Throttle Body Boring and Plate
 

I know there are other threads on this but I have a specific question. Rather than just mail it in to a special service I'm wondering about just taking it all the a machine shop as it would probably be cheaper and faster. Thing is Id have to find a throttle plate to fit. I think the f22's are 60mm. I wanna go up only a little bit. 64mm?
In order to do this I need to know where I can find a throttle plate at that diameter and if there are any special provisions I need to make or can the TB, spacer and upper manifold be bored out without needing to do anything more?

Might be easier to just buy an aftermarket one. If it helps basically all 90s Hondas throttle bodies are interchangeable.

Yeah, Ive found that out. But the highest the honda tbs go are 62mm. and I think those are in over sea's hondas. and buying one already bored costs a bit.

Plus I wanna be able to find an efficient way of doing this in case I want to start selling them for cheaper than most companies. Refurbish and modify used parts for cheap. Instead of $150 for a brand new, bored TB I could pay $30 for the TB and then however much to have it machined.
I thought I saw somewhere that the tb plates arent perfectly round. Is that true or could I find a round metal plate at whatever diameter the tb is bored to and use that?

They aren't perfectly round. Notice they are still at a little angle when they close, so it's an ellipse. And the edge is beveled to match the angle too. It needs to close very good, with very little air leakage. That way the idle air is controlled through the needle valve (idle-air valve).

Yeah, looking at the TB the inside is actually smaller than the opening. Would it be possible to bore it straight and round all the way through and make a circular plate to match? I have an extra TB to work with.

The screws fastening the brass butterfly to the shaft are staked, so you might destroy the screws by removing them. Then you have to get the shaft out of the way.

Then you have to worry about sealing air-leakage through the throttle shaft. After all, you have reduced the distance air must leak, and the shaft might not seal as good any more. Then you have to fabricate a new butterfly and fasten it onto the shaft.

All in all, it's a fair bit of work. But not impossible.

I did fine getting the throttle body apart. When I got a new one to see if I needed a new map sensor or tps calibration I took apart the whole thing, cleaned it and put it back together. Works fine on my car. So that shouldnt be hard getting it all ready to be bored. I just need to find a TB. It appears they are designed more than just a circular piece of metal. But I could actually start off a mm bigger and fine tune it by hand to seal properly.

So do you think id be able to get a piece of metal cut 64mm in diameter perfectly round and have the TB bored the same and be able to fine tune it by hand?
Why are throttle bodies smaller at the inside than the outside anyways?

I thought of another thing - don't know if it's a problem...
The air passageways for the idle-air screw and the IACV come out into the TB as little holes upstream of the butterfly. When you bore it, will you machine into a larger part of the passageways resulting in a big hole?

If you bore the TB to 64mm you should get a brass plate a couple mm larger than that in order to fine-tune it's shape and edge-bevel.

I think the bore is a trade-off with controllability at small openings. Also the taper leading into the valve might change the velocity profile a bit, giving a bit more velocity near the wall.

Ok. I think as far as the idle air screw passage way, while analyzing the TB, I think it shouldnt be a huge problem, and I could always adjust the screw tighter.

I may just go to a junk yard and fish around for the right size plate.
The angles by what I understand are just the edges, keeping the plate from sticking? 76 degrees for an f series throttle plate.

I could always do just 62mm, or even keep the 60 and have that bored all the way through.