We decided to run a piston scuff test with our NA 402 crate engine. First we built the test engine with .001 less piston to wall clearance than normal to see if this would live, the tighter piston should quite the cold start. Ran our traditional 3 hour break-in with RPM steps and various loads applied. After break-in oil was changed from valvoline 10-30w to 10-30w Mobil-1, coolant was Dex-cool. Engine leak down after break-in was.
1-6%
2-5%
3-6%
4-5%
5-5%
6-5%
7-7%
8-6%


The test:
1-Warm up engine to a coolant temp of 230f. (!!)
Warm up engine oil to 210f min.
2-Accelerate the engine to torque peak RPM -500(4500RPM) at WOT, hold for 5 minutes at 230f coolant temp. Do not allow oil temp to exceed 266f.

3-Accelerate the engine to torque peak RPM(5000RPM), maintain load at WOT and hold for 2 minutes at 230f coolant temp. Do not let oil temp exceed 284f.

4-Accelerate the engine to power peak RPM(6000RPM), maintain load at WOT and hold for 1 minute at 230f coolant temp. Do not let oil temp exceed 284f.

5-Reduce engine speed to 1500 RPM and remove load. Run for 2 minutes and listen for audible piston noise. If noise is detected stop test.

Repeat steps 1 through 5 for a total of 7 cycles.

Thats 56 minutes at wot with coolant temp stable at 230f. Oil temps stayed between 210-260F during the duration of test.


Leak down after scuff test.
1-3%
2-4%
3-2%
4-3%
5-2%
6-2%
7-4%
8-4%

The rings seated better during the scuff test, possibly aided by the high coolant temps. The engine will now be disassembled for inspection of pistons, bores and rings.
We also kept the EGT's between 1400-1650f during the test, so our heads will be inspected for valve and seat wear.


Kurt

 

Wow...that's awesome guys. I know who I'll be looking to to build my engine.

 

Interesting stuff.