6BTA 5.9 370 hp (How to test exhaust pressure)

[fromhold]

Im looking for info on how to test to see if my exhaust pressure is correct and that I am not having back pressure issues.

I have Twin Cummins 6bta 5.9 370 hp engines.

Boat is a 1989 Atlantic Express. Boat was I believe originally gas powered. At some point during its ownership it was repowered with Cummins 6bta 5.9 370 hp engines and the exhaust system was corrected to accommodate the engines, however I don’t know how or if it meets the needs of these engines.

The outside air intake was definitely inadequate and I am currently adding intake vents to bring me up to spec.

Stock exhaust riser with 5 ” outlets
Main wet exhaust hose going back to muffler and out stern of boat is 5″ diameter hose.
Each run has two 5 ” 90 degree elbows due to restraints of having to go around fuel tanks to continue to stern of boat. Its 5″ hose going into the muffler and out of the muffler to the external exhaust outlets however
The diameter on the external exhaust outlets measure 4.5 inches in diameter.

When fully loaded with fuel and gear these outlets are partially under water until planning then they rise out of the water and water flow is strong.

Engines maintain 180 degree temp and the pyrometer gauges read in normal operation temps when cruising at 2500 rpm.

Topic

[fromhold]

email

I sent and email from [email protected]

[34atlantic]

atlantic express

I wanted to chat with you about a few things I have a 1989 atlantic that I am in the process of repowering with 6bta 370hp can you email me [email protected] so I can give you my number. I tried to send the info in messenger but you are right it is not working

[Rob Schepis]

There was no “ramping up” from 355 to 370. 355 is the real hp, 370 was a metric marketing hp that looked good in brochures and at boat shows when comparing to the competition’s engines. Yanmar was big on this when the popular 6LP went from 300 to 315 and it’s big brother the 6LY from 350 to 370.

Yes the SMX 160 tstat flows more coolant. It also keeps the engine that much further from an overheat so that if things start to climb a diligent operator has more time to react.

That turbo looks good.

1 user thanked author for this post.

Tony Athens

[fromhold]

Continuing this thread

After having these conversations about my exhaust design and possibly being at or under the 12 inch minimum lwl I took apart the wet elbow from the turbo and inspected it. Any comments on the turbo pictures will be helpful.

[fromhold]

Idler oulley

Correction to previous statement
I can do idler pulleys I just need to remove sea strainers to gain the room I need so I will buy them and do that upgrade in the next couple weeks

[fromhold]

Propping

That’s where it’s a little confusing for me. What do you mean exactly by propping for 355 hp at 3150 not 370 for 3000.
I understand that they are 355 hp ramped up to 370 but not sure how exactly since I’m new to the Diesel world. I need a little insight on what you mean.

Doesn’t according to spec the 370 hp have to make 3125 at WOT?

I read about about the SMX 160 but how a little confused. If the boat has a 180 thermostat and runs at 180 temp. Does the 160 simply mean the thermostat opens sooner to allow coolant to run earlier?

The idler pulley I also read about but that would require me to pull the engines. In the article I see that they are drilling into the center of the pulley. I cannot do that the way my engines are set in the engine room there is not enough space between the bulkhead. What would the idler pulley change accomplish?

If I can understand this stuff better I can surely get it done.

[Rob Schepis]

Remember for propping it’s 355bhp @ 3,150rpm, not 370 @ 3,000

It sounds like you like to get up and go. You’ve done some good upgrades so I am surprised you have not switched out the stats to the SMX 160’s? Idler pulley upgrade and keeping an eye on that serp belt and all that spins up front on the engine is super important.

[fromhold]

Height

I’ll measure again to make sure but I’m definitely at 12 inches or more. The motors sit high on the rails plus motor mounts.

Not to get off the subject

When I run 2500 rpm cruise speed my temps are 180 and my pyrometers are at 900. My speed is 22-24 knots. I’m sure once I get props dialed in some things will improve.

Originally my boat was surveyed with a weight of 15,500 lbs. The props were stamped at 21dx23.25p. I recently weighed my boat loaded on a new lift scale at 19,500. I’m talking with a prop guy now to see what I need. I’m not making any black smoke whatsoever. I don’t make any smoke from running out of the bay at 1000 rpm to full plan and cruise speed. Exhaust is clean but I’m not making Wot rpm.

I also removed the fuel distribution blocks and put in all new fuel lines with push on fittings as per Tony. I’ve done a lot so far and contrite to make changes.

I just really want to make sure my exhaust is good.

I just addressed an outside air intake issue too. I had only 120 square inches of air intake to engine room. I am in the process of adding another 180 square inches to get to the 300 I need

[Rob Schepis]

You have done some other real good stuff there…

fromhold wrote:

Can you tell me how I would measure or determine that the wet elbows are in position not to cause seawater to get back to exhaust at turbo? I’m trying to do all I can to make it correct.

Click on the link in my post and see CARDINAL RULE #1.

[fromhold]

Exhaust

I’m just really trying to make sure that all is right with these motors after reading all of the things here on the forums and Tony’s tips.
A year ago both long blocks were replaced one purchased from Cummins in Kearny NJ and one from Tony at Seaboard. Everything was overhauled and checked. New Turbos, fuel injectors, new fuel lines, new smx double double filtration, after coolers and heat exchangers serviced, new exhaust gaskets And yes the wet elbows were inspected and in good shape. I went a little heavy on paint when cleaning everything up. I did other upgrades based on Tony’s advice. Removed heater grid and relay, added wolverine oil pan heaters etc

WOT fully loaded is 2800 but that is a prop issue I’m having reconditioned. My wot no load is 3300 rpm. I had tachs adjusted for accuracy with two photo tachs to ensure I was correct

I’m not familiar with risers and what I would need. The wet elbows are pretty close to the hatch top. Can you tell me how I would measure or determine that the wet elbows are in position not to cause seawater to get back to exhaust at turbo? I’m trying to do all I can to make it correct.

[Rob Schepis]

Yes 6″ at the elbow and yes on the test port. That’s where a test gauge would go. Why do you feel the need?

What rpms is she hitting WOT when the boat is all fueled up and loaded heavy?

That exhaust looks scary as to no riser and the fact that the elbows exteriors have been painted. Those mixers deteriorate from the inside out. Here’s an example – pristine exterior, failing interior.

Have you ever pulled the mixers and inspected the interiors of the mixers?
And the condition of the turbo outlets for signs of a seawater damage?

Have you ever measured the spillover height? (loaded water line to bottom of turbo outlet) My guess is about 8″ or so..

https://www.sbmar.com/articles/designing-a-marine-exhaust-system/

[fromhold]

Serviceable port

There is a port on the turbo flange that I have a parameter coupling in are you referring to that port

[fromhold]

More pics

Here are some more pic (starboard side)

[fromhold]

Wet elbow

Maybe I’m wrong I believe the hose is 5 inch maybe it is 6. I did replace a 90 degree fiberglass elbow and that was a 5 inch inside diameter

[Rob Schepis]

fromhold wrote:

Stock exhaust riser with 5 ” outlets

Stock riser? Are you referring to the Cummins wet elbow? That takes a 6inch exhaust hose.

Do you have a serviceable test port close to the turbo?

How about some good pictures, especially that this is a gas to diesel repower, no one here but you can see or know exactly what you are dealing with.

[Author]

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