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Rb20 Gt35 Dyno Graph Boost Curve ?

joe blo

By joe blo,
in Engines & Forced Induction

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joe blo Experienced

joe blo

Posted
Posted

Hey mates I'm just looking at the dyno sheet I got with this beast. I'm wondering about the boost curve. Does it show that it doesn't make full boost until 7500 rpm? I would expect it to make that at worst case 5700rpm then the line to stay flat till max rpm.

It's a gt35 .82 rear on a rb20. Garrett turbo. China stainless manifold. 38mm wastegate screamer pipe.

Boost controller is a turbo smart dual stage manual one.

No idea what spring is in wastegate

Looking for some ideas on if that's how it shud be or if something's goin on with setup.

I understand its not the ideal size turbo but that's what's on it. Il live with it

Thanks mates

post-34298-0-01513500-1409233809_thumb.jpg

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MrStabby Grand Master

MrStabby

Posted
Posted

Have a look through the RB20 Dyno sticky thread. For example, the dyno sheet on the top of the last page shows the sort of shape you should be aiming for manifold pressure (boost). I'd guess your setup is always going to be horrible with a turbo that big. Suggest you change your mind about living with it. You want to enjoy driving your car don't you? :)

joe blo Experienced

joe blo

Posted
  • Author
Posted (edited)

Yea I've seen a lot of dyno sheets on there. I believe it should be as I suggested and reach full boost at a certain point in the 5000rpm range and hold it but want to confirm something may be up with mine and if something isn't right suggest what is causing it.

Edited by joe blo
scotty nm35 Grand Master

scotty nm35

Posted
Posted

The turbo is too big, and the .82 housing is more suited to a 3L engine. A stock RB25 turbo can make that power, and come on by 3k on a 2L.

It could make bulk KW if you were willing to rev it to 12k and make use of that amount of airflow. (porting heads, massive cams etc.)

Lithium Grand Master

Lithium

Posted
Posted

Yes, the peak boost is at 7500rpm but that's not so much a factor of turbo lag as it is boost control - its boost creeping which is why it keeps climbing and ending up at it's highest there. Looks like the gate is opening at around 6000rpm, which is closer to your expectations and I'd say is probably more or less what you're going to get on an RB20.

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Lithium Grand Master

Lithium

Posted
Posted

Yes, the peak boost is at 7500rpm but that's not so much a factor of turbo lag as it is boost control - its boost creeping which is why it keeps climbing and ending up at it's highest there. Looks like the gate is opening at around 6000rpm, which is closer to your expectations and I'd say is probably more or less what you're going to get on an RB20.

joe blo Experienced

joe blo

Posted
  • Author
Posted

Yea I did consider it could be boost creep but I thought that if it could hold the 12 psi setting fairly well it should be able to control 21 psi.

If I put a spring closer to 21 psi in the wastegate could that make it better? Could probably assume the current spring is below 12 psi

scotty nm35 Grand Master

scotty nm35

Posted
Posted

That will increase the boost, you should hit 21psi by 10k or so. :P

An electronic boost controller may help with the boost curve, but a heavier spring will definitely be required in the wastegate.

bcozican Experienced

bcozican

Posted
Posted

as said totally wrong setup so 7500 would be correct

to give you an example I ran an rb22 with gtx3076 with 0.82 tial 44 Vipec 88 and e85 with basically everything you can get for that setup (cams dialled in etc) and had full boost at 5200

as all said above get rid of that turbo its never going to work

Dose Pipe Sutututu Grand Master

Dose Pipe Sutututu

Posted
Posted

food for thought (ignore if you wish).

  • Sell turbo
  • Sell manifold
  • Sell gate

then

  • buy a brand new hypergear highflow
  • stock manifold
  • spend all leftover cash on hookers and cocaine
  • and whatever is left on tyres
  • Like 1

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