Why no supercharged diesels?

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Sun 19 Mar 2017 15:14
Why no supercharged diesels? - Metropolis.

I know diesels are falling out of favour these days. Nevertheless I've always been curious, why not supercharge a diesel car instead of turbo?

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Sun 19 Mar 2017 16:04
Why no supercharged diesels? - badbusdriver

Short answer is that there is no need. Turbo charging provides the same thing, but more efficiently.

Back in the early days of turbo, there was huge lag (the delay vetween you putting your foot down and the turbo getting up to speed and providing the boost), whereas superchargers are driven directly from the engine, so no lag. But this puts extra load on the engine and is less efficient, Turbo's use the exhaust gas, ie, waste gas, to do the same thing. Modern turbo designs minimise the lag almost completely, and for higher performance applications, 2 or more turbo's can be used. This can be together, or as is sometimes the case these days, in sequence. So you get one smaller turbo (which spins up quicker) dealing with initial acceleration, then a bigger turbo takes over.

That is why there are so few supercharged cars these days either.

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Sun 19 Mar 2017 16:08
Why no supercharged diesels? - gordonbennet

Two stroke Diesels were often supercharged, if you haven't ever heard a Deltic in full song then punch in that word on Youtube and treat yer shell likes to a wondrous sound.

I'm almost certain that Curvy Mazda 626 had a 2 litre supercharged Diesel around 1992 but it wasn't a success and was rapidly dropped, in the back of my mind the engine was a 6 pot, but happy to be put right if that wasn't the case, EDIT no i'm wrong it was a 4 pot.

Edited by gordonbennet on 19/03/2017 at 16:40

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Sun 19 Mar 2017 17:35
Why no supercharged diesels? - bathtub tom

Don't forget that supercharged Commer diesel 2-stroke engine - wonderful howl!

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Sun 19 Mar 2017 18:21
Why no supercharged diesels? - corax

Don't forget that supercharged Commer diesel 2-stroke engine - wonderful howl!

www.youtube.com/watch?v=5pwhm_xoDiY

Can someone explain, how is this truck sometimes changing gear without the driver touching the gearstick?

EDIT - ah, he's pressing a pedal. Probably something that has been done for years, I am not a trucker!

Edited by corax on 19/03/2017 at 18:24

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Sun 19 Mar 2017 18:44
Why no supercharged diesels? - gordonbennet

Can someone explain, how is this truck sometimes changing gear without the driver touching the gearstick?

EDIT - ah, he's pressing a pedal. Probably something that has been done for years, I am not a trucker!

Wonderful, my very first artic was a '71 build Foden S39 with that box, but with a Gardner 180 engine not the Foden two stroke, that chap knows his stuff, pleasure to watch.

That lever you see to the right of the steering wheel is the air shifter for the three ranges, the gearstick on the left is a four speed, the ranges were unequal, you didn't just split each gear into three, there was a sequence to follow.

I believe earlier models had two gearsticks, one was the normal geearstick, the other was a manual operated range shifter which the lever on the right in video replaced, before my time, but good days, they couldn't just get some bod from the agency and plonk their bum on the seat when lorries were like that, and driving those things gave satisfcation because you had to drive them properly, that gearbox is a lot less forgiving of mistakes than you might think watching those two chaps.

Edited by gordonbennet on 19/03/2017 at 18:56

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Sun 19 Mar 2017 17:45
Why no supercharged diesels? - SLO76
It was a 4cyl right enough but was very limited performance wise with only 75bhp and wasn't that brilliant on juice in the real world. While the 4cyl petrol twin cams were excellent engines with at least 30bhp more than the diesel and were really only 7-8mpg worse off than the more expensive diesel. The supercharged diesel was pretty pointless.
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Sun 19 Mar 2017 19:34
Why no supercharged diesels? - focussed

A two-stroke diesel has to have a positive displacement supercharger to scavenge the cylinder, in other words, the supercharger pushes air into the cylinder through ports in the cylinder wall, when the piston is at or near BDC, to scavenge, or push out, the exhaust gas through the exhaust valves or in the case of the TS3 Commer the exhaust ports.

There have been turbocharged diesels whch also run a supercharger.

One such six cylinder four-stroke diesel had an exhaust driven turbo-supercharger - a normal turbo- plus a roots-type supercharger belt driven from the crankshaft via an electrically operated clutch, similar to the a/c clutch on a car, but bigger.

The supercharger provided positive boost immediately from idle until the turbo spooled up then the supercharger was clutched out and the engine ran on turbo boost alone.

The reason for this level of complication was to achieve a big petrol V8 level of performance with a diesel, but without high levels of acceleration black smoke.

Disadvantages? Mainly complication, cost and horrendous noise from the supercharger - it sounded like a bandsaw when it was clutched in.

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Sun 19 Mar 2017 19:44
Why no supercharged diesels? - gordonbennet

Focussed, that engine you describe sound like a recipe for a short life...

peers out of corner of eye at VW and Ford recent offerings of small engines blown to hell and back to eke more power than anyone would expect for examples.

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Sun 19 Mar 2017 20:11
Why no supercharged diesels? - focussed

It was a 3.6 litre straight six from a major manufacturer putting out 230 hp at 3900 rpm.

Now which manufacturer of trucks always builds their own straight sixes?

Not used in vehicles AFAIK - marine only.

Cast iron block and head, direct injection etc.

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Mon 20 Mar 2017 21:44
Why no supercharged diesels? - Metropolis.

Got to admire Mazda for being so daring in engine design. Their perseverence with the rotary engine, even putting one in a Holden, really interesting company at times!

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Tue 21 Mar 2017 09:15
Why no supercharged diesels? - corax

Got to admire Mazda for being so daring in engine design. Their perseverence with the rotary engine, even putting one in a Holden, really interesting company at times!

It's an interesting and different engine, but not my cup of tea. Screaming revs and no torque. They still don't seem to have got over the seals problem, so I don't know why they persevered with it, unless they treated the engines as having a low shelf life, and expected them to be rebuilt regularly.

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