2700rpm range at 63mph. In the AT version of this car, 63mph is where the tranny cuts over to 5th gear, so I think it's somewhere in the 1200rpm range. This does have a small effect on gas mileage, though, since the MT is rated for 34 hwy, while the auto is rated for 36 (2008 figures).

As others have mentioned, you really aren't using that much more gas (34 vs 36 in my case, not accounting for the lower efficiency of an auto) by cruising at a higher rpm, but you will have an easier time using a lot more if you have a heavy foot. Try to stay light on the pedal, even when accelerating. It depends on the car/driver, but sometimes the cruise will do a better job in the flat portions than you can. You may want to try that.

The is an EXTREMELY broad statement. For the most part a manual and automatic will cruise at the same rpms. The gearing is usually dictated by what the car is intended (luxury, sport, towing).

 

[yelo333]

Originally posted by: alkemyst

The is an EXTREMELY broad statement. For the most part a manual and automatic will cruise at the same rpms. The gearing is usually dictated by what the car is intended (luxury, sport, towing).

Hmm, do you have any examples? I don't disagree that gearing would change based on intended use. However, it's been my experience (which is quite limited!) that the MT version of a car is generally geared shorter than an equivalent AT one. This is assuming that MT & AT have the same number of gears.

BTW, here is the thread I mentioned in my post above.

Google just turned this up, too.

 

[Ragnarok2]

Originally posted by: Oiprocs
On the freeway at 70MPH, my '93 Prelude VTEC (190hp) runs at ~4000 rpm.

Is there any way I can drop that to ~3000 rpm when I'm in 5th gear? The reason I want to do this is I want to get better gas mileage out of it at that speed, so I figure less revolutions would mean less gas used. I think because it's a sporty car that they gave it more response/pep at higher speeds, but I don't really need that aspect.

Edit

If I can't get this changed, I'm just going to drive at 60-65mph instead. But I'd rather not live in the right lane for the duration of my ownership in this car.

Please whatever you do don't forget to put in VTEC in there. As a matter of fact you should have highlighted it. Also Mivec > Vtec

 

[alkemyst]

Originally posted by: yelo333

Originally posted by: alkemyst

The is an EXTREMELY broad statement. For the most part a manual and automatic will cruise at the same rpms. The gearing is usually dictated by what the car is intended (luxury, sport, towing).

Hmm, do you have any examples? I don't disagree that gearing would change based on intended use. However, it's been my experience (which is quite limited!) that the MT version of a car is generally geared shorter than an equivalent AT one. This is assuming that MT & AT have the same number of gears.

BTW, here is the thread I mentioned in my post above.

Google just turned this up, too.

You can head over to edmunds and the like. Also in your own quoted articles NO ONE is describing a 1500 rpm difference at the same speeds with the same vehicle: manual vs automatic.

I will say they are not going to be exact as the different transmissions affect the powerband differently. Also number of gears has no difference. Final drive ratio will be the one easily comparable one though.

Some manuals have lower numerical rear end gears but wider spaced transmission gearing and some have narrow spaced...comparing to the automatics you may end up with lower or higher gearing at any particular shift.

In the end I would expect at most a 500-600rpm difference between a manual and automatic car in top gear.

 

[Arkaign]

I had a 5g Prelude, and that sounds about right. Couple mpg/general things you can do :

(1)- Amsoil or the like. A good synthetic will both increase your engine's lifespan, as well as lubricate much better, giving you slight but real improvements in fuel economy/power.

(2)- Look into some wheel/tire solutions that give a larger diameter compared to your current setup. Not anything huge, but a slightly larger profile setup will mean that at any particular rpm, you will actually be covering more ground/moving faster. This will throw your speedo off a bit, so find one of those 'speed stations' that the cops leave out and test the difference. You might be going 43 when your speedo says 40, for example, or 66 when your speedo says 60. It may not be that drastic, but it is definitely something to check.

(3)- If you have the SH or a model with the rear deck spoiler, you can take it off. The Prelude is a FWD vehicle, and you'll never be traveling at a speed (hopefully) that the slightly increased downforce will make any legitimate difference. Removing it will lower the drag on your car, also giving you a small but tangible improvement in fuel economy.

 

[oiprocs]

Originally posted by: Arkaign
(3)- If you have the SH or a model with the rear deck spoiler, you can take it off. The Prelude is a FWD vehicle, and you'll never be traveling at a speed (hopefully) that the slightly increased downforce will make any legitimate difference. Removing it will lower the drag on your car, also giving you a small but tangible improvement in fuel economy.

You really think that would help? What is small but tangible?

 

[PeeluckyDuckee]

Originally posted by: Arkaign
I had a 5g Prelude, and that sounds about right. Couple mpg/general things you can do :

(1)- Amsoil or the like. A good synthetic will both increase your engine's lifespan, as well as lubricate much better, giving you slight but real improvements in fuel economy/power.

(2)- Look into some wheel/tire solutions that give a larger diameter compared to your current setup. Not anything huge, but a slightly larger profile setup will mean that at any particular rpm, you will actually be covering more ground/moving faster. This will throw your speedo off a bit, so find one of those 'speed stations' that the cops leave out and test the difference. You might be going 43 when your speedo says 40, for example, or 66 when your speedo says 60. It may not be that drastic, but it is definitely something to check.

(3)- If you have the SH or a model with the rear deck spoiler, you can take it off. The Prelude is a FWD vehicle, and you'll never be traveling at a speed (hopefully) that the slightly increased downforce will make any legitimate difference. Removing it will lower the drag on your car, also giving you a small but tangible improvement in fuel economy.

Interesting. So for the 5th gen Prelude, stock size is 205-55-R16, what would you recommend going up to? What benefit would there be if my fronts were a little bit wider than the rear, would it help with traction on dry road during fast corners? What about getting lighter flywheels? Would that improve MPG any?

Spoilers is more or less for aesthetics, for selling vehicles, as rarely would there or should there be a time where a spoiler would make a difference in handling, within city and highway limit speeds.

 

[Dman877]

Even Honda 6-speeds cruise at high rpm. My TSX does 70 at 3k in 6th. 3k in 5th puts it at about 56 mph. They do this with their 4-bangers because of the lack of torque. My father had a 325i with a 5-speed and in 4th, at 3k it would be going 60+. My friend's Saab 900 (late 90's model) would actually do 65ish in 4th. If Honda geared their 4-cyl cars like that, I think they would feel awfully slow. Fortunately, I like shifting the 6sped in my car and 65 - 70 mph is fast enough for me on the highway.

 

[alkemyst]

Originally posted by: Oiprocs

Originally posted by: Arkaign
(3)- If you have the SH or a model with the rear deck spoiler, you can take it off. The Prelude is a FWD vehicle, and you'll never be traveling at a speed (hopefully) that the slightly increased downforce will make any legitimate difference. Removing it will lower the drag on your car, also giving you a small but tangible improvement in fuel economy.

You really think that would help? What is small but tangible?

I'd put money on it'd be a wash.

Add that to holes in your decklid and it's a definite loss.

The SH doesn't have a huge spoiler. I don't even think it was designed for more than looks anyway and has nothing to do with aerodynamics.

 

[alkemyst]

Originally posted by: Dman877
Even Honda 6-speeds cruise at high rpm. My TSX does 70 at 3k in 6th. 3k in 5th puts it at about 56 mph. They do this with their 4-bangers because of the lack of torque. My father had a 325i with a 5-speed and in 4th, at 3k it would be going 60+. My friend's Saab 900 (late 90's model) would actually do 65ish in 4th. If Honda geared their 4-cyl cars like that, I think they would feel awfully slow. Fortunately, I like shifting the 6sped in my car and 65 - 70 mph is fast enough for me on the highway.

Speed at top gear has nothing to do with lack of torque. With the honda's it puts them in their ideal powerband for cruising. These are not 5500 rpm redline cars.

 

[oiprocs]

Originally posted by: alkemyst

Originally posted by: Oiprocs

Originally posted by: Arkaign
(3)- If you have the SH or a model with the rear deck spoiler, you can take it off. The Prelude is a FWD vehicle, and you'll never be traveling at a speed (hopefully) that the slightly increased downforce will make any legitimate difference. Removing it will lower the drag on your car, also giving you a small but tangible improvement in fuel economy.

You really think that would help? What is small but tangible?

I'd put money on it'd be a wash.

Add that to holes in your decklid and it's a definite loss.

The SH doesn't have a huge spoiler. I don't even think it was designed for more than looks anyway and has nothing to do with aerodynamics.

Point taken.

Yeah I read some more on prelude/honda forums, and I'm pretty much dealing with the same thing as any other prelude driver out there. The 60-65 range is good enough for me, and I saw some people on there who couldn't get past 19mpg, so I'm not going to bitch anymore.

 

[terentenet]

Oiprocs, if you want better mileage why don't you get a nice diesel? On the highway my 535d cruises at 100mph and averages 30mpg. RPM is about 2500rpm.
With my engine I can probably get 40mpg at 70mph.
Smaller engines (2.5L diesel) have 190hp and will get you 45mpg at 70mph.

A diesel will get you high speed with low RPM. Check the picture below, my 535d at top speed and still under 4000rpm.
pic

 

[jagec]

Originally posted by: Arkaign
(2)- Look into some wheel/tire solutions that give a larger diameter compared to your current setup. Not anything huge, but a slightly larger profile setup will mean that at any particular rpm, you will actually be covering more ground/moving faster. This will throw your speedo off a bit, so find one of those 'speed stations' that the cops leave out and test the difference. You might be going 43 when your speedo says 40, for example, or 66 when your speedo says 60. It may not be that drastic, but it is definitely something to check.

I would not trust those at all. Far better to use a GPS or even to time yourself between mile markers.

 

[oiprocs]

Update #3

Miles: 378
Fillup: 13.24
MPG: 28.5

This tank was driven at 70mph freeway speed. I'm not seeing a huge loss over 60mph, even though I'm running at 3900RPM versus 3100RPM. Sounds like I'm not going back to the slow lanes.

Originally posted by: terentenet
Oiprocs, if you want better mileage why don't you get a nice diesel? On the highway my 535d cruises at 100mph and averages 30mpg. RPM is about 2500rpm.
With my engine I can probably get 40mpg at 70mph.
Smaller engines (2.5L diesel) have 190hp and will get you 45mpg at 70mph.

A diesel will get you high speed with low RPM. Check the picture below, my 535d at top speed and still under 4000rpm.
pic

Holy sh!t. That's nuts. I can't stop staring at your speedometer. It's like, yearning to go farther.

I would love to get a diesel, but I can't afford to purchase a new car. I've tried searching for used diesels, but all I find are 80's Benz's, and I'm scared one of those will die on me within a few months, or require a bunch of expensive repair. I can get about ~2000-2500 for my Prelude (damn salvage title...it's worth ~3500 ), so if you've got any bright ideas let me know. But this last tank at 70 was nice, as I only gave up 4MPG in comparison to a 60mph tank.