Propane injection - Page 2 - PeachParts Mercedes-Benz Forum

tryan · #16 01-29-2003, 10:40 AM

if anybody is going to get a ford powerstroke, get a 96 or 97. the new ones ('99 up) run like crap.

propane is a akin to nitrous . longevity is compromised.

adjustable systems seem to be okay from the deiselstop board, but the unadjustable systems chunk the cheap powdered metal connectin rods that ih is using.

psfred · #17 01-29-2003, 07:01 PM

All the American truck diesels in current use are pretty short on horsepower by Mercedes diesel standards -- a 7.3L turbodiesel should be producing upwards of 350 hp and 450 ft/lbs of torque over an rpm range of 4600 or so, and they don't, don't even come near!

Peter

Wasuchi · #18 01-29-2003, 07:34 PM

Check out the numbers on the new Powerstroke (6.0)..... a lot better (hp & torque wise) and not much higher rpm than the 7.3.

tryan · #19 01-30-2003, 11:08 AM

i have had 5 powerstrokes.

ford hp and torque figure keep on moving up the rpm scale. governed redline is 3000rpm in 5th. 3600 in 4th ( actually faster )

bigger hp numbers mean sales at the cost of loosing bottom end.

my 2001 runs on 7 cylinders most of the time because of the returnless heads that trap air and let the fuel get hot in the heads. 6.0's are the same f'in nightmare.

the 96 and 97's had 21:1 compression, no wastgate and could pull from 1100 rpm. ( got in trouble with the epa on these models)

99's could not get of of a wet paper bag.

NOTHING compares to a mercedes diesel.

psfred · #20 01-30-2003, 08:20 PM

At least they have adequate compression -- older Cummins were 16:1!

Peter

rwthomas1 · #21 01-30-2003, 08:36 PM

Don't confuse low compression with low power. Low compression makes more room for air and fuel without overstressing the connecting rods and head bolts. 21:1 is simply too high for a hard pulling "working" motor. 21:1 makes starting easy and has more initial power due to the higher compression ratio. BUT when you add too much boost and fuel under load something will give. GM diesels have a bad reputation in heavy-duty use partly due to there high 21.5:1 compression ratio. Surprisingly when the compression ratio is reduced to 18:1 and the motor is boosted and fueled like a powerstroke or a cummins the GM's will make plenty of power reliably. http://www.peninsulardiesel.com/ They know a little about doing this..... Cummins and powerstrokes regularly see 30+psi and survive quite well. As far as I know there was never a PS with a 21:1 compression ratio. RT

psfred · #22 01-31-2003, 12:09 AM

I hate to sound critical, but low compression DOES equal low power. Also lots of smoke and low efficency (and therefore more fuel consumption). Raising the boost is simply taking an inefficient engine and stuffing more air in it, raising the effective compression ratio to what it would be if the engine were designed properly.

Durability is more a case of proper design than compression ratio -- MB uses hardened cranks and substantial bearings, for instance, along with a pretty advanced oil filtration system. If and engine runs high boost without problems, but dies if it has 21:1 compression rather than 18:1, I'd say the basic design is poor -- and GM is famous for inadequate design, especially in diesels. If running at 21:1 destroys the bearings, the design wasn't stressed properly.

My Volvo is designed to 23:1, and usually has more like 26:1 in most new engines, and they run 300,000 miles in automotive use, not bad. Makes good power for its size (104 hp on 2.4L) -- boost is about 13 psi, I think. Huge bearings, though......and oil cooled pistons, etc.

American diesel practice has been, up to 1994 or so, to make constant speed, stationary engines, circa 1940, and stuff them in trucks and tractors. No real changes in 50 years -- low compression (for a diesel, they won't even run without external heat under 16:1), very long stroke on small cylinders, direct injection, and fixed injection timing, with a usable rpm range of about 1800 to 2200 rpm.

There have been exceptions (Mack, for instance, uses high compression -- 30 to one in some cases), but the Germans have been out front on this for a very long time.

Short stroke, high compression, variable injection timing, indirect injection engines produce considerably more horsepower and torque over a much wider (1000 to 5500 rpm) range with better fuel consumption and far less smoke -- take a look at any modern diesel, particularly the new Volvo and Cummins big truck engines.

After all, over the road trucks in the US had draft tubes for blowby until the early 90s......pitiful.

Even the new pickup engines are seriously low on power by MB standards -- my 603 puts out about the same horsepower and 50% more torque that a Chevy Vortec by displacement.....and that's a gas engine!

Oh, and the theoretical max boost from a single stage turbocharger is about 20 psi -- no way you can get 30, sorry, unless you have either an axial compressor or a two-stage centrifical compressor.

I think the record for boost probably still stands, though -- Napier made a diesel aircraft engine in 1953 -- called the Nomad, that had a 12 cylinder horizontally opposed design, 1200 ci displacement, with a coupled 8-stage axial compressor/3 stage axial turbine. The last and greatest of the turbocompound engines, produced 3700 hp and 400 lbs static thrust.

Needless to say, at 12:1 compression ratio, it was almost impossible to start, and at 8 atm (118 psi) boost I don't know how they kept the heads on. No one ever bought it, and when Rolls Royce bought Napier out, they discarded the diesel, added three feet to the "turbo" shaft along with some combustion chambers and made the RR Avon turbojet out of it!

Peter

rwthomas1 · #23 01-31-2003, 12:12 PM

I have seen the boost gauges in cummins running in excess of 40 psi. Holset HX40 turbos and a really modded engine for pulling competition so I don't know where the 20psi theoretical limit is coming from. The new Duramax runs 20psi stock...... Plenty more is available when chipped. GM may have a ***** history regarding design but Detroit Diesel designed the 6.2-6.5 liter and it is a good engine when used within its design limits. That said GM's, volvos, VWs, MBs, etc. with high compression definitely last a long time, many over 300K. What I said was they would not last if they were operated at maximum usable power ALL the time. Especially without intercooling. Peninsular found that in marine environments 21:1 compression ratio GMs operating under marine constant type loads would fail piston ring lands and blow headgaskets. Going to 18:1 pistons solved the problem with no real decrease in efficiency. GM trucks (6.2-6.5) won't survive for long hauling 10K loads unless modified. Your volvo won't last long hauling a comparable load either. Its been 8 years since 1994 in a very competitive diesel market and the technology in the new engines reflect it. Navistar, Cummins, Isuzu, etc. know what they are doing when it comes to diesel truck engines. If it was beneficial for them to run 21:1 ratios then they would redesign the engines and thats what they would offer. But they haven't, at least not to my knowledge, YET..... Maybe the super-high compression, high boost, multiple stage compressor diesel is just around the corner. I hope it is. Sounds good to me. RT

psfred · #24 01-31-2003, 07:38 PM

Intake pressure is somwhat more complicated than sticking a pressure gauge on a hole, alas. Standing pressure waves are very common (and no one does anything about them since they don't affect performance much), and if you drill in at that point, you get lots of pressure, but if you put in a pitot tube, you won't see much more than 20 psi off a single stage turbo.

A single stage (one compressor) centrifugal compressor is very unlikely to make much more than 20 psi -- it stalls above that speed and the air re-circulates around the vanes (and heats up something horrible, too). This is why a current design jet engine has about 12 compression stages, with stator vanes between to re-direct the air.

Also, take a look at the intake to the turbo, too -- then estimate how much air is going to go in at a pressure drop of a couple psi, since that is all that's going to develop at normal road speeds -- no ram effect.

On top of that, there is a rather large engine underneath, consuming air at a rapid rate! My brother and I get a hoot out of the local pulling tractor crowd -- they are claiming 5000 rpm on a 500 ci Cummins tractor motor with "dual turbos", what ever that means, 250 psi in the intake, and a six inch turbo throat. Ha, first off that cast intake (stock) won't stay together, let along attached, and the rate a which air would have to enter the turbo would suck loose dirt off the ground!

I take any and all "performance modified" claims with a grain of salt (about the size of a VW Microbus) -- very few can be verified scientifically, and the ones that are aren't that astonishing.

As to running flat out all the time at high compression, I still maintain that failures at 21:1 and not at 18:1 are a design fault -- peak pressure and compression load will be the same if you use more boost to get the same horsepower output. Any road vehicle engine is a variable speed engine by defintion (except for diesel-electric), so I would expect the Volvo to handle it's design load perfectly well. Tow 5000 lbs with it and ti will die pretty quick, but then so would a 6.5L Powerstroke in a Peterbuilt hauling 100,000 lbs. Outside the design specs, to say nothing of inadequate for the use.

Diesel design in the US, for trucks in particluar, is WAY behind Europe. Hopefully, they will improve, but Cummins, I know for a fact, did next to nothing in the R&D department for more than 30 years, only getting excited about it about 10 years ago when the EPA finally cracked down on particluates. Even then, they cheated. Deliberately made the engines to fail emissions standards to aviod both an engineered solution and to produce marginally more power....... Very sad, it's very hard to catch up --

The Volvo truck engines are VERY nice by what I hear, and the exhaust stacks are usually almost completely soot free -- I've never seen even a hint of black smoke from one!

Peter

rwthomas1 · #25 02-01-2003, 02:16 AM

I agree to disagree. We should go enjoy our diesels now. RT