The 12V71TI engines in the ferries behave in an identical manner. Difficult to light when cold unless you use ether, and heavy blue smoke until they get sufficiently warm.

Light off three of them in a confined engine room space..........what a racket......

I don't know of any links to what your asking and I know that these higher compression diesels are not being made anymore due to the extremecost! The 50:1 diesel I told you about was one we engineered for the Dept of the Navy and was an inline 8 cylinder connected to a Carrier refrigerant pump about the size of a large chest freezer. The unit was designed to take an ambient temperature of a comfortable 75 degrees Farenheit and turn it into a 105 or lower deep flash freeze in less than 5 minutes! We never knew what the Navy wanted this for and we didn't ask but I believe since the Navy was doing some climate survival studies on the effect of humans and the environment that this was it's purpose. The goal of getting it cold ASAP was because it was not efficient and even with a boost pressure of 50:1, it sucked fuel like flushing a toilet! It cooled, er froze a room of about 400 square feet in size! The engine had an electric motor of 2.5 HP driving the lubrication pump constantly whether the engine was running or not. The engine drove none of it's necessary accessories, coolant pump, oil pump, fuel pump etc. except for it's DI pump and a 400 CPS Dynamo. This design was later used by fisheries in Alaska to flash freeze the catch of the day, although not to these exact specs because of cost, but smaller and simillar. I've worked on power generating systems that had higher compression ratios in Alaska. These were the only power station for smaller towns some years ago. The size of the starter motor was designed to turn them over at a high RPM to get them started! Machinery made for an intolerable climate would not be anything you would see here in the lower 48.
I should also point out that after reading your questions, I think you think I meant that these engines were 50:1 at a normal startup. Not so and I didn't mean to confuse anyone, but sometimes I get lost in my little engineering details, heh heh! A 50:1 diesel will first light up at about 25:1. I'm not sure if I'll do a good job of explaining this one but here goes. When an engine begins to gyro, that is turn and run on it's own, the metal are stressed in a totally different way than you would think on a engine designed to run at a constant speed. A 50:1 diesel in your car or truck in stop and go driving with varying engine speeds would not last the entire month under those conditions! Balancing is crutial to high compression and high RPM constant speed diesels. When a diesel engine, or any engine for that matter begins to gyro, the metals stress not from up and down or side to side, but in a spherical pattern. When the engine is running at high RPM and turning over to the left, the casing will want to turn and gyro to the right. If your engine design was to have a center point of balance, like the crank, turning to the left while the engine casing rotated to the right, you could run it at very high ratios and counteract the destructive force behind having one part immobile and the other part at a fast velocity. In essence, your engine block and internals become a total part of the driving force,see? Two opposing forces counteract each other! I didn't believe it when I saw this either and it all sounds very star trek but it has been done. I guess that the closest thing we would see today would be a jet turbine. Multiple cylinders in a rotating casing running on lubricating oil has been tried and was a test pilot project powerplant in large heavy trucks, but it was all very hush-hush, trade secret and all that. When these truck specialty motors were taken "out of service" they were destroyed so as to protect our corporate interests, but it sure was fun and some of the research technologies are being used today. Variable compression and volumetric efficiency are more commonplace now. As far as I know, there are not many people lucky enough to say they saw, much less worked on a counter-rotating force diesel with a CR of 50:1 and 14,400 RPM! Guys, I really miss my days at Chrysler and this is why it was some of the best times of my life!

As FI mentioned above, when we refer to compression ratio, we're talking about static compression ratio. Simply take the volume of the cylinder with the piston at BDC and compare it to the volume of the cylinder at TDC. That's your ratio.

If you then manage a higher effective ratio via the use of additional boost pressure, that's another condition altogether and it's got nothing to do with the static compression ratio.

Even 25:1 is significant for a diesel when looking at static compression ratio. Clearance for the valves becomes a significant problem. Were these DI engines?

Yes. A piece of thin paper would be the only thing you could fit inside the cylinder for instance. At first, we wanted to be behind an explosion barrier when at first start!

You mentioned that your Cummins has a compression ratio of 30:1. It's presumed that you are not talking static ratio, again. What's the static ratio of this engine?

Does it differ from the typical Cummins 6BT?

I know on the boats with the older 2 stroke diesels they have heaters that you have to use or they won't start. Block heater or air box heaters. They smoke like crazy when they start.

With the new electric 4 strokes I don't know what they use, never had to start one when it was 80 degrees out.


I know the little Yanmars don't have glow plugs or anything, they just have big starters. You crank the heck out of them and they start.

But on a boat in the water the engine compartment usualy stays warmer remmeber, 30's is cold it doesn't get down much colder than that because of the water. A 617 would probably start in the 30's with no glow plugs.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200

The Static ratio is 22.5:1. In out ward appearances it does not differ from the 12 valve offered from late 1993 to 1998. The difference was in the size of the bore and stroke and these engines were marked by a maltese cross on a certain part of the block stamped into the casting. To be honest, In my opinion, they didn't make the greatest dino-diesel burners and were awfully loud which is why they were discontinued at least for consumer use. But they were rock solid with an inline DI pump that looked like the Benz 300D pump with an extra injection sleeve added and made great veggie/ plant fuel burners and were flex fuel ready in 1994. My truck runs better off of biodiesel or veggie oil than dino and my fuel economy is better too. Not every truck came with one of these. Remember the Cadillac fiasco of the late 1970's when Cadillac owners sued GM because when they opened the hood of their cars, they saw Chevrolet on the valve covers? Simillar situation. Not widely advertised on the service books and definitely not in the sales pitch, but GM had a bunch of overstocked Motorhome 350 V8's they needed to get rid of and they were installed in the Cadillac! Most who got their engines exchanged now find their cars in the junkyard, but the ones (and only a few) who didn't care about having a Chevy engine in the engine bay are still driving those Caddy's around with 300,000 miles or more on them and they run great even some 30 years later! Sometimes a mistake will turn out to be a bank error in your favour!
Now for the counter-rotating diesel.... Picture this....Your standing in front of your 300D or whatever watching your engine run, block and head plus accessories just sitting there motionless while everything inside is whirring and clacking away, right? Now if you could take that same OM 617 and install it in a steel sleeve with an outer hull and cylindral rod bearings in between, your motor would have the crank turning to the left while your block and accessories turned to the right, right in front of your eyes, your motor is running in two different directions with a DI pump for each cylinder and your transmission could harness the output from two rotating forces going in opposing directions!! Wouldn't that look COOL! Since the pressure exerted from the ignition of each cylinder forces a powerstroke and stress in one direction, the rotation in the opposing direction counteracts it and you can increase your output and RPM! Sort of like a reciprocating turbin hybrid! How Cool is that!!!! When we built one of these realising that if we didn't do our homework, parts flying off during a self destruct phase could kill us, I really thought that if I could be a part of this and see it and help build it, it would be worth the risk! I've seen stuff most people dream about!
However, right now the weather is good and I'm building a small storage barn here in my backyard and need to get cracking on it, but i'll be back tonight. I love talking about this stuff and even though there is a lot I don't know, it's a fun topic huh?

While the ball is there to get hot, that's not it's only operation. It's also there to force the incoming air to swirl.

I would think that the air would be swirling quite a bit already since the only way in or out of the precombustion chamber is through the 5 small holes in the tip of the chamber that protrudes into the main combustion area/hollow depression in the piston. I can imagine that the flow of air and combustion gases through those 5 little holes is violent to say the least. RT

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When all else fails, vote from the rooftops!
84' Mercedes Benz 300D Anthracite/black, 171K
03' Volkswagen Jetta TDI blue/black, 93K
93' Chevrolet C2500HD ExCab 6.5TD, Two-tone blue, 252K

The ball is there to increase the air-fuel mixing via turbulence. The angle between the injector and the ball enhances this effect to aid a more complete combustion process.

Hey, my masters degree in fluid dynamics just came in handy!

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Scott C.

2006 E320 CDI (120k miles)
FOR SALE: 1998 E300 Turbo Diesel - Black w/Tan Leather - Euro delivery (236k miles)

OK, everyone back on track!!!! Why do some need glowplugs and some don't? Does the length of stroke make a difference?

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

I don't believe that differences in stroke can make any difference with regard to the need for glow plugs or not.

Furthermore, the determination of the need for glow plugs is heavily dependent on the application. Put a diesel in a pickup truck and the driver expects it to start in a similar fashion to a gasser.........no long cranking. So, glow plugs are a necessity. I don't know of any light duty vehicles without them.

Put a HD diesel in a truck or a ship and the expectations are completely different. These fellows will crank them for a couple of minutes, if necessary. They'll haul out the can of ether, if required. They'll run the engine all night. Doesn't really bother them. Hence, the manufacturers eliminate the glow plugs from these engines to save money. There is no doubt that they would benefit from glow plugs in cold temperatures.

I've always wondered that myself.

7.3L PSD Compression Ratio: 17.5:1
5.9L Cummins Compression Ratio: 16:3:1

The Cummins can start at 32*f without any help. The PSD will not even cough at 32* without glowplugs.

Ahh, I remember my first Wanderlodge, a '77 3208 Cat powered. I went to test drive it just after Christmas, in Michigan, it was 8*F out when I arrived early in the morning. It cranked about one turn and started, wasn't plugged in or otherwise warmed up. Sure smoked like crazy when it first started though.

The simple answer is surface to voume ratio. The amount of heat lost to cylinder walls in a little 3liter six compared to a 10.4liter V8 is substantial. Less leak-down at cranking speeds also.

My '88 Wanderlodge had a "cold start aid", a pushbutton that would dump a metered shot of ether into the intake if there was no oil pressure for starting, never used it / never needed it.

Most guys with big diesels know that ether can stretch head bolts and other bad things, don't use the stuff. Many of us carry WD-40 for emergency starting fluid, isn't good for much of anything else LOL.

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Gone to the dark side

- Jeff

My understanding is that there are two main types of diesel engines: Indirect and direct injection. Directly injected diesels have almost always been used on large trucks, buses, farm equipment, boats, generators, etc. Fuel injection for diesels until recently was all-mechanical so they were smoky and noisy especially when cold. So, when Mercedes put a diesel engine into a car, they developed the prechamber concept (indirect injection) to help with some of the noise and emissions. At least this is what I remember reading in a book about Mercedes-Benz when I was on vacation a few years ago. I believe all the other automobile & light truck engines - VW, Peugeot, Izuzu, Ford, GMC etc used the prechamber indirect-injection design.

So, in a direct injection diesel the heat of compression is enough to easily ignite the fuel when injected (at least in temperatures above freezing), but in an indirectly injected diesel the fuel is injected into the prechamber first, and the prechamber takes a much longer time to heat up from compression alone...so you need to heat the air in the prechamber with a glow plug or some other type of heater. IIRC someone on this forum described the prechamber as kind of a "heat sink" where it draws away some of the heat from compression....I guess that's why the OM6xx engines don't start at all when cold if no glow plugs work.

Interestingly, I remember seeing an ancient stationary diesel engine in a museum in England and the display caption described using a glowing hot "punk" type stick, that the operator had to put into the pre chamber to heat the engine before starting.

Now the common-rail, electronically fuel-injected direct-injection diesels such as the CDI, are quieter than even indirect injected diesels with their new technology. but they still have glow plugs or intake heaters to make starting easier in very cold temperatures, but don't really need them above freezing. Older DI designs may have had more crude cold start aids for below-freezing like an ether injection system.

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1976 240D "Katja"