Originally Posted by JakeFusion

Yep. With all else being equal, power remains the same... but down probably 300-500 RPM.

Torque goes up the number of cubes... or around 30rwtq across the range.

However, you can add about 8 degrees of overlap and retain essentially the same drivability. And that should add 20-25HP or so.

But you can't really get "better" heads as the 3.9" bore limits things for the most part.

HOWEVER, the MAST 240 LS3 heads flow really well. More than a stock LS3 heads, but they are an aftermarket LS3 head with a rolled valve angle (improves mid-lift flow) with a smaller valve and port (so more efficient) and designed for the 3.9" bore. Even though 240cc intake runner volume is higher than most of the cathedral port stuff, remember the LS3 has more volume and a similar CSA so it's not "too big." Plus, being an 11-degree head, it's closer to an LS7 than an LS3.. and aftermarket LS3s make a TON of power.

If I were building a 383, it would definitely be with the MAST 240s and at least a Medium Runner FAST intake. I'd then cam it with something like a 240/246 114+4 with good lift @ .670" or above and some lightweight roller rockers. It would scream uptop despite the long stroke. And be efficient everywhere. Plus a 15 degree cam wouldn't be horrible in a 383. Really stock-like streetable would be something around 8-10 degrees. So you could tame it down a bit at the expensive of some power. But a LLSR setup as a 240/246 would drive really nice as it warmed up and act more like a 235/241 or so. Plus the lobes are more aggressive so you get more vacuum than a 235/240 hydraulic would give you.

Originally Posted by FCar2000TA

For me personally, it isn't worth the cost. I'll just wait until I can afford a whole short block, then I'll take a 5.3L block to R.E.D.