Look up Noise Pollution on OSO. He just completed a 540 build and drilled and tapped his Dart intake under the t-stat housing and it looks fine.

Thanks Scott, but according to what was posted on this thread, it looks like drilling and tapping for the bypass may not be necessary. I looked at my new design T-stat housing, and I think it also allows water in the block to circulate with the T-stat closed like the old ones did. Which makes me wonder, was the bypass redundant on the stock Merc motors that utilized it? Still need to do a little bit more research to be sure, but it looks like there are a lot of HP500's running around out there without the bypass with no issues.

Why didn't the small block Chevrolet's use one of these?

Again, with the late model 4 hose t-stat housing, you do not need the bypass hose. Recirc is done in the housing.

No reason for extra work.

Not sure why this discussion is still going. IMHO.

Edit In: This is the t-stat housing I'm speaking of...

http://www.mercruiserparts.com/images/COMMON/39675.png

Scott, you should know by now that I just like to stir up drama. ;)

So, when I run this thing on the dyno, I believe we will be running it with just the circ pump and a standard automotive style T-stat housing - at least that is the way that I typically see them running on dynos. Will this present a problem without the bypass hose, or do they have ways of dealing with this. I would have to assume that there are a lot of engines running on dynos with the Dart style single plane manifolds on them.

Many will run no tstat with/witout restrictor under automotive t stat housing.

Always a good idea on wht they want you to have on motor and/or with you to go to their dyno. You don't want to go unprepared.