Piston to bore clearance

Hi guys, firstly thanks for the HP Academy really enjoying the information.

Watching the build of the 2JZ short motor you stated that the customer had purchased a new standard block and new standard bore pistons, when you had the block at the machinist there was a slight issue found with (I think) cylinder 1 so the final piston to bore clearance was slightly larger than you would normally aim for, you were aiming for 35thou clearance but ended up with 40thou.

So just wondering.... this is a 6 cylinder aiming for 1000bhp so you are aiming for 167bhp per cylinder, if this was a 4 cylinder aiming for 1000bhp > 250bhp per cylinder would your target clearance remain the same at 35thou or would it be larger because you had increased your target to 250bhp per cylinder?

Also if your aiming for 35thou clearance on your 2JZ iron block if the was an aluminium block would this change the target clearances at all?

Last one > at what point is the clearance too much? assuming we have correct ring gaps I guess the issue here is the piston slapping the bores? would this give the motor an overall shorter life or would this lead to a failure quickly?

Cheers.

Yes, you'd want to account for the specific power level of the engine when selecting the piston to wall clearance. This does go hand in hand with the application though so it can't be considered in isolation. 0.0035" is relatively tight for a 2618 forged piston in the first place so I'd definitely add to this as the power level dictated. One of the other reasons we stuck with CP's recommendations is because we are running the 2JZ on E85 which runs cooler than pump gas.

Generally an alloy block will expand more as it heats up compared to a cast iron block due to the thermal expansion coefficients of the respective materials. Again this is accounted for in the recommendations of the piston manufacturer.

If the clearance is excessive you'll suffer from piston slap where the piston rocks in the bores which physically can be heard. This also increases wear and the rings don't tend to seal as well since they aren't supported as well by the piston. lastly we see the oil consumption increase.

Perfect thanks Andre

at what point do you start getting piston slap? 5-6 thousandths piston to wall clearance with a forged piston and iron block? or does it need to be closer to like 10 thousandths piston to wall clearance to start hearing/getting piston slap? where does this start/stop typically? obviously every setup will be different but just looking for a general rule of thumb on this.

@Sam it will depend on the specific alloy used in the piston as well as the piston design. in my experience you're likely to start getting a little noisy above about 0.006" when the engine is cold.