6BTA exhaust question

[Mikey]

As I start to install in my B31 the pieces of exhaust system that came with the 6BTA's I got out of another B31 I have come upon a question. It appears that part of the exhaust water from the engines goes directly into the exhaust just south of the turbo and part goes through a T and is routed to a pipe that reenters the exhaust downstream from the mufflers I think. This appears to be the correct routing having taken my clues from the marks on the fiberglass and rubber hose pipes and mufflers as I reassemble them.
Does this sound correct and why is part of the water routed so. Is this because there is more than the upper end can consume?
Bet Bruce or Vic can answer this.
Thanks Guys
Mikey

[In Memory of Vicroy]

Mikey - don't have a clue why they set it up that way. On mine all the water goes into the exhaust elbow right downstream of the turbo. The only reason I can thank of is that the water injection holes in the elbow were partially clogged and the bypass was to increase water flow. The setup you describe could perhaps be dangerous if the holes stopped up and cut off the water flow to cool the elbow and everything downstream to it until the "T-ed" water entered the exhaust pipe. With it all going thru the one inlet on top of the elbow, if they clog up the engine will start to overheat and give you some warning.

UV

[Mikey]

Weird, huh, Vic. Thought it might have something to do with the fact mine are 300's. I knew from crawling around in the bowels of A.J. that they were different. Maybe I should ask Tony Athens.
THanks Mikey

[In Memory of Vicroy]

Yeah, I'd do that, he will know. I don't think I've ever seen any B series Cummins rigged like that. Did you look at your elbows real carefully? There are about 3 different ones made from different materials. The cupro-nickel ones are the most expensive and seem to last the best. I lucked up and have those and since I'm usually in fresh water, they will probably outlast me.

UV

[glculp]

On my b series engines the back pressure was too high. In order to get the backpressure within tolerances I had to divert exhaust water from the exhaust. Mine has a Tee in it with a ball valve to adjust the back pressure to almost any setting that you want, I then dumped the water out the transom. This may be what you have.

[Mikey]

GL
How do it know? How do you know the back pressure of the exhaust water at the pipe? What were the symptoms and how do you adjust the ball valve?
THanks
Mikey

[glculp]

Mikey,My engines were brand new and cummings sent a mechanic to do the intial start up. He was the one that discovered the high back pressure, it was 5.5 on one engine and 6 and change on the other. Cummings recomends only 3.0. He told me it was the mufflers, I said no way, he said I would have to take them out, I said no way. He left but did not sign off on the back pressure. I consulted the muffler company, after all I had the custom built for my Bahia Mar. After several weeks of back and forth he finally contacted Cummings and they yes we know about this problem and here is what you have to do, bleed water off at the back side of the exhaust until you get the desired results. I had to buy a manometer and then scrounge enough mercury to fill it. There is a plug at the end of the exhaust and through some creative plumbing we hooked the meter up. We already had the bleed off in front of the meter, we ran the engines under load and gradually opened the valve to acheive a 1.5 to 2.0 pressure. Cummings said there was too much raw water going through the engine because the pump was too big.

[In Memory of Vicroy]

Gail - that is sure interesting info. For those of you that don't know him, Gail Culp is the proud owner of the rocket ship "Fun Ticket" that Garry Jordan has been talking about, the pretty green Bahia.

I never really thought about the water flow affecting the back pressure, but guess on the hi hp versions of the 6B's its a legitimate issue. So Mikey, there is your answer from a couple of guys that know. Learn something every day here......

UV

[Rawleigh]

On my 440 Chryslers with a 3" exhaust I bleed about half of the raw water off thru an outlet in the side of the hull next to the engine block for that very reason. It has the added advantage that you know immediately upon start up that the raw water pump is working properly.

[In Memory Walter K]

When I had 440's and were going to get new ones, Chrysler wouldn't honor their guarantee unless I enlarged my exhaust system. Said the aft valves were burning out without the larger system. At that time, the cost of their engines with the changed exhaust system added on, came to the price of the 6BT's that would accept the exhaust system sans the mufflers. Best boating decision I ever made. Walter

[Mikey]

O.K. Guys, if the mufflers are causing the problem can I run with straight pipes and still hear myself think? Also do straight pipes (five inch) reduce the back pressure too much?
Mikey

[Capt. Mike Holmes]

Mikey, I have 5" straight exhausts. The 6BT's are not that loud, I don't consider the noise excessive. I had mufflers, took them off, can't tell the difference. 5" is enough, just make sure they are as straight as possible. Any sharp bends or excessive elbows will cause back pressure problems. I know this from experience.

[JP Dalik]

Mike,
I'm going moving away from the 6" exhaust with muffler to a straight 6" out the back this fall. The reason is to move the exhaust outboard and allow room for in deck fish boxes. I've been on a C series straight pipe down east boat and the noise is next to nothing with no muffler.
We have enough racket coming out of the engine boxes that the exhaust note is bearly audible.
The one thing I would recommend is a surge tube. Since the pipe is straignt and there is no baffled exhaust to block incoming water a surge tube is a way of allowing water to flow up the exhaust without it coming into the open exhaust valves when at anchor in large seas or med-mored into the tide.

[Capt. Mike Holmes]

JP, I agree , but haven't used surge tubes, for a couple of reasons. I don't do that type of anchoring, is the main one. I am planning to add exhaust flappers, instead of surge tubes, because, to be honest, I don't think the tubes would hold all that much water before allowing it go go to the engines anyway. I really don't think the danger is as great with the engine and exhaust elbow well above the waterline as in a larger boat with engine mounted lower than the waterline. Thanks for the input. I listened to one of my engines running in the driveway on a water hose with no exhaust at all when we first lit them up, and it was quieter than a Ford diesel van parked next to it with a muffler!

[Mikey]

Gang
I intend to use the flapper like Capt Mike and may go to 6" pipes. Mike, you said you started your engines with a garden hose for the cooling. Assume you didn't leave them running long. I want to do the same thing since they haven't been fired off in four years, but was told (by a questionable source) that this was insufficient water. Shouldn't think so if I just get them running and don't belabor the point.
Now for one more question. Since we sanded off all memory of a water line and painted below the old one I have no idea where it will fall. Not a problem, we can put it in the water with a full fuel tank and get a clue. BUT, how do I bore the transom for the exhaust pipes? Shouldn't they be about half submerged? Should I go to the expense of putting her in the water to get an accurate line or just assume about an inch to two inches below the old line, using the old exhaust hole for reference. Here's the crux of the problem, I am repowering from 454's to Cummins 6BTA's and a Cabrera fuel tank (bigger), so she will sit lower, but how much?
Thanks, guys
Mikey

[In Memory Walter K]

Mikey, Normally the chines should just kiss the water. I put on a heavy teak deck and 6bt's and with a full tank my chines are half submerged which is a pain in the ass because my boot stripe which covers my chine grows grass on it's west facing side during the summer. If you use your old holes as guides and enlarge above them, I can't see you doing it in any other position. If I had my choice now, I'd have moved mine up. Walter

[Bruce]

mikey,
I would use surge tubes on your application with no mufflers. They do work.
Second if I were doing the job you are in adding a larger fuel tank, I would put the boat in the water to reference the water line with a full tank, deck and engine boxes laid in the boat.

You don't want them under water.

[Mikey]

Bruce,
Thanks, I think.
I was hoping that wouldn't be necessary, but considering all that I am doing it's a small price.
Walt, Thanks.
I didn't want the boot stripe under water and that was the point. So Guys, looks like a short dunk and then the real thing.

Now, what about a short run of 6BTA's with a garden hose for cooling. O.K?
Mikey

[In Memory of Vicroy]

Sure the garden hose will work, just make sure it's on the intake side of the raw water pump or the impeller will burn up in 22.7 seconds flat. Just don't run it much more than an idle - those raw water pumps put out about 5 times what a garden hose does.

UV

[Mikey]

Vic,
Thanks, got the message.
Mikey

[Capt. Mike Holmes]

Mikey, yesterday I found a pair of flappers for 5 - 6" exhausts in a boat resale shop down here, new in the bag, for $10/each. Sorry, they only had two. I agree with Bruce about splashing the boat to make sure of the waterline. We took some weight off mine during the repower, but like Walter I added a teak deck, and some other junk. My waterline with 200 gallons of fuel on board has the chines at the stern underwater, as Walter described. I raised the exhaust exits through the transom while enlarging the holes from 4", but the pipes are still half submerged with a full load. This is only an issue when idling or running slow, of course - on plane, no water touches the transom area. I ran fiberglass pipe through the transom and glassed it in, then added extensions to get the exhausts to the edge of the transom platform. Keeps water from spraying all over the covering boards and into the cockpit, helps with the "station wagon" effect sucking exhaust fumes into the cockpit. Also, I like to be able to check visually for water coming out my exhaust pipes occasionally.

There is a 1962 express for sale on Yachtworld, black hull with red bootstripe (looks a lot like mine!). They have done some interesting things with the shelf behind the windshield - turning the area into a long electronics box. Worth looking at.

[Capt. Mike Holmes]

Mickey, remembered a few things. If you go with 3" exhausts, I have a couple of the 5" rubber elbows for you. They are left over from when I straightened my exhausts. I did use one on the port engine, to get the exhaust headed towards the outboard side. I recommend using 45's instead of 90's where it is feasible, to make a more gradual turn - less back pressure. It is possible to turn the Cummin's turbo housings "upside down" to get the exhaust on the side you want it, but the engine box space on a 31 is so limited that it would not be possible to have the port exhaust come off the inboard side without remote mounting the air cleaner. Normal setup is to have the turbo on the right of the engine, from the back facing forward, air cleaner on the left. I installed the exhaust flappers, and discovered another advantage to using them. They deflect the spray from the exhaust downward, keeping it from coming up into the boat, as I mentioned in my earlier post.

[Capt. Mike Holmes]

Excuse me, I should have said the turbo (and air cleaner) is on the left, the exhaust elbow on the right! Take a look at the express on the jetty rocks in the photo posted here yesterday. Has a more modern windshield - a venturi type angled forward. Nice tower setup, also. Seems I remember when that happened the guy was thinkiing of parting it out, - I'd like to have had that tower.

[Capt. Mike Holmes]

One more thing, on the bootstripe, I raised mine higher, now have bottom paint over the chines. Bottstripe is no longer under water.

[Mikey]

Capt Mike,
Thanks for the replies. There are two solutions to the cramped space for the exhaust elbows. Turn the turbo over or use a remote dry exhaust that crossed over the engine to make the outboard connection. Like the latter but the freight is about a grand. The turbo routine I have seen in Key West and am considering doing it. Do you personally know anyone who has done it? Love to talk to someone with the beast in front of them. Thinking about running straight exhaust after reading the above emails. If I do I will probably run 6" overboard. Who's flappers did you steal er buy. Need to do that as well.
GReat hearing from you. Still reading all of your article in Southern. Are you writing dfor anyone else. How is the Black Sheep. A baa-baa-baa-Bertram of course so must be good.
Mikey

[Rawleigh]

Good Lord Mikey, where is it coming from China???

[Bruce]

Mikey,
Here are two pics of the exhaust I did on the last 31/Cummins install. While they are QSB's, the BTA has the same dimensions.
I left them big to let you see detail.
bruce



,

[Mikey]

Bruce,
Nice installation! I will use some of your technique, but my problem is the space between the end of the turbo and the new Cabrera engine boxes. Don't want to hack away at them if possible. I can hear Spanish cursing from here. The exact dimension is not yet known but it is about 5" total.
Also what do you think of this talk of running 6BTA's without mufflers? It would simplify matters but I'm worried about noise. If I opt for the straight pipes and since I have to buy the pipe anyway what about 6" over 5" out the stern? Damn, I am being a nuisance about this but only want to do it once.
Thanks
Mikey

[Mikey]

Rawleigh,
Worse that China . . . California!
Mikey

[Capt. Mike Holmes]

Mikey, yes, a friend of mine with 6BT's in a 36 Trojan turned one turbo over - but he has lot's of room in his engine room. Don't remember which brand the flaps were. I'll look at the bag the next time I go to the boat, probably tomorrow evening. Spent all day with her. Changed fuel filters this morning, then hauled for a pressure wash and to clean the props. Been too long since I did this, never had that many barnacles before. I test ran Saturday, only got 15.7 Knots, 2500 RPM. After grinding all the shellfish off today, I got 25.7 knots at 2800 rpm. I'm happy.

[Bruce]

The water in the exhaust cuts quite a bit of noise and I don't think that the noise without mufflers is annoying.
Besides unless you are super insulating the engine box and surrounding spaces, the BTA series has enough static noise anyway.

[Capt. Mike Holmes]

Bruce, sort of like, you fine me for safety and environmental problems, and I'll cut off your oil. The oil company I work for just reported 2nd quarter earning up 18% over last year, which was up 16% over the year before that - which was a record setting year for profits in itself. Rank and file employee raises rose about 1.5 - 3% each of those years, Where do the money go?

[mike ohlstein]

Bruce,

That high dollar blue hose is so slick, it keeps blowing off the turbo in my truck. Any similar instances on the boats?

[Bruce]

Mike,
I havn't had a problem with that in marine applications.

You might try taking some 30 grit paper and rough up the surface where the hose goes on and use ABA clamps.

I always wipe the hose and surface with denatured alcohol when assembling.

Last resort would be to use some permatex red aviation gasket glue.