I have a TWM 3-barrel TB on my 20B; each barrel diameter is 44 mm. I find it works well; near sea level throttle response goes pretty much the full stroke. At 10,000 ft the last 20% or so does little. I’ve never had it at WOT very long near sea level, but at higher altitudes WOT will result in 6200 -6300 rpm (2.17 : 1 redrive).
I have the stock injectors in the housing ports, and slightly smaller secondary injectors in the TB. But you may recall that I have a short manifold, so the secondary are not very far from the ports (photo). I found early on that the engine idled, and ran better at low rpm, on the secondary only. So I wired the EC2 to stage the primary rather than the secondary – running secondary only up to 16-17” MAP. Works good.
As I see it; injection at the ports is good for cold starting. Injectors some distance away from the ports gives better vaporization. Injectors too far away from the ports; like maybe more than a foot or so, results in liquid fuel on the runner walls, especially when cold or at lower rpm. I think Mistral found this out when they initially had the injectors quite a distance from the ports.
Al
P.S. Happy Birthday, Ed. I’m only a few months behind you, but if you ever mention it, I’ll deny itJ.
-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Jeff Luckey
Sent: Saturday, February 13, 2010 8:46 AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Runner velocity
After reading this, a question comes to mind:
What is the difference between throttle body injection and port injection? I’ve heard people say that w/ the injectors up near the TB, you get better fuel/air mixing. Is that an old-wives-tale? Which one makes more horsepower, gives better throttle response, etc? It seems to me that fabrication of intake manifold would be easier for injectors near the TB.
Apparently there are benefits of port injection (‘cause that’s what the production engine uses) but I don’t know what they are..
What are the pros and cons of each?
BTW – Happy Birthday Ed :)!
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Lynn Hanover
Sent: Saturday, February 13, 2010 08:09
To: Rotary motors in aircraft
Subject: [FlyRotary] Runner velocity
This is a free download of the Bernoulli Principal. Fun to play with and educational.
The amount of fuel air entering the chamber is a function of runner cross section, velocity and time.
The depression, or vacuum generated is a function of displacement and RPM. So the depression is about fixed by the 2606CCs and say, 6,000 RPM. The "M" in RPM is the time. So............
That leaves only Porting to increase intake open and closing time, (lengthen time period) and manufacturing the ideal intake runner set/ Throttle body combination.
In my mind the runner size would be identical the the port opening for 4 to 6 inches out from the port opening. Then blend into one "D" shaped pipe for the 180 bend over the engine top. Then taper to a larger pipe of about 2 1/2" to blend into a plenum just big enough to fit the throttle body mounting plate.
So, the cross section would be reduced gradually from the throttle body to the end of the "D" shape, then remain constant right up to the port opening.
I would upset the inside radius of the "D" shape with a number of burs stood up with a three corner punch, to generate some tubulance.in order to keep flow attached.
Just a guess. I could be completely wrong.
Later, I tried a 75MM at one point and while it did nothing to improve engine power and performance, in my case it had an undesirable down side – now to be fair it could have been partially the results of having all 4 injectors back near the throttle body – but in any case, if you suddenly opened the throttle like in a panic go-a-round – the engine would bog and hesitate for a fraction of a second (seemed like minutes {:>)), the engine never stopped, but I just didn’t like it. So I went back to the 65mm.
So the important thing is to match your induction system to your real operating regime – NOT what you would in your wildest dream like for it to be {:>).
Ed Anderson
You are only 70??
Run hard and put away wet comes to mind..............
Lynn E. Hanover