Spark blowout or slipping clutch??

[ToddEdge]

I made a few pulls on Friday at our local dyno and the car made good power until right at 5000 rpm and everything took a sharp dip on the graph. Basically the graph climbs to 5100rpm and then nosedives. You could hear the motor feel like it was hitting a wall and didn't want to go to redline. The shop thinks it is a slipping clutch but, I wanted to know what might indicate spark blowout. We also realized the car was making 21#'s so way more boost that it should have made(pulley swap coming). We datalogged the car and everything was in check(iat's, fuel pressure, duty cycle, etc.). The first pull it did look like a slipping clutch as my mid-rpm's had a dip. After the 3rd pull the clutch seemed to be warm enough to grab. I just dont' want to blow $2K+ on an RXT clutch to find out I had old plugs gapped wrong.

Thanks,
Todd

 

[04svtcobrablack]

What is your spark plug gap at.

 

[ToddEdge]

What is your spark plug gap at.

I'm going to pull a plug tomorrow to check. The car was built by Modular Powerhouse 5 years ago and to my knowledge has been untouched. The dyno sheets I have show it at 18psi but, the pulley must have been changed since it made nearly 22psi on the dyno and never dropped until all the power died just over 5000 rpm. The shop thinks the clutch was slipping the full pull but, really let got at 5100rpm.

Thanks,
Todd

 

[ModularSpeed]

My experience, slipping clutch caused the RPM to raise significantly quicker than without slipping clutch.

Spark-Blowout for me, the car acts like it hits a rev-limiter.

 

[ToddEdge]

I went ahead and pulled the 4 plugs on the drivers side and they are TR6's. The gap was between .026 and .028 across all 4.

ModularSpeed - I also would have thought the rpm's would have jumped but, it was more like there was more load on the car and it had a tough time getting to 6500. The numbers were off across the board but, it jumped to 22psi and never dropped. I'm hoping with a larger pulley(shooting for 18psi) and new plugs gapped a little tighter that this might be the fix. The first pull, the dyno graph did have a large dip that is very indicative of a bad clutch. Pulls 2 & 3 were both better but, off from what they should have been.

Thanks,
Todd

 

[ModularSpeed]

What did the A/F look like?

Sprak blow-out usually happens at around the same rpm, just about every time.

Did you log the voltage too?

 

[racebronco2]

I would guess it's fuel related, like your pumps are pegged.

 

[65fastback2+2]

you'll definitely smell a slipping clutch typically as well

 

[sprstr1000]

Do u trust ur tuner

 

[sprstr1000]

Sounds like the car was not exhibiting slipping clutch symptoms
Are you gonna let this shop do the tuning?

 

[jmstekguy]

I would guess it's fuel related, like your pumps are pegged.

agreed, DL the fpdc and the maf V and see what its at, plug gap should be around .025" for that kind of boost level imo, do you have a pic of the dyno sheet?

 

[ToddEdge]

Both the pumps and the MAF(stock with Mafia) had plenty of room before either were maxed out. That was my assumption but, we datalogged it and weren't anywhere close. The air fuel was a consistent 11.2-11.4 the full pull. Timing was 17 degrees. I'm going to speak to the tuner today to see what his thoughts are.

Thanks,
Todd

 

[ToddEdge]

I pulled the passenger side bank of plugs this afternoon and noticed one looks odd. About 1/16" of the electrode is gone. I can't tell if it broke off or melted off or what. The odd plug was I believe #6(passenger side, 2nd from the front). Any ideas what would have caused this? Could this be part of my dip after 5100rpm?
On the dyno it was 11.2-11.4 the entire pull and we heard no detonation. I looked in at each piston using a flashlight(no special bore light...) and they all look about the same with a little fluid at the bottom of each piston.

Thanks,
Todd

 

[ModularSpeed]

Grab some new plugs, gap to .025 and pop them in.

Fluid on pistons? Like, how much?

 

[ToddEdge]

I could only see the tops of the piston with the bad plug and two others. I'm guessing #2, #4, and #6. You could just see a bit of liquid at the bottom of the piston. Not a puddle but, enough around the sides where the flashlight would reflect back.

I just got some new plugs and plan to install them tonight and to put it back on the dyno the end of the week to see if my power woes are over.

Thanks,
Todd

 

[LeKiD]

You melt a plug from a lean condition , probably your pump are maxed. Even if the wideband was givin 11.4 , it was a dual sensor or single ? Was plug on the left or right bank ,

Do a leak down test before put it on a dyno . It can be water from a head gasket failure.

And if you just melt a plug with no more damage your been lucky . But find why you had liquid On your piston , not common

 

[metaman]

The spark blow out sounds like a miss because it is. If there is no sound of a miss from the engine than it is not spark blow out.

How old is the blower belt? Sounds like it could very well be belt slip.

 

[scottGT500]

Sub'n

 

[ToddEdge]

The spark blow out sounds like a miss because it is. If there is no sound of a miss from the engine than it is not spark blow out.

How old is the blower belt? Sounds like it could very well be belt slip.

I'm installing BF idlers and a new belt but, it hit 22# and never dropped so I don't think I really have any belt slip.

 

[metaman]

When mine had blow out it broke up and sounded out of tune under boost. Unmistakable from a clutch. You don't have to get the most expensive twin disc clutch around. Other clutches will hold the power and cost much less.