Lower RPM at high speeds?

[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.

Update that was glanced over by many posts:

So my last tank of gas was spent driving 60mph during my commute to school.

Miles: 372
Fillup: 11.479
MPG: 32.4

That definitely cheered me up, plus after a couple days I got used to the slower speed. It also really didn't affect how long it takes me to get there.

This next tank I'm going to try 65mph, and see how much I get with that. If it's 28+, I think that's good enough.

Edit2

Update#2

Miles: 361
Fillup: 12.232
MPG: 29.5

I guess that's not bad. An increase in 5mph resulted in a decrease of 3mpg. I guess I've figured out some sort of sweet zone.

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.

 

[thedarkwolf]

No easy way no. Might be able to swap the whole trans or just the diff gears from another honda but then you would loose some get up and go all around.

 

[oiprocs]

Damn.

 

[Colt45]

If you can find a six speed with the same basic ratio, and more overdrive on 6th, that would be good.

otherwise, change gears in the diff, but you'll have less torque and higher top end in every gear, and less torque isn't really something you want in a honda

 

[oiprocs]

Hmm. I'm guessing that six speed you're talking about is a whole new transmission? $1000-2000?

It seems I'll have to start making enemies in the right lane now. Oh well. That's only like an additional 10-15 minutes of driving, and since I commute an hour, I guess it's fine.

 

[sniperruff]

time for a V6

<--- 75mph at just a tick over 2k rpm, if i drop to ~55mph then it drops to 1.5k rpm...

 

[JulesMaximus]

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.

Yes, drive slower. That is really the only choice you have with that car.

 

[natto fire]

The engine load is what is really determining your gas mileage. Notice you do not have the push the pedal very hard to maintain your speed. My '89 Prelude would run in the 3600-4000 rpm range, and with only a 6800 RPM redline, much lower than the VTEC's. It still managed 32 mpg on several highway trips.

 

[spidey07]

No way without a transmission change. Even then the motor is going to be working harder and using more gas. You're car is from the era of small motor/60 mph for best mileage. Get a newer car where best mileage is in the 75-85 Mph range.

 

[GoatMonkey]

If it was rear drive you could just swap out the rear end gears for a different final ratio on all of your gears. I'm not sure how that's handled in a front wheel drive transmission though.

 

[oiprocs]

Yeah, it seems like I just have to drive it slower, as I noted in my OP and as Jules dutifully confirmed for me.

Cruisin' @ 60 FTW.

 

[oiprocs]

So my last tank of gas was spent driving 60mph during my commute to school.

Miles: 372
Fillup: 11.479
MPG: 32.4

That definitely cheered me up, plus after a couple days I got used to the slower speed. It also really didn't affect how long it takes me to get there.

This next tank I'm going to try 65mph, and see how much I get with that. If it's 28+, I think that's good enough.

 

[RichieZ]

wow and i thought my car was bad, in 5th at 4000 RPM its doing 85

 

[alkemyst]

Originally posted by: sniperruff
time for a V6

<--- 75mph at just a tick over 2k rpm, if i drop to ~55mph then it drops to 1.5k rpm...

Has nothing to do with the OP's issues...V6 in his car with nothing else changed would turn the same RPM.

Oiprocs...just out the honda forums...there are a million of them. Clubsi.com is a good start.

 

[Apex]

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.

Get really tall tires.

 

[oiprocs]

Originally posted by: Oiprocs
So my last tank of gas was spent driving 60mph during my commute to school.

Miles: 372
Fillup: 11.479
MPG: 32.4

That definitely cheered me up, plus after a couple days I got used to the slower speed. It also really didn't affect how long it takes me to get there.

This next tank I'm going to try 65mph, and see how much I get with that. If it's 28+, I think that's good enough.

Boy, you two just skipped over this didn't you?

 

[jagec]

Originally posted by: spidey07
No way without a transmission change. Even then the motor is going to be working harder and using more gas.

I disagree. I wouldn't be a bit surprised if a transmission change improved his mileage at freeway speeds, even though the engine has to work harder. In fact, I'd be surprised if it didn't. Even the small-engine cars produce more power than is necessary for cruising at a constant speed.

Originally posted by: Apex

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.

Get really tall tires.

Hehe, that's true. Forgot about that "solution". Of course, you have to budget for a GPS or a bicycle computer to show your true speed, since the speedometer will read low.

 

[PeeluckyDuckee]

I have the 5th gen Prelude and if I recall it does 65mph @ 3000rpm and 75@ 4000rpm. Climbing steep hills on the highways I usually would downshift to 4th gear as well on occassion for those spirited runs and to maintain momentum.

There's times when using 5th gear would actually net your worse mileage than keeping it in 4th for those uphill battles if your engine has to work harder in 5th.

Our family's V6 Intrigue runs 65mph@1900rpm. What a difference, and torqued much better that the engine doesn't have to try hard to move. And it really does move. Sometimes I end up doing 90mph from my usual 75mph cruise without noticing and having to put in much effort 'cause the engine is just so quiet. A welcome change from having to listen to the I4 revv and revv and revv.

 

[Demon-Xanth]

Wow, that's pretty high for a cruise RPM. I can't even get that high without using a trick to make the ECU ignore the speed sensor. Otherwise it says "Excuse me, WTF are you doing?" at about 3500RPM in 5th. At which point the CHP asks the same question (doing 115 isn't a good idea...)

But lowering RPMs doesn't always increase gas mileage. When I had some taller rear tires, I actually lost a half an MPG once you took into account the odometer scaling offset. The engine is happiest at 2500RPM, the larger tires made it work harder at around 1800RPM and I had to downshift for hills much more often. If I swapped out the 3.55 gears for 3.92s that were an option, I'd still get the same MPG. I even got the same MPG at 80 that I do at 70. But those $200 speeding tickets really suck.

The key is to cruise in the car's sweet spot. If 4k is the sweet spot, that's where you're going to be best at, if 3k is, you might just have to slow down a bit. FWD cars don't have as many options when it comes to messing with ratios as RWD cars.

 

[jtvang125]

I know on the B series Honda engines you can pretty much swap transmission gears between each other. I'm not sure about the H series engines in the Prelude though.

Also I'm pretty sure the engineers at Honda figured out that that rpm range provides the best gas mileage while still maintaining some power at higher speeds.

 

[nwfsnake]

Jack it up and slap some DUBs on it!

 

[thecoolnessrune]

I love trucks 75mph is 2200rpm in my 95 bronco and 2000rpm in my 04 Expedition

Though my fuel mileage is far worse.. I wonder about the engine wear comparison though..

 

[jagec]

Originally posted by: Demon-Xanth
The key is to cruise in the car's sweet spot. If 4k is the sweet spot, that's where you're going to be best at, if 3k is, you might just have to slow down a bit. FWD cars don't have as many options when it comes to messing with ratios as RWD cars.

FR cars, anyway. Other layouts are just as hosed as FWD when it comes to swapping ratios.

 

[yelo333]

Originally posted by: sniperruff
time for a V6

<--- 75mph at just a tick over 2k rpm, if i drop to ~55mph then it drops to 1.5k rpm...

Originally posted by: PeeluckyDuckee

Our family's V6 Intrigue runs 65mph@1900rpm.

Originally posted by: thecoolnessrune
I love trucks 75mph is 2200rpm in my 95 bronco and 2000rpm in my 04 Expedition

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.

 

[thecoolnessrune]

Originally posted by: yelo333

Originally posted by: sniperruff
time for a V6

<--- 75mph at just a tick over 2k rpm, if i drop to ~55mph then it drops to 1.5k rpm...

Originally posted by: PeeluckyDuckee

Our family's V6 Intrigue runs 65mph@1900rpm.

Originally posted by: thecoolnessrune
I love trucks 75mph is 2200rpm in my 95 bronco and 2000rpm in my 04 Expedition

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.

Indeed, if i come off a stop up to 70 using 2000rpm steady, i'll edge just over 17mpg in my Expedition. If I spend the tank going up to speed at 3000-3500rpm, then I'm down to 14-15 mpg. A light foot is key to getting the most out of any vehicle. Once I'm up to speed, it doesn't matter if I'm going 55-70. There's about a .2mpg difference. But only if I use a light foot to get up to speed.