Re: Rebuilding my 350 Mag, Need opinions
reversion is when there is enough overlap in intake and exhaust valves being open (as in the same overlap that comes with larger duration cams that yield more power...), that it sucks water back into the engine from the exhaust system. not a problem with cars and dry exhaust, but potentially a big problem in a boat. The other issue is that the stock manifolds don't flow worth a ... If you're going to do a little bit of cam and are worried aobut reversion, you can get aftermarket stainless risers for the factory or glm manifolds. the point is to move the water further away from the engine so it can't be pulled back up into the engine. (note that if a lot gets pulled back in, and fills a cylinder up... water doesn't compress... stuff breaks, etc...).
I really don't have first hand experience with the glm manifolds, but understand that theyu flow about the same as stock manifolds, but are cast from aluminum and a good bit lighter - a big deal in a small boat. On other exhaust systems, I looked into revolution marine - like those pretty well, price is something like 1000, have a dry joint between manifold and riser and are designed to flow a good bit better than the factory set-up as well as to help with reversion. imco thumper power and kodiak are similar price with the imco's being touted as a good lightweight replacement for the factory set-up (Imco makes a great products in my experience), but doubt they would help with the reversion issue if you want to go with a reasonably radical cam for more power... then eddy marine and imco powerflows more like 2500 - 3000, these flow better, the imco's are supposed to make the mostr power by a little over all the rest of the manifolds (according to the engine builder that set up the 383 in my boat now, who had run a wide range of commercially available set-ups on the dyno for a local performance boat manufacturer to see what combination of off the shelf parts would make the most power) I currently have a set of these i bought second hand / unused, very well made. Then there's the true headers, from 3000 - 6000 and somewhat prone to crack depending on who you talk with...
That's my impression from having a 383 built by a top notch marine engine builder and doing a pile of reading and shopping before winding up where I'm at... earlier this year... sounds like you've got a good handle on the kind of power you'll make... will be a big step up.
...and yes that's more than an alpha drive is rated for... BUT the guy who built my set up said, no catching air or hammer down holeshots from zero... otherwise keep the drive aligned right, filled with good merc synthetic oil and run it... he also said definately oil cooler on the engine if I was going to run it... There are several guys on the river localy that are running a lot more power than I am... one that's running a stout blower motor in front of an alpha and is running well over 80 mph (on radar). Note that I do have the impression that I'll probably eventually break the drive... so I did pick up a spare at one point when i had the chance to do so for cheap. I'm also thinkin new heads, bigger cam and more carb in the next few months... we'll see what happens.
you could upgrade to a bravo... but aside from the big cost, it's 200 pounds (ie a really fat chick sitting on the engine compartment) right in the rear of the boat... a lot in my 17 1/2 foot toy or any smaller boat for that matter... I actually think I just bought an alpha ss outdrive for a very reasonable amount of money... (shorter, more streamlined gearcase, made for running faster in light boat, etc...)
How's that for a 5 min stream of consciousness dump? Hopefully a little bit helpful... just to be clear, I'm a lot more of a backyard hack than any kind of expert, but I like my toys...
