Project CBR250RRi

[motthomas]

Its about time I stuck a thread up on this. I'm hoping that having something like this to keep updated will give me the motivation to push on and get it done.

The idea has been in my head to do an EFI conversion on a CBR250 ever since I read the feral injection website. I always thought I didnt have the know-how to do it what with building an ecu and designing the software to control the injectors. At least that was until I found out about megasquirt.
The megasquirt ecu did away with the need to be able to assemble complex enough electronics and design base software so brought it all back within reach. The idea got put on the back burner for a while until last summer when I started seriously researching it again and one thing led to another and now I hope Im in far enough to have to finish it. Actually finishing it within 2012 is my new years resolution!

Theres a few things to get and do before I start doing anything to the bike.

• Throttle bodies sized and spaced
• Injector selection
• Sensors. Coolant temp, intake air temp, MAP
• Fuel Pump
• Fuel filter and pressure regulator
• Air filter / airbox
• ECU
  

The easiest bit is the ECU. I'm going to use the microsquirt ECU from Bowling & Grippo. The tuning software for it is free and it supports both fuel control and ignition control. If a wideband oxygen sensor is plugged into the ECU, it allows for datalogging and closed loop injection if needed.

I have chosen my throttle bodies already. I'm going to use GSR400 throttle bodies. The reason is because the OD of the intake stubs is the same as the CBR carbs so there will be no need to make up reducers to fit the throttle bodies to the engine. Also, having the same diameter bores will make for the best throttle control across the range. The problem with having too big bores is you end up with effective 100% throttle happening too early and losing some control over the throttle. Besides, bigger throttle bodies just wont fit in between the frame rails of the CBR.
The GSR throttle bodies will need to be modified though to suit the spacing of the CBR intakes. The spacing between #1-#2 and #2-#3 will need to be reduced while the spacing between #3-#4 will need to be increased. And with that, I'll need to get completely new butterfly valve rods made up to suit the new spacing.
The throttle bodies got bought from yahoo auctions japan and hopefully I'll have the gen soon enough to send them off to a machine shop to get the work done on them.
Here they are stripped down with most parts removed:




I picked up a set of GSXR750 injectors over the weekend that will hopefully fit the GSR TBs. They are a higher flow rate than I have calculated I'll need for the CBR but I got them for nothing so if they dont work I've lost nothing. If they are too big it will be obvious straight away when trying to tune the idle.
The GSXR TBs have a few other bits that will be handy aswel. I'll be able to use the MAP sensor off them and the way the fuel rail is structured it should be handy enough to modify the spacing. I havent got a chance to pull them apart yet to see how they go together.



The fuel pump is the part thats bugging me at the moment. I can either go with an external pump or in-tank pump/filter/regulator assembly.
I want to make this conversion in such a way that I can easily revert back to stock carbs at any time. From that perspective the external pump works best as all I'll need to change is to tap in a return line fitting into the tank and that could be blocked up easily enough.

The disadvantage of the external plumbing is space. Where to mount the pump, regulator and filter and route the plumbing so it all stays tidy and servicable. Thats where the in-tank assembly comes up trumps. If I can get hold of a spare petrol tank for handy money it will be worth modifying it to accept the internal pump assembly. It would tidy up things a lot what with only having the one fuel line running from the tank to the fuel rail. I would lose fuel capacity but I think that will be a small price to pay.


Thats about all for now. The next steps are to make up drawings for the machine shop to modify the TBs and make up new throttle rods and also to see about getting hold of a spare tank.
Watch this space.

[zane]

why dont you use the cbr carbs as throttle bodies and remove float bowl etc?

[Hessian]

It sounds sensible, but there will be naysayers you know

[ricjames]

.....just what i was thinking. Be hell easier to mod the stock one's than adapting others... does the micro squirt use a TPS as well?

[akeizm]

Yep, sure does.

[motthomas]

(23/01/2012 21:50)zane Wrote:  why dont you use the cbr carbs as throttle bodies and remove float bowl etc?

I suppose I wanted to use something that had been designed for use with injectors so I would get the best performance out of the whole system. I didnt like the idea that if the injectors were spraying up through the main jet passage the already atomised fuel would need to pass along a relatively narrow path and around a corner before mixing with the air. There would be a lot of wall wetting going on.

Yep the microsquirt can either use speed-density calculation using the MAP signal or it can use alpha-N using RPM and TPS only. I think I will end up using the alpha-N settings as from what I've read its hard to get a clean MAP signal from ITBs. I will be hooking up the MAP sensor anyway though and trying both calculations to see what works best.

[wogstaa]

Oh man... I hope you get this thing working good.
Can't wait to see the progress

Good Luck!

[Eclipze]

Nice work!

I looked into the megasquirt a few years back. I'm hoping things have changed, as when I look at them the max RPM was much too low for a CBR250 engine.

One thing to keep an eye on, is the power consumption of the fuel injector pump. CBR250's don't produce a lot of power, particularly at idle. So get the smallest/least power hungry pump that's suitable ;-)

[jlyall]

So that's why you wanted those carb measurements yonks ago.

Ah well I hope to see this one finished and tidier than the FI job.

I will be following this one closely.

[Merudo]

According to their website it appears it can go up to 16,000rpm.

Also I'm with you Mott on using TB's with injector mounts designed for FI. surely that would have to be better than butchering a set of carbs and trying to emulate a FI fuel rail and throttle body.

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