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The Italian motorcycle company Ducati currently produces the Desmosedici RR, a road-legal version of their MotoGP race bike. The engine powering this bike is a 989cc V4 with sixteen valves (sedici=sixteen), desmodromic valve actuation, and over 200 horsepower at 13,500 rpm.
If one were to engineer
a V8 engine out of parts from the Ducati engine, it would be perfect for powering small racecars in certain race classes, or possibly a production supercar. This 32-valve V8 (trentadue=thirty two) would displace 1978 cc, or just about 2 liters, and potentially produce over 400 horsepower.
Since Ducati currently engineers their powerplants with 90 degrees between the cylinder banks, and 90 degrees between the crank pins (cross-plane), it would be possible to make this V8 without balance shafts, unlike other V8s made by combining two in-line four cylinder motorcycle engines (see link). Overall, the Desmoventiquattro V8 would have fewer compromises.
The only drawback to this design would be that the increased crankshaft mass would prevent the engine from revving as quickly, and the full 13,500 rpm of the four cylinder might not be reached. One could even re-design this engine rather easily to have a longer stroke, thus increasing the displacement and increasing low-end torque at the expense of high-rpm power.
Ducati Desmosedici RR
http://en.wikipedia.../Ducati_Desmosedici
Ducati's production race bike [discontinuuity, Jan 22 2007]
Wikipedia article explaining different kinds of V8 engines
http://en.wikipedia.org/wiki/V8
[discontinuuity, Jan 22 2007]
Powertec RPA 2.6 Liter V8
http://www.powertec...ng.com/v8_index.php
V8 engine based on two Suzuki Hyabusa motorcycle engines. It powers the Radical SR8 race car. [discontinuuity, Jan 22 2007]
Article about the Desmosedici engine
http://www.motorcyc...02ducatimotogp.html
Includes a good cutaway view of the engine [discontinuuity, Jan 22 2007]
Scroll down for a sound clip of the engine
http://www.diseno-a...Desmosedici_RR.html
[discontinuuity, Jan 23 2007]
Why Buy a Ducati?
http://www.pashnit.com/bikes/ducati.htm
general info about reliability, mileage, comfort, etc. [discontinuuity, Jan 26 2007]
Wankel Engine
http://en.wikipedia...Engine#How_it_works
Read the word under the animation. [BJS, Jan 26 2007]
1957 Moto Guzzi V8 sound file at top of page
http://www.vintageb...to%20Guzzi%20V8.htm
[normzone, Sep 01 2009]
[link]
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Wait... So this differs from any other 32-valve V8 how? Also you must remember that torque is what actually moves the vehicle. If the motor is making 200HP at 13500RPM, it is making a paltry 78 lb-ft of torque at the same rpm. |
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Basically, it is designed to rev very high and make lots of top-end power. The short stroke and desmodromic valve actuation of the motorcycle engine allow it to reach 13,500; otherwise this is just a 2 liter quadcam V8. I'm sure that some specialized manufacturers build small-displacement, high-revving V8s for racing, but to my knowledge, none use desmodromic valves or produce quite so much power from such small displacement. And using pre-existing Ducati engineering and parts would mean that this V8 would be cheaper than designing a new one from scratch. |
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[+] Ok then. Now that I fully understand this, I realize it is in fact a very good idea. |
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Hmm. After looking at the fourth link, it looks like the Ducati engineers put a weird firing order on this engine, although they also made plans for a more normal one. |
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You know you could also add some low-end torque without sacrificing the high redline by twin-turboing it. BMW's new twin-turbo 3.0L I-6 makes its peak torque at idle speed, and holds almost all of it up until its 7000RPM redline. |
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[acurafan], I think twin turbos might be pushing it. You would need some very high-octane race fuel to do that, since I imagine the compression ratio is already pretty high. Of course, you could fit custom low-compression pistons, but that would defeat the purpose of using all Ducati parts. Good idea though -- you might get 500 HP with turbos! |
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I have always believed that the best setup would be an engine with a very large bore, very short stroke, and twin-turbos: extremely high revving yet would make some real torque. Btw, if you use direct injection you solve a lot of problems with pre-ignition. |
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Great idea as long as you only plan on driving you car for a week or two. This is a race engine designed to be rebuilt after every race. ICE are amazing things capable of incredible amounts of power and flexible enough to either operate at peak power capacity or for extremely long time but not both at the same time. I suspect this engine would under normal road conditions be nearly un-drivable and would have a very short duty cycle and would absolutely require the use of race gas otherwise its just a regular old engine making about 2/3 to 1/2 or less of this HP. |
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The Ducati bike (the production bike, that is) has a 3-year warrenty and runs on 95 octane fuel I beleive. Granted, with twin turbos it might wear out pretty quick, and three years is pretty short compared to a car warrenty. |
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Pretty much the closest thing you can get now to a high-rpm race engine is in the 2000-2004 Honda S2000. Up until 2004, it revved to 9,000RPM and made its peak torque at 7,500RPM. For the 2004 model, the engine's stroke was made longer for more low end torque, and the redline was lowered to a not-as-astonishing 8,000RPM. Part of the reason was the lack of low-end torque, but I'm sure another factor was reliability. |
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Mazda rotary engines have always had high redlines, usually around 8 or 9 thousand rpm. Of course, they don't have any pistons. |
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Rotaries also have good power density. The current Renesis motor in the RX-8 displaces 1.3 liters (depending on who calculates it, of course) and produces about 240 horsepower. The fuel efficiency is pretty terrible, though. |
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By the way, I think the current S2000 displaces about 2.3 liters. |
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Honda stroked it to 2.2 from 2.0. The fuel efficiency of the Honda is also pretty terrible considering the size of the engine. That seems to be the case with high revving engines. |
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God, I love the sound of a Ducati. I wonder if I could get that for a ringtone (just had my first cellphone forced upon me). |
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well, given that the S2000 is a performance vehicle and not an economy vehicle, I don't find it surprising that the fuel economy isn't very good. |
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I can't really bun this idea--people have already been making V8's by mating two Hyabusa engines together for some time now. It's basically just a plea to make a low-displacement high-performance V8 with desmodromic valves--a great idea, but not really an invention per se. |
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EPA Mileage, City/Highway (mpg) MT 18 / 24
1.3 Liter RENESIS 2-rotor rotary
Transmission, 6-speed manual overdrive (short throw shifter)
Horsepower, SAE net 232 @ 8,500
Torque, SAE net (lb./ft.) 159 @ 5,500
Redline 9000
Displacement (L) 0.654L x 2
Bore x Stroke (inches) Not Available
Compression Ratio 10.0 : 1 |
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Displacement (cc) 2157
Horsepower @ rpm (SAE net, Rev 8/04) 237 @ 7800
Torque (lb.-ft. @ rpm) 162 @ 6800
Redline (rpm) 8000
Bore and Stroke (mm) 87.0 x 90.7
Compression Ratio 11.1:1
City/Highway 20 / 26 |
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The point of this idea is that the Ducati motor is ideal for adaptation into a V8, and it would be very easy to use stock parts from the four cylinder to build the V8, since all the real design work has been done by Ducati. |
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Ducati engines are notoriously unreliable. |
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Besides, its not just raw HP that you need. They say "you buy horse power, you drive torque". You would be much better re-tuning for less HP and more torque if you were to use an engine like this in a car. |
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Motorcycle engines just would not have the required torque to pull most cars around. If it's a race car, however, why not use a race engine designed for a car. |
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If you connect this engine to a CVT, only the HP would matter. Any car equipped with a CVT pulls hardest from its HP peak rather than the torque peak because it can have a lower (and therefore more advantageous) gear ratio at the peak HP than at the peak torque. To the best of my knowledge, a 200HP @ 13,500 RPM engine with a CVT will pull just as hard as a 200HP @ 6,000 RPM engine with a CVT. What it would lack in torque, the CVT would make up for in low gear ratio. But then again, an engine held constantly at 13,500 RPM would sound annoying to say the least. |
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[webfishrune] [Ducati engines are notoriously unreliable] |
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Really? I've never owned one, so I'm not in the know, I just love the way they sound. |
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Are we talking about a Jaguar level of unreliability (You need to own two, so as to have one to drive while one's in the shop), or the old school Harley level of unreliability (Four hours of riding, one hour of maintenance), or what? |
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Is this like "Lucas, Prince of Darkness" kind of unreliability (British electronics)? |
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Please explain - I'd never heard that before. Then again, I just watched them go by, and being a Moto Guzzi guy myself (stone reliable) I've never experienced it. |
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it think its because they are loaded up with little gee-gaws like desmodromic valves and the like. |
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I thought the Desmo Drive was just a gear driven OHC as compared to pushrods or chains. That shouldn't be a reliability issue, although who knows, I work with enough designers and wanna-be designers to know how that works. |
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Desmodromic is different from a gear-driven camshaft. It's actually an alternative method of interfacing the camshaft and the valves. |
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As for reliability, They require frequent "valve checks" (every 6000 miles) to keep the desmodromic valvetrain properly maintained. However, they aren't actually prone to breaking. |
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more directly to your question [normzone] I think the problem is that these engines(ducati that is) are tuned right to the wall and require a lot of attention to stay there, like the racing engines they are. Very powerful but not overly dependable over the long haul. |
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"A Ducati Moto GP race engine is toast after 400 miles, completely unfeasible and unwanted for a road bike" |
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Per the sound clip link, so a detuned version is probably ok for 6000 miles before it needs an enema. |
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[jhomrighaus], I'd wager you're right. |
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Since rasberry re-tart posted the specs for the mazDa RENESIS engine, I just want to point out that the output speed of the engine is three times faster than the rotor actually spins. |
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In other words, if the tacometer says 9000 rpms, then the rotor is only turning at 3000 rpms. |
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"Without a doubt, Duc's are more maintenance intensive than Japanese bikes. Valves need to be checked / adjusted every 4 - 6K and belts every 10K. I don't do anywhere near the mileage that you do and I also do all of my own work on my bike (the 2 valve twin is a very simple design), so maintenance is not a big deal with me. If you were to pay a mechanic to do a full maintenance (valves, oil, carb sync), expect to pay $300 - $400 every 4 - 6K miles and add another $150 - $200 if belts require replacement. Now, that said, is not to say that a Duc will not hold up to the rigors of extensive mileage. In fact, I know several guys who have put extensive (50K plus) trouble free miles on their Duc's. If you maintain them, they will reward you." |
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I imagine the Desmo V8 would be less reliable, probably about 6,000 miles before an overhaul, like [jhomrighaus] says. But then again, race engines are almost always overhauled after each race anyways. And making the engine a V8 and eliminating the weird firing order that Ducati originally built into it would probably smooth out the power pulses and contribute to a longer life for some of the internal parts. But again, the idea here is to make a high-powered motor for racing, not for driving on the street. Most of the engine (or at least the bottom end and the cams) would need to be completely re-designed to make it practical for street use. |
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By the way, [BJS], where did you get those figures? I thought the whole idea of the rotary engine was that it could rev to high rpm's with no trouble. |
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You know, you could get some good low-end torque to make this engine suitable for a daily driver by making this thing (whatever the vehicle) a hybrid. The Lexus GS450h does 0-60 in 5.2 seconds and has a 3.5L V6 and 2 electric motors while the GS350 with the same V6 engine and no electric motors completes the same task about a second slower. The motors would also allow you to not rev the thing as high in normal driving, therefore increasing the overall longevity of the motor. |
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//I know several guys who have
put extensive (50K plus)
trouble free miles on their
Duc's// |
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50k is not *that* many miles.
I do about 20-30k/year on
my 'bike. Mind you, my bike is
built for touring and i'm told
there is a guy in the US who
has done over a million miles
on his. I have met people
wpersonally who have done over
250k. I currently ride a BMW
K1100LT. |
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I'm a bit late to the party to make any real impact, but still... |
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I was reading about desmodromic valvegear the other day. Up until that point I had regarded it as the ultimate, with complexity and cost as its downside. |
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Apparently it is possible to design a conventional system to outperform a desmodromic setup. Part of the problem is that the maximum acceleration the valvetrain can stand is limited by the interface between the cam and the valve. If the forces there are too high, one of the two starts to break up. Valve float can be addressed for conventional valvetrains; what we have now that wasn't around in the heyday of desmo systems is really good modelling that has identified why the valves are floating. Progressively wound springs can effectively eliminate the phenomenon. |
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As for the flat-plane idea - it appears that the Powertec V8 you have linked to already features one. |
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Given that, and the existence of a number of quite sophisticated V8s based on motorbike engines, I can't bun this idea. |
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The original idea was to give the Desmo V8 a cross-plane crankshaft, although a flat-plane one would probably be needed for extremely high rpm's (see third and fourth paragraphs of the main text). |
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Does anyone else know what other motorcycle-based V8s are out there? The Powertec engine is the only one I've ever seen. |
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"By the way, [BJS], where did you get those figures? I thought the whole idea of the rotary engine was that it could rev to high rpm's with no trouble." |
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Go to the "Wankel Engine" link that I posted. |
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The idea of morphing motorbike engines into car engines by doubling up has been done several times. |
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The Radical/Powertec mentioned above has done well for itself, if only as a trackday/race-car engine. |
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The current dog's doo-dahs is the one developed for the Caterham Seven RST-V8, using the heads from a 1000cc Suzuki racer and a custom block etc. The finished product fits 430/500bhp (N/A or supercharged) in a 19x19x20in cube and weighs in at 90kg! |
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The desmodronic valve system is special because it uses the cams to force the valves shut (I assume it has springs as well) and to avoid valve bounce. I don't know enough about motorbikes to comment further, other than you're gonna need a custom made block, heads and cams, plus probably modified drive, as the cams will have to be twice as long and will have twice the friction load. Oil (and water?) circulation is also gonna be interesting! |
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//desmodromic//
Wasn't she Othello's wife? |
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A few observations:
1) high friction valve systems are great on the track, bummer for the street.
2) this would be in the exotic category in price and maintenance so "practicality" is not an issue.
3) Go ass to ass and have two oil and water pumps, keeps everything simple.
4) Crank loads. The longer the crank the higher the stresses and loads, double the distance between the first piston and the flywheel, quadruple the crank loads. |
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So in conclusion: neat idea, might work. A new crankshaft will need to be developed from scratch or you will need to drive from the center (not a bad idea). |
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You get a bun because I had essentially the same
ideas back in college. On different occasions, I
wanted to make V8's and V12's out of 4-cylinder bike
engines, and later I wanted to make an aftermarket
desmo system for a Chevy small block. |
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Moto Guzzi V8 sound file (link). |
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I'm not sure there's any need for the desmo valve
system. I'm pretty sure it's only there as a USP.
Honda, Suzuki, Kawasaki and Yamaha have no
problem matching them (or beating them in motoGP)
for power. I thought the desmo system was thought
up to beat valve float? and became unnecessary once
they figured out that it was spring resonance causing
it. |
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pretty sure Ducati did this in the '30s for a racing airplane. |
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[edit] okay Bugatti and it was 2x 8 cyl engines, but I was pretty close |
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////desmodromic// Wasn't she Othello's wife?//
Thanks, [coprocephalous], I think you've got it figured out better than I had. I kept thinking a Desmodrome was a bicycling track for South African bishops. |
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