Boost/Compression Ratio Calculator

[86 CUCV]

For an IDI (InDirect Injected) diesel to produce clean cold starts with short glow cycle times, and to produce fewer cold start emissions, the CR has to be somewhere at/above 20:1. The precups/prechambers cool the charge on a cold engine. A DI (Direct Injected) diesel (like the current Duramax, Cummins, PSD) starts well cold at a lower CR. So, a higher CR was an IDI cold start compromise.

I did a short tech piece on the Isuzu C240 I-4 2.4L diesel recently. It too is an IDI engine that has 20:1 CR. Its 3.0L DI siblings are, on the other hand, just over 18:1 CR.

Diesel farm tractors with DI diesels (of those I've seen the data for) run at anywhere between 15 and 18:1 CR. The Duramax/PSD/Cummins ran at 17.5-18:1 (the LMM Duramax is now at 16.8:1). The marine 5.9L Cummins runs with 15:1 CR. And so on...

Tractor, industrial and marine diesels are usually run at high load for extended periods, and tend to have a lower CR for improved durability. Certainly, tractors, OTR diesels, marine diesels and so on are also designed with efficiency in mind. If a higher CR was a better compromise (for efficiency), they'd all have a higher CR. They don't because of increasing durability issues with increasing CR.

Jim

PS - Here's a question for the thinkers out there.... What effect does CR have on crankshaft harmonics?

Pretty sure changing CR will affect the frequency in some if not all critical vibration orders.
Most of the engines I worked with in my Navy career were good sized like 16 ton that's where a great deal of my diesel education comes from.
In relation to crankshaft torsional vibrations one of my favorite engines used a crankshaft torsional vibration absorber (Fairbanks Morse 38 ND 8-1/8 OP) engine.
The absorber insisted of a hub with plates and free floating pins of different diameters and weights. Great component. Better to absorb than dampen.
I know there is a similar unit for gassers called the Rattler.
Is one available for the 6.2/6.5 to your knowledge and what is your opinion on dampen vs absorb.
New here and seeing that your knowledge and ability to express it make you well worth following
Thank you

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Pretty sure changing CR will affect the frequency in some if not all critical vibration orders.
Most of the engines I worked with in my Navy career were good sized like 16 ton that's where a great deal of my diesel education comes from.
In relation to crankshaft torsional vibrations one of my favorite engines used a crankshaft torsional vibration absorber (Fairbanks Morse 38 ND 8-1/8 OP) engine.
The absorber insisted of a hub with plates and free floating pins of different diameters and weights. Great component. Better to absorb than dampen.
I know there is a similar unit for gassers called the Rattler.
Is one available for the 6.2/6.5 to your knowledge and what is your opinion on dampen vs absorb.
New here and seeing that your knowledge and ability to express it make you well worth following
Thank you

Thanks for your comments.

Generally, a damper recommendation depends on the owner.

For example, if the owner plans to own the same vehicle for some number of years, then I'd recommend the Fluidampr. It's a little pricey, but it does a better job of damping, and it never-ever wears out or deteriorates over time. Plus, you could sell the damper if you needed to, to recoup some of the cost.

Most owners are best served by using the original equipment GM/AMG damper, if a replacement becomes necessary. Avoid the cheap imports like the plague. A genuine piece will cost ~$100 and an import will cost about half that.

I don't know of any other aftermarket type dampers for these engines - a "Rattler", for example. Jim