Hey HT, just want to make sure I'm reading the specs on these pistons correctly. ( part # on these pistons is SC7101 if you need to look up any more info.)

The sheet that came with the pistons shows a bore diameter or 3.209(81.50mm) and calls for 0.0030 ptw clearance. It then says the piston size at gauge point 0.5 inches from the bottom of the skirt is 3.206... Thats a difference of 0.0030. If I'm reading this correctly these pistons have the tolerances built in and im good to go at 81.50 mm bore?

Also, this B16 is going to be turbo / water meth around 380-420 whp and used pretty much exclusively for road courses with very light duty "daily driving". From the research I have done 0040-0.0050 seems to be a standard ptw for bigger power / more extreme use than daily driver. I'm leaning towards what CP says, but am open to what you guys think about the bigger PTW clearance.

 

They don't have a clearance built into them. It depends what kind of
Power your going for as to what PTW you should run. Generally I like .0035 to start. A little loose is a lot better than to tight. .0035 is plenty for your power level. You don't need .0040 until the power starts getting higher

 

Yes, you are correct.

When you buy a set of pistons, you buy/order them for the size of the cylinder that piston is going into. For example, CP piston 81.5mm, 81.5mm (3.209") is the intended final bore size, and the actual diameter of the skirt measured at the manufacturers gauge point will read close to or the same as its intended clearance. If these pistons call for .003" clearance, when mic'ed at the gauge point it would read approximately 3.206".

.004-.0045" sounds reasonable for the application. You will definitely have more cylinder pressure and heat, but simultaneously have a relatively cool intake charge with that water meth kit and those pistons aren't very big, therefore there are not large dense areas of aluminum (pin bosses, thick skirts) to expand so much as to worry about opening up clearance larger. Being its not a DD, piston slap is obviously not as much of a concern upon cold start ups.

 

I'm running 0.004". 81.5 mm Turbo B16, 350+ whp@12 lbs. I don't have piston slap issues on cold start, etc. I would not run smaller than 0.004".

 

You are aabsolutely right. I had piston to wall contact at. 0035 and mid 400 whp level. Im now at .0045 with no issues. I feel that cp understates the recommended ptw a bit

 

This makes me nervous to hear. Im at .0035 on a benson block. Its laskey built. Looking for 4xx-6xxwhp. 84mm lsvtec setup, 10:1 comp.

 

Tight for 600's.....

I've seen motors WAY more loose than .005 run just fine/no smoking. Granted I assume they aren't daily drivers.....

Loose is fast.....

 

Mine isnt a daily but wont be ran on anything less than 400whp....time will tell! "Crosses fingers"

 

I would go .0045".

 

Thank you guys, planning on going 0.0040