Turbo cobra stops making power at 5300???

[99cobra09]

Your saying that the computer is trying to compensate with timing, well maybe that's the problem. The knock sensors may be very sensitive and are being interrupted by the turbo's noise/wastegate. Have the tuner either turn them off or decrease the sensitivity.

If the tuner thinks its a spark issue, which i doubt since many people use them on cars with 1k hp. Maybe have a buddy or something lend you his coils and see if that is the issue.

 

[static74]

My hotside looks the same as yours, same turbo, same wastegate, pushing 700rwhp through an auto all day no problem on 18psi. Stock heads, mach 1 intake. Im using e85 though.

Your issue is not back pressure or flow of the exhaust through the hotside. Whats after your downpipe?

Have you looked at the other usual suspects? MAF counts? Compression test? Obama?

 

[Parts-is-Parts]

You need valve springs Chad.
My turbo Marauder would not make any power past 4300 with stock valve springs at 13psi.

Turbos are a totally different animal.

 

[qwik01cobra]

My hotside looks the same as yours, same turbo, same wastegate, pushing 700rwhp through an auto all day no problem on 18psi. Stock heads, mach 1 intake. Im using e85 though.

Your issue is not back pressure or flow of the exhaust through the hotside. Whats after your downpipe?

Have you looked at the other usual suspects? MAF counts? Compression test? Obama?

Open downpipe 4".

Everything looks spot on. Brand new motor. MAF counts are fine. I have a 2600 and a MAFia

 

[qwik01cobra]

You need valve springs Chad.
My turbo Marauder would not make any power past 4300 with stock valve springs at 13psi.

Turbos are a totally different animal.

I guess anything is possible but I'm finding that very hard to believe especially considering the post above yours

 

[thomas91169]

If it was a wastegate location issue he would have trouble controlling boost as there wouldnt be enough wastegate to bypass flow from going through the compressor. Though I do agree that the placement of the wastegate on one bank is a little weird, you would imagine the wastegate should be placed at the "Y" pipe right before the hotside,.

My first reaction was "spark blowout" but you would get pig rich past 5300 if this was the case (due to much more unburnt fuel now present due to misfire/blowout). Although lowering the gap on plugs is a free way to check and rule this out, so I would definitely start there. If no change, then you know its not blowout. Also you can try to drop boost down to 10 and see if your powerband becomes more linear and doesnt fall off, then start ramping it back up to see where you start getting issues.

Without seeing the dyno chart and what the ecu is doing/calculating for its kind of hard to diagnose things like this over the internwebs.

Your saying that the computer is trying to compensate with timing, well maybe that's the problem. The knock sensors may be very sensitive and are being interrupted by the turbo's noise/wastegate. Have the tuner either turn them off or decrease the sensitivity.

Do 03/04's even have knock sensors?

 

[watman02]

You need valve springs Chad.
My turbo Marauder would not make any power past 4300 with stock valve springs at 13psi.

Turbos are a totally different animal.

how is 13psi boost from a turbo different from a super charger? Please explaine?

 

[thomas91169]

how is 13psi boost from a turbo different from a super charger? Please explaine?

Not only that, but what correlation does the amount of restriction (boost) have to do with valve float?

I always attributed valve float to rpm and the spring material not being able to keep up with the speeds in which it is compressed and rebounded from the cam lobe.

 

[watman02]

Not only that, but what correlation does the amount of restriction (boost) have to do with valve float?

I always attributed valve float to rpm and the spring material not being able to keep up with the speeds in which it is compressed and rebounded from the cam lobe.

you can have boost pressure keep intake valves open but it usually takes a large valve (ie surface area X seat pressure being low LS motors can have this problem!) the c heads valves are tiny. and 12psi is 12 psi i dont care what is making it!!!!

 

[01yellercobra]

Because a turbo also causes back pressure. It's a restriction in the exhaust path. Too much pressure can cause valve float if the springs aren't up to it. When I did my buddies he only needed the 120's on the exhaust valves. But we did both since the engine was out of the car.

 

[watman02]

I agree he needs to check the back pressure on the hot side, but being this system and turbo has been run before on Cobras (with what i would assume is the same spring the op has) it should be up to the task. unless his waste gate is not functioning properly witch should cause high boost pressure. OP needs to do some diag work and get back to us.

 

[ultraspeed]

I would suggest putting another waste gate on the other bank only on one side like that could really hurt things! Also the 4v does not have the issues like the 2v does on valve springs stock valve springs with stock cams will hold just fine. It can really only be a few things 1.) weak firing 2.) wastegate 3.) the tune I would start adding another Waste Gate to get even production from both banks , then a Boost A Spark.. Or get a good datalog of the car and let us see what the tune is doing as that could be a issue and I also agree from earlier id be running a tad richer on fuel 11.6 11.7 just for slight comfort. Also what was the timing at start of boost and end of rpm?

 

[rotor_powerd]

Wastegate positioning is horrible but that shouldn't cause your problem unless you're floating the exhaust valves on the driver side. At 15 pounds of boost, you are probably seeing 25-30 pounds on the exhaust side. With the wastegate relieving pressure only on the passenger side the driver side will build more pressure to compensate, which puts more pressure on the backside of the exhaust valves.

Data logs will tell the full story.

 

[qwik01cobra]

New PAC racing valve springs and new OEM ford COPs problem solved

 

[gt347mustang]

New PAC racing valve springs and new OEM ford COPs problem solved

Thanks for the update, many times threads like this are never updated with fixes.

How much were you able to increase boost with the new springs?