Hole in Valve - Burned Piston

[Benag]

I thought I would post my story for reference sake and because I have some questions concerning the overall process.​

It started just after I installed the big 16g. I hadn't upgraded anything else yet and was boosting too high and burned or blew a hole in the first cylinder exhaust vavle. I didn't know that this was the case though until I took the head off. It sounded like a constant popping (pop pop pop pop) when under acceleration. My brother said it simply jumped timing and that is what's causing the popping sound. I said ok well let's replace the timing belt and reset the timing then. We found that the timing was off a good bit so we fixed it and put on the new timing belt. It sounded exactly the same, though it did drive a little better. I bought a compression tester and found that the first cylinder had no compression. The second has ten less than the third and fourth. 0 160 170 170.​

So I then pulled the head off and found a fingernail sized hole in one of the exhaust valves on the first cylinder. In the second cylinder I noticed the top of the piston looked melted around the sides. I'm not sure how long it had been like this.​

Anyway, now everything in the engine has been fixed: good compression, good timing, new fuel pump (255 lph) - it had to be replaced because the car was missing at higher rpms. The problem is that it doesn't even run as good as it did before all this work was done. It now seems as if the exhaust (3" downpipe, factory catback) is really making it hard for it to breath or something, and the turbo and blowoff can barely be heard. It is much slower than it was, but it runs better. Anybody have any input? I am now in the process of getting a catback and fuel pressure regulator.​

 

[ThingyNess]

I'd check your cam timing once more. Assuming the compression is good, having your t-belt off by a tooth or two makes it feel wildly different. There aren't many things that can make it feel that gutless assuming your static compression is okay, and your timing is right.

The 3" exhaust will definitely not be what's choking the engine. You might want to take a multimeter and probe your O2 sensor when the car's warmed up and in closed-loop mode as well.

If it's pegged to either 0v or 1v instead of cycling like it's supposed to, you may have a sensor issue causing you to run richer or leaner than the O2 sensor can compensate for, and that can cause a pretty hefty power loss too.

 

[Benag]

I once got a check engine light for both O2 sensors at the same time, but I never replaced them and the light went away. I'll test them anyway. And my exhaust is only 3" on the downpipe. The other half is factory.

Oh yea, and I got a cel P0420. Catalyst Efficiency Below Threshold. And I want to say that I think this is because the downpipe omitted the cat, so I guess it isn't a big deal. I tested the O2 sensor, seems to be fine. I'm going to put the catback on and check the timing again and see what happens.

 

[No_Skillz]

Get that FPR dialed in, do a boost leak test, then try again. Any logging devices so we can see what the ECU is doing?

 

[Benag]

None yet. I noticed the intake filter was dirty and I cleaned it. That seems to have helped a good bit actually. I am about to clean it with the recharge kit and I'll repost.

 

[MelloEclipse]

ahhh that scares me...i just bought a GST with a 16g and no other supporting mods...i'm driving real easy til i can get them too..

 

[nates6969]

as long as your running factory boost, a 16g isn't going to hurt your car anymore then the t25 as it will not flow any more air at ~11psi. At that boost both turbos will feel relatively the same atleast until the t25 starts dropping off at redline of course. Bigger turbos are more efficient so the density of the air will be slightly higher causing you to need a bit more fuel then stock but at 11psi, the variation is charge air temps are minimal. The only way a 16g will be harder on your car then a t25 is if you were running say 16psi, where the t25 can no longer supply the amount of air flow to maintain a pressure of 16psi at high rpms and the 16g can. big turbos just allow you to run more boost and hold it through redline.

So many people think a bigger turbo is going to cause a need for way more fuel, or make your car faster, at the same low boost as the smaller turbo...this is a huggggge myth and is entirely not true. if both a small and large turbo hold 11psi to redline and both are still in their efficiency range (charge temps about the same)...both cars will run just as fast

So all I can say to you MelloEclipse, if your car has no boost leaks and is running good at stock boost, drive it however you like....however once you get raising that boost...get some fuel control as you will need more fuel

 

[TSG59_Steve]

So many people think a bigger turbo is going to cause a need for way more fuel, or make your car faster, at the same low boost as the smaller turbo...this is a huggggge myth and is entirely not true. if both a small and large turbo hold 11psi to redline and both are still in their efficiency range (charge temps about the same)...both cars will run just as fast

A bigger turbo would have a higher CFM therefore it would be faster than the smaller turbo with the same boost levels.

 

[nates6969]

yes you're right TSG59_Steve about a bigger turbo does flow more CFM. however an engine will only require a larger volume flow rate IF you increase volumetric efficiency.

In an engine the only air factors that will variate performance are temperature, pressure, and volumetric efficiency. At low boost the charge temperatures between the two turbos are about the same, the boost levels are also constant...therefore density of the air is equal between both setups (simple ideal gas law). the last factor is the volume. This is multiplied by the density to determine the mass of the air in the cylinders. From there the ECU can then calculate how much fuel to inject to obtain the desired A/F. Usually a bigger turbo will increase volumetric efficiency slightly, which would increase perfectormance however the increase between those two particular turbos in question would be minimal...Air flow is not a factor at all in computing the net power output of the system. And just like a said, all the larger airflow will allow you to do is keep supplying the motor with the amount of air needed to maintain a certain intake pressure for a farther range in the rpms. For example, as the engine climbs to say 7000rpm, the motor is intaking a much greater volume of air then at 4000rpm. This is why many smaller turbos loose boost in the high end, it just simply cannot continue to supply the engine with the amount of air needed at that rpm, and therefore the pressure begins to drop off. at say 11psi both turbos will supply the same air flow (cfm) throughout most of the powerband, however the large turbo will just be spooling slower as it does not have to work as hard to maintain that boost level due to its larger compressor wheel design.

haha I could continue to elaborate and will be happy to if you want...I used to think the same thing as well until I took fluid mechanics in my mechanical engineering program this year. If you question anything I said, please ask. I'd just hate to change the origional purpose of this thread though

 

[Jeff_Ciesielski]

Just for the sake of reference, did your valve happen to look something like this?

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That valve is from my 93 NT. Timing problems to the max

 

[Benag]

Yea that's what it looked like, except the hole was a little bigger... I'd say twice as big. Cleaning the filter didn't really change anything noticeably. Maybe the fuel filter is really dirty. I've had problems with it a couple times before. I don't mind if the topic is changed, but it may be a good idea to start it in a different thread. I am also taking mechanical engineering in college and agree with what you said. The difference at say 11 pounds is there but it is minimal. A T25 will be working harder to charge 11psi and so the air from this turbo will be more heated because more energy was required, making the air less dense.

 

[nates6969]

haha glad someone understands what I'm talking about!

 

[Benag]

Well I changed the fuel filter and now it seems to be back to normal. Does anyone know a good fpr name?

 

[TSG59_Steve]

If you question anything I said, please ask. I'd just hate to change the origional purpose of this thread though

Discuss: http://dsmtuners.com/forums/showthread.php?p=151213051#post151213051

 

[02HtownSubie]

Just for the sake of reference, did your valve happen to look something like this?

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That valve is from my 93 NT. Timing problems to the max

That looks like my #3 cylinder exhaust valve now. The hole in my exhaust valve is a bit larger. Does anyone think the piston rings is burnt as well? The piston seem to look normal. Suggestion/input please.

I was messing with my AFC before it happen. I had it set to -5 on all RPM because it was running rich however I "decided" to try to do a +5 on all RPM @ 19 PSI of boost. Backfire throughout, let go the throttle. The car shake, poping and popping. Result is hole in exhaust valve. Running rich do this to the valve?

 

[Splitpi]

@02HtownSubie

Are you sure you were running rich when you went +5? Did you log it? Simply setting the dial to a richer setting doesn't mean the engine is running 11:1 to 9:1 or lower Air:Fuel ratio.

 

[02HtownSubie]

I do not have a data logger. I do know the car running rich, when I set it to -5 on all RPM that car ran great. I've been running with the -5 setting for year without any problem and don't know what took over my head that make me decided to put +5 on all RPM using SAFC. The car started to backfire under 19 PSI load. I WOT to about 5,500 RPM upto to 3rd gear and let go because of backfire/popping.

Now I knew there's a hole in my exhaust valve after removing the head, the next question is do you think the piston rings is still OK? As I stated the top of piston looks normal.

So my exhaust valve has a hole on it, what happen to that broken piece? Does that mean my turbo exhaust turbine wheels is damaged?

 

[Turbo Talon DL]

You ran 19 psi on stock injectors and NO AFPR using only a SAFC? You also dont have a datalogger? Theres no way to tell if you burned up a ring because you cant even do a compression test on the cylinder. The valve melted so you can probably assume the piston ring is damaged. You can always pull the piston and visually inspect. You should just pull the turbo apart and look at the turbine through the back of the T-housing. The wheel will probably require rebalancing also.

 

[No_Skillz]

I'm guessing you ran extremely LEAN, which burned a hole through your exhaust valve, and that's the source of the backfiring you were hearing.