zenoah 230/40 port modification and timing.

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zenoah 230/40 port modification and timing.

Postby jungle massive » Tue Jul 22, 2014 12:40 am

looking for some figures of what to aim for with regards to port timing on a zenoah 23cc engine.
I would like to clock mine up, and machine the ports to get the best duration, overlap etc and perhaps gain more power and or torques.
it is for a 2wd 1/5 sedan.
are these figures magical secrets kept amongst engine builders?
I have a big power pipe if that helps.
( I have experience with four cylinder 1:1 engine modification cam timing, etc.and access/experience for the milling, grinding, clocking up)
I have two engines that I will be working on.
a modified 230rc ( with transfer mods, small gasket )
a dead stock 240rc.
jungle massive
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Joined: Tue May 13, 2014 12:34 am

Re: zenoah 230/40 port modification and timing.

Postby Rallyfinnen » Thu Jul 31, 2014 9:55 pm

Well..it depends :) What character of the engine you want, what pipe you have etc..
In my humble experience, main factor is exhaust timing and shape in cobination with the pipe.

Here is a sort summary of what I found in tuned engines, and from my own experiments:
A common exhaust shape is a flat roof with a 'cut' in the middle. The roof usually at around 175-180deg and the 'cut' extending up to even over 190deg duration. The cut is usually a half circle shape at 1,5-3mm radius. The 'cut' I found is most likely there to give a smoother power curve, but this again depends on the pipe and duration. I had ports at abt 180deg with rounded roofs and no 'cut' that ran really nice too. Trial and error..

Inlet port is usually not modfied much (not much room to make it wider etc), but some choose to increase duration by cutting piston skirt. I prefer a duration of 160deg or less, but i have seen some engines have up to 180deg.. High duration effectively kills low end torque. Pipe influences this too.

Transfers I found best (and easiest) to have staggered at more or less standard durations, but enlarging them does have an influence. However you need to know what you are doing here, since it might reduce power and increase fuel consumption if the 'flushing' is inefficient. A CNC machine would be nice for this..

Piston can be lightened and compression is usually kept relatively low to allow higher top revs. Cutting the piston top flat or partially flat is common.

Crank needs to be straightened with high tolerance (less than 1/100mm in my opinion), and flywheel balanced.

Ignition advance can be played with by removing the locating pin (?), running external ignition systems etc.

I'm just a hobby tuner, and experimenting has been much more expensive than just buyng tuned engines and racing them.. but tuning is a hobby too :)

Have fun :)
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Location: Sweden

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