Black Betty

iTrader: (60)

I have a little over 7900 miles on Betty and I've noticed what seems to be a significant increase in gas mileage. I thought his might be due to me driving a little less lead footed now that I have gotten over my initial infatuation of the new relationship with my new girlfriend. Then last night I noticed something...

When I first got her I noted that with the cruise set at exactly 70 MPH in 6th gear the tach showed exactly 3K RPM. I think the warm engine neutral idle speed was about 800 RPM. Now I noticed that 70 MPH cruising yeilds a tach reading of only 2750 RPM. Idle is at about 700 PRM. Will anyone with a 6MT that is much newer than mine please note and post their RPM cruising at exactly 70 MPH, and also the engine idle speed with the engine fully warm in neutral?

King of Torts

I'll take a look when I drive home later today . . . my car has about 1200 miles on it, and I'm getting better gas mileage too (but attributing that to the less hard driving, as well).

chasemyaccord

iTrader: (2)

Are you serious Torts? I haven't noticed better mileage on mine yet...I'm on my 4th measured tank (I forgot to reset the fuel info a couple times) and I'm still hovering at ~20mpg with pretty conservative driving.

I don't know about the RPM's at 70mph in 6th, but I'm pretty sure mine idles in neutral at around 700 RPM's. I remember it being slightly below the 800 RPM tick mark. I have 1970 miles on mine.

Geez, based on your avatar, I wonder what your RPM's were at while "cruising" at 150

djkymar

iTrader: (5)

Im cruising at 80 MPH at 3K RPM and with 70 its about 2800 RPM. I have a lil over 3000 miles on mine IP.

ELP_JC

Something's wrong with that math; if 80=3K, 70 has to be 2625 rpm.
I also noticed 80 @ 3K rpms on my test drive, which was a bit of a disappointment (too high), but have to take into account the higher rev limit of 7,500, I guess.

And speedo signal is fed from tranny or differential, so you could be driving on your rotors and your speed will always show the same at 3K rpm (or any other rpm, for that matter). And an electronic cluster either works or not. My guess is you didn't pay attention until now. Later.
JC

mal_TX

MT's are mechanical transmissions... the gearing will not EVER change. The rear tires turning at a certain speed will _always_ result in the same ratio of RPMs at the flywheel.

Unless your clutch was slipping and now it is not, your story has to be explained by your being mistaken about the RPMs when new or your tachometer or speedometer losing accuracy. I can't imagine your tires are worn enough or over/under-inflated enough to throw your speedo off this much, but I suppose it is possible.

Anyway, 70mph in 6th is most definitely NOT 3,000 rpms in any g37, new or old. 3,000 on the tach is more like 80mph on the speedo.

As for idle, yes that can vary depending on what the ECU is doing, since in that case the tranny is disconnected from the engine. My car idles right around 700-800 w/ the AC on and maybe a little lower with it off (500?).

King of Torts

Well, Chase, I was only getting around 17 mpg on my first couple of tanks and am now getting 20 mpg. So I guess I was just driving it much too hard at the outset!

fkat

I was going to post a similar question in the tech section. I got the car on 1/26 and still on my original tank of gas from the dealer. Has 210 miles. 2700rpm @ 70mph the last time I checked. Will check again.

King of Torts

At 70mph, I'm showing around 2800 RPM. My car has 1200 miles on it.

ELP_JC

That's very weird, if yours is a 6MT indeed. I test drove a 2nd manual today, and just like the first, it showed those same rpms but at 80, not 70. Even 80 at 3K is high enough to almost write it off, but 70 would be ridiculous.

I guess we need to ask ourselves where the hell is the speed sensor. I don't think that many of you can be that wrong. Something's fishy for sure. Later.
JC

djkymar

iTrader: (5)

I have manual and i def getting 3K RPM going 80 and 2800 RPM going 70 i check today myself again after i read the post. My other SUV which is 3.5 liter and 4AUTO going same 80 with 3K RPM but its different car and different story.

Black Betty

iTrader: (60)

It seems we are all in about the same range. Perhaps I was at 80 MPH when it was 3K RPMs... it's been several months and now I have doubts if I'm remembering it correctly.

King of Torts

ELP, I have no idea what you're talking about. Speed sensor? Write it off? What's the problem with 2800 RPM at 70 mph?

cskubis

I don't understand the problem some seem to have w/ our engines turning 3K RPM @ 80MPH. This engine redlines at ~7500, and is designed to rev ... that's how it makes its power. This is not a big V8 designed for low-end torque.

For comparison, I used to have an Integra GSR that would only do 60MPH @ 3K RPM. This motor was designed to rev as well (8K+ redline) and proved to be very reliable.

I also had a Ford 5.4L 4x4 that turned ~2200RPM @ 80MPH. Different engine, different tuning.

I guess my point is don't get hung up on the RPM's. They're hard to get used to if you're coming from something different, but after a while they won't bother you.

Black Betty

iTrader: (60)

I understand that that RPM range is normal for this engine and that's not the problem at all. I just thought that it had changed where the reves were at a given speed and shouldn't have. But like mal_TX said, I found out that I was mistaken. I was at 75 MPH wnen the engine is at 3K and that's normal. The AT boys should be at even higher RPM since their gearing is shorter in top gear.