Exhaust and intake for 6BT's

[Carl]

So I went into this with the understanding I needed to go minimum of 5" exhaust and go up to 1-1/2" on the raw water intakes.

I have 4" exhaust
I have 1-1/4 on the raw water, which I did all new with crash valves a few years ago.


I picked up an installation manual along with a service manual for the 6BT's off E-bay.
I figured it's nice to know what is required from manufacturer.

So giving it a read the manual says

Minimum recommended Exhaust size for 6BT is 4"
Minimum recommended water intake for 6BT is 1-1/4"

That has me thinking maybe leave as is, make sure the exhaust pressure where its supposed to be when we sea trial and done.
I think 3" or 1-1/2psi max pressure was the number.
Make sure motor temp is where it needs to be.


The comes my conscience... do it once, do it right.
Bigger is better...

...yeah, maybe, but what do I get for a bigger expense?

So, anyone have a clue what can I expect to achieve going up to 5" exhaust.
Bob Lico says 6", but that is 6BTA's


I hear better performance, better for the engine, better economy...got it.
Can anyone pin any kind of number on any of those betters?


oh boy....here comes the yada yada...

thinking if I was pushing 330hp motors, a 1% increase is 3.3hp, two motors is 6.6hp....its something, maybe 1/4 knt
but on 210's, 1% is 2.1hp...two motors is 4.2 extra hp...yeah its something, but is it really.


just wondering in my planning stages.

I don't want to cheap out, but no need to toss money and time away either...


Any thoughts, idea's or

[John F.]

Carl

Take a look at Walter’s old posts. He wrote on at least one occasion that he went to the Cummins 6bts because he was able to keep his 4” exhausts and I think his 1 3/8” shafts. If Walter was ok with it and Cummins is ok with it, I’d be ok with it. You’ll be spending enough.

John

[Tony Meola]

Carl

I will give you one depends.

If you are going to run your exhaust in the outside alley rather than the shaft alley, and you do not exit straight out, but rather put a bend in the exhaust pipe lets say two 45's so that you keep the exit point in the same position on the transom, you might then need to go to 5. If you remember JJ who used to be on here, he put in the 270's and he did that and he would up going to 6 inch exhaust due to the back pressure created by the bend.

As a comparison I have the 270's and I am using 5 inch exhaust running down the shaft alley. My 31 came through with 5 inch exhaust.

The difference between the 270 and what you are installing are the fuel pumps, Turbo and I believe injectors.

If you are running down the shaft alley, I would use the 4 inch they recommend. If you ever change engines again (cough cough) then worry about it. You will not notice the performance difference going to 5.

Remember Keep it simple.

For peace of mind reach out for Bruce.

[Carl]

Carl

Take a look at Walter’s old posts. He wrote on at least one occasion that he went to the Cummins 6bts because he was able to keep his 4” exhausts and I think his 1 3/8” shafts. If Walter was ok with it and Cummins is ok with it, I’d be ok with it. You’ll be spending enough.

John

Thanks John. I have been reading over the old posts. I see many many times where Capt Walter said he was able to use the stock exhaust...it was one of the big reasons for not re powering with Chrysler gassers as they wanted larger exhaust and the 210 Cummins did not. Only problem is I have yet to confirm the stock size exhaust Walter had to begin with. Nor did I see any mention as to whether he ran mufflers or straight pipe. I am leaning toward mufflers which might mandate going up a size.



Tony- Yes I'd like to keep simple and do it once. If I am having to upgrade, I don't mind going a bit further so if down th eraod more hp is wanted the setup can handle it...but if items work as is I am good with leaving. Exhaust may or may not be one of those things.

From what I am picking up on is 4" works, but may not with mufflers unless I bleed off some water from the exhaust.

[1962 31]

I run 4 inch with my 210s at dead 650rpm idle its loud come up a little in the rpms and its hardly noticeable at cruise you hear the engines over the exhaust sound
and im stock 1 1/4 intake also no problems

[Carl]

I run 4 inch with my 210s at dead 650rpm idle its loud come up a little in the rpms and its hardly noticeable at cruise you hear the engines over the exhaust sound
and im stock 1 1/4 intake also no problems

Thanks, I remember you saying that is what you were running. I assumed its straight no mufflers. Any idea what your back pressure is?
The 1-1/4" intakes I am going to follow your lead and stick with those. Could change out in short time if I found an issue wit cooling.


I know my wife isn't going to be a fan of loud when trolling at idle for extended periods...and I tend to do lots of trolling, inshore and off.
Running is running and I know I will have to do sound insulation again. It was loud sitting over the gas motors.

It would be great to leave exhaust as is...

[1962 31]

pm me your number ill text some video of it idling she probably wont like it lol