> Re: Dave Leonard's stock turbo
     >
     > At 14,000 feet density altitude, the pressure at the intake side of the turbo is approximately (30-14 = 16" Hg.) 16" of Hg.  If his MAP is 36", then the pressure ratio is 36/16 = 2.25.
     If 42", then
     > the pressure ratio is 42/16 = 2.62!!  The HP (or in this case Horsepower as estimated by the mixture flow rate of 25 lb/min) is approximately 240 HP, not considering losses through the
     intercooler
     > and plumbing.
     >
     > Having spent a few years in Product Engineering in the auto industry at FoMoCo, I am confident that the stock turbo will sustain operation at 6-7 psi boost as I understand it is rated by
     Mazda.
     > However, that said....I am also confident that this insured continuous operation was not considered at anything greater than probably 6,000 feet density altitude.  At 6,000 feet density
     altitude the
     > pressure ratio at 42" Hg would be 42/(30-6) = 42/24 = 1.75.  Hp, I would estimate would be in the 250-260 vicinity which is again in the 25 lb/min mixture flowrate.  This is still at the
     limit, but
     > not off the charts, especially since there is considerable pressure loss through the intercooler and plumbing (1-2 psi) which reduces the mixture flowrate to a more realistic 20-22
     lb/min and
     > equivalently lower HP.
     >
     > I am still convinced that the stock turbo will maintain sea level normalized (30" Hg) MAP to at least 12,000 feet without issue.  It will not provide 42" MAP to 18,000 feet density
     altitude (42/12 =
     > 3.5 pressure ratio).  If you gotta go there, you gotta pay the price of a turbo that is sized to do that!!  It will provide 42" MAP until one gets near the outer limits of HP and
     pressure ratio
     > caused by the reduction in the intake side of the turbo intake caused by increasing altitude.  Still....it seems like a great low budget addition for our 5,500 msl field altitudes and
     8,500 msl
     > normal flying altitudes here in Colorado for my RV-7.
     >
     > Doug Dempsey

     Doug, how would one go about loading down the stock turbine so it did not run at such high
     RPM's? I think over speed is killing the stock turbo charger.

     Paul Lamar

Paul:

In the auto, normally the biggest issue is to get responsiveness ie...short lag time, such that when one asks for more power to pass, the power is there....right now.  This is then balanced against
getting as much boost at sustained WOT so as to achieve the maximum HP desired.  A difficult task handled better by some than others.  Saab and Subaru seem to have gotten the equation pretty well
accomplished.

However, since responsiveness is of virtually no importance to our aero application, it would indeed be more appropriate for a larger mass flowrate, and longer time spool up turbo which would
probably come along with the higher flowrate.  That said, I would like to use the stock setup as I am aware of the extensive effort put into these systems by the OEM, especially manifold cracking.
A cracked manifold releases WAY too much heat into the cowl and into the vicinity of fuel carrying devices...NOT GOOD.  In a dragster, hose it down and tow it back.  In an airplane, one has a Class
A problem.

It would seem to me that the intake side needs to pump more mass flowrate at the same rpms which would suggest a higher flowrate compressor side turbine.  That assumes, however, that the exhaust
turbine is capable of driving this increased load.  These issues as one can see are not simple and and often, not intuitive....therefore I would leave the exact details to the turbo designers.

In my case, I plan to monitor (limit) the MAP with a wastegate to avoid over boost at low altitudes and will monitor pressure ratios at altitude to avoid spinning those little turbines into the
ether trying to accomplish what I am requesting with WOT at those 12,000 plus altitudes....when I am showing my brother and his Bonanza what high altitude speed is all about!

By the way, when the compressor turbine is operating very far away from it highest efficiency point, it creates unbelievable amounts of heat compressing that air...which can go into the only
available medium....the intake air.  This rapidly pushes the engine toward detonation due to the very high combustion chamber intake temperatures.

What amazes me most about Dave's "experimental" affair is what that little Hummer was able to withstand under those conditions without blowing it brains out trying!!  It must have been ingesting
400+ deg F air going into the combustion chamber.  Very impressive.  Any other IC engine would probably have left parts over a five mile radius...before the turbo failed..with holes in all of the
pistons and then valves disintegrating and then bearings failing...thus necessitating, for certain, a landing without benefit of power!

Doug Dempsey

Amen to that. One thing we know. It is a ROBUST little devil!

Paul Lamar
 
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