Bleeding boost

[JUSTA3V]

I'm not 100 percent this was 3v tech so I stuck it here.

My issue is during a run I make 20 PSI but once I hit fourth and am nearing the top end of the track my boost starts bleeding from 20 down to 16 PSI. It does it every time.

From 6500 to 6700 I would say. Im 99 percent sure I have no leaks and am now wondering if its my valve overlap causing it? It seems too consistent to be belt slip at this point.

I don't feel the car lose any power as I cross the line. I only noticed the boost gauge dropping as I watched the video playback.

My slip shows the car is strong on the top end. Ignore the low ET vs MPH...I still cant get the car to 60'



I did 6 passes and the boost gauge does the same thing, around 6500 its starts falling to 16 PSI from 20 right before I lift at the end of a run.

Am I overthinking this? Is it more likely just a coupler is leaking under max boost?


Any suggestions are appreciated.

My cams are Comp 127200 NSR and my VCT is limited.

thanks,

 

[BruceH]

FWIW your cams have less overlap and more lsa than the stock units. What blower do you have?

 

[JUSTA3V]

D1SC

 

[hamish]

Only in 4th or that rpm range?
Anychance you can swap out the gauge with a friends?

 

[JUSTA3V]

Any gear at that rpm it bleeds

 

[BruceH]

Any gear at that rpm it bleeds

I've had a D1 before and it took a whole lot of belt tension to get it not to slip. That was with the separate 8 rib belt.

 

[05stroker]

Sounds like belt slip to me. I have always had to really crank my belts down. What rib/ pulley setup do you have?

 

[JUSTA3V]

10 rib. Gates green belt. 3.400

I can post a video. But you can't see much unless you know the boost gauge.

 

[mrt2you]

I had a friend with a GT500 with the same problem. we could never figure out his problem until his A/C compressor clutch started making noise.
it turned out the A/C compressor clutch was binding at higher rpm. replaced the complete compressor and that solved the problem.

I have seen 2 other GT500's with the same problem. we only changed the A/C clutches on them.

 

[JUSTA3V]

Prochargers run on a dedicated belt system

 

[05stroker]

Crank on that tensioner some and re data log it. Mine is 12 rib with a grooved pulley and I still fight it.

 

[JUSTA3V]

Will do. Thanks

 

[07 Boss]

Is it me or are those times not consistent with running 20 psi? I would think you would be well into the 11's regardless of 60' times.

 

[05stroker]

Is it me or are those times not consistent with running 20 psi? I would think you would be well into the 11's regardless of 60' times.

Lots of veribles there, I am only running 21 psi but I have 12:1 CR and made a 5.78 pass at 123mph. Every set up is different. Takes a lot of support to make a car as fast as it should be on 20psi.

 

[JUSTA3V]

car makes 650 rwhp with a 3.400 pulley at 6800 rpm

And the boost gauge reads 20.

Where do you think I should be?

 

[05stroker]

Your mile per hour is good for about 10.50.

 

[JUSTA3V]

That's what I was thinking

 

[Kobie]

I'm confused. Which time/mph are you running? 13.437/100.72 or 11.244/132.26 ?

 

[JUSTA3V]

the 11.2 at 132.

If I'm making 650 and only trapping 100 mph, I would have more issues than I would want to try and solve.

 

[702GT]

A D1SC on a Ford 3v spun to 20 psi and people assume he is trapping 100mph... what doing a 1/4 mile burnout? He would at least post his "It always smells like burnt rubber when I go down the track" problem, LOL.

OP I'd say belt slip as well. Not sure cranking down on the tensioner is going to solve it. The procharger tensioner may max out, then you'll be throwing belts instead of slipping. I would look at one of those aggressive grooved pullies for the blower possibly. Or have one made. My buddy had one on his V2 2v making 620whp@7200rpm on a 2.59 pulley. The pulley chewed up his belts more but he never had slipping issues after he swapped in that pulley.