Please help on Holset HX35 + HX55 compound turbo set up

[CefiroA31]

Hallo everyone,

Need some help for wastegates sizing and HX35 compressor choice in my compound turbo set up :

Engine : Nissan VQ30DET, 3 liter displacement with 9:1 compression ratio.

Low Pressure Turbo : Holset HX55, 71 mm x 99 mm compressor, 86 mm x 77 mm turbine, 25 cm T6 twin scroll turbine housing. I plan to boost it to 1 bar (15 psi) for the street, but will boost it to the max of its ability when racing.

High Pressure Turbo : Holset HX35, I have 2 of them, 1 has 54 mm x 83 mm 8 blade compressor, 2nd has 52 mm x 78 mm 7 blade compreesor, 12 cm and 14 cm T3 twin scroll turbine housing, with 70 mm x 60 mm turbine. I plan to run low boost on the HX 35, only 0,5 bar (7,5 psi), so I can maximise flow capability of the HX55.

Questions :
Will a Synapse 50 mm wastegate be enough to hold boost at 0,5 bar for the HX35?
Will a Synapse 40 mm wastegate be enough to hold boost at 1 bar for the HX55?
Which Hx35 compressor will works best at 0,5 bar? 52 mm 7 blade compressor or 54 mm 8 blade compressor?

Thank you.

 

[viperlp01]

You may need to run a 4 port controller on the large turbo to make sure boost pressure stays in check. The 50mm gate should be able to evacuate enough exhaust gas to the large turbo. I would run at least 10-15psi on the small charger and let the big one eat. From my testing and hearing about others you want to be in a comfortable spot in the compressor map to make sure that the flow from the large turbo is not affected by the primary turbo being out of its efficiency range.

 

[CefiroA31]

Hi John, Thanks for your input, it was your car build thread that first bring me to compound turbocharging, really awesome car she is. What rpm do your h1c and hx52 starts to spool? Off to find some good deals on the wastegates then.

 

[viperlp01]

They spool at almost the same time to start and the HX52 hits full boost about 500 rpm of so before the H1C hits full pressure. I hit 40psi at 5400 rpm. That combo on a 3.0L is going to be nuts without a doubt.

 

[CefiroA31]

Hi, some update on my compound turbo project.
Change the engine to a 2jzge vvti with 2jzgte pistons, rods, and headgaskets to lower compression.
Got the compound turbo system running :
1. Divided manifold to a hx35/40 hybrid as small turbo, 60 mm 7 blade compressor, with t3 twin scroll 12cm housing
2. 50 mm wastegate (17 psi spring) flowing to 1 scroll of the big turbo
3. Exhaust from hx35/40 flows to the other scroll of the big turbo
4. 45 mm wastegate for the big turbo) (7 psi spring), which is a hx55 with 71 mm compressor, 80 mm turbine, t6 25 cm twin scroll housing.

Tested on the dyno with 93 octane pump gas. Problem :
On the dyno at 3rd gear, boost is coming late and low max boost. Boost started around 4200 rpm. Max boost around 5500 rpm.
With boost source connected to bottom ports of wastegates (small turbo wastegate boost source at the intake; big turbo wastegate boost source at the charge pipe between the turbos cold sides), max boost is 7-8 psi at the intake manifold.
With both wastegates unconnected to boost source max boost is 17-18 psi at the intake manifold. Tested with boost gauge at the pipe between cold sides, the big turbo is boosting to 7-8 psi. Which means the small turbo is also boosting to 7-8 psi for the boost to be compounded to 17-18 psi.

Obvious issues is there are some exhaust leak in wastegate connections (cold sides piping seems to be leak free). However I dont think that it will make the boost so late and low.
Thinking to check backpressure which may be pushing the gates open. plays around with wastegate boost source, try it to the top port, adding some manual boost controllers.
My target is to have early spool up around 3000 rpm and full boost of 25 psi reached around 4000 rpm.
Any other ideas to troubleshoot this set up is very welcome.

Thank you

 

[bastarddsm]

The way you have the exhaust feeding the HX55, is screwy. I would not divide it like that. I'd think on a 2jz you should have 25psi by not much past 3000 on that HX55 alone.

Also it doesn't take much exhaust leak to make it really really laggy.

 

[CefiroA31]

Hi, I was thinking of making an equivalent to a quick spool valve with the routing of the exhaust from the hx3540 and its wastegate to the hx55.

Reason is I think a hx55 with a 86 mm x 80 mm turbine is pretty big, very close to a GT45 turbine size. And I have seen most GT35R with 68 mm x 62 mm turbine and 0.63 a/r housing starts spooling around 3000-3500 rpm in 2jzs here on 93 octane. So will be very surprised if te hx55 as a single will make 25 psi before 4000 rpm.

Ok will try to fix the exhaust leak first to see if it improves.

 

[bastarddsm]

From my personal tests, a QSV doesn't work very well unless the housing is extremely large. By forcing all the exhausts through a single scroll all the energy is lost in "choking in the nozzle" and the spool is much much worse. I tried it with a 12cm housing on my HX35, and it was like 1000RPM slower than with both of them open. I then put in an 18cm housing, and the spool was about the same with or without the QSV.

 

[CefiroA31]

Wow thats interesting. Mostly seeing info on qsv from supraforums where most says its proven to work up to 500 rpm quicker spool, even on midsized turbos such as Precision 6266. Ok then if the exhaust leak is fixed and spool up dont improve much will try to route the exhaust from the hx35 and the waste gate into a sinle pipe tothe hx55. Many thanks on your input.

 

[LandSpeed-DSM]

By forcing all the exhausts through a single scroll all the energy is lost in "choking in the nozzle" and the spool is much much worse. I tried it with a 12cm housing on my HX35, and it was like 1000RPM slower than with both of them open. I then put in an 18cm housing, and the spool was about the same with or without the QSV.

Exactly what I had come in here to say.

In 3rd I have 20psi right around 5k on a 2.0L with my HX52 in 16cm housing, for comparison.

You want as little restriction as possible between turbine stages. This will bring them both up faster.

As John pointed out, your PRs, even with 3.0L displacement, are too low currently to make a compound setup "worth it."

The widest part of the map, where it extends furthest to the right, for the Pro52 wheel is found at ~3.0PR and the HX35s all have their widest point around ~2.7PR

Running the HX35 between 2.0-2.5PR puts you in a fairly efficient spot on your 3.0L to keep the now re-compressed air coming out of the HX55 from winding up over >260*C in the hot weather Jakarta gets.

There are a few common reasons to run staged compressors.. one is for response/torque, while another is to reach a PR that you otherwise could not with a single stage or to do so more efficiently than a single could by splitting the work between two compressors operating in their sweet spots.

A third is to use a "medium" sized turbo to spool a very large turbo that you would otherwise not be able to light off on just motor alone.

It does not seem with the way you have it implemented currently you are achieving any of those.

 

[viperlp01]

Before there were wastegates they used to limit boost by restricting the outlet of the turbo. Essentially what your doing.

https://www.youtube.com/watch?v=juzliyakVJs

Listen to how fast the turbo's spool when I actually start to make positive pressure. The torque curve was damn near vertical when I started turning the boost up. It will work, you just need to simplify the cross pipe you got going on.

Also run WAY more boost.!!! 17psi worth of springs in the gate, and let her eat.