I know its not boat related but hoping for some fedback from engine builders. Puting together a turbo Nissan for my kids car and changing the stock cast pistons to forged. Last season he had a detonation issue with the ecu tune and cracked a couple of ring lands. What is a ballpark acceptable difference in piston weight so I dont have to get the motor rebalanced.

I don't like to see an engine more than 10 grams out of balance. You can lighten up the new pistons if they are heavier than the old cast ones. It is pretty easy to take material out just above the pin boss. You shoud be able to remove at least 15 grams pretty easily. Hope this helps, Eddie.

Thanks for the reply. The new pistons are about 60gr lighter than the stock pistons. Sent the rotating assy out today. This motor is called a sr20 basically what was the foundation for the drifting wave in the 240sx and Silvia (Japan only) engine. Factory intercooled turbo, main bearing cap girdle, windage tray,oil sprayers for cooling the bottom of the pistons, forged crank, variable valve timing and some other little features stock. Pretty neat little 2 liter. Very easy to get 400hp to the rear wheels with stock components on pump fuel. Not many street cars will run with a 2000lb 400hp car, very humbleing for me being a v8 guy. Thanks again.

t,
This is a 4 cylinder correct ?? If so, the weight of the pistons does not affect the balance of the crankshaft. As long as all four pistons weigh the same, or within a gram or two, there is no need to rebalance anything. In a 4 cylinder engine, there is two piston and rod assemblies moving up at the same time as there are two moving down so they counteract eachother. When you balance a 4 cylinder engine, you do not put bobweights on the crankshaft like a V-8 or V-6, you just balance the crankshaft by itself, and then make sure that the rods and pistons all weigh the same. If someone is trying to tell you otherwise, you need to find another machine shop

Bill Koustenis
Advanced Automotive Machine
Waldorf Md

BillK is 100% correct. If this assembly was already balanced, you only need to weigh the four new pistons against themselves.

Thanks for the reply. I guess I should have been more specific. The machine shop didnt direct me I just dropped the assy off and asked therm to balance it. Thats ok at least all the components will be the same weight and I will know the crank is balanced.