Y-Pipe Covers

[greg82255]

Hello,

Just discovered which Y-pipe I have via another post. I want to add thru-hull exhaust to my boat and would rather not pull the motor to remove the Y-pipe. Are there some kind of caps that can be secured to the two top ends of the Y-pipe so water does not get into the bilge? They would need to be 3" in diameter. I have seen caps for the oval-shaped Y-pipes but not the one I have.

http://www.cpperformance.com/p-12573-y-pipe-insert-caps.aspx

 

[Bondo]

Re: Y-Pipe Covers

Ayuh,... Rubber pipe caps can be found at most plumbing supply stores...

 

[wire2]

Re: Y-Pipe Covers

Capping the Y pipe connections will slow your speed on plane. The flared prop hub will create a vacuum.
The hub face is ~5" diameter, or 15.7 sq inches. 1 ATM is 14.7 psi, so vacuum pull on prop *could* be as much as 168 pounds.
However, the vacuum will be partly broken by the exhaust relief ports sucking in air.

Better to install a Y diverter on each bank to choose open or closed thru hull. That way, some exhaust will always flow through the prop, cancelling the vacuum.

 

[90stingray]

Re: Y-Pipe Covers

I agree... at some point you WILL want it quieter. Having a selectable exhaust is the way to go!

Here's some exhaust if you want to go thru the hull and still be hooked to Y pipe... but not selectable.

http://cgi.ebay.com/ebaymotors/THRU...7245573QQptZBoatQ5fPartsQ5fAccessoriesQ5fGear

 

[greg82255]

Re: Y-Pipe Covers

I have looked at that exact product, but the problem is that the diverters they make do not fit my Y-pipe. Mine has 3-inch circular diameter ends, and those have the oval-shaped 4x2.75" (or something close to that) ends. If there were a diverter that fit then I would definitely use the diverters. Would a standard 3" diameter T-shaped stainless steel pipe work? If not, is there something out there that will?

 

[wire2]

Re: Y-Pipe Covers

I made my own from 3" stainless tube, elbow and straight. Then put a ?" stainless shaft through the thru-hull portion, added a butterfly disc, actuated by a small pnuematic cylinder, powered by manifold vacuum.

 

[gbeltran]

Re: Y-Pipe Covers

Capping the Y pipe connections will slow your speed on plane. The flared prop hub will create a vacuum.
The hub face is ~5" diameter, or 15.7 sq inches. 1 ATM is 14.7 psi, so vacuum pull on prop *could* be as much as 168 pounds.
However, the vacuum will be partly broken by the exhaust relief ports sucking in air.

Better to install a Y diverter on each bank to choose open or closed thru hull. That way, some exhaust will always flow through the prop, cancelling the vacuum.

The exhaust relief ports sucking in air? That requires an explanation. None of this really makes any sense. 5 inch diameter circle has 19.634 square inches of area.

 

[wire2]

Re: Y-Pipe Covers

The exhaust relief ports sucking in air? That requires an explanation. None of this really makes any sense. 5 inch diameter circle has 19.634 square inches of area.

The prop is designed to draw exhaust from the engine at speed. It can/does by creating a vacuum in the water at the prop. The flare on most props enhances the effect.
Even with some restrictive bottlenecks, it flows virtually as well as large diameter thru-hull pipes. The only real difference is sound level.

The exhaust passage is continuous, from the Y pipes, through the transom, into the outdrive, past the relief ports, down the leg and out the prop.

If the Y pipe is blocked off, the prop will still create a vacuum at speed. On plane, the relief ports are out of the water, so some air will be drawn in and released from the prop.

You're correct, 5" dia = 19.6 sq", I fat fingered the calculator.

My point still stands, the static vacuum of a blocked Y pipe will pull on the prop, slowing the boat and using more fuel.

 

[greg82255]

Re: Y-Pipe Covers

My point still stands, the static vacuum of a blocked Y pipe will pull on the prop, slowing the boat and using more fuel.

So what you are saying is when I am getting on to plane, it will be a problem, but once I am on plane it will no longer be a problem?

Also, how much did it cost for all the materials you used to make that diverter?

 

[gbeltran]

Re: Y-Pipe Covers

I can see the reasoning, but I'm not buying any loss in speed or planing. If there is any low pressure in the water and those exhaust reliefs are open then air will find it's way to the low pressure area, any drag caused by that will be negligable. There is probably just as much drag caused by the vortex behind the prop when exhaust is going out the hub as when it's capped off.

To the original poster, CP Performance sells caps for Mercruiser, Rex Marine may also sell them.

 

[greg82255]

Re: Y-Pipe Covers

To the original poster, CP Performance sells caps for Mercruiser, Rex Marine may also sell them.

CP Performance sells the oval shaped caps. My Y-pipe has 3" diameter circular ends. I don't think they will work on mine. That's why I started this thread, to see if anyone makes 3" circular Y-pipe caps.

 

[gbeltran]

Re: Y-Pipe Covers

Sorry, didn't see that part in your original post. If it's just a 3 inch hole, there is no reason something from home depot, lowes, or your favorite hardware store wont work.

 

[wire2]

Re: Y-Pipe Covers

So what you are saying is when I am getting on to plane, it will be a problem, but once I am on plane it will no longer be a problem?

Also, how much did it cost for all the materials you used to make that diverter?

I think you will have noticeable drag at all times on plane. Do us all a favor; when you have the proper caps, make a wot run in 2 directions, record the max speed. Now temporarily remove the caps and make a similar run, 2 directions. It will prove me right or wrong, I have no problem with either one.

As I recall, a 3" ss tube 90? elbow was ~$30, I got a short bit of straight for $10 from a weld shop. The rod & cylinders I had in the junk box, I made the butterflies from a bit of sheet ss.
It took a few evenings to cut & fit the pieces together, then tig weld them.
They are actually the tail end of the double wall ss headers I made several years earlier.

 

[gbeltran]

Re: Y-Pipe Covers

I don't think I'd remove those caps with the boat in the water. I would look at it this way, no one has ever said "hey, I can plane easier and pick up some speed by getting rid of my thru hull exhaust and run it thru the prop instead."

 

[greg82255]

Re: Y-Pipe Covers

I just winterized the boat so any test I do won't be until next year. If you are still curious then I will do it and add to this thread once the boat is in the water. The material sounds fairly cheap considering how much a silent choice system costs.. but I don't actually have a tig welder, nor do i know how to tig weld. If I bring 2 pieces of SS pipe to a welding shop will they do it for me (assuming I cut the pieces to the right size/shape)?

 

[wire2]

Re: Y-Pipe Covers

I meant for the OP to do it for a trial only. I believe the Y pipe ends are well above the water line when sitting, (in most boats).

Thru hulls are very slightly more free flowing than prop;
with my set up, if I run at 4000 rpm closed, then open the T-H's, the tach goes to 4100. No discernable change in speed. (But it sure sounds good.)

 

[wire2]

Re: Y-Pipe Covers

.... The material sounds fairly cheap considering how much a silent choice system costs.. but I don't actually have a tig welder, nor do i know how to tig weld. If I bring 2 pieces of SS pipe to a welding shop will they do it for me (assuming I cut the pieces to the right size/shape)?

Most shops will, especially if they're not real busy. That's considered a "gravy job", (real easy).
But you'll have to find a shop that does ss tig, not all do. Google "stainless welding (your town)"

Try to make the pieces fit together with almost no gap, can hold it together with masking tape.
The welder will put several small tacks on it to keep it together, remove the tape, then weld all over.

 

[greg82255]

Re: Y-Pipe Covers

Any idea what they would charge me to weld 2 of those pipes? I have no idea how expensive/inexpensive SS welding is.

 

[greg82255]

Re: Y-Pipe Covers

Also, I you mentioned that you put a 1/2" stainless shaft through the pipe and used a butterfly valve disc. How did you seal the 2 holes where the shaft goes through the pipe?

 

[wire2]

Re: Y-Pipe Covers

Any idea what they would charge me to weld 2 of those pipes? I have no idea how expensive/inexpensive SS welding is.

I'm gonna guess less than $200 for both sides. It's easy enough to do with a bit of experience, a tig welder and a bottle of argon. I do it in my basement.
Stop by a shop & ask first.

Also, I you mentioned that you put a 1/2" stainless shaft through the pipe and used a butterfly valve disc. How did you seal the 2 holes where the shaft goes through the pipe?

I welded 7/16" ss nuts on the tube for bushings, then drilled and reamed to ?". I welded a cap over the blind end, cut a groove for an O ring in the shaft for the other end. The butterfly disk keeps it centered.

I should add; I milled a flat on the shaft for the disk, then drilled & tapped for two 8-32 allen head screws. Then made the clamped lever from 16 ga ss sheet.

1 more bit; I found the easiest way to cut the ss tube was with a 3/64" metal cutting disk on a 4?" angle grinder.