Engines in tandem?

[desotoman]

Hi Jack,
   Thanks for posting. If everything is just additive like you state, what do you think of Jon's post? Would it be better to run two engines as one Big engine? Regards, Tom

[JackD]

Remember the Yammama 4cyl 2 stroke mile bike?
 It had the best of everythimg from tires and riders to weight and HP. But was unrideable in a dirt track.
they even built a variation that had 2 jugs firing together in an effort to change the power delivery but it was still out of hand.
It was a real screamer, but just didn't do that job very well.
Recip engines are pretty job specific with limits by design.

[JackD]

The bikes often exceed the available traction and that leads to slower speeds, reduced tire life and speed ratings.
Everything is a speed secret until you make it work for you.
I remember Vance Breese on his first trip to Bonneville with his HD road racer that dusted the factory cammers in part because it was narrower and that was kinder to the ability for it to hook up.
His riding skills made more of a difference on the road race track. Making the package small and hooking it up can often make up for a lot of power.

[Rex Schimmer]

To much good stuff to resist posting a long one.

First: The Yamaha TZ750 dirt bike. Jack was right, that engine was just to peaky to be able to get traction and that was really a function of it being a two stroke with expansion chamber dynamics that made the horse power peak narrow. Although Kenny Roberts did win the Indy mile on one in absolutely one of the most exciting finishes ever. He was in second on the last lap, one of the Harley boys was leading, well Kenny knew if he could get a good drive of the last corner, i.e. traction, he could win. So he laid it in to turn four and got the wheel against the cushion, rolled on the throttle and it hooked up and he blew by the Harley right at the finish. Man was the Harley guy surprised!

More TZ750 stuff: When Don Vesco set the world motorcycle record with his liner with two of the TZ750 in it he said the biggest problem was getting the thing to hook up when the engines came on the power ban, it would just spin the tire. Although he set the record he came back next with a pair of turboed Kawasaki 900s and as I understand it he would short shift until he got into high gear and then he would turn the boost up adding horse power as fast as the tire could take it. Jack probably has some good recollections of both of these engine combinations.


Torque and horse power: Remember it is horsepower that makes you go fast, especially at B'ville. Horse power is a measure of work, i.e. force expended over a distance where as torque is just a measurement of force about and axis. So you can have a jillion lb-ft of torque but at zero rpm you are doing no work so you aren't going any where. So if you couple two 100 hp motors together, you will get 200 hps and also twice the torque.

Singles, twins, fours, twingals etc. Seldom, every thing that you say in your post regarding power pulse etc is true for an ideal engine, which would be an engine with a moment of inertia of zero and a structural stiffness of infinity. Not many of those around so we have reciprocating weight, the rods and pistons, and rotating mass, the crank and flywheel all of these combine to make a spring/mass system that actually attenuates the firing pulses of the engine to take out or at least reduce the sharp peaks that we would see if we had the "perfect" engine, i.e. no mass, infinite stiffness. There was a very good article in "Cycle" mag a couple of months ago by Kevin Cameron, I think,  about using heavy flywheels to calm down cam shafts. now I admit that this sounds like the two are not connected but read the article and you can see what affect adding rotating inertia has on smoothing out the firing pluses of the engine and how this can keep the cam from throwing the lifters off of the cam face. So my thinking would be if you have an engine that is really peaky but makes good power add fly wheel until it is calmed down and at B'ville the reduced rate of engine acceleration would probably not be noticed as it is the big V cube (speed the power of three) that we are fighting and at the top speed of a vehicle drag is much more of a force than accelerating additional flywheel weight.

Just some rambling please feel free to through me under the bus.

Rex

[JackD]

What he said.

[hawkwind]

To much good stuff to resist posting a long one.

First: The Yamaha TZ750 dirt bike. Jack was right, that engine was just to peaky to be able to get traction and that was really a function of it being a two stroke with expansion chamber dynamics that made the horse power peak narrow. Although Kenny Roberts did win the Indy mile on one in absolutely one of the most exciting finishes ever. He was in second on the last lap, one of the Harley boys was leading, well Kenny knew if he could get a good drive of the last corner, i.e. traction, he could win. So he laid it in to turn four and got the wheel against the cushion, rolled on the throttle and it hooked up and he blew by the Harley right at the finish. Man was the Harley guy surprised!

More TZ750 stuff: When Don Vesco set the world motorcycle record with his liner with two of the TZ750 in it he said the biggest problem was getting the thing to hook up when the engines came on the power ban, it would just spin the tire. Although he set the record he came back next with a pair of turboed Kawasaki 900s and as I understand it he would short shift until he got into high gear and then he would turn the boost up adding horse power as fast as the tire could take it. Jack probably has some good recollections of both of these engine combinations.


Torque and horse power: Remember it is horsepower that makes you go fast, especially at B'ville. Horse power is a measure of work, i.e. force expended over a distance where as torque is just a measurement of force about and axis. So you can have a jillion lb-ft of torque but at zero rpm you are doing no work so you aren't going any where. So if you couple two 100 hp motors together, you will get 200 hps and also twice the torque.

Singles, twins, fours, twingals etc. Seldom, every thing that you say in your post regarding power pulse etc is true for an ideal engine, which would be an engine with a moment of inertia of zero and a structural stiffness of infinity. Not many of those around so we have reciprocating weight, the rods and pistons, and rotating mass, the crank and flywheel all of these combine to make a spring/mass system that actually attenuates the firing pulses of the engine to take out or at least reduce the sharp peaks that we would see if we had the "perfect" engine, i.e. no mass, infinite stiffness. There was a very good article in "Cycle" mag a couple of months ago by Kevin Cameron, I think,  about using heavy flywheels to calm down cam shafts. now I admit that this sounds like the two are not connected but read the article and you can see what affect adding rotating inertia has on smoothing out the firing pluses of the engine and how this can keep the cam from throwing the lifters off of the cam face. So my thinking would be if you have an engine that is really peaky but makes good power add fly wheel until it is calmed down and at B'ville the reduced rate of engine acceleration would probably not be noticed as it is the big V cube (speed the power of three) that we are fighting and at the top speed of a vehicle drag is much more of a force than accelerating additional flywheel weight.

Just some rambling please feel free to through me under the bus.

Rex

Bravo Rex a most excellent ramble  

[ack]

I believe Rex has got it right.  Torque is what you use to tighten your head bolts horsepower is what you use to go fast.  The fastest wheel driven car on earth uses an engine that makes very little torque but turns very fast.   It has always puzzled me why someone would build a vehicle to go from 0 to 300 plus with 3 or 4 gears.  I would use a 10 speed if there were one available.

[Sumner]

Great post Rex and I agree with you Ack that the more gears the better.  Hooley and I have had this discussion more that once with him sugesting at times about putting a 2 speed glide in the Stude, especially since on one run he screwed up and went from 1st to 4th and still easily ran 190 on his lic. run.  I say no way let's keep the 4 speed.  Likewise I love the 4 speed overdrive in my truck, but don't see the point of one when people suggest running one in a LSR car.  With the wide spread in the gear ratio between 3rd and 4th it is a bad choice in my opinion.  Our close ratio Muncie has worked good so far, but we now need something that is stronger with a tall 1st gear and the rest close ratio.

I still belive that with a motor that is gear ratio limited (has to run a 4 speed) torque is very important.  Bikes with their narrow power bands and high HP learned way back that more gears will help get the job done.

I just recently had a high school buddy and his son give me a '60's Suzuki X-6 250.  I sold a number of these when I had my motorcycle shop and took one to the drags once with only mildly ported cylinders and ran 14.1 @ 94 mph.  Not bad for an other wise stock weight 250 in '68.  This was probably the first production bike to really take advantage of high HP, low torque and 6 speeds to get the job done.  It is still a fun bike to ride.

I guess it is the package that you are dealing with that will determine the torque/HP thing.

c ya, Sum

[JackD]

My first bike at Bonneville was a junk parts 250 Yamama. The closest ratio in the box was 3rd to 4th in a six speed. That is what I wanted for the final shift so I geared it to run the target in 4th. That meant it would not even move in 1st and needed a 25mph tow from the door handle just to get going in low gear. I always did it with the engine running.
The no dead motor tow starts except for liners came from the HD that sometimes would not start with a tow from the truck and when you let the clutch out the rear wheel stopped and spit the rider.
On the other hand, top speed of the meet in the low 300 mph range was set by a Blown Alky SBC in what started as a Sports Racing car in high gear only after the trans broke.

"What works for you is good for you. If it is faster than the other guy, it is the worst for him."

[desotoman]

Rex,
   Thanks for the post. You and Jack have made a believer out of me.   I guess the guy who told me that twenty years ago was pulling my leg.   Thanks for the explanation.
   
  Years ago I bought a Suzuki TM 400 dirt bike off a friend of mine who said it was just too peaky power wise to ride. He was right. You were either digging 4" trenches with the rear tire or not moving. I went to the dealer and asked if they made a flywheel for this bike, and they did. Had a choice of a two or four pound flywheel. I bought the four pound, put it on a lathe and cut the weight out of the center of the flywheel leaving the  outside 1"of the flywheel in the stock configuration. I bolted that on the bike and could not believe the difference. I now had a bike I could control. It was not peaky at all, and still just as powerful. When the guy I bought it off of road it he wanted to buy it back. He could not believe the difference, in fact he could not believe that is all I did. Bottom line is, years ago I learned a flywheel can be a tuning tool most people overlook. Regards, Tom

[JackD]

Look at the parts in a Model A motor and remember how it was used. Get some help with the flywheel.
So that was 20 years ago. I don't know much about the modern stuff, things might have changed. LOL

[panic]

"90-270 degree design"

H-D twin firing sequence is 315-405

[russ jensen]

2 engines are not dbl trouble or dbl pain .both trouble & pain go up by  at least a factor of 4. He was right on about not doing it.  Tractor pullers run all sorts of weird combos and figure that each eng will contribute what it can.

[Dean Los Angeles]

Final Round - 1960 Smoker's Fuel & Gas Championships.
The Odd Couple Chrysler-Olds against Tommy Ivo's Twin Buick.


The Odd Couple later evolved into a Chevy-Hemi twin. Try tuning that! They were moderately successful too. There have been lots of twins in drag racing. Tommy Ivo's four engine was the peak of insanity. If two engines is four times the work than four engines is

In 1971 I ran a twin engine bike . . . well mini bike . . . with two McCulloch 125's. Both engines had oil filled slipper clutches that didn't engage until 7000 rpm. No gear box. If the tuning was off the harmonics were obvious, and the power went to hell. Set two records.

[JackD]

That race in the picture was forever called "The Hookup vs the Shut Up."  A 90 inch WB was and is a handfull.
The class A bikers have lost the art of making the bike small , but they will re-figure it out again.