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View Full Version : got an idea about exhaust, but may not work


DooSPX
08-08-2006, 06:47 PM
I was brain storming about what to do with the big egg muffler on my 91, and I was going back to cars and trucks for idea's... would making a H-pipe from marine grade plastic work? and most important, on a automobile, it works well, will it help the performance on a ski boat?

TMCNo1
08-08-2006, 08:41 PM
Get 2 regular inline mufflers fron SKIDIM and mount on the inside of the stringers where your rubber pipes are now and use the extra pipe to hook them to the exhaust risers. A friend of ours has a 1990 MariStar 210 that had the big across the back of the engine muffler that broke at the pipe connections and he installed 2 inlines and they work fine. No change in sound either, same performance.

M-Funf
08-08-2006, 08:55 PM
I was brain storming about what to do with the big egg muffler on my 91, and I was going back to cars and trucks for idea's... would making a H-pipe from marine grade plastic work? and most important, on a automobile, it works well, will it help the performance on a ski boat?

H-Pipes and X-Pipes do help with the performance on car engines. Without knowing more about the design of the marine engines, I would probably guess that an X-Pipe in a boat would help with performance...

I don't know how it would work out with the available space, but if you moved the mufflers to inside the stringers you might have room. I believe that for an X-Pipe to work, the crossover distance needs to be short, so having an X-Pipe or H-Pipe that spans the distance from outside to outside the stringers probably wouldn't help.

It's worth a shot if you've got the time and $$

phecksel
08-09-2006, 01:01 PM
I was brain storming about what to do with the big egg muffler on my 91, and I was going back to cars and trucks for idea's... would making a H-pipe from marine grade plastic work? and most important, on a automobile, it works well, will it help the performance on a ski boat?
Crossover pipes help lower the initial back pressure seen by the engine, effectively doubling the exhaust pipe diameter.

DooSPX
08-09-2006, 01:05 PM
I know what they do, but do you think that it would work and help in a towboat phecksel??

thanks man!

bigmac
08-09-2006, 01:10 PM
I know what they do, but do you think that it would work and help in a towboat phecksel??

thanks man!

I'm thinking that your typical modern ski boat engine is already about as free breathing as one could make it relative to air intake and exhaust. To go farther would require more radical engine mods, I suspect...

DooSPX
08-09-2006, 02:40 PM
I would think that it would work though, and I will try to explain why. the crossover pipe will help increase the exhaust gases velocity, therefore increasing the scavaging effect, basically like a vaccum pulling the exhaust from the riser off the manifold.
as the typical modern towboat has dual mufflers, there is still nothing to help promote scavaging of the exhaust gases. My 91 has dual exhaust ofcourse, but has the big dinosaure egg sitting behind the motor, and when I pulled it to work on it, I looked it over real well, and it seems it does nothing to help the power from the boat. it looks really restrictive. heance, why a few members on here who have pulled the big dino muffler off, say they feel like they gained a decent amount of power. I believe that is the reason MC went back to the dual muffler design, well that and the fact that the big single muffer is prone to leak.

DooSPX
08-09-2006, 11:54 PM
anyone else have any idear's. lol

Jesus_Freak
08-10-2006, 12:18 AM
Yes, targeted scavenging has its advantages when appropriate (CR-250 dirt bike, for example). Raising exhaust gas velocity has a price : static pressure and entropy. These get you on the top end. Just like we all know, it hangs in the balance between low-end versus high-end and where you need the power and/or fuel consumption to be optimized. Cannot help you with this particular configuration, but just would advise more is not always better.

DooSPX
08-10-2006, 12:34 PM
thanks Jesus Freak!
im from the old school days where larger exhaust pipes are not always better. am I correct in thinking that dual 3" exhaust w/o any crossover is too big for a VERY mild 351cid motor?
thats why I was thinking that a balance pipe would help with the performance of the boat.
but I guess a ski boat is a different animal when it comes to exhaust??

rcnjson
08-10-2006, 01:04 PM
My opinion is the manifolds (at least mine are) the bottle neck. They are pretty small and have abrubt bends, not good for flow. I mean it is basically 4 tubes flowing into a log. The 3" with no baffleling is too big. The issue with too big is stale air, or exhaust gasses that just aren't flowing and scavenging as you mentioned before. A mild 351w on the street would be fine with 1-5/8" primaries and 2-1/2" exhaust. I have a 302 that makes a ton of power, on the sauce of course, going through 1-5/8" headers. I would say you can get rid of the single muffler, go to duals and an H pipe but you don't need to be bigger than 2-1/2" and the big HP gains would be had closer to the motor. i.e. getting some sort of header on there.
that is my buck two eighty
k

DooSPX
08-10-2006, 11:40 PM
thanks rcnjson for the info!
the stock size on my 91 PS 190 is 3" with a big dinosuare egg muffler.
would there actually be any benefit to taking the big leaking muffler off and adding a H-Pipe in its place?

Leroy
08-10-2006, 11:54 PM
Doospx; where do you want the gain in performance? Top end is pretty limited by prop and RPM's it could boost the pull?

I say how hard can a muffler experiment be? Try it! If I get what you are talking about I believe my boat has a large crossover so it must do something.

Jesus_Freak
08-11-2006, 02:43 AM
As I had hit on in previous threads, and related to what Leroy has pointed out, I had a problem with top-end that was dictated by hull/prop/RPM. I could not change anything with fixing a damaged head gasket (larger role than exhaust design) and swapping out old/bad plug wires, plugs, cap, rotor, etc. At the same time, however, I realize every powertrain is different. Agreed that either extreme on the exhaust ("stale" or "restricted") is non-deal, but these non-idealities may represent 2% of your power issues instead of 20%. Can you try it relatively easily?

jimmer2880
08-11-2006, 09:42 AM
Remember that when our boats are not on plane, they have lots of back-pressure. It's the water trying to come back in our exhaust. It's my understanding that it is one reason why ski boats have so much torque and such good top-end HP (When on plane, the exhaust has no back-pressure from the water)

DooSPX
08-11-2006, 10:48 AM
Remember that when our boats are not on plane, they have lots of back-pressure. It's the water trying to come back in our exhaust. It's my understanding that it is one reason why ski boats have so much torque and such good top-end HP (When on plane, the exhaust has no back-pressure from the water)

dang, I never thought of it that way.... good thinking jimmer