Weighing Fueling Options

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wyly
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Re: Weighing Fueling Options

Post by wyly »

Not sure what the final compression was with my Wisco big bore kit, builder said he might shave the pistons if he thought it was too high, I think the Wisco's had a higher riser than your kit.

though I had no issues with my carbs at the time of the rebuild I handed the carbs over to the builder to go over them again. He bumped up the jet size to Dave's recommendation and rebuilt only the best kits... while I had some issues in the beginning sorting them out I eventually got them to a point where they performed reasonably well... When the builder finally had time near the end of racing season to see the bike again he spent an hour dialing in the carbs, throttle response since has been spot on all through the rpm range... My Pipemaster exhaust look like a 6 x 6 but in reality they're 6 into 2 then back into 6 so probably close to the original oem 6 into 2...

My suggestion, probably the least expensive option imo... buy a 2nd set of rebuilt carbs from Dave, Mike, fall down Phil or Bert at SCM(if they have a set)then take your bike to Dave who is closest to you for a final tune. I've met a few guys who claimed they know it all but in reality very few know how to make the cbx run flawlessly...
CBX a work in progress, still improving...GS1150EFE completed and awaiting modifications.....RD350, remnants in boxes scattered throughout the garage

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wyly
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Re: Weighing Fueling Options

Post by wyly »

checked with my mechanic and my wiseco big bore has a 9.5 compression...he didn't do a dyno test but he estimates after all modifications I have a 5-8% gain in torque and hp.
CBX a work in progress, still improving...GS1150EFE completed and awaiting modifications.....RD350, remnants in boxes scattered throughout the garage

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EMS
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Re: Weighing Fueling Options

Post by EMS »

How does your mechanic know what the compression is? Did he measure the effective combustion chamber volume with pistons installed?
A 67mm bore together with the standard crown piston results in a 9.92:1 already. You would have to remove approx. 1cc from the top of the piston - about the size of a gambling die - to come up with 9.5:1. How large is your "big bore"?
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Re: Weighing Fueling Options

Post by wyly »

he measured it, he's very detailed oriented and recorded everything and put in a file. I don't question his ability he's spent a number of years wrenching/tuning on the world Super-bike Circuit, the bike has never run better than it does now.

I have a 1150 big bore...

He sent this text to me-"Wiseco is full of shit with their predicted CR. Even with the gasket surface milled it ended up at 9.5:1. I didn't have to machine the piston domes."
CBX a work in progress, still improving...GS1150EFE completed and awaiting modifications.....RD350, remnants in boxes scattered throughout the garage

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Re: Weighing Fueling Options

Post by EMS »

There are a lot of numbers thrown around by manufacturers, sellers and builders. What is the bore diameter?
Technically there is not bore that will make an 1150. A 67.5mm bore will make a 1145 and a 68mm bore will make an 1163.
The 67.5mm with the standard dome piston shape will result in a 10.05 compression ratio if the cylinder head remains untouched too. You can easily verify this yourself. It is basic math and geometry.
A good mechanic is not always a good engineer and many times they can build a motor from available parts but they lack the understanding of the design parameters.
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Re: Weighing Fueling Options

Post by Larry Zimmer »

I'd say your mechanic is right in the ball park with his torque/HP gain numbers, Wyly. Good stuff. Have fun.
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Re: Weighing Fueling Options

Post by Syscrush »

Alright, I've been posting info and questions in a few different places, and I want to concentrate resources and a record of the research/planning in one place, so here comes an update.

As noted earlier, the work done by mlynch001 to use his OEM carbs as throttle bodies was a big factor for me. He has shown that it's possible to install injectors while retaining close-to-OEM looks (which I care about a lot), plus the entirety of the OEM intake tract (which I care about even more). With the wacky heads and canted intake ports of the CBX, I am much less willing to make changes to the manifolds, airbox, and TB/carb placement than I would be with a more conventional head.

One option for converting the carbs to TBs is the way that mlynch001 has gone: remove the slides and float bowls, and machine injector holders into the float bowl replacements. Another option that I'm giving careful consideration is the approach used for these VMax CV to EFI conversion kits, helpfully shared by Gearheadgregg. That approach would be a bit less simple for a CBX than for a VMax, as the VMax has a perfectly round slide, while the CBX does not. Here are my current thoughts about pros and cons for the 2 approaches:

Float Bowl Replacement
Pros
  1. Potentially ideal injector placement.
  2. No obstructions in the airway.
  3. I think there may be a bit more room for fuel rail etc. under the carbs rather than over them (some space above the carbs is used on my bike for the oil thermostat).
  4. The caps can be made smaller or replaced entirely with flat stock, which frees up more space above the engine if it's required for other modifications.
  5. The machining is almost certainly simpler.
  6. Using a single block for each set of 3 carbs would add stiffness and stability to the rack, which seems helpful for injector and fuel rail retention.
Cons
  1. Injector servicing requires dropping the engine and pulling the carbs.
  2. Solution would be 100% CBX-specific.
Slide Replacement
Pros
  1. I think it would look a bit more stealthy.
  2. Injector servicing could be done with the carbs (and engine) left in place.
  3. The slides could be used for other bikes. It's a long shot, but there might be a market for these on some very popular bikes (The DOHC CB650 carbs supposedly use the same slides and they fit the very popular SOHC4 bikes).
Cons
  1. Non-ideal injector position and orientation may mean problems for tuning.
  2. Fuel has to spray onto a deflector, which means a disruption of the fuel flow pattern, plus an obstruction in the airway.
Phil in Toronto
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Re: Weighing Fueling Options

Post by Syscrush »

I came across this not long ago, and have decided that this is the approach I wish to take. EMS has noted that getting a good vacuum signal for the computer can be tough with individual throttle bodies, and this is my preferred solution. It's a circuit design for using multiple MAP sensors for ITB engines:

https://github.com/jharvey/MultiMAP

More info can be found in this incredible Ferrari build thread in the post from user "mke" with timestamp "1/18/19 12:22 p.m." - sorry, I can't see any way to link to a specific post there.

What the circuit does is use one MAP sensor and one diode per throttle body, inputting into an op-amp and some other components. In this configuration, the output of the circuit will correspond to the MAP sensor that has the strongest vacuum (lowest absolute pressure) at any given moment. To quote the post linked above:
The idea is the when you have say 4 vacuum hoses on an ITB setup going to a canister as is usually done 1 is always pulling vacuum but 3 are leaking vacuum and you end up with a signal that is about 1/3 to 1/2 what you'd see on a plenum setup
This approach should aid with tuning off-idle throttle response, which is obviously a big deal for a street-ridden bike. The Ferrari guy had this to say about it:
Once I got the engine running I was almost amazed how well it worked with the engine showing about 35kpa at low idle and under 40 up to about 2000 rpm (red line on graph). From other similarish engine setups I'd see with a canister I expected the 2k number to be more like 85-90kpa. I'm really happy with this....now the fuel pump wasn't playing nice that day (lt blue line) but that's another story. The PCB is designed so it can be just cut off to hold 2-12 map sensors.

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Re: Weighing Fueling Options

Post by Syscrush »

Another big question is whether to go with batch fire or sequential. For batch fire, you can get all of the timing information that you need from a trigger wheel on the crank, which is straightforward. The programming and tuning is also simpler, which is a big plus.

In theory, sequential firing (where the fuel for a given cylinder is injected during or slightly before the time that the intake valves are open) allows much finer control and should result in better low-RPM street manners and emissions. And I care about both.

To be able to do sequential firing of the injectors, you need information from the cam - either a phase signal to complement the crank angle sensor (so that the ECU knows the difference between the intake and power strokes for a given cylinder), or just a direct cam angle sensor.

The problem with doing a cam angle sensor is that the space inside the cam cover is small and oily. The oil rules out an optical sensor, and the size makes a Hall effect sensor tricky. It might be possible to grind one tooth off of the tach drive and then read from that gear with a Hall effect sensor, but the steep angle of the teeth and the small working space may significantly complicate that.

My plan is to do a trigger wheel on the crank (in place of the existing ignition signal generator), and see if batch mode meets my needs. If not, then I will look for a way to pick up a phase signal somehow, probably leveraging the tach drive opening & mount, but likely just getting the signal from an unmodified exhaust cam lobe.
Phil in Toronto
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Re: Weighing Fueling Options

Post by Prolink-Phil »

Brilliant, with a knackered set of carbs on my hands, I'm also looking for something more modern, just wish I was more of a techno phobe, well done Phil in Toronto

Phil in Adelaide

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Re: Weighing Fueling Options

Post by BiKenG »

I forget now, do all CBX models’ carbs have the same bore size?

Can anyone confirm whether or not the slides are in fact round?

I’m not currently in a position to check either of the above.

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Re: Weighing Fueling Options

Post by Syscrush »

One decision about EFI that one has to consider is whether to run open-loop or closed-loop.

Open-loop operation means that the computer uses a set of tables and inputs from sensors to determine how much fuel to deliver. Those inputs would typically be: engine RPM, throttle position, engine temperature, and something like manifold pressure or airflow. The bike is tuned based on feel, plug reading, and maybe performance on a dyno (optionally with a sniffer), much like with a carbureted setup.

Closed-loop operation includes an O2 sensor in the exhaust, which is used to give the ECU feedback on the current AFR of the engine as it runs. This feedback can be used to tune the fuel delivery in real time, aiming for a specified target AFR.

An open-loop setup is less expensive, probably easier to install and maybe easier to get going initially, but will generally require more work to really dial in the tune for different conditions. It is also unlikely to result in an AFR that's stable enough to prevent poisoning a catalytic converter - and since running a cat is one of my goals, I never gave real consideration to running open-loop. If your requirements are different, you may make a different choice.
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Re: Weighing Fueling Options

Post by Syscrush »

Feeding a high pressure EFI system at 40-60 psi is very different from keeping the float bowls of CV carbs full via gravity. The normal approach in a car is to have the fuel pump deliver fuel to the fuel rail at full pressure, and have a mechanical fuel pressure regulator bleeding flow & pressure off to keep the pressure in the rail at the specified pressure. That bled off flow goes back to the tank via a return line.

This approach can be made to work on a motorcycle, although sometimes there is also a secondary tank called a surge tank used (mlynch001 took this approach). The surge tank would be gravity-fed from the main tank, and the high pressure pump delivers fuel to the rail, and the regulator bleeds off the return to either the surge tank or the main fuel tank. The drawback of returning to the surge tank is that this can result in a significant heating of the fuel.

Another option is to have an in-tank pump with an integrated fuel pressure regulator - The FPR bleeds off into the tank in which it resides, and the fuel in the line to the rail is delivered at the specified pressure. Such an approach can be inside either a surge tank or the main fuel tank. This is one type of returnless system.

The last option (of which I'm aware, at least), is an electronically controlled returnless system. Here, the ECU modulates the power to the electric fuel pump so that the pump is delivering the volume of fuel required, at the specified pressure. This is easier to plumb (no return line), should result in less noise (not that you'd hear it in normal running), less heating of the fuel, less demand on the charging/electrical system, and longer life for the pump (since it's not running full blast 100% of the time as with the mechanical FPR systems). The downside is that it's another variable to monitor (fuel pressure) and control (pump duty cycle).

By using a surge tank, you can avoid having to cut & weld or otherwise modify your OEM tank. The downside is more plumbing and points of failure, and you have to find a home for it on the bike.

My first choice is to have a returnless system in the modified OEM tank, using the ECU to control the fuel pump. If something dissuades me from that approach, I'll go with an in-tank FPR and still run returnless - I want simpler plumbing for a cleaner look and fewer points of failure. When a point of failure represents the potential for highly flammable liquid being blasted onto a hot engine and my body, I think that fewer is better. In keeping with the other plumbing on the bike (oil cooler, thermostat, brake lines, etc.), I'll be going with braided stainless lines and A/N fittings.
Phil in Toronto
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Re: Weighing Fueling Options

Post by EMS »

Phil: I think the worst thing you did was park your bike! :naughty: You need to get on that thing and ride. :mrgreen: :DD
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Re: Weighing Fueling Options

Post by EMS »

How about this, to give you a few more sleepless nights...

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