which engine kit

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A couple of your links broke.
The 29cc I'm not a fan of. Its cheap and for 20.00 you can replace the head and piston if it goes bad but heard too many horror stories. On the other hand I put one together for the kid next door and he beats the crap out of it and it still runs like a bat out of heck!
The ported ones will give better performance. Of course.
The 28.5 ported is on my neighbors and is very similar to my 27.2 non ported. I can out speed him though we have different exhaust pipes..

Not sure if the 30.5 is a head kit or not.

Not sure the motor you have so there are other items to look at to make each kit compatible to your low end.
 
actually the bottom link for the 29cc is the only one that worked, and that was actually for the GP290 topend, which is a 28.5 with stock 28mm stroke. its not the 35m bore, but the 36mm bore, which is the only bore cy to get imo. but that is a fully stock gp290, so should be run with a stock stroke and .020 gasket. but then it ll have High Compression so i would suggest some higher than normal octane for it.

try to relink the motors, or give part of the discription so we can know which ones you are looking at.

the tope one is ok, but I prefer the ESP modified/race ported version. the compression and squish band has been corrected, so you can run normal 87 to 93 oct gas, and it no longer wants to heat soak with the corrected compression ratio he works on them.
 
the 3rd option will install right on your stock motor/crank setup.

i strongly suggest you get new crank bearings and oil seals and a full gasket set and do a full rebuild on the lower end. the stock cy bearings tend to fail more often than not. especiall when a Big Bore is installed.

TFE SS crank bearings are 13.00, oil seals are 6.00 and a new gasket kit is 9.00
 
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