Ultimate IO-540 80mm EFI Throttle Body

For those thinking of replacing Bendix style mechanical injection with EFI, we now have CNC'd throttle bodies to bolt directly in place of RSA-10 servos on forward facing IO-540 sumps.





The throttle plate is 80mm and the air horn base accepts 3.5 inch ID SCAT hose, K&N filters or rubber couplers. The TB has an O-ring seal on the base so gaskets are no longer required. The shaft is Stainless, supported on sealed roller bearings. The throttle arm is 7075T6 and incorporates internal stops. Under 2 pounds total weight and mounts an OEM Bosch TPS. There are no internal restrictions like on mechanical servos so the body offers full manifold pressure potential up to 375hp.

I want one, very nice work Ross!!

rv6ejguy said:

There are no internal restrictions like on mechanical servos so the body offers full manifold pressure potential up to 375hp.

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Time out. It may have no venturi, but it still has internal restriction. The throttle plate and shaft are right there in the middle of the fluid flow, so there is drag, even wide open. For example, Rod Bower previously published values showing about 0.19" Hg loss for the open 3.5" (88.9 mm) diameter throttle valve in the ram throat of his intake, on a 580 at Lycon.

Always best to quantify. At 1560 lbs per hour (a 540@2700, mid 4-digit altitude), an RSA-5 has a carb loss of 12.75" H2O. An RSA-10 is 4.9" H2O loss, an FM-200 is 4.0", and an FM-300 is 2.6". So, as seen on a manifold pressure gauge, that is :

RSA-5......0.94" Hg
RSA-10.....0.36" Hg
FM-200.....0.29" Hg
FM-300.....0.19" Hg

Got numbers?

DanH said:

Time out. It may have no venturi, but it still has internal restriction. The throttle plate and shaft are right there in the middle of the fluid flow, so there is drag, even wide open. For example, Rod Bower previously published values showing about 0.19" Hg loss for the open 3.5" (88.9 mm) diameter throttle valve in the ram throat of his intake, on a 580 at Lycon.

Always best to quantify. At 1560 lbs per hour (a 540@2700, mid 4-digit altitude), an RSA-5 has a carb loss of 12.75" H2O. An RSA-10 is 4.9" H2O loss, an FM-200 is 4.0", and an FM-300 is 2.6". So, as seen on a manifold pressure gauge, that is :

RSA-5......0.94" Hg
RSA-10.....0.36" Hg
FM-200.....0.29" Hg
FM-300.....0.19" Hg

Got numbers?

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There is probably little difference in restriction for a stock 540 at cruise power and altitude however, for highly modified engines (say aerobatic stuff north of 350hp, where every hp is important) operating near SL, this will certainly have lower drops than any of the servos listed above. Doubling the flow rate (hp) approximately quadruples the pressure drop.

Your figure represents around 210hp, not really the target audience of this piece.

Aircraft mechanical FI metering systems must have a restriction to function. EFI meters fuel via a MAP sensor/ rpm which presents no additional restriction to airflow.

Of course the shaft and blade present restriction to airflow and mechanical servos have these too so that part is roughly the same. I was referring to the bulk of the metering system inside the throat.

If I ever get some time to dust off the flow bench, I'll flow a couple for interest sake.

Aircraft mechanical FI metering systems must have a restriction to function.

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Yes and no. A dual diaphragm fuel control actually receives a significant percentage of its air diaphragm force from dynamic pressure, and the only restriction that entails is a mast to place a pitot in the airstream. Bendix-style units do restrict the whole throat diameter to generate a vacuum signal for the other side of the air diaphragm, but an AFP control does it with a tiny little venturi in the middle of a much larger primary passage. The majority of the passage is not restricted, so carb loss is reduced in comparison.

Here, take a look. This is an RSA-5 and its bolt-on replacement, an FM150, which has 2.75" less drop at 1560 lbs. Note the straight sides in the FM-150:

Of course the shaft and blade present restriction to airflow and mechanical servos have these too so that part is roughly the same.

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An accurate statement.

Don't get me wrong. It's a nice piece, and it absolutely should record less carb loss than a diaphragm fuel control....but it ain't a zero loss device.

RT 80mm vs. AFP FM-300





Total open area minus obstructions and throttle shaft:

80mm 7.0 square inches
FM-300 4.065 or 5.84 without the shaft area figured in.

Always trying to make product improvements based on customer feedback.

We've just done our 3rd run of 80mm throttle bodies. This time we addressed the lack of vacuum taps on some of the IO-540 intake manifolds by adding 4 threaded holes (2 on each upper/lower flange side) to accept hose barb fittings.



The 2 not used can be plugged with the provided Allen screws. We provide 2 barbs as well.