1979 kz400 engine modification

Hi All,
new to this forum but not to bikes.
i recently started a cafe racer project, converting a disassembled 1979 (or 80) KZ400 to a fire breathing machine (if you can call a KZ400 - fire breathing :laugh: )
anyway, when i got the bike, the engine was destroyed, rod bearings were gone, chain tensioner spread like confetti inside the engine.
i have rebuild the engine, replacing the crank, rods, pistons and cylinder (came with the new pistons and rods), manually honed the cylinders.
replaced all rod bearing and crank bearing, making sure all bearing clearance are up to spec (plastigage).
other than that, ported and polished the heads, intake path was P&P, combustion chamber was polished to a mirror finish, valves were lapped and all gaskets were replaced.
carbs were replaced to Keihin CVK (off an ER-5).

the engine starts easily, pulls great, no smoke nor any other problems... i can truly say that the engine is fantastic and the P7P really improved its breathing capabilities at higher RPM.

now, i want to get some more out of the engine.
engine replacement is not an option, as it is illegal were i live.
since it is the new KZ400 engine (the one with the external oil line running from the case to the head), i was wondering if i can bore the old 400 cylinders to accept the 440 pistons (which i can buy from ebay or something)
can i go any bigger than 440? i know that the linear wall thickness will be too thin...
any other modification can be made to get some more ponies out of this little thing?

also, i have a microsquirt module around, the original idea was to go EFI and EI, and boost it... but that will require to drop the CR down to 7.7 or 8 ...
i have the fabrication skills, i have the engine build know how,

thank you for your input.
Ravivos.

also, one more questions to the experts out there...
is the KZ400 and KZ440 cam timing are different? if so, what is the difference, which is the preferred one?

This will answer any of your questions

www.dotheton.com/forum/index.php?topic=39120.0

As for the cam p.m. me.



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Nebr_Rex wrote: This will answer any of your questions

www.dotheton.com/forum/index.php?topic=39120.0

As for the cam p.m. me.

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Man, that's a great thread, very informative.
not sure why you choose not to go with computerized fuel injection, especially for a highly modified engine like yours.
As for the 440 pistons and the ability to just bore the 400 cylinder - didnt really got an answer for that.
As for the cam, i saw your cam work on your thread, absolutely fantastic, although i wonder of and how you are going to make the cam lobes more durable to wear and tear, forging?

PMing you right now.

I choose not to use a computer to prove one is not needed,
To give people a choice. As for the cam the factory pumps oil
thru the cam and out a hole on the cam lobes. The 400( 64mm )
can be bored to 440( 67.5mm ). But pistons are scares. The
Wiseco's are readily available and take it from 443cc to 464cc.
The 400 sleeves can not be bored to that size.

P.s. the head needs to be milled if Wiseco pistons are used, they
have a shorter dome.
.

Thanks for the info, that sure helped alot.
actually, manage to get a set of 440 pistons off of ebay yesterday, hope they turn out to be 67.5 and not 64.

how did you manage to get a 69mm piston into the cylinder? did you replaced the linear or is there a difference in linear thickness between the 400 and the 440?

the 69mm Wiseco pistons comes with a 15mm wrist pin? or did you bored the small end of the rod?

Now find the rings. The 440 liners are needed for a 69mm overbore.


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Just got the pistons and a bit worry that the 400 liners might be too thin after boring them to 67.5.
any opinion on that?