In a message dated 12/12/2005 9:52:45 PM Eastern Standard Time,
montyr2157@alltel.net writes:
Who else but Lynn,
Well, I just bought a 89-91 NA automatic motor.
The plan is to Pport it.
Basically leave the exhaust alone. Leave the
splitters or not? The archives are a bit inconclusive here. In one post Lynn
says to keep the splitters. In another he says the Pport is very sensitive to
exhaust back pressure.
All rotaries are sensitive to exhaust tuning, just exactly like a 2 cycle
dirt bike engine. They are 4 stroke cycle engines but tune like 2 cycles. I
would leave the splitters installed. I would add a bit of a radius to the
opening line, and a slight radius all around the port, and then polish it
all, just to keep any chrome flaking from involving the apex
seal.
The factory racing Pports have very small exhaust ports. I think you will
loose more power trying to muffle the engine without the splitters than leaving
them in will cost. By far, the most important feature of the system, is that the
primary pipes should be as close to the same length as is possible. Both pipes
at the same angle to the centerline of the collector.
Muffler design is still not established, but there are some promising
designs flying now.
I have some turbo housings I can take the
insert out of and put into the NA housings if need be.
Other info I have says the exhaust should be
ported to Close 55 deg ATDC vs 48 ATDC for stock while leaving the exhaust
opening alone.
Leave exhaust timing close to stock. That 6,000 RPM is nothing, hardley
running.
Intake timing:
IO 80 deg BTDC
IC 60 deg ABDC
13 in intake length?
31 in length header primaries 1 7/8-2 in
dia
Collector lengths as multipals of 12 or 13 inches should work fine. Even
just 13" would work.
And save a lot of space. The shorter the system the more accuratley it must
be built. I saw a National champion winning Pport 12A with about 10" primaries.
But that is good up to 10,000 RPM. The longer setup would have a slight
advantage in torque at lower RPM.
3 in collector into muffler
2 in dia after
muffler.
For 6,000 RPM cruise I would go at least 2 1/2" tail pipe.
7500 max power
5500-6500 cruise power running LOP.
2.17 drive and a 68 in
prop.
I would go with the 2.78 reduction. Better choice of props, (right handed)
and the engine has so little torque that it shows much better with more revs. My
12A has 139 foot pounds at 6,500 RPM or 173 HP. But at 7,500 RPM it has 152.5
foot pounds or, 218 HP.
Plus the just talked about "P" factor will be under the correct rudder
pedal.
This allows for a longer (more efficient) prop. Start with as long as you
dare and work back as required. I would want the cruise to be just over 6,000.
Speed-fast hopefully.
If it sounds like this I won't be
upset:
I would be. Come to the track with me next year, and you better wear some
Depends the first day. When my car goes by at 9,600 and tickles the rev limiter.
It makes your nose run. And mine is not the best sounding rotary by a long shot.
We are limited to 103 dB. Years back, it was just too painful, so we ran a
muffler when none was required. More like 110 dB in the car. And not a good
sound at all. Just a nasty racket. Leave the splitters in.
Who says they won't Idle? That is music to my
ears!! Sewing machine be damned! A proper sound should cause
spontaneous incontinence amongst the granolas.
The Bridgeport engines are much worse at idle (2,000 RPM) than Pported
engines, (1,200 RPM) just because there is less intake open time, and far less
overlap. Another reason for the 2:78 reduction, you can tolerate a higher idle
speed without dragging the brakes all of the time.
Run an MSD, at least on the leading plugs. Should make one hell of an
airplane engine.
Lynn E. Hanover