Time for new rings??

[2eighTZ4me]

New wastegate installed. Made a couple pulls at around 18psi last night. Pulled in the garage and opened the hood and smoke is spewing out my valve cover vent, and my catch tank vent off the side of the block (while idling). No visible smoke out the exhaust though. Checked oil - no water. Head gasket appears to be intact. The "mule" motor in the car now is a stock 80 ZX F54/P79 with 130K on it. I'm guessing now that I've applied boost, the rings are crapping out. That's the only thing I can think of. Just replaced valve stem seals. Ideas??

[HowlerMonkey]

A few weeks ago, someone with a "shopping list" hit my infiniti M30 (L28et) and stole only things specific to this car such as dash switches, rear view mirror and three ecus I had in the car.

 

While stealing ecu #3 (the one running the car) they neglected to unbolt the harness and instead yanked it until the ecu connector broke off.

 

This messed up my harness and, though I was able to get it plugged into another spare ecu, the car had intermittence issues with 2 and 4 and the bad connections caused both cylinders to run lean under boost on the highway.

 

I heard it and let off but came home with low compression and piston slap when the car is cold so I will assume the skirts were slapped off of two pistons.

 

In your case, you might look through the sparkplug holes and see what you can of the piston tops since you will sometimes see where detonation has burned around the piston top toward the rings.

[2eighTZ4me]

Time for new rings AND a #3 piston..... although the rings looked fine.

 

 

 

Went through the motor Wed. and replaced pistons with a set of dished pistons (these were flattops, and I was told they were dished) new rings, new rod bearings, ARP studs and the motor is back in the car awaiting the tranny. HowlerMonkey - you were spot ON!! I didn't hear any slap, but man was she smokin' something fierce.

 

So there you have it - I broke it reeeeeeeal good.

[Zmanco]

Why do you think the skirts broke? Perhaps from running it too hard (18 psi) with excessive piston slap? I don't recall ever seeing that failure on our L engines.

[2eighTZ4me]

Skirts broke (my guess) from either detonation or lean condition. The car has been tuned for lower boost (rather rich, I might add), but I found my boost leak and buttoned that up and was taking it for a jaunt. When the boost hit in 3rd gear at about 50mph, it broke the back tires loose and the motor just shot to redline. I didn't have a chance to look at my mixture - it all happened so fast. Taking it back to the tuner as soon as he's back in town to have it all straightened away with more boost.

 

I can't help but think though....I'm not using MS for spark control - I have a (rather antiquated) Electromotive HPV-1 unit for spark. I would normally be detonating at anything over 34 degrees potentially, but I've got it set for 18 degrees initial, 30 degrees at 3K, and then it backs off 3.5 degrees from 3000-5500RPM. That puts me about 26.5 degrees at anything over 5500. Rev limiter is set to 6250. That's not really a heck of a lot of timing to cause detonation. My mix under 5psi boost gravitated toward the 11.8 - 12.3 area, and the several pulls I did at 10psi showed very similar mix readings. So - I honestly don't know what broke it. Things that make you go "hmmmmmmmm".......

[S130Z]

I had the horrible smoking happen to me, it ended up being 3 pistons broken at the rind lands. I will let you kow that my timing is about 21~ degrees at 15psi. I started loosing power over that number, most likely caused by detonation.

[Zmanco]

26.5 degrees advance at 18 psi boost with flat top pistons sounds pretty aggressive to me. What's the CR? I'm running low teens advance at 15 psi with a CR of 8.3. From what I understand, the air/fuel mixture burns much faster when it's compressed and rich such as under boost, so it really doesn't need a lot of advance.

 

Going back to the broken skirts, so do you think the engine already had piston slap and the extra detonation "rattled" the pistons enough to break the skirts? For some reason those pictures really surprised me - seems like it would be really hard to break the skirts unless the pistons were really loose in the cylinders.

[HowlerMonkey]

I've seen skirts slapped off of more than a few engines whether turbo or not.

 

The non-turbo car did it because some kid got the car hand me down from mom and proceeded to run to redline only seconds after starting the high mileage engine....with the engine at about 11 degrees F.

 

One turbo engine I had did this because the thermostat stuck open in the dead of winter while I was on the highway running hard.

 

I saw the temp gauge go down but that's pretty common since the temp sensors are easily stressed when pulling the connector off and will exhibit intermittence.

 

I figured it was the intermittence and kept at running hard and the car changed how it ran as the engine cooled rapidly.

 

When I pulled over on the side of the highway, the side of the block seemed to be about the same temperature as a beer out of the fridge.........guess the L28 cooling system works pretty well in 10 degree weather.

 

I am swapping the longblock today and may have pics of mine later on tonight.

 

I'll run lower boost and bring the timing back until I confirm the path from the ecu to the injectors is no longer weak causing lean condition in a cylinder or two (this is a sequential infiniti M30 ecu).

[HowlerMonkey]

LOL....just noticed the "kaboom".

[2eighTZ4me]

I've gotten mixed timing numbers from many folks on this forum, so I don't know really who to believe. I'm pretty sure it was detonation that killed the piston. I have since dropped back on the timing to about 22 total at 5500rpm. I have also decreased my boost duty targets until I can get it back to the dyno for the final tune. Add insult to injury, the brand new Spec clutch that I bought is slipping under extreme boost. Gotta figure that one out before going back to the dyno. It's always somethin'......

[510six]

Broken skirts, the several L28's I have seen with broken skirts are two turbo motors running 17+ psi on fairly large turbos with stock cast pistons. The third was an L28 with a shot of nitrous, the thing all of these motors had in common is that they detonated due to less than conservative timing on pump gas . With a cast piston NA L28 conservative timing with pump gas is the ticket to engines living , because it doesn't take much detonation to break stock pistons.

 

Currently with a stock NA L28 on E85 246rwh was made with 28* of timing under boost, this was possible due to the higher octain of the E85 and the CDI AEM (EMS) ignition . Years ago I ran 80 10 lb bottles of nitrous through a cast piston L28 stroker in a year with no engine failure, due to fairly conservative timing and a MSD digital 6 CDI on pump gas the car ran mid 12's.

 

Using a methanol injection system will also enable more aggressive timing due to lowering the intake temps and raising the octain.

[2eighTZ4me]

510six - I believe you are 100% on the money with your analysis. My wastegate wasn't opening, as I had the boost targets set on the high side - next thing I know, the gauge is reading 20psi, and that was that. Live and learn I guess. The motor needed a once over anyways. Methanol is looking like the route I'll be going eventually. Either that, or go EDIS and let MS control the timing too.

[510six]

What type and heat range of spark plugs are you using? If you are using a NGK BPR6ES the plug is to hot for anything over 10-12 psi I would suggest using a set of NGK BPR7ES-11 gapped to .30 or .32 this will help to eliminate potential hot spots in the combustion chamber. Running a CDI ignition IMO is not a bad idea as the extra voltage keeps the spark from being "blown out" as combustion pressures rise. Methanol injection provided it is tuned correctly will provide octain and cool intake temps and these are never bad things with a forced induction motor.

[HowlerMonkey]

I second the bpr7es plugs but make sure they aren't the ones with the V in the ground electrode.

 

My new theory is that broken piston skirts with no other damage to the pistons is from pre-ignition most likely ignited by the hot spark plug.

 

This pre-ignition damages very differently than detonation in these engines where you see broken ring lands or the piston top burning around toward the rings.

 

Every broken skirt I have seen is on the driver's side while the spark plug is on the passenger side....Hmmmm.

Edited May 28, 2010 by HowlerMonkey

[2eighTZ4me]

I just ordered 12 of those bad boys from a small engine parts dealer. Lawnmower plugs eh??? This oughta be interesting. Howler - I don't know if they've got a V in the ground electrode. Can you tell from this link?

 

http://www.mfgsupply.com/m/c/BPR7ES-11-BOX.html?mv_pc=Froogle

[Zmanco]

The NGK BPR7ES has a traditional ground electrode. I run them as well but limit advance to around 10 degrees at boost above ~10 psi just to be safe.

[510six]

Running the colder plugs is a good step in the right direction, I still would suggest using a CDI, a quality unit can be had for less than $200. If you are still using a distributor a loose bushing or a worn bearing can let the distributor shaft "wobble" and create spark scatter and incomplete ignition esp. at high rpm. When I was still using a distributor a new bushing was made using aerospace plastic and it eliminated timing issues.

 

http://www.summitracing.com/search/brand/Summit-Racing/Product-Line/Summit-Racing-Street-Strip-Multi-Spark-Digital-Capacitive-Discharge-Ignitions/?autoview=SKU

[HowlerMonkey]

The turbo distributor could really use a counterweight on the rotor.

 

I use the crank trigger setup when I run a 280zx turbo ecu but now must use the distributor when using the M30 sequential ecu.

[2eighTZ4me]

I'm running an Electromotive HPV-1 crank fire ignition. No dizzy to mess things up. It's about as solid and reliable ignition as you can get - aside from the fact that it's old and doesn't have much adjustability for backing the timing down under boost. Looking in to replacing eventually, but not in the cards just yet....

[510six]

http://www.megamanual.com/ms2/wheel.htm

 

So you are retarding your timing under boost in a similiar manner to using a shot of nitrous. It works, I would start out with about 15* in the higher compression NA motor on pump gas under boost.