Turbo Boost?

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Mar 15, 2013 | 08:38 AM

#16

Kjewer1

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Joined: Aug 2009

Posts: 102

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From: MA

Quote:

Originally Posted by 720Deere

Why do people equate boost pressure with horsepower? High pressures do not always equal more power. The volume of air flowing is just as important as the pressure and sometimes high pressure is simply a result of a constrictive intake path.

This is all correct! Technically it's mass flow, but I know that's what you meant. Air mass flow and fuel mass flow equals power potential. Injection timing, AFR, etc will determine how much of that HP potential you actually realize. If you can flow more air/fuel mass at less boost pressure, you can make more power. Increased boost pressure is heat, and also increased turbine drive power or shaft power requirement (increased back pressure). Moving more air/fuel at less boost can come from bigger displacement, cams, free flowing manifolds/IC/piping, rpm, bigger turbine, etc.

Displacement is a big factor. As an exmple, I have to run about 45 psi on my 4 banger to run 8s, while a V8 with 3 times the displacement can run more like 15 psi to do the same thing.

This is a more extreme example than the 6.7/6.0 comparison above. If you do the math here you'll see it doesn't add up. That's due to the other factors I mentioned. In this case the 4 bangers are more efficient and run to much higher rpm, so I don't need 3 times the absolute pressure. More like double. But when comparing one diesel engine to another, things aren't going to be this different.

Some of you guys already know all this, but hopefully someone that doesn't finds it interesting.

Mar 15, 2013 | 08:49 AM

#17

Fear no Hill

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Joined: Feb 2012

Posts: 50

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From: NW Oregon

This is a very good and interesting discussion. I was comparing boost and power of my previous truck to the new one. I see there's more dots to connect than just turbo boost.

Good stuff, thanks

Doug

Mar 15, 2013 | 10:26 AM

#18

parkland

Lead Driver

Joined: Jan 2006

Posts: 6,267

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Quote:

Originally Posted by Fear no Hill

20-23 psi just seems low for a 400hp engine, maybe not. I'll reserve judgement on the power of these engines until I get a few towing trips under my belt.

Another question - has anyone experienced a bit of shuddering when starting from a stop under load? I had this happen a few times and don't know if it's a concern or not. Once I got over 10-15 mph it went away.

Regards, Doug

There are a few reasons why the 6.7 runs lower boost than for EG a 6.4 powerstroke.

Biggest reason is probably the EGR. Because they use urea, they run less EGR into the intake. Less EGR means more fresh air in the mix, so it doesn't need to force as much air into the intake.

And then, also because of urea injection, I believe they are able to use a better injection timing and pattern, thus burning more with efficiency in mind rather than emissions.

So basically, I think just the injection strategy is optimized to burn well for power, where on the 6.4, a lot of the injection strategy was for emissions.

If you take an older single shot engine, (EG cummins mechanical 5.9 ...DT international mechanical engines ...), you'd need a lot more than 20 lbs to make 400 HP, but the new electronic engines with piezo injectors can make better use of the air by changing timing on the fly, and using multiple injections.

My 6.4 with spartan 310 tune can make a whack of power with 20 lbs of boost, but the EGR is disabled and the programming doesn't push the turbochargers as hard to make boost.