cb350 removing material from piston skirt. and rpm peaks

delirium trigger

delirium trigger

Active Member
anyone had any success with lightening stock pistons?
also how fast can u spin a cb350 before reliability greatly suffers? and what does it take to get it there?

thanks
 
I've not tried to modify stock pistons before, but the problems you're likely to experience with the CB350 is that the engine stops making usable power up past 9K RPM or so. K0 and K1 models are the exception to this as their cam profiles are slightly different. Lightened pistons will help, of course, but that's not the full story.

As far as reliability issues go, oiling will be a concern. Honda builds a rock-solid, bullet-proof, bottom end. The top end of things leaves a bit to be desired though. There are oiling solutions available, but they don't come cheap.

For usable power you're going to want an aftermarket cam to push the powerband a bit higher. Depending on the grind you may need new valve springs and modified pistons as well.
 
what kind of outcome is predicted with say an aftermarket cam or a 69' head and a 67.5 piston kit? streetable or unreliable? power gains and rpm gains? im kinda suprised the companys selling them dont offer ballpark info
 
What is the objective here? Light pistons don't really make much difference to power. They do reduce forces on the big end bearings though and that helps with longevity if you know what you are doing. Double the revs and forces go up by 4 times, so keeping revs down helps more than lightening a piston.

On a race motor where every gram adds up, it can be a good idea, but you will be surprised how little weight comes off for a whole lot of machining. Forget holes in the skirt which typically lead to stress cracks.

Where we want a motor to make 2x stock power with much higher revs, it's a must but I wouldn't bother on a street motor.

Hondas have nice high red lines but on the dyno most of the old bikes peak long before the red line. Many riders rev way past the point of peak power and that increases wear, shortens life and is slower than changing up at the right time.
 
Without major modifications to head, cam's, carbs, ignition, it isn't going to rev more than stock
Without modified oiling system, it WILL seize cam bearings at high rpm.(even stock ones seize cm bearings)
I fit lighter pistons to my CB360's to give big ends an easier time but with stock cam and points ignition it can't rev over 11,500~12,000 (starts misfiring around 11,000rpm)
You need to find lighter more modern pistons instead of trying to modify the stock ones (Wiseco's are even heavier than stock, I don't like them)
'Screamers' can be fun, but only if you have somewhere to ride them
 
im already looking into another cam and pistons, possibly blue printing the crank shaft, what other modes to head do u think?
how close to this do you think i can get on around 1.5-2000$? i gotta crack open the engine and change all the rings etc. so i havent decided if i should build a monster or keep it stock. are all these mods worth it? what kind of performance can i see?
im a huge sleeper fan, and there is nothing i love more than surprising ppl in newer machines, but reliability is an issue, dont drive it daily, its just a toy, but dont wanna be ripping it apart and dropping money on it every year.
 
also what will help the stock cb350 (71) make power right to the redline? intake? exhaust? minor port and polish? (is there any guides on this forum to port and polishing?)
and also what is the actual redline on this bike? it reads 9500 but i keep hearing ppl reving it to 10,500 on a regular basis and they havent got there legs blasted with engine shrapnel yet.
 
You need external oil line to cam bearings, and, probably the needle roller conversion would be a good idea (but it's VERY expensive)
10,500 is fine while accelerating but holding it up there will break it
Electronic ignition will allow it to rev to about 14~15,000 rpm, but, the rods will probably break at 12,500~13,000 rpm plus the big ends 'slide' instead of rolling
Exhaust usually needs most work on 350 twin, the intakes are really a bit big for stock motor so don't need much work (or you increase port volume too much)
 
So my minimum plan was lengthening the intake plenums to 6 inches, including the cone filter. And a high flow 2 into 1 exhaust. I know ur the guru around here pj so thanks for your help. So with that external oil line (any info would be good, custom made?) Custom exhaust, and electronic ignition I can bounce it off 12000?! Or am I missing something? What about a 69 head for increased revs?
 
Do you have the book by A.G. Bell on high performance 4 strokes, or Kevin Cameron's book? Or any of David Vizard's books? That's a great place to start if you want to make more power without destroying the motor.


Moto Capellini (sp?) have some neat parts for the 350 that might give you some ideas.
 
pistons arent really the place to start.

Think of how things all work together and start making mods that will be good for the over all package.

also peak HP numbers are all well and good but whats the point if its only at 9500rpm+

I would much rather have and increase of 10% over the whole midrange then 15% for the last 1000rpm, at least on the street that is.

cam and head work should net more then cutting stock pistons.
actually why not go to wiscos?

but in reality its a street motor and you might only ever notice the gains when drag racing another stock 350 so maybe just spend the budget building a mild and super reliable motor and spend the change on proper suspension rearsets and tires.
 
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