Diesel vs gas......................

[blt2ski]

OK folks, there have been a few to many diesel vs gas threads that have shall we say gone to "Hell and a hand basket"! So if all of you would put in you BEST, no flaming reasons for going gas vs diesel, pro and con, I will either leave your thread, or copy and paste pertinant info to the 4 posts of pro and con of diesel or gas. This can include the GM 8.1 vs Dmax or Ford V-8/10 vs PSD etc too.

Be real and honest in you answers, not hear say, flaming etc PLEASE!

If posts are good ones, I will leave, if inflamatory or trolling in nature, they will be deleted! I will get this stick'd to the top for future parusing for those that need this type of info.

Added 6-23-04

We are getting closer to answers I am looking for etc.

Stuff like Ken's - T-Bone posts are good. There are a few others of you that have not posted, some with a 9 point question and answer type to figure out how you went with one or the other. If you are one of those, PLEASE repost in this thread. I may have to look up whom has done this and PM you, but if you think this is you, you now know what to do.

Also, for those of you with $ per gallon for either fuel right now, I would prefer to see a post with ...."in my area, diesel is typically .10 less than unleaded" then explain your numbers. As currently in the Seattle area, diesel and unleaded are any where from 2.05 -2.30 per gallon, with mid test .10 more and premium about .20 more, with equal high low splits. Two weeks ago those prices were upwards of .30 -.40 per gallon more. people were posting $ per gallon that were for me. "I wish" If someone is reading your post a year from now, they may want to know where your paying 1.65, when the price of fuel is over $3 per gallon. Let's keep prices out of it if possible.

Bert and tin tipi, got into a good discusion on the pros and cons of RPM's, drive train etc. I would prefer to NOT see the quote of the other in responding threads, maybe just write a quick wording of re tranny gearing, instead of the whole 40 words or so in that paragragh, so the repsonse is shorter if possible quicker and easier to read etc.

I have deleted some 15+/- posts, that were off topic etc. Please note, I am trying to keep this at the top, as the ONLY gas/diesel thread in this area. So if one is trying to decide, we do not have to go thru this BS any more. As such, I will be deleting ANY future posts close to resembling this type of topic. I may have to change "this" title to a better one, if one has a better sounding title, to be more positive, better claification, let me know here, or in a PM/e-mail, what ever you feel most comfortible with.

Again thank you for all of you that are keeping responses positive, etc.

Also we could use a few more positive reasons to go gas, as many can see I have both gas and diesel, both have a place! Both have positive reasons to buy that fuel, lets keep the threads etc to that purpose only!

Marty

[Rvndave]

I only drop a gear when I chose.....ahhhhh the joys of a 6 speed manual.

[BertP]

Rvndave wrote:
Play with numbers all you like. When your done calculating I will tell you this. We have been towing a large tt since 1987, we have had many different tv, in every case the diesel had much more power, and the gasser couldn't come close to the diesel MPG. So figure it anyway you like, but remember this when we are climbing the same hills on the same road and doing 65 MPH vs the gasser doing 40MPH I know which engine has the most power. When I buy fuel and divide fuel used into miles traveled it is clear the diesel uses about 1/3 less fuel vs gas, same load, same road.

There is no doubt that the diesels get better fuel mileage thant he gassers, but that has nothing to do with how much power is being produced by each. Perhaps when large (8.1 size) direct injected gassers become available, things may change, I don't know. However, my DMax (LLY) puts out 310 HP which is less than both the 8.1 and 6.0 gassers. The $1 million dollar question, though is not how much power do the engines produce but how much of that power actually hits the road? Dodge has shown over the years the problem of putting a 4 speed auto behind an engine that has a narrow power band like the CTD. Every time it upshifts, the max power available from the engine is cut in half. That's too big a drop. As long as the truck can hold a gear going up a hill, you're fine. But, if you have to drop a gear, you could be in trouble because the upshift becomes too expensive in terms of power loss. Still, the gassers produce more power than the diesels.

Bert

[BertP]

DavidPhillips wrote:
I see how you got it now.

The only problem I have figuring it that way is due to the torque curve not being linear and same with the HP.

Why is that a problem? You just have to eyeball it a bit but with engines like the DMax and 8.1 where the torque curve is fairly flat, it's not too hard.

DavidPhillips wrote:
At this point it sounds like either gasser will out pull the DMax on a hill.

In theory, yes. But, as I mentioned earlier, there are more things at play here than just the power output of the engine. In my calculation, I assumed 0 driveline loss but we know that in reality that isn't possible. The question becomes what is the actual driveline loss? And, is the loss across the allison constant with rpm? If the loss increases with input rpm for example, then it is entirely possible that the DMax will get more power to the wheels in 4th than the 8.1 can in 3rd even though the 8.1 is producing more power than the DMax. I don't know if that is true or not, though.

DavidPhillips wrote:
Could that mean that you can't use max rated figures or just that the DMax has very little power when it compares to a gas engine?

The LB7 version of the DMax produces 300 HP. That's more than some gassers and less than others. You have to look at how much of that HP can be delivered to the wheels across its operating range.

DavidPhillips wrote:
I figured it the same way for my 4 cylinder and it blows the DMax away.

That must be quite the 4 banger if it can develop more than 300 HP!!

DavidPhillips wrote:
Not really important I guess, and I'm getting busy around here.

Anyway thanks for the debate. Maybe we can continue it later.

Anytime 🙂

Bert

[Rvndave]

Play with numbers all you like. When your done calculating I will tell you this. We have been towing a large tt since 1987, we have had many different tv, in every case the diesel had much more power, and the gasser couldn't come close to the diesel MPG. So figure it anyway you like, but remember this when we are climbing the same hills on the same road and doing 65 MPH vs the gasser doing 40MPH I know which engine has the most power. When I buy fuel and divide fuel used into miles traveled it is clear the diesel uses about 1/3 less fuel vs gas, same load, same road.

[DavidPhillips]

I see how you got it now.

The only problem I have figuring it that way is due to the torque curve not being linear and same with the HP.

At this point it sounds like either gasser will out pull the DMax on a hill.

Could that mean that you can't use max rated figures or just that the DMax has very little power when it compares to a gas engine?


I figured it the same way for my 4 cylinder and it blows the DMax away.


Not really important I guess, and I'm getting busy around here.

Anyway thanks for the debate. Maybe we can continue it later.

[BertP]

The diesel nembers are higher in 4th and 5th but the gasser has the highest numbers overall with 324 HP available at the rear wheels in 3rd.

To obtain the numbers, I just took whatever the engine rpm was at a particular gear (I assumed a locked torque converter for simplicity), figured out what the max torque and HP numbers were for that engine at that rpm and worked it through. . For the DMax, it was easy because it hits a max torque at 1800 rpm and maintains that torque capability through 3000 rpm. So for 4th gear, axle torque = engine torque (520) * tranny ratio (1) * RE ratio (3.73) = 1939.6. You can then solve for HP: HP = 1940 * 683 / 5252 = 252. The 8.1 was a little more difficult because I had to get a copy of the power curve and eyeball the numbers. As a result, they may be off by a bit, but they should be fairly accurate.

This also shows a problem we have when dealing with torque rather than HP. If I have an engine developing 600 lb-ft of torque and I ask how much torque is present at the drive axle (assuming 0 driveline loss), what would be the answer? The only answer we could give is: Unknown. Without additional information such as the gear ratios of the RE, tranny and any other gears it may be going through, there is no way of knowing how much torque is on the drive axle. On the other hand, if I said that I had an engine developing 300 HP and asked how much HP is present at the drive axle (assuming 0 driveline loss), what would be the answer? 300 HP.

This also illustrates the point about max acceleration. Your assertion that max acceleration in a particular gear occurs at max torque is correct. However, as seen above, at 60 mph, the 8.1 can put a max of 167 HP to the rear wheels in OD. Downshift to 4th, though, and that increases to 234. Drop another gear and it climbs to 324 in 3rd. So, max acceleration in a truck with an 8.1 l engine, allison tranny and a 4.10 RE will be realized in 3rd gear at 60 mph.

On Edit: Incidentally, another thing I found interesting when researching this problem is that for 2007, the 6.0 l gasser is rated at 367 HP @ 5500 rpm. So, in our example above, we would get the most power to the ground with the 6.0 l gasser in 2nd gear (around 350 HP).

Bert

[DavidPhillips]

Yes, I see.

Actually I was using the 4L80E transmission for that reason. The rpm's shown above would be correct for those tires with that transmission and the stated differential at 60 mph. However the allison is the same comparison. No problem there.


I don't know how you figured the torque / horsepower above.

Can you show what you used?

Diesel ...... Gas
4th 1.00 1940/252 1804/234
5th 0.71 1377/179 1280/167


I don't see what this says, diesel numbers look higher.
Also is it rpm, hp, torque?

[BertP]

The specs you gave were not for exact trucks because the 6.0 l gasser is not available with an Allison tranny. So, I am using the 8.1 l as the gasser. If you get the gear ratios for the other tranny, you can just plug them in and see what happens.

According to 1010tire.com, a 245/75R16 tire turns 682.8 revolutions per mile. Let's make it 683. That means that at 60 mph, the tire is turning at 683 rpm. Engine rpm by transmission gears would be:

............3.73.....4.10
1st 3.10 7897 8680
2nd 1.81 4611 5068
3rd 1.41 3592 3948
4th 1.00 2548 2800
5th 0.71 1808 1988

Based upon the above, it is obvious that neither truck can do 60 mph in either 1st or 2nd gear and the diesel would not be able to do it in 3rd gear. So, what torque/horsepower can we have to the ground in the gears that will work, assuming 0 driveline loss?

………….Diesel……….Gasser
3rd 1.41 ------- 2457/324
4th 1.00 1940/252 1804/234
5th 0.71 1377/179 1280/167


As you can see, the 8.1 will have substantially more power (about 28% more) to the ground in 3rd gear than the DMax can in any gear at 60 mph.

On Edit: If you ran the same gear ratios for the 6 l (I know you can't get the allison behind the 6, but it is an interesting exercise), you would still end up with the gasser ahead. I calculated that it would have around 275 HP to the ground in 3rd which is less than the 8.1 but still higher than the DMax.

Bert

[BertP]

kudos383 - I had a similar thing happen to me. I have a 2005 Silverado 3500 Dually D/A with a Wildcat 28BH 5er which is a little over 10,250 lb. Coming out of Kelowna, BC las year, my tranny was in 3rd and the best speed I could get was just over 50 mph. The climb was about 15 miles long and varied from 6% to 8%. I have a feeling the much of what happens in a situation like that is a result of the tranny programming. I should have been able to grab 4th, I think, but the controller wouldn't let me. So, I slowed down.

Bert

[DavidPhillips]

If you need more details then consider this in your calculations.


60 mph

gasser

OD gear 2034 rpm
3rd gear 2712 rpm
2nd gear 4015 rpm


diesel

OD gear 1850 rpm
3rd gear 2468 rpm

[DavidPhillips]

Yes, I must agree that the drag racers would be tached up to wide open throttle.

My mitsubishi is pretty much the same way. If you let the rpms drop you will not have any power. That's why when racing I would keep the revs up over 6500. Easy to do with a stick.


Pulling a load it's hard to drive like that because at some point you need to shift up. Certainly you want to get the revs as high as possible before the shift so it will be higher after the shift. The tranny is normally setup to shift centered around the peak torque point. You will normally shift up to just under the peak torque point and shift down to just over it.


In every gear the engine will follow the torque curve.

So to compare the two trucks I brought up in my original post that you had a problem with which seemingly started this whole unresolvable ordeal we need to see the gasser could possibly drop in speed on the hill where diesel did not.


As in my original post comparing these two trucks show me some proof that the gas powered engine could not slow down on a hill where the diesel did not.

I don't really care about any information other than these exact two trucks.

2006 Silverado

Tires
245-75-16

Gas Engine

300 hp @ 4400 rpm
360 lb. ft. @ 4000 rpm
4.10

Diesel Engine

300 hp @ 3000 rpm
520 lb. ft. @ 1600 rpm
3.73

Going 60 mph up a hill with a load.

The diesel could possibly stay at 60 mph while the gasser slows down.


So unless you have this information you can't say that it is not true and therefore must be just wanting to keep up with the posting of the same thing over and over.


If you go back and look at the recent posts you can see where I brought up something and you ignored it because you have no reasonable explanation for your side of the story.



Now if you want to change gears and reprogram the transmission, put in an engine chip or whatever to the gasser then you will need a lot more money than the diesel will require in upgrades to still out pull the gasser. We are talking about these trucks the way they came from the factory.



So looking at the vehicles in question from my first post, described above.

Both vehicles can't possibly have exactly the same pulling power. One has more and one has less. It's virtually impossible for the diff to compensate exactly for the precise speed of 60 mph. So which vehicle will slow down from 60 mph before the other if the hill gets steeper?

[kudos383]

no cruise is off,havent tried it with the cruise on.and yes I love how the 8.1 will pick up to speed quicker than the diesel.even while loaded

[BertP]

David - talk to the 1/4 mile folks. Ask them why they always time their shifts to straddle the peak HP point and not the peak torque point.


kudos383 - When you say that your chevy drops to 60 - 65, is that on cruise control or with you manually controlling the throttle? Either way, it could simply be the way that GM has programmed the tranny to shift. You can't force the tranny to stay in a higher gear.

Bert

[kudos383]

all this bickering,I have a perfect example.I have an 03 30ft 5er wt 9000lbs.I pull it with 2 different trucks.allover wva and ky mtns.truck 1 2006 chevy 2500 4x4 4.10 EC LB 8.1 ally.pulls fine works really good but will drop to 60 to 65 on the 7% grades.truck 2.2006 f250 6.0 ps.4x4 LB EC 3.73 rears,pulling the same trl I can run 7% grade at 70 to 75 also pulls really easy.but i prefer my gasser.but admit my deisel will pull the same load easier and at lower rpm's.

[DavidPhillips]

Read the quote in your last post Bert.

It says first gear.

Your vehicle output will be higher in a lower gear than in a higher gear. You have to look at it differently for each gear. That's why you want to use first gear to see the difference. If your transmission did not shift you would still have more acceleration for that gear in the torque peak. Each gear has a torque peak and a horsepower peak. For that gear the torque peak is where the most acceleration is. If you shift to a lower gear the overall output goes up but the torque peak in that gear is where the most acceleration is.



The statement about 2000 vs 4000 is supposed to illustrate the effect of calculation of peak horsepower. Naturally in the same gear at double the rpm you would be going twice as fast. However that does not mean you can accelerate harder. Acceleration is the difference of speed over time. It does not matter how fast your going. You may be at 30 mph and accelerate to 50 mph as compared to 60 mph and accelerating to 100 mph. which one would take longer? That would be the one with the least amount of acceleration. However the calculation of horsepower would say you have double the horsepower. Would you then accelerate twice as fast? If it takes you 10 secs to get from 30 to 50 would you go from 60 to 100 in 5 seconds?

That's what that illustrates.


To elaberate on this point.. You have the same torque, the same gears. You calculate the peak HP from any rpm, make up a number.

Now double the rpm and calculate it again. You have double the horsepower.

So is acceleration going to double? I don't think it will. I do think we will see that we can go twice as fast. If acceleration doubled you would be going more than twice as far in the same amount of time. And horsepower is not supposed to progress that way.