Short pistons - more HP???

crazypj said:
As the guy knows nothing about engines I really don't think it would be a good idea to confuse him even more talking about volumetric efficiency and, what basically amounts to porting a head
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Your answers are terrible.

First of all there are many ways to increase volumetric efficiency of an engine without porting the head. The easiest method would be to optimize the length of the existing intake and exhaust systems, which are always compromised on production engines. Also someone can add a ram-air box around the carburettors, which would also increase volumetric efficiency. All without every taking the engine apart, a lot more simply than boring or stroking or correctly installing new valve springs.

Installing pistons that are higher compression than the originals would increase mid-range power, without altering the bore or stroke.

There are huge gains to be made in power by paying attention to very basic engine needs. An acquaintance of mine who has done really well vintage racing in a 500cc class, spent a day with a dynamometer juggling exhaust types and lengths and increased his rear-wheel horsepower by 24%!!!

Ignition timing, jetting, intake and exhaust length, these are simple things to try that might give your bike a boost. Then simply swapping in pistons with a bit higher compression, a half or one point, can also make a noticeable difference.

Just because a few top racers or bored rich people do some ridiculous things to their engines, does not mean that it is the only way or best way to go for 99% of motorcycle owners. Usually with very smart basic tweaks all the power anyone needs can be found while maintaining the practicality of the vehicle.
 
My answers are from 40+ yrs experience
CB360 never was a motor designed in the 1930's that kept getting upgraded and bored/stroked bigger unlike British twins (even re-designed BSA A65/A50 was still closer to the A10 than a brand new design although it was much newer than Bonneville)
It's well known the 88/99 got bored and stroked into the Commando then got various things re-designed to prevent breakage (and it was real impressive in the 70's when Peter Williams was racing the JPN, 30bhp lower than the other bikes on grid)
I've already posted in multiple threads about 360 intake and exhaust, short pipes don't work with stock carbs, majority of intakes are way to short to work properly, etc, etc
The easiest way to get better performance from a 360 (or the CB/CJ250) is to bore it so the intakes work properly
It's at least on par with a tuned T100, (Triumph 500 twin) with a genuine 115mph (or 120 with a smaller rider/tailwind/downhill) up from about 92~95mph stock
 
NortonGuy said:
Your answers are terrible.

First of all there are many ways to increase volumetric efficiency of an engine without porting the head. The easiest method would be to optimize the length of the existing intake and exhaust systems, which are always compromised on production engines. Also someone can add a ram-air box around the carburettors, which would also increase volumetric efficiency. All without every taking the engine apart, a lot more simply than boring or stroking or correctly installing new valve springs.

Installing pistons that are higher compression than the originals would increase mid-range power, without altering the bore or stroke.

There are huge gains to be made in power by paying attention to very basic engine needs. An acquaintance of mine who has done really well vintage racing in a 500cc class, spent a day with a dynamometer juggling exhaust types and lengths and increased his rear-wheel horsepower by 24%!!!

Ignition timing, jetting, intake and exhaust length, these are simple things to try that might give your bike a boost. Then simply swapping in pistons with a bit higher compression, a half or one point, can also make a noticeable difference.

Just because a few top racers or bored rich people do some ridiculous things to their engines, does not mean that it is the only way or best way to go for 99% of motorcycle owners. Usually with very smart basic tweaks all the power anyone needs can be found while maintaining the practicality of the vehicle.
Click to expand...
 
Personally, I don't understand his comment about rich or racers, if I had any cash does anyone believe I would be screwing around with CB360's?
Any idea what motorcycle mechanics actually get paid or were paid in the 70's, 80's, 90's?
I do, I worked as one because I love bikes not money
 
crazypj said:
The easiest way to get better performance from a 360 (or the CB/CJ250) is to bore it so the intakes work properly
Click to expand...

Just out of interest PJ, and a total thread jack...but how much overbore does a CB250 have to have in order for it to match the factory intake and gain some performance?.
 
Is that so it matches the size of the intake valves? Ive heard they kind of strangle the motor because they are oversized, but thats a big jump haha
 
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