Manual Trans Small Engine hwy cruizing rpm

[Dave424]

My current car revs at 4k at 80mph. I also had two civics before... a 1984 and a 2004. both were manual and had very similar gear ratios. I know 90's miatas were geared even shorter with 4-5k hwy cruising rpm.

My current car makes peak torque of 110 ish at 4200 rpm... I understand that lugging is bad for an engine... but really, is cruising at 4000 rpm any better?

I understand that load vs rpm issue has been discussed before. But what I would like to know is why manufacturers undergear vehicles to such degree? At what point does higher rpm with lower load cause more wear than mid/low rpm with higher load, or vice versa?

 

[Nick R]

Inb4 "slow Down and the engine won't be spinning as fast"

 

[Dave424]

I commute on I5 where speed limit is 70. I have to drive in the upper 70s in order to stay out of the way of most that drive 90 plus. =/

 

[Mark_Walk]

My 2011 Mazda 3 with 5spd automatic turns 3,000rpm at 87mph
Same car with close ratio 6spd MT turns 3,000rpm at 76mph

 

[Mark_Walk]

Engine is 2.5L with about 170hp by the way.

 

[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.

 

[Radman]

Manufacturers that gear cars toward city driving want to give the illusion that the vehicle is peppier than it really is. Highway cruising a peak torque on a low output engine makes perfect sense to me. My Suzuki is a high reving vehical on the highway. My Nissan's turn allot less RPM's for the same speed. Use good oil & good filters and don't worry about it.

You are worried about premature wear as am I. I used to drive below speed limit to drop RPM's. Now I just don't care and want to see how long the engine will last.

 

[aquariuscsm]

My car runs 3000RPM at 70mph. Engine doesn`t hit its powerband until you hot 3500-4000 rpm. Then after 3500 it feels like a two-stroke dirtbike hitting it`s powerband :^)

 

[aquariuscsm]

Originally Posted By: Radman
I used to drive below speed limit to drop RPM's.


Haha I was the same way! My 3000GT was at like 3500 rpm at 70mph and it would freak me out! BUT,little did I know that`s the way the engine was made,to be driven at high rpm,so I`d set the cruise at 135+ and it was smooth as glass!

 

[Dave424]

Originally Posted By: Radman
You are worried about premature wear as am I. I used to drive below speed limit to drop RPM's. Now I just don't care and want to see how long the engine will last.


I am kind of at the same point. I used to stay at 65-70 keeping it at 3500 or less... but now I am getting tired of worring about it as I was becoming hazard on the early morning raceway. It has 100k mile warranty... but still I'd hate having to go through it. It sure is annoying though.

 

[Quattro Pete]

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.


Big +1 on this entire response!

 

[rslifkin]

A lot of manufacturers do it, especially with manuals, because lots of downshifting for hills annoys people.

 

[Dave424]

...but then I still wonder, how can an engine that has made 2X the revolutions in the same distance traveled, last as long?

 

[Food Scientist]

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

 

[Nick R]

Because at operating temps, cruising, engine wear is essentially nonexistent.

 

[zorobabel]

I hate short gearing for regular (non sporty) cars. If people don't like to change gears they should buy automatics.
I say 4000rpm cruising is worse than 2500rpm cruising. At 4000 rpm the oil filter will be in bypass mode most likely.
And once the car gets older and it starts to develop vibrations those 4000revs aren't going to be as smooth anymore.

 

[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.

 

[Quattro Pete]

Originally Posted By: Dave424
...but then I still wonder, how can an engine that has made 2X the revolutions in the same distance traveled, last as long?

Most of the wear occurs at cold startup. Once you're up to temp and cruising on the hwy, wear is close to nil.

 

[Burt]

Originally Posted By: Dave424
My current car revs at 4k at 80mph. I also had two civics before... a 1984 and a 2004. both were manual and had very similar gear ratios. I know 90's miatas were geared even shorter with 4-5k hwy cruising rpm.


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

 

[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?