Maximum Cummins 6B power without a turbo?

[BoatingBeginner]

Any idea just how much HP I could get from a Cummins 6B without a turbocharger? I just want to keep things as simple as possible, and space is tight overhead...

I understand clamping on a non-standard fuel pump can work wonders...?!

Thanks!

 

[BoatingBeginner]

Are the naturally aspirated 6B not marinised?

 

[TQA]

Any idea just how much HP I could get from a Cummins 6B without a turbocharger? I just want to keep things as simple as possible, and space is tight overhead...

I understand clamping on a non-standard fuel pump can work wonders...?!

Thanks!

If you increase the amount of fuel being injected you get more power at the expense of smoke prodction though.

Assuming your Cummins runs the old style PT pump then you can adjust the maximum fuel delivery pressure from the gear pump by changing buttons within the pump assembly to change maximum fuel delivery pressure.

You don't need a new pump just your old one ' adjusted'.

I used to teach this stuff and as an experiment would increase the fuel supply to a non turbo Ford 6D engine and get a 30% power increase.

However we only did this on a day when local residents were NOT hanging out their washing.

 

[BoatingBeginner]

If you increase the amount of fuel being injected you get more power at the expense of smoke prodction though.

Assuming your Cummins runs the old style PT pump then you can adjust the maximum fuel delivery pressure from the gear pump by changing buttons within the pump assembly to change maximum fuel delivery pressure.

You don't need a new pump just your old one ' adjusted'.

I used to teach this stuff and as an experiment would increase the fuel supply to a non turbo Ford 6D engine and get a 30% power increase.

However we only did this on a day when local residents were NOT hanging out their washing.

Thanks very much for that.

Presumably, the efficiency of a normally-aspirated engine with boosted fuel wouldn't match that of an untweaked turbo-charged version?

Out of pure interest, I wonder how easy they'd be to supercharge...

 

[TQA]

Thanks very much for that.

Presumably, the efficiency of a normally-aspirated engine with boosted fuel wouldn't match that of an untweaked turbo-charged version?

Out of pure interest, I wonder how easy they'd be to supercharge...

The smoke is unburnt or partially fuel so poorer efficiency.

For more power and at least the same efficiency you need the turbo and a change to the fuel pump settings.

But you may need improved cooling as well. You don't get "out for nought".

 

[penfold]

Thanks very much for that.

Presumably, the efficiency of a normally-aspirated engine with boosted fuel wouldn't match that of an untweaked turbo-charged version?

Out of pure interest, I wonder how easy they'd be to supercharge...

Horsepower for horsepower it will be worse; for a given level of tune a turbo engine will be more efficient as it's making use of otherwise waste energy.

Supercharging is less efficient and more expensive than turbocharging; why bother? Especially as turbocharged and turbocharged intercooled versions of the 'B' are readily available. Hell, Cummins are still building what is a modified 'B' and getting 480hp out of it.

 

[Skylark]

Very roughly, a 6 cylinder naturally aspirated diesel engine would develop in the order of 25 to 30 bhp / litre displacement.

A turbocharged and intercooled version would develop approx 50 bhp / litre. (on-highway truck application).

Engine power is always limited by the amount of air (oxygen) available for combustion. Increasing fuel is easy but it requires 15 x its weight of air to burn it all (stoichiometric (when all of the fuel is burned with all of the air) is about 14.5:1).

Power can be increased quite significantly by increasing boost but, again in general, life expectancy (durability) will be reduced. There are many variations of a base engine and they will be rated depending upon the duty cycle. Nominally, the same engine fitted to a work boat will be rated far more conservatively than when installed in a recreational mobo. The work boat will run about 2,000 hours per year, the mobo about 100 hours.

Turbo overall efficiency is about 50%. This is made up of the compressor stage, turbine stage and mechanical (bearings etc). Superchargers generally come in two versions, with and without internal compression. The Roots type has low efficency and the screw type is a bit better but can't match the turbo. Because they are both driven mechanically, they can deliver boost at lower engine speeds. Their one advantage. Their low speed torque and low speed transient response "feel" better than a turbo.

The above is a gross simplification and no doubt someone could pick holes in my argument. I spent 20 years working with turbos, matching them to many car, truck, off-highway and marine engine builders.

 

[BoatingBeginner]

Thanks very much for your comments - that's really helpful for me.