PEH

Was you Hemi a stock engine, low rpm application (2.76 rear end?). Racing motors blew pushrods all the time (still do on drag motors) since the lifter bores are still vertical and the pushrods most certainly were not -- they are canted about 15 degrees. I don't know of any other sucessful pushrod hemi type motors -- much easier to use overhead cams.

And diesels DO have combustion chamber design -- there are several out there, including the nearly zero clearance prechamber type in the MB. What you won't see is domed pistons -- too hard to cool. There is no penalty for vertical valves and mostly flat combustion chambers -- flame quench isn't an issue with a diesel (although adequate swirl of burning fuel/air is) and there isn't enough room to play with shape much.

The new TDI/CDI designs appear to have a steel "prechamber" cast into the piston crown, and inject the fuel in two stages -- slow and small to start ignition, then the main charge.

Peter

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

Peter,

Th Hemis I had were only stock:'54 Chrys, '54 Desoto, '57 Chrys, 58 Chrys. I went 600 miles in 7 hours in the '57 from Reno NV to Salt Lake City UT. That included stopping twice for gas. It used a lot at 100MPH+.

I had Perkins Diesel in a Fordson (English built) farm tractor that had direct injection and cup type combustion chambers in the pistons. It was a 1956 so that type of combustion chamber is nothing new. Started easily unless very cold. It had no glow plugs or manifold heaters. For cold starting there was a compression release (rocker shaft moved off center manually to keep valves open. This allowed the starter to crank the engine fast and when compression was reapplied it usually kicked off. It was kind of a stupid design as it took 2 people to start it: one by the steering wheel on left side where starter handle was located and another on right side by radiator where compression release handle was located.

I finally sold it for parts because I couldn't keep the head gasket from leaking water into the engine. I tried shimmimg up the sleeves more than the spec called for, refinished the head surface ETC but nothing worked, It ran OK but overheated because an air bubble would form in the engine stopping the water from circulating. Also I got the Case tractor described in a previous post, so I didn't need it anymore.

I probably told you a lot more than you wanted to know. LOL

BTW, what is flame quench? I'm always want to learn more about Diesels. Also how do the the CDIs ignite the fuel with a lean initial stage and then add more fuel? The precombustion chamber engines ignite a rich mixture in the pre chamber and then leans out when this rich mixture is blown into the cylinder area. Usually a stratified charge starts rich for ignition and leans out for cleaner burning.

P E H

PEH

That tractor sounds like the old Model A engine the local antique club uses for the planer -- always dribbles water out the head gasket on one side!

The old chyrslers were geared pretty high, so you never spun that engine real fast. True of most Detroit creations, they weren't high rpm engines. My brother helped with a USCAC team for some time, they were about the last ones to use a Hemi, and the one thing he says is that they lost power all the time with bent pushrods. Long way around the corner for the valve on the bottom side!

Quench area is the area where there is so much cooling (in a gasoline engine) that the flame goes out. Give both a potential power loss and higher emissions of CO and unburned hydrocarbons. Wedge designs have a lot of quench -- basically the entire area on the "thin" side. Hemispherical heads have the least, since there usually isn't much area where the piston is really close to the head.

The small, short initial injection on the TDI/CDI engines is so that the main fuel is injected into burning air/fuel mixture. If I understand correctly, it is timed to "use up" the normal ignition delay. Acts like a spart plug. I have also heard of some work on various other systems to properly ignite the fuel to eliminate the ignition lag common to diesel engines with plunger type injection systems. The problem, I think, is that the time required to get good fuel atomization with rising pressure results in poorly atomized fuel at the start of injection -- the root cause of diesel "knock" and soot production.

Mack has used high pressure mains and "valves" on the injectors (5000 psi) to attempt to overcome this specific problem. The waisted pintles on the Bosch injectors common to MB and other automotive diesels is another -- the taper in the pintle (the litttle "pin" that pops up into the nozzle) allows more atomization and better spray pattern while the pintle is rising than a straight or simple taper pintle. It goes all the way up into the nozzle when fully open, changing the spray pattern.

I wish I knew more, but I suspect the subject is a full time engineering type of thing, and I'm really a chemist these days!

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

I had three Peugeot diesels that were pushrods. Spent too much time adjusting valves.

I think overhead cams end up with more power cause of less reciprocating mass in the push rods.