Manual Trans Small Engine hwy cruizing rpm

[IndyIan]

Originally Posted By: SVTCobra
I would have to guess that the engine has a lower Brake Specific Fuel Consumption at those engine RPMs to give better fuel economy.

Any chart I've looked for even small 4 cyl has best efficiency around 2500rpm and nearly WO throttle. Which is what would happen with small engine geared for efficiency on a hill.
I agree with the above posters that the high gearing is done to make the car feel peppy on the highway and reduce the need to downshift.
I got a surprise when I test drove an 03 Neon R/T with a 5spd and found it had the same top gear ratio as my 3spd auto Neon...

So any hope of much better hwy fuel economy is gone.

 

[Burt]

Originally Posted By: Quattro Pete
Originally Posted By: Burt

Get a diesel. My 335d loafs along at 2,000 rpm @ 80 mph. 3,000 rpm at 120.

Sorry for a little OT, but what sort of real world MPG are you seeing with your 335d?



I bought it used and have only had it a couple of months. I get about 31 mpg in mixed freeway and city driving. In my 2002 maxima I would get 24 mpg in the same use. I have not got a good highway tank in so I don't want to speculate too much, but am sure if you want to drive 60 mph or so, it will yield over 40.

 

[Hokiefyd]

My '07 Corolla had a 1.8L engine and 5-speed manual transmission. 5th gear was 25 mph per 1,000 rpms. So 2,000 rpm = 50 mph, 3,000 rpm = 75 mph, etc.

Mileage was 38-40 mpg at a steady 70-75 mph.

 

[Quattro Pete]

Originally Posted By: Hokiefyd
My '07 Corolla had a 1.8L engine and 5-speed manual transmission. 5th gear was 25 mph per 1,000 rpms. So 2,000 rpm = 50 mph, 3,000 rpm = 75 mph, etc.

My family's old Escort 1.6L was geared similarly. About 2000 rpm at 50 mph. It got really good hwy mpg, but it couldn't climb even a very slight incline in 5th. But that's what the lower gears were for...

 

[Hokiefyd]

Originally Posted By: KrisZ
You guys have been spoiled by big, slow turning V8s for far too long, that may explain the "fear' of cruising at higher RPMs.

3-4k RPM at cruising speed is nothing, otherwise there would be a lot of broken engines in Europe and Asia, where most engines have 1.0-1.6 liters of displacement.


This is me. It took me a while to get used to fast-spinning engines. Now that I'm used to it, I love a little engine speed. But growing up on pushrod V-8s, I wondered why these little Hondas and Toyotas were still running after turning 3,500 rpm on the highway. Impossible!

 

[rslifkin]

I don't mind an engine spinning fast on the highway, I just don't like to have to hear it do so!

 

[subiedriver]

My '04 subie 2.5 with a 5 speed turns 3000 rpm at 70 mph. I don't do much interstate cruising, so the car is rarely driven faster than 70. Most of the time, its 55-65 mph. The subie 2.5 is awesome, because its torque plateu starts at 2200 rpm, so I can pull hills in 5th at 2500 rpm, no problem.

 

[mechtech2]

On a motorcycle, RPM are usually much higher on the highway.
It just becomes a number after a while.
It appears you have a basic commuter car, not a dedicated highway cruiser.
It is not biased for 80+ mph, although it certainly can do it.

 

[Nick R]

Originally Posted By: mechtech2
On a motorcycle, RPM are usually much higher on the highway.
It just becomes a number after a while.
It appears you have a basic commuter car, not a dedicated highway cruiser.
It is not biased for 80+ mph, although it certainly can do it.


True that. At 75mph, our Shadow is turning close to 5500RPM, and it acheives 60+ mpg doing that, without a hiccup. And this is a carbureted engine too.

My Cruze with the 6A turns 2900RPM at 75mph, the nox turns about 2100. Better than the cavalier, that did 3300ish, and my focus did 2500.

 

[Whimsey]

I don't have a tach in my 1996 5 speed manual Zetec Contour so I don't know the RPM's. I have to judge by noise and feel. I know there is a formula to determine the RPM's at specific mph based upon tire dimension and gearing in that gear. Anybody know the formula? I had it years ago but "missed placed it"

. All I know is cruising in 5th at 70 to 80+ mph the engine is quiet. The road noise in the car is louder, not well insulated. But it's not tiering. We drive from NJ to Key West every other year at least and the ride at high speeds is pleasant. It's not luxury car quiet but ok for long hours on the road. Plus I get 35+ mpg at those speeds

.

Whimsey

 

[sciphi]

Originally Posted By: Nick R
Originally Posted By: mechtech2
On a motorcycle, RPM are usually much higher on the highway.
It just becomes a number after a while.
It appears you have a basic commuter car, not a dedicated highway cruiser.
It is not biased for 80+ mph, although it certainly can do it.


True that. At 75mph, our Shadow is turning close to 5500RPM, and it acheives 60+ mpg doing that, without a hiccup. And this is a carbureted engine too.

My Cruze with the 6A turns 2900RPM at 75mph, the nox turns about 2100. Better than the cavalier, that did 3300ish, and my focus did 2500.


My Cruze Eco 6M turns about 2500 RPM at 75. Mine's also geared lower than Nick's. At 60 mph mine's at 1800 RPM on the dot.

 

[GMFan]

My 2011 Mazda6 2.5L 6spd MT turns at 3,000 RPM at 75mph in 6th gear. 3,500 RPM is the sweet spot on this motor for power.

 

[Nick R]

Originally Posted By: sciphi
Originally Posted By: Nick R
Originally Posted By: mechtech2
On a motorcycle, RPM are usually much higher on the highway.
It just becomes a number after a while.
It appears you have a basic commuter car, not a dedicated highway cruiser.
It is not biased for 80+ mph, although it certainly can do it.


True that. At 75mph, our Shadow is turning close to 5500RPM, and it acheives 60+ mpg doing that, without a hiccup. And this is a carbureted engine too.

My Cruze with the 6A turns 2900RPM at 75mph, the nox turns about 2100. Better than the cavalier, that did 3300ish, and my focus did 2500.


My Cruze Eco 6M turns about 2500 RPM at 75. Mine's also geared lower than Nick's. At 60 mph mine's at 1800 RPM on the dot.


For some reason, the manual is geared lower than the automatic is on the cruze.

 

[sciphi]

It's part of GM's "EPA Games" advertising where they get to hype the "42 mpg Cruze" in all their ads, conveniently omitting that it's one model with a manual transmission specified for fuel economy that nobody will pick. Well, besides me.

Highway speeds and RPM's vary too much between cars. Although more makers are figuring out that the folks who buy new cars with manual transmissions don't mind downshifting occasionally when going uphill, and putting in super-tall 6th gears for better highway fuel economy.

 

[mechtech2]

35+ mpg at 80+ in an old Ford Contour is stupendous.

 

[sparky123]

Personally, I don't want my stick shift car buzzing along at too high of an rpm at cruising speed. 2800-2900 is about perfect in my 5-sp 2010 Focus @ 75mph. My last stick car was @ 3500 rpm at 70 mph. Way too high IMO.

 

[MCompact]

My ti is turning 4000 rpm at 80 mph, and returning 32 mpg.

 

[Quattro Pete]

Originally Posted By: sparky123
My last stick car was @ 3500 rpm at 70 mph. Way too high IMO.

My old Audi A4 1.8T was like that, but the engine sounded great at that RPM and not tiring by any means.

 

[Thermo1223]

Originally Posted By: sciphi
It's guaranteeing that it's "easy to drive", with no-downshift passing or accelerating up most hills. With proper care, it'll last just as long as an engine ought to. Unless a small engine is a diesel, revving the snot out of it won't harm it. The lighter internals mean less wear/tear. Constant drastic changes in speeds will kill the engine well before the RPM's will. It's not the fall that kills, but the sudden stop at the end.



Actually revving the snot out of small diesel won't matter either, their built even tougher.

VW speced older TDI's to have a rotating assmebly good til 10,000 rpms but you are lucky to get past 5,000 because of the time it takes to combust diesel fuel. It burns slower than gasoline so it was near impossible to inject fuel fast enough to burn in such a small window. Audi got a little better with the TDI Lemans car.

One way to test a TDI's MAF was to just hold the throttle wide open in neutral. If it hit 5200 rpms it worked fine lol.

 

[exranger06]

Originally Posted By: Whimsey
I know there is a formula to determine the RPM's at specific mph based upon tire dimension and gearing in that gear. Anybody know the formula? I had it years ago but "missed placed it"

Engine RPM divided by transmission gear ratio divided by differential gear ratio = wheel speed (rpm). Multply wheel speed by tire circumference (in inches) and you get vehicle speed in inches per minute. Multiply by 60 and get inches per hour. Divide by 12 and get feet per hour. Divide by 5,280 and you get miles per hour.

Work backwards to get engine rpm for a given speed.