Has anyone run the S300 over the S475 without wastegates or BOV's? I have two boost gauges so I will be able to watch drive pressure and boost but am concerned about over-spooling the little 60/68. Maybe even some predictions before I shoe-horn this beast in the truck and have to pull it back out to add to it. BTW, WG will have to be external because these are non WG'd housings.

Thanks in advance,

Luke

 

I'd put an external waste gate before your high pressure turbo to decrease the drive pressure driving the S300 since its a non w/g turbo. Wouldn't worry so much about over speeding the S475.


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^^^What he said. BOV is not a bad idea either, it'll help the life of your turbos, especially if you drive it hard

 

I was thinking that I may be able to get by with just a BOV to regulate boost but now I thinking that drive pressure is equally as important too. I am also trying to decide what I should set my timing to. Doesn't head pressure increase the more I advance the timing?

 

Just clarifying, cylinder pressure increases. With higher cylinder pressures you increase the chances of the head lifting. Most run 16.5 - 17* timing with good luck on stock head bolts and gasket. Remember, more boost does the same thing. Combine the two and it isn't if you're going to pop a head gasket but when...


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i've blew so many damn head gaskets i dont even wanna talk about it, doesnt matter if you have studs or whatever you can still blow one just as easy

 

You could always park it, it won't blow head gaskets in the driveway. My main concern is not cooking a turbo. I'm gonna try to start it on the stand this weekend and maybe get it in the truck next. I am dying to see how these turbos do with the Steedspeed.

 

I suggest getting an external waste gate. Connect it between the manifold and bottom turbo. Let the big turbo do the work when pressures get high, and have both working to get up to pressure. That's my plan once I get my 150's in. Currently, my set up is working very, very nicely un-gated. HX35/40 w/16cm exh housing, over S400 (71mm).

 

How fast do they spool? What kind of boost are you seeing? What WG do you recommend? My small turbo is a T4 flange. I read several different forums and some people are popping HG's with 35 lbs. and others have over 100k miles and see 70 lbs. daily. I have never ridden in a truck with twins on it so I am curious to know what mine will do. When I pulled my motor because of a couple of bad oil leaks, I decided to install studs while I had it out. #6 was BADLY burned which led to building a new motor with twins. I don't think the pyro was working, it only indicated 1250 but it was very smokey.

Smoke is what I am trying to get away from, that and burnt cylinder walls and melted pistons. What I don't want to do is solve one problem and cause another.

Sorry for the long post but with the money that I've spent, I am nervous! I am finding it hard to get consistent answers on this. I certainly welcome any constructive criticism on my setup. I am by no means a pro so any opinions from people who are would be great. What kind of HP #'s does anyone think I will see with this setup?

Thanks for all the replies guys, I really appreciate the input!

Luke

 

You might get by if you keep your injectors on the small side. My first run down the track Saturday, the allen screw on my boost elbow vibrated shut. Essentially I was running ungated. The result was that I blew a big hole in a new hump connector. Didn't have my eyes on the gauge right then, but I hit 90psi+ with the gate working.

If you can manage it, it's best to have a gate on both turbos. Don't use a BOV on a diesel. When it blows, the lack of restriction will let your turbo seriously overspeed.

As far as HG, you never know. Some guys blow them using studs, I'm still on the original and just using the allen bolts, and I'm sure that I've hit triple digit boost more than once. But I am only running 18 degrees of timing.