Hi Paul,
Thank you for the information. Now I know I'm on the right track, at least for my project that is.
I have another question dealing with weight and simplicity please. I read the following by Tracy:
"I found the use of short (about 1 and a half inches), straight intake manifolds to be very
interesting. Up until this point, the engine sellers have all stressed the importance of long
intake runners and tuning for good horsepower. I always thought this was an attempt to convince
builders that it took super smart engineers and hundreds of hours of dyno testing to arrive at a
good intake system. In other words, they were saying, don't try this at home, kids. I accept
their use of short, straight intake manifolds as proof that the ones on my 13B rotary were not such
a bad idea after all.
As further evidence that this does work, take a look at motorcycles. These are some of the
highest power per cubic inch engines in the world and the carburetors are coupled directly to the
intake ports on the heads."
I will inquire more detail from Tracy over at his forum. I just want to know your opinion on this
as it will really simplify things a lot for me. Also, with the carbs mounted almost against the
block, do you think that carb heat would still be required?
Once again thank you for your time and patience.
Hennie
Short manifolds do indeed work for max power. Especially if you are using small pipes
like Tracy is using. Short pipes cut the skin friction drag of the air
flowing through long small pipes. However they don't give the best BSFC at cruise
5000 to 6000 RPM because they are not taking advantage of the organ pipe effect.
Ram charging Dodge called it. IMHO something around 15 to 20 inches with a 2" inch
P-pipe works great and gives good BSFC in the bargain.
Tracy has been around the block on these manifolds. A couple of years ago
he and Ed Anderson were hot for dynamic chambers. :) He will soon figure out Mazda knew
what they were doing on the Lemans engine. :) Mazda had a race fuel limit at Lemans
so a good BSFC was critical.
Paul Lamar ...No rotor no motor.
Is the best design to use 4 separate tubes(4 port
13B) full length to the throttle body or can the box plenum between the
T.B. and the individual tubes be considered as part of the desired length.
Geir
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Do you still have this intake manifold? IMHO given the
work and cost involved in making a new one it might not be worth it.
However if you want to make a new one use four tubes wrapped up
and over the engine about 15 to 20 inches long. Looks like you
have room over the top of the engine. I could be wrong about
that so you need to mock it up and check cowl clearance.
Please send us a picture of the throttle body that you have now.
You might be able to use it as is.
Here is a trick that will save money if not time.
Use a 3 inch square extruded aluminum tube for a plenum
and build the square throttle body plate into the front of it
using a stock Mazda throttle plate shaft.
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Here are a few more ideas. Take your pick. They would all
work about the same.
Let me know if you going to build your own and I will send
you patterns for cutting the sheet metal transitions.
Paul Lamar
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