Hitting a train when letting off WOT throttle...

[Stingin' Away]

The title may be confusing but it is the only way I could explain it. Here's what happens:

WOT pull, top of 3rd or 4th, let off the throttle, and it feels like I hit a train. I am equating this to the throttle plate closing and all the air being dumped back through the front of the turbochargers. Whether this is normal or not, I do not know. I've had performance cars in the past that were N/A and did not "jolt" like this after I let off the throttle.

Countless articles point in the direction stated above regarding the air going the "wrong way" through the charge pipes since there is not an atmospheric BOV. Would a BOV help in this situation? Many articles state aftermarket BOVs are not needed unless power gains are doubling.

Any info is appreciated. Mods are in my signature, or lack there of.

 

[Stock_stinger]

It already recirculates the air to relieve sudden pressure from throttle plate closing. This is to prevent back pressure and turbo surge. Just a thang of turbs

 

[Stingin' Away]

It already recirculates the air to relieve sudden pressure from throttle plate closing. This is to prevent back pressure and turbo surge. Just a thang of turbs

Hmmmm. I wonder if it's normal then. Seems like there is a bunch of strain that is being put on the front end of the turbo. I'm hoping this doesn't affect the bearings or turbines.

Good thing for warranties.

 

[Terry@BMS]

Log it, and check psi vs. psi2 to see if BOVs are hanging.

 

[Stock_stinger]

Judging by the title it sound like your saying the car is slowing down aggressively when letting off

 

[Stingin' Away]

Log it, and check psi vs. psi2 to see if BOVs are hanging

Next nice day I'll take it out and log.

 

[Stingin' Away]

Judging by the title it sound like your saying the car is slowing down aggressively when letting off

Neg-o-tive. When letting off WOT throttle, I'm moved forward in my seat for a split second. The rest of the slowing down is from engine "breaking" being so high in RPMs. More of a jolt forward if you will.

 

[General_Vodka]

I had the same thing happen to me a couple times. Now either it went away or I don't do as hard of pulls.

 

[oddball]

The Stinger's transmission doesn't overrev as easily as most in higher gears. It's just how the trans is set up. You immediately switched from hard accel to a brisk decel. Most cars let the trans overrev and you just coast. Not so in the Stinger.

Air doesn't go "the wrong way" due to the BOV. It circulates - in a circle. Now, you'll have a problem if a BOV isn't opening all the way, leaving too much pressure in the charge pipe, and causing the compressor wheel to cavitate. But that's a completely different sensation to what you're talking about.

 

[Stingin' Away]

The Stinger's transmission doesn't overrev as easily as most in higher gears. It's just how the trans is set up. You immediately switched from hard accel to a brisk decel. Most cars let the trans overrev and you just coast. Not so in the Stinger.

Air doesn't go "the wrong way" due to the BOV. It circulates - in a circle. Now, you'll have a problem if a BOV isn't opening all the way, leaving too much pressure in the charge pipe, and causing the compressor wheel to cavitate. But that's a completely different sensation to what you're talking about.

I wasn't stating that the air is going the wrong way due to the BOV. More so meaning that letting off the throttle and the throttle plate closing, the air that did not enter into the throttle body either recirculates or is directed back towards the cool side of the turbocharger. Air going back towards the cooler side allows the turbine to spin in reverse = no good.

I'm thinking the car isn't recirculating as efficiently as it was when it was stock. I never had that much "jerk" when letting off the throttle without the tune. I'm not seeing this as a negative, just an observation.

 

[oddball]

I wasn't stating that the air is going the wrong way due to the BOV. More so meaning that letting off the throttle and the throttle plate closing, the air that did not enter into the throttle body either recirculates or is directed back towards the cool side of the turbocharger. Air going back towards the cooler side allows the turbine to spin in reverse = no good.

I'm thinking the car isn't recirculating as efficiently as it was when it was stock. I never had that much "jerk" when letting off the throttle without the tune. I'm not seeing this as a negative, just an observation.

There is no air going back towards the turbine. It recirculates. A turbine that cavitates makes a very specific noise and you would notice. That happens when the BOV can't keep up, or isn't operating correctly. Regardless, that's not what's happening here. Nothing going on in the air stream will cause a decel feeling. Any issues in that area will cause noise, and, in severe situations, damage the turbo.
The car likely accelerates a fair bit harder, and keeps it going for longer, than it did stock. So letting off the gas hits the drag in the trans that much harder.
It's the trans.

 

[ZedsGT]

I mean you have well over 400 ft lbs of tq x whatever the gear ratio is and then you stop at the TOP of a gear. It would be like that in any car

 

[oddball]

It depends on the overrun clutch in the trans. That was a common weak point in 60's/70's/80's transmissions. A smooth overrun tends to be weaker, but lets the car coast easier. My **guess** is part of the high rating of this trans was using a different style, size, whatever, of overrun clutch. Or, hell, it drags so much that there might not be one and it just depends on the converter to take the beating.

 

[Stingin' Away]

I mean you have well over 400 ft lbs of tq x whatever the gear ratio is and then you stop at the TOP of a gear. It would be like that in any car

Depends on the car. I have a Malibu as a daily and very seldom do I put it to the floor in that. Letting off after WOT, the car hesitates to decelerate. The revs stay up and the trans does not catch nearly as quickly as the Stinger.

The convo above is probably accurate. Transmission doing it's job, not a recirculating issue. As I always say, 10yr powertrain warranty is nice to have.

 

[Micah_221]

The title may be confusing but it is the only way I could explain it. Here's what happens:

WOT pull, top of 3rd or 4th, let off the throttle, and it feels like I hit a train. I am equating this to the throttle plate closing and all the air being dumped back through the front of the turbochargers. Whether this is normal or not, I do not know. I've had performance cars in the past that were N/A and did not "jolt" like this after I let off the throttle.

Countless articles point in the direction stated above regarding the air going the "wrong way" through the charge pipes since there is not an atmospheric BOV. Would a BOV help in this situation? Many articles state aftermarket BOVs are not needed unless power gains are doubling.

Any info is appreciated. Mods are in my signature, or lack there of.

Did you ever find a solution to this or is it a serious problem? I am experiencing it myself.

 

[oddball]

Did you ever find a solution to this or is it a serious problem? I am experiencing it myself.

"Feature as designed".
It's the overrun design of the trans.

 

[JohnnyBquick]

"Would a BOV help in this situation?"
I am just learning about Stingers. Do they have BOV's?
(compressing bypass valves, really)
I have added them on my other past turbo cars from the late 80's.

 

[oddball]

They do. Two of them. Recirculating. You can see them right in front of the engine, very proudly displayed.

You can replace the stock BOVs with a variety of aftermarket units. This is really only useful if you want a vent-to-air setup for noise, or some potential for holding higher boost pressures and/or recovering during shifts faster.