[94cobra69ss396]

I thought the 03-04 Cobras had forged pistons? That's a new one for me. I'm glad I put forged pistons in my Cobra. I've done a few 5th and 6th gears pulls and never had an issue.

[Vettezuki]

Originally Posted by SeanPlunk

It's not detonation, lots of people have blown motors going wide open in 5th or 6th. This post explains it.

ZO6 FTW.

[enkeivette]

Wow, that sucks. I've hit 140 in my car before but I was still in 4th. I wonder how my motor would do...

[Vettezuki]

Originally Posted by enkeivette

Wow, that sucks. I've hit 140 in my car before but I was still in 4th. I wonder how my motor would do...

You have forged internals right? They typically have larger cold tolerances and heat into operating tolerances. This is why a lot of after market forged stroker kits light up knock sensors. They be slapping hard until heated. This also why, on these kind of built motors, you don't really want to go blasting until they are up to operating temperature and the tolerances are in place. Otherwise, they just sorta run crappy and you can get blow by etc. At least this is my understanding.

[SeanPlunk]

Originally Posted by 94cobra69ss396

I thought the 03-04 Cobras had forged pistons? That's a new one for me. I'm glad I put forged pistons in my Cobra. I've done a few 5th and 6th gears pulls and never had an issue.

They have forged everything, crank, rods, pistons.

[silvertermi04]

Originally Posted by SeanPlunk

They have forged everything, crank, rods, pistons.

but u dont have to worry about it. its only if u boost at low rpm. like my car it makes almost 14 pounds of boos. to ask it to boost that much from a 5th gear roll is alot even with forged everything at low rpms, thats why u see all those high speed runs and street racing where they take 4th up to the max and then go to 5th so they wont be at low rpms. plus even if u take 4th all the way up u can top out the car in 5th gear. dont even need 6th.

[Vettezuki]

Originally Posted by silvertermi04

but u dont have to worry about it. its only if u boost at low rpm. like my car it makes almost 14 pounds of boos. to ask it to boost that much from a 5th gear roll is alot even with forged everything at low rpms, thats why u see all those high speed runs and street racing where they take 4th up to the max and then go to 5th so they wont be at low rpms. plus even if u take 4th all the way up u can top out the car in 5th gear. dont even need 6th.

My understanding of the post was because of the prolonged high heat and very tight Piston to Cylinder wall clearance, not loading or stress. Basically the pistons start to bind in the cylinders as the expand too much under heat. That's what I got out of it. Also, I'm pretty sure HS runs (at least in typical Corvettes) are all done winding out 5th. 6th is just for mileage on the freeways.

[heypal]

Originally Posted by Vettezuki

My understanding of the post was because of the prolonged high heat and very tight Piston to Cylinder wall clearance, not loading or stress. Basically the pistons start to bind in the cylinders as the expand too much under heat. That's what I got out of it. Also, I'm pretty sure HS runs (at least in typical Corvettes) are all done winding out 5th. 6th is just for mileage on the freeways.

Thats what I have always been told.

[94cobra69ss396]

I couldn't imagine that Ford would build a forged bottom end that had too tight of clearence that the piston would expand beyond the limit of the cylinder wall. If I recall correctly weren't those engines also hand assembled by guys in SVT as well.

I'm running a Vortech without an intercooler or aftercooler and forged piston in my Cobra and I've run it hard at Willow Springs without any issues. Even after a 20 minute session in 110 degree weather.

Your Cobra has a heat exchanger to help with the intake charge temps. I'd bet that my intake temps are higher without having a cooler of any kind than yours is with your heat exchanger.

[Vettezuki]

Originally Posted by 94cobra69ss396

I couldn't imagine that Ford would build a forged bottom end that had too tight of clearence that the piston would expand beyond the limit of the cylinder wall. If I recall correctly weren't those engines also hand assembled by guys in SVT as well.

I'm running a Vortech without an intercooler or aftercooler and forged piston in my Cobra and I've run it hard at Willow Springs without any issues. Even after a 20 minute session in 110 degree weather.

Your Cobra has a heat exchanger to help with the intake charge temps. I'd bet that my intake temps are higher without having a cooler of any kind than yours is with your heat exchanger.

I know where you're coming from, but it does seem to be a real issue. Here's what another user said from the same thread Sean posted.

The rebuilt of my Cobra will be done the 2nd week of January because of a 5th WOT my 1st and last one believe me!!!! I just had the estimate for the rebuilt $$$$$$ EXPENSIVE My fault no one to blame but me. Since i blew my motor there is a thread like this one that comes out each week, and someone reply by saying they did not know about the 5th and 6th gear WOT. Lets see on this thread if we have another one. I say again this subject should become a STICKY!!!!!!!!! It would save lots of motor,money,and stress,and the wife going crazy lol