disel engines dont rev out very high and most have really big turbos, they put out alot of torque and are fairly effecient. so if 2 engines, one gas and one desil of the same size displacement, were tested then the desil would have more low end torque and gas would have better top end because gas engines can easily rev to 6-8 thousand rpms while a typical desil can rev to about 4000 or so. you also have to take into consideration that most desils have turbos, so thats where they get alot of there hp.

billyman- id also like to know what program this is, i could spend years messing with it.

It’s called Desktop Dyno 2000. Google it and you’ll find it all over the place for less than $40 (usually from $35 to $39). I got mine from Summit Racing Equipment like 2 years ago. However, I ordered just yesterday the new Dyno2003.

This is the company that created it….. http://www.motionsoftware.com/

Click ‘products’ and go shopping.

I’ve also been in contact with one of their tech/designer guys about doing something with 2 strokes (specifically motorcycle, snowmobile, weed wacker, chain saw, RC, etc).

Hopefully, something this year could be released. *crosses fingers*.

Diesel engines have more torque then gas engines because for their ignition process. Since diesels rely on compression, you would need to shove more fuel and air into the cylinder to create a sufficient amount of fuel/air mixture for the compression process to ignite.

All things being equal, a gas engine will out do a dsl in tork and horsepower. Inotherwords if we change just the minimum (the fuel and only the necessary stuff like ignition and fuel system) The gasoline engine will nearly double the power output of the dsl engine.

then how come they use desil engines in semis? they put out alot of torque. its like a 2 stroke in a way because like a 2 stroke there is certain ways that they have made the engines produce more power.

I think it's because of fuel mileage and longevity, definetly not cuz of wieght or cost. I don't think a two-stroke is available anymore in a truck. They have made incredible gains in dsl engines as of late with turbos, intercooling and computer controls, ect., but still not up to the power output of a gas engine.

Let's see if I can recall some of my A&P mech. book learnin'( it's been almost 25 yrs. already!) I think a larger bore engine (all else being equal) has more torque and horsepower because the Brake Mean Effective Pressure (B.M.E.P.) of the expanding gasses has a larger working surface area (top of the piston) to push against. If the fuel/ air mixture is reacted (burned) at the same rate, it will take longer to get to the outer wall of the cylinder, but we're talking milliseconds, and don't really need to concern ourselves with that, due to the (relitively) small bore size.
Maybe what some of ya are thinking and talking about with Diesels having more torque is because of B.M.E.P.
Relitively speaking, Diesel fuel burns a lot slower than gas or alcohol (again, we're talking about extremely short periods of time, like milliseconds) and gives a slow "push" on the piston for a longer duration. That combined with a longer stroke (typically more than the bore diameter, or "under-square" ) gives a Diesel the advantage in torque production, especially at lower R.P.M.
There are so many variables involved though, that can change the rate of flame propagation (the speed the flame, or burn radiates from the ignition source) that would be different using different fuels, and the air density, a hot or cold plug, compression ratio, chamber shape, etc. Basically, all we're trying to do is get more pressure in the combustion chamber, to push harder on the piston for just the right amount of time, and get the whole process started at just the right time so we don't get detonation.
And that's another thing, but we'll save that for later...I think I've babbled on long enough (for now anyway )

Wow, this thread has made me dizzy. I'm gonna grab a frosty beverage, and "dumb-down" with a couple episodes of Family Guy on the Tivo.

You're exactly right about the bmep that does give more power. Back to the original topic of bore size having more tork, larger bore= more tork.

Although I disagree with you if you're saying that a dsl engine with the same specs has more bmep, it does not .

Any dsl engine is getting good tork figures not from it's heat/pressure ignition systym or even from it's continual injection after the ignition occurs. They are getting good figures from the shear size of the engine and also from forced induction. In otherwords they are consuming many more times the quantity of air that a typical gas engine does.

guver - A deisel enginre dervives torque from increased compression. A deisel engine the same size as a gas engine will produce far more torque at a far lower rpm.

Example:

VW Jetta 2.0L 4cyl 8valve gas engine - 115hp, 102lb/ft@4800rpm

VW Jetta 1.9L 4cyl turbo deisel engine - 91hp, 155lb/ft@1800rpm

as you can see the deisel far exceeds the gas engine in both the amount of torque and the rpm at which it maxes out. I have driven this car, and the engine has so much torque at such a low rpm, that you can put it into first - not give it any gas - and dump the clutch, it wont stall - it will actually begin accelerating on its own without applying the gas, just based on the amount of torque it has at idle rpm.

In order to be fair to compare the two fuels, you must also boost the gas engine with the same amount of boost that the dsl has. Otherwise you got your power improvement not from the change in fuels, but because the engine has been turbocharged to maybe two atmospheres.

And while it should be noted that while it is true higher compression does give more power, it is not because it's a dsl, it's because there is a higher compression.

I think maybe you are trying to compare a dsl engine and all of it's many other advantages/benefits to a gasoline engine. And coming up with a fair comparison stating that it is because it is fueled with dsl , that's why you conclude that it has more power.

What I am saying is that it is not due to the fuel, but all of the other things that most dsl's have is why they are getting good numbers. A general statement like "dsl engines have more tork" is just not true, because "gas engines have more tork"

In your example , the gas engine will blow the dsl away in all races, hauling all loads, excellerating, ect. The dsl may attain more engine life and better fuel economy though.

I notice that your dsl engine above has 53 hp at it's tork peak.
The gs engine has 93 hp at it's tork peak

ps the best of both worlds is to get hi tork and be able to produce it at high rpm.
pss you must take the turbo off, or give me one too to be fair. Then the gas engine nearly doubles tork and hp. I like when that happens.

he he he, this is an interesting thread...

so far i have not really read anything that completely explains it.

although i can not give a perfect answer myself, i can put in my 2 cents...

i am a 1:1 car guy. there are a lot of things that affect H.P. and torque on any engine regardless of size.

the weight of every single moving part inside the engine pl ayes a roll on the H.P. and torque.
along with:
port timing
port size
materials used
fuels used
displacement
ignition system
Ignition timing
air fuel mixture
compression
bore
stroke ect...

this subject is way to hard to give an exact answer because there is always a !QUOT!except!QUOT!

like when you say a smaller stroke engine revs higher then a longer stroke engine..... this is normally true......
***EXCEPT***
what is the bore was a lot bigger then a longer stroke engine, and the piston/rod/crank Assembly weighs more.... it would not rev higher.

i mean of course there are norms, like when you increase weight of the engine rotating Assembly, then torque will increase, and H.P. will drop, and Revs will drop...

but the point of my long and boring story is that no matter how perfect you think your answer is, there is always a what if. and that makes this thread a hard on to answer perfectly.

but in general most of what i have read above makes sense and is true to a point.

sorry this was so long and boring, i just wanted to throw my 2 cents in..... maby 3 or 4.

I do think that increasing the weight of the moving parts of an engine will have very negligble effect on tork, but all else being equal it will decrease tork.

All the items you mention above, do play a role into the equation, that's why I was just trying to cut thru all the extra stuff and get down to comparing just one variable at a time like bore size or fuel. It makes it too tough to say a general blanket statement (like cats are bigger than dogs) without a lot of qualifiers or questions, you cannot make an accurate staement like that.

I guess really to get back to the original, bigger bore = more tork. That is without changing anything else or all other things being equal of course

ps what about those big cats???? Oh never mind....

he he he, yeah i agree with you guver... i think we are pretty much thinking on the same track here. and i see what you are saying about IF you only change one thing.

by the way.... for you people that don't get the general statement of !QUOT!more weight=more torque!QUOT! think of the statement !QUOT!an object in motion tends to stay in motion unless acted upon by an equal or opposite force!QUOT!

this means that the heavier the item, the harder it is to stop (think bowling ball vs. feather). so if you have a nice heavy piston coming down, the car is going to have a harder time resisting movement of that motion, then it would if it were a nice light weight piston.

now the plus side of a light weight piston is 1 you can rev it higher (again assuming nothing else has changed) 2 you will see an increase in H.P. and 3 the throttle response will be faster.

there is a lot more to engine weight then just the piston, there is the weight of the rods, crank, flywheel, anything spinning...

anyways.... enough about that, i am sure most of you know all of that already.

my point exactly. i think actually the turbo on desil engines doesnt do much, except maybe let it rev out a little higher. at such low rpms it shouldnt add much power and at 1800 rpms i doubt the turbo spools up like it would in a normal gasoline engine.

guver- have you ever riden in a desil truck? my dad drove a power stroke for a while and it was one of the most powerful trucks ive ever riden in. come to think of it, it pulled more g's than alot of cars.

not exactly.... when you said the turbo diesel truck does not spin enough RPM's to spool up a turbo...

you have to remember that the big truck has a piston the size of a 5 gallon bucket. (well not really but you get my point) but a car engine has a piston the size of a a coke can. (also not exactly, but you get my point)

Turbos work off of exhaust pressure, the coke can may spin faster, then the 5 gallon bucket can still push just as much if not more air trough the turbo.

how did this subject get on turbos, instead of bore and stroke like nitro had first asked about?

anyways, just thought i would throw that one in.

I have to go with Billyman here.

I can compare a normal 350, (350 crank, 350 block) and a 377 (350 crank in a 400 block) and the 377 makes a bit more torque than the standard 350 but also revs higher and makes more HP. Nitro, a large portion of what you say is also true. If you take a 400 crank and put it in a 350 block you get a 383. When comapred, the 377 and 383 have MUCH different characteristics. The 383's are great stump-pulling truck candidates while the 377 would be the choice for [drag] racing in a car. When you look at their characteristics on a dyno the 383 hits its torque peak consistently markedly ahead of the 377, with all items equal (heads, cam, intake, carb, ignition etc.) but this in between would be not what you would seek for either. The 383 would get more items that focus on torque (smaller intake runners, medium to low rise intake, maybe 1 3/4" headers vs. 1 7/8" and larger intake runners with hi-rise intake for the 377). So yes, in this drastic example (relatively long stoke, small bore - relatively short stroke, big bore) but any increase in displacement = more real torque.

This is a non-debate item, give the gasoline the SAME AMOUNT OF BOOST IN PSI and then comapre the two. You wouldn't compare any engine to one the same size with turbo and expect to see the non-turbo make more torque, it just wouldn't make sense. I have seen a BONE STOCK Buick Turbo with a 3.8L turbo (gasoline) in a HUGE HEAVY car pull the front tires and run an 11.40 at over 120mph...STOCK.. all he did was work the waste gate on the turbo to up the boost (the only change to make to the car is the racing fuel from the track). find figures for a single-turbo 3.8L and compare them to the 3.8L's with the same PSI of boost.

I have ridden in a dsl truck, They make lots of noise,sometimes smoke, can't pull a heavy load up a hill at 60 mph and watch a gas job pass them.

It may seem like I'm anti dsl, that would be somewhat true. There have been incredible amounts of money spent on the technology in the last 10 years. They have improved them quite alot, the ignition principle is top-notch, not having a burnable mixture in the cylinder until it's time to lite it is a very good thing. Also the heavy expensive components are good for dependability (not cost or weight) The fuel itself is considerably safer as well and maybe cheaper to store, transport, and carry on board. Turbos and intercoolers are the savior of the dsl engine.

If a gas engine had half as much money and technology spent on it it would be leaps and bounds ahead of dsl instead of just a bit ahead of dsl in power.I have spent considerable amount of time and money testing building and dynoing converted dsl engines to know that by changing the fuel to any gas fuel will nearly double the tork and hp of any dsl engine even when dropping compression ratio and backing turbo boost down to a safe level. Also the fuel mileage will be just about cut in half too.

Here is the order of hp for different fuels that I'm familiar with and this is just my opinion too, they may not be exact. I'm sure that other fuels and different types and specs come into play as well. Maybe someone has more info it would be interesting.

Nitromethane
Methanol
Ethanol
Race gas
Pump gas
Propane
Natural gas
diesel

anyone can confirm or add to this? Ps I'm just comparing fuels only.

Here is some things I will conclude that will increase hp and tork both

higher compression
lighter parts especially reciprocating parts
bigger engine like bore and stroke
cooler air more dense
higher pressure air like sea level or more boost
better volumetric efficiency

The opposite of these things will do just the opposite