Hi Shadowmaker,
As Mikey mentions you are a turbo expert.
When a turbo is specified as 1749, 1752, 2052, 2056 etc. I know in 1749 that 17 represents the hot side or impellor and 49 relates to the cold side/ compressor. Do you know what is being measured by 17 and 49. For example, is 17 the diameter of the inlet or turbine wheel.
Could you explain please.
Lastly, do you know anything about air fuel ratios for diesels.
Thanks
'Head'
No, I'm not an expert on turbos as I don't repair or modify them for living. I'm always looking for better options for my van or for my friends TDs/TDIs/CRs. 49 is the big end diameter of compressor wheel. 17 is representing the flow capability of hot side, but can be missleading sometimes. For the rule of thumb bigger number flows more. You also need to know how new unit you are considering about as 1749vc out flows 2052v. Actually I think 2052v would out flow 1749vc, but with our restricted heads, 1749vc can make higher boost levels with better efficiency, which makes it a winner. That's called engineering.
Fuel ratio isn't that important with diesel. You can run AFR 40 and it will not do any harm to your engine. Actually it's safer to run it lean, but try that on a gasser and you have your engine inside out.
It's the overfueling that brakes diesel engines and there are two reasons for that: 1. your squirt of fuel from the nozzles touches piston and burns over it, will make a hole in the piston. 2. uncomplete burning due to lack of oxygen continues after exhaust valve -> excessive heat load for the valve, head and turbo. Also exhaust pressure will hit the roof as gas expands when heated. There is always the matter of too much advance as that causes knocking similar to the gassers.
Now people are using 18-19 AFR if they measure it during dyno runs, but I always monitor EMP (=exhaust manifold pressure) as it is more accurate reading about what's going on inside the engine. Also good and easy indicator is that you don't want to smoke excessively on WOT @high rev area.
I'm no engineer (thank god), so I'm just rambling here...