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Discussion Starter #1
Hi everybody.
Had a question for the compound turbo Gurus here about compound vs single turbo performance. Had an oil seal drama on my atmospheric turbo on my compound Rodeo. I have temporarily removed the atmospheric turbo and just running the high pressure as a single. All exhaust pipework is the same bar a bypass pipe that sits in place of the atmospheric turbo. One thing I have noticed is a significant increase in lag running the single turbo around 500rpm later to come on boost. Was always under the impression that a compound setup would have a slight increase in lag than if the same high pressure stage turbo was used by itself as a single. I have never run this particular turbo as a single so never had a comparison previously. My grasp on compounds is not as good as I thought. Can anyone explain the theory behind this?
Cheers Paul
 

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Info would help. What turbo are you using?
 

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Generally, I'd think there wouldn't be that much difference at the beginning of the boost. In compounds, The high pressure turbo does most of the work at the lower boost levels. Like Red mentioned, what turbos are involved?
 

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Discussion Starter #4
Generally, I'd think there wouldn't be that much difference at the beginning of the boost. In compounds, The high pressure turbo does most of the work at the lower boost levels. Like Red mentioned, what turbos are involved?
Just to clarify, this setup is on a 2.8 4JB1T.
High pressure turbo is aTD04HL-19t atmospheric is a garret GT2871R. Not a perfect match for turbos but does give a reasonably even split between turbos. The td04HL is a litttle on the big side as a single for my engine, so would expect it to be laggy, but found it performed very well when in the compound setup with the Garrett. Just wouldn’t have expected low end to have been improved by the compound setup so much
 

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Yes, that smaller turbo seems a bit big for a 2.8 L. Specs show a 46mm inducer which is essentially the same as the Holset Super HX30W. Fine on an engine about 3.9 L or bigger. There seem to be several turbine housing sizes for those as well. I see 6 cc, 7 cc, and 8.5 cc. You'd want as small as possible for that small engine.
 

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Discussion Starter #6
Yes, that smaller turbo seems a bit big for a 2.8 L. Specs show a 46mm inducer which is essentially the same as the Holset Super HX30W. Fine on an engine about 3.9 L or bigger. There seem to be several turbine housing sizes for those as well. I see 6 cc, 7 cc, and 8.5 cc. You'd want as small as possible for that small engine.
I understand it is too big, when I previously ran a single I was using td04L-19t low rpm performance was great, which is expected. I just find it odd it that when used in combination with the larger atmospheric Garrett the low end performance was so much better.
 

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1/ When running as a single, waste gate the secondary at a higher psi.
2/ Check for boost leaks around any plumbing you swapped going from compounds to a single.
 

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Discussion Starter #8
1/ When running as a single, waste gate the secondary at a higher psi.
2/ Check for boost leaks around any plumbing you swapped going from compounds to a single.
Had wastgate pressure increased when I ran it, definitely no boost leaks. Everything is back to compound setup now with the smaller td04 as the secondary.
 

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I have very little experience here but have a thought. I have a TDI, basically stock. When at warm idle it can show a little boost. I mean tiny, the atmosphere turbo, although not make significant boost could be making .25 psig, enough to help the little one spool.


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