Soooo... Whats up with the melting pistons?

[WOTjunkie]

Before I got my Cobra a few months ago I thought I did good enough research on all the "issues" these things have but I guess I didn't do good enough because I never found anything about pistons melting. But then all of the sudden, the past few days I've come across multiple threads and actually heard from the mouths of others about pistons melting. So is this a common occurence or does this just happen under certain circumstances? I appologize if this has been covered already but when I heard about it I did search and just came across all the horror stories of this tragedy. So if you guys can, please let me know if this is something I'm gonna have to worry about or if it's just something that happens to the stock innards of the motor under extreme power. Thank you..

 

[Fox-4]

Just read this from CobraBob's site. Hopefully it will shed some light for you.

Over the years, we've heard of numerous cases of '03-'04 motors being severely damaged from wide open throttle highway runs. Usually from a roll (40-50 mph) to 140-150 mph. So the question is always, why does this happen. And note that not every WOT run to 140 mph will result in an engine failure. The thing to remember is that the motor and drivetrain was not designed for this. Here is some helpful information from Thomas91169 from SVTPerformance.com.

1) 5th and 6th gears are Overdriven, which puts a lot more strain and load on the motor, which gets enough strain as it is from the Eaton blower.

2) The 2003-2004 Cobra motors are designed with tight PTW (piston to wall) clearance, and just "eh" pistons.

The main issue is when you hit 5th, you have already been WOT for quite some time, so your motor is already heated. Lets not forget the Eaton isn't exactly the epitome of efficiency, and the heat exchanging system can only pull out so much heat. So after being in the throttle for a easy 30 seconds (with a stock or near stock motor), you are now hitting your OD gear. Load on the motor is increased by XX%, which just pours on the heat. Heat causes the piston to expand into a cavity it doesn't have room for, the piston meets the wall, and you are now on the path to a rebuild. Not to mention your tuner doesn't compensate for a 5th gear pull. If he did, you would get maybe 15* of timing and you would have a 10.5:1 AFR to keep cylinder temperatures and pressures down.

Cooling mods help the situation but you are talking about Russian Roulette when hitting 5th & 6th gear and still laying into it. The best flowing coolant can't keep the cylinders cool enough under these extremes to keep the pistons from making contact with your cylinder walls.

The ultimate way to have a motor withstand the stresses of boost and the heat involved with a Roots/twin screw boost source, and to live at those conditions, is to build it properly. This means forged and coated pistons that better withstand heat and don't expand, proper PTW clearance to compensate for piston expansion, etc.

You have to remember too, a Corvette ZO6 isn't a 3600lb pig with just marginally better than stock mustang aerodynamics. It's also naturally aspirated (less heat and combustion pressures) with slightly better gearing. The stresses on the motor aren't multiplied when it hits its OD gears as much as they are when an '03-'04 Cobra hits the OD gears. (It is likely that) SVT never tested the '03-'04 motor at OD loading during WOT because that's not what the OD gears are even designed to do.

 

[Jimmysidecarr]

The negative effects of too much heat too fast is not just excessive piston expansion .

The pistons will not melt even under sustained WOT unless something else besides too much heat, that is also very VERY important and extremely damaging, happens to occur.

And that "VERY IMPORTANT SOMETHING ELSE" is also the MAIN CAUSE of piston deaths and melting.


This "VERY IMPORTANT SOMETHING ELSE" has not even been mentioned yet.
















It is---------->DETONATION!

 

[WOTjunkie]

Thanks guys. Very helpful info. Hearing all these stories all of the sudden i was like WTF?!?!?! It still has me kinda nervous though but whatever. I'm not putting down anything serious right now but I'll just make sure I have the right stuff when I do

 

[1wild-horse]

It is---------->DETONATION![/B]

Yeah that should have been the first answer, due to too lean a mixture, too much timing and low octane gasoline.

 

[Brutal Metal]

Detonation and sustained top speed runs are NO Good for your pistons!

 

[SilverCobra7]

Reading this thread had me nervous at first... best way to fix it. Don't run that B.... at wot on 5th & 6th gear! lol...:burnout:

 

[SVTDice]

Very stupid question but, If you can not hear the detention (Idle or driving) Can there still be detonation?

 

[unit213]

Very stupid question but, If you can not hear the detention (Idle or driving) Can there still be detonation?

You're not going to get any spark knock at idle...and yes, there absolutely can be detonation if you can't hear it. If a tree falls in the woods and you're not around to hear it, does it still make a sound?

 

[20psirabbit]

i <3 jimmysidecarr

 

[04sleeper]

The negative effects of too much heat too fast is not just excessive piston expansion .

The pistons will not melt even under sustained WOT unless something else besides too much heat, that is also very VERY important and extremely damaging, happens to occur.

And that "VERY IMPORTANT SOMETHING ELSE" is also the MAIN CAUSE of piston deaths and melting.


This "VERY IMPORTANT SOMETHING ELSE" has not even been mentioned yet.
















It is---------->DETONATION!

This.

 

[mustanginky]

Very stupid question but, If you can not hear the detention (Idle or driving) Can there still be detonation?

and to add, generally, by the time you hear it, it's too late anyways. if you heard it with a blower car and got out of it safely, you're lucky.

 

[Bruha]

Agreed... Detonation is the not so silent killer. Heat is bad. Heat can help cause the detonation. I believe a lot of tunes are to be blamed to.

 

[SVT_BERTO]

I did 1 6th gear pull in my Cobra. I can promise you my next Cobra won't see a 6th gear pull...shit was scary. I kept thinking "what if" a piston shits the bed at that speed?!

 

[CobraBob]

Getting a proper tune (you don't want a lean condition) and insuring you are getting enough fuel will help prevent detonation. Some people upgrade their pumps/injectors when they start running out of fuel. I always recommend upgrading sooner than later. Don't push the fuel system to its limits before you decide to upgrade.

 

[earico]

Getting a proper tune (you don't want a lean condition) and insuring you are getting enough fuel will help prevent detonation. Some people upgrade their pumps/injectors when they start running out of fuel. I always recommend upgrading sooner than later. Don't push the fuel system to its limits before you decide to upgrade.

+1

A fuel system is something you should never save money on.

Supra guys do long 150mph+ overdrive pulls all the time. With factory cast pistons! Been there and done that myself. Had one for 7 years.

Are you guys not putting enough buffer in your tunes? If you tune for an A/F of 11.8 in 4th gear on a dyno there is no way in hell you still have a 11.8 on the street at 150mph in 5th gear.

I'm new to Terminator tuning.

Is heat soak worse at the higher speeds? Is the blower pushing hotter air at 150mph?

If so can we tune in enough fuel to cool the cylinders at high speeds?

Is there a way to have injector duty automatically increase when IAT2s increase?

 

[Silver2003Cobra]

well, you don't hear much about people grenading their engines any more from over heating.. it used to be (3 or 4 years ago) every other thread was about someone destroying their engine from sustained high speed pulls..

I think that the "weaker" engines already went bye bye and the ones out there now are going good..

 

[Driver500]

+1

Supra guys do long 150mph+ overdrive pulls all the time. With factory cast pistons! Been there and done that myself. Had one for 7 years.

Are you guys not putting enough buffer in your tunes? If you tune for an A/F of 11.8 in 4th gear on a dyno there is no way in hell you still have a 11.8 on the street at 150mph in 5th gear.

I'm new to Terminator tuning.

Different engines.

Different PTW clearances, materials, geometry, it goes on and on.

How to alleviate the problem has already been posted. 5th and 6th gear pulls on stock pistons is a no no. End of story.

 

[cobra=trouble]

the stock pistons where meant for 8 psi of boost only ''with the factory clearances''. add more hp..like T/S in it's only a matter of time or when.