DD 8V71T specs. What components went into turning 435 hp to 462 hp in later years?

[Shearerlegal]

I have 8v71TI's spec'd at 435 HP. I found a later model DD brochure for the same engines (7082-3300, 7082-7300) spec'd out at 462 HP. Does anyone know what components Detroit changed to make the extra horsepower in the later version 8v71TI? Both early and late versions list the same N90 injectors. Thanks in advance.

Scott

 

[jim rosenthal]

Interesting question, because you would think that they would put larger injectors in, to get more hp. Maybe they raised the compression or turned up the boost? It's difficult to understand how you could make more power without adding more fuel consumption.

 

[Avenger]

More RPM?

 

[Photolomy]

I was wondering where the 430HP spec comes from. Is that at 2500 RPM?

 

[oscarvan]

More RPM?

Yep.

Only way to get more fuel out of the same injector is more injections per/time.....

Probably (and I'm guessing) needs more cooling and lubrication.

 

[Avenger]

Uh, no.

The injector only pumps just so much per firing cycle. More cycles doesn't change how much fuel the piston sees.

I was referring to horsepower being a function of RPM and that the same engine can make more horsepower simply by increasing it's rated RPM.

 

[Captain Ralph]

The next HP step for my 675/650HP 12V71TIs is injectors and turbos. Then 750/720HP.

HP takes air and fuel, the only way to gain this from the Penski play book is turbo and injectors. The real big HP leap requires cooler air; TI to TA then both.

There were some piston changes to lower the starting compression ratio from the natural to turbo versions. Also changing the blower speed ratio. Other than these, the Penski block is all the same.

More HP equals lower engine life, but I doubt that many of us really pull much of the available HP out of our engines anyway.

For the 12V71T, there are 6 Penski HP tunes; 675/650, 750/720, 800/775, 850/825, 870/840 and 900/870HP.

Before the questions start coming in, the first number 675 is the flywheel HP, the second number 650 is Shaft HP. Most factory package ratings were shaft HP. The sales folk like the bigger numbers so they sell my engine as a 675HP model.

In the OP, you may be taking about the same engine/tune, just different HP ratings before and after the clutch & gear.

 

[oscarvan]

Uh, no.

The injector only pumps just so much per firing cycle. More cycles doesn't change how much fuel the piston sees.

I was referring to horsepower being a function of RPM and that the same engine can make more horsepower simply by increasing it's rated RPM.

That's what I was saying. We are agreeing.

 

[Captain Ralph]

Uh, no.

The injector only pumps just so much per firing cycle. More cycles doesn't change how much fuel the piston sees.

I was referring to horsepower being a function of RPM and that the same engine can make more horsepower simply by increasing it's rated RPM.

Only to a point,, rite before it blows up.

 

[madhatter1]

A great example of this is Cummins 6BT's. I have 260HP @2600. They go up to 315 @2800. Then 355 @ 3000. But all make similar torque across the range. Yes mine are slightly low torque but I can swing bigger props that the higher RPM engines. So great cruise speed. The 315 in a 36 gives about the same numbers as my 34 gets with only a slightly higher fuel burn. Only so much realistic HP capacity for a given displacement. Cubic HP is important in boats traveling uphill everywhere they go.

 

[jim rosenthal]

I recall reading here (can't remember who posted it) that companies that use diesels in truck and heavy equipment do their maintenance by hours of run time and by gallons of fuel consumed- because inorder to make power, you burn fuel, and to make more power, basically you burn more fuel. That also takes more air, and cooling of the intake charge air, and in turn getting rid of all the waste heat that isn't turned into power.... but it seems like essentially to make more horsepower, you have to burn more fuel. Is that true? At least it makes sense to me.

 

[Photolomy]

For the most part, yes. However, power is related to work. What actually gets produced more is energy. How much of that gets converted to work (power) depends on other factors. But within certain limits, the more fuel (and air) you can burn, the more power. Fuel is generally not the issue, it is getting enough air (oxygen) that is the task.

 

[jmooney]

This comment is not exactly about this thread , but Cap Ralph mentioned switching blower speeds. This was recommended to me by RPM Diesel . They said no downside, just more air and less smoke. Has anyone done this ? I didn’t really think that I needed this , so I didn’t pursue the issue.

 

[oscarvan]

Intersting..... how does one do that? New vane wheel with different vanes on it? Or completely different turbo? Do the standard ones have waste gates on them and are producing more than you need anyways?

 

[Avenger]

He means the Roots blower, not the turbocharger. It's a drive gear change.

 

[oscarvan]

He means the Roots blower, not the turbocharger. It's a drive gear change.

Ah, that makes sense. Thanks.

 

[Avenger]

BTW, there's no free lunch. Increasing blower speed costs horsepower. Anybody tells you there's no downside needs to consult with an engineer.

 

[Captain Ralph]

BTW, there's no free lunch. Increasing blower speed costs horsepower. Anybody tells you there's no downside needs to consult with an engineer.

Correct.
Now, if there is a turbo in front of the blower, all bets are off. It is the correct combination of these that work in harmony with another factor, the injector.
Also, don't forget cold air...

All components must work together to ensure the correct fuel / air mix.
There is no back yard Frankensteining here.
It's by the DDC book and usually not shared.

I have my notes that will be buried with me. When I come back riding my DD trike with flames coming out my hair, I may need it..

There are not many sweet mechanical songs in this world, A properly tuned DD is on the top of my list, Then maybe the Philly Harmonic.. Maybe a 12V71TI screaming on playback when I'm planted.

 

[kelpy]

How does one change blower speeds when the center to center dimensions / diameters of the camshaft drive gears, the blower drive gear and the blower drive quill shaft center are fixed?

 

[jim rosenthal]

If anyone's interested, there is a really handsome ALF pumper on BaT right now, featuring an 8v71 DD, a natural, well-restored and just aching for a new home. Former property of the Concord, NC FD. Beautiful old truck.