Topic: Drastic engine modification. Would it work?

[Boomologist]

Hi,
Awhile back when I had a CB750/4 on the bench I had a thought (happens once or twice a year).
If I took an old cam and cut it in two between 2 & 3 cylinders, turned one half of the cam 180 degrese and welded it back together that should cause 1 & 4 to fire at the same time and 2 & 3 the same.
Anyone ever tried something like this?
In theory that set up should double the available raw horse power when starting out 
What would it do to the top rpm?
Would there be any benefit to this?
Any thoughts would be appreciated.

[hcritz]

That's a pretty interesting idea...
I think what you would end up with is basically a Big Twin...one big power stroke per revolution as opposed to two smaller ones.
It would probably feel more like a V twin in operation...definitely lose some of the smoothness of an in line four.
I don't think that there would be Any real operational reasons it wouldn't work...but I'm not sure there would be a lot to gain.
Possibly a bit more torque down low...but the basic hp/cc would remain the same...
Bet the clutch/primary chain rattle would be AWFUL!!!

[scunny]

that would make it a 4cylinder inline twin  

[HondaMan]

It's been done!

Two guys on a flattrack racing team in 1972 in Macomb, Illinois did it. I helped them rework the ignition system.
They did it because the pulsing torque digs into dirt better on those tracks then does the smooth power of the 4.

It worked fine, sounded like a 350 twin. I never got to ride it, but they never broke during a race 1972-1974.

[MRieck]

Big Bang engines used in MotoGP. Was also used when 500cc 2 strokes were used. It improved traction by cutting the number of power pulses from 4 to 2. Easier on the rear tire also.

[Tim.]

Sounds interesting - might have difficulty welding the cam together perfectly aligned though - might be easier to build up and grind the lobes into correct position.  I'm no metal worker, so I'm talking out my arse, but off the cuff keeping the cam in perfect alignment would seem near impossible welding it together.

I say go all the way and rework the crankshaft, cam and ignition to make it a giant thumper 

[Rick4004]

Apparently this firing order is hell on camchains. Most engines using it are have gear driven cams. The big power pulses (like a twin) combined with light flywheels (not like a twin), really get the cam chain accelerating and decelerating leading to premature failure.

Rick

[MRieck]

Apparently this firing order is hell on camchains. Most engines using it are have gear driven cams. The big power pulses (like a twin) combined with light flywheels (not like a twin), really get the cam chain accelerating and decelerating leading to premature failure.

Rick

That is true. Just the redline of GP engines mandate gears let along firing order. I remeber seeing Muzzy's ZX-7 with the gear conversion. You should see a Muzzy Raptor(real race product)...the cam gears, clutch basket and shift drum are real works of art.

[Jay B]

The whole drivetrain would take more abuse. Instead of transmitting 2 small power pulses per revolution, it would have to handle pulses twice as big, half as often. More stress on the primary chain, clutch and gears.

Some tuners did basically this with the HD XR750's on certain tracks, they were known as "twingles" because the two jugs fired 45 degrees apart on the same revolution. Like Hondaman said, more time for the tire to dig in and grip.