Barnhart wrote:

Does anyone know exactly what it takes to get a 13b/20b to detonate?

Is there a rule of thumb that you don't go over a certain amount of
boost, unless you have a certain type of fuel, keep the TIT
below a certain temp, have the right compression ratio, keep
the fuel mixture at a certain point and other variables to juggle?

At how much boost does this become a problem?

Barny
MGDQ 20bt

Jim Mederer of Racing Beat is fond of saying: "JUST DON'T LET IT

DETONATE!" :)

I don't know  exactly but the best indicator is intake air temp. My best
guess is 140 F. If you can keep the temp less than 140 F I think you
will be OK. Back in WW II P38 pilots were trained to watch the intake
manifold temp and keep it below 138 F to prevent detonation in
their turbo charged V12 Alisons.

Air intake temp goes up with boost all other things
being the same.

Some of the other factors that enter into the intake air temp
are;

A. Outside air temp of course.

B. Mixture. Lean mixtures are hotter. The evaporation of fuel cools the

mixture.

This is why you can generally hold your hand on an intake manifold on an

NA engine

generating considerably power while the rest of the engine will burn your

hand.

Also lean mixtures affect the actual combustion process I think. I am not

sure

why. One of the reasons the drag racers can get 800 HP out of a high boost

turbo

two rotor is they use alcohol for fuel. This greatly cools the mixture.

C. Effectiveness of the intercooler. Again, outside air temp among many

other things.

The best insurance is a large intercooler with a good inlet duct and an
unobstructed air outlet.

Don't forget the intake manifold air temp gage along with the boost gage.

BTW Having said all that Tom Parkes is getting away with NO intercooler
on his turbo three rotor in his Lancair ES. Go figure :)

Paul Lamar

Trying to work on a MAP that will give me 2-3 lbs of boost at cruise, and 10
lbs at WOT.  My idea (yeah , this is gonna work) is to be able to lean it
out at cruise like a NA and have the boost for higher rpms.  Or something
that would be close to it.  Definetely going with an intercooler.  No
wastegate.

Barny
MGDQ 20bt

Sounds like a good plan. Just watch the intake air temp.

Paul Lamar
 
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