Adjustable Exhaust Outlet

[Carter Powell]

Has anyone ever installed an adjustable exhaust dump valve something like an auto heat riser valve on the back of the midsection. I was thinking of trying to adapt something like this inside of a Bobs exhaust housing and then run a cable up to the dash for a push and pull operation. I think that the idea is sound but thought I would consult the vast knowledge of this board for the truth!

Best Wishes

Carter Powell

[HowieDean]

They sell one that bolts directly to your mid... has a vac hose running some where... and dumps at high rpm... All their stuff can't be junk cause the're still in business.... Might be worth checking into....

I've been toying with the idea of water injection into the tuner...
MSD make the control modual and the syliniods for jetskis... They have switchable programs to change spray volumes at different rpms.... Would take some plumbing but it works really well on highly ported jetski's to get some of the bottom end back....

They use one of the wires that wrap around a spark plug to sense rpm so the electrocs should work... you'd have to talk to one of their techs about which control modual to use... I know the twin cyl ones fire both plugs every rev...

Let us know how what you find..

[Greg Moss]

John tiger did that and wrote an article about it in Hotboat. You may be able to research it on their web site. It works of a cable to the dash. Howie the long hair got in your eyes when you looked at the Land and Sea cata log The one they make is for the OMC V-8 Greg

[Carter Powell]

Howie, I am familiar with what water injection is for but spraying it into the tuner? What am I missing. What would this accomplish?

Carter

[HowieDean]

A mind is a terrible thing... For your application it would hurt not help.... You would use it if you've ported and relieved the exhuast alot... When you spray it creates back presure... which gives you back some of the bottom end torque you distroyed when you openned up the exhuast....

I haven't looked at a Land & Sea catalog for a long time... thought they used to have one for merc... You can use the one for the OMC... You would just need to pull your liner... and drill the hole in the side of the mid instead of in the back..... Also looks like you could adapt it to the Bobs piece without a whole lot of trouble... Cut a piece of alum plate.. drill a hole in it.. bolt the little red valve to it... grind out the plug openings in the bob's thing then bolt the plate over it.... Give them a shout and get the dimensions... Bet it would work......

[Greg Moss]

Or you cpould just read John Tiger's and it explains everything.

[DRAGIN FLY]

Land and Sea catalog page 15 part # 117-002 for Merc Yamaha Suzuki and OMC also part # 117-001 for OMC V8's phone # 603 329 5645 hope this helps

[Greg Moss]

This is an E-mail I ahve gotten from John Tiger I hope it helps Greg:

I've gone through all my Hot Boats from that era (95-98) and only found one story, "Get Shorty" from the May 1997 issue (pp 94-99) that refers to that exhaust snout I built. I don't think I ever did a story on that system alone. This story shows several good photos of the valve and related parts. Construction was pretty simple; I used a Bob's Machine snout that I welded on to the centersection after opening up the rear with two 1" x 2" oval holes. I then cut the end of the Bob's snout off at a 45-degree angle. I built a butterfly shutter plate from 3/16" aluminum to fit inside the snout, then fashioned a stainless rod with a flattened side as the butterfly shaft. This was done much the same as a carburator's throttle plate or choke shutter. The snout was bored to accept the throttle shaft, then the assembly was put together using small screws and locttite/star washers so it couldn't vibrate apart. A bellcrank was affixed to the end of the shutter shaft to operate the shutter open and shut. A Morse deisel engine cable was used so the shutter could be locked open or closed with a dash-mounted control. These cables are available from most marine catalog distributors. Simple Morse 33c ends were used to attach the cable to the shutter and exhaust housing.

Hope this helps...

JWTjr.

[Talon2.5]

i posted a design i was thinking of quite a while back and dam if i can find it in the "search" thing


sorry skip

[Tony Brucato]

I think the theory behind the water injected exhaust tuners on some PWC is that by changing the exhaust temperature you are also changing the speed of the sonic wave in the pipe. A cooler exhaust would act like a longer tuner=more low end power. By having a RPM controlled pump you can remove the water for high RPM power.

[H2Onut]

Isn't it basically the same effect as having a slider exhaust on a Go cart motor, I now in the Enduros everyone was running them, This dates a few years back. I have seen those dumps advertised, One of which is driven off of speedo, at 55mph it supposed to open up.


Mike

P.S. Found this article :

In response to the numerous questions received concerning open (or "above water") exhaust, perhaps it’s time to shed some light on this subject. Generally, most outboards will lose about 5% of their rate (powerhead) horsepower through the exhaust system and gearing losses. Of course, all the manufacturers rate hp at the propshaft now; today’s engines (at rated power) are actually more powerful than the same engines of a few years ago. For example, Mercury’s three-cylinder 50 of the late ‘80s was actually powerhead rated at 70 hp earlier in its life. OMCs old 235 was, with a few minor detuning changes, rated at 175 hp for the last half of the ‘80s.

It is possible to achieve a small, slightly noticeable power gain by relieving the exhaust on high-rpm outboards. The gain is more noticeable on a modified engine. However, for the small power gains realized, the noise generated is for most lakeside residents, intolerable. Don’t get me wrong; I love the howl of an unmuffled outboard as much as anyone. It’s even fun to listen and differentiate among brands and sizes of outboards by their open exhaust notes. Maybe I’m getting old, but unlike when I was younger, I can sympathize with the folks who have invested tons of dough in a lakeside retreat, only to spend each dinner hour inundated with 90-mph outboard runs. My point is that it’s not worth risking further restricting legislation for what is basically a 1-2-mph modification.

If you insist on doing it, however, do it right. Most "con-competition" jobs I’ve seen include a provision for closing up the open exhaust for quiet operation. In fact, Land & Sea of New Hampshire (603/329-5645) makes a kit that uses the speedometer pilot tube pressure to open a valve at about 56 mph, so the exhaust outlet stays closed at slower speeds. The kit is relatively inexpensive, although it requires expertise to be correctly and attractively installed. Most just opt for the less expensive "manual block-off" method. On OMCs and Yamahas, the holes are drilled in the gearcase between the upper and lower anti-ventilation plates. On Mercury outboards, holes are drilled in the midsection, either on the rear flat area above the gearcase or just under the upper anti-ventilation plate. Take the gearcase off to be sure about the location. It’s relatively easy to plug the holes, either by fabricating block-off plates or by simply threading the holes to accept pipe plugs. Either way, the noise level increase is quite substantial, so be prepared for reactions? You may or may not see a measurable increase in the speedometer. Many times, the gain realized is a small increase in punch, with a large increase in "seat of the pants" speed, largely due to the noise increase!

—John Tiger
Outboard Tech Editor

[Markus]

I have one and I like it. It did not fit the Yamaha too well though. Some drilling and tapping, new screws and some epoxy did the job, though.