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Minimum RPM for cruising?


We are talking first gear, LA freeways, rush hour.

On the other hand, I5 south of Tracy, I wouldn't cruise at less than 5000 rpm in top gear. After all you wanna get some where, don't ya?
I mean if you were just cruising with traffic going the speed limit like maybe a CHP was right on your ass or you just didn't want to keep checking the rear view mirror. In other words, what RPM is too low @60mph.
For cruising on the highway, keep it in top gear (5th on a 5-speed, 6th on a 6-speed), and decide what speed you want to go. If you want to go 60, go 60 - whatever RPM that works out to.
If Im cruising @ 60MPH, I usually leave it in 4th or above 3200 RPM, Heck there were times I left it in 3rd just to keep the engine rev (sounds sweet) but only for short distances. If I have to travel far with no traffic, Im on 5th at 2680 RPM.

Im just on the other side of the San Rafael Bridge =)
Would be interested to know on a mechanical level - it is a good question.

Obviously if it was say 1200rpm, it wouldnt be doing the engine too good and wouldnt be at its most efficient and economical level. If it was 5000rpm, this would not be economical either - both petrol and maintenance and longevity of the engine. ie - additional wear from the high speed rpm.
For maximum efficiency (gas mileage), you want the engine in the highest gear possible without bogging.

For maximum acceleration, you want the engine in the lowest gear possible without exceeding redline.
I checked the Acura manual awhile back just to be sure. They state 52 mph (just over 2k rpm) in 6th speed if cruising. How about someone with the 5 speed posting Honda's recomendations for comparison. Thanks.
I don't have my manual handy, but your engine will be turning the same number of revs going 48.4 mph in top gear with the five-speed as 52 mph in top gear with the six-speed, assuming the stock R&P in each case.

[EDIT - Corrected mph figure.]

[This message has been edited by nsxtasy (edited 05 April 2002).]
Originally posted by Roadrunner:
I checked the Acura manual awhile back just to be sure. They state 52 mph (just over 2k rpm) in 6th speed if cruising. How about someone with the 5 speed posting Honda's recomendations for comparison. Thanks.

I never thought to look in the manual. I'm kind of a "When all else fails, read the manual" person. Seems to me that cruising at RPM's less the 3,000 is lugging the engine.
Thanks for all your input.
On most engines, 3000 rpm is about where you would be upshifting. 2000 rpm is about where lugging starts.

Actually, on the NSX engine, you can drive it at remarkably low rpm (much lower than 2000) and it will still accelerate - slowly, but it will accelerate.
lugging the engine is not a great thing, but how do define lugging. I see no problem with going down to idle in any gear. But at low rpms in high gears, I wouldn't recommend giving it a lot of gas. To lightly accelerate from 1200 rpm to 2000 in top gear should be fine, as long as we are talking lightly. But as a general rule, If I'm cruising and not limited by speed, I select the gear that keeps my rpm between 2000 & 3000.

NSXTASY, those are prime indicators. But some people might think that anytime you are at low rpm's under load you are lugging. When rock-crawling in 4-low (obviously a different hobby vehicle), there are many times I can have my engine below idle rpm and be giving a little bit of throttle to climb over an obstacle and I wouldn't consider it lugging as everything is running smoothly, but I am on the verge of having the engine die. I know on some rare occasions in very slow 'n' go traffic, I have allowed my braking to drop the NSX below idle in first gear and the car felt fine, and then I would slowly accelerate to higher rpm as permissible, but if I can avoid clutching in those situations I will. I just know that at low rpm's the throttle should be treated delicately.

at low rpm's, one your oil pressure is low, and if you give it too much throttle to where you feel the effects of lugging or you cause the engine to knock, you are putting some serious stress on your rod bearings, and piston pins at a time when they are receiving minimal lubrication. Also, the ideal place for maximum force on your piston to occur is when your power stroke is 1/2 way completed, and at higher rpm's this is closer to being true when under full throttle. At low engine speeds, under full throttle, you can develop high pressures earlier and with the piston being closer to top dead center, the force doesn't transfer as well to spinning the crankshaft and transfers more energy into squishing the oil out and pounding the bearing surface. Now I am not saying this is going to cause immediate catastrophic engine failure, but it is significantly increasing wear & tear.