Not being too familiar with semi-truck engines I never realized Cummins 885's have much lower compression ratio's compared to other diesel engines. Their compression ratio's are more inline with gas engine compression ratio's at 10:1 NA and 8.5:1 TA. I've seen some engines with up 23:1 compression ratio. I'd guess 855's are one of the lowest compression diesel engines made but also one of the best diesel engines made? What is the reason/advantage for the lower compression and why don't other diesels have lower compression? I did read the 855's aren't the best cold starters.
BC compression ratios come in several HP groups, average 400 HP is 14 to 14.5, 350 15.5. And all has to do with injector fuel rates and injector timing. Older small cams ran in the 17.5 range with a advanced timing of 36 thousands injector pushrod travel. Where big cams averaged 64 to 66 for early models which was revised to 69 to 71 injector travel at .203 before TDC which is retarded timing. 69 would be faster, 70 nominal, 71 slower. All this was done at the time to meet EPA. Faster timing does have advantages with compression ratios and has it's disadvantages too. Faster has quicker throttle response but less torque hang time, Slower/retarded timing slightly less throttle response but better torque hang time between shifts. But have to remember comparing a 855 PT injection system that ran from 1700 to 2100 rpm to any electronic controlled fuel system that runs 1150 to 1600 is apple and orange. * I have seen some BC 855's that started fairly well down to 20*, but everything was just right internally. Perfect compression and fuel delivery, and timed on the faster side.
Generally, indirect-injected (precombustion) diesel engines usually ran the higher compression ratios. Somebody correct me if I’m wrong, my memory may be hazy. I have no idea if it still holds true nowadays
Some of that went away with the BC IV's, 444, and Mechanical N14- with step time control. Advanced timing during start up and idle.
Cummins NTA series were the worst for cold start. The word was if a kid with a Popsicle walked past one it wouldn't start.
And that's pretty much correct--average B model cat was 14.5 to 15.5
Yes that's true--and kind of a animal to it's self, was not a great seller.
Curious why 10:1 and especially 8.5:1 are listed in a quick search? I read something initially that said 10:1 and thought it was a misprint. Then I googled it and several sources confirmed it. Lower compression I think would make for harder starting. Might explain why it used to be common for truckers to leave the engine running all night. I've heard people use the popsicle analogy in reference to Perkins engines and I've experienced the opposite. If the engine is properly set up it will start when cold. I can start my tractor with a 3 cylinder Perkins at -20C without being plugged in.
My C15 is 16:1 decompressed. ACERT were 18:1 direct Inject.
It is. Stay warm themselves, plus fuel then was cheap compared to now, and it kept air system somewhat warm. These days most all are equipped with auto start/stop.
Used to figure engines would slobber some from not holding compression as idled so long, would burn around a gallon an hour at base idle, not really all that much. Smoking was mostly poor cold ring seat or turbo seals seating oil slobber oil burn.
Yeah, diesel is stupid expensive now and has been for a long time. Gov't. doesn't care because most of the cost is taxes. How diesel can be more expensive than gas is just pure greed. Gov't. goes after pharmaceutical companies for over charging prescriptions while at the same time are gouging people on fuel, especially diesel. In Eastern Canada there are places that don't have natural gas so have to use heating oil. Read where one homeowner was paying $1200/month in the coldest month's. Federal gov't. was giving rebates for people using heating oil and it created a big uproar. Other provinces also wanted rebates on heating their homes despite having natural gas. Natural gas is over priced but nowhere near the cost of heating oil. Other provinces thought it was favoritism. I didn't understand the big uproar. Let the people complaining switch to heating oil and they'd still pay more with the rebates. $1200 a month just to heat an average size house seems absurd.
That's where turning up the idle came into play to stop the slobbering and keep the engine warmer. There were a lot of people floating around some stupid theories like it takes more diesel to start the engine than to just let it run all night. That would be really insane if idling uses a gallon an hour. I let the engine run because it takes 10 gallons of diesel to start it. Some engines would glaze the cylinders too. I was told not to idle my 3204 for lond periods because it could get so bad it wouldn't throttle up. The guy at shop said some newer Cat engines could idle all day with no I'll effects.
There is not an engine made that can idle all day without ill effects
Incorrect---depends on how it's spec'd. ----A 3406/3408 with oil retarder/engine brake will set and idle for hours on end with about 5 psi air pressure on the manual lever. It will load the engine just enough to keep oil at 195* along with coolant at 195* putting a constant load in the cylinders. One big reason Canadians bought trucks with Cat engines was the massive brake HP built by a retarder/with a set of jakes also. * And winter time is deadly on any two stroke Detroit, doesn't matter it's idled up. The blower can't provide enough pressure to keep it from slobbering without a load.
That's pretty cool
A K100 like this that I drove had a DITA 400 cat with retarder and jakes. Never touched brakes, Ashland from top to bottom 48 mph, and in winter it was warm taking a nap. *
I forget what newer dozer engine the guy said could idle for hours with no ill effects. Idle RPM may play a role too.