Auto vs Manual Transmission
 

I own an Automatic BRZ.

I know people who own Manual tranny cars can rev their engines and when they drive, their RPMs are typically higher. For example, the cruising RPM is around 4k is what I hear.

In comparison, Im usually cruising at around 2.5k-3k RPM.

My question is, is it bad for the Auto transmission if I keep my RPMS high at like 4k at all times while driving?

over/under on 'shoulda bought a manual' responses @ 6

You don't cruise at an rpm, you cruise at a speed. If the speed you're driving at happens to be at 4K RPM, then such is life. If you're cruising at 4K RPM in a lower gear when you could up shift and lower your RPM, then you're just wasting gas.

No, your car will blow up

i keep my rpm at 4k in 4th gear all the time for a long time just in case i need to downshift to third for that break necking torque when i need to overtake another vehicle and make a lot of noise

I'd say that you actually do both. for any given speed, you pick a gear that puts you in an rpm range that matches your intentions. if you're 'cruising', which to me, means that you're maintaining that speed without much variation, then 4k sounds high. i'll leave it at 4k if i anticipate wanting to accelerate. otherwise i'd just select the gear so i'm around 2.5k to 3k. lower and it bogs the engine.

OP - your cruising rpm range sounds right to me. waste gas on accelerating, not cruising.

i saw your name when you replied and I was like "I hope his avatar is of shuimai"

Was not disappointed.

Pull it thru that torque valley baby!

MT. > Auto

Is it bad for the transmission or engine though?

Not if you don't mind overheating your headlight fluid which is situated right next to the transmission.

AT and MT have their place. Just as AWD and RWD have theirs. You can not drive two cars at the same time. Some bought a Silver car, me, and others have bought blue or even now yellow! Would I buy a Yellow car, no. But does that make silver "better"? No not for a Series 1.0 or 2.0 buyer. But, for me yes. Just as MT is "better" for those that love it!

So Enjoy your car! Shift it at redline, or at 2000 rpm, whatever!

No.


humfrz

MT, never spend any time at 4k rpm.

The only reason to do that is to make noise.

...or you're going faster than 90.

If I'm doing over 90 I'm in 4th gear over 5k rpm thankyouverymuch.

But I suppose those that live in flyover states with 90 mph speed limits probably do hang out at that rpm.

:thumbsup:

The only problem is if you're cruising at 2.5K rpm, and you accelerate, then lugging the engine will cause knock and that's bad. Your automatic transmission will automatically downshift if you need to pass someone. Us MT guys have to do that ourselves.

There ain't no power below 3K so I save that for long steady stretches, to save gas.

-Mark

Let's rephrase the question to:

Is it advisable/advantageous to cruise at 4k rpm instead 3k rpm for normal street driving, or on the highway/freeway?

My short answer is NO ...... ;)

One of the few times that I "cruised" at over 4,000 RPMs, in a low torque, low HP car, was at 14,000 feet in a loaded down miata.

Why? Because just in case I needed every bit of power that puppy had to pull (push) me through a curve ....... especially on what were the gravel sections.

Do you see the guardrails to save you ...... ?? You don't, because there weren't any.

Yep, your machine will be happier cruising at 3,000 rather than 4,000 rpms .....and you will save gas ........:thumbsup:


humfrz

My car is supercharged -> no torque valley :D

OP - just because you can, doesn't mean you should. Don't focus on a number or specific RPM (except redline); just pick the gear that provides what you need at that time. Choose your gear by feel and engine sound. If you need more acceleration, downshift. If you need to save gas, stick to 2500 to 3000 rpm. There's no need to buzz up and down streets or the freeway at a constantly higher rpm unless you just want to make noise, run at a higher oil temp or waste fuel unnecessarily. With the AT (which I have as well), I shift manually or keep it in sport mode , which keeps the revs about 500 rpm higher than normal mode. normal mode tends to bog the engine in stop and go traffic, and is more suited to freeway cruising.

Like @humfrz illustrated, there are times when you would drive at higher revs, like in the canyons or on the track, when you want to keep in a certain power band. But not typically needed for every day normal driving.

Listen to your engine, it'll tell you where it wants to be for an RPM range.

If you are going at a steady speed for a long stretch, keep your RPMs under 3000 to save some gas. As for the autobox, it'll automatically keep to a safe and fuel conscious RPM range. If you want to cruise at 4k RPM 1) you should have gotten a MT 2) Watch your transmission temps and make sure it's in a happy range. 3) (Q for for those with a slushbox) Does Torque Pro have tranny temps and what is a happy tranny temp for this car?

I've got the AT and the only time that I'm up around 4k is in the mountain portion of my commute. I don't worry about overheating the headlight fluid as I ponied up for the optional headlight fluid cooler.

I can't think of a single good reason why you'd want to drive around "cruising" with your engine at 4000 rpm. If you were climbing an incredibly steep hill with a car loaded w/ cinderblocks and that was the only way to keep the car up to the speed you wanted, then OK. Otherwise... why?!?

Think of riding your bicycle. Would you want to pedal furiously w/ very little resistance in the pedals to go a certain speed, or at a comfortable 60-70 rpm cadence (what most casual bicyclists use, including myself) w/ a bit of resistance felt to work against? On a bicycle, you choose the gear that gets the job done most efficiently and with the least amount of effort/wear from/on the rider (the engine) in a given scenario. Cruising around at 4000 rpm is like riding a bike on a flat smooth road in the lowest gear, requiring you to pedal like mad. Even worse, unlike on a bike, when you take your foot OFF the gas in your car, the engine will create a lot MORE resistance and slow the car down faster than it would in a higher gear. Going down a steep hill, that's desirable.. OK, that may be an another instance where "cruising" at 4000 rpm might be a good idea; going down a steep hill and using engine braking instead of overheating your brakes.

Otherwise, I'm stymied by the original question. Why would you want to? The upper ranges are for acceleration and power. I routinely cruise flat roads between 2000 and 2500 rpm, and downshift when I need more power.

Still confused by the desire to stay in the upper ranges....

Barry

Um, because cruising sometimes means (Texas highways for me specifically) going 80+ and 80 is right at 4000 RPMs? Nothing you can really do about it except change the final drive ratio and I don't care that much.

That's a specific situation where you don't have the choice to upshift any more as you're mechanically limited. Then of course, it makes sense to do so.
I wish socal cruising speeds were 80+ (without drawing attention). :)

Just making a point to say cruising at 4k RPMs isn't going to kill your car or anything like that. And sometimes that cruising at 4k RPMs is just that, you're cruising at 4k RPMs, lol. Just seems like a lot of replies here are like "WHY?!!?!" um because that's the gear ratios they put in the car and I'm going at a normal rate of speed?

I drive around the city with rpm's really low, cruising at high rpm is just making noise and wasting gas. You can easily drive around town in 5th (MT) at 60km/h+ without lugging the engine, just don't floor it and expect it to accelerate.

This engine doesn't lug until you're well under 2k rpm, makes no power below ~2.5k, sure, but it's not lugging.

Or you're putting in shittier gas than California gets...

About 80% of Socal has cruising speeds of 80 mph, you just live in the 20% where cruising speed is 20 mph

;)

"Um," ... I'll try not to respond in a similarly snarky manner. Your point is, of course, obvious, but irrelevant to the original poster's question. He was talking about CHOOSING to "cruise" at 4K rpms, implying that there were other options. Sadly (or not), where I live cruising at 80+ garners you a LOT of negative attention by the police and endangers the lives of the rest of the folks who at least make an attempt to stay w/in the typical 55 mph and 65 mph limits of our state. If you have 80 mph highways, then of course you have no choice but to exceed 2.5K rpms. At those speeds, drag becomes more of a factor anyway so more power IS needed to maintain those speeds.. hence the lack of higher gear ratios usually available.

I stand by my point, but I'll preface it with "If you have a choice,".. just to make everyone happy.

Best,

Barry

Wow some of these responses really make me think some of the MT crowd have inferiority complexes. Guys - its a transmission. In AT manual mode the driver still has the choice of gear and can set the desired RPM for speed.


Having said that, in "normal" auto mode the transmission wants to be in 6th gear - just like any other auto would. Around town this means your cruising at 25 mph in 6th gear at like 1100 rpm. You can override this by using the "sport" auto mode which at 25 mph will be in 3rd gear at around 2100 rpm. Or shift yourself in manual mode of course.


Personally, I have a drop-in performance intake air filter so the engine torque has enough pull to make small speed adjustments around 25 mph in 6th without forcing a downshift (this bugged the crap out of me with the stock filter). Around town cruising in normal mode is quite nice actually now. Assuming you have a flat town...

:bellyroll::bellyroll::bellyroll::bellyroll:

Good, because you should preface it with that if you actually mean having a choice.

It seems to me that a careful read of the original post to which I originally responded (prior to getting caught up in our current little tiff) ......

... makes it painfully obvious that a choice was involved. Maybe I'm just supernaturally gifted with otherworldly perceptive abilities... :sigh:

Granted, the OP may be operating on a few fallacious statements, i.e., that MT drivers keep their rpms higher than AT drivers as a general rule, and that MT drivers generally cruise at 4K rpm. The last part, especially, doesn't describe the way most of us MT drivers drive, but hey, that's his perception. His question is obviously regarding gear selection; there's no other possible way to "keep my RPMS high at like 4k at all times while driving." Sooo... there you have it. Please forgive me for not stating the obvious.

Have a swell day,

Barry

My interpretation was both trans can choose. No, the MT really does hit 4k at 80mph because that's the ratio. We/MT users CANT choose anything else. And AT has different ratios which lowers it to 2500 or 3000 or whatever then HE can choose to go higher due to the AT. So a one-sides choice? I guess?

But in reality, it's neither here nor there. And I don't care enough; I'm just responding to kill time on a Friday afternoon

LOL.. Yeah, I'm just waiting for my wife to get home so I can finish assembling a Caesar salad and slice some bread I just made to go with.. OK.. glad it's all in fun.

Just to clarify, though.. to drive at 4k revs "at all times," meaning, not ONLY when going so fast that you have to be at that engine speed in your top gear, you'd have to shift to lower gears and REMAIN in them to keep your engine revs that high at lower speeds. Doing so is possible with either MT or AT vehicles. He was asking about the advisability of doing so. The question had nothing to do with the final gear ratios of MT vs AT. You are correct re/ the difference in ratios of 6th gear; the MT 6th is .77, while the AT 6th is .58. Both final drives are 4.10. So, yes, the rpms would be lower in the AT at the speeds you're describing. The thing is, that has no bearing on the original question.. that's all.

Enjoy your Friday,

Barry

but we havent made it to 6, yet. the fun cant end.

sidenote -texas has lots 75 mph strips so youll get blown by while doing 80.

edit: op never answered the why? as posed earlier.

Lool damn guys. I didn't expect to come back and see 3 pages.

Thanks for the replies, I got the answer I needed!

I just don't like how the normal mode on the auto shifts my RPMs so quick. I'd turn a corner and id get stuck trying to go up a damn hill because it shifted to 5/6th gear so quick.

I was just curious if it was BAD for the engine/transmission, not so much that I would actually keep it at 4k RPMs.

Again, thanks guys!

IBTL

I cruise for a few miles at around 4k on my work commute. It's at a spot called "Malfunction Junction" and I like to keep my RPMs up for when some moron tries to kill me so I can scoot out of the way.

Florida drivers are THE worst.

Since the OP is in Ontario where the "maximum" speed is 60 if he is cruising at 80 he is in a pile of trouble. If he hits 90 and gets caught he losses his car for a few weeks and pays a $5k fine and impound fees. I had no doubt it was choice he was talking about. The presumption he was doing 80 just didn't fit.