Variable Geometry Turbos - was<VV> RE: JetHot coatings on turbo exhausts

[FrankCB@aol.com]

Frank,
       It was good talking with you during the Convention.  Instead of a 
wastegated turbo, you might try looking at a "variable geometry" turbo which uses 
vanes to change the angle of attack of the exhaust gas entering the turbine 
impeller.  Thus at low exhaust flow the vanes are mostly closed to keep exhaust 
gas velocity high and the vanes can adjust as the exhaust gas flow changes.  
The vanes are open while cruising (to minimize delta P in the exhaust flow) and 
also at full load (max. gas flow) to eliminate the need for a waste gate.  
These units come with different names such as VGT, VNT (the Garrett used in the 
89/90 Shelbys/Chryslers as well as modern diesel turbos in Europe), VATN (the 
Aerochargers as sold by Corky Bell and used in many hi output motorcycles).  
The tricky part, as I see it, is in controlling the movement of the vanes.  
Shelby/Chrysler used 3 vacuum/pressure solenoids (controlled by the ECM) to put 
manifold vacuum or pressure into a dual chambered "pot" with a control rod 
attached to the vanes (probably something like Dale's vacuum advance/pressure 
retard unit for the Corvair turbo distributors).  I'm still trying to discover the 
LOGIC of the control.
       The DIY MegaSquirt EFI controller is normally configured to fire half 
the injectors for each revolution of the crankshaft ("bank fired" injectors).  
However, according to their website, some users have fired ALL injectors at 
once (using only one bank) and used the second bank to fire WATER injector(s) 
using a SEPARATE air/water map that uses MAP and RPM inputs to activate and 
control the water flow differently from the gasoline flow.  I wonder if you could 
use ALCOHOL injectors for this since gasoline injectors would probably not 
last very long in water service.
       I agree that you'll need the hi-temp version of JetHot.  I would also 
suggest you get the INSIDE of the piping coated as well, IF you can be sure 
that the coating won't come off in pieces and erode the turbine blades.  When I 
insulated the piping upstream of my turbo with external wrap, the turbo lag 
was much reduced and the max boost went from 8 psig to 10 psig.  However, the 
downside was that the upward elbow disintegrated after 6 months.  When I showed 
the remains to the chief metallurgist at work he said it was due to 
overtemperature and not rust.  Also, I found that the same overtemperature and resulting 
overexpansion of the long crossover section had loosened the clamps at the 
ends of the manifolds.  Therefore, I'd recommend that you consider installing 
some sort of slip joint or expansion joint in that crossover unless the internal 
JetHot coating can keep the metal temps down to a safe level.
       Regards,
       Frank "small engines need boost to compete" Burkhard      

In a message dated 7/1/04 8:56:15 AM Eastern Daylight Time, fparker@umich.edu 
writes:

> My next Corvair project will be a Corsa turbo like I bought new in 66
> except with modern low inertia wastegated turbo and fuel inj with micro
> processor controlled water/alcohol fuel injection. A motor like this that
> has boost immediately in 1st gear will build temps fast and will need the
> 2000 deg version that JetHot sells.
> 
> regards,
> 
> frank parker