Valkyrie

A friend of mine has had two newly-built engines blow in less than a year. Both at the track, but neither under full power.

The car is meticulously maintained and both engines were built with new parts.

The first time was going down a straight up a hill, but it was at maybe 4-6K RPMs and may have not even been full throttle.

He suspects the this engine may have been due to a failing MOP, but at the time he was using premix as well. Will an engine blow suddenly if the rotor housings lose lubrication? I assume this basically shouldn't happen if the MOP is functioning, especially since fuel and premix oil should the rotor housings at least somewhat lubricated.

The engine was rebuilt and the MOP, coils, and fuel pump were all replaced. Since the last rebuild, he installed a high-flow catalytic converter, got a retune, and also recently installed a V-mount.

This time the engine suddenly blew after applying throttle during a corner exit. He wasn't using premix, but the MOP was brand new.

There was plenty of fuel left in the tank. Boost was only 0.8 bar or so, which is what the car was tuned for. This was the second or third track day since the last rebuild.

It has stock 99-spec turbos and a Power FC and should be making maybe 320 hp with the v-mount. I think he is using #9 platinum plugs all around.

Any ideas?

Banzai-Racing

iTrader: (11)

Post up the map

Valkyrie

I will ask if he can get it.

He suspects his compressor may have cracked and been sucked in by the engine.

gxl90rx7

iTrader: (1)

running 9's all around does not make your engine any safer than factory. you have to run colder trailing too to make a difference. what plug wires is he using. although most likely a fault of the tune

also get the injectors tested. maybe an injector is underflowing, AFRs look good but one rotor ends up running a bit rich the other a bit lean and pops

Valkyrie

What would make a tune suddenly blow the engine if it had run perfectly before?

Moe Greene

iTrader: (2)

Who tuned the car If you don't mind me asking?

(Not saying its the tune nor tuner that caused the engine to blow, just super curious)

Jaiyurai

iTrader: (30)

Too little information for anyone to give you a solid answer.

Post a list of his modifications.
Post a image of his tuning map.

fendamonky

iTrader: (6)

Running without a functional OMP or premix shouldn't cause a sudden catastrophic failure (at least I don't think so, not immediately), it probably WOULD score the hell out of the housings though... The oil is acting as a lubricant between the metal on metal contact.


My guess would be in the tune. I had a relatively new engine chip the corner of an apex seal once during a low-load uphill (I was driving in to work on a Sunday and was intentionally babying the car to see what kind of fuel economy I could achieve during a commute). Even low boost can blow an engine if the map doesn't account for it.

I'm no expert professional though... So take my opinion on this with a grain of salt

arghx

iTrader: (3)

The biggest ones are overboosts and temperature compensation.

adam c

iTrader: (2)

OMP will not cause sudden catastrophic failure. This sounds like bad tuning to me. I wouldnt return to the same tuner again. You should let us know who tuned the car.......... unless it was you

$lacker

iTrader: (9)

Did he send broken engine-internals through the turbo hot-sides and then use the same turbos on the next engine?

DaleClark

iTrader: (55)

Unfortunately there are SO many factors at play here that a definitive answer will probably not be forthcoming.

Could have swapped plugs and put the plug wires on wrong, MAP sensor vacuum line could have popped off, wastegate line could have failed and overboosted, intercooler could have been seriously heat soaked...

There's also the possibility that the two engines blowing had nothing to do with each other.

Dale

arghx

iTrader: (3)

just an FYI, there can be protections for overboost and for high temperatures in the tune, if it were set up to do so. Stock ECU has this built in. Stock ECU also has limp mode which covers most failure modes of the OMP.

IRPerformance

iTrader: (41)

A failing omp will result in a loss of compression and damage to the rotor housings, but it won't "blow" a motor like that. 99% of the time a motor failing like you claim can be related to the setup and tune. Post the map or any logs and go through your fuel system. From what you are describing it sounds like he starved the motor of fuel. The stock tank baffling in these cars is inadequate. Compound that with age causing the baffles to break loose inside the tank and it is very easy to starve the motor of fuel, especially when exiting a left hand corner. Add a surge tank or aftermarket baffle and don't track the car below half a tank of gas.

BLUE TII

iTrader: (9)

You have to take apart the engines and look them over with a discerning eye to figure out what caused them to let go sometimes.

The couple engines I have had let go under light load all showed extensive previous damage that did not keep the engine from running "fine".

Warped or unevenly worn apex seals or overheated apex, side and corner seals that finally let go under light load where the seals undergo a very different stress than at full load on the rotary (gas sealing pressure is very low at light loads).

Fine cracks that form along the rubbing surface of the apex seals can suddenly crack through the apex seal with thermal or mechanical shock which is common under light load high rpm conditions.

Seal springs weakened by thermal stress allow the seals to slap in and out of their slots harshly instead of being cushioned under light loads high rpm (not much combustion pressure behind the seal to cushion it and not much spring pressure).

Overheated seal springs (usually the delicate side seal springs) can suddenly break under a light load rapid rpm change from this hammering or even low rpm hammering down into the port and back up onto the side housing on an early opening street port and then interfere with proper seal clearances and break the engine.

Valkyrie

That's what I thought, but he said it was mostly full and the car wasn't under a lateral load. His car is also a 2002 model which I think has slightly improved baffling.

I end up starving my motor once or twice every track day at one particular track... I guess I'm lucky the engine has survived so far. It happens even with 5/8ths of a tank or more.

I really need to get aftermarket baffles...



BTW, what is actually happening when your engine suddenly loses power due to fuel starvation? Is it actually knocking?

j9fd3s

iTrader: (3)

if you are lucky, no fuel = no knock.

if you're unlucky, it leans out before it stops running and goes into detonation.

AlienHack

i would like to know that too

Valkyrie

Is this more likely if you're at high RPMs?

There's this one steep uphill lefthand corner that keeps giving me problems, but RPMs tend to be fairly low when I get on the throttle and then freak out when the engine nopes out on me.

I wonder if a surge tank needs two pumps of the same capacity, or do I only need the second pump to be high capacity?... I think I'd rather just get a new baffle.

Valkyrie

Is this more likely if you're at high RPMs?

There's this one steep uphill lefthand corner that keeps giving me problems, but RPMs tend to be fairly low when I get on the throttle and then freak out when the engine nopes out on me.

I wonder if a surge tank needs two pumps of the same capacity, or do I only need the second pump to be high capacity?... I think I'd rather just get a new baffle.

Valkyrie

By the way, he seems to think that you have to replace the apex seals on both rotors even on such a relatively new engine. Is that true? I figured you could just do it one the bad rotor.

Fritz Flynn

iTrader: (263)

If I was a guessing man I'd say the tune is fine and it's not getting enough fuel.

Probably not getting enough fuel because the pump isn't getting the proper amount of electricity. This is likely overheating the pump and causing it to die.

Have you replaced the fuel pump, possibly more than once?

Valkyrie

I think he replaced the fuel pump relatively recently, but only as a precautionary measure. Like I said, it's a VERY well-maintained FD. Harnesses, injectors, hoses, coils, etc. all get replaced every couple years. I have been told the gas tank was modified to reduce fuel starvation (on another note, I just got a new baffle in the mail from FEED).

I'll try to get pics once the engine is apart.

FWIW, it was retuned once the high-flow catalyic converter was installed, but not after the V-mount install because the tuner said it would be current tune would be able to handle the V-mount (boost is the same).

Tuning is absurdly expensive in Japan ($900+ just for labor at any run of the mill shop, much less anyone especially well-known). Someone who spoke Japanese could probably make some decent money with remote tuning.

Valkyrie

Turns out it was the side seals, not the apex seals. I think they had seized.

AlienHack

The million dollar question is why did the side seals get stuck? In a fresh motor?

maybe bad gaps when the engine was assembled?