Water level

[jw.]

A question for you open exhaust boys....I like quiet but there's not too much distance between the inside of me turbo and the top of the water in the exhaust and I'd like piece of mind. So, I can either lift the turbo or stick the exhaust straight out of the back, which seems easier. But how noisey is the direct method? And, what happens if a big gloopy wave slops up the transom?

[Jon Fuller]

Jeff, My exhausts exit the boat after approximately 12" of 5" pipe from the turbo. They're not what i'd call noisy, certainly not compared to the straight thru' systems on N-A petrol motors, just a kinda muted V-8 sound in my case + big whistle, although i'm sure it must vary from motah to motah and turbo type ect.

you can see from this pic that my exhaust tips are level with the water line, not ideal, and I have some fairly elaborate mechanical flappers to stop any surge up the pipe when they're not running.

I'm still nervous tho', so have some rubber caps that I fit when moored if i'm in an area where i'm likely to get wash running into the transom. Better safe than sorry I reckon.

[MrRob]

what kind of power do you have Jon?

[Jon Fuller]

325s

[jw.]

Originally posted by Jon Fuller
I'm still nervous tho', so have some rubber caps that I fit when moored if i'm in an area where i'm likely to get wash running into the transom. Better safe than sorry I reckon.

Thanks for that, Jon. Food for thought.

[glen76]

what bout if ur kill cord was pulled at any sorta speed or an emergency stop was needed??

surely some sort of swan neck or somet would eliminate that wouldnt it, i know of one v8 written off after a kill cord pulled at 30mph and water went up the standard outdrive exhaust outlets!

[SplitPin]

Originally posted by Jon Fuller
Jeff, My exhausts exit the boat after approximately 12" of 5" pipe from the turbo. They're not what i'd call noisy, certainly not compared to the straight thru' systems on N-A petrol motors, just a kinda muted V-8 sound in my case + big whistle, although i'm sure it must vary from motah to motah and turbo type ect.

you can see from this pic that my exhaust tips are level with the water line, not ideal, and I have some fairly elaborate mechanical flappers to stop any surge up the pipe when they're not running.

I'm still nervous tho', so have some rubber caps that I fit when moored if i'm in an area where i'm likely to get wash running into the transom. Better safe than sorry I reckon.

A TurboCharger in the way that it works acts as a silencer! That is why on most cars, a turbo engine usually only has a exhaust tailbox and no intermediate box.

[Jon Fuller]

Originally posted by glen76
what bout if ur kill cord was pulled at any sorta speed or an emergency stop was needed??

surely some sort of swan neck or somet would eliminate that wouldnt it, i know of one v8 written off after a kill cord pulled at 30mph and water went up the standard outdrive exhaust outlets!

Pulling the kill cord is certainly a problem, but that aint limited to just boats like mine or JWs, any 4 stroke motor will do a load of sucking back if it's switched off at high rpm, and You'd need dry exhausts to guarantee avoiding water entering the exhaust ports.

As long as the motor keeps running, shutting the throttle at speed doesn't seem to be a problem.

[Jon Fuller]

Originally posted by SplitPin
A TurboCharger in the way that it works acts as a silencer! That is why on most cars, a turbo engine usually only has a exhaust tailbox and no intermediate box.

The turbo is the highest point on my exhaust system, my worry has always been that if water did get back up to the turbo, it's then down hill all the way to the cylinders

[Matt]

Stutting?

[Jon Fuller]

see what I mean!

[Jon Fuller]

Originally posted by Matt
Stutting?

picky git!

[jw.]

The decision has been made to blank the original Volvo exhaust and route an alternative through the transom. It's not possible to take a 90° bend from the turbo directly out the back because of the wing engine and its bracket at that side. The plan is to take a 180° up and over the turbo as a dry pipe, lagged, and then a 90° as the water injection nozzle. The nozzle will clamp to the dry pipe to allow adjustment of the angle if necessary and also if/when there is corrosion only that section need be replaced.

Now, is it best to have a transom termination and an inboard rubber section or a rigid pipe through the transom with a diaphragm seal (transom/pipe) on the outside?

Pic below for info. Any and all comments/ideas are welcome before I put a big ole in the boat.

Ta.

[Jon Fuller]

Jeff, personally, I would go for a S/S exhaust tip, with internal 'flapper' and maybe an additional external rubber 'Salisbury' type rubber flapper, just for good measure. This will give you a tail inside the transom about 2 inches long for a flexi hose to join to your wet bend.

Exhaust tips with reliable, mechanical flappers are available from people like Stainless marine, not cheap, but to be honest, by the time you've pissed about mekkin it yourself, you'll spend a pretty penny anyway.

Here's their kit:

http://www.stainlessmarine.com/exhaust1.html

And here's a firm that do the high temp silicon hose for ya wet bend to tip connection, with a nice 'bulge' section to allow some movement without stressing the tip or inner pipework: (I used trident on mine)

http://www.tridentmarine.com/stage/wetex_elbows.htm

Just out of interest/noseyness, why are ditching the 'through drive' exhaust?

[Rockey]

j/w will be intrested to no if you get any extra performance with the straight though system ?









ps thanks for ava jf

[jw.]

Originally posted by Jon Fuller
Just out of interest/noseyness, why are ditching the 'through drive' exhaust?

Thanks for all that, Jon.

The water level in the pipe is less than 50mm below the turbo when the boat is at rest. I just feel it's vulnerable if at anchor and bobbing about. Especially so if it had water aboard or I filled it accidentally when under way and the motor stopped.

I've toyed with a riser but it would be difficult and still only give about 100mm extra safety. That was partly the enquiry the other week about mounting the turbo upside down. It would give extra height but a lot of crossover plumbing. I also considered mounting the turbo vertically down on an elbow and simply extending the down pipe but there is still the inlet plumbing, limited gain in height and I'd need to remount the header tank to ensure the turbo stayed full of cooling water.

Having an outlet behind the transom which I could be sure was properly closed if I left the boat on a mooring would give me piece of mind. There is also the condensation which must occur inside the turbo and exhaust manifold and can't be good for the engine in the long term.

I'd thought about extending the exhaust with a hypalon trunk angled downward, just like an elephant trunk bailer, with the last 100mm or so made with it's edges joined face to face so it layed flat closed when the engine is stopped. My thinking for this was to move the exhaust away from the transom to prevent backdraught fumes and just generally keep the crud away from the boat.

Rockey, yeh, it will be interesting to see what the electronic fuel management makes of it.

[Jon Fuller]

Originally posted by jw.
I'd thought about extending the exhaust with a hypalon trunk angled downward, just like an elephant trunk bailer,

Scorpion do exactly that with the ten metre cabin rib (and others i'm sure) when fitted with the Yanmar 315's/through transom exhaust.

[jw.]

Originally posted by Jon Fuller
Scorpion do exactly that with the ten metre cabin rib..

Great minds etc....

Been browsing Stainlessmarine's site. Those Yanmar risers look just about right!

[Jon Fuller]

The Scorpion solution.

[jw.]

Oo, ta. Pretty much as I'd planned it.

It's interesting to see they're keeping those Bravo drives cool.

On the latest Volvo DPR drives, they've changed the oil spec from 75w90 to 75w140. They must have come across a problem or two.