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Boost Creep Question

3LGODZILA

By 3LGODZILA,
in Engines & Forced Induction

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3LGODZILA Proficient

3LGODZILA

Posted
Posted

ok while i have my turbo off im trail fitting my split dump, i had a bellmouth on before.

ive taken 2 pics, the 1st one is how much the wastegate flap opens inside the bellmouth dump and the second is inside the split dump. is this the boost creep that people talk about using a split dump because it seems like it opens fully and is only very slightly less then the bellmouth. i have die grinded the wastegate pipe out slightly should i go more or leave it, coz i dont think ill get much more out of it with the die grinder.

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3LGODZILA Proficient

3LGODZILA

Posted
  • Author
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as you can see ive marked the bottom blue line wen it was inside the bellmouth and the top blue line inside the split. sorry its a bit blurry but u can see the different angle the wastegate arm is at

wlspn Proficient

wlspn

Posted
Posted

Any chance of seeing a pic of dump pipe, seperator area? Wouldn't think it's going to restrict flow dramatically, if at all, as it'is open almost all the way, but would obviously be nice if you could get it all the way open...

wlspn Proficient

wlspn

Posted
Posted

OK. Hard to suggest too much without seeing it in person as can't really tell how much metal you have to play with...

Could possibly champfer the edge where the wastegate flap is touching to allow more movement but if you're getting concerned you may do more damage than good its probably best to just leave it.

I truly believe things will not be greatly, if at all, affected & you don't want to ruin it for little to no gain...

& just to clarify I think you will find when people refer to boost creep they mean boost level slightly altering from the set level

3LGODZILA Proficient

3LGODZILA

Posted
  • Author
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yeh wat i understand is the boost creep is caused by the flap hitting and not opening fully, i was expecting it to foul like half open but it seems to open heaps just very very slightly less then a bellmouth as u can see in the pics.

wlspn Proficient

wlspn

Posted
Posted (edited)

Alright, was a bit tired yesterday so here's a better explanation of boost creep. What I said yesterday was more boost spike I suppose...

OK, say you have boost set at 10psi...

The wastegate flap does not stay 100% sealed until you reach 10psi then instantly open fully. (although that would be lovely!)

Instead as boost pressure builds the wastegate flap slowly creeps open, leaking some boost, & should fully open at 10psi.

This is not good because as soon as the wastegate flap starts to open boost builds slower.

Do you follow me?

What you are talking about is what I would consider to be slight restriction of movement of the wastegate flap.

Edited by wlspn
Birds Grand Master

Birds

Posted
Posted

When the wastegate flap cannot fully open it will cause overboosting - not only this but it can damage the diaphragm in your actuator.

I had one of these split pipes on my turbo - it wasn't a JustJap one but as I understand they are all much the same. Initially my wastegate was jammed shut and I had infinite boost until rich and retard kicked in. I diegrinded the bottom of the wastegate pipe until it had enough room to swing freely, but it still wasn't opening to a full 90 degrees angle. Die grinded the side of the wastegate pipe nearly all the way to the weld and it still wouldn't get 90 degrees. Still had issues so I gave up and put stock dump on. Issues weren't as bad but I still had them so I put it down to the actuator. Replaced actuator and it was alright from then on.

Recently I got a custom exhaust done including custom 3 inch dump pipe, haven't looked back. I recommend doing this - it's just as cheap as one of these split dump pipes, which as far as I've heard are pretty useless anyway (the wastegate pipe is not loud at all, nor does it help with flow).

NSNPWR Rising Star

NSNPWR

Posted
Posted
Alright, was a bit tired yesterday so here's a better explanation of boost creep. What I said yesterday was more boost spike I suppose...

OK, say you have boost set at 10psi...

The wastegate flap does not stay 100% sealed until you reach 10psi then instantly open fully. (although that would be lovely!)

Instead as boost pressure builds the wastegate flap slowly creeps open, leaking some boost, & should fully open at 10psi.

This is not good because as soon as the wastegate flap starts to open boost builds slower.

Do you follow me?

What you are talking about is what I would consider to be slight restriction of movement of the wastegate flap.

Thats not boost creep...its known as wastegate creep, where the wastegate creeps open before the desired boost pressure is reached...you can fix this by using a heavier actuator, applying a spring to the actuator flap arm (so there is more resistance on it, holding it closed) or if youre using a sh1tty bleed valve, trying a different type of boost controller like the Turbotech pnuematic units....also, the internal gate flap doesnt fully open (as in 90 degrees open) even when youve reached your desired boost level...pump some compressed air into the actuator line with the rod etc connected and see how far it moves...

Boost creep is a separate issue, its where you have reached your desired boost level but as revs rise, boost continues to rise, the wastegate cant pass enough gas and the exhaust wheel gets oversped...this is common on cars with tight rear housings and very free flowing exhausts, particularly those using decat pipes!

Harey Veteran

Harey

Posted
Posted
Boost creep is a separate issue, its where you have reached your desired boost level but as revs rise, boost continues to rise, the wastegate cant pass enough gas and the exhaust wheel gets oversped...this is common on cars with tight rear housings and very free flowing exhausts, particularly those using decat pipes!

Thats exactly whats happening in this scenario but just for a different reason. The wastegate is unable to open completely due to an issue with the dump pipe. This can cause the boost to creep as the wastegate opening at say 80% is not able to flow enough air to maintain the same boost level.

NSNPWR Rising Star

NSNPWR

Posted
Posted

and like I said, they never open all the way to 90 degrees anyway...

To the OP, hook the actuator rod up to the wastegate swing arm, push some compressed air down the vac line and you'll see how far it opens...will give you an idea then as to whether your dump is going to restrict its movement.

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