Ok well taking in that account then Alex, how far can the SOI be advanced to in the ECU and well the PD engine i would say revs to 4500rpm given its rev range on the ARL/ASZ/BPX 8v engine...
Then the question comes to what is the limit of pressure a OE headgasket can take and the cylinder peak pressure limit, given those two limits what would the bhp and torque be limited to?
Then we can look at if the headgasket and cylinder was to be reinforced, what advantages there would be on this, over say normal route, as in the TDI forums i have never seen a meation on cylinder pressures and head gaskets be a
problem on some of the most powerful TDIs in the US, pulling huge numbers over there with race injectors and modified cams and retro fitted turbos. There is alot of talk on oil temperature and pressures to the turbo etc, but nothing of meation of head gaskets or cylinder limited pressures?
If you could explain/expand on you meation of these, it would let us all understand better your thoughts of why they dyno graphs and company claims of power, and also question them when they boast they can modify the TDI to such levels?
The SOI is kind of critical if you start pulling it in the "earlier" direction.
As an exapmle compare ARL and BPX engine. They only differ 10bhp, but if you look at the power curve, the BPX engine has its max. power @ 3750 revs, the ARL @ 4000.
This has some reasons, like combustion efficiency, BMEP, cylinder pressure and so on.
The OEM surtanly has to develope to meet the 250.000km specification, so there is room to change mappings and raise those parameters.
As a rule of thumb you can calculate 2mg/stroke for every degree of duration in the most effective combustion/injection window with stock 550cc nozzles. (By the way the 550cc nozzles flow 55mg in OEM calculated best injection window, 520 cc nozzles 52mg and 465 do 46.5mg....)
Like stated before, in ARL engine the OEM starts injection at 23.5 BTDC and ends 4 degrees PTDC to reach 55mg/stroke, in tuning conditions I know of some using 26.5-27 degrees SOI and 6-8 degrees end of injection.
BUT: If you try it on a dyno/track or any other way to compare real power gain, you will see, that injecting past 5-6 degrees does almost nothing for power anymore, it just makes sound and warm air...(there are several professional tuners i know who will confirm that out of their own track/dyno testings and expierience). There is a LITTLE gain when you go further than 6 degrees, but in relation to the injeted more quantity the power gain is to little.
Then there is another point to mention: ignition delay. This parameter describes the delay of ignition with raising rev numbers, it s a physical effect, when combustion happens it needs a surtain time to burn up fuel. The diesel fuel is actually slow burning and so this effect is stronger in a TDI than i a gasoline engine.
Calculate 0.1sec for that, which makes 2 degrees of delay @ 4000revs.
With raising revs this delay gets more and more overproportional.
This you must calculate with when setting up mapping.
So, even if you set SOI at 27 degrees and let it end at 6 degrees you have 33 degrees of duration, and as an result from that you have "only" a bit more than THEORETICAL 66mg/stroke what creates 370Nm/272lbs/ft at the best operating point. But in practic you already loose efficiency, so there will be max. 355-360Nm
(Now i would like to know
how to gain almost 200Nm from 310 up to 500 like has been shown on here already???? You would need 46degrees/92mg for that*g*)
However, know lets say we can create 360Nm @ 4000revs
With the correct amount of airmass/boost you would see 205hp with that torque @ 4000revs.
BUT:
These 33 degrees are IMHO no option for a mapping what I would sell to a normal customer who wants to drive 10min WOT on highway.
So then, if climbing higher in rev band there are some issues showing up, first is the above mentioned ignition delay and as a second you need more and more airmass to get an acceptable lambda and EGT.
So lets look to the lambda first: OEM calculates about 18-19:1 for a smokefree mapping, if you dont mind a little grey haze take 17:1 which makes a 1,15:1 AFR.
To hold up this AFR you need at least 1,8bar of boost @4500revs, clearly we dont have to talk about doing this with a stock turbo, but even with one of those hybrids you wont do that durable. Take a look at a compressor map from an 56mm compressor in a therefor made 56mm housing, at a pressure ratio from 2,8 and over 22lbs/min flow this will be critical even for this compressor. BUT (again) the Hybrids work with 56mm wheel in a GT1749 compressor housing. Take a OEM 56mm housing in your hands and compare it to one of those hybrid housings. You will see the 1" outlet on the hybrid housing and almost twice outlet diameter on the OEM 56mm housing. And a different A/R of both housings.
Now take a guess which of those housings will flow better....
The consequence out of that: You cant hold up full injection quantity when revving higher because the car would start to smoke, raise EGT and so on...So there is no way to make 230-240-250-260 hp. Not with stock nozzles and not with an hybrid like a gt1752 or 1856...
To your question concerning PCP and BMEP: The bad thing about that is, that no one measured this before, all you can have and will find are more or less educated guesses...
Regards, Alex
