Thread: Opinions Please.........

Originally Posted by JDNSW

I don't think there is any inherent emissions problem with two stroke diesels - other problems, yes. Probably not for two stroke petrol engines either - provided they do not use crankcase compression which means mixing oil with the incoming cylinder charge. But the main advantage of the two stroke diesel (simplicity) is probably lost with all the extra gear needed to get emissions down, and the power weight advantage has been largely lost with the almost universal use of turbochargers. I doubt very much if this conversion can have very efficient scavenging (intake and exhaust are the same end of the cylinder), although if it is running with a very high air/fuel ratio, as seems to be the case, this is unlikely to matter too much.

As I said above, the only possible advantage of this conversion would be that it uses an existing engine. The conversion would be a lot cheaper than fitting a new, different engine.

I can see a lot of problems though with things like gearing, torque distribution etc.

John

I think the emissions problems with the two strokes are the inconsistent amount of internal EGR, burning of the lube oil (smoke), not burning the lube oil (hydrocarbon emissions) and the inability to completely control the cylinder A/F ratio.
They are all gone from some markets and dwindling rapidly in every other market.

Originally Posted by Dougal

I think the emissions problems with the two strokes are the inconsistent amount of internal EGR, burning of the lube oil (smoke), not burning the lube oil (hydrocarbon emissions) and the inability to completely control the cylinder A/F ratio.
They are all gone from some markets and dwindling rapidly in every other market.

Most of those factors only apply to two strokes using crankcase compression, and air/fuel ratio is fairly irrelevant for diesels. I do not know whether two stroke diesels pose an emission problem - they have never been all that popular.

John

Originally Posted by JDNSW

I do not know whether two stroke diesels pose an emission problem - they have never been all that popular.

John

Ummm, Detroit.
Nissan UD
etc.

They were very popular and they were phased out because they cannot meet emissions standards despite being sort of direct injection.
Even 2 stroke home lawncare equipment is gone in some markets. Weedeaters, lawnmowers, honda have changed their motocross bikes to 4 stroke, their jetskis are now using 4 stroke turbocharged engines to get the required power and meet emissions.

There are direct injection two strokes in outboard motors etc. But they are a recent development.

California is of course the first to ban 2 strokes unless they prove they meet the current emissions regs.
http://www.bikersrights.com/states/c...a/2stroke.html

Originally Posted by Dougal

Ummm, Detroit.
Nissan UD
etc.

They were very popular and they were phased out because they cannot meet emissions standards despite being sort of direct injection.

I am aware of them, and others, but through the history of diesel engines, they have never been as popular as four strokes - except possibly in ships. What I don't know is why they have ceased to be popular as they were. Is it really because of the inability to meet emission standards? My guess is that rather than that, it is because the advantages they had over four strokes have disappeared with the ubiquitous turbocharger. These advantages can never have been all that great in practice, because the majority of manufacturers never made a successful one.

As far as petrol engines go, yes it is emissions that have killed them - although for a lot of applications they were already going, as a more prosperous society was no longer prepared to put up with the drawbacks that seem to be inherent in them, for example in lawnmowers in this country, where, while still available, and usually cheaper, they sell a far smaller proportion than they used to. (Although I think it is correct to say that they are still in widespread use where light weight is the dominant concern, such as small outboard motors and brush cutters.)

John

Originally Posted by JDNSW

I am aware of them, and others, but through the history of diesel engines, they have never been as popular as four strokes - except possibly in ships. What I don't know is why they have ceased to be popular as they were. Is it really because of the inability to meet emission standards? My guess is that rather than that, it is because the advantages they had over four strokes have disappeared with the ubiquitous turbocharger. These advantages can never have been all that great in practice, because the majority of manufacturers never made a successful one.

As far as petrol engines go, yes it is emissions that have killed them - although for a lot of applications they were already going, as a more prosperous society was no longer prepared to put up with the drawbacks that seem to be inherent in them, for example in lawnmowers in this country, where, while still available, and usually cheaper, they sell a far smaller proportion than they used to. (Although I think it is correct to say that they are still in widespread use where light weight is the dominant concern, such as small outboard motors and brush cutters.)

John

The turbo made no difference to the demise of the 2 stroke diesel. Gemmies were either supercharged and later turbo charged and essentially had to be.
Noise is one factor of them as is fuel usage, but the power these engines produce is astounding for such a simple engine. Unfortunately they need revs to be any good and higher revving uses more fuel, creates more emissions and more noise. Subsequently design laws cant be met.
There are however, still a considerable number used in marine and industrial applications. On highway is where they now are becoming few and far between.
I still get plenty of 71 & 92 GM's coming in for machining, particularly head rebuilds.

Cheers
Andrew

Originally Posted by LOVEMYRANGIE

The turbo made no difference to the demise of the 2 stroke diesel. Gemmies were either supercharged and later turbo charged and essentially had to be.
Noise is one factor of them as is fuel usage, but the power these engines produce is astounding for such a simple engine. Unfortunately they need revs to be any good and higher revving uses more fuel, creates more emissions and more noise. Subsequently design laws cant be met.
There are however, still a considerable number used in marine and industrial applications. On highway is where they now are becoming few and far between.
I still get plenty of 71 & 92 GM's coming in for machining, particularly head rebuilds.

Cheers
Andrew

The blower was purely for exhaust scavenging and intake air. Detroits without turbochargers did not run with any significant boost.

There is a commonly held erroneous belief that these engines need to be revved. Wrong. Get some engine performance charts and check the torque curve of Detroits against competitive engines. In particular check the clutch engagement torque (800 rpm) which exceeds all competitive engines. The 8V92TA / TTA series had 840 ft. lb /1139 Nm at clutch engagement. The equivalent Big Cam NTC400 Cummins had 600 ft. lb / 814 Nm. Maximum torque was 8V92TA 1242 ft. lb / 1684 Nm. @ 1400 rpm & NTC400 1150 ft. lb. / 1559 Nm. @ 1500 rpm.

The noise was principally blower noise. The distinctive exhaust note can be easily reduced by proper exhaust systems but many owners wanted more noise and modified the systems to produce a louder mor sporty note. I saw the extreme of this in a Road Commander with a late 8V71N, 333 hp @ 2300, fitted with full height straight through dual 4"stacks, no mufflers, on a Nullabor runner about 1980.

The 8V92TA was doing it easy in the automotive rating of 435 hp. The marine engines could be had at 545hp @ 2300. My experience with them was that fuel usage was little different to other engines doing the same job. Their longevity was legendary in all applications. Keep clean air and filters up to them and they went almost forever. Detroit Diesel had an oil analysis programme going in the mid 70's and maintained there was no need to change oil until they told you to.

The entire injection system is contained in the camshaft operated unit injector in each cylinder and can be simply over hauled or exchanged for around $120 per cylinder. Compare that with the cost of a total injection system overhaul in anything else.

DD virtually owned the engine business in highway coaches by virtue of low weight. Low weight means more bums on the bus. The 6V92TA, popular in the coach business weighed only 2020 lb. Three bums lighter than an equivalent 855 Cummins.

Originally Posted by Brian Hjelm

The blower was purely for exhaust scavenging and intake air. Detroits without turbochargers did not run with any significant boost. There is a commonly held erroneous belief that these engines need to be revved. Wrong. Get some engine performance charts and check the torque curve of Detroits against competitive engines. In particular check the clutch engagement torque (800 rpm) which exceeds all competitive engines.

The 8V92TA / TTA series had 840 ft. lb /1139 Nm at clutch engagement. The equivalent Big Cam NTC400 Cummins had 600 ft. lb / 814 Nm. Maximum torque was 8V92TA 1242 ft. lb / 1684 Nm. @ 1400 rpm & NTC400 1150 ft. lb. / 1559 Nm. @ 1500 rpm. The noise was principally blower noise. The distinctive exhaust note can be easily reduced by proper exhaust systems but many owners wanted more noise and modified the systems to produce a louder mor sporty note.

I saw the extreme of this in a Road Commander with a late 8V71N, 333 hp @ 2300, fitted with full height straight through dual 4"stacks, no mufflers, on a Nullabor runner about 1980. The 8V92TA was doing it easy in the automotive rating of 435 hp.

The marine engines could be had at 545hp @ 2300. My experience with them was that fuel usage was little different to other engines doing the same job. Their longevity was legendary in all applications. Keep clean air and filters up to them and they went almost forever. Detroit Diesel had an oil analysis programme going in the mid 70's and maintained there was no need to change oil until they told you to.

The entire injection system is contained in the camshaft operated unit injector in each cylinder and can be simply over hauled or exchanged for around $120 per cylinder. Compare that with the cost of a total injection system overhaul in anything else. DD virtually owned the engine business in highway coaches by virtue of low weight. Low weight means more bums on the bus.

The 6V92TA, popular in the coach business weighed only 2020 lb. Three passengers lighter than an equivalent 855 Cummins.

Brian, hit the ****ing ENTER key ever now and then

Originally Posted by rovercare

Brian, hit the ****ing ENTER key ever now and then

Ron, call the shop steward. Rovercare is trying to take your job.