Thread: How not to treat a genuine SR20VET

If you happen to score yourself a genuine SR20VET, please do NOT:

1. Overboost it to 20psi on a T28;

2. Let it run lean due to a faulty Inlet Air Temp sensor.

If you do both at the same time, you may well find out that it has done this:



Of course, it's widely known that overboosting and leaning out are two of the best ways to destroy a motor. So I guess doing both at the same time makes me a chump.

The detonation also made a complete mess of the headgasket. Compression was 150-70-60-60 . You can see the signs of detonation on the other cylinders:




The bits of #4 piston went through the turbo's exhaust wheel, fortunately GTiR turbos are cheap & plentiful over here.




Fortunately, the bores were completely unmarked!




The debris had also bent both exhaust valves and one intake valve on #4. Fortunately, the valve guides were unharmed.

So I then set about rebuilding the motor:

I chose a set of Arias forged pistons, as they were available with the same 15cc dish as the stock pistons - as opposed to the usual 12cc dish in DET's.
Despite having no valve reliefs and a bigger squish band, there was over 2mm piston-valve clearance on the VET cams - which have more lift than the SR20VE cams I'm using anyway



The rest of the parts were just genuine Nissan SR20VET stuff:
- main bearings
- big-end bearings
- thrust washers
- Head gasket set
- 2x exhaust valves
- 1x intake valve
- head bolts
- head gasket set


The head got a bit of a tickle while it was apart - the chambers were cleaned up a bit and the valve seats got a 3-angle grind, along with the remaining valves being refaced. That was all that it needed in the eyes of the cylinder head shop, the chambers were already well deshrouded and the ports were plenty big enough from the factory.




Intake ports:




Exhaust ports:




Chamber size is 40.5cc:




Head gasket in place, ready to accept the cylinder head:

yeah, thats what happens, Im surprised the bore didnt get damaged at all from the detonation. It usually does, Ive had ring lands crack and detonation damage on top of the pistons and block and had scoring of the block wall where the cracked ring lands were from the dislodged pieces just floating there and being pressed into the wall by the rings.

Yeah I'm fortunate that the ring lands remained intact, which is surprising considering how narrow they are:

thats a very interesting break, Wow, those the stock pistons? they come with a coating, nice if they are stock. But yeah it almost apears that there was piston to valve contact that caused the break, maybe over rev. doesnt quite look like detonation. Weird

Yeah those are the standard pistons.

You can't see it in that picture, but it looks like the fracture started right above the end gap of the top ring. I'm guessing what happened is that the ring got so hot that the gap closed to nothing, and its ends tried to shear. Cos of the shape of the dish there's not a hell of a lot of material there, either.

When that bit broke off it hit the spark plug electrode and closed the plug gap, so the car dropped a cylinder - that's what made me pick up on the problem. When it dropped a cylinder it was only just past the 4000rpm VVL switch point, so it certainly wasn't done by an over-rev.

i was gonna say either that it just got hot enough that it started to crack it but not detonate, Good pistons and good design for sure. Those new ones should do the trick though. Just gotta get the a/f situated.

Good luck with the rest of the motor. Looks good soo far.

Oh wow. The build looks great!

Some carnage... but it looks like you bounced right back up

what turbo u putting on...?