Cascade Crew

DBL_TKE · Posted: Thu Mar 06, 2014 8:29 am Post subject: Turbo questions

For the past couple of months I have been researching like crazy in order to do a proper turbo build, though some info is harder to come by than other stuff. I gave myself a crash course in learning how to read a compressor map last week. There's lot more to it than I originally thought and I still don't quite have it down, But my first question here is how do you properly determine what size wastegate and blow off valve to use? I get the general idea but is there an actual mathematical formula?

Dewey316 · Posted: Thu Mar 06, 2014 10:26 am Post subject:

It depends a lot on the turbo/motor/power combo. Really, bigger turbo's you can usually deal with a smaller wastegate, since you won't need to bleed as much pressure most of the time. BOV on the otherhand, the more air you push, the bigger you need. This stuff seems to be a bit of a black-magic-art by the guys who do it, i would really just call and talk to a vendor who deals with big motors and turbos and see what they say.

With a big single like you're going to run, you might want to consider setting up the BOV as a recirc valve instead, that way you can still control pressure stalling the turbo, but you don't have to completely recharge the intake tract to get back in the power.

Dewey316 · Posted: Thu Mar 06, 2014 11:07 am Post subject:

I should also add a little more because it isn't as simple...

if you want really limit the boost on a big motor, with a quick spooling turbo, then you will need a large wastegate. For example, if you wanted to limit yourself to 6lbs of boost, you are going to need to pass a lot of exhaust through the wastegate. If your running 36psi, then you won't need to pass as much. That is what I mean by engine/turbo/power combo, its a matter of how much exhaust you end up actually passing through the wastegate.

aaron_sK · Posted: Thu Mar 06, 2014 6:22 pm Post subject:

Dewey316 · Posted: Fri Mar 07, 2014 6:52 am Post subject:

Twilightoptics · Posted: Fri Mar 07, 2014 6:20 pm Post subject:

Pretty much what Dewey said. Personally when selecting a turbo itself, I find the power I want to make and the rpm and what boost level I want to make it at.

I have a sneaky suspicion you're not going to need much wastegate at all unless you're pushing extreme small block rpm. As far as the compressor map - do the math. What's your displacement/peak rpm/etc and plot it on the map of your turbo and see where things start to line up.

That turbo is bigger than what I work with all day on 7.6L Inline 6 at 2700rpm at 40psi. And the Diesel has more heat to add to the equation.

DBL_TKE · Posted: Sat Mar 08, 2014 12:32 pm Post subject:

I've been considering running twin 38mm wastegates because since the turbo is a twin scroll It'd be beneficial to keep the hot side divided as well. Seems like most people that run a single WG tend to be around 50mm. I'm intending to keep my max boost in the 16-18PSI range.

Dewey316 · Posted: Mon Mar 10, 2014 6:29 am Post subject:

With a twin scroll, if you really want to go dual WG if you can, controlling the flow and keeping the exhaust paths separate is ideal. You will need to be very careful to get them to balance correctly, but it shouldn't be too big of a deal.

I am pretty sure you would have more than enough WG with those, I think your on the right path, unless you bring the exhaust together, then split it again for the twin scroll mount, putting a WG on each of the exhaust banks will be your only option. If you do bring them together, you loose the real benefit of running a twin scroll.

DBL_TKE · Posted: Mon Mar 10, 2014 7:29 am Post subject:

Yeah. I've been reading up on the benefits of keeping the twin scroll separate. Though I did see a clever way of doing that and still running a single wastegate. They ran a short Y-pipe from the wastegate to each side.

Dewey316 · Posted: Mon Mar 10, 2014 7:34 am Post subject:

BigDaddyVu · Posted: Thu Apr 24, 2014 10:39 am Post subject:

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