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First recorded activity by BoatBanter: Aug 2017
Posts: 4,961
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Yanmar Offers a Turbo Diesel Outboard
On 10/13/2017 5:32 AM, John H wrote:
On Thu, 12 Oct 2017 17:48:36 -0400, "Mr. Luddite" wrote:
On 10/12/2017 5:05 PM, Keyser Soze wrote:
On 10/12/17 4:53 PM, wrote:
On Thu, 12 Oct 2017 16:42:10 -0400, wrote:
I was curious so I looked it up.Â* A fully dressed 454 with cast iron
heads weighs 685 lbs from the factory.Â* A CumminsÂ* 5.9L diesel by
comparisonÂ* is 1200 lbs or 515 lbs heavier.Â* Twins would mean a weight
difference of over 1,000 lbs.Â* That's quite a bit, even for a 39' boat.
Major difference is:Â* The 454 develops 450-500 lb-ft of torque at 3200
RPM (depending on year)Â* while the diesel CumminsÂ* develops peak torque
of 610 lb-ft at 1600 RPM
The extra torque probably comes from the longer stroke in the diesel.
(4.0" vs 4.75")
They make gasoline engines "square" or even over bore to reduce the
reciprocating forces of a longer stroke for a given displacement
It lets them run at higher RPMs.
===
I believe the extra torque is mostly a result of the higher
compression ratio in a diesel.Â* The higher ratio effectively increases
the duration of the power stroke compared to a gas engine.
I thought it was the result of a combination of factors, including
higher compression ratio, more heat content of the fuel, higher turbo
boost pressure, and greater heat content of the fuel, and continuous
pushing of that fuel into the cylinders.
Probably all you mentioned ... oh and also the greater heat content of
the fuel in case you forgot. :-)
He probably missed that with his cut'n'paste.
yup.
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