LouC wrote:
Then why is it that a diesel with much more torque but the same hp or even less than a gas engine pulls a load with ease vs a gas engine straining?
There is obviously much more to it than the theory or else why in the world would pick up truck buyers spend $5000+ more for a diesel that has the same hp as a gas engine?
Think Hemi Vs Cummins.....or Hemi vs Ecodiesel.
A heavy duty diesel is built to withstand 100%, or near 100%, HP output over extended periods of time. A trucker would not hesitate to keep the pedal to the metal at redline for 20 minutes straight during an extended hill climb. No-one outside of Nascar would think of doing that to a gas engine. (and Nascar engines have a short life).
LouC wrote:
http://www.ramtrucks.com/en/performance/#light_duty
The Hemi and the Ecodiesel are seen as roughly equivalent for towing the same load and the Hemi has about the same torque and much more HP. But does the HP make a difference in this application??
http://www.ramtrucks.com/en/performance/#heavy_dutyThe Cummins has much more torque and lower HP and a much higher tow rating.
So let's reconcile these stats with the theory. I'm obviously not an engineer but I've towed with lower power vehicles (98 Jeep 4.0~185 hp, 225 ft lbs torque) and higher power vehicles (07 Jeep 5.7~330 hp, 375 ft lbs torque) and the greater toque of the Hemi is abundantly clear, at RPMS where its not developing that much HP, like less than 2,000.
I would have to say it relates to what the manufacturers consider to be an acceptable continuous output. Gas engines can have a high maximum output for their size, but one must presume a lower continuous output. Unfortunately, the manufactures do give us a rating for maximum continuous output or what we might call cruise output.
LouC wrote:
Getting back to Rick's problem, if you're sticking with the 5.7 as most people would, make sure the boat is propped a bit on the high end of the rpm range and do not use the cheap 2 piece crap exhaust that most I/Os use, if you're going to spend money spend it once and get a Hi Tek one piece stainless system like Deafwish has, that joint sooner or later is going to leak, rust the exhaust valve stems and your back where you started. Other options that reduce the possibility of this happening again are adapting a Merc dry joint system (may be difficult because IIRC the hose diameter is different on the outlet side) or full closed cooling (which all I/Os should have anyway). Why you ask? Well take off a cyl head on one of these raw water cooled engines and look at the cooling passages. They are necked down with rust which causes localized overheating of the combustion chambers, because of inadequate water flow and the fact that the open system is not pressurized, that allows localized boiling. You may never know this because the engine may not actually overheat. And this is why, big boats with relatively small engines don't have such great engine life. Another compromise using GMs pretty good design in a way the real engineers from GM (not Merc and Volvo) did not intend. They were designed for a 15 lb closed system, with AF/water not rusty water. A system that keeps the coolant from boiling till roughly 265*F. Raw water cooling you can get boiling in the cyl head at much lower temps, like a bit over 200 even though the engine temp is not at 200. That is the temp in the intake manifold, not the cyl head because the temp sensor is in the intake. I am amazed that mine has lasted as long as it has, but the next engine will not be raw water cooled for sure. The fact that most people find raw water cooling and 2 piece exhaust 'good enough' does not mean its GOOD. I bet the real engineers from GM would cringe at how their products are abused in this application.
I agree completely agree. I wish I had sprung for the Hi-Tek exhaust last year instead of putting on OSKO cast iron. I installed them 1 year ago with the standard gasket they supplied, and they had slight leaks in less than a year. I sanded the mating surfaces this year with a flat block, and re-installed with the Volvo Metal gasket with Tef-Gel on both sides. I'll take it apart a year or two from now and inspect again. Wouldn't have to do that if I had gotten the Hi-Teks.
The inside of my raw water cooled engines have never looked to0 bad, even at 25 years, but the manifolds/risers and thermostat housings get very bad because they do not stay immersed with water. Note that I do not winterize here in So Florida, but if I did, I would do as LouC does and use anti-freeze to prevent corrosion during the layup.
_________________
"Knot Easy" 2000 Horizon 240 Volvo 5.7GS /SX
tow: 2017 Honda PILOT EXL-AWD
prev. boats:
'87 Chaparral 198CXL 4.3 OMC Cobra
'69 Jetstar 16ft Ski Boat, 115hp Yamaha
'68 Aluminum Jon Boat, 3hp Sears
'64 Water Wings
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