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
 
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