I bought a guy's long stroke 2.8. He used parts from his 2.2 in building it, including the TWM/Tec3 fuel injection, with 40mm TBs.
I think 40mm is too small for a 2.8 race motor with 40mm intake ports. I purchased a suitable manifold and am using my Weber 46s (taken from my 2.7 motor). Runs great. I haven't dynoed it with my exhaust and the Webers, but his setup dynoed at around 220 RWHP. Which is pretty much the same as my 2.7 did, though at a lower RPM. I think there is more HP to be had here with a larger injection stack bore.
In addition, these 40s don't line up with the 46mm air horns (though that could be solved with other horns I suppose). Somehow, having a sharp step down in the intake like this doesn't seem like a good (or even neutral) thing.
I'd really like to move to EFI, and the 2.8SS I am slowly assembling could use this as well and I could just swap it all over.
I posted on the parts for sale forum to see if anyone wanted to downsize from 46 to 40 and would trade, but haven't gotten a nibble. I don't want to sell the whole shebang and buy a new one. The old setup has all of the parts (except for a fuel pump), and his mapping will be a good baseline. Plus TWM 46s (with air horns I have and a fuel rail I have) go for $1,600. Etc.
I see that these TBs have a straight bore. It looks like I could have a machine shop bore them out to 46, and on down a bit into the manifold too. I can smooth out the manifold I think to blend it into its 40mm head end.
That would leave purchasing larger butterflies, and I suppose (I haven't disassembled anything) having a shop cut the slots in the throttle shafts wider on each side.
Anyone done this? Anyone see issues here? Know where one might purchase butterflies? Or would it be easier just to purchase some brass (or whatever it is) stock and make them?
Walt Fricke
(Happy camper as he got 4 seconds faster with this motor than his previous personal best and using last year's slicks last weekend.)