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Date: Sat, 29 Dec 2001 15:53:53 EST
Subject: V-8 engines for IV's 
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          <<  Lancair Builders' Mail List  >>
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In an email dated 12/29/01, glcasey@gte.net wrote:

<<<<<<Gary Casey
ES project, inverted direct drive small block, 325 hp. >>>>>>>>>

I'd be interested to know just how you're going to make that work. 

Let's try some real-world numbers to estimate reality. Assume you're using a 
real (as opposed to mythological) prop with sufficient diameter to absorb 325 
HP (for the sake of conversation and the benefit of the doubt, say 84"). On a 
standard day, at sea level, climbing at 100 KTAS, 2700 Prop RPM gives a tip 
speed of  0.90 mach (well beyond the high efficiency range of contemporary 
"real" props), with the tip-mach climbing right along with the aircraft. At 
225 KTAS, the prop (at 2700 RPM on a standard day) has a tip speed of 0.95 
mach at sea level and 0.99 mach at 10000 ft. (and worse on a colder than 
standard day). If you've got a prop that makes 85% efficiency at 0.9 tip 
mach, I WANT ONE TOO.

Now, lets assume you really do have some magic prop which will work at 0.95 
tip-mach, making 2700 RPM really usable. At 2700 RPM, you'll need 632 lb-ft 
of torque to make your claimed 325 HP (At 2400 RPM, a more realistic upper 
limit, you'll need 711 lb-ft of torque for 325 HP.) 

You don't say whether or not you are normally aspirated or not, but if so, 
the following comments apply. If the engine is a normally-aspirated 420 CI 
smallblock, then to make 325 HP at 2700 RPM, you have an engine which makes 
about 230 PSI BMEP. That puts you and Dave Blanton in about the same 
dreamworld. (If it's smaller, say 383 CI, you'll need 252 PSI BMEP, and are 
now probably ready to patent the first perpetual motion machine.)

FYI, the best we have made on our HIGHLY DEVELOPED (custom-made heads, 
dual-plug, high-compression, very-fast-burn combustion chambers, special 
valve train, proprietary intake system, trick injection system, special 
exhaust system) normally aspirated smallblock is about 221 PSI BMEP. I can't 
help but doubt that you are achieving the thermal efficiency necessary for 
230 BMEP at 2700 RPM on a normally aspirated engine. And that doesn't even 
begin to address the issues of heat rejection.

If you are turbocharging to get there, I'd have some questions about 
longevity. Remember, a TSIO-550 making 325 HP at 2700 RPM only needs 176 PSI 
BMEP, and guess how long one of them will run at max power. (Or at 65%, from 
the reports we hear).

Anxiously awaiting your reply,

Jack Kane
EPI, Inc.



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