Turbo vs. Supercharger.

[scirocco81 at vwmail.net (Eric S)]

--- Neal Tovsen <nealtovsen@yahoo.com> wrote:
>Sheesh! Another self-proclaimed forced induction
>zealot who has not read his Corky Bell books! Man, you
>guys need to get with it! <grin>

Yeah yeah! :-P

>difference, or care. Eric's big "turbo advantage" only
>works when the turbo is operating well within design
>parameters at sea level, with enough headroom to spin
>faster at higher altitudes without blowing up or
>running off the efficiency charts. So a production car
>does receive this advantage, but modified turbo cars
>running higher-than-stock boost should be very careful
>at altitude!

Yes, this must be taken into account.  People modifying the TDIs with the VNT turbos have found a weakness to VNT...it spikes breifly (IE, its not very quick to control overboost situations)...several who have modified their ECUs (which does change the Nozzle control program) and who run at altitude have found that the VNT-15 is just too damn small...spiking the turbo to 23-24 PSI at 10,000+ ft has grenaded several that I know of.  People who have stepped up to the VNT-17 or 20 have had no issues with overspeeding at altitude...larger compressor.

>A variable-diameter supercharger pulley that could
>vary RPM independant of engine speed would not be
>terribly difficult to design. This would compensate
>for various altitudes, just like a turbo, and could be
>built to guarantee that you wouldn't exceed the
>maximum RPM of the charger. However, the advantages to
>a production car probably aren't enough to warrant the
>additional cost/complexity, and a race car team would
>find it much easier to simply change pulleys when they
>race at altitude.

Yeah...its too cost prohibative/complex.  I suppose, in my case, a really simple solution would be to set the pully for boost at altitude, and add a blow-off valve to the intake (post compressor of course).  That way, if you did head down to lower altitude, you wouldn't be over-boosting constantly.

Hey Neal...how about a test?  You've got an G60 8v...a TDI VNT turbo should bolt right on to your motor (the VNT-15s that VW uses have the turbo built right into the exhaust manifold)...all you'd really need is some sort of controller for the nozzle...it could make an interesting project!

BTW...my TDI engine that I am swapping into my Mk1, is the older design...uses the traditional wastegate...I think its a GT-15??  So, I might be considering a VNT at somepoint....but figuring out the nozzle control is the biggest issue with sticking one of those on.

--
Eric
www.VintageWatercooleds.com

79 VW Iltis
81 Scirocco S (*TDI* swap and complete restoration in holding pattern)
81 Rabbit Truck LX Diesel (FOR SALE!)
81 Rabbit Truck 2.0 16v Motronic
83 Scirocco Wolfsburg
91 Cabriolet (2.0 Crossflow 8v swap and mechanical rebuild in progress)