Thinking of compound turbos - Diesel Truck Forum - TheDieselGarage.com
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post #1 of 12 (permalink) Old 04-09-2008, 10:32 PM Thread Starter
 
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Thinking of compound turbos

Ok so I have been looking into two turbos. What do ya'll think about a smaller hx30 over a hx50. It would have to have an external wastegate. However, I think it would spool great. I tow alot of stuff with the truck. I am also considering using the stock 35 over a 50 or s400. Any ideas would be great. Also anyone who has built these setups before feel free to way in on any tricks or tips I should know about.
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post #2 of 12 (permalink) Old 04-10-2008, 06:08 PM
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I'm building a set of compounds for my truck right now. They are actually a very similar set up to what you are looking at. I'm doing an hx35/h2e(which is kind of between an hx50 and hx55). I'm building these as a small set of towing twins that are supposed to be a very fast spooling set up. I have a 35mm external gate on the top turbo and the stock gate welded shut.

How much power are you looking to run, this set up is not capable of supporting the power that a 35/s400 set would do, but should spool much easier with small injectors. I'm not sure how long I will run these because they may be a little smaller than I want, so I will let you know how they work out, and I may be putting them up for sale in a while. I also plan on trying the set up with a 35/40 hybrid over the h2e.

Here is a link to my build up process. Its taken me quite a while because I've had a lot going on and we changed the plumbing around a little in the truck, but it will at least give you an idea.

https://www.thedieselgarage.com/forum...ad.php?t=32973
Sean

2000 2500 reg. cab 4x4 auto 577hp
09 6.7L QC LB stick, 4x4.

TOTAL PERFORMANCE DIESEL 707-545-FUEL (3835)
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post #3 of 12 (permalink) Old 04-10-2008, 07:28 PM Thread Starter
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No I'm want them just for towing and messing around. I don't want to add any more fuel than what I've got. I just want something that has more top end with the fastest spool up i can get. I also don't want to boost over 40-45 psi. I don't know a whole lot about turbos, but I would guess that with a small turbo on top you would have to have a pretty big wastegate.
Or maybe I am just in need of a project. About what did you spend on your setup? I would have to buy the flanges and clamps, I think I can weld, and bend everything else up myself. I guess my choice really depend on what I can come across in the way of a turbo for cheap.
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post #4 of 12 (permalink) Old 04-10-2008, 10:27 PM
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Getting the oiling set up was my biggest expense to be honest, and that could've been done a lot cheaper. My cousin is a cat mechanic and was working with me for a lot of the project. And when it came to the oil fill and drain for the bottom charger he said he could get the right stuff from cat and it would look like it was made to go together. So he ordered it up and when I got the bill it was over $400 for stuff we couldn't return and could've picked up for less elsewhere. Live and learn I guess.
If it weren't for that, I'd still be under the $1000 mark. If you can bend 4inch tubing more power to you. I just got pre bent pieces and welded them up myself. Another hint, Use 45* bends for the down pipe there are less interferences with the firewall and you have more room.

This would probably be a fine set up for what you're trying to do and the fuel you have. I'm going to try running a set of 7x10 sticks I have coming but those will be really hot with this set up I can tell you already but I think 100hp would work great.

I also scored my gate for free, so that made up for the other expenses and then some. Good luck, and let me know if you have any other questions.
Sean

2000 2500 reg. cab 4x4 auto 577hp
09 6.7L QC LB stick, 4x4.

TOTAL PERFORMANCE DIESEL 707-545-FUEL (3835)
www.totalperformancediesel.com
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post #5 of 12 (permalink) Old 04-11-2008, 01:54 AM Thread Starter
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I got a line on an HX50 for $250, but it doesn't have a wastegate. Do you think I should put an external one on it. I saw your post and it gave me some good ideas and direction.
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post #6 of 12 (permalink) Old 04-11-2008, 10:34 PM
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With the fuel you have, I wouldn't worry about wastegating the bottom turbo. It should be about a 17cm housing with a 73mm turbine wheel which will give it plenty of room to clear out the exhaust you have. I would just gate the top turbo so that you don't get it spinning too fast, or create a bottle neck and start backing up the exhaust, which leads to high drive pressure and higher egt's. Essentially once that bottom turbo starts moving air, you want the wastegate to open up top and give it as much drive as possible so it starts moving air even faster. I have another link that shows the turbos in the truck with the external gate mounted up. That should help a bit too.
https://www.thedieselgarage.com/forum...ad.php?t=66073
Sean

2000 2500 reg. cab 4x4 auto 577hp
09 6.7L QC LB stick, 4x4.

TOTAL PERFORMANCE DIESEL 707-545-FUEL (3835)
www.totalperformancediesel.com
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post #7 of 12 (permalink) Old 04-12-2008, 04:15 PM Thread Starter
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those turbos look pretty goo in there. Tight fit though. I think the external wastegate is a good idea. Right now the factor one doesn't keep up. It's supposed to be regulated to 23psi I think but I can boost up to around 40. So its clearly not enough. I think that the top turbo should be limited to around 20-25lbs. Also since you seem to know so much about this stuff, do you think i'll need a blow off valve to keep boost below 50psi?
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post #8 of 12 (permalink) Old 04-14-2008, 04:44 PM
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It depends on what injectors you run. Honestly I would run a pressure regulating valve instead of an actual "blow off" valve. They are a lot cheaper. I plan on building an intake plenum with 2 built in, so I can run 200hp sticks and not worry about over boosting and blowing my head gasket before I get it o-ringed. Rip Rook sells these valves as "blow off" valves but they only cost about $27 a piece instead of $300 or more. So that is the right that I'm going to go.

also, a quick piece of advice, roll your beads before assembling your intermediate pipe in the charge air system. The rest of that pipe gets in the way of the bead roller if you don't.

As for the external gate part, the stock gate is only 19mm so a 38mm wastegate can flow 4x the volume of the stocker, which should more than adequately reduce drive pressure and slow down the turbine speed for your application. Your top turbo will still be pushing a lot of boost, but thats because it is essentially being fed boosted air as well.
Sean

2000 2500 reg. cab 4x4 auto 577hp
09 6.7L QC LB stick, 4x4.

TOTAL PERFORMANCE DIESEL 707-545-FUEL (3835)
www.totalperformancediesel.com
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post #9 of 12 (permalink) Old 04-14-2008, 06:08 PM
 
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Lets not forget that the factory wastegate only vents the back three cylinders. That makes an external gate that vents all six way, way better
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post #10 of 12 (permalink) Old 04-14-2008, 08:51 PM Thread Starter
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That's a good point. I did not know that. Like I said I get around 40psi with the stock charger alone. I believe that's way to much to be good in a compound set up.
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Lets not forget that the factory wastegate only vents the back three cylinders.
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