I got a call the other day from John at Hytech asking me if there was a Honda TB that could be bored to 80mm. I told him no, the most I had been able to bore a honda TB was 70mm by installing a sleeve. I know Honda now has a stock 70mm DBW TB but I have not seen it yet.
Anyways, since I had a 70mm TB started, I decided to see if I could push it even further and try to accomodate an 82mm bore. I have to have room for the sleeve wall thickness.
My concern was the flange since the sleeve was going to remove most of the space there and there would not be much room to put a gasket. So I installed a .125" thick 6061 aluminum flange that gave me room to get to 80mm and still have enough wall to fit a gasket.
To my amazement, there was room. Honda, very kindly, made nice and deeeep bearing wells on the Civic Si that allow the bearings to be pushed all the way out. The shaft is just long enough to reach the bearings on both sides. So I made one and it ended up being 80.125mm in diameter with a 84mm tapered inlet.
I have no idea how he is going to control such a large TB. A tiny opening of the butterfly lets a lot more air by than that same opening on the 60mm TB.
Here are some pics:
The "impossible" just takes a little longer.
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