NADA! After the 4" riser / tip install everything stayed the same [ no surprise there! ] so I figured opening up the restrictive exhaust manifold/ riser passage by removing the restrictor [ also called turbulator] I could gain a few RPM's = zero increase. Without head work and cam change I didn't expect anything other than a nice sound! Having low hours [ about 240 ] on the engines, I'm not about tearing the engine down to improve performance yet! The 6.2 MX engine with the ECM555 is limited to 5150-5200 rpm I think. Raising the rev limiter I could possibly gain a few rpm's with the freer exhaust. I'm at 5000 rpm with the B1 26 labbed props, 1.65 drive ratio.
The props were tuned from factory specs [ I measured them originally 25P +cup] to true 26P +cup, hence the rpm drop to 5000 from 5150 I had @WOT before. The mid range acceleration was phenomenal with 25P but hitting the rev limiter constantly in rough water made me to increase the pitch. So far only Dustin Whipple is authorized to change parameters in the ECM555.

Tom A., I currently have the thru hull with flappers right after the hull. I am thinking the extension without those flappers WOULD increase the noise. That's what I'm trying to confirm.

Spectras only, sweet job on the tips...I can run mine thru the props or thru the hull and yes, the sound is unbelievably different. I'm just trying to see if the tips get the current state of thru hull even louder.

Not to jack your thread but for the experts? I am running EMI THUNDER exhaust with tips that stop at the transom with out side flappers only! My Q? Is, I have a set of long angled cut tips with nothing but pipe no flappers inside or out will it make any diffrence in noise or will water get rushed back through the exhaust with out the flappers while backing up etc. if I put them on?

It's quite a bit louder on a stock big block. On a stock small block, it's noticeable but not a tremendous increase in sound.

That's from my personal experience doing it to both.

The same sound comes out if your tips are 2"s or two feet. The thing to think about like the boat above is if you gunnels hang over the transom. I'm sure that deflects noise down and away from the cockpit. Longer pipes would lessens the deflection.

Ok but what about not have any flappers on the tips inside or out?

Never thought about it cause I wouldn't do it.



Even on the 24 with it's exhaust as high as it is still has internal rubber flapper 6"s inside the tip.

Have friends with jet and flat bottom boats. They run dry and wet headers over the transom. The wet are louder then most inboard wet exhaust because they introduce the water at the very end of the outlet and they don't run flappers.
Flappers keep the noise down some at slow speeds because it lets a little water build up and slows down the exhaust and quiets it as the exhaust gasses has to push the water out and the flapper open (loosing energy) at the same time. Once you get into the throttle it makes no difference. Now it just depends on how far down stream you introduce the water.

Also I will never use those internal metal flappers with the bar across the middle again. They drove me nuts. I would be working on the boat or something with the motor running and when you were at just the right angle you would hear what sounded like a bottom end knock. They thumped all the time when at idle anyway but at just the right angle to the motor it would scare the crap out of you. And once you can pick out a noise but then with the motor cover closed I would run a little hard and come back to idle and hear it thinking please be those stupid flappers. One day I walked out with a sawzaw and a long blade and chopped those SOB's out. Put 2 of the rubber caps on the ends and never been happier.

I was wondering this myself.. the first time I took out the 33 my wife asked if it was quieter.. I walked to the back by the benc seat and was louder but thought it would be louder having 2 bbc's now!!

Have internal flappers, so maybe I'll take the ext flappers off!!! Would be left with lil 2" tips.

I have wide open exhaust on my stock 454's. Never had any problems with water. Tried putting some Corsa mufflers on it a few years ago. Hated the sound and lost abot 300 RPM. Went back to the open exhaust.

just a small vid of my Fountain 502/500 Shot Gun exhaust sound ...



http://www.youtube.com/watch?v=WqjCAyrokGw