racerguy180

The Honda VFR800 has "vtec". If they would offer car v-tec I think that the bikes would be more managable with power delivery.



If someone were to design a variable exhaust port for the renesis, I think coupled with the variable intake system together they would work well together.



my .02

Old Grey

In actual fact in a piston engine the stroke makes no difference to torque





If both engines have 100psi in the chamber a small piston will have less area so there will be less force pushing the on the rod. PSI, pounds per square inch, 6sq"=600lb, 4sq"=400lb. Larger piston, more square inches more force pushing the rod. It was found small bore engines have smaller valves and ports, larger valve and ports just would not physically fit. Small ports and valves come into tune at lower rpm giving the impression of more torque.

It may be due to the rotor only going 1/3 of the crank rpm, like peddling in top gear

Or the ports having a large time area like a twin cam, as the power curves are similar

Lynn E. Hanover

I have been off the net for a time, while moving from Florida to Ohio. Now I read this...................



Torque is the same measurement used in determining HP for our street racers. The instantanious torque is simply how much force on the piston or rotor face and how far out on the crank (lever arm) you are pushing. There is nothing else involved in measureing torque.



On a dyno you place a drag on the crank that applies pressure to a sensor that is mounted one foot out from the centerline of the crank. So that pressure shows you avarage torque in foot pounds. So you see "Foot Pounds of Torque"



So if two pistons have the same area and the same pressure on them the longest crank throw produces the highest torque number.



So if that big nut on the back won't come off, do you use a shorter wrench handle and try again, or slip a long pipe over the breaker bar, and hang on the end of that? The long pipe gets my vote.



Since the world standard for measuring HP is the dyno, resolving avarage torque is a simple matter. The measured avarage torque times the RPM divided by the constant 5252 = HP. So, the torque gage tells you directly what the torque is.



HP is the torque (force) times the rate the force is being applied, so RPM says one revolution (to get the avarage) Per minute

(the rate) in increments of one minute. So one HP is 33,000 pounds lifted one foot in one minute.



Torque is a measurment of force.

Horse Power (actually a big draft horse) is a measurement of work. So there must be a time function. It is one minute. The "M" in RPM.



The big truck engines have little HP, some less than car engines, but huge torque. So, 600 to 700 foot pounds of torque at 1,800 RPM is normal. Do they have short strokes or long strokes? Long strokes is the correct answer.



My 250 HP rotary has a max torque of 178 foot pounds.



The new X16 rotary will have a longer stroke than current models. Why is that? To develop more torque at lower RPM, where car engines need that torque. Truck engines seldom rev over 1,900 RPM. When you bother to look, your car engine is usually turning between 1,800 to 2,200 RPM in cruise. To have the flexibility to operate at higher power than normal, the car engine must be able to turn up much higher revs to develop more HP. The big truck engine cannot, so it uses 10, 12, or 16 gears in a transmission the size of a VW to get that heavy load up to road speeds.





Lynn E. Hanover

Old Grey

Correct, but I think you missed





For the engines to have equal capacity and different strokes the pistons have to be different sizes. The smaller piston gets less force pushing down but a greater leverage form the longer stroke which make is equal to a larger piston with more force and a shorter leaver.



Read the book they compare a 1" stroke to a 22" stroke of the same capacity

Lynn E. Hanover

This what I read: "In actual fact in a piston engine the stroke makes no difference to torque"



If the engines are the same size (cubic inches of displacement) In a math problem they would have the same torque. True enough.



When my son started Motorcycle school at MMI in Pheonix I started reading his text book. One of the first items I got hung up on was the HP calculation. They had it wrong. They also had the idea of torque wrong. There was no way that anyone had learned any accurate information from that book. And to see that no instructor had ever noticed that their calculations were not provable was disturbing.



In life there are often items that don't seem to fit together. Engineers seem to dive for the math book when faced with a problem. One of my jobs as a Federal employee was to help young engineers understand how things work, so they could avoid foolish mistakes.



Years ago all engines had long strokes. They were copies of steam engines, that had long strokes. It worked pretty well with the dreadful low octane fuel available. During WWII many clever folks added a extra fuel tank up on the fire wall with a valve to switch back and forth between the Coal oil in the new tank, and the crummy gasoline in the cars fuel tank. The engines had very low compression ratios and once up to temperature would run on coal oil, (crummy Kerosene). So you start each trip on gasoline and under way you switch to coal oil. Before arrival you switch back to gasoline, so the car could be started for the return trip. Gasoline was rationed,

coal oil was not.



So on the one hand we still have engines with long strokes, in big trucks. They turn very slowly to keep piston speed down. They have very long connecting rods to reduce rod angularity and resulting piston drag down. So the engines are tall and very heavy. But they get as much as 4 MPG with a big load on them. Very good efficiency.



Short stroke piston engines have high rod angularity and high drag on the piston sides. The idea of the short stroke is to get a high displacement engine in a compact size and weight. Also the ring drag being the function of piston speed, the short stroke cuts way down on piston speed. Piston speed is how far the piston travels in feet at a test RPM. So if you have half of the stroke you have half of the distance, and half the ring drag.



There are hundreds of reasons for using a short stroke in autos. Themally they expose less cold cylinder to the burning mixture. In your long stroke engine you will find your avarage cylinder pressure has been much closer to zero before the exhaust valve opens. The head will have room for bigger valves, and the list goes on and on.



So if we compare the two (same displacement) engines at the same RPM, will the torque be the same?



Nope. They will produce their best torque at different RPM. The long stroke engine will have it while turning very slowly, say 1,900 RPM. The short stroke engine at perhaps 3,200 RPM.



Archemedes said :give me a lever long enough and a place to stand, and I can move the Earth. The key is then that the longer the lever, the lower the amount of force required to move the load. So, big trucks have long strokes, and cars (and rotaries) have short strokes.



As long as the problem is on paper the instant torque will be the same.



Archemedes didn't know about ring drag increasing at the square of velocity. It is the avarage torque being measured by the dyno, and the readings include all of the design flaws into a single torque number. Since we drive dynamometers, we have to deal with avarage torque.



If you mount your engine in a system that allows it to rotate around the crank centerline, and restrain it with a transducer that is one foot from that centerline, you need only an accurate RPM reading to have a rolling dyno. Years ago big radial aircraft engines had such transducers in their engine mounts. So the engineer could read out HP for each engine, and lean accordingly.



Lynn E. Hanover

j9fd3s

thats what our guys do, and it works pretty well. my job seems to be "well, mercedes tried that in 1937, and it exploded"



seems like everything has been tried, and 70years ago it didnt work, due to a materials/or complexity, but it is neat to show a suspension engineer a bugatti from the 20's with cockpit adjustable damping...

Old Grey

Not exactly, short stroke piston engines have a shorter distance from the crank centreline to the big end journal, there should be less angularity. In actual fact rod length will have a bigger effect on angularity. If you have a short stroke engine the angularity will be very high with a short rod, but very low with a long rod. In long stroke engines they use long rods to reduce the rod angularity because of the larger distance between crank centreline to the big end journal(stroke).



Pro Stock in the US is limited to 500cu and they can use different length rods, long rods to reduce angularity to reduce wall friction, but they use a short rod 5.9", even with it's increased friction. Why, the short rod enables them to use a shorter block, the shorter block allows a straighter line between the manifold and the head, the inlet flow and velocity is a higher priority. There is actually no difference in power between a long and short rod in a racing motor but there is more wear with a short rod.





A short stroke engine can make the same torque as a long stroke engine, with the same displacement same valve sizes and same induction flow capacity, at low rpm. The short stroke engine has less bore wall friction so the power at low rpm can be the same, but at higher rpm the steadily increasing friction(and other factors) of a long stroke engine will not make it suitable for high rpm.

Lynn E. Hanover

Us old people use "Sayings" to cover the situation. It is a big help when a case of CRS is active. (Can't Remember ****)



"Everything old is new again"



We are born with the dots too far apart to make any sense. As we learn about things the dots get closer together. Then one day on your own, you connect the dots between two subjects. Often wrongly, eventually correctly. On avarage half of the things you know for sure are completely wrong. Since being right is more fun than being wrong, we tend to select things to learn about that interest us, and work more diligently on those items, often to the exclusion of all else. Men tend to do this and the ladies tend not to. So, the woman you marry will have to tolorate you being under some dreadful looking rusty *** car all of the time. She will try to change you, but it won't work.



My mother, could weld aluminum with a gas torch and blue glasses. The weld beads were as nice as anything you can do with a TIG machine. There were no TIG machines during WWII. Try that some day.



Lynn E. Hanover

Lynn E. Hanover

Well the premis is off a bit here. To have the same displacement, the longer stroke engine must have a smaller bore size.



In general the long stroke engine will always have its best torque at a lower RPM, than a similar sized short stroke engine. A short stroke engine will always have its best power at a much higher RPM than a long stroke engine.



Smokey Yanuck beat the snot out of his fellow NASCAR competitors with longer rods. If he could have thought of a way to do it, he would have had the wrist pin a foot above the piston. The slight improvement in torque was only one factor. The main advantage was dwell time at TDC.



So his engines got better fuel efficiency than short rod engines.



Even today there is not one rod manufacturer that does not offer two or more rod lengths for each engine. The only folks using the shorter (stock length) rods are generally doing so as a result of a rules package.



Have you seen pistons with the wrist pin hole intersecting the oil ring and second ring grooves? How long is the rod that needs that much more room?



The rotary has a huge piston and a short stroke, and has **** poor torque. The new 16X has a smaller piston (back to 12A width) and a longer stroke. What Smokey would have done right out of the box.





Lynn E. Hanover

j9fd3s

i cant even solder too well anymore!