# Trucks & Gear Ratios



## Y-Guy (Jan 30, 2004)

Ok I'm toying with the idea of moving up to a Diesel 250/2500 truck. I'd like the better mileage and tow capacity they offer. I love my Av but I'm close to my limit and the front buckets limit us to taking 5 people and with the kids taking friends is probably going to happen - should have seen that coming.

So anyway I picked up brochures for Ford/GMC/Chevy and all show the Diesel rigs max out with 3.73 rear ratios... I am wondering why? Would it be to much power? Very confused. While I'm at it what's the difference of the 250/0 and the 350/0's?


----------



## jgerni (Nov 10, 2003)

Diesels develop their HP/Torque Low in the RPM range so 3.73s work well. I donâ€™t have a diesel truck but do have a 2001 VW Jetta Diesel car (love getting 50+ mpg). It develops it max Torque at 1900 RPMs.

They probably add an extra leaf spring in the 350/3500 single wheel series but other than that I believe they are the same. One issue the manufactures were having with the single wheel was that they had the suspension to hold more weight than the tires were rated for. Thatâ€™s why the 2500HDs had a strange GVRW of like 6094lbs. I think this issue has been solved with the new 265 size tire instead of the 245.


----------



## Aquaduct (May 30, 2004)

Y-guy,

jgerni is correct. For your bemusement, I'm posting something I put on rv.net just before they closed a thread. Perhaps it will help your overall understanding.

And by the way, I don't know what your brochures say, but a quick look at the Ford Superduty website lists towing capabilities of the various engine packages. The 6.8 L V10 gas engine actually has a higher rated tow capacity than the 6.0L Powerstroke Diesel. The V10 generates a little more power, but at higher rpms, and is geared at 4.3/1 vs. the PSDs 4.1/1. The PSD is heavier, though, which counts against tow rating. And the diesel is about $5000 more than the V10. And they don't have diesel in every corner gas station. And they're typically noisier and smellier (although that's getting better all the time). That's what I'm refering to in the following post as the downsides of diesel. So just be careful of broad generalizations.

And the 150/250/350 numbers are marketing names that actually used to indicate hauling capacity (1/2 ton, 3/4 ton, 1 ton respectively). Now they remain marketing names they indicate relative structural capacity with no quantifiable relationship to reality.

The post that triggered my response:

You guys corn-fuse me. Please provide the proper term for the following statement (since now the word Power now only relates to Horsepower -news to the rest of us - and Torque is not measured in time):

" My new diesel has more () than my gas truck since it was able to move X load over X distance in X time X min faster "

Power = The rate at which work is done, expressed as the amount of work per unit time and commonly measured in units such as the watt and horsepower.

Torque =The moment of a force; the measure of a force's tendency to produce torsion and rotation about an axis, equal to the vector product of the radius vector from the axis of rotation to the point of application of the force and the force vector.

My response:

You're correct, those are the scientific definitions. But the intersection can be a little difficult to understand. I'm a powertrain engineer with a heavy duty truck engine manufacturer (a hint: we don't make small engines like you folks are talking about) and perhaps I can make things a little clearer.

Acknowledging the physics that you mentioned and realizing that torque is the measure of the force that moves stuff and pushes you through the back of your seat, lets skip ahead. Torque and power are related as follows:

Torque = Horsepower x 5252/rpm (in our US units, not metric)

So at any operating point, if you know either the torque or the HP, you can calculate the other. Note that the real differentiator is engine speed. Also notice that for a given HP, the lower the rpm, the greater the torque will be. So how does this apply to this discussion?

I once saw a comparison that illustrated things pretty well. It took 2 engines, a Cat C12 heavy truck diesel and a Mustang Cobra engine. Both produced peak power of somewhere shy of 450 hp. The C12 was about 5 times heavier than the Cobra (2000 lbs vs 400 lbs). The C12 displaces 12L, the Cobra 4.6L.

The trick ended up being that the C12 hits rated power at about 1800 rpm, the Cobra somewhat shy of 7000 rpm. So they took a point on the HP curves of something like 375 hp. The C12 hit that at 1200 rpm and 1650 lb/ft of torque and the Cobra hit it at 5500 rpm and 350 lb/ft of torque. I'm not sitting with figures in front of me, but you can use the above equation to get more precise.

Torque can be changed by gear ratios so they went on to add a gear reduction (think transmission) to the Cobra of about 4.5/1 and it ends up giving you an output speed of 1200 rpm AND torque of 1650 lb/ft. Of course the reason you don't put a Cobra engine in a Peterbilt is that the C12 is puttering along at 1200 rpm for that torque while the Cobra engine is screaming at 5600 rpm for that torque. The C12 will definitely last longer. Of course, the Pete also won't go 170 mph since there's only so many tire rotations you can get out of 2000 rpm. The Cobra, on the other hand, won't carry much more additional weight than perhaps 2 people and a small bag of scones.

So, why do diesels typically produce more torque? There are a couple reasons and one of the main ones has to do with rpm again.

Remember that a diesel is a compression ignition cycle with compression ratios up to 2-3 times a gasser. So the base engine components are heavier generally. Also understand that there's one inviolate limit in the design of an engine, mean piston speed. The max is a little better than 19 m/s. You can't get air into and out of the cylinder any faster than that. As engine speed increases, so does piston speed. Also, as stroke increases, so does piston speed since the crankshaft offset must also increase (I'll leave you to ponder that geometry problem).

A diesel with it's heavier components generally runs slower than a gasser and, therefore, doesn't really concern itself with rpm speed limits. This allows the engine designer to increase the stroke, lengthening the lever arm (crankshaft offset) and producing more torque. If you notice, a gasser's bore tends to be bigger than the stroke where a diesel will have a bigger stroke for the same displacement. Hmmmm, tricky eh?

In addition to geometry advantages, the diesel can continue to fuel expansion farther into the power stroke while chamber volume is increasing. Gassers are knock limited so turbos can only get 10-15 psi boost from a turbo where diesels can easily run 30 psi and up to 50 psi under some circumstances (that's also why not all gassers are turbocharged, the benefit is relatively not that great). And, finally, diesel fuel has about 10% more energy than gas.

So, yes, diesels generally produce more torque and are, therefore better pullers. In addition, diesels get 25-40% better fuel economy and, at idle, consume about 50% less fuel. The downsides highlighted so far in the thread are about right, although I will say that current diesels are getting better and cleaner all the time (professional pride doncha know).

I hope this helps. For the record, I tow an Outback 25RSS with a 2004 5.4L Eddie Bauer Expedition gasser. Yeah, I know I could tow cheaper with a diesel, but the TV is my wife's and I'd prefer getting some nooky to saving money.


----------



## Y-Guy (Jan 30, 2004)

Thanks guys for the replys that confirms that I thought but hadn't had time to read up on them. Aqua thanks for the post, very detailed and helpful. (a thread locked on RV.net.... imagine that







)

For now its mostly academic, but with the kids, dogs, stuff, generator it makes me wonder if a full size HD truck would have been better in the long run than my Av. The good thing for me is that my dealer in Stockton gave me a very good deal so based on the KBB and NADA I appear to come out okay if I sell/trade it.

Since I have no Ford/Chevy loyalty I'll just keep looking and comparing them and reading the various forums and reviews. That will keep me busy for months LOL


----------



## lukn2doit2 (Jun 4, 2004)

Y-guy, I have been pondering this idea since I brought the outback home with my wife's Tahoe. It will pull it and its stable, but I have a crazy time getting the RPM's up to 3k or more to use the torque!!! I about didn't make it up a mntn hill in north ga this past 4th because I just couldn't get a running start to get the rpm's up in 1st...

Just for my 2 cents...

I looked for a few engines that were on the cheaper side, along with towing capacity ratings a good percentage higher than the Tahoe.

The chevy/gmc 2500HD with the 6000 has an excellent mix of LOW torque and 10200 # with 4.10. I do believe I saw on the chart that it was over 300ftlbs at 1000. The chevy showed a GVWR of 9200 and the gmc 8700 or so.

I like the ford, but you have to got to the v10 (even though the 5.4 in the f250 is a different breed than the 5.4 in the F150 - better low in torque) - the 5.7 hemi in dodge (on SALE now) is hard pushed to get that much low rpm torque.

If I could get out of my (her) Tahoe I'd get a 2500HD GMC with the camper mirrors and the 4.10 with the 6L. For a list of about 31k to 36k and $5000 rebates - it would be nice.

As our garage has told me, just run the Tahoe till the tranie falls out and then replace it with a GOOD rear end - that would be cheaper than trying to get out of your 04 into an 04.

Guess what I've found is that I can (in my area) go to a Chevy/gm dealer and actually find a truck for towing an RV.
1. low rear end
2. class 4 hitch
3. trailer tow package (lighting)
4. trans cooler
5. camper extended mirrors
6. LT tires and SMALL wheels

all factory

crazy thing is, nissan is right up there at 9400# with a LARGE part of is torque at 1000rpms - but I wanted a bit more wheel base.

ok, that was about 20 centz

I learned some from the info above, great...










y-guy, i know we will, but i'd really like to know how your quest goes...


----------



## hatcityhosehauler (Feb 13, 2004)

Small Block for diesel trade up? Hmmm, that seems to be contagious. Before I bought the Av, I looked at a 2500HD with the Duramax/Allison combination, and I was instantly in Love.....What a nice truck. Since I was replacing a 1/2 ton chevy pickup (no extra cab....needed the back seat space for the kids), I was not concerned with the ride. The DW on the other hand felt it rode and handled "like a truck". Imagine that. Needless to say, 4 months later, I purchased the Avalanche, for about $3425 less then I could have had the 2500 for.

Well, the day we brought 26RS home, I told the DW that the next truck would be at least a 3/4 ton chassis, and after the latest gas price gouge that occured this spring, the diesel entered back into discussion. Steve, keep us informed on your research.

Tim


----------



## JimWilson (Feb 24, 2004)

lukn2doit2 said:


> The chevy/gmc 2500HD with the 6000 has an excellent mix of LOW torque and 10200 # with 4.10. I do believe I saw on the chart that it was over 300ftlbs at 1000. The chevy showed a GVWR of 9200 and the gmc 8700 or so.


Where did you see that HP chart? I don't think GM's 6 liter has that much torque come on so low.

I've got the 6.0 and 4.10's in my truck, and I can tell you it runs out of breath when you attached a heavy load (in my case it's about 8000 pounds of backhoe and trailer).

Since the 6.0 is a small block it makes it's peak torque up relatively high in the RPM range (for a V8 anyway). I don't think you'll find it making 300 lb ft until somewhere around the 3000 RPM range. IIRC, the redline is close to 6000 RPM, which is pretty high for a V8. If you got 300 by 1000, and the peak was around 350, you'd have an awfully long and flat torque curve for a small block. While it would be nice, it's probably not gonna happen.

Short strokes have there drawbacks...


----------



## lukn2doit2 (Jun 4, 2004)

Jim,
I hope I was in the right place... And looked at the chart right...

right at 1000 the 300lbft starts and then crosses 300 on its way down again at about 5500??

the HP is a very steep curve.

Im prob looking at the desiel, uh - or even an aftermarket vortec config?

http://www.gm.com/automotive/gmpowertrain/.../lq4_curves.htm


----------



## chetlenox (Feb 3, 2004)

Y-Guy,

Ever thought of a diesel Excursion? Seems like it would fit your bill relatively well. Carries lots of people, easily tows a 7k lb trailer, and gets relatively good gas mileage (I've averaged 12.5 towing, 16.5 in-town, and 19.5 highway). The only downsiden to me was the price (especially of the diesel option). So I tried to avoid some of that by buying used, although it took me a good 6 months to find the right truck. Before you do, make sure your wife doesn't mind the added smell and noise of the diesel. I've got the old 7.3L powerstroke and I don't find it bad at all, and I hear the new 6.0L is even better in both regards. My wife actually prefers it (she grew up in small town Texas, so trucks are nothing new to her). Also, you'll probably find that the unloaded non-towing ride is not as smooth on an Excursion compared to your Av. The springs are very stiff and the E-load tires don't give much.









Anyway, you said you weren't a Chevy vs Ford man, you ought to give 'em a look. We have the same trailer and pull in the same mountains as you do, and we are very satisified with our Ford.

Chet.

PS - Great mini-article on HP vs Torque, Aquaduct. It's always great when somebody gets into these posts that really knows what they are talking about. I definitely learned some things!


----------



## Y-Guy (Jan 30, 2004)

Thanks Chet, I thought about the Burbs, but I really want to keep a truck bed for now. With bikes and genereators I'd rather not have to deal with those two, plus I need to haul stuff enough that another small trailer wouldn't be as practicle. I'm still thinking though. The cheap route is to add the air bags and see if that stiffens the ride up, then to add a trans/temp gauge. I may start going to some of the auctions with a friend of mine, but still reading up on things so I know the right truck when I see it. Chevy is kicking in $4,000 through August and with some of the other deals its not to bad.


----------



## jgerni (Nov 10, 2003)

How about a 3/4 ton Avalanche. I believe they can come with the 8.1L and 12,000lb towing capacity with the 4.10. Would be quite the thirsty beast though.


----------



## Y-Guy (Jan 30, 2004)

I thought about it for a moment, I do love my Av. But I ruled it out for two reasons. 
1) Can't tow a 5th wheel, and who knows in a few years what we may want, I don't want to limit myself with not being able to tow more if i want to.
2) No Diesel option, the Av's do like to drink a lot of fuel, understandable its a heavy truck but going heavier I would like to get a bit better mileage if I can.

We went and looked at the Ford 250/350, probably just as well they didn't have exactly what I wanted on the lot too. (Tim Allen grunting) MMMMMore power is what those baby's said out loud! I really liked the trucks appearance and features, with the kids we opted to skip the test drive and the fact that I didn't want to get that into shopping there since I know another dealer a few miles away will cut me a much better deal.

I'm going to look at the Chevy/GMC this week, since they have a pretty good owner rebate but without some of the features the the Fords have it would be tough to go that way. With the 05's on the way I'd probably hold off for a while if i do anything at all unless came across at one heck of a deal. The 05s are in production now and sounds like they've tuned the Diesel engine a bit more for about torque, and better equipped for camping too. I can't see the need for a 350 with the beefed up springs since I don't intend to ever own a truck camper, but might go that way for the future if we go with a 5er years down the road.

Oh well its fun shopping if nothing else.

Speaking of... went inside a 30' Cougar, oh my that is one nice setup, had bunks in the back and a ton of storage. But didn't have the remote A/C and a couple other things that the Outbacks have that I like.


----------



## JimWilson (Feb 24, 2004)

lukn2doit2 said:


> I hope I was in the right place... And looked at the chart right...
> 
> right at 1000 the 300lbft starts and then crosses 300 on its way down again at about 5500??


Okay, the Sierra C3 is a different animal. It doesn't have the "normal" 6.0; it's equipped with an engine that has a unique intake and exhaust, as well as some different computer tuning (there may be other things as well). That makes it a bit more powerful.

But I'm still surprised that it makes that much torque so early, especially given the redline it has (and the fact that it's a short block).


----------



## lukn2doit2 (Jun 4, 2004)

Jim,
I found the engine charts here...
http://www.gm.com/automotive/gmpowertrain/...vehicle/lq4.htm

The "brochure" shows the different varients for the different GM models and your right - I guess the C3 is the top model listed for the Denali. The 2500HD is further down the page...



> I've got the 6.0 and 4.10's in my truck, and I can tell you it runs out of breath when you attached a heavy load (in my case it's about 8000 pounds of backhoe and trailer).


Ill have to keep that in mind... id be at 6000, plus truck grear - and thats with the current setup, no "camper growth".

Thanks JimWilson


----------



## hatcityhosehauler (Feb 13, 2004)

Had my Avalanche in the dealer for service this week,and the was looking at what current incentives GM was offering on the Diesel Crew Cabs. I even picked up a brochure to try and convince the DW. According to GM's literature, the Duramax is producing 590 ft/lbs of torque at 1600 rpm. I am really starting to think this one over, and think that if I can work a deal that keeps my payments in the same neighborhood as the Avalanche, I may take the plunge.

Tim

Edit: I should note that this is with the Allison 5 speed auto tranny. The torque/HP ratings are lower with the 6-speed manual.


----------



## JimWilson (Feb 24, 2004)

The dmax is a beast. Almost 600 lb ft of torque at 1600 is really hard to beat. If you've ever towed a heavy trailer with a diesel you'd know what I mean. It's definitely got it's good points!


----------



## Y-Guy (Jan 30, 2004)

Test drove a used 2004 Ford 250 Diesel tonight for the heck of it. Grrrrr that's a truck! They were really trying to get me into it, but since the truck was just about 1 year old with 22,500 mile there was no way I'd consider it. But it was nice to drive one that had some miles on it. Inside it was nice and quiet, but standing outside you sure could hear it. With the max torque at 2000 RPM it cruised great on the freeway here at 70 MPH. Since I'm in no rush to do anything its fun to see the sales guys try and try to get my bite. Oh well its fun shopping at least. If the truck had the moon/sun roof and the power rear slide window things might have been different - guess its a good thing they don't have the truck I'd want on any lots around here.


----------



## camping479 (Aug 27, 2003)

Sounds to me like you're teetering on the edge there









Kind of like the time my wife and I went to the local animal shelter to "just look" at puppies.









Mike


----------



## Y-Guy (Jan 30, 2004)

LOL Mike been there done that, now we have 2 dogs. A new truck won't pee in my house or dig in my yard will it?


----------

