Our boat came with mufflers with a baffle . Can i take a 3and 3 quarter hole saw to the back plate and relieve some of the exaust pressure.The race boats seem to run straight thru hull.Less exaust pressure more horse power right.Our last boat had 500 efi with silent thunder .I took this off & added rubber flappers .The boat is a 353 with 525 efi & boxes turning 5200 rpm 87plus mph gps. By the way Troutly what mufflers have you ordered. Thanks Rex

Hey Troutly, was your boat just equipped with straigth through's or did you have some type of muffler from the factory. I know this seems like a dumb question, but I am trying to find a good switchable system to install in our new boat.

Currently it is just straight headers...sounds great, but the bass fisherman on my little lake are sure gonna' raise some hell about it.

I am considering having National Marine install swithchable thru-prop exhaust when they have the motors pulled to install the Stellings boxes. I am looking for any ideas so fire away!

Corey

Troutly ,Are the hpi suppose to let the motors produce more horsepower. I hope your old ones come off easier than mine .I tried to remove mine but mine would not budge. They are sealed with 5200.Probably going to tear them up getting them off. I would like to here what 5 blade props you like the best. Do you know anybody running herings on a 353 or 382. rex

Good Stuff - You're probably not losing any power at all with your current setup.
The best switchable system is Corsa's Captains Call, but if you don't have the exhaust "horns" in your boat, they'd have to pull the engines. There are lots of clamp-on switchable mufflers - Livorsi, Teague, Drew, etc....

Troutly, Sorry to here about your PITA mufflers. I dont mind loud so do you think if I drilled out the back plate & the deflector ring from corsa muffler it will produce more power. C SPRAY , I do have the corsa switchable exhaust but I also have the corsa mufflers with the baffle & defflector ring & plate . I have been told that these mufflers hurt the peformance of high performance motors . I have the 525efi motors. Just wondering. Rex

Stock Corsa tips as used on the Formulas with boxes vs straight pipes is about a 2 to 2.5 mile per hour loss/gain (gps). We tried the open pipes in the Keys last weekend, with 3 people and 50 gallons of fuel we gps'ed at 81.4. With the Corsas and this load it never got over 79. The Bam sight suggests a 270 factor results in 1040 propshaft horsepower, with open pipes.

hhttp://www.go-fast.com/boat_speed_predictions.

John B

Do the stock Corsa tips have the diverter to allow extra flow thru hub? (Quick and Quiet Plus?) Having the extra path allows for a slightly more restrictive tip muffler, the extra path thru hub bleeds off some back pressure. I know you can get the Corsa tips without, just wondering which setup showed that much speed loss.

JOHN B & TROUTLY ,What props are you running. I am drilling out the back plate & deflector plate on my mufflers.I feel this will do the same as taking them off. I have been using the merc lab 33 bravo .They have about 21% slip. I have ordered a set 6 blade herings . Jim Hering said to try these first .Then the five blade. He said he had some 382 boats with hering props on them doing very well..have any of you tried hering props. I hope they are fast because they are very expensive. Rex

Good Stuff, I am running labbed Hydromotive 5 blades (28pitch) at 5100-5200. Labbed 31 B1 Mercurys ran about the same top speed at 5300-5400. The P-5's are far superior at low speeds, less slip.

Troutly, My 525's idle at 94 DbA (4-4) with the CMI's wide open! And 91 DbA closed, and 88 closed with the silent choice on.

John B