BoaterEd — Volvo horsepower ratings, are they correct?

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Regal 1900 Bowrider

Posted — Mar 02 2007. 17:04:45

I just bought my first boat so I am a complete newbie. I bought a new Regal 2400 bowrider with the Volvo 8.1Gi DPS. I know I am overthinking this whole engine and horsepower question but I can’t help it, I’m an engineer. Are the ratings that the engine/outdrive manufacturers publish for real?

Here is my quandary:

Volvo lists the 8.1Gi at 375hp and lists the torque at 660Nm or 487 lb-ft. It lists the displacement at 8.1 liters. Here is the URL reference: http://www.volvo.com/volvopenta/global/en-gb/newsmedia/pressreleases/2000/newgenerationv-82000.htm

This press release indicates that the only differences between Gi and the GXi engines are that the high-output version has a hotter cam and a forged crank.

GM indicates that the non-high output 8.1 liter, designated the 8100, puts out 392hp and 503 lb-ft of torque. Here it the introductory page URL: http://www.gm.com/automotive/gmpowertrain/engines/specialized/marine/

(Click on the engines at the bottom of the page to get the detailed data for each engine.) Note that the 8100 and the 8100 High Output both top out at the same torque of 503 lb-ft. However, the 8100 reaches max torque at 3200 RPM, 800 RPM lower than the 8100HP. My understanding is that getting max torque at a lower RPM is better in the boating world.

So Volvo lists the non-high output 8.1 liter motor at 375hp and 487 lb-ft and GM lists it at 392hp and 503 lb-ft.

To further confuse my attempt at understanding this, I found an article in Boating Magazine that indicates that the boat manufactures fudge on the actual horsepower ratings of their engines. http://www.boatingmag.com/article.asp?section_id=8article_id=483page_number=1

Here is the quote from the article:

“Here’s an important lesson when you’re shopping for a boat. Manufacturers allow themselves a fudge factor when publishing horsepower ratings. An outdated (at least, to our way of thinking) industry agreement permits a leeway of plus or minus 10 percent in published horsepower. Sometimes an engine model may have less than its rated power, and sometimes it may have more. Unofficially, from Volvo, the 280-hp 5.7Gi engine is “very strong 280 hp…it’s actually closer to 300 hp.””

This was a very enlightening article about boat performance relating to horsepower. It was also an eye opener regarding how boat companies fudge in order to get spacing in their horsepower offerings. Volvo’s unofficial quote is consistent with what the above-listed GM marine engine data indicates with respect to the horsepower of the 5.7Gi (5700). GM shows it at 292hp rather than 280hp. Here is the reference. http://www.gm.com/automotive/gmpowertrain/engines/specialized/marine/2007_5700_marine.pdf

Just to complicate things a bit more, I was looking at parts lists for the 8.1Gi and the 8.1GXi on this site: http://www.marinepartsexpress.com/VP_Schematics/GAS/8.1Gi-A-B-C-D,8.1GSi,8.1GXi-A-B-C/ENGINE/

Regal 2100

Notice that there are two different part numbers for the Crankshaft for the 8.1 liter in the six part lists. That would make sense if a forged one was used for the GXi and a non-forged for the Gi engine. However, you’ll find that in the various versions of the engine, the GXi 420hp engine uses both p/n’s as does the Gi 375hp engine.

One last twist, look at this website that sells the GM engines. They list the two 8.1 liter versions at the same HP as Volvo and torque at slightly different levels from both GM and Volvo. Further, they list the motors as being an 8.3 liter engines rather than 8.1 http://www.cpperformance.com/products/Engine_Parts/engine-long-block.htm

Sorry for the novel. So after all of this, here are my questions:

What are the real horsepower and torque ratings of the 8.1Gi and 8.1GXi engines?

Is the crankshaft and the camshaft really different between the 8.1Gi and the 8.1GXi or is the difference in performance driven by ECU software?

What is the real displacement of the engine?

Would/does Volvo de-rate the 8.1Gi from GM’s listing of 392hp down to 375hp through ECU software? And if so, why?

Regal 2400
Regal 2400 Bowrider
Regal 2400 Bowrider
Regal 2400 Bowrider

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