Mark 40H carb CFM?

[Schiada]

Working on a 40H . Need to know what the 1" carb used on the 40H flowed?
Motor looks to need 35 to 40 CFM X2.
Thanks Randy

[Schiada]

Flow Test

So,I am going to flow the AJ33A,AJ54ATand the N2150S. Should know somrthing soon.

[sam]

isn't the Carter significantly larger?

[Schiada]

Yes, it is like 1 3/8",but I had it so it goes also.

[Schiada]

Back from the flow bench.

So the test is done.

Test plate with 1 1/4 " hole = with a clay radis = 153.3 cfm at 28

40H carb = AJ 33A = 68.4 cfm at 28

300 carb = AJ54AT = 70.8 cfm at 28

Also tested a N-2150S carb.

Test plate with 1 3/8 hole = with clay radis = 197.4 cfm at 28

20H carb = N-2150S = 94.4 cfm at 28

A 40ci motor needs 72.049 cfm at 7500 / 2 = 36.0245 cfm
A 40ci motor needs 76.853 cfm at 8000 / 2 = 38.4265 cfm

So,we are good to go with the carbs on the 40H! They will not hold back the motor.
Just a FYI.
Randy

[ZUL8TR]

units

What are the units of the #28?

[Schiada]

The standard for flow testing. SAE.

[ZUL8TR]

28

Found it. It referes to 28" of water column (approx 1 psi) pressure difference across the test piece at the tested air flow.

What is the actual pressure difference across the carb from atmospheric to the lower pressure in the crankcase in the outboard running at 7500 or higher?

Thus the cfm values obtained in the flow test are only relative amounts for comparison at 1 psi pressure drop but not what might be happening thru the engine. But none the less usefull.

[Schiada]

And their is also the reversion that takes place in the intake track. It mite not be mush but I bet the air flow is all over the place.

Now we can also add the reed cage. Still trying to workout testing the reed cage?

[ZUL8TR]

air flow

From the engine parts I have dimensionally measured in my 2 cylindere jobs (Merc and Yamato) the carb has the smallest flow area, next larger flow area is the reed valve opening after the air has left the cage and passing thru the lifted reed and third largest is the reed openings on the top and bottom faces of the cage or reed plate.

The internal flow area of the round reed cage in the Merc is dependent on the cage type and model. The most restricted areas in the cage are the right and left passages from the front to the rear that feed the rear top and bottom reed valves. I have not measured these passages.

Flow testing the cage is a challange due to its internal configuration plus the reeds on the outside. Add to that the rotating crank counter weights and the complications become greater as half the open reeds face the rotating air and the other half are are with the rotating wind.

Would be nice to have a clear engine to see the dynamics of this rotating cyclone in action at 7000+.