What is it about a diesel engine that makes it so much more powerful and able to make huge power increases?

 

Much higher compression, for one. Also, diesel has more energy per gallon than gas, and it burns slower, so the torque is applied throughout more of the "power stroke" (Ford forum, isn't it?) than in a gas engine. Older, non-turbo diesels would see compression in the 20:1 range, whereas the newer, turbo ones have dialed that back to maybe 16:1. A gas engine might be 8:1 or 9:1 on the high side (without mods), slap a turbo on that and it might need to drop down to 6:1 or 7:1.

Jason

 

Thanks for the input! It certainly enlightened me and it makes a lot of sense.

 

Wait a minute.............while all the fuel info may be correct.......since when is ANY similarrily aspirated or displaced diesel even close to performance to its gasoline equivilent????


Compare a 6.9 non turbo diesel to a 6.8 gasser....


Heck, even compare a VW 1.9 Turbo diesel to the same dispalcement gasser.


Of course the diesel is built EXTREMELY heavy to be able to run those very high compression ratios and boost numbers............but everything being equal, a gasser will always make more power.

 

But torque is what makes a diesel a better tow vehicle. Gassers make more horsepower since they usually turn higher RPM, but the diesel makes more torque at the low RPMs you want to get a heavy load moving. Horse power is a function of torque times RPM if I recall. Torque is just there.

I have a 94 F250 460 gasser that I use to tow an 8,000# trailer. I can easily if stupidly get my trailer up well over 80mph on a flat since I have the horsepower to get high speed.

But the 7.3 diesels and other brands pull away from me on hills since they are able to keep in their cruising gear while I am downshifting to keep my RPMs up.

For speed you want horsepower. For hauling you want torque. For best of both worlds you want both plus a lot of gears.

Just my opinion,

Jim Henderson

 

Again, not true..............you may be getting outpulled by TURBO diesels but not by the old normally aspirated 7.3's.


I'll have to find the specs, but I'm sure the 460 had more torque than the 6.9 and 7.3 non-turbos.

 

i will guarentee my old 1995 f350 with a 460 can outpull the non-turboed 7.3 and 6.9.

 

Somebody should tell the 18 wheeler companies that they may wanna stop using diesel engines.....lol. Bottom line I will never be convinced that a gas engine will produce more torque that a diesel.

 

Are you actually reading the text???

Find me a Cat, Detroit, Cummins etc.... that the 18 wheelers use (or that Ford, GM, DCX use)that aren't turbocharged or supercharged.


Using the fuel description (in post #2)and energy content and everything else, diesels are definetly more efficient.....but spark ignition motors will have more power....including torque...all things being equal.

 

Yes I am reading the text but I still cant understand your argument. If a gas engine has more power and torque then it would take less fuel and energy to accomplish the same task....if as you say all things are equal. Thereby making the diesel less effecient...but you are saying they are more efficient.

Every single heavy duty piece of equipment in the world runs off of diesel so why then dont you ever see heavy equipment running on gas. Its like you see a lot of cars have a V6 and a 4 banger but their is almost no difference in gas milieage.

Also at some point dont we need to talk about transmissions here...I am not an expert by any means but this has got to be a factor, in towing and overall power to climb hills, etc.

 

Bizarre statement.....you are kidding; right??

You're comparing apples to oranges.

Pick ANY normally aspirated diesel engine.........6.2 GM diesel, 6.9 Navistar (International) any of the old Mercedes or VW non turbo motos in the 1.6L to 3.0L range.

Now find any comparable gasser (displacement wise) there will be no comparison in power OR torque. However, the gasser will burn more fuel to achieve those power levels.





Hmmmm......maybe because diesel motors run at extremely low RPM for hours at a time with little ill effect???? Or the before mentioned adavantage of reduced fuel consumption at any given power level (does that answer your first statement)


You're killin' me!!!

First pearl of wisdom from you yet!!!

 

I got my little book here I checked on an 85 setup like my truck 460 vs. 6.9
460-225HP@4000rpm/365lb-ft@2800rpm
6.9-170hp@3300rpm/315lb-ft@1400rpm

Only thing is it doesn't state with/without turbo. There was no real call for diesel performance back then though, everyone was putting money into making power with gas. As technology has evolved, I believe the diesel is coming out on top, especially with ratings near 300hp and 600lb-ft stock. Does ford even have a big-block gasser anymore, I heard they were dropping the V10 which would give you a 5.4 or a diesel. No real contest there .

Heres some newer numbers though from another book.
For 1993
7.3 turbo/IDI-190hp@3000/395lb-ft@1400
7.3 non-turbo-185hp@3000/360lb-ft@1400
460-230hp@3600/390lb-ft@2200

For 1994
7.3 turbo/DI-210hp@3000/425lb-ft@2000
7.3 turbo/IDI-190hp@3000/395lb-ft@1400
7.3 non-turbo-185hp@3000/360lb-ft@1400
460-230hp@3600/390lb-ft@2200

The new 6.0 diesel is rated at 325hp and 570lb-ft

How often do you see a diesel without a turbo? They are like p-nut butter and jelly. They were made for each other. The diesels always operate at such lower rpms, is what I think makes them so much more efficient. I see older diesels touting 18mpg. I get 10mpg unloaded with the wind at my back. Needless to say, I will be keeping my eyes open for a 7.3 donor truck to convert my 85.

 

Nobody "was putting money into making power" back then concerning the factory.........even the gassers had pathetically low power numbers.




The bottom line.....as you have shown fairly well.... is take away the forced induction and the diesel will not have as much power as a gasser.

Yes, the architecture of the diesel lends itself to these compression ratios needed to make the power, so does the cetane (anti-knock) capability of the fuel..... you could also build a gasser to those specs but you would have to run some kind of race gas...$$$$$.....and the thing would get low single digit economy.....mo-$$$$.

And obviously there is no current production gasser that would live very long at 30 pounds of boost like a Cummins would.

As far as efficiency goes, you need fuel to make power. My buddies Duramax is getting around 13-14 MPG....just slightly better than my V10....but with 650+ pound feet of torque he doesn't mind.


But I stand by what I originally stated........Cubic inch vs. cubic inch......blown vs blown (running comparable boost) or unblown, the spark ignition motor will make more power than an oil burner.............just not as efficently.

 

The next big event (IMO) will be the variable cumbustion chamber displacement, thus vaiable compression ratio technology developed by Saab. This differs from the variable displcement that is achieved by shutting down cylinders and actually changes the position of the heads. Presently engines, both gas and deisel have lower compression ratios to handle the increase in air/fuel volume delivered by superchargers, especialy at higher RPMs. check this out from their website: "The 1.6 liter, 5-cylinder engine produces 147 Ib.-ft. of torque and 150 horsepower per liter of engine displacement" pretty intereseting stuff. see more at http://www.saabnet.com/tsn/press/000318.html

 

One other reason diesels are more efficient than gas engines: No throttle. Any throttled engine has vacuum in the manifold (at lower throttle settings - idle, highway cruise, etc). If there's vacuum in the manifold then there is vacuum on the face of the piston during the intake stroke. If there's vacuum on the face of the pistion, then there is atmospheric pressure pushing on the backside of the piston at a pressure of approx 10 pounds per square inch of piston surface (very rough estimate, engines don't usually attain absolute vacuum of 27 inHg). If the piston has a diameter of 4 inches, thats 12.56 square inches, which is 125.6 pounds of force pushing against the piston during the intake stroke. The engine has to overcome that force while running. That is power consumed by the motor that is not available for moving the car. It's called pumping loss.

I have read that gas engines operate most efficiently (most power per unit fuel consumed) at 70% throttle or greater. That would coincide with the lowest manifold vacuum reading. Piston powered aircraft usually operate in this region of throttle setting because it's the most efficient for them. However, on the ground, it doesn't take 200 hp to propell a car down the road at 60 mph, so we have to sacrifice efficiency in favor of controlling the speed and also in the interest of engine longevity (with all that extra hp, the engine would be running at near max rpm at that throttle setting!).

I would love to see a test that would confirm this. Drive a gas engine at a certain rpm with an electric motor. Vary the throttle setting and measure the power consumed by the electric motor.