Performance question.
 

I recently purchased a 253 convincor with a 540. It had Imco resonators/mufflers on it. The through hull is 4 inch. When I pullled the resonators off, there was a separate insert inside. Other than being noticeably louder, can I expect it to run or perform any differently.
Thanks

No one has a comment? What are your thoughts?

More info needed.

HP at what rpm ?

What is the minimum area left open by the biggest restriction in the muffler ?

If you have 02 bungs, you can use those to find out what your exhaust backpressure is. You want none for best performance.

Thanks for the reply. It's supposed to be around 600 hp but I'm not sure at what rpm. It has the 5200 rev limiter in the msd ignition. I took the bung and the resonators off and put the rubber exhaust flaps on. The bungs we're about 2-1/2" I.d.

It ran 72 when I water tested it. The selling add said 74 all day and 78 at it very best, in optimal conditions. This was before I made any changes.

It takes a lot to make a boat faster. I've spent the better part of my life finding this out. lmao

Heat, DA, humidity, etc will effect speeds. It may breath better and have better throttle response. I would not expect much in the way of top end numbers.

Try different trim settings. Congrats on the new boat!

My muffler (custom) inserts cost me 3 mph. Proven a bunch of times, so my info for my set up is a fact.

Different boat, different motor, different mufflers will provide different results.

In fact, a choked exhaust will require less carb jetting.

I tuned a deal a long time ago, that took 8 more jet sizes when I found the performance issue (exhaust 'choke') and gained a million more hp. 450-500hp 454. The million more hp is not a fact. LOL. It equated to about 70hp, give or take 10.

As a side note to help. MSD (and some other) rev limiters start dropping cylinders a little before the required limit rpm, in order to help limit the rpm at the required time. So, if you plan to use your engine at 5200rpm, I would put the limiter at 5600-5800rpm. Yeh, 5800 would be better.

Rev limiters are not to be used as a governor. They are to be used to keep the motor from overreving and crashing the valve train or spitting internal parts out from catastrophic events like breaking a drive or coupler and free reving or boat jumping in air, you miss the throttle, and the engine free revs.

Stuff like that.

Many don't know they are driving up against the 'soft part' of the limiter and wasting performance and engine reliability.

Thanks for the replies. I took them out for the sound. I wanna hear it! Hopefully I wont have to mess with the carb now that I
Have played with it.

Every time SB hears horsepower he plays with it . :party-smiley-048:

Did you get the one with the yellow interior? That was a deal with all the upgrades that boat had. I think there was a post on here from 2 owners ago (the one that built that motor) and about the question if it actually made 600hp. I think he ran a best of 76 and he had the boat for years. I think is handle on here was "glen george" or something like that. My buddy tried to buy your boat but you had a deposit on it I think. The guy selling it seemed like a straight shooter.