3000RPMs at 70MPH?

[cincyken]

I took my 2007 M35 on a 750 mile trip over the last 2 days. I have only had the car for 2 months now, and it did great with one concern. At 70MPH on the speedometer, the engine is cranking 3,000RPMs. This seems very high to me. My Volvo 850 5 cylinder cranks 2500RPMs at 70MPH, and my wife's 2013 Tuscon 4 cylinder cranks 2300RPMs at 70MPH.
Does this not seem high? 3,000RPMs at 70 MPH?
According to the owners manual, the car has an automatic 5 speed with a 5th gear ratio of .839 and a differential ratio of 3.538. I am using standard tires...245/45/18.
When i do the math, it indicates that 3000 engine RPMs should equate to 80MPH.
My concern is whether or not the car is actually shifting into 5th gear.
Any words of wisdom?

[EniGmA1987]

Its all about how a car is geared. The 5 speed trans M's are geared like that, so there is nothing wrong with it

[Brian35XR]

Nothing wrong with it as in that's how the car was designed so that's how it's supposed to be...

But if you ask me there is definitely something wrong with it!!! Poor job by Nissan/Infiniti.

[svard75]

Mine performs the same way. It's not fuel efficient but it's better in a sense it doesn't always need to downshift to get it over a hill.
I actually have to replace my cats and thought of going with high flow cats but at the same time didn't want a constant drone on the highway. So definitely not aftermarket exhaust friendly either.
But reliability, looks and function should trump this minor problem. If you really can't live with this then think about some new front/rear axle gears. 2.95s?

[CPJ LB]

I actually have to replace my cats and thought of going with high flow cats but at the same time didn't want a constant drone on the highway. So definitely not aftermarket exhaust friendly either.

I know we discussed HFC's on your other thread, but you should try and go to the G35/350z classifieds and pick up a set of used OE cats... I know you can get a pair for less than $150

either in this forum or G35 Driver.... they also have Canadian classified sections
http://g35driver.com/forums/canadian-classifieds-66/

[Larz]

My 07 M35 RWD did 70mph at about 2800rpms. My 09 M35 RWD with the 7-speed gear box does it at about 2300-2400rpms.
Yours sounds about right to me as well. You might want to check alignment and balancing to be sure your tires are rolling as smoothly as possible.

[Brian35XR]

Mine performs the same way. It's not fuel efficient but it's better in a sense it doesn't always need to downshift to get it over a hill.
I actually have to replace my cats and thought of going with high flow cats but at the same time didn't want a constant drone on the highway. So definitely not aftermarket exhaust friendly either.
But reliability, looks and function should trump this minor problem. If you really can't live with this then think about some new front/rear axle gears. 2.95s?

How much would that cost for an M35x since there are two differentials and can you buy them ready-fit or do you have to have custom gears made somehow?

[svard75]

Custom. The lowest I ever found were 3.6

[cincyken]

There is a state measured 10 mile distance on the interstate near where i live. I locked the cruise control on 60MPH and drove the 10 mile course in 9 minutes and 2 seconds. That indicates my speedometer is off by 6MPH, so when it says i am doing 60MPH, I am actually doing 66MPH. Can Infiniti calibrate speedometers?

[EniGmA1987]

How much would that cost for an M35x since there are two differentials and can you buy them ready-fit or do you have to have custom gears made somehow?

It would be expensive. Probably so much that the cost of gas difference between the MPGs over the lifetime of you owning the car would barely brake even to doing the mod.

[svard75]

I actually have to replace my cats and thought of going with high flow cats but at the same time didn't want a constant drone on the highway. So definitely not aftermarket exhaust friendly either.

I know we discussed HFC's on your other thread, but you should try and go to the G35/350z classifieds and pick up a set of used OE cats... I know you can get a pair for less than $150

either in this forum or G35 Driver.... they also have Canadian classified sections
http://g35driver.com/forums/canadian-classifieds-66/

Hey Thanks man. I checked it out and found one guy but missed the boat. They were OEM cats too! I'll keep my eyes peeled there.

[cincyken]

My concern about the 3000RPMs at 70MPH was not related to fuel consumption but wear and tear on the engine. Lots of revs on a long trip.