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Hi Mike;
Hopefully your nephew makes a fast and full recovery.
I attached a bellmouth/velocity stack chart, I wish the guy I received it from remembered the source...
The difference between a good and simple intake could easily be 10%. A tuned intake in the tuned range even more. Any approximation could go a long way.
Best power is probably closer to 13.5 AFR @ 27* @ WOT @ 7000rpm in a stock 13B NA-> say 13-14 AFM.
Oil/Water Temps ~160F according to Lynn.
Best power will probably be just rich of peak EGT. I've heard of peak HP EGT's as high as 1800F. IIRC, Lynn mention 1600F and measured @ 3" from the exhaust port - and Lynn probably has more high power dyno/race time than the rest of us combined.
For Al:
Top speed is the intersection of too many curves (engine HP/ load, prop thrust, airframe/prop drag)
One answer to less than peak HP rpm (@top speed) is to start iteratively lopping off the prop tips until peak HP engine rpm is restored for whatever air speed.
If the top air speed is prop HP limited (for a particular V); a dive "trading altitude for kinetic energy=HP" may allow the engine to achieve and maintain a higher HP output and consequently top speed -> an indication of being over-propped (assuming it is not pitch limited). One hint, of the possibility, is that full power is less than WOT and not completely out of whack compared to car intakes/HP/loads...
The best answer is to probably get Paul Lipps to design an optimized prop for your engine(HP curve) vs airframe(drag curve). Expect to fly/chop at least 2 props until it is optimized.
Again, ANY drag clean-up goes a long way at top speed.
Cross your fingers
Cary
Sorry for my absence on a topic I started. My nephew had a skateboarding accident last weekend and is in the hospital in a chemically induced coma until his brain swelling is under control. And I thought car powered airplanes were dangerous. Stay away from skateboards.
Tracy - My mixture monitor shows stoich at full throttle. I suspect an airflow issue rather than fuel.
Al - my vacuum gauge is located in the plenum directly behind the throttle plates.
Lynn - I agree that the TB inlet is horrible and needs a bell mouth. The inlet is also pretty obstructed by the cowl which isnt visible in the pics I sent. I think I'll make an attempt to clean this up some and see if it gets me anywhere. If not I'll live with it for a while.
Kelly - always tough to determine if the problem is an engine issue or if the load is simply too much for the engine to overcome. I'm going to experiment with the shallow dive several have suggested and see what happens.
Mike
velocitystacks.jpg
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