Whipple 2.9 - Is this boost loss normal?

[04OWwhipple]

I was just watching a video from the previous summer of my car and I was focusing on the boost gauge. It seems to bleed off in the upper RPMs. Can anyone chime in if they have the same thing happening on their 2.9?



I don't know if this is just a normal thing or not for them not to keep up with flow in the upper RPMs or if I actually was/am having some kind of issue.


Stock engine 4.6
Whipple 2.9 w/standard inlet
3.25 upper w/stock lower
Kooks longtubes and full exhaust



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[MG0h3]

I suspect you have belt slip. Another possibility is a severely dirty air filter.

I'm at 4k' and see several psi less than people at or close to sea level. I have zero boost loss per my gauge. Swings to 18/19 immediately and climbs a little more towards redline.

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[04OWwhipple]

I suspect you have belt slip. Another possibility is a severely dirty air filter.

I'm at 4k' and see several psi less than people at or close to sea level. I have zero boost loss per my gauge. Swings to 18/19 immediately and climbs a little more towards redline.

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I was thinking that I might be having that issue. I just wasn't sure if the 2.9 standard inlet normally bleeds off up that high. I was hoping to run hoping to be able to get away with a 2.75 pulley with my new engine and this has me wondering what the issue is.

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[cj428mach]

I have a thumprrr tensioner for sale if you need it to help fight belt slip.

 

[MG0h3]

Only time I've seen bleed off like that when it wasn't belt slip is when the blower is too small for the engine. Wont be the case for you.

Do you have a snub idler or the whipple tensioner?

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[04OWwhipple]

I have a thumprrr tensioner for sale if you need it to help fight belt slip.

I might pick it up in the future if you still have it but right now I don't have much in the way of liquid funds at the moment. Do you have it posted here?

Only time I've seen bleed off like that when it wasn't belt slip is when the blower is too small for the engine. Wont be the case for you.

Do you have a snub idler or the whipple tensioner?

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It didn't really seem right in my head either, as I think the blower should be able to keep up with a 4.6 at 6500 RPM. I have a snub idler.

 

[cj428mach]

https://www.svtperformance.com/threads/thumper-tensioner-and-vmp-maf.1167041/

FYI my 2.65 VMP with a GT500 TB and 5" crusher intake doesn't have a drop off in boost, a 2.9 shouldn't have an issue unless the standard inlet is a bottleneck.

 

[jony51999]

My standard inlet 2.9 on a 4.75 stroker hit 22 then bled off to 10 the first time on dyno.

After some feedback and parts (tensioner related) from cj428mach I went back and hit 23.5psi at 3500 and held dead nuts until the tuner let off the throttle. I’d say it’s absolutely belt slip. My tuner said if you can get the belt on yourself it’s not tight enough!

Other than that, the big snub idler to ensure belt wrap and a good tensioner setup should set you straight.


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[04OWwhipple]

My standard inlet 2.9 on a 4.75 stroker hit 22 then bled off to 10 the first time on dyno.

After some feedback and parts (tensioner related) from cj428mach I went back and hit 23.5psi at 3500 and held dead nuts until the tuner let off the throttle. I’d say it’s absolutely belt slip. My tuner said if you can get the belt on yourself it’s not tight enough!

Other than that, the big snub idler to ensure belt wrap and a good tensioner setup should set you straight.


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Ok, so it sounds like I definitely have some kind of issue then if mine isnt holding steady. That run in the video was in 90+ degree heat but I would still think it should hold steady. I don't have any signs of belt dust from the belt slipping. Once I get the car back together and on the dyno I will have to recheck the boost to see if it is still dropping or if that day was a fluke.