i wish you would have called me,i would like to check out retter,s shop.

i don.t think your headers vs dyno headers would make much difference.sea pump& alt will eat a little but again,not much.i do believe the boat will pick up a mile or two top speed.

It was kind of a last minute thing, we didn't know till pretty much thurs night if we were gonna do it this weekend or not.

Was talking to dave about that last night, he thinks there could be a pretty decent power loss from his 2.25 open dyno headers to my 1 7/8 headers with long tailpipes that have baffles in them.

I rememeber kevin gaining a significant amount of power just by removing the baffles in his cmi tractor pipe tail extensions .

I know that we're not talking about the same apples, but when I pulled the baffles out of my Corsas it ran like an entirely different boat for the better.

i did not know you had any baffel,s in your tail pipes,that would make some difference.how long are your tailpipes?i thought they were short with the long stellings headers.i may be wrong but i think your headers flow better than most marine headers and would work well with a smaller inch engine.

Many of hundreds of years ago, and I've talked about this in the past, what got me to critique exhausts (car and boat and etc) was I had a car that took 8 more jet sizes larger at the track when the exhaust was dropped and collector extensions bolted on. Perfect tune was done to both - exhaust on and exhaust off.

As the years went on (not many) as I became focused on this I found the two biggest reasons for why jet changes out of the 'ordinary' was:

#1: Exhaust change
#2: Cylinder head exhaust port change (either from porting or change of cylinder heads)
#3: Camshaft overlap change either by LSA or extra exhaust duration...or of course both

Yes, the above can effects jetting more than cid change, compression change, and etc. if the exhaust is that f*ked up.

So, wanna know how much power changed in that 454 above that took an extra 8 jet sizes made with dropping the exhaust and adding collector changes made ? How about almost 80hp ! Yup, no schit ! Was a healthy, but no means crazy, approx 500hp 454.

Anyway, baffles in the exhaust can kill the airflow thru the engine enough that it effects the carburetors greatly and large jet changes need to be made.

Okay, I have been to dynos many times testing parts I've made for customers and for helping others and some for myself. When ever I would hear the dyno operator say " Wow ! What a great engine, it is very efficient and not using much fuel !" I'd fall over and know exactly what we where dealing with - something limiting the exhaust - be it wrong exhaust lobe, bad exhaust port, pooched exhaust system...something with the exhausting of the engine would almost always be the issue.

Edit in: Many times at the track (few on the water) I have proved this also with cars / boats doing tuning. One boat I was tuning on the water for a chunk of the day. I unbolted the screw type baffles, boat responded with another mile an hr or so, went back to the carburetor, and another 4# et sizes larger it had gained another 3mph total. Best tune with baffles vs best tune without the baffles. edit done.

I actually coined a personal term from this "Drink-a-bility." If an engine is not using the fuel it should be using, and it has okay power or lower than it should, it has "No drink-a-ability."

I'm glad that you. MT, reported this on your engine..as it can be discussed , because frankly, not many report or even worse, don't even now this is happening on their engine.

On a side note and related, someone mentioned Corsa - yes, their flat round plate used as a baffle, is an exhaust (and power) killer. I feel this is why many of these plates work their way loose. Just too blunt at blocking exhaust flow, no aerodynamics too it at all, and with all the pulsing going on in front of it.

My tails are nearly 4ft long. They are 4.5" OD, with 4" ID inner pipe, then have waffle style baffles in them.

The stellings "green" headers, were used on the 575HP 540 Mercury engine back in the day. While they are a good header, they were not designed for 800+hp forced induction engines.

If you go to CMI"s website, anything over 750HP forced induction, they recommend their Big Tube headers.

Borowski's dyno headers are 2.25 primary tube, and dump into a 5 or 6" pipe. I'd like to think thats a little less restrictive, than 1 7/8 ID primarys , 4" id tails with baffling, hooked to a series of tubing with water dumping into them running the exhaust wet. Enough to make a difference, I don't know how much if any, I havent tried it back to back.

Either way, comparing power from a dyno using completely different exhaust, correcting to air temp of 60* and a higher baro, than one thats correcting to 77* and lower baro, running accessories vs not running accessories, and some other variables, its not really apples to apples. I more or less wanted to run it on a dyno where the engine is going to be in the state that it will be going into the boat, both for tuning purposes, and ease of rigging. Now all I have to do is bolt my transmission on, and drop it in. My exhaust is on, bellhousings, flywheels, dampers, rear plates etc. Whether or not I gained power, should be told when I get it in the boat. I more or less did some changes to the recipe , due to the fact the heads I had were jacked up and in need of work, added intercoolers for a little safety margin, and replaced rockers with new ones and added stud girdles. I'm happy that I made around the same power as last time, with a full point less compression, my exhaust system, running the sea pump and alternator on it. I picked up 57HP going from 6psi to 8psi, if I had another pulley, I'm pretty sure I could have approached the 850-875hp range from a 468, but didn't have any more pulley options, and think I'm gonna keep it around 7-8psi and not push the envelope too hard.

joe,you have a combination making more power than before with a full point less compression and with a very safe tune up.i would consider that a win.

Turn it up! It's not our money