Best Primary and secondary size for Turbo LX9?

[farmerz24]

Hi Guys,

I will be doing an 3900 LX9 into a 05 subaru legacy. It will be turboed with the HE351ve turbo. I hope for 600whp, possibly even more. Eventually perhaps this turbo will be compounded with an HX55 or similar.

Question: I am going to be using the schedule 10 1.5 inch stainless weld-els for my primary. I think that this is actually a 1.75 inch inside diameter.

My question then is: What size should i use after my 3-1 merge? 2.25 or 2.5 ? This would then merge again both 2.25 or 2.5 pipes into a single pipe to mate up with the turbocharger inlet flange. At this point would 3 inch be sufficient to to use for the merge of these 2 secondaries?

the turbo will exit into 4 inch exhaust, flattened into a slight oval shape for improved ground clearance. Let me know.

[Guest]

Hot side of the turbo is generally considered to be "small" when compared to N/A header/exhaust systems. In your case I'd likely go 1.5" to 1.675" with primaries no longer than about 14" to 18", then using 2.25" or 2.5" to a 2.5" merge to feed the turbo. Going too big will reduce velocity, which will increase spool up time. There is also pressure to be accounted for here, which up to a certain point is desirable, because it's heat and pressure (actually pressure differential across the turbine) that run the turbocharger.

Basically making everything fit with nice transitions will be desirable. The final merge point to the turbo inlet I try to make either straight in so whatever size matches the turbine inlet nicely.

[farmerz24]

so you are saying the 1.5 sch 10 with its 1.75 inner diameter is too big? I wanted to use the thicker material for better durability, cost, and heat retention. otherwise i need to build this in like 16ga stainless?

[Guest]

I haven't had a 3900 head to look at up close, the 1.75" might be a good match, but that's getting on the side of too large to keep the velocity up with the displacement IMO. A lot of times I find with turbo exhaust pre-turbine is, except for very rare cases, the design itself is pretty inconsequential, due to the pressure involved as compared to an N/A application, where large is (for the most part) better.

[Mars]

I went with dual 2" pipes from the manifolds, to a collector and kept them seperate the whole way. I'm pretty sure 2" is plenty large enough, most 4.8 / 5.3 and even some 6.0L turbo builds use 2". i merged the dual 2" pipes into a fully divided twin scroll T4 flange and used one wastegate per bank.

Works VERY well in my car.





The factory 3900 manifold (the front one) flows really well I'd say almost ideal for a turbo setup, and you can weld mild steel to it no issue, there is enough steel content, it welds up nice.

[farmerz24]

i like the fact you used the factory flex bellows.. How does it hold up under boost.

How did you do the crossover? I am going to come under the front of the oilpan, the turbo will be mounted in the same area as the factory turbocharger location. So the drivers side will come under the front of the oilpan. In this case the 3900 manifold is pointed to the rear of the car. Using it on the passenger side means it would be facing forward instead of rearward. I dont mind building a little shorty header. I will have to get some flanges laser cut up and see how well the 1.5 sch 10 fits into it.

[RedZMonte]

My LQ1 turbo setup used Stockmanifolds to 2.25" X-over pipe to feed a Single T04-E turbo (T4). Before I sold the car i did make a Single Shroty Style manifold that collected 3-1 and was going to use a 1 5/8" primaries to a 2" X-over intoa Divided Twin scrool flange... I never finished the project. The Schedule 10 is strong stuff, I would go with a 2"-2.25" depending on what size the turbo inlet is on that turbo, 2.5" will slow the gasses and cool them and cause you slower spool.
If you support the turbo and have good welds, you wont get cracks in the piping. the heat mixed with the weight of a turbo is what really kills the manifolds/welds. I did not have a Flex in my X-over, I thought about adding one when i did the shorty headers but again never finished the project. My stock manifolds were cast iron and the X-over was alluminized steel, the tubular one was going to be 2"
304 Stainless.

http://60degreev6.com/forum/gallery/browseimages.php?do=browseimages&c=3&userid=6041

http://s221.photobucket.com/user/redzmonte/library/Monte%20Carlo%20Z34

[Mars]

The stock bellows holds just fine. I've run some high boost on this setup too.



There is the Xover pipe, and manifold. 2" pipe. 14ga.

Placement :