Diesel Question

[91GranSport]

I see a lot of manufacturers using "turbo diesels". Why don't they use "supercharged diesels" instead? Superchargers are less complicated than turbos.

[eclipse5302]

Because diesels can take up to 35psi and more without a problem. It would take a pretty big supercharger to make 35psi. More bang for the buck...Thats my guess.

 

My dad used to work on busses way back in the day, and he's told me they used to do BOTH! Thats right, they used a supercharger that was FED by a turbo. So the supercharger would help out with boost until it ran out of steam and then the huge turbo would take over (once it started making boost). He said they went like hell.

[GnatGoSplat]

There ARE supercharged diesel engines. Just not many.

My GUESS is it's simply a matter of turbochargers being able to supply more boost to the engine and also being more efficient. Diesel engines operate on compression alone, so their cylinder pressures are MUCH greater than that of a gas engine. Since a turbocharger can create greater boost pressure, it will have more of an effect on increasing power while the supercharger's boost increase may not look like much at all to the diesel engine. Also, a diesel engine is not as powerful as a gas engine and will also tolerate significantly greater boost, so the way to get the greatest boost and greatest amount of power is through a turbocharger.

 

Well, those are just my guesses. You don't have to worry about preignition with the turbo on a diesel engine as you would on a gas engine.

[Jeorge]

If you want a Supercharged one you'll have to get a old mci grayhound Tour bus. they are the onlything I have ever seen a S/C in....and they SUCKED. the turbocharged ones are alot faster and more reliable.

[Steve LS]

Alrighty then, I'm no diesel mechanic but I own two and have worked them to near death. There are two types of diesels or I should say were. There was 4 stroke Catapillar, Cummins, Mac , most tractor manufactures had their own Then there was a 2 cycle just like a chainsaw,snomobile,weedwacker,dirtbike. That was the Detroit diesel.No mistaking the sound of a Detroit diesel. No it was not a POS they were unkillable as most diesels are. A Detroit fired on every stroke. Air was feed to it by a supercharger, always.A Detroit could not run without its Supercharger. Detroits were the kings of superchargers and are where the huge ones you see sticking out of the hood of those serious dragsters came from. Any how they have a four exhaust valve head. No intake valves. The injectors inject every stroke, when the piston comes down the SC forces air in through a port in the side of cylinder wall and pushes the exhaust out the now opened exhaust valves. When the piston comes back up and closes the port and the exhaust valves are closed the SC has also supplyed the cylinder with fresh air. The piston compresses the air, the injectors squirt and BOOM down she goes again. This happens every stroke. A Detroit produced nearly twice the HP per cubic inch as a four stroke. Same as gas engines.Its downfall was when pollution regulations went into effect they just couldnt meet up. To any. They could not be built to run cleaner. They were loud as hell. The blown through port SC made the engine seep oil out every orifice and vent and they had lots of vents. They were actually made to "weep" as they called it. Its not much oil but you cant get through a DOT checkpoint with a Detroit without getting written up for oil leaks. The new Detroits are now four stroke and are still great engines.

 

Now the turbo chargeing question. Please remember I'm no text book and am now going by my misspent youths memory.

 

As we all know a turbo runs off of exhaust force and a SC runs at the rpm of the engine. When a truck starts up a hill or up through the gears the exhaust pressure becomes greater from adding more fuel and air and you can hear the turbo really start to work (feel it to). A supercharger doesnt do any thing extra until RPMs increase. On a truck RPMs dont increase they just start lugging and that turbo really pumps the air in there from the extreme radical exhaust pressure. A SC will not do that.Those big trucks actually have a stack temp gauge those guys need to watch on long hills because the cylinder and exhaust temp gets rad. They may have to back off and downshift a gear.Never think a supercharger can compare to a turbo. Why do you think those F1 cars are the meanest hytec things on four wheels and sound like a really pissed of nest of hornets ? TURBOS!!!! It just takes a better built engine to accept all the available boost. Something most gas engines are not. For economical and weight reasons. Also Diesels run at really low RPMs (see specs below). they make their huge peak torque at what is just above idle on our automatic trans gas engines.

 

A four stroke diesel can see gains of nearly 100 percent with turbo charging. They run really high compression 16/1 some as high as 21/1 . You get alot of air in there to compress when that diesel blows it really blows, hows that for hy-tec. They are really big engines and built heavy so they can take all that compression as well as charge. Turbo charged diesels have different pistons/rings ,valves and springs from their NA counterparts.

 

A two stroke (old Detroit) only saw gains of about 15 percent with addition of turbo and many were turbo.

 

Detroit made a 12V71 NA thats a V12 with 71 cubes per cyl. Thats a 851ci. Produced 390 HP@2100 & 1078 tq @1200. 18.7:1 comp.

Remember a NA Detroit is still SC

My little 671 NA. Thats a inline 6 w/71 cubes per. totals 425ci produces 226 hp @2100 & 575 tq @ 1200 18.7:1 comp. If you think a 427 Chevy can run with that on a loaded truck (50,000 lb. gross) you got another thing comin'. It also gets 7mpg loaded or empty.A 427 Chevy wouldnt get but 3-4 pushed to the limit like that and would be spent after less than 100,000 miles. My truck has 636,000 no BS and is still strong.

 

Hope ALL this helps

[Steve LS]

BTW jeorge the smaller Detroits were used in buses back in their time because of the smaller size. Those big truck engines would not have fit so well under there and the Detroit was easier on fuel. I'm not sure what engine they are using in buses now. There all making better, smaller, effecient, environmentally kind engines now adays just like cars. Buses dont need the huge engines used for hauling freight.

[Steve LS]

BTW GranSport turbo charged diesel dont have the complications that cars do . They are pretty much hooked to the exhaust and intake and go. I've been told todays trucks are all electronically controlled for lean/rich and timing too. But with diesel fuel, low RPM range they just arnt as complicated as turbo charging a gas engine. And room and tranny weekness's arent a problem either.

 

Pickup trucks thats another story , and I know little about those built for light duty engines.They also run higher RPMs than 2100 which all "real" truck engines run. Most feel with the added $ for the diesel option there is little gain with buying diesel.

[eclipse5302]

Man, I wish my dad was on this forum now, he used to work on nothing but diesels back in the day. He could talk forever about them.

 

636k miles?!? Damn, thats impressive! Thanks for the info!

 

Jason

[Steve LS]

Theres many a Mac truck that has gone 1,000,000. thats right one million.

[eclipse5302]

Wow

[SuperBuick]

Why do you think those F1 cars are the meanest hytec things on four wheels and sound like a really pissed of nest of hornets ? TURBOS!!!!

 

 

 

F1 cars are not turbocharged, they are 3.0 litre N/A V-10s. The CART cars are turbocharged, 2.8 litre motors. CART makes more HP than F1, but F1 is still the absolute highest level of motorsports there is. Not trying to nit-pick, just wanted to point that out. F1 cars USED to be turbocharged, but for the past few years (at least 5 I believe), they have been N/A.

 

-Tom

[Steve LS]

No way ! :oops: You gotta be kidding me. I havnt kept up on publications (magazines) in decades. watching the races on Speed channel its hard to even know what the cars are let alone powered by. Most of the times the narrators only talk in terms of car # drivers name or team name. Of course in F1 red is Ferrari and the Silver is the Mercedes but doesnt that go by a different name now ? If you miss the before race you mis the tecnical stuff. Why do those cars sound like that if they are NA. Are you sure ? How could they be that snappy ? I actually assumed twin turbos.A Ferrari V10 ? Are you sure ? Why did they stop Turbo ? I dont mind being corrected its better than everyone saying what a dumb ass (which I am) and I dont even know it. I saw bits and pieces of alot of road races on Speed this year but got little information on the cars. I guess I better do some reading on this. :oops:

[SuperBuick]

They stopped the turbos because the cars were going just way too fast, and drivers were dying left and right. They are all v-10s now, yes even ferarri. the sound like that comes from the extremely high rpms (18,000 plus rpms) and the way the cylinder heads open the valves, pneumatically (the only way they can keep up with those speeds supposedly) and how the valves open in a swirling motion (hard to describe in text) meaning that all 5 valves in the cylinder head open and close in a swirling motion (first one, then a millisecond later the next, and then the third [intake valves in this case]). this causes the air to swirl into the combustion chamber, sucking in more air than normal. I wish I could think of a better way to describe it. The N/A motors give decent torque at low (relatively speaking) rpms. to me the motors sound like air wrenches as they accelerate. Theres some VERY VERY VERY high tech stuff there in F1, VERY high tech.

 

 

-Tom

[Steve LS]

18,000 no way ! Wow I was figuring 10-12,000 . I really have been out of touch . I understand what your saying about the valves opening in sequence. So are you saying no camshafts but a air piston setting them off ? 3 litres spread out over 10 cylinders turning 18,000? would about sum up to one angry hornet. Yea they do sound like a air wrench. I am bummed that Ferrari wouldnt be a V12. It just aint right.

[SuperBuick]

I understand what your saying about the valves opening in sequence. So are you saying no camshafts but a air piston setting them off ? 3 litres spread out over 10 cylinders turning 18,000?

 

Yep, Yep!!! Also, supposedly the v10 has better balance overall than a v12 (balance...is that the word I am looking for?)

 

Most of the motor technology is secret, but I do know they have the pneumatic valve opening. Its some pretty sweet stuff!

 

-Tom