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Intake Plenum Mod

DanH

Legacy Member
Mentor
Back when Barrett built my 390, there were fewer fuel injection choices. I wanted Airflow Performance, and elected to go with an FM-200, as Don Rivera had not yet invented the FM-150.

The early 390 uses the horizontal intake sump with an air plenum separate from the oil, and tuned length intake pipes. The mounting flange was sized for a Bendix RSA-5, meaning the diameter is 2-5/16". The FM-200 is larger, at 3-1/16" To mount an FM-200, Don created an adapter which necks down to the Bendix size. Here's a photo. The green gasket is the FM200 bore diameter. The hole is the RSA-5 diameter:

Adapter Restriction.jpg

I've long told myself if I ever had a reason to pull the sump, I was going to mod the flange to eliminate the restriction. Well, recently an oil leak developed. Ahhh, an excuse!

First task was to machine a new flange from billet, same thickness as the adapter.

New Flange.jpg

Weld the flange to the sump.

Welded.jpg

Weld in additional material inside the oil chamber...

Add material inside pan.jpg

...and under the chin, because....

Add material to underside of inlet.jpg

...the next step is to fire up a die grinder with an aluminum hog and cut away the restriction. Need the extra material so the upper ramp can extend to the larger diameter at the original angle, and the lower side can be cut level with the plenum floor. A few dabs of high temp epoxy filled the previous stud locations.

Welded and cut.jpg

Make a new gasket, bolt it up, go fly.

Installed.jpg
 
Only one flight so far, and down low it was too windy and bumpy for WOT. Fairly smooth at 2500. Not bad for an old -8 with fat tires.

First run.jpg

I'll report more as I go. I'm really interested in cruise.
 
27.2 inches… what did it bounce up to ( normal fluctuating) . Did EGT change? ( as in leaner / more air ? )
 
I think Dan has the newer Hartzell Aluminum… I found it faster at 2650-2675 than 2700 ….
 
74" BA, F7497. No MP bounce. I use a restrictor and a very soft silicone hose.

I don't expect a large increase anywhere. Don Rivera and I got talking about it, so he ran the restrictor plate on the flow bench with an FM-200. The bench numbers say I might get an additional 0.2", maybe 0.3" Hg. Arguably it's not worth the trouble...except a little bit here and there adds up. In this case I lost a little speed to the 380-150-5 tires and taller wheel pants, and hopefully this will put it back.
 
Dan - as always very nice work.

While I’m a big fan of the new FM-150C I‘d guess your 390 likes the FM-200 better. I’ll be running that on the Cold Air Sump IO-540 (if I ever get to the top of Thunderbolt’s build list).

I’m still struggling with the inlet filter build for the new RV-10 James Cowl. I suspect I will just end up blatantly copying what you did.

Carl
 
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