3SGTE Ring land failure

[Jetboat3sgte]

This question has been asked many times on this board but, this is a variation on the theme!

How much power can a 3SGTE produce reliably on standard pistons. The twist is - I am running it in a jet boat so it is highly loaded and thus heat generation could be an issue. What boost level can stock internals handle

Current setup is Gen 3 block/gen 2 pistons/ T3 turbo with super60 compressor/water air intercooler (inlet air temp after butterfly is 32°C) Running 14-15 psi boost. Haltech E6K ECU and 550 cc injectors. 3" exhaust about 300mm long straight out back of boat.

Tuning, running 12.9 AFR up to 3000 rpm 12.5 to 3500 and 11.8 to max revs which is about 5500 rpm. EGT running at 710°C at max revs. timing is 16° at 14 psi/5500 rpm. Have a knock block and have not detected any detonation so far. It is relatively easy to tune as a jet unit will draw a given load at given rpm so it is basically a dyno.

My experiences so far are broken ring lands on 2 separate occasions, when I removed the pistons there is no sign of detonation on either the piston top or the head.

Am wondering if I am just not "hearing " detonation what maximum timing is sensible. I have experimented with less timing advance, but this heats up the manifold (too retarded) and resulted in the death of several ceramic turbos (EGT of 900°C).

Any experience out there to steer me in the right direction.

[fivebob]

Lower your AFR between 3000-3500, 12.9:1 is too lean at that point.

In my experience all 3S-GTE ring land failures occur just below the deepest point of the intake valve pocket, so, if you want to run stock pistons, I'd suggest radiusing and polishing the intake valve pockets.

[Mr Revhead]

In my experience all 3S-GTE ring land failures occur just below the deepest point of the intake valve pocket, so, if you want to run stock pistons, I'd suggest radiusing and polishing the intake valve pockets.

so does that mean that section of the piston is where detonation occurs? or is there another reason for the failures?

[fivebob]

In my experience all 3S-GTE ring land failures occur just below the deepest point of the intake valve pocket, so, if you want to run stock pistons, I'd suggest radiusing and polishing the intake valve pockets.

so does that mean that section of the piston is where detonation occurs? or is there another reason for the failures?

Interesting question, and one for which I don't have a definitive answer.

I've seen about 20 3S-GTE pistons, all have failed in the same place, with the crack originating from below the inlet valve pocket (usually the left valve pocket). That's not to say that they do not fail on the exhaust side too, just that I haven't seen one that has.

As I see it there are two possibilities.

1. That is the weakest area of the piston and the force transmitted to the ring lands at that point is greatest. Hence my recomendation to radius the pockets in an attempt to remove any stress risers created by the sharp edges.

2. That is the furthest point from the initiation of combustion and has no squish to prevent detonation. So detonation is more likely to occur there, hence the recommendation to polish the valve pockets to reduce the chance of detonation. That said however it seems strange that it does not occur on the exhaust side (or if it does it's with far less frequency), which is hotter and likewise has no squish to combat detonation.

It could also be a combination of both, which would go some way to explaining why it does not occur on the exhaust side.

[Jetboat3sgte]

Thanks for the input so far guys!!

It has indeed failed below a valve pocket on the inlet side, front valve in this case.

Is it due to detonation of just failure due to compression pressure ? Given 8.8:1 static compression increases to 15:1 at 14.7 psi boost.

I have another block some 8.5:1 gen 1 pistons, and new rings coming tomorrow, so should have it going again by the end of the weekend. Guess I will limit boost to 10 to 12 psi, richen the fuel mixture and hope for the best.

cheers Karl

[strx7]

water injection is your friend...............

are you running a water to air intercooler?

[Diesel PWR]

detonation happens on the inlet side of the pistons because it is the coldest side of the chamber, fuel falls out of suspension and you end up with areas of poor mixture quality and end gas explosions, detonation is what broke your lands, i would be checking the accuracy off your knock block and tune.

[Adydas]

water injection is your friend...............

are you running a water to air intercooler?

Would be good, im sure you could pipe it to suck the water from the lake etc and then pump it back into it? Better yet use the it like a "ram air setup" so the boat has a sealed hole around a pipe forcing water over and into a wta and then ejecting it out somewhere fancy, ( on the driver if he wants a luke warm shower perhaps? )

Man i wanna make a boat now..

[fivebob]

fuel falls out of suspension and you end up with areas of poor mixture quality and end gas explosions,

I find this rather hard to believe as the piston crown temp, and swirl produced in the cylinder, would preclude this occuring at normal operating temperatures. Also aftermarket pistons, which often have a higher CR, do not show any signs of detonation, even at higher advance levels than stock. Therefore I think it's more likely to do with the design of the piston than any inherent fault in th eco

detonation is what broke your lands, i would be checking the accuracy off your knock block and tune.

It's rather obvious that detonation caused the problem, along with countless other 3S-GTEs. However, unless the base timing is out by a considerable margin, the ignition advance quoted is well within safe limits for a 3S-GTE with an intake temp of 32C.

[RedMist]

My bet is you are breaking the ring lands on cylinders 2 and 3. I wonder if its more of a block design issue and two and three are hotter than one and four, causing detonation or micro seazures.

The pistons from the rally car engine had a light peppering of detonation on all four but the only ring lands to break were, number 3 as described above, and 2 on the lower ring land (between oil control and 2nd ring) and then it was't anywhere near the valve pockets...more a 10mm distruction midway between exhaust and intake.

[Jetboat3sgte]

detonation happens on the inlet side of the pistons because it is the coldest side of the chamber, fuel falls out of suspension and you end up with areas of poor mixture quality and end gas explosions, detonation is what broke your lands, i would be checking the accuracy off your knock block and tune.

If this is the case richening the mixture would make the problem worse. Which is contrary to most theories on detonation.

[Jetboat3sgte]

My bet is you are breaking the ring lands on cylinders 2 and 3. I wonder if its more of a block design issue and two and three are hotter than one and four, causing detonation or micro seazures.

The pistons from the rally car engine had a light peppering of detonation on all four but the only ring lands to break were, number 3 as described above, and 2 on the lower ring land (between oil control and 2nd ring) and then it was't anywhere near the valve pockets...more a 10mm distruction midway between exhaust and intake.

In my case cyl 4 both times

[strx7]

In my case cyl 4 both times

Your engine faces North South in the boat and gets a fair bit of cooling from the air going past it????

[RedMist]

In my case cyl 4 both times

The dogleg port? Now thats a bit different. Had heard of them cracking the block on 4, apparently reasonably common, but not breaking ring lands. Would be interesting to see how the EGT's for each cyl sit.

We did a massive amount of flow work to the dogleg port in order to get it to flow match the other three on a gen 3 head.

[Jetboat3sgte]

In my case cyl 4 both times

The dogleg port? Now thats a bit different. Had heard of them cracking the block on 4, apparently reasonably common, but not breaking ring lands. Would be interesting to see how the EGT's for each cyl sit.

We did a massive amount of flow work to the dogleg port in order to get it to flow match the other three on a gen 3 head.

My egt is in port 4. and O2 can be in port 4 or after the turbo (normal postion). I am running a gen3 NA head off a 1994 caldina.

Based on your work it appears that #4 should run richer than 2 and 3.

Where does #4 cyl crack. Im really interested as in the last stages of its life I couldn't check the AFR as the wideband was reading really erratically, EGT was stable. I put this down to a leaky headgasket as water really stuffs up o2 sensor readings.

[Jetboat3sgte]

In my case cyl 4 both times

Your engine faces North South in the boat and gets a fair bit of cooling from the air going past it????

Yep north south still on factory lean, but no airflow past engine as is under a cover. Using raw water cooling straight fom the jet unit, engine temp varies from 60 to 90°C depending on speed.

[fivebob]

My bet is you are breaking the ring lands on cylinders 2 and 3. I wonder if its more of a block design issue and two and three are hotter than one and four, causing detonation or micro seazures.

I doubt that it is a block issue, though #2 & #3 are more common failures, with #2 being more common in Gen III+ and #3 in Gen 2 engines, I've seen all pistons fail.

Both my engines had severe failure of #2 between the second ring and the oil control ring, with minor failures in #3 between first and second rings. However in farmenrdaves engine #1 piston failed, #3 and #4 had broken lands between below the top ring. In all cases the crack originated on the left side of the piston (when looking at from the intake side).

In the case of both my engine failures, one MR2 & one Caldina, occured under the same circumstances, long uphill road on a hot day and too much boost for the stock ignition map. When the Caldna failed I noticed that the oil temp got very high (125C+ when it normally runs about 95C) and I know that oil cooling plays a big part in controlling detonation in the 3S-GTE.

When all said and done, engines detonate, it's just that with the stock pistons this causes ring land failure. As nothing can be done about the brittle nature of the stock piston then, as I see it, the only option is to reduce the chance of detonation, and remove any stress risers from the piston.

For my own peace of mind, along with using water injection, as I recondition the engines I am going to be replacing the pistons with Mahle forged items, as these are made out of 4032 alloy this allows for closer bore/piston clearances and as such have none of the forged piston slap on start. Only issue is that they seem to only available in 0.5mm oversize which may run into that other 3S-GTE probolem of thin walled blocks

[Diesel PWR]

detonation happens on the
inlet side of the pistons because it is the coldest side of the chamber, fuel falls out of suspension and you end up with areas of poor mixture quality and end gas explosions, detonation is what broke your lands, i would be checking the accuracy off your knock block and tune.

If this is the case richening the mixture would make the problem worse. Which is contrary to most theories on detonation.

when the fuel falls out of suspension you end up with parts of the mixture being extremely lean. Ive seen heaps of ring land faliures and they are often on the inlet side. Im not saying mixtures have anything to do with your faliure but it may answer why the intake side.

[fivebob]

when the fuel falls out of suspension you end up with parts of the mixture being extremely lean.

Extremely lean pockets don't cause detonation, they might just inhibit it as the flame propagation speed decreases dramitically when there's no fuel to burn

More likely, if you follow your line of thinking, is that it would be caused by having denser mixture on the inlet side. However combustion chamber swirl should stop that from occuring.

[Jetboat3sgte]

In my case cyl 4 both times

The dogleg port? Now thats a bit different. Had heard of them cracking the block on 4, apparently reasonably common, but not breaking ring lands. Would be interesting to see how the EGT's for each cyl sit.

We did a massive amount of flow work to the dogleg port in order to get it to flow match the other three on a gen 3 head.

Redmist you will have to explain "dogleg port" to me, all the ports on my head appear straight through and are the same. I am also running a ST215 caldina turbo inlet manifold.