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#21
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VW Reality
On Feb 2, 5:48 am, Stealth Pilot
wrote: Bob I admire your work so I'm going to irritate you with an argument. I wish someone would post a concise guide to a style of VW conversion that is durable and simple. have never seen one that had the tests of time behind it. 1600 or 1835cc for preference. ------------------------------------------------------------------------- Dear Stealth, Allow me to share with you something I just saw on the internet. Some old geezer said: "As far back as Rockford, at least three builders of converted VW's appealed to Pope Paul to use the EAA's bully pulpit for educating homebuilders about the realities of automobile engine conversions. At least two of us (me and Ted Barker) even offered to provide the required torque-stand. But the EAA was (and is) more interested in selling tent-space and full-page ads than in contributing to the basic store of USEFUL homebuilt information." Ain't that a hoot? Stupid ol' fool actually thought the EAA was about doing something USEFUL, like, mebbe, what you said up there at the top. -R.S.Hoover |
#22
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VW Reality
I could be very, very wrong, but my understanding of efficiency is that 25% efficiency means that a quarter of the energy goes to torque and 3/4 to heat. That would mean you throw away THREE horsepower's-worth instead of four, no? Jim since such engines are no more than 25% efficient when it comes to converting the heat of combustion into torque at the crankshaft. That means that for every horsepower measured at the crank you must generate at least four horsepower's-worth of heat in combustion. |
#23
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VW Reality
RST Engineering wrote:
I could be very, very wrong, but my understanding of efficiency is that 25% efficiency means that a quarter of the energy goes to torque and 3/4 to heat. That would mean you throw away THREE horsepower's-worth instead of four, no? Jim since such engines are no more than 25% efficient when it comes to converting the heat of combustion into torque at the crankshaft. That means that for every horsepower measured at the crank you must generate at least four horsepower's-worth of heat in combustion. You are correct, but that is also exactly what he said ---. i.e. generate four hp in heat, only one available at the shaft. Charles |
#24
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VW Reality
"Charles Vincent" wrote in message
t... RST Engineering wrote: I could be very, very wrong, but my understanding of efficiency is that 25% efficiency means that a quarter of the energy goes to torque and 3/4 to heat. That would mean you throw away THREE horsepower's-worth instead of four, no? Jim since such engines are no more than 25% efficient when it comes to converting the heat of combustion into torque at the crankshaft. That means that for every horsepower measured at the crank you must generate at least four horsepower's-worth of heat in combustion. You are correct, but that is also exactly what he said ---. i.e. generate four hp in heat, only one available at the shaft. Charles Well, with only slight rephrasing, that is what was said at the beginning of this thread. The rephrasing would be that we "throw away 3 horespower's worth of heat out of every four". Actually, that is slightly worse than I was taught; but I really did not regard it as the primary issue under discussion--so I let it be. The number that I was taught a little more than 40 years ago was 30% when running at a moderately high percentage of power. I understand that there has been considerable improvement since then, which could have brought the efficiency up to around 33%, and I have read recently (from a forgotten source) that the theoretical maximum is around 37% efficience for spark ignition engines. So, for the moment, it is unclear (at least to me) whether the 25% figure is slightly low, pertains to rich mixture opperation, or is related to the low compression and the intake and exhaust plumbing of the engines in question. In any case, even the 25% figure is really much better than we can obtain from our supposedly more efficient automobile engines--especially when you consider the waste in time spent idling or simply "spun up" to avoid lugging (because the cost of not doing so is far greater). However, the basic point of Bob's original post is very real; even on the highway, cars and trucks normally run at a very low percentage of power--and the few exceptions, such as pulling trailers far about the rated limit, seem to result in increased failure rates and short TBOs. I admit that I still believe a 1600, and especially an 1800, is fully capable of producing 60 hp on takeoff and 30 hp in cruise with a 52 inch diameter prop--and that the addition of thermal barrier and dispersant coatings might allow a climb power approaching 40 hp. But none of that detracts from the basic points--that cars and trucks normally opperate at surprisingly low ower levels, and that 100 maximum continuous hp from a Continental O-200 really does mean continuous. Taken in that context, tha 1600 might well be 40 hp maximum and 30 hp cruise; and the thermal coatings might raise that to 45 hp maximum and 33 hp cruise. Peter (Former engineering student and shade-tree mechanic) |
#25
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VW Reality
On Feb 4, 12:23 pm, "Peter Dohm" wrote:
I still believe a 1600... ------------------------------------------------------------------------------ That'll make a fine epitaph. An engine doesn't give a **** what you believe. Nor what some huckster has told a tent-full of the faithful to separate them from their money. Engines are painfully honest -- often fatally so. Build a few. Put your beliefs aside and listen to what the ENGINE has to say. -R.S.Hoover |
#26
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VW Reality
Peter Dohm wrote:
"Charles Vincent" wrote in message t... RST Engineering wrote: I could be very, very wrong, but my understanding of efficiency is that 25% efficiency means that a quarter of the energy goes to torque and 3/4 to heat. That would mean you throw away THREE horsepower's-worth instead of four, no? Jim since such engines are no more than 25% efficient when it comes to converting the heat of combustion into torque at the crankshaft. That means that for every horsepower measured at the crank you must generate at least four horsepower's-worth of heat in combustion. You are correct, but that is also exactly what he said ---. i.e. generate four hp in heat, only one available at the shaft. Charles Well, with only slight rephrasing, that is what was said at the beginning of this thread. The rephrasing would be that we "throw away 3 horespower's worth of heat out of every four". Actually, that is slightly worse than I was taught; but I really did not regard it as the primary issue under discussion--so I let it be. The number that I was taught a little more than 40 years ago was 30% when running at a moderately high percentage of power. I understand that there has been considerable improvement since then, which could have brought the efficiency up to around 33%, and I have read recently (from a forgotten source) that the theoretical maximum is around 37% efficience for spark ignition engines. So, for the moment, it is unclear (at least to me) whether the 25% figure is slightly low, pertains to rich mixture opperation, or is related to the low compression and the intake and exhaust plumbing of the engines in question. In any case, even the 25% figure is really much better than we can obtain from our supposedly more efficient automobile engines--especially when you consider the waste in time spent idling or simply "spun up" to avoid lugging (because the cost of not doing so is far greater). However, the basic point of Bob's original post is very real; even on the highway, cars and trucks normally run at a very low percentage of power--and the few exceptions, such as pulling trailers far about the rated limit, seem to result in increased failure rates and short TBOs. I admit that I still believe a 1600, and especially an 1800, is fully capable of producing 60 hp on takeoff and 30 hp in cruise with a 52 inch diameter prop--and that the addition of thermal barrier and dispersant coatings might allow a climb power approaching 40 hp. But none of that detracts from the basic points--that cars and trucks normally opperate at surprisingly low ower levels, and that 100 maximum continuous hp from a Continental O-200 really does mean continuous. Taken in that context, tha 1600 might well be 40 hp maximum and 30 hp cruise; and the thermal coatings might raise that to 45 hp maximum and 33 hp cruise. Peter (Former engineering student and shade-tree mechanic) That (the last paragraph) does seem to agree pretty well with my results. For whatever that's worth... Richard |
#27
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VW Reality
wrote in message
... On Feb 4, 12:23 pm, "Peter Dohm" wrote: I still believe a 1600... ------------------------------------------------------------------------------ That'll make a fine epitaph. An engine doesn't give a **** what you believe. Nor what some huckster has told a tent-full of the faithful to separate them from their money. Engines are painfully honest -- often fatally so. Build a few. Put your beliefs aside and listen to what the ENGINE has to say. -R.S.Hoover Sorry to have upset you. Peter |
#28
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VW Reality
"cavalamb himself" wrote in message ... Peter Dohm wrote: -----------------much snipped-------------- I admit that I still believe a 1600, and especially an 1800, is fully capable of producing 60 hp on takeoff and 30 hp in cruise with a 52 inch diameter prop--and that the addition of thermal barrier and dispersant coatings might allow a climb power approaching 40 hp. But none of that detracts from the basic points--that cars and trucks normally opperate at surprisingly low ower levels, and that 100 maximum continuous hp from a Continental O-200 really does mean continuous. Taken in that context, tha 1600 might well be 40 hp maximum and 30 hp cruise; and the thermal coatings might raise that to 45 hp maximum and 33 hp cruise. Peter (Former engineering student and shade-tree mechanic) That (the last paragraph) does seem to agree pretty well with my results. For whatever that's worth... Richard Actually, it's worth a great deal because it provides further confirmation for the maximum continuous power; and does so within a range of speeds that approximate maximum performance climb for a lot of small experimentals. That's probably about as close as it gets for a useable rull of thumb. BTW, it seems to me that they are not that far from Veeduber's maximum continuous numbers. Peter |
#29
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VW Reality
Way back when I was a university student I got stuck fixing a girlfriends VW
"Bug". (I think she liked the Bug more than me but kept me around 'cause I could fix it.) From that experience I developed a strong dislike for the "Bug". My Volvo 544 was both more comfortable and more reliable while providing about the same gas milage. Once while chasing VW parts in the Volvo (Never happened the other way 'round) I struck up a conversation with a German mechanic at a VW shop. Refering to the little flat 4, he said, "Well, it was a good idea when it made 36HP - not so good when they increased the power. "What do you drive?", I asked. He pointed to a brand new Caddy and gave me a slow wink. If you want a light weight engine why not look hard at state of the art Japanese "liter bike" engines instead of a 60 year old VW design? My Kawasaki cranks out 108HP and is reputed to be bulletproof. Of course a PRSU would be manditory given that the little Kawi would be turning almost 9,000 RPM. Somebody made a 2.8 liter V8 out of a pair of Hyabusa cylinder blocks. Making a flat 4 shouldn't be any harder. See: http://thekneeslider.com/archives/20...usa-v8-engine/ |
#30
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VW Reality
On Mon, 04 Feb 2008 13:06:29 -0600, Charles Vincent
wrote: RST Engineering wrote: I could be very, very wrong, but my understanding of efficiency is that 25% efficiency means that a quarter of the energy goes to torque and 3/4 to heat. That would mean you throw away THREE horsepower's-worth instead of four, no? Jim since such engines are no more than 25% efficient when it comes to converting the heat of combustion into torque at the crankshaft. That means that for every horsepower measured at the crank you must generate at least four horsepower's-worth of heat in combustion. You are correct, but that is also exactly what he said ---. i.e. generate four hp in heat, only one available at the shaft. Charles What he's forgetting is the 1 available at the shaft is STILL heat energy. Fuel makes 4 Pistons catch 1 cooling and exhaust loose the other 3. -- Posted via a free Usenet account from http://www.teranews.com |
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