RV-3 IO-320 Lower Cowl

After we had ordered the new TMX-IO-320 engine from Mattituck for our RV-3, I got serious about doing dome detailed reading on the few RV-3 Web sites that we reference, particularly Randy Lervold. As I was reading the details, I suddenly remembered that he had some difficulty with the lower cowl configuration for his IO-320, and sure enough, he had detailed the problems for us in this write-up:

http://www.romeolima.com/RV3works/Airframe/airframe.html#Finish

The basic problem was that the O-320 cowl did not have room for the IO-320 throttle body and FAB ? what we needed was an O-320 cowl with an O-360 snout. I called Van?s to talk about this, and found there were two options ? buy an O-360 snout, cut our snout off, and glass the new one in place, or have the cowl made with the O-360 snout from the start. It turns out that this is actually an available option from their fiberglass shop, and it was easy to obtain. Furthermore, it happened that Tony Partain was headed our way, and could exchange the cowls for us (we had the wrong one, as the previous owner of our kit had bought a standard O-320 cowl).

Before we sent the old cowl back, I stood the two lower cowls together in the hangar for some comparison photos. It is fairly obvious which one has the bigger snout!

Side view ? IO-320 cowl on right, O-320 cowl on the left:


Front view ? IO-320 snout (left) is also wider:


Paul

Paul,
With all due respect, I prefer my cowl. Sure, some will say I went a little overboard on the cooling exit area, and perhaps others will say its going to be too drafty in the engine compartment, but I think it will show off the cool looking oil sump.


Actually, I just glassed the RV-4 scoop on last night.

pics rob of the combo cowl, pics! please

I think you've missed a chance to do something really cool though Rob - you could do the removable scoop that some folks have done - that way, you don't have to pull the whole lower cowl to do oil changes, etc...held on with camlocs. Oh well, "it might have been..."

Actually Rob, I like the "non-pink" version better myself....but this is Louise's airplane, and the "Pepto Cowl" is fine with her!


Glad to see someone else making rapid RV-3 progress - stay out front of us so we can keep cheating off of you please!

Paul

Good point about the removable scoop. Some people make real pieces of art when it comes to the lower cowl and FAB setup. In hindsight I should have repositioned the AFP injector vertically, bought one of those pink cowls, and used the stock FAB.

It looks like you guys are making great progress!

You CAN make the O-320 cowl work!

I'm using the Precision SilverHawk injection on my RV-3B, but I do not like
the look of the O-360 induction scoop. To my eye, that snout is just too
big for the airplane! So I resolved to make the 0-320 lower cowl work,
even if some extra glass work was required.

I'm happy to report that with a little customization of the FAB, the stock
O-320 lower cowl fits with no modifications. The clearances are pretty
tight as shown in these photos:





One requirement to make this work is the "reversed mixture arm" on the
servo. This positions the mixture control cable above the pivot point
and away from the cowl.

The second key is to recess the top plate of the FAB to allow the servo
to project below it and actually in to the top of the filter element. The
stock K&N filter is just large enough to fit around the lower end of the
Silverhawk servo. The following photos shows how I used 0.25" spacers t
o raise the FAB top plate 5/16" from the "normal" position at the lower
end of the servo. This doesn't sound like much, but it was enough.





In my installation the filter element is offset slightly from the center
of the FAB bowl. A lot of careful measuring and iterative trimming
of the air box top plate was needed to get everything aligned,
but no surgery on the cowl itself.

Cheers,
- Dan Benua

danbenua said:

I'm using the Precision SilverHawk injection on my RV-3B, but I do not like
the look of the O-360 induction scoop. To my eye, that snout is just too
big for the airplane! So I resolved to make the 0-320 lower cowl work,
even if some extra glass work was required.

I'm happy to report that with a little customization of the FAB, the stock
O-320 lower cowl fits with no modifications. The clearances are pretty
tight as shown in these photos

Click to expand...

Is there enough clearance between the air box and cowl to allow for the "wet dog shake" the engine makes during start up and shutdown?

Kevin...

Not sure if there any numbers out there, but I would guess that the FAB, that low, would be looking at 0.5" movement? Maybe more? 1"?

The odd occasion I've run the engine without the cowlings on, it is quite enlightening how much it moves

Andy

That's a nice looking Mod Dan, but I too am a litlte worried about your clearances for the engine's movement. When I built my -8, I have about .5" (or more) clearance from teh air box to the cowl, and it still knocked the paint off the exterior (of the cowl) in a few hours due to banging the lower cowl during start-up/shutdown.

Hope it works out OK for you! Maybe you have enough enough clearance - hard to tell.

Paul

Clearance

Yes, it may turn out that I need more clearance on the sides
of the airbox. If I find evidence of rubbing, I'll just bump out
the cowl scoop sides where necessary. Since I will be doing
my own paint, and my cowl will be a single color, this type
of mod will easy to do later.

- Dan Benua

danbenua said:

Yes, it may turn out that I need more clearance on the sides
of the airbox. If I find evidence of rubbing, I'll just bump out
the cowl scoop sides where necessary. ...
- Dan Benua

Click to expand...

Or just "bump in" the sides of the FAB, depending on how much room you have between the edge of the filter and the side of the FAB.

Another option is to go with James style snorkel and cone filter.

Thanks Paul, That explains everything

I know this is a Rv-3 thread, but I have been struggling with the silverhawk installation in a -9a, and have been going bonkers over it during the holiday. I have the same interference as what is shown before, and have shaved off offending parts of the FAB and glassed in the holes. But it still intereferes in some areas, and I was beginning to think something else was afoot. Thanks for the timely information!

Rather than step backwards to a new cowling, I am going to cut off portions of the snout, attach .75" spacers the FAB, cover in tape, and then fair in a new surface that hopefully dos not look too horrific, and glass over the area. If all else fails, I'll order the other snout.

Thanks again for the post.

Dan,

I too think you're going to have an issue with the Dynafocal shake on start-up/shut-down, with the clearance I see in the pic, just my hunch. I too tried to get the FAB-320 to work but you've taken it a step further, nice work!

Randy, your 3B flies often out of 00V (soon KFLY).

Lower Cowl Option

Just an update to this thread, when I ordered my finishing kit I was told they only do one cowl option for the RV-3 now - the carb version.

I'm going to order the FAB-320-1 for the carb and make it fit for the IO-320 engine