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.

Yes it was the one with the yellow swim platform, and yellow and teal interior. The guy I bought it from was a straight shooter. He followed through with what he said he would do and when. The boat showed and ran well. I had been casually looking and I passed this one over a couple of times just because of the age. When I read it closer I realized what it was and drove the 5 hours the next morning to put the deposit on it. I thought I saw a couple of posts from what could be the owner previously to who I bought it from. I'd be interested in any more info he can provide.

From NY ?

The boat was originally from the finger lakes here in NY. Whitey where do you boat?

I bought it from Mallinson OH and brought it to Tawas MI. I boat all over the state, but mostly in BayCity Mi. He said he bought it from Syracuse NY area. Not sure if that's is near finger lakes.

I am sure I will see you out on the bay Whitey51. I have a 97 253 named "Gimme Fuel" with a 548efi. I run out of Standish to Bay City or out of the Saginaw River to Bay City.

I don`t see that making any difference 99 % of the time.. SB being the 1% :drink:

Gimme fuel Lookin forward to seeing you out there. Still waiting on the vinyl decals for mine. "God's Gift"

Sooo, I got her out and stretched her legs a bit. I put roughly 80 miles on it. It seemed to rum great at all speeds. No hesitation or stumbling. There Is a fare amount of no wake zones, so it idled for around Two Miles right off the bat.
After the first leg of the Trip (40 or so miles), I noticed the transom was loaded up with exhaust soot.
When I ran it before bought it, it didn't do that. But, I'm not sure if it didn't do it because the exhaust was so much further from the transom, because of the resonators, or if taking them off caused the carb to richen up.

What are your thoughts?

If I understand SB's previous post I would have thought opening the exhaust would lean it out. Is that correct?
So I don't really know if it's an idle mixture issue or jet issue. Please let me Know your thoughts.
Sorry for the long post.

Unrestricting exhaust will lean it out.

Willing to bet $$$ the soot is from the shorter tailpipes.....exhaust probably 'curling' back into transom more from aerodynamics.

Soot wiil usually not happen at idle....hard for engine to idle with an A/F mixture that rich.

Should I try to rejet it? If so, how many jet sizes? Or leave it and throw the tips back on. Without the bungs? I want it to be correct; And that much residue is excessive.

Your motor will tell you. If you are not a tuner, than better off left alone.

And yey, when things are tuned right on, there will be no soot.

So, all to your abilities, which I cannot answer for.

Well hmm. LoL I've played around with it a bit in Sbc, but never a BBC. I'll keep YA posted.