Quote:
Originally Posted by Vekke
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1.9 SDI is more efficient in steady speed driving (highway cycle) than the 1.9 TDI. Making that boost wastes diesel if you are not needing it in the first place!
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i'll read the very interesting study that you attached.
but i'm not sure that you are right.
I did some homemade volumetric efficiency assessment with obdii data logging. first thing i noticed, SDI engine hasn't a MAF. no straight comparision could be done at ease.
Then I found that the smoke map on the SDI was limiting fuel injection below "torque curve", so FSI style inejction control on the SDI has some not accessible obdii data figures of air mg/stroke but I'm guessing that air intake temperature and somekind of pressure on the big air intake is used to evaluate mass of air.
Because i Found the same smoke map on SDI and 110 hp engine I think that stock SDI doesn't has the expected better performance, because it was too much difference on fuel injection. maybe a dyno and some sensor will help.
But I guess that if vnt turbo engine vol.efi is in the range of 80 to 95% in my 1.9 VNT15 geared and no load on the throttle and even higher in a 1.9 TDI PD with KP39 turbo, i'm not sure why with the same smoke limiter map the SDI will be capable of doing +30% more torque and power if the same efficiency and if the same injection quantity per stroke was burnt.
SDI engine had 2 gear ratios both of them shorter than that TDI ones in the same platform, so they have almost the same on road European cycle fuel consumption or a little lower. So you are right that it was less engine losses involved but not the expected ones I think.
But Stock SDI air intake is too different to that of any TDI engines from 90 to 160 hp I've seen or also the exhaust is different. Intake and Exhaust engeenering are too realeted to performance on an atmospheric.
I did the test with maybe too old engines.
It seems to me that 1.9 SDI it was capable of doing a lot of more torque and power. 125 Nm and 64 hp seem to me someking of low performance compared with the 1.9 VE TDI (90 ALH or 110 like... AFN/AHF/ASV). but if smoke limiter is already cutting the injection this means there is not air enough to tune the engine.
According to data I found SDI road 4.1L/100km with 39.6 km/h/1000rpm 5th gear
and TDI road 4.1 L/100km with 47.8 km/h/1000rpm 5th gear.
So maybe it is an amazing 20% better efficiency. (47.8/39.6 =120% o 17% less fuel consumption tith TDI gear fitted to SDI engine.)
Skoda Fabia 1.9 SDI Comfort ficha técnica, prestaciones, consumos, dimensiones de este coche - km77
Skoda Fabia 1.9 TDI Elegance ficha técnica, prestaciones, consumos, dimensiones de este coche - km77
Do you think a 20% difference due to engine bsfc is realistic?