Help With Bike Tb's

[Joel]

I'm trying to figure out how to attach an air filter or air box to my throttle bodies. I'm thinking of fabricating something to fit inside the flange (see pic) that gives a good air flow into the chambers, but there's some holes I'm worried about blocking as I don't know what they do.

 

The TB's are from (I think) a Honda CBR. There are some sprung pins on the top of the TB's which open a series of holes when lifted, but they're not connected to anything and I don't see how they could operate by vacuum. Any ideas what function these might perform?

[Guest Alan_builder]

I'm trying to figure out how to attach an air filter or air box to my throttle bodies. I'm thinking of fabricating something to fit inside the flange (see pic) that gives a good air flow into the chambers, but there's some holes I'm worried about blocking as I don't know what they do.

 

The TB's are from (I think) a Honda CBR. There are some sprung pins on the top of the TB's which open a series of holes when lifted, but they're not connected to anything and I don't see how they could operate by vacuum. Any ideas what function these might perform?

 

Just in case I forget when I get to the end, please check what the injectors can provide. They look like the white Zetec ones, on 2.5 bar they give about 150 bhp and at 3 bar about 165bhp, do check that out as I am running on memory. The SAAB dark blue ones do 225bhp on 2.5 bar (the standard Zetec pressure rail pressure) Some pressure regulators are adjustable but 3.25 bar is about as much as injectors seem to like, all to do with spray patterns as I understand.

 

I think you will find all the holes and pins are to do with slow running, tick over. How they work only Honda may know.

 

The Ford series use a throttle bypass valve, this is controlled by the ECU so the tickover speed is computer set, (850 rpm +/- 2 rpm for example). Bikes don't want the extra weight. I am going to use the one from the Hyaundi / Vauxhall as it has tubes to fit pipes to for easy installation.

 

Your ECU will probably need a pipe to it pressure sensor (MAP SENSOR) and so will your fuel regulator. To stop each cylinder leaching each other you will need to fit some one way valves.

 

So after all this extra stuff you can block the holes up and forget the pins. So I hope that answers your question.

 

 

 

[Longboarder]

There's not much call for lots of little holes and stuff on throttle-bodies. On some 750 GSXR ones I had there was a small drilling in each front flange and a screw below and this was an adjustable air bleed that bypassed the butterfly. I think it was for fine balancing of the four bodies but they whistled when the screws were opened and when closed the car ran just fine so I didn't use them. Slow running air bleed is a possibility but you would have an ECU operated IACV and some pipework to go with it.

The other thing you might have holes for is to provide vacuum for stuff that wants a vacuum. Like a MAP sensor or the vac operated advance/retard on a distributor.

I suspect if using an aftermarket ECU you can ignore them all except if you want to use MAP for ECU load.

I would look at buying a piper blank base plate and big filter and some trumpets. Just cut out the baseplate to fit the flanges on the bodies, ignoring the various TB drillings.

You can identify injector flows from the number on the side of the injectors. Look up Stan Weiss. Flows usually given at 3bar which is where most after market injectors are run.

My experience of mapping is to avoid rising rate fuel pressure regulators in NA cars and use the fuel maps to get it right. Blowers or turbos are different. As yet I haven't used a RR that advised me to fit a lambda sensor either. And Omex said don't bother. The ECU ignores it if the engine is below normal operating temperature and above 4000 revs so it's only working when cruising.

 

Nigel

[Joel]

Thanks for the replies, very informative...

 

I'm using a Megasquirt ECU, which if memory serves me correctly does have provision for vacuum attachment, though until now I hadn't considered that I might actually need it. There are quite a few vac take-offs on top of the TB's, which I've currently got connected together to hopefully give some brake vac assistance. Let me know if you spot any obvious flaws in this plan.

 

The injectors are zetec ones, which should be more than capable enough for my application - I'd be frankly amazed if my lowly pinto made 165BHP !!

 

Getting back to the original problem, I've got an ITG JC50 air filter already, but the fuel rail cuts into the space where the back plate would normally sit, and I don't know if or how 'normal' trumpets would attach the the CBR throttle bodies, hence the idea of fabricating something. Presumably Honda have a solution - I might pop down to my local bike shop and poke around the parts depot.

[Snapperpaul]

I would fabricate 2 small plenums, 1 for each pair of bodies, open ended to extend past the fuel rail, then modify a standard Pipercross back plate to fit the plenums, you can now fit standard dome filter or the piper air box.

 

Trumpets would fit in the small plenums

Edited May 14, 2011 by Snapperpaul

[Guest Alan_builder]

Hi Joel,

 

Snapper Paul may have a good point about the Vacuum control on the fuel regulator, I have not investigated Mega Squirt that far as yet. On the other side having variations in air pressure influence the fueling seems sound, as there will be different amounts of oxygen to be burnt. controlling it from manifold air pressure might not be.

 

If you navigate your way to My throttle bodies and look at the last 2 pictures you will see what I have been saying. As Snapper Paul has seen the need to say the same thing again, I think, what I said earlier may not be clear.

[Guest dinger]

Joel,

Regarding your air filter, I had a similar problem with my dunnell bodies, the fuel rail stopped me from fitting the back plate, ITG do a filter.with an uncut foam backing so you can fit trumpets, measure and cut four holes and then this slips over your trumpets, just make sure the trumpets are not too long,

Cut the holes slightly smaller and can stretch over securing the filter, you then shouldn't need to worry about covering the holes,