tuned port injection conversion

So a buddy who of mine who used to build piston airplane motors for a living and I had a few too many beers, and rather than get anything productive accomplished, start talking about playing with converting an sohc 4 motor (we were staring at a cb550 and cb350f motor both recently finished on the bench) to tuned port injection. Even though the benefits may not be all too copious, I can't say I have ever seen it done, and after talking the whole thing out, it seemed like it would be fairly straight forward.

We came up with why couldn't an intake manifold similar to what is used on honda k20/k24 motors be fabricated and directly applied? I know the accepted norm is 4 carbs/individual throttle bodies give the best performance, but with a well tuned injection system I have a hard time seeing how it wouldnt improve performance even with a single throttle body. Sure you may wind up with a little more low end, a little less top end, and a tiny lag in throttle response, but the advantages in tuning certainly seem to be worth it imo. I'm sure determining the volume required inside the manifold, injector size, runner length, etc would be relatively simple to figure out, the computerized part is a little bit of a grey area for me.

I'm not sure if I will go as far as to build the system (time is at a premium these days) but I'd be interested to talk this out for academic purposes. If a full concept was thought out, out of curiosity I may give it a shot.

Thoughts?

What was the choice for fuel delivery?

4 throttle bodies would be better and easier.

DohcBikes said:

4 throttle bodies would be better and easier.

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+1

While a little baby manifold would be a sight to see, I think the consensus is IRTB is probably easier.

I think the main advantage of a manifold (at least on cars) is being able to meter one air mass, but I'm pretty sure that's mainly for idle and fuel efficiency reasons.

Probably what would give you a larger payoff is making a monstrosity of a header with wideband 02 bungs on every runner, and pop that bad boy on there to tune each cylinder. Like balancing carbs only with the magic of computers, EFI style. Once you're done you could put a normal header back on.

Nah.

Run closed loop efi, 4 tb's with the xact same parameters and build a permanent 4 into 1 with a single o2 sensor after the collecter.

Going to have to basically copy what honda, yamaha, kawi does on their bikes, or pay the price. Something tells me you don't have the r&d money to reinvent efi.

DohcBikes said:

Nah.

Run closed loop efi, 4 tb's with the xact same parameters and build a permanent 4 into 1 with a single o2 sensor after the collecter.

Going to have to basically copy what honda, yamaha, kawi does on their bikes, or pay the price. Something tells me you don't have the r&d money to reinvent efi.

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I mentioned it mainly because it was also in the realm of many-beer ideas, not that it would make for a practical EFI conversion.

Anyways, in terms of the manifold idea, the biggest problem you'd have is working out the proper volume and layout. There's some science to it, and there's also a bit of a dark art to it. Runner length makes a lot of difference in terms of powerband- long runners for low RPM, short runners for high RPM. You'll notice that all the high performance car manufacturers out there (Ferrari, BMW, Porsche, etc.) have made variable-length intakes. This is because they want the best of both worlds, but it's also very very expensive and extremely complex. So, if you were just fabbing up a homebrew manifold you'd want to find that happy medium runner length that gives you an acceptable range. Bust out the slide rules and advanced calculus.

Now that you've got your theoretical runner length, how big is the plenum, where do you put it, and where does it pull the air from? A forward facing ram-scoop looking thing is probably the best bet, but how are you going to make that fit on a CB550? It ain't gonna be pretty. The size is more math, but the packaging is gonna be even more test fitting and fab work with the engine in the bike. It's not impossible, just a lot of time for not much of a reward!

I might make up my own version of a microsquirt efi to fuel my twin turbo supercharged two stroke conversion.

Ichiban Moto said:

I might make up my own version of a microsquirt efi to fuel my twin turbo supercharged two stroke conversion.

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Bad Ass

i heard they have a pill for that microsquirt thing now

it clears it right up in 48 hrs

Wow, lots of great responses.

Dohc, for what reasons would an ITB setup be easier? Do you mean in terms of components available, tuning, or both?

I have always been of the thought process that for practical purposes, the least moving parts something can be made with, the lower the chance for error. Also, while ITBs are a dime a dozen, I don't think I have ever seen a setup like I am referring to. And if I actually go through the frustration of injecting a 350f I'd like to do something completely out of left field lol.

The idea for the dimensions of the manifold is to copy the current distance from the carbs to the motor as a start point. I figured if I ask around someone would be able to tell me what volume the plenum should hold based on air flow for whatever test motor is used, or at least give me a good place to start. I'm thinking the shape will be more important than the size once it hits a certain volume. Every performance intake manifold tends to use a very similar shape, seems like I could copy it to scale.

I don't see how it would be all too difficult to lay some carbon fiber to make one, and the rest of the components should be available for purchase. The only part we didn't try to determine is the electric part of the system.

if you want a a starting point to goof around with i have already fabbed a few single carb intakes for the 350f i use them to test run bikes and

break in motors they are not elegant but they work

and with the 350f you had better figure out wher you are going to get the power to run the fuel pump and processor and injectors they dont

have a big electrical system

cxman said:

if you want a a starting point to goof around with i have already fabbed a few single carb intakes for the 350f i use them to test run bikes and

break in motors they are not elegant but they work

and with the 350f you had better figure out wher you are going to get the power to run the fuel pump and processor and injectors they dont

have a big electrical system

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Yeah I'll take you up on that, what single carb do you use on it? I was gonna guess somewhere around a 40 or 45mm based on area.

I have a 350f motor rebuild and broken in on my bench, frame and other parts go to powdercoat today. I have a little free time while the roughing on my house renovation gets done, so until I start doing the finish work I have a few hours a day I can play with this. As far as power, I'll be putting a call into ricks. I'm sure they can do something for me. Also the bike it's going in has minimal draw, led lights being about it.

vm34 mikuni and if i was going to mod it a bit i would go 36mm flat slide but the 34 works like a charm

Interesting, would have thought larger.

Alright since the majority seems to think ITBs are the easier option, I am exploring that as well. I found that aprilia sr50 throttle bodies can be bored to the right size, and I can get 4 of them if that route seems more effective. I also shot an email off to find out a little more for the exact electrical requirements, and exactly how I'd have to wire this. I'm clear on the components I have to put together, but a little fuzzy on how the whole thing jives, particularly where timing is coming from if the microsquit system drives my coils.

The timing would require you to switch to a hall sensor and a magnet on a rotor, in the spot where your points previously went. Pretty sure this also means you take out the mechanical advance, as it gets handled electronically.

Hall effect detects that magnet going by, so it's sort of like a non-touching points setup. It sends a signal to the microsquirt, which then decides when to fire the spark.

I've heard that you can also rig up a points system to send a signal, but I dunno anything about it aside from the fact that it's theoretically possible- the points would work only as a switch to send a signal to the microsquirt.

The ignitions with electronic advance may not be better than one that leaves the mechanical advance in play... the trigger signal will come from an advanced curve off idle regardless. I have also seen optical triggers coming to market that will be sweet, but expensive.

i have a hall effect system being released this month that could adapt to that and can trigger the microsquirt

and it can have up to 5 event triggers including vacuum sensing or voltage input (slide pot) as in tps switch

and i can out put triggers for it

in one bike i have it triggering the on and off for the nitrous

but it would be nice to adapt a halleffect cam trigger to

Tune-A-Fish said:

The ignitions with electronic advance may not be better than one that leaves the mechanical advance in play... the trigger signal will come from an advanced curve off idle regardless. I have also seen optical triggers coming to market that will be sweet, but expensive.

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I'm already running that in the motor so I guess I am ahead of the game