Slyp_Dawg HalfDork
10/11/15 1:11 a.m.

not so much the science of selecting them, moreso the actual sizes... this is specifically for a Honda CBR 600F4i engine being stuffed into my college's Formula SAE car. We are a first year team still getting the car sorted and for the time being we're running the stock ITBs just so the car will move under its own power. I'm on the team tasked with creating a new (and rules-legal) intake for it, and I can't for the life of me figure out what the mounting standard for the stock injectors is, and thus can't track down weld bungs to use for when we fabricate a new intake for the car. Follow-up question: other than cost (we already have the factory CBR injectors vs having to buy aftermarket car ones), for a bike-engine-car with a fabricated intake, is there any advantage to sticking with bike injectors or are we likely better off going with more standard car injectors? I believe for the time being we will be trying to use the OEM ECU but Megasquirt is somewhere down the line, once we get the car to where it's driveable and our focus shifts from assembly/get-it-running to development, if that makes a difference

rcutclif Dork
10/11/15 9:23 a.m.

To start, I'd run the stock injectors with the stock ecu.

Next, don't the injectors mount into the itbs? If that's all stock parts, then it should be pretty easy to get it all hooked up.

What part of the intake are you making? Something to replace the black plastic airbox? Or something to go between the itbs and the head?

bentwrench HalfDork
10/11/15 12:51 p.m.

Changing the intake will more than likely require a retune, but you are going to have to do that anyway as you will probably be changing the exhaust.

Does your CBR have 4 or 8 injectors? Some bike models used a second set of injectors in the airbox.

I would not wait on the MSquirt if you are making these changes. The factory ECU will need to be tuned and the expense of that is equal to a MS ECU. Are the stock injectors high or low impedance?

Slyp_Dawg HalfDork
10/14/15 12:58 a.m.

the CBR engine we have, as set-up, is just running 4 injectors directly in the IRTBs, but we can't run IRTBs in FSAE (need a single 20mm restrictor downstream of the throttle body) so up until pretty recently we had planned to take the butterflies off of the IRTBs and just use them as injector mounts. At this point it seems a little more likely that we will end up ripping them off completely and custom fabricating everything to fit between the single throttle body and the intake ports of the cylinder head. Given that, other than ease of hooking up to the stock wiring harness, is there any real benefit to sticking with the factory injectors? I brain-farted earlier and realized that in a pinch we can just make/have made new injector weld bungs on the lathe taking dimensions from the injector ports on the factory IRTBs, so the original question has sort of shifted in that respect, but it still stands (to a point). As far as engine management goes, I definitely think we should switch to Megasquirt ASAP but I don't know if that's in the plans just yet (we're still trying to get full support from VCU so money for the program is rather tight at the moment

bentwrench HalfDork
10/14/15 7:56 a.m.

You cant change the VE of the motor and expect the tune to be anywhere near right.

It might run OK with the OEM tune, but it might grenade. 50%-50%.

With a restricted inlet and AlphaN it will be dead rich. SD might run OK.

Also the OEM ECU will probably have some sort of traction control (squid control) strategy or some such to soften up the power. In a car with 2x + the traction, that will be lost power that could be used.

Check with the Legends/Dwarf/MiniSprint car crowd for goodies, Headers, oil control, shallow pans for ground clearance, oil coolers, & because of the increased traction clutch baskets take a beating, a shifter to disengage the starter (when the motor gets spun backwards when the car spins-out, the one-way clutch on the starter causes the starter to get destroyed = end of day unless you have a spare)

oldeskewltoy UltraDork
10/14/15 10:55 a.m.

Furious_E Reader
10/14/15 12:27 p.m.

Having been on a first year FSAE team (well, Formula Hybrid which is the same damn thing with the added complexity of the electrical BS and 350cc less IC engine) with no backing from the school, let me offer you this piece of advice: KEEP IT AS SIMPLE AS POSSIBLE!!!

Path of least resistance is the MO for year one, get a car together that can actually run, pass tech (don't know how FSAE is, but the Hybrid guys are insanely stringent), and get on grid. You don't want to be left with a pile of great, but half finished ideas come May/June, especially when you're trying to solicit funding from the school and recruit new members. Having a complete and at least somewhat functional car will go a long ways towards accomplishing those two goals.

Lots of great ideas get thrown around this time of the year, and they seem simple enough to implement on paper, but come March/April/May you WILL be spending every waking moment in the shop just to get the bare bones of the car together. The side projects and extra work you create for yourself can easily sink your chances of actually driving the car at competition. We spent our first two seasons finishing the build AT competition, learn from our mistakes!

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