Engine/Transmission (1998.5 - 2002) where are you at 80 mph ?

[damon]

When I first bought this truck (first diesel) I could hardly stand the sound and feel when ran over about 2100 rpm's, which equals roughly 70 mph in my truck. After always driving gassers, it just didn't feel right. But now, with some months in the drivers seat, I've found myself cruising the highways at 80 much more often than I ever thought I would, and it doesn't bother me now to run this fast for hours on end.



Just for comparisons sake, I got curious as to how a truck with bigger tires, a 3. 55 ratio, a Gear Vendors O/U drive, or even different exhaust or turbo setup may affect the running #'s.



So here I am at 80 mph, on a 70 degree day, running empty on the flat at less than 500 ft above sea level, how does your truck compare ?



RPM = 2450 +-

EGT = 725

Boost = 14 psi



Oh yeah, one more thing:



Radio = LOUD, so I can hear it

 

[JRodgers]

I got a 2002 ETH stock with 3. 54 rear and 6spd. It runs at 2250 rpm at 80 and radio on loud. Mileage sux though. It gets about 17 mpg while cruising at 80. If I cruise at 1900 to 2100 rpm, then mileage climbs back up to 19. 5 range. I am considering bigger tires and 19. 5 wheels to drop the rpm a little for 70-80 cruising, but havent decided yet on what to do. The cost for either the wheels or the GearVendors looks to be close to about the same give or take a little.

 

[damon]

the best mileage I've ever got was 16, and it drops to 14-15 when I'm running 80 on the highway to work and back. My tires are 265/75 -16, and I'm hoping that bigger tires will help a little when I finally wear these out.

 

[Rob Thomas]

I have 3. 54's, a 6-speed, and 315 tires, @80mph I'm right at 2000rpm's, if I drop to 1900 and 77-78mph, my mileage is much better, about 19ish mpg.



Later, Rob



EDIT: EGT's @ 1900 rpm's, flat ground, 750*

Boost @ 1900 rpm's, flat ground, 4-6 psi

 

[klenger]

I rarely drive over 70 MPH. Of course, I don't drive empty on the freeway very often so it doesn't matter to me anyway. The only time I drive on the freeway out in the open is when I have the 5er hooked up. Otherwise, most all of my driving is in town. To answer your question, I am getting used to running at higher RPM if the opportunity comes up.

 

[Qualey]

"It gets about 17 mpg while cruising at 80"



My 3500 6 speed with 4:10s has achieved a best overall tank average of 15. 2. This was on secondary roads averaging ~60mph with no load. I find that towing has a huge effect on my mileage (I knew it would affect it some, but was surprised at the vast difference). I would kill for 17 mpg!! I was looking at the Gear Vendors, but many have stated that they got NO MILEAGE INCREASE? According to the manufacturer one should see a 20% gain. Why the discrepancy? Perhaps I'd notice more having the lower gears? In sixth gear, wherever the needle points on the speedo, the tach is in the exact postion.



Matt

 

[bigbrassmonkey]

80 mph= 2000-2100 rpm, 600-700egt, boost 7-14psi, avg 19mpg,but at the flick of the foot I can be at 120 in 4-5 seconds

 

[kluther]

2250 rpms at 80 mph

800 ex temp

15-20 boost

overhead comp says 21 mpg . i have never calculated my mileage i want to believe i'm really getting that great of mileage ken

 

[ACoyle]

80 = 2150 RPM (Something like that) 600 EGt 14 - 15 # Boost. The sweetest sound on the highway, don't need a radio. I usually listen to the Cummuns channel.



A ride like no other.

 

[LSMITH]

80mph=2050 or so RPM for me, boost is 5 psi and EGT is 640 on flat ground with no wind. Digital boost and EGT guages too, so no kentucky windage on the needles. Mileage at 80 is 18. 2-18. 5 if I can run the tank out, slow down to 65 and it goes up to nearly 21. Mine is just starting to smooth out and wants to run HARD at 80. I would like to drop the gearing a little and cruise at 2100-2200 at 70 MPH, get into that smooth quiet powerband.

 

[damon]

the sound in the sweet spot is unrivaled IMO, and 80 mph at about 2100 rpm would be very nice.



ACoyle - what size tires are you running ?



many times I've thought that the 3. 55 would work better for me than the 4. 10 that I've got, but I did not have many choices (1) when I bought my truck. So I guess I'll have to "tire up" to get the same ratio.



That's a perfect excuse for the wife..... "I'll get better mileage. But I'll have to lift the front in order to fit the right size, and... ... ... . "

 

[Snow man]

80MPH= 2350 or so in my truck. Stay with the 4. 10,you'll give up quite a bit of the spunky feel these trucks have. if you ever go to a tight TC and/or exhaust brake,the 4. 10 works much better with both of these too,not to mention they tow much better due to being in the powerband at reasonable speeds.

 

[ACoyle]

Hi damon - I have 4. 10's as well. I think I have 285's, I'll verify that tonight. They are upsized form stock. BTW I should ask 80 MPH actual or by the GPS? It makes about a 12% or so difference.



Always leaves me with a question. If you upsize the tires, should you drop the gearing? One could make a real study of getting the power band matched to the gears matched to the highway speed that you wnated to be at for all the above.



I once considered the Ricksons and backed out because I wasn't able to handle the math. I figguerd that I'd be way out of my poer band on the highway.



AC

 

[monkfarm]

transmission temp at 80???

Can Anyone with a 6 sp (and a transmission thermometer) tell me what the temp is at a sustained 80 mph??? I was running the OEM fluid, (without a fast cooler) and my tran temps were cruising above 220 deg at a sustained 80 mph. When the temp warmed up to 70 deg, the temp went up somewhere around 240 or maybe even above. I drained out fluid and it looked fine, and didn't seem to eat up any (I measured, there was enough fluid in there) but maybe my temp sender unit is faulty.

 

[cwarner]

At 80 I'm around 2100rpm's

EGT's at 600

Boost 10-11 (flat ground , no wind ,light foot)

Last time I checked mileage I get 17 in combined city/highway and i've never been able to check highway mileage empty. On the freeway with a 2 place enclosed snowmobile trailer (maybe 2000#'s) at 80mph I got 15-16.

 

[The patriot]

I got a 12 valve, but I've noticed that mileage takes a beating whenever I go over 2000 rpm's, which is about 65 mph~ish in my 98 according to the speedometer. I believe it's really about 70.

Eric

 

[monkfarm]

3.54 gears

I certainly like my highspeed gears, and you can always shift down to get the jakebrake action going. (I guess unless you have that auto) I have plenty of spunk at highway speeds.

 

[SOOT]

With 4. 10's @ 80 I turn about 2750 RPM's and my milage sucks only about 12 empty:{ 10 loaded. If I back off to around 65-70 then I get about 15 MPG empty, 10 loaded:{ I would do a back flip if I ever saw 18 or 19 MPG out of this hog.

 

[Sled Puller]

where are you at 80 mph?





On the highway???

 

[chuck3]

80 mph 2100 rpm

700 egt

6 to 10 boost.