So the other day i was driving in my moms minivan with the family on the highway, cruising at 80 mph w/ the RPM's @2500. She owns a 2003 Chrysler town & country limited edition. Now today i was driving my badass G35 6MT 03 coupe and i was cruising at 80 mph w/ my RPM's @3000. What does this mean that the minivan has a more efficient engine? I was just curious so if anybody knows about this lemme know Thx!

 

im not an expert on car physics/engineering but i think that's just a result of the gear ratios (in this case, highest gear) for example i read in one of the car mags you can set cruise control on a new GTO at 75mph in 6th gear at 1500rpm.... must be nice mileage for highway drivers

 

just different gearing on cars.... im surprised that doing 80 in the van it was only at 2500rpms .... doesn't mean the van is more efficient

 

75 mph>6th gear@1500 rpm?!? That sounds like GOOD gas mileage to me!
And yea i was surprised too when i noticed my G going @3000RPM>80mph and the van at 2500 rpm. But oh well i guess its not a big deal....

 

The van can afford to drop into a really wide gear to save gas, hardly anyone would ever track or drag it. Where as the G is meant to get up to 155mph, if it had a wider 6th gear you'd never reach 155mph or it would take forever and a day to get there. So in short the van is geared for fuel economy, and the G is geared for performance.

 

its also weird because chances are the minivan has 5 gears.. and you have a 6 speed..

 

^^^^ this may be the problem

 

It might sound good, but the mileage est is a little less than the G's. Rated at 17/25 for the 6 spd & 16/21 for 4 spd auto. Gotta look at the axle gear ratio and the gear ratio in the transmission for 6th gear to get the final drive ratio in 6th. Another thing to remember is that the GTO is a 6.0L V8, 400 Hp motor, so even though its spinning at 1500 in 6th gear, the fuel flow could be just as much or higher than the G.

I'm not sure if it applies to the GTO's but alot of the large displacement motors are now going with active fuel management or the action of shutting down half of the cylinders when it's not required such as at highway speeds or low power requirements to save gas.

Generally what I've noticed is the lower the number of cylinders the higher the RPM to maintain a given speed. 2 of my previous cars a 90 corvette and 94 Trans AM would do around 1500 RPM in 4th gear at 55, where my last car '01 Grand Prix GTP would do 55 at 2000 RPM. All 3 had the same HP rating of 240-245.

 

I appreciate everyones input! The one about the van being geared for fuel economy and the G for performance seems to hit the spot. Damn i love these forums!

 

Nothing to sweat about, but it's to do with gearing for performance, or hwy cruising.
C.

 

also just thought of this: (even though im SURE you make sure your amazing ride is in tip-top shape) other factors can play a role too such as tire pressure, etc.

 

^ exactly. This seems to come up about every second day. If the G were a family cruiser designed for economy and quiet the gearing would be a lot different. A taller gear in 6th would improve fuel economy but would neccesitate more downshifting for passing and accellerating.