Has anyone tried the new Comp Cam's Thumpr, Muthr Thumpr, or Big Muthr Thumpr cams?  Just curious if it really does what is advertised... (Big cam sound, while keeping streetabilty and bottom-end torque on a mild engine) I know it's not really "new", it's been out well over a year now...  

After looking over the specs, what they look like is a set of cams with a narrow lobe separation angle and 5 degrees advance if installed at the quoted intake centerline.  The narrow LCA give overlap, which contributes to that low speed lope and the ICL tries to get some torque back into the cam.  Then they throw in a bunch of exhaust duration.  Even the Thumpr seems a bit big for a normal 302, with 227/241 intake/exhaust @ .050.  Not real big for a 351 however.  You might have to jet up a little - that big exhaust duration might lean it out a bit.  With those specs, probably sounds as advertised.  On a shock tower car the extra exhaust duration is usually a given anyway.  

"On a shock tower car the extra exhaust duration is usually a given anyway."

Explain why the suspension style has anything to do with how long the exhaust valve is allowed to stay open; maybe I'm not understandind what you are trying to say.  

The header pipes have to make a sharp turn right off the head to clear the towers.  It's a bit worse on the 289/302/351W because of the head layout than on a 351C but it's still an issue.  The turn adds a bit of restriction.  Most stock small block ports don't flow well anyway and turning the pipe right off doesn't help.  If the pipe could come out straight from the port and then do a gentle sweeping bend it would not be a problem.  Even if the head is ported, or if using a modern head with good ports, you still have the header pipes turning almost as soon as they leave the flange.  So extra exhaust duration helps crutch around that issue.