Weighing Fueling Options

[Syscrush]

It looks like the vacuum take off plug for synchronising to me?

That makes perfect sense, thanks! It's funny, I looked at it for a long time saying to myself "What's the point of a vacuum port that's just blocked off with a screw?"

Of course that's what it is. I don't need to preserve it, as I should be able to do sync with a laptop instead of the rack of gauges when I'm done, since I'm planning to feed 6 individual vacuum signals to the ECU via CAN.

[Syscrush]

Please keep on coming with the updates what you are doing is fascinating stuff

Here's a preview of the really basic design:



It gives some sense of how the new TB will fit in the same position as the stock carb body, look similar to the stock carbs, but should flow much, much better.

[Rick Pope]

Yes, that's the vacuum port.

But, there's no "pumping loss" from lifting and holding the pistons. The vacuum is the same, whether a piston is involved or not. Essentially, it's not moving, or very little, so requires no energy, only tension.

[Syscrush]

Yes, that's the vacuum port.

Thanks!

But, there's no "pumping loss" from lifting and holding the pistons. The vacuum is the same, whether a piston is involved or not. Essentially, it's not moving, or very little, so requires no energy, only tension.

Well, lifting the slides absolutely requires doing work, which is equivalent to energy, and work done over time is power. There's no question that it's engine power that's lifting the slides - it's a textbook definition of a pumping loss, though it's probably small.

As for holding them: to use your term, tension that would otherwise be used to draw air into the cylinder is being used to hold the slide up against the spring and gravity. That has to have an associated pumping loss. I don't know enough about fluid dynamics to estimate how significant it is, and honestly I'm not doing this to improve power, so it's not a primary concern.

I just feel good about flow when I see the new model vs. the OEM. Kinda like how I insisted on getting the right '79 cams even though it makes no practical difference to me in how I ride the bike.

Once I have the injector, vacuum port, and throttle all sorted out, I'll try to do some CFD and share the results here. I don't have the expertise or energy to try to model the OEM carbs for a before & after, but the dyno will shed some light on that.

[Syscrush]

OK, here's the first attempt at a compromise position on the injector.



The good:

1. Looks like it'll work with the same angle to the airflow as on the Triumph. Probably not a huge factor, but it can't hurt.
2. I think I found the clearance to fit downstream of the throttle plate while still leaving enough of the outlet to seat all the way in the intake manifold.
3. Should be able to have plenty of material to hold the injector securely and keep it almost entirely out of the airflow.

The bad:

1. The port around the injector gives it less clearance than the Triumph application. The diameter of my port is 14mm, on the Triumph it's 19mm. Again, probably not a huge factor, but it can't help.

The ugly:

1. Fitting the injector in this orientation will require moving the throttle plate about 20mm upstream, toward the inlet, away from the head. It'll fit, but that will complicate the mounting and tuning of the throttle cables to the rack.
2. It's not obvious how/where to fit fuel rail.

I can open up that port a bit or sneak the throttle assembly a few mm back downstream if I install the injector at a steeper angle - especially if I'm willing to let the nozzle into the airflow a bit. I'll keep fiddling with it and see what I come up with.

[Rick Pope]

Agreed. it takes some energy to lift the slides, but it's pretty small. Once they're "up", no additional energy is consumed until the next lifting event. In any case, the loss is pretty small.

[Syscrush]

The sealed bearings arrived today. It really looks like they should fit and work fine. The 8mm ID is a tiny bit larger than the OD of the throttle shaft - unless I learn of a good reason not to, I will probably put a little dab of fuel-resistant sealant to seal the inner race to the throttle shaft. The action of the bearing is extremely smooth and light - I'm quite pleased.

[Syscrush]

So, that leaves reusing the OEM throttle plates, shafts, and linkage, or building for readily-available and standard butterflies like the Weber ones. In addition to having options for larger sizes, going with the Weber butterflies would let me use more parts that are fresh and new, and having fresh new parts is very appealing.

Interestingly (to me at least), the Honda throttle plates seem to be the same 78° that Weber uses.

This doesn't affect my plans in any way, but I thought I'd share in case anyone else also finds that interesting.

I think I've started to cement my status as a competent CAD beginner. I have my model incorporating my exciting new ball bearings, plus an OEM throttle shaft and plate that you can play with. I haven't modeled the linkage because that's already designed by Honda. The model is parameterized so I can push the throttle assembly upstream or downstream by changing a single number.

CFD features are by subscription only, so I'm gonna just live without it.

I have decided to change the injectors I'm using - gonna replace these Triumph units with the injectors from a BMW K1600 - for reasons of cost, consistency, and fitment. The BMW injectors have a longer nozzle which will let me simplify the port design, and they come in sets of 6 when bought used, so I can score a set that should all match perfectly. Good motorcycle injectors are very, very expensive when bought new, which is driving my choice to something readily available used.

Anyhow, here's the current draft of the design with new components added:

[Syscrush]

Well, I've been busy with researching and modeling injectors, refactoring my design to make the construction more logical and maintainable via parameterization, and filling in details.

By going with the BMW K1600 injector, I get the following benefits:

1. Longer nozzle means I can eliminate that port.
2. Eliminating the port plus adjusting the angle lets me move the throttle shaft back downstream closer to the OEM location.
3. Refurbished units are available in sets of 6 from the same bike, so they should be well matched in terms of dimensions, electrical characteristics, and flow.
4. Donor bike is rated at 160 crank hp, which is in the same ballpark as my anticipated 120-140 crank hp.

Here's the updated model, showing the bearings, throttle assembly, injector, fuel rail with one potential rail retention approach, and the boss/port for a threaded vacuum nipple. I've also added some purely cosmetic features that are just meant to make it look more like the OEM carb body at a glance. I'm not trying to mimic it exactly, but just to have something that doesn't immediately stand out as being wildly different. As designed, these throttle bodies will fit to the OEM carburetor mounting rack hardware, the OEM intake tract on both the inlet and outlet side, will accept the OEM throttle shafts, plates, & linkages, and will also accept the OEM float bowls (purely cosmetic).

For the top side, I haven't decided between modifying the OEM caps to clear the fuel rails, or have something custom made. If I go the custom route, then the caps could incorporate the retention for the fuel rail as well, which I think would be nice and tidy.



The next step will be to start getting quotes for having this manufactured x6. If you don't hear from me for a while, that probably means I'm recovering from a heart attack brought on by those quotes...

[Syscrush]

Here's another quick clip that shows how the new design compares to the OEM carburetor body. The 3D scan of the original carb is turned off and on from a variety of views. I think that this shows clearly that the new design will fit all of the mounting points of the OEM carb, and gives a visualization of the repositioning of the throttle shaft 8.5mm upstream from the OEM location.

[Syscrush]

Reviewing the model again today, I realized that I have quite a bit more material around the BMW injector than what's needed, because I based the mounting boss design on what I had done for the shorter Triumph injector and the relatively large port required around it. By reducing that material, I could move the injector downstream enough to get most of the way back to the OEM throttle location. The only downside is that it would mean that at least part of the injectors would protrude through the front of the carb caps.

If I did that and moved the injector to the underside of the carb there are quite a few benefits:

1. Restore the OEM throttle location.
2. Retain the OEM carb caps (which are a very visible feature).
3. Hide the fuel rail underneath where it's not as prominent.
4. Ensure more clearance between the throttle cables and the fuel rail.
5. Custom replacements for the float bowls would be much easier to machine than custom carb caps.

Given all of this, it almost seems like a no-brainer to go this way.

There are 2 reasons I'm still not quite ready to give up on having the injectors on top:

1. I have a dumb hangup about wanting to be able to access the injectors and associated plumbing & wiring without having to go through all of the pain of a carb re&re. I should probably just let this one go. There's no reason to think that any of those things would require frequent service, and they can be bench-tested before installation.
2. The current design has the injector spraying somewhere in the general direction of the intake valves, which can only help in terms of atomization and fuel delivery. This one is really hard for me to let go of.

The whole point of this exercise is to improve rideability and fuel consumption. To go through all of this effort and expense to then just intentionally blast the fuel spray onto the roof of the intake port seems really counter-productive. Do I think it would make a night vs. day difference? No. but the thought of it still stresses me out.

I think it's time to take some measurements off of the head and intake boots to model from throttle plate to intake valve and see what this all really looks like and decide from there.

[Rick Pope]

Your commitment to this project is amazing. I thoroughly enjoy seeing the progress and thought process, both when moving forward and retracing your steps.

Have you considered just having the float bowls on the outside bodies? It's unlikely anyone would notice, and it may free up some valuable space.

[Syscrush]

Your commitment to this project is amazing. I thoroughly enjoy seeing the progress and thought process, both when moving forward and retracing your steps.

That means a lot to me, thanks very much. As someone who always has a few build threads that he watches religiously, it's nice to know that someone else is interested in what I'm trying to do here.

Have you considered just having the float bowls on the outside bodies? It's unlikely anyone would notice, and it may free up some valuable space.

Yes, I have given a lot of thought to dressing only the outermost TBs for looks and keeping the rest as simple as possible. Exactly how that will shape up is still TBD.

[Rick Pope]

My projects tend to be a little less technical. https://www.rvnetwork.com/topic/142018- ... -planning/

[Syscrush]

My projects tend to be a little less technical. https://www.rvnetwork.com/topic/142018- ... -planning/

WHOA!