External Wastegate Size for HX35 4.0

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LRSimons
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External Wastegate Size for HX35 4.0

Post by LRSimons »

Have a line on a 38mm for a pretty good price. However, this seems a little small based on what I've read. If anyone has any experience that would be great.

I'd like to be able to run low boost, having to run 8+psi is the main reason I'm wary of going with the 38. I'm new to tuning and would like the safety factor of getting a spot on tune on very low boost, then working up from there.

BTW stock hx35 internal wastegate is held shut, going to weld it when the turbo comes off next. From some research it seems the internal gate is useless for anything below 15 psi.
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Re: External Wastegate Size for HX35 4.0

Post by SkylinesSuck »

It depends on too many things. I would say go bigger though. I had a single 38mm on my HX35/40 hybrid and it didn't boost creep, but I was running like 30+ psi (and it was loud as hell externaly gated). When I went to a full HX40 it did terribly so I had to go twin 38's. It's all very dependant on manifold design, boost level, engine, etc. No way to tell, so just go big.

BTW the HX35 and HX40 are pretty innefficient at low boost. If you never plan to run more than that you might want a different turbo.
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Re: External Wastegate Size for HX35 4.0

Post by Cummins90 »

SkylinesSuck wrote:BTW the HX35 and HX40 are pretty innefficient at low boost. If you never plan to run more than that you might want a different turbo.
I moved to a Mitsubishi super 20g/td06H just for this reason. Even on the conservative side the hx35 at 10psig in the 4.0I engine is in the 64% efficiency island at 5000 engine rpm. The S20g is at the 68% island at 20psig at 5000rpm.

Getting back to the wastegate question I don't see why a 38mm wouldn't be effective.
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Re: External Wastegate Size for HX35 4.0

Post by SkylinesSuck »

What's the cost/benefit ratio of a 38mm vs a 50mm and the possibility of the 38 bring too small?
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Re: External Wastegate Size for HX35 4.0

Post by LRSimons »

Thanks for the replies.

Regarding the turbo size and boost, when I mentioned running below 8 psi I'd like to use that as a starting point for getting a good base tune. I highly doubt the head gasket will survive much past that point, and once that's upgraded I'll crank it up. Pistons will probably let go around 15 psi based on the experiences of others.

Anyways, the turbo is already set up and I'm not changing it. Think it will spool just fine, wide open it starts screaming at 1700 rpm.



Still torn on the wastegate, the possibility having to switch it out or run two definitely overshadows this decision. Too bad big wastegates are pretty rare on CL.

Still have some time to think about this, need to get the MS3 set up next.
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Re: External Wastegate Size for HX35 4.0

Post by SkylinesSuck »

Are you looking for used name brand gates or something? There's plenty of new knock off 50mm's out there. I have had good experience as well as many of my friends using all manner of China WG's and wouldn't be afraid to use one again.

And on the subject of boost vs the head gasket and pistons, what experience are you hearing? HX35's on our I6 motors? I'm sure I don't need to tell you 8psi from one turbo ≠ 8psi from another turbo. I think you could easily run north of 15psi on a stock head gasket. Cylinder pressure kills head gaskets, not boost. Good tuning is key.
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Re: External Wastegate Size for HX35 4.0

Post by LRSimons »

Just looked on ebay for cheesy wastegates, and sure enough $55 gets a brand new china special. Not something I would have thought to cheap out on but this could be promising for saving some money. Yes, I was looking for a used name brand unit.




On the turbo side of things, yes I (somewhat) understand the psi vs cfm aspect. Was using psi as a general measurement of power considering we're not comparing turbos at the moment.

After some more reading, here's what I'm understanding of flow vs power- A turbo flowing flowing the same cfm as the engine it's connected to consumes na (when both are in their respective efficiency ranges) will theoretically double the na power level at 1 bar or 15ish psi of boost because the engine is taking in double the air it was na.

The HX35 I have flows around 58 lb/min according to the compressor map. The 4.0 consumes about 20 lb/min na according to an online calculator. Assuming the HX35 is at peak efficiency pushing 30 psi or so for the stock diesel application, it should more than triple power at peak efficiency (oversized). However at that level of boost the intake temps would probably be too high to make any power.

Here's where I'm trying to covert this to horsepower. If the combo would in theory make 450-500+ whp at 2 bar, it should make about 75 more than stock at 8 psi or so. However this model is linear and not really applicable.

Feel free to correct any BS in the above.



All this bench racing is making my head hurt!



Regarding breaking stuff, I guess there are really only a few documented failures. I was/am under the impression than the head gasket is the weak link but I could be wrong. It seems most of the documented builds on the dyno result threads came in at around 200- 250 whp. Granted, a vast majority had different goals and were hindered from bigger numbers by more drivetrain loss. Guess I'll break something eventually and we'll know for sure. :lol:
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