Why don't boat engines use more turbochargers ?
03-04-2002, 11:08 PM
#12
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Whipple you state that turbos can't make power down low. Look at the numbers I just posted before you and explain why you think they are low. The motor is making 1000ft lbs at a very slow speed so I would love to hear why you think there will be ANY lag. The torque curve on this motor is virtually flat from 2750 through 6000 rpms...where is the drivability issue?
03-05-2002, 09:29 AM
#14
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As an old twin turbo car guy, I always understood that the key to making good power throughout the RPM range was maintaining positive pressure difference across the cylinder. check300, do you have data on pressure in both the intake and exhaust manifolds?
Yes, exhaust pressure is higher on turbo engines and that means higher pumping losses as the piston works against that pressure on the exhaust stroke. This pressure also helps to spin the turbine, whereas belt driven superchargers use crankshaft HP to spin. But there is a hidden advantage for the turbo. What spins the turbine is not just pressure and flow, but heat.
As the exhaust passes through the turbine it expands, and its temperature drops. That means that some of the heat energy that is normally wasted by an internal combustion engine is recovered by the turbine and turned into useful work spinning the compressor. I'm remembering this from a turbocharging book that I read 20 years ago so forgive me if I don't have it quite right. Because of this thermal efficiency advantage, I think turbos will always have more power.
As far as low speed planing problems, I have no experience, but I wonder if the solution for any high powered boat is to have a transmission. Turbos or not, 100+ mph boats setup to achieve top speed often struggle to get on plane. I don't know, maybe it's simpler just to build engines with higher low RPM torque.
Mercury's Blacktrac 2 speed transmission didn't catch on, supposedly because it took up space inside small boats, but what about the Konrad from WPM, with the trans inside an extension box? They packaged that trans and drive with a Roots blown 540. First gear in that sucker must be a blast!
Yes, exhaust pressure is higher on turbo engines and that means higher pumping losses as the piston works against that pressure on the exhaust stroke. This pressure also helps to spin the turbine, whereas belt driven superchargers use crankshaft HP to spin. But there is a hidden advantage for the turbo. What spins the turbine is not just pressure and flow, but heat.
As the exhaust passes through the turbine it expands, and its temperature drops. That means that some of the heat energy that is normally wasted by an internal combustion engine is recovered by the turbine and turned into useful work spinning the compressor. I'm remembering this from a turbocharging book that I read 20 years ago so forgive me if I don't have it quite right. Because of this thermal efficiency advantage, I think turbos will always have more power.
As far as low speed planing problems, I have no experience, but I wonder if the solution for any high powered boat is to have a transmission. Turbos or not, 100+ mph boats setup to achieve top speed often struggle to get on plane. I don't know, maybe it's simpler just to build engines with higher low RPM torque.
Mercury's Blacktrac 2 speed transmission didn't catch on, supposedly because it took up space inside small boats, but what about the Konrad from WPM, with the trans inside an extension box? They packaged that trans and drive with a Roots blown 540. First gear in that sucker must be a blast!
03-05-2002, 10:30 AM
#15
The problem with those 2 speed trans is they lower 1st gear and not raise / overdrive for faster top end. We are allready at 1:1 and then the drive ratio. We need multi speed trans. The weismans are using something along these lines.
03-05-2002, 10:38 AM
#16
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The reason the Gentry motors would not live is because of the RPM's. The rules in open said you could turbo if you ran no more than 350 ci. So what they did was make the stroke smaller on a big block and turn the RPM's up.
Carl Myers tried the same thing, with pretty much the same results. But boy when they ran they hauled ass.
Team Yahoo
Carl Myers tried the same thing, with pretty much the same results. But boy when they ran they hauled ass.
Team Yahoo
03-05-2002, 04:28 PM
#19
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Just when you thought you knew it all. I left Schwitzer were I was a turbo designer the last turbo I designed was a variable geometry design on the turbine side. The first to work doulbled fuel economy provided boost at idle if needed. It was a small turbo for low rpm big for high rpm and cruse every trucker that ran one loved it. One trucker raced every body and beat others so bad they claimed he had an an empty trailer.
03-05-2002, 04:45 PM
#20
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Why not a turbo diesel? Low end power. Big hp and torque. Low revs with high reliability. Ive heard the new diesels are actually lighter than a similar gas engine. My slightly tweaked Ford PSD makes 300hp and 590ft pds. The only drawback I see is a bit of smell when idling and that has been reduced over older diesels.
