Duramax vs. 8.1 (my opinions after tow)

[Steve Cornell]

I just returned from a 1700 mile round trip to Daytona with my 03 Duramax and here are my opinions of the 2 trucks since I have made the same trip with the same trailer with both of them.

The Trucks.....

01 2500HD CC 8.1 \ Allison 3.73 gears stock tires
This truck weighed 7380 lbs with me and the wife.
1375 miles on the truck when the trip was made.

03 2500HD CC Duramax \ Allison 3.73 gears 265 tires, I haven't yet weighed the new truck.
the truck had 1925 miles when the trip started.


The Trailer......

36' triple axle 36'x 8.5' gooseneck car hauler with living quarters and a 96 Impala SS inside.
The trailer weighs 14,850.
So I have a total Gross weight of around 22,200 lbs.


Mileage......
on the 01 8.1 - 6.69 averaged over the entire trip.
on the 03 Duramax - 9.05 averaged over the entire trip.
(this is running 70 mph on both trips)
The 35% better mileage while loaded is about what I expected pulling this heavy load at these speeds.


Power..........
I really liked the torque of the Duramax, from a dead stop it gets up and going a bit faster but there's not much difference.
The 03 Duramax was much better at cruising speeds and didn't shift out of overdrive nearly as much as the 01 8.1 however It still shifted out of OD too soon while in cruise (about 3 mph) I would think the latest updates would be installed but I'll check.
Pulling a hill is where the BIG difference is, on the long steep grades the Duramax would pull good but it won't keep up with the 8.1 pulling this load, there is one particular hill that I documented on both trips (Fancy Gap in Va. on I-77 northbound) hitting this hill at 70mph with the 8.1 I could top it at 70 mph, I have pulled this hill many times with the truck and could even back off and slow down and get back up to speed,
I hit the bottom today with the Duramax at 70 mph and I topped it at 58 mph, however the diesel was in 4th gear and the 8.1 would be in 3rd and "screaming", this is the only place I see where the 8.1 had an advantage.

I'm not disappointed but I never had the desire for more power with the 8.1 and with the Duramax I now can see I'll be getting "Jucied" in the near future :D

These are my opinions from owning both trucks, if you don't mind the lower mileage and like to hear the Big Block "scream" it will pull every bit as good as the Duramax.

Unloaded I was getting 12-13 mpg with the 8.1 and have been getting 17.5 with the Duramax but I haven't had it on a trip yet empty and it had less than 1900 miles on it so it should get better.

Note.. all the numbers are compensating for the larger tires on the 03 (4% more circumference)

This was also my first trip for the new TTT mirrors, I'll post my thoughts on them in the Accessories forum.

[ 03-24-2003: Message edited by: Steve Cornell ]</p>

[huntindog]

Steve, thanks for the report. I wish you had the stock tires. I'm not sure what size is stock on a 2500, but my 3500 came with 215s. That would be a 23% difference! Or the same as 2.88 gears!

[Steve Cornell]

huntindog,

The 2500HD comes with 245\75\16 tires
I installed 265\75\16 tires
this makes the speedometer 4% slow.

[Oongawah]

Steve,

It'll be interesting what the results are when the max is broke in.

[Mark Heiken]

Steve,
Great comparison on the 2 rigs. As you stated about your milage increasing as the Dmax breaks in so will the power increase. First tow with mine, I wanted my 454 back. Put a few more miles on and I'm sure you'll be imoressed. You also hit on the second thing.JUICE. That will impress you even more. With juice and all else stock mine made my buddy with a much played with Power Stroke feel rather ill. Now he has a new 6.0 PS, so we'll see what happens this summer!?!

[huntindog]

Steve, I've read a lot of articles over the years about the effect of taller tires on gearing. Every article has said that the easy way to figure it is to take the percentage of increase in hieght and apply the same percentage to the gears to decide what the new gears should be.ie: 30" tire stock-33" tire aftermarket = a 10 percent increase and 3.73 gears stock would need to be 4.10s in order to go back to stock rpms.

Your 245s vs. 265s is an 8 percent increase over stock and would requre 4.02s to maintain the stock gearing (4.10s are the closest choice).With this large a disparity in the effective gearing, I'm not suprised that the 8.1 appeared more powerful.
You state that your speedometer is off by only 4 percent. Was it slow stock?
This formula I have been using for years appears to be accurate on other vehicles I have owned.

[ 03-24-2003: Message edited by: huntindog ]

[ 03-24-2003: Message edited by: huntindog ]</p>

[Steve Cornell]

huntindog,

The stock tires (245s) calculate out to 30.5" tall
The 265s calculate out to 31.6" tall
All tire brands will be slightly different but if you use the tire measurements this adds up to just under 4%

Many are running 265 tires and have checked the speed with GPS and other means and have found that the difference is around 4%, I also checked on this trip and found this number to be accurate.

The 8.1 didn't "feel" more powerful it just pulled the hills faster :D which makes sense, it has a wider operating (RPM) range.

[ 03-24-2003: Message edited by: Steve Cornell ]

[ 03-24-2003: Message edited by: Steve Cornell ]</p>

[TraceF]

I originally joined the Diesel Pages because I wanted to talk about my DMax towing. I was like beeler, I was thinking I had made a huge ($) mistake and that my 2000 454 would easily outpull the Duramax.

The truck has racked up almost 9000 miles and I am a lot happier. I am running the Juice 90 but even without it the truck seemed to break in and it runs much better than when I bought it.

Don't worry- it'll come around.

[huntindog]

Steve, My mistake. I was thinking that the 245, 265 was the height of the tire. I forgot that it's actually the width, which has an effect on the height. Now it makes more sense

I will never forgive the tire makers for going metric and making our lives more complicated!LOL.

[Mike Fultz]

Steve: Fancy Gap Northbound is a great test hill. I pulled my Haulmark 24' double axle trailer up that hill, loaded, coming out of Winston Salem this past January in my '03 2500HD CC DA I kept it at 65mph the whole way up and dropped out of OD about 3/4 up the mountain, the only time on my trip the truck dropped out of OD. I watched carefully the temps and they stayed cool. When I do this hill in my 98 3500 BB gasser, it drops out of OD about 1/2 way up and screams close to red line the rest of the way up, and the temps rise quickly.

[ryeguy]

Thanks for the comparo.

Quick question: what do you think of the tri-axle trailer you tow? Are you happy, or would you go for a tandem dually instead? That's my next decision.

--Rob

[Derek M]

FYI

I found some info on the tirerack's web page that listed the number of rotations per mile for the stock Bridgestone 245's versus my current Michelin 265's. The difference in rotations per mile was roughly 4.5%

[Steve Cornell]

ryeguy,

I have never pulled a tandem dual RV but I would think that they would pull great, I have pulled many other small dual wheel trailers and they handled good, the dual wheel is not an option (as far as I know) on a car hauler as the fender wells would be to wide to fit a car without ramps.

There is no comparison on a triple vs. a tandem however on a single wheel trailer, I have pulled both (goose & tag) and the triple handles much better, another thing I always have built into my car haulers is to go with 6000 lb axles instead of the standard 5200 lb axles, this gives you a 16" E rated tire with a 3042 lb load rating instead of the "wimpy" 15" trailer tires, this really helps with sway on the road.

I had a 26' tag built this summer with 7000 lb axles and "G" rated tires (tandem) it handled very good also but I still prefer the triple.

[ 03-30-2003: Message edited by: Steve Cornell ]</p>

[britannic]

This site has some good calculators for gears etc., http://www.4lo.com/, just copy and paste to your browser address window.

Here's a site for tire diameter calculations: http://www.rx7turboturbo.com/robrobinette/tire_diameter.htm