PARADOX_sf

Hello.
I am building K series darton sleeved engine. The piston bore is 87mm. I have a set of wiseco pistons and wiseco's suggested piston to cylinder wall clearance is 0,075mm. I think it is a bit tight. Today I found that 30 degrees C difference (from about 5 deg to 35 deg) increase piston size with 0,03mm. My target is 600-700whp. What piston to cylinder wall clearance would you advice me to use?
Thank you!

CRAWFORDBUILT

Go with Wiseco's suggested clearance. Not to sound like a dick but they will understand the metal structure and it's thermal characteristics better then you will.

wantboost

iTrader: (2)

.075mm is .00295" which honestly does sound tight... I've seen a lot of people have skirt wear issues with that low of a p2w... on b,d,h and k series motors. Some even have the piston contact the cylinder walls, causing more than just skirt wear.

I know a lot of boost ed k series guys run .004-.005in (.1016-.127mm) for high boost/HP motors or .0030-.0035in (.0762-.0889mm) for a more milder setup

Most people have come to the conclusion that Weiscos' recommended p2w is based around a low boost/horsepower setup or even an a naturally aspirated setup. The cylinder temperatures at high pressure/horsepower levels will definitely cause the piston to expand more, you even said it yourself, with an 86F (30C) caused the piston to expand .03mm (.00118in) which effectively leaves overall p2w at operating temp much lower than what wiseco recommends.

Granted the p2w is a static number and will obviously shrink when everything heats up.
Also, there is a specific temperate, 68F (20C) to measure bore diameter, piston diameter as well as to assemble a motor. This is because the components at that temperature are of proper size and havent expanded much from their original tolerances. Also your tools need to be calibrated for that temperaure

Measuring things like bore, piston diameter, ring gap, etc can all be skewed because different materials expand at different rates at different temperatures. So where p2w could be .075 on a cold day it could be .07 on a hot day or even .08 on a cold day.

Also when dealing with a climate controlled assembly environment, you want to allow any parts you bringinto the room time to reach cdoom temperature before measuring/assembling those components.

Again because while the block that's been sitting in the room for weeks at 20C, those pistons you just brought in from, say, your 23C house will have prematurely expanded compared to the bore they are going in..

A really good example is say you're installing an inter fence fit aluminum bushing into a steel ring... you put the aluminum part in the freezer and heat the steel part. The aluminum bushing will literally drop into place because the cold caused the bushing to shrink, while heating the steel caused it to expand

EG1834

I would shoot for about .004". Besides pushing the pistons a little harder than normal, those Darton sleeves typically won't expand as much when they get to temperature either, so there is plenty of reason to go with a looser clearance.

sleepencivic

Please do not use their recommend clearance for 600-700 hp your asking for problems. Call the tech number they told me for turbo applications in the 400-500 hp range with the coated pistons to use .0035- .0040 measured off the coating....I have used weisco shelf pistons in several builds with great success. I recommend .0045-.0050 for your hp goals