I'm really curious and didn't want to introduce this to dieselguys turbo thread and potentially rob it.
I post out of genuine curiosity.
I started to think of this as I was mulling over the thoughts generated by Dieselguy's most excellent idea of the ball bearing turbo.
Just as examples I recall (not to single any one person out I assure). I profoundly apologise if it seems that way.
It is not meant so.
I read expressions like (generalisations all):
When I drop my foot I often wonder.....and I'm quite prepared to be corrected but several things intrigue me:
What rpm you're doing at 70mph
I can't rev it past 3000 rpm no matter how I push it.....(I get that as a test if there's no power to back it up)
and
I know some have been run at maximum boost as a regular event....
and
drive it like ya stole it (like the Fangio cobweb blow-out) to de-coke it.
and
I have gas leaking into my coolant res....etc
and
I wonder how much this actually has to do with the top end/bottom end
and
I often get 22 psi boost on my gauge
I may open a whole world of hornets but am intrigued.
From my point of view as an agricultrural engineer our working engines were used at constant revs (loads varied but they were run mostly at their sweet spot) determined at the design stage to give optimal power/torque curve crossover point and hence a sweet spot for running most loads the driveline was capable of.
It was, in fact, the best general running conditions to load / accelerate / get good economy the engine (without lugging) would put out. It generally worked through the inconsistencies provided by variations in soil moisture and consequently, draft (not sure how to spell that for the US readers), load on the PTO powered implement.
Bearing in mind these were still high speed diesel engines, (like 1850 rpm being the sweet spot) there was no real point in a turbo engine being pushed past the boost offered by the turbo....If necessary a decent operator would select a different gear from the tractor meter to keep revs as desired.....thus avoiding black smoke and lugging etc..all the bad things
My understading is even though automotive diesel engines will cope with variable running speeds, they like constant revs at acceleration (not flet to the boars)...they like to be operated very differently to the gasser engines.
My big question is why would anyone try to operate one of these engines outside of idle to 2400 rpm?
What is the gain.
It introduces erratic pressures in the CC.
It introduces huge variants into the loads on head gasket bolts - in fact it is quite a shock loading on and off.
Case in point is I use a constant 2000 rpm to accelerate simply as I got into that habit due to the slushbox TC they gave us. I am getting out of that now I have direct coupling. Despite this for my engine this feels to be the sweet spot for loading.
Even with the GDE Hot Tune I still accelerate at 2000 rpm to 2100 rpm and ease up to whatever speed I need for road speed.
I push to 2400 rpm to hold my speed on most hills when loads require and the trans kicks down a gear when needed. When my EGT drops and stabilises again.
So given the lengthy description (apologies) What is the gain in floggin the car over 2400 rpm...It can't make appreciably more power and its air/fuel ratio is even further form the stoichiometric ratio than the stock turbo can supply. (enter shortcomings of CAC sheesh 3 (mostly) to 9 degrees C cooling)
When climbing the steepest hills here I am happy with the way it pulls loaded to what I can legally pull in this country and find no gain in planting the foot harder.
Why do I say this: Remembering I use UltraGauge:
There is no apparent gain in rpm that I can note by pushing the foot down.
EGT increases drammatically (and needlessly).
MAF reading tells me that it declines suddenly after the max boost of the turbo----it just does not draw in any more O2 and the cloud of unburned fuel out the back grows tremendously.
Max Boost (measured at the outlet of the CAC does not climb which tells me that given the resistance to flow of air through the system there is no more air available to make more power even though fuelling may be heavier.
This rarely gets to greater than 15 - 18 psi.
I have minimal oil vapor to wipe out periodically (at oil changes) from my Samcos.
They, in fact, stay pretty clean and I catch little blow-by oil when i operate within these parameters.
I note no oil use and carefully measure 6 l every single time. It never changes.
Perhaps my driving conditions are different to yours and I can amble along more peacably.
Is there a reason to go as hard as I am lead to believe some do?
Just seems that the way they are driven is much like a gasser would be driven rather than my understanding of sound operating for a diesel (even HS auto)....and that is not to say don't ask it to do an honest stint of work, do this by all means. In fact that is my preferred de-cobwebbing methodollogy.
Happy to be pulled apart rabidly attacked or otherwise.
Thanks chaps.
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