muffler baffle? or internal damage?

[hcooperrn]

Have another question now, I think I know the answer from searching and hoping to confirm. Still haven't been back out on the water to isolate my noise issues from another post, hopefully this weekend.

A few days ago, though, I installed the FAE. Before I put the flanges on, I got a flashlight and looked up inside the exhaust. Port side was nice, clean, open all the way to the elbow. Starboard side has a vertical piece of fiberglass hanging down, leaving a little less than half the diameter open. I thought it was some fiberglass that had flaked off, so I grabbed a long screwdriver, and nope, it's solid.

Is this how they baffle the fiberglass muffler? Is the port side just missing? I think I read a thread that baffles do break off, is that what happened?

I'm wondering, though, how hard this is on the engine and performance. If it were just an exhaust pipe, sure, plenty of room, but add the water coming with it, and if there's a couple of inches in the bottom, I now have a exhaust bong in reverse going on, right? With the FAE and the upward angled flange, I think that will decrease the flow back up into the exhaust when shut off, just seems like the baffle, if that's what it is, would only increase the back pressure when starting and completely prevent any scavenging when running?

Any harm in cutting it out?

[Greeko]

It will bring down the engine performance slightly. If you have it too deep into the water you will feel it bigtime!!! Adjust the depth and you will be fine!

I never had any problems with back flow

[dom w. forte]

If the engine ecm was calibrated for mufflers the air speed and volume change will be effected by being straight through and it cant tottally adjust for the difference, we have the same problem when people put dual exhaust on a single exhaust vehicle without changing the ecm calibrations , because the vehicle is louder they think they improved overall performance but if you do a back to back track test you will normally see performance and fuel economy losses.

[hcooperrn]

I've read several posts about people who have changed their mufflers over to straight stainless pipe that they got from FAE, and at least one other who went with flexible wet exhaust pipe to get rid of the mufflers and the cracking risk. I get what you're saying about the need for the ECM to compensate, it makes sense, though we aren't talking about adding cubic inches, just a change in exhaust back pressure -- the change to overall flow should be within the realm of the ECM to handle, unless MEFI is just that sensitive?

All my fuel injection tuning experience has been in cars and motorcycles, I haven't looked at the fuel/spark maps of a boat to see the differences yet.

In the car world, if the ECM is using MAP, so as long as the cylinder can evacuate without a residual positive pressure, the negative pressure created during the intake stroke is what determines the injector pulse-width, right? That's why I was worried -- if the cylinder has back pressure left over after the exhaust stroke, it won't take in as much during the intake = performance loss. As long as there is little to no pressure left, it should still be good. You're absolutely right, though, unless a situation is created where there is true scavenging and a negative pressure at the end of the exhaust stroke, there would be no performance gain. Right? Or am I misunderstanding?

If the ECM can't handle the differences, then wouldn't everyone who has installed an FAE have had a noticeable drop in performance? It's going from two straight out openings into a single, tapered, just like taking dual exhaust on a car and moving it back to a single pipe.

Not being argumentative at all, just really curious to learn about all of this in the marine world, especially if I want to plan on more ci's and a custom tune someday.

[dilpickle]

I've read several posts about people who have changed their mufflers over to straight stainless pipe that they got from FAE, and at least one other who went with flexible wet exhaust pipe to get rid of the mufflers and the cracking risk. I get what you're saying about the need for the ECM to compensate, it makes sense, though we aren't talking about adding cubic inches, just a change in exhaust back pressure -- the change to overall flow should be within the realm of the ECM to handle, unless MEFI is just that sensitive?

All my fuel injection tuning experience has been in cars and motorcycles, I haven't looked at the fuel/spark maps of a boat to see the differences yet.

In the car world, if the ECM is using MAP, so as long as the cylinder can evacuate without a residual positive pressure, the negative pressure created during the intake stroke is what determines the injector pulse-width, right? That's why I was worried -- if the cylinder has back pressure left over after the exhaust stroke, it won't take in as much during the intake = performance loss. As long as there is little to no pressure left, it should still be good. You're absolutely right, though, unless a situation is created where there is true scavenging and a negative pressure at the end of the exhaust stroke, there would be no performance gain. Right? Or am I misunderstanding?

If the ECM can't handle the differences, then wouldn't everyone who has installed an FAE have had a noticeable drop in performance? It's going from two straight out openings into a single, tapered, just like taking dual exhaust on a car and moving it back to a single pipe.

Not being argumentative at all, just really curious to learn about all of this in the marine world, especially if I want to plan on more ci's and a custom tune someday.

I might be wrong, but I believe the marine engines use Speed Density rather than MAP.

[hcooperrn]

Yes, sorry, I didn't use the system term. Speed Density uses both engine RPM from a tach signal and manifold pressure from a MAP sensor, right?

[dom w. forte]

The boat is an air density system which uses a map sensor , what im saying is if you picture a graph with an ideal centerline for fuel and timing as you change either air speed or volume you can move to the right or left of center , center being desired performance , im not saying that the ecm wont compensate but it only can adjust so far and this could possible not be ideal, as to the FAE system going from dual done to single could in fact increase air speed which will pickup low end torque , but this all depends on the overall exhaust hole, ive never meassured the size of the exit.

[hcooperrn]

Makes sense, maybe someone who has removed their baffles or gone to the stainless pipe will chime in to say if they noticed any performance difference. At this point, I'm thinking remove it if only to make both sides equal since one side is missing already.

As for the FAE increasing the velocity, the exhaust still has to be 'pushed' out, so there wouldn't be a chance to scavenge, right? It would have to create a low pressure pocket in front of the water, wouldn't it? On a crossover exhaust in a car, it is achieved because atmospheric pressure is lower, and it can freely go out I think water pressure would be too high?

[hcooperrn]

Thanks for the replies and discussion by the way, I've been away from racing for several years now, it's fun to think about stuff like this again.

[dom w. forte]

What kind of racing were you involved in? I worked with my brother at Turbo Action they are a racing automatic transmission company , we did a lot of work with Chrysler on drag racing and there torqueflight .

[hcooperrn]

Nothing too fancy or even remotely professional. My dad did autocross with Corvettes, that's when I first started learning about computer tuning, I built a circle track car years ago, and up until my daughters were born a few years ago, I had a drag bike I played with. I've probably done the most tuning on my street bike, a Honda Blackbird with a TunerPro; big bikes have a lot of potential when you open up the intake and exhaust if you get the programming maps to match up.

[dilpickle]

Makes sense, maybe someone who has removed their baffles or gone to the stainless pipe will chime in to say if they noticed any performance difference. At this point, I'm thinking remove it if only to make both sides equal since one side is missing already.

As for the FAE increasing the velocity, the exhaust still has to be 'pushed' out, so there wouldn't be a chance to scavenge, right? It would have to create a low pressure pocket in front of the water, wouldn't it? On a crossover exhaust in a car, it is achieved because atmospheric pressure is lower, and it can freely go out I think water pressure would be too high?

The shape of the FAE outlet & its placement in the thrust from the prop will actually create a low pressure area where the exhaust exits the pipe, I think they actually have a video of the suction effect on their website where they had an open ended FAE pipe on top with a fan to measure air speed. This effectively increases exhaust velocity & should increase efficiency as well. I believe the only loss noticed when installing the FAE come from the small amount of extra drag in the water from the pipe.

Sorry above, I was getting my acronyms messed up-I was thinking Speed Density as Dom describes as opposed to MAF (Mass Air Flow) where the engine measures air flow & compensates rather than figuring fuel off of tables that only reference engine RPM & Intake vaccum (Manifold Absolute Pressure) with active feedback possible from O2 sensors.

[hcooperrn]

Ok, so if there is some efficiency to be gained due to the FAE when moving, that just leaves the effect of losing the baffles and whether the ECM can keep up. I'm guessing there are a fair amount of people who have lost a baffle and don't know it, along with those who have taken out the mufflers and replaced with straight pipe, all with no major issues.

If the increased flow were to create a lean condition, the response would be to cut power through timing. Since no one has complained about that, I'm leaning toward the increase in flow is probably minimal to the point that it is managed, or that the power loss in minimal. Either way, it seems like the decreased back pressure (not having to blow water and exhaust under the baffle) when starting the engine would only be a good thing. However, they did put them in for a reason, I'm sure; was it sound or performance?

All theoretical at the end of the day, right? I think I read someone call these "tractors not hot rods", we aren't running them up to high RPM's where exhaust flow becomes starts becoming critical.

[dom w. forte]

Yes these are all truck engines keyed to low and mid range torque, so it sounds like FAE uses water flow to scavange the exhaust for better flow. As to the baffle I would prefer to have the baffle in both sides but it shouldnt hurt to remove in this case because the FAE probably would keep the flow close to the same.

[dom w. forte]

What year Corvette did he autocross , I started autocross with a 1969 Mach1 , then a 1965 mustang conv., then 1981 Corvette, then 1968 corvette, then 1985 mustang gt , the Fox body mustang was hard to compete against with its short wheel base.