Throttle Body Unit comparisons

[Saville]

Hi all!

In looking around for an RV to buy, I notice some have "O" engines (as opposed to "IO") and have throttle bodies on them allowing - as I understand it - retro-fitted fuel injection to a carbed engine.

This might be something I'd want to do if I should buy a carbed RV, if the application of these TB's are safe. So I'm looking for data/opinions on them.

So far I've run across 3 manufacturers on RV's:

Ellison Throttle Body
Airflow Performance Throttle body
Rotec TBI-40 Throttle body

I'm wondering what the opinions of the engine gurus are about throttle bodies in general and these three in particular.

Thanks!

[SHIPCHIEF]

Sure, I'll take a shot at this:
Ellison & Rotec are similar. Ellison is out of production? Rotec is in production and you can order a new one from them.
We have a Rotec on an O-320 equipped RV-4. My son Peter removed the Marvel carb and installed the Rotec + a Raven inverted oil system so he could continue learning aerobatics after some initial training in a Citabria.
I have an RV-8 with a parallel valve O-360. These typically are carburated as well, however mine was Bendix fuel injected and mounted vertically in a Brantley helicopter. When I got the engine, the Bendix injector throttle body had been robbed of a few parts, so I got an AIrflow Performance FM-150 conversion kit.
This kit is a lot more complex than the Rotec, which installs and operates like a carburator, although it seems to have better mixture distribution and will operate while the aircraft is inverted or in negative G. It receives fuel from a low pressure source, an electric boost pump and engine driven fuel pump at about 6 PSI.
The Bendix and Airflow injection requires fuel pump discharge pressure around 35 PSI nominal, so if upgrading you will need new fuel pumps. The injection servo unit (throttle body) discharges fuel to a distribution spider you will mount on top of the engine, with small fuel tubes to each cylinder head, where you will install the injectors. there are 1/8" pipe plugs in the heads, next to the spark plugs. That's where the injectors go. So make sure your heads have these plugs.
I am just a noob for operating the Airflow injector, but so far, I think I spent my money wisely.

[Saville]

Ellison may be out of business, but a lot of flying planes use the Ellison TB. I was wondering how they stack up against the alternatives.

[MikeS]

I was surprised to read that Ellison is "out of business". First I've heard of it. I looked to see if the website is still there and it is and when I called a nice lady answered the phone, so they're not completely gone. But they will be soon, at least for sales of new throttle bodies.

They have no more than 5 each of the EFS-3A and the EFS-4.

These are the best carbs in the world and I'm sorry to see them go.

The lady said they will be supporting them indefinitely.

Manufacturing costs and Mr. Ben Ellison deciding to retire are the reasons given.

[blackbeard10]

Have Ellison throttle body on my 4. O 360 A1A Very Pleased.
Ellison is not out of business. They are answering their phone. Be careful with such a comment before you post for many to see.

[KRviator]

I've installed a Rotec TBI-40 on my OX-340. The only major pain was it is shorter than a standard carb so your FAB won't line up with your snorkel, and the mixture arm moves left/right, nor fore/aft, so you'll need to fab up a new bracket and bellcrank.

Other than that, it is a nicely made bit of kit, and I'm hoping it'll perform as good as it looks.

[dypen]

Are carburetor heat necessary for these systems when the old carburetor replaced?

[Saville]

Originally Posted by blackbeard10

Have Ellison throttle body on my 4. O 360 A1A Very Pleased.
Ellison is not out of business. They are answering their phone. Be careful with such a comment before you post for many to see.

Shipchief wrote:

"Ellison is out of production?"


Complete with question mark.

I wrote:

"...*MAY* be out of business...."

As in, "Well maybe they are out of busines but there are a lot of them out there....."


No one wrote a definitive statement that they were gone. Lighten up.

[N941WR]

You are talking about three different types of fuel delivery systems.

A carburetor has a float where the throttle bodies do not. Thus the Ellison and Rotecs can work when inverted. (So can pressure carbs, but that is a different story.) The throttle bodies have a slide vs. a butterfly valve and float for the carb. Both throttle bodies and carbs deliver fuel at the intake and the fuel-air mixture flows up the intake tubes to the cylinders. Each cylinder gets whatever fuel-air mixture reaches it, thus CHT's are very difficult to balance.

The Airflow Performance injection system is not a "throttle body" because they deliver fuel at the cylinder, same as most other traditional aircraft injection systems. However, like a traditional fuel injection system, they do have a fuel servo at the intake, before the intake runners, and meters the fuel to each cylinder individually, rather than all at once. They also require higher pressure fuel pumps, as mentioned earlier.

The major advantage to an Airflow system (and other true injection systems) is that the fuel quantity delivered to each cylinder can be tuned by adjusting the opening size in each cylinder's injector. Thus, you tend to get better balanced CHT's and better fuel burn numbers.

[RV10inOz]

You have three good choices;
1. Airflow Performance
2. Precision Airmotive
3. Avstar

My suggestion is go with Don Rivera at Airflow Performance, he is a big supporter here on VAF.

Next in line is Precision.

The single biggest problem I have seen from the certified guys is far too many are flowing insufficient flow at takeoff. There is a broad range of flow spec and they have all (the problematic ones at least) been at the very minimum or less

I wonder if all the old guys have retired and some unskilled cheap workers have managed to get a job there? Who knows?

The others might be a few bucks cheaper but I can't see any compelling reason to do that. If you are going to do that much work and spend that much money, do it right. So option one and two are your only choices in my opinion.