The fuel flow seems correct, and coolant temps seem correct for the speed,
and HP, so mixture is close. The EGTs are way too high, probably back
pressure and perhaps too large a header diameter. And the probes are a bit close
in. About 3 inches is the compromise between accurate reporting and long
life. Each header pipe should be exactly the same length to the collector.
Put a shop vac hose down each pipe as you build up the system and mark the
length with tape. Make the second pipe the same length. Shallow angle into
the collector. Collector about 4 diameters long. Long collector broader HP
range. Short collector higher peak HP but very short range. Header tube ID
to match the exhaust liner ID as close as possible. You want high velocity
right into the collector. Header length in any multipal of 11" to 12" to the
collector. If the muffler is close to the collector that is the end of
tuning. And best to have a see through muffler.
The other problem is the 13BREW irons are from a twin turbo engine
and have huge port runners. You want the highest possible velocity at the
port face on the iron. That requires small runners in the manifold and
irons. Some builders do use turbo irons for NA road race engines, but those guys
shift well above 10,000 RPM. That is because of the big runners that still
flow well at those RPM. Those engines have no bottom end power and not
much mid range.
Dave Lemon blends 2 of the 3 runners and ports in a 6 port iron to make
his E production engines. This is the same idea as the turbo irons but with
more material to play with. He shifts above 10,000 RPM with a really big
street port.
Read this: _http://mototuneusa.com/thanx.htm_
(http://mototuneusa.com/thanx.htm) Look at "High velocity porting"
So the selection of turbo irons for an NA engine is an error in my opinion.
Daryl Drummond uses the stock intake manifold gasket on 250 HP 12A GT-3
engines. So the runners are amazingly small. (High velocity)
The Pport gets back runner velocity with very early opening of the intake
port. Lots of overlap and late closing of the intake port.
The bridge port opens even earlier than a Pport, plus you control where it
closes by moving the closing line at the top of the port. I think you are
stuck so long as the turbo irons are installed, unless you add a turbo,
which ends most of the muffling problems.
Rather than bridge port the irons, I would swap them for non turbo irons or
add the turbo. Get on the "Nopistons" list and look at the swap and sale
items.
Lynn E. Hanover
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