Dual Exhaust conversion

[TRBenj]

There arent as many gear heads over here as there are on CCFan, but I thought some might appreciate seeing the results of my project.

Im aware of a few other conversions that were performed by the factory or at dealerships, but I havent seen any that made use of the existing single outlet with an added symmetrical pipe. Instead, they moved the outlets up tight to the stringers and required the plugging or reglassing of the original hole. My method made it more interesting since it required the steering system to be re-routed. What fun is an easy project anyways?

[ffmedic74]

RE: Dual Exhaust conversion

HOLY CRAP! Great looking motor. Please post the details of your engine build. What kind of exhaust risers did you use?

[jonfo]

RE: Dual Exhaust conversion

The one in the first pic reads HI-TEK on it.

[cward]

Hat's off TRBenj!

Clean...

[surroundsound64]

RE: Dual Exhaust conversion

That is awesome!!!!

[Nautiqueman]

RE: Dual Exhaust conversion

you ought to post a mp3 file with the sound of that baby...

[Andrew]

RE: Dual Exhaust conversion

NICE i HATE the look of that offset single exhaust!

did u downsize the piping any to maintain backpressure?

[TRBenj]

Re: RE: Dual Exhaust conversion

did u downsize the piping any to maintain backpressure?

Thanks guys.

Backpressure is never good. All piping is 3.5", which goes up to 4" right at the tips.

[TRBenj]

Re: RE: Dual Exhaust conversion

Please post the details of your engine build.

Engine was originally a 240hp PCM 351w, mated to the 1.23 tranny.

-ignition: Performance Distributors DUI, 8mm Taylor Spiro-pro wires, .055" plug gap
-heads: Ford GT40p cast iron heads, fresh valve job/resurfacing, FRPP 1.6 aluminum pedestal mount roller rockers
-intake: Weiand Stealth dual plane, stock 1" 4-hole carb spacer w/ PCV
-cam: Cam Research custom grind, .490/.490 lift (1.6), 218/222, 110 LSA
-exhaust: Hi-Tek SS headers, 1.75" primaries, 3" collector, 3.5" outlet. 12 lbs/side. 3.5" mandrel bent/welded pipes, 4" tips. Pipes and headers ceramic coated.
-carb: Rebuilt and rear metering block conversion (replaceable jets) performed on stock 4160 Holley (600cfm). Low profile (2") SS flame arrestor.

The carb is not dialed in yet, but it should be in the neighborhood of 350hp.

[WakeSlayer]

RE: Re: RE: Dual Exhaust conversion

dang dude, that is awesome !

[Andrew]

Re: RE: Dual Exhaust conversion

did u downsize the piping any to maintain backpressure?

Thanks guys.

Backpressure is never good. All piping is 3.5", which goes up to 4" right at the tips.

???? no backpressure will result in a significant loss of low end power! i don't know too much about pipe sizing when u have under water exhaust, but in the automotive world, i 3" single exhaust is about the sweet spot for the medium size v8 that u find in nautiques..... if cc had the hp/torque levels close to optimum performance, then ur probably gonna notice a drop in ur holeshot. u'll gain a good bit of power on the top end but imo top end is pretty insignificant unless ur barefooting....

[TRBenj]

Re: RE: Dual Exhaust conversion

???? no backpressure will result in a significant loss of low end power! i don't know too much about pipe sizing when u have under water exhaust, but in the automotive world, i 3" single exhaust is about the sweet spot for the medium size v8 that u find in nautiques..... if cc had the hp/torque levels close to optimum performance, then ur probably gonna notice a drop in ur holeshot. u'll gain a good bit of power on the top end but imo top end is pretty insignificant unless ur barefooting....

Not exactly. To quote an expert:

Just to clear things up (and this comes up ALOT) no amount of back pressure in an exhaust system is "good". It doesn't add anything...well, other than to add to overall pumping losses of the engine. If an engine runs better with back pressure it is because the ancillary systems have been tuned to take into account the exhaust system that is adding the back pressure. If you remove the back pressure (i.e. the exhaust system) and then re-tune the engine for the free flowing exhaust it will make more power than it did with the restrictive exhaust.

This is exhaust theory in its most simplistic form...I'm not referring to 12" long zoomie pipes but full length exhaust systems. Backpressure doesn’t add torque or low end...no matter what you've been told over the years by shade tree mechanics. Your boat is no exception to this rule.

With the new exhaust, Ive made some gains on the top end (more to come as I dial in the carb) but Ive seen a bigger improvement in holeshot. Ive picked up 400 RPM going to WOT from idle- I now get a solid 3600 RPM with my Acme 470. The motor makes the most power/torque in the midrange (2500-4500 RPM).

I do barefoot, by the way- and I foot with some pretty big guys that like to go fast (45-46 mph). That shouldnt be a problem now.

[surroundsound64]

RE: Re: RE: Dual Exhaust conversion

If anything you'll only loose some fuel economy because the exhaust gas is scaveneged a little too good, taking some of the new unburnt air/fuel with it during the time both valves are open.
A small price to pay for our expectations from our boats.

[east tx skier]

Tim, are those the MC "by design" tips or are they just similar looking? If you were talking to Mike, I'm guessing they aren't the 07 muffler replacement tips they're using. He didn't seem to be touting those too much from a performance perspective in another thread I read.

Either way, great looking mod. 350 hp, holy cow!!!

A little off topic, but what's the reason CC opts for single exhaust outlets? Is it another way to balance out the wake or is there another reason? Didn't they do doual exhaust outlets on some Air Nautiques in the early 2000s? Just curious.

[thedude]

Very clean install, nice job. Any chance of a sound clip? I guess it would sound similar to a 5.0 mustang running open headers out of water. What type (if any) muffler are you using, do you have a pic of it? I'm just curious.

Matt