Gas engine and Diesel of same specs.Pull the same.

wilber1 wrote:
If you want to compare diesels with gassers, comparing normally aspirated gassers with turbocharged diesels is a waste of time. Stick some sort of blower on a gas engine and fuel consumption aside, the differences become much less apparent.

Well a turbo charged diesel can still get about 12 mpg towing 11,000# at 60 to 65 mph. Try that with a tubroed gas engine more like 8 mpg if lucky.
I like my diesel as good mileage, long engine live, low maintenance, and lots of power.

If you want to compare diesels with gassers, comparing normally aspirated gassers with turbocharged diesels is a waste of time. Stick some sort of blower on a gas engine and fuel consumption aside, the differences become much less apparent.

wnjj wrote:

transamz9 wrote:
Hp is a number and nothing else. It just tells you how much work you can do over time. I don't care how you look at it, it takes torque to move the load.

Incorrect. It takes torque AND RPM to move the load. That is HP. It's also the torque and RPM at the wheels, not the crankshaft that matters.

transamz9 wrote:
As far as the OP question, it's a loaded one with not enough info. Same specs? Does that mean same cu/in? Same hp? Same torque? Same speed? Same acceleration? This could go on for ever because you will never get the same specs out of the two engines.

This is true. A diesel with the same HP as a gas will pull better because it also makes more HP down low. A gas with the same torque as a diesel would pull better due to the much higher HP.

Yes I agree with you. It does take torque and RPM (hp) to move the load. I need to re-phrase what I said.

I don't care how you look at it , it takes torque to keep the RPM's up. A gas motor can't make the torque at highway speeds to keep the RPM's up when put under a load without going out of it's optimum RPM range.

Again, I agree that hp has to be made to "move" the load but without torque you have no RPM's.

transamz9 wrote:
Hp is a number and nothing else. It just tells you how much work you can do over time. I don't care how you look at it, it takes torque to move the load.

Incorrect. It takes torque AND RPM to move the load. That is HP. It's also the torque and RPM at the wheels, not the crankshaft that matters.

transamz9 wrote:
As far as the OP question, it's a loaded one with not enough info. Same specs? Does that mean same cu/in? Same hp? Same torque? Same speed? Same acceleration? This could go on for ever because you will never get the same specs out of the two engines.

This is true. A diesel with the same HP as a gas will pull better because it also makes more HP down low. A gas with the same torque as a diesel would pull better due to the much higher HP.

This is kinda a loaded question in the first place. If you are talking about matching HP and torque nubers anyway. It's going to be extremely difficult to find any gas engine that will match a Diesel HP and torque. For instance the 6.0 PSD puts out 325hp from the factory and nearly 600ft lbs of torque and that is the advantage of a diesel. I don't think there has ever been a diesel made for a pickup that if you tried to match the HP to a gasser would match the torque also and i think that was the original question.

Hannibal wrote:
So then an occasional 5k rpm isn't a problem. I've been saying that for a while now. More peak hp than torque at the flywheel still equates to more torque at the drive wheels. It's also in the gearing.
A boat motor and a pickup truck engine are both internal combustion engines. Your Merc 250 is designed to run 5-6k rpm continuously. The 5.7L Hemi, during R&R, was run at 5400 peak hp rpm full load for 300 hours. When torn down for inspection it showed only normal wear. Nothing melted or broke.
Are you implying the marine diesel unit will run forever?

The difference is that the 5.7 liter Hemi or any motor for that matter that is on the road is tuned from the factory to run best (efficiency wise) at speeds that is will normally see on a regular basis. On a vehicle motor that is going to be in the 1500-2000 RPM range normally. A diesel motor is run at those speeds 95% of the time even when loaded. A gas motor can't run at those speeds loaded because of the torque it takes to keep the load going. Hp is a number and nothing else. It just tells you how much work you can do over time. I don't care how you look at it, it takes torque to move the load. When you run a motor out side of it's optimum RPM range you will have excessive wear.

A boat motor is different. The difference in the spec sheet is that the RPM range that they put on the specs is not the max on a marine engine. It is the optimum range to prop it at. For each inch of pitch change equals around 250 RPMs give or take. You have lower unit gear ratios to deal with also.

What do you think the most reasons that all the big ship use diesel engines for? Fuel usage and durability are the biggest. Will they run for ever? If you don't destroy the block most will. Re-sleeve them install new parts and fire it up.


As far as the OP question, it's a loaded one with not enough info. Same specs? Does that mean same cu/in? Same hp? Same torque? Same speed? Same acceleration? This could go on for ever because you will never get the same specs out of the two engines.

Dave H M wrote:
Has this post turned into a poop pyramid? :S

No, we are comparing Gas and Diesel engines. That is what this thread is about. ;)

Has this post turned into a poop pyramid? :S

So then an occasional 5k rpm isn't a problem. I've been saying that for a while now. More peak hp than torque at the flywheel still equates to more torque at the drive wheels. It's also in the gearing.
A boat motor and a pickup truck engine are both internal combustion engines. Your Merc 250 is designed to run 5-6k rpm continuously. The 5.7L Hemi, during R&R, was run at 5400 peak hp rpm full load for 300 hours. When torn down for inspection it showed only normal wear. Nothing melted or broke.
Are you implying the marine diesel unit will run forever?

Hannibal wrote:
I'm not the one stating opinions as fact about an engine I know nothing about. I was hoping you could enlighten me about the Merc 1350 with facts but all I got was baseless opinion. Then a diversion with the SB 350 and LS1.
Why does the little Cummins need to turn 5k rpm? HP? :B

The Cummins is turning it for wheel speed. From experience of building a few motors in my time tells me from the bore/stroke specs that motor will put out more peak hp than torque. It's all in the tuning.

Again, this is a marine motor, completely different animal and not a good example for this topic. Boat motor's full throttle operating range is specs to help with the propping of the LU. It is not the red line of the motor just the most efficient WOT range . Example, my Mercury Racing 250 Pro XS has an operating range of 5000-6000 RPMs but 6300 is when it sets an alarm. It came with a 5 year warranty and is designed to run at thoses speeds day in and day out. There are guys that play with these motors and turn 7-8000 RPMs day in and day out.

A 1000 hrs is a lot of hours on a marine engine unless it is a diesel unit.;)