It is 40mm.
If you are going to do it you need to have the enlarged butterflies. The gap is only to allow clearance so you do not get binding. Too much gap and you will loose the low end as SHOs with no butterflies are slugs on the low end.
The butterflies we do are CNC machined with laser cut butterflies so you know you are getting a good quality product.
Matt, the original set of SS BBB's were 42mm not 40mm. 42mm were found to be to thin and could warp (bend) under the clamoing pressure of the connector.
Im glad to see that they are NOW Cnc'd with matching plates, I know the first 50 sets of butterflies that I sold Kurt and Mike for this were just over sized bores and used with stock plates.
Also the issue with binding and stops... The plates if done correctly should not be round, they should be oblonged like a egg, also the edges of the plates should have a bevel on them cut on the bottom front of one side and the top back on the other side.. If done correctly like from the factory the plates seal the bore and they dont rely on the stops.
As far as not running them Matt is right, in low rpm starts you will notice a slight power loss, but that is only untill the car gets rolling.. Sam in autocross where your in a gear where your RPMs are not at 1000-1800 you would be all set if you did not want to run them..
Whoever buys oversized BBB's just look at them.. if they are sealed around the bore then you have a good peice, if you can see a little light it wont be bad, if you see lots of light then your add extra air with no fuel and will become boggy for a few seconds (or less)
IIRC when I did my white 91 back in 03 I did a set larger then the original SS ones, i was looking at them on one of my wooden benches at about a foot off the bench and dropped it, and it made one of the tubes look like a pringle potato chip.
in short if someone sell a good product stick with it!
