Head studs

[CAJUN 93]

when your talking huge cubic inches (800 plus) cylinder pressures increase rapidly. a drop in static compression and timing will conteract that. what applies to a 903 inch motor will be slightly different in a 359 incher. still the idea is the same.

in gas engines the big inch natural aspirated or nitrous injected motors are set up much differently as far as timing than the small inch turbo and supercharged motors

daryl

[wannadiesel]

Bruce Mallinson's method works very well for long term reliable HP. We can get away with the ridiculous timing we run because we aren't working the trucks hard. His customers are OO's who lose money when the truck is broke, they need million mile reliability with their HP. And when the truck is running, it's pulling a load. I, for one, am just out screwing around. If I was trying to build a 400 HP Cummins 5.9 to do actual work I would lower the compression, retard the timing, and throw a lot of fuel at it.

[dpuckett]

Yup, what Dave said. Also, keep in mind most the big engines dont have an advance for the timing vs RPM like the VEs, and they run at a pretty consistent RPM.

I emailed them several years ago, asking what they thought was good timing for the 5.9 engines, and they said in their experience, stock timing was good enough. (this was in the days of a 270 hp upgrade being on the cutting edge of HP evolution). Reduced cylinder pressures will go a lot farther in longevity than slightly lower EGT or less fuel burned, or so the theory goes. I am not sure I agree completely, esp for those who hot rod or have a plain daily driver, but their presentation makes sense.

Daniel

[Begle1]

Advanced timing is a crutch for injector inefficiency.

When you advance your timing, fuel starts to burn before TDC; you are using energy to push already burning fuel through the compression stroke. That takes energy, and it increases pressure.

But it is necessary to allow complete combustion; if the fuel doesn't have the time to burn efficiently, it will be dumped along with excess oxygen and will continue to burn in the exhaust manifold, raising exhaust gas temperatures.

More efficient injection systems require less of a timing advance to fully burn the fuel; higher pop pressures and better atomization spreads a finer mist farther throughout the cylinder. Since the fuel is better mixed with the oxygen, it burns faster.

The optimal engine design has the timing set at TDC and a fuel that burns instantaneously.

High compression is a crutch for injector inefficiency too.

[KTA]

The optimal engine design has the timing set at TDC and a fuel that burns instantaneously.

High compression is a crutch for injector inefficiency too.

I suggest you take a course in Thermodynamics before making incorrect statments such as above.

[Begle1]

I suggest you elaborate... Please?

[DTanklage]

The optimal engine design has the timing set at TDC and a fuel that burns instantaneously.

and how do you plan on keeping bearings in this "optimal engine design" of yours?

[Begle1]

and how do you plan on keeping bearings in this "optimal engine design" of yours?

When I find the magical mystical mushroom fuel that burns instantaneously, it'd be worth it to beef up the bearings. But as it stands, the only way we can speed up ignition speed is increasing atomization, improving injector pattern, running cetane booster, or using a fumigated fuel like propane or methanol. Any and all of the above would make the fuel burn more instantly; with #2 Diesel you'll never even get close to the "optimal", but you'll get closer, so you'll see benefits.

If you go to the absolute theoretical optimum, things become impossible. But it's still the best direction to go in.

Kind of like making a cable between two poles pull perfectly taut. All of the energy in the universe can't make a cable perfectly taut, and if you had all that energy you'd only break the pole...

[KTA]

Buy the book and study it, it would take 100 pages to properly explain it and how it all works. Long and short is the higher the compression the greater the heat, the greater the heat the greater the effeciency. From a theoretical side more compression makes more power for everything else the same. The reality is the hard parts of the engine can only take soo much heat and pressure so its a give and take as to the optimum design features.

[Begle1]

Buy the book and study it, it would take 100 pages to properly explain it and how it all works. Long and short is the higher the compression the greater the heat, the greater the heat the greater the effeciency. From a theoretical side more compression makes more power for everything else the same. The reality is the hard parts of the engine can only take soo much heat and pressure so its a give and take as to the optimum design features.

And if you have inefficient injectors, you can increase the compression to make them work better.

When I said that "high compression was a crutch for inefficiency", I didn't mean that high compression was only a crutch for inefficiency. Compression has plenty of positives as well. No engine will work without any compression at all. It's not something that you want to totally remove.

But historically, high compression was used because it let engineers get away with inefficient injectors. Haven't Diesel engine compression ratio's been dropping steadily for the past 100 years? Turbochargers have a lot to do with it, but so do more powerful and precise injectors.

[dpuckett]

Actually, in the last 5 years, they have been headed back up, thanks to the Egotistical Pinhead Administration's outrageous requirements for tailpipe emissions.

I dont think there were many diesels with compression of more than 30:1. Most automotive diesels, IIRC, were in the 20-25:1 range for NA; 16-18:1 for turbocharged, regardless of whether it was 1960 or 1990.

Diesels werent really mass produced til Robert Bosch came up with his high pressure injection system in the 1902s. And even then, it took Clessie Cummins' determination and hard work another 30-35 years to gain a foothold on American highways in trucks, with gasser having a majority til the early to mid 1960s.

Daniel