1JZ/2JZ “Supra” rod bearing options

[KnightEngines]

Australian made ULX110 10/40

[n2xlr8n]

that is what I would call a good recommendation for crower & acl .

Absolutely x2.

[ptuomov]

Here's another novice question about rod bearings.

Suppose that you run Clevite H or HX type bearings. The big end bore specification is min/mean/max 55.024/55.033/55.042mm (2.1663/2.1667/2.1670").

Would you rather run a bearing in a big end housing that is 0.010mm (0.0004") too loose relative to the max vs. too tight relative to the min, assuming the bearing clearances are correct and the same?

Without much experience or knowledge, I would rather go too tight for more crush, but I don't really know when those bearings start deforming too much. Or are these spec ranges so tight that it doesn't really matter?

[ptuomov]

We ended up running ACL bearings originally intended for Gord Sierra Cosworth YB turbo engine.

[jed]

ACL is a good choice. What was the shaft size rods and mains and was the crankshaft and rods factory or after market, what was the final bearing vertical clearance rods and mains and why did you arrive at that clearance, what was the clearance at 75'/80 from vertical, what brand oil, weight and synethic or not.
Have you ran the engine yet and what was the oil pressure and how did the bearings look at tear down.
I have to say I have checked maybe 10 new or slightly ran short blocks and the bearings clearances were always
more than factory specification called for.
Glad to hear you got it running and hope it performs as designed or expected.

[ptuomov]

ACL is a good choice. What was the shaft size rods and mains and was the crankshaft and rods factory or after market, what was the final bearing vertical clearance rods and mains and why did you arrive at that clearance, what was the clearance at 75'/80 from vertical, what brand oil, weight and synethic or not.
Have you ran the engine yet and what was the oil pressure and how did the bearings look at tear down.
I have to say I have checked maybe 10 new or slightly ran short blocks and the bearings clearances were always
more than factory specification called for.
Glad to hear you got it running and hope it performs as designed or expected.

It’s a 33 year old forged stock 938 S4 crank that is extremely durable, handles any relevant power level, and does not wear. They came out at the middle of the tolerance range from the factory in the late eighties and they are right in the middle of the tolerance range decades later regardless of the mileage. The nominal 52mm shaft size specification is almost exactly the same as that of Ford Cosworth YB. The rods are custom I-beams with 157.50mm length that is very close to an existing imperial size (6.2”) which means there were good forging a to start with. Clearances are in the 0.04-0.05mm range which was achieved by using one regular and one extra clearance shell ACL/YB bearings. The tunnel size in the rods worked out nicely such that the same rod can be used with both stock Porsche/Glyco bearings and ACL/YB bearings. The oil is 10W-40 (break in), 15W-50 or 20W-60 (synthetic) depending on the day, high viscosity being there for the cams and lifters. The stock nominal pressure specification is 8-10 bar (116-145psi !!!) and it works out well even with 70mm/2.75” main bearing sizes at 8000rpm. The four cylinder versions of the same engine (944/968) have been run with 87 psi oil pressure to 8500 rpm. The car has been on the dyno for a couple of weeks now (passes not continuous running!) with 8000rpm redline. The break in for the new rotating assembly took about 20 seconds as it has Nikasil plated bores, which are either permanently right or wrong. No issues so far, other than air conditioning compressor isn’t yet sold on the 8000 rpm.