Uprating a 4-cylinder turbo-diesel engine

[Paulista]

Consider the following:

1. Manufacturer XYZ markets a 4-cylinder after-cooled turbo-diesel as well as a 6-cylinder after-cooled turbo-diesel, both for the truck market.

These engines share a (near) identical design, with all major parts interchangable, excepting of course, fuel-injection pump, inkectors, turbo, cam, crankshaft etc.

The 4-cylinder is rated at 145 HP/2600 RPM and the 6-cylinder at 210-HP/2600 RPM, which does justice to the previous para°.

2. Mariniser ABC uprates the 6-cylinder to 370 HP/2800 RPM, whence it is known that:

a. The heads, pistons, con-rods, cam, crankshaft and compression ratio are the same as for the OEM factory engine;

b. The turbo is replaced by a larger off-the-shelf turbo;

c. Ditto injectors and fuel-injection pump, with calibration data and specs available for both these from an injection shop.

QUESTION: Is there enough data to make an intelligent guess as how the 4-cylinder version could be prepared to churn out around 250 HP/2800 RPM ?

 

[Fabrico]

I would factor displacement into the assumption.

 

[Metalguy]

Sure sounds like it to me, but crankshaft vibration could be a big factor.

 

[ivymike]

...with the 6-cyl being worse in that regard?

 

[Metalguy]

Not if it's an inline 6--perfect primary balance. Look at most of the big highway truck diesels--6 cyl. inline.

 

[Paulista]

Much obliged for the feedback, Fabrico, Ivymike and Metalguy

The OEM 4-cylinder 150 HP/2600 RPM has a counter-rotating mass geared to the crankshaft to mitigate vibrations. This is not a particularly noisy or rickety-rick engine.

Would this balance be affected if this engine were uprated to 250 HP ?

To select a turbo for the intended 250 HP 4-cylinder engine, would it be permissible to, say, scale down the compressor flow-rate of the 370 HP 6-cylinder by 4/6 and then look for a turbo that fits the bill at the same boost levels under varying turbo RPM ?

Similarly, could the overall flow-rate requirement of the fuel-injection pump be also scaled accordingly, that is multiplied by a factor 4/6 ?

For a given RPM, would injection duration (milliseconds) for a 4-cylinder be longer than for a 6-cylinder ?

In principle, could the injectors for the intended 4-cylinder 250 HP engine be the same (or nearly so) as those used on the 6-cylinder 370 HP version ?

 

[ivymike]

6--perfect primary balance. oh, you meant engine vibration. I thought you were talking about crankshaft (torsional) vibration, which is usually a bigger concern on an uprate than balance-related vibration (unless you swap Al for Steel pistons).

Would this balance be affected if this engine were uprated to 250 HP ?
Uprating won't affect your component inertia, based on your stated aim of not changing the rotating or reciprocating assemblies, so it won't impact engine balance. You'll have increased torque recoil to worry about.

 

[Fabrico]

Aside from horsepower, you are also getting into how the engine will run. Turbo sizing and fuel timing can greatly affect throttle response. This may or may not be important to your application.

I would question the counter-vibration component. Keep in mind that it is doing a job and not just going along for the ride. It may work fine, and at the same time may self destruct. At the very least, it would likely have a much shorter lifespan.

In addition to RPM, bore/stroke ratios should be considered in flow rate, duration, and timing calculation. The HP increase is a sizable one. Engine life will not be the same. It would not be unrealistic to downgrade the percentage of expected life by at least as much as the percentage increase in horsepower. Like the saying goes; There's no substitute for cubic inches.