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1995 Landrover Defender 130,4BD1T Compounded HE221 + WH1C,4L85e.
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I am getting closer to finally getting my 1995 defender with a Isuzu 4BD1T compound HE221 and WH1C setup mated to 4L85e ,LT230 conversion running . I am unsure of the best basic way to control my compound setup.
I am thinking that the low psi WH1C turbo would control its wastegate and also feed the spring side of the external waste gate and on the other side of the external wastegate the back pressure via a regulator from the exhaust manifold.
The high psi HE221 turbo would be standard.
The intake maximum boost would be controlled by fuelling?
Any information would be appreciated.
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IMO you're best to set the big turbo on it's own wastegate and the little turbo wastegate to the max boost you need.
This means the small turbo boosts higher initially and then scales down as the big comes on stream.

Your best efficiency comes from unloading the small turbo as much as possible. But this risks overheating the small turbos compressor wheel. So you've got to compromise by dropping the boost on the big one. I'd start with about 12psi on the big and see how you like it.

How the turbos interact is mostly about turbine size. You want the big turbine to be roughly twice the choke flow rating of the little. This lets the little spool up before the big starts to rob it's exhaust pressure difference.
 

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I am running a wh1c and 42mm HX30 on my 4BT and after getting many issues straightened out and a drive pressure gauge installed i can give a little insight.
I have the 30 gated to open at 40psi on the bench and the wh1c at 18psi this has resulted in ~ 42 psi at the manifold under WOT under 2,000 rpm with manifold psi climbing to
46 if I keep in it much beyond 2,000.
I have also installed a stop on the 30's wastegate that limits it's travel to .100" this has made the wh1c seem "happier" as the 30 and wh1c seemed to argue about who was gonna lead in the dance. My combo tends to run with between 3 and 10 psi drive over boost except when spooling, on the rare occasion that I'm on level ground for any length of time drive and boost are within 1-2 psi of each other at peak torque rpm's.
I am still doing a bit of fine tuning but it's real close now so it's taking more driving between adjustments, my last change was lowering the 30's gate to 38psi this shifted the load to the wh1c by ~ 5psi above 2,100rpm so next I'll lower the wh1c's gate to 16psi as I want to keep max manifold psi under 45psi.
All in all I'm really happy with it now runs it strong and will pull interstate grades at the speed limit with part throttle and EGT's of 1,050*, last weekend on a return trip from Phoenix
I got stuck behind slower traffic and ended up at 55mph on a good grade requiring a downshift into direct and with WOT I was able to get back to 75mph without much drama this doing this did see EGT's near 1,200* and more manifold PSI then I feel is safe for a Cummins head gasket hence needing to unload the wh1c a bit....there is a LOT going on between the two turbos and one little change affects much more that I would have thought before I started on this journey so now progress is pretty slow.
We all have our own path to the ideal tune so your results WILL vary but this should at leas help light the path for you, you have MUCH more control over your combo that I do...
GOOD LUCK!! I'll be following your results to see where it leads.
 
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IMO you're best to set the big turbo on it's own wastegate and the little turbo wastegate to the max boost you need.
This means the small turbo boosts higher initially and then scales down as the big comes on stream.

Your best efficiency comes from unloading the small turbo as much as possible. But this risks overheating the small turbos compressor wheel. So you've got to compromise by dropping the boost on the big one. I'd start with about 12psi on the big and see how you like it.

How the turbos interact is mostly about turbine size. You want the big turbine to be roughly twice the choke flow rating of the little. This lets the little spool up before the big starts to rob it's exhaust pressure difference.
Dougal
I posted a similar question about wastegate control on my compound 4JB1T a while back, I took your suggestion on controlling the HP turbo using full manifold pressure, and gating the atmospheric on its own
Have to say it was much better, boost came in earlier than the previous method of controlling to maintain a fixed P/R across the HP turbo.
I’m shortly setting up a Banks gauge with full data logging of temp and pressure at every stage to really get some firm data on turbo and intercooling and efficiency.
Paul
 

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Hate to go off topic, but how did the hopped up 4HE1 turn out? Considering that as an option as well, with an ASTR style starter.
 

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Hate to go off topic, but how did the hopped up 4HE1 turn out? Considering that as an option as well, with an ASTR style starter.
Never proceeded any further with it unfortunately. Had some major issues I found with the particular engine I had, so returned it and got my money back. Sticking with the 2.8 4JB1T it’s still holding together, as well as having lot of spares. Bigger inline injection pump going on it soon. I have a 4BD1T sitting around now if I want to go bigger
 
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