Report that engine failure

[CEF33Y]

See, this is why I still come here. Actual info/feedback. Awesome.

Ahh, that makes sense re filter now that I think about it.

So, still my fault, as I kept thrashing with excessive blowby 😆. The top of the pistons are "black"

I need to update this with some photos.

Is there a direct correlation between compression and blowby? I.e I didn't think 150ish compression was bad. (Even though the FSM quotes compression to be 174psi/300rpm)

The restrictors/head studs etc was in prep for the elite 2500+ flex sensor install, so still going ahead, just need to sort out the bottom end first.

Rabbit hole well and truly breached... haha.

[Dose Pipe Sutututu]

1 hour ago, CEF33Y said:

Is there a direct correlation between compression and blowby? I.e I didn't think 150ish compression was bad. (Even though the FSM quotes compression to be 174psi/300rpm)

Kind of, one of the many factors. Any motor will have some combustion gases escape the combustion process and end up in the crank case. The more boost, the more that effect is exacerbated and that pressure generally is relieved by flowing into the head and out of the cam cover breathers.

This is why you often see big RB setups with catch cans as big as their sumps, RBs love to breathe and the only way that pressure escapes is out of the cam cover breathers OR if you have a sump vent into a catch can.

It's not uncommon to see a catch can have a catch can -> sump drain, sump vent, 2x cam cover fittings going into it. Meanwhile some random 2JZ or 1JZ with 700kW runs a $30 eBay catch can and it's dry lol.

[CEF33Y]

15 minutes ago, Dose Pipe Sutututu said:

Kind of, one of the many factors. Any motor will have some combustion gases escape the combustion process and end up in the crank case. The more boost, the more that effect is exacerbated and that pressure generally is relieved by flowing into the head and out of the cam cover breathers.

This is why you often see big RB setups with catch cans as big as their sumps, RBs love to breathe and the only way that pressure escapes is out of the cam cover breathers OR if you have a sump vent into a catch can.

It's not uncommon to see a catch can have a catch can -> sump drain, sump vent, 2x cam cover fittings going into it. Meanwhile some random 2JZ or 1JZ with 700kW runs a $30 eBay catch can and it's dry lol.

Tell me about it! My brother has a 2jz JZX 90, and runs pretty much a single breather hose into an always empty coke bottle. 

I'd never thought much about the oil being forced though the valve stems into the combustion chamber. 

 

I think while I'm welding the head drain/vent fitting to the sump, I might add another couple of fittings for some more vents.

[GTSBoy]

5 minutes ago, CEF33Y said:

I'd never thought much about the oil being forced though the valve stems into the combustion chamber. 

It shouldn't normally be much of a problem. But, add high crankcase pressure to a moderately worn set of valve guides and you can get a bit going through. Valve stem seals used to be (mainly, in the mostly NA days) a throttle off thing, where the high vacuum in the cylinders would pull oil through the worn guides. Now, we have mucho boosto to help and we can get it on throttle.

Edited August 1, 2023 by GTSBoy

[Dose Pipe Sutututu]

5 minutes ago, CEF33Y said:

I think while I'm welding the head drain/vent fitting to the sump, I might add another couple of fittings for some more vents.

Since you're going tits out, I would suggest this:

• head drain/vent (make sure the drain is above the sump oil line, if not it is pointless
• the biggest catch can you can fit
• sump breather to catch can
• catch can to sump drain
• decent sump that's baffled, the Aeroflow ones look decent (ignoring the brand)

Silly RB will push oil into the catch can and it will just flow back into the sump. Happy days!

[CEF33Y]

Thread bump, again!

Although, no bad news this time. Posting for the sake of possible root cause.

Basically, I rebuilt it (mostly stock), installed Haltech + sensors, had it running fine on new ECU. 

Still not really understanding why it cracked pistons last time.

Got to tuners, and while checking timing, noticed +-10deg of timing scatter while revving.

Changed CAS, and it was rock solid.

While not definitive, can't imagine seeing 20+ psi with that amount of scatter would be a good thing. Also glad I found something.

 

Bit more of a run down;

Carried out a stock rebuild, a set of stock pistons, out of a spare bottom end.

Everything stock apart from head studs and oil restrictors. (so I can pretend I didn't let the Nissan out, ha.)

Armed with the measuring gear and FSM, set about doing overhaul.

Oil restrictors as per oil control thread for a RB25, stock oil pump, drifting.

Head drain/vent from rear of head, to passenger side of sump above oil level.

Two dash 10 vent lines from drivers side of sump (unused atm)

Hi octane style cam cover breather kit

Splash covers over last 2 cam caps.

Both breather lines from cam covers to vented to atmosphere catch can, not plumbed back into sump (wanted to see what it was actually breathing).

Got it run in (did about a 1000km) no to low boost scenario, As I had questions over old ECU setup.

Installed haltech +sensors for flex

Retune on E85 (finding CAS Issue along the way), made 300rwkw at 20psi, out of wastegate.

Did a drift day the next day (yes, it was a big weekend!) and was checking catch can throughout the day, ZERO blowby.

I mean nothing. Lines from cam covers are not even wet.

Done a bunch of street driving, spirited and catch can is still dry.

Early days I guess, but pretty happy so far.

Also now run 10w60, up from the 10w40 that I used to run.

Oil pressure is significantly better, especially when hot (as you would expect)