turbo mounting question

Which drivetrain to choose, so many choices, 4-cyl? 6-cyl? NA? Turbo?
inkedfireman
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turbo mounting question

Postby inkedfireman » 19 Oct 2009, 18:43

I have a question about turbo mounting in general.

Why are turbos always hung off the manifold without support? It would seem to a newbie that from a manifold strength standpoint, you'd be way better off not hanging all that weight from the manifold alone. Wouldn't having the turbo mounted on some sort of a bracket, with a flexible coupler to the manifold, eliminate a lot of cracking? This would seem to be especially helpful in MidLana where you have the turbo way off to the side remote from the head.

Denny, curious, with no practical experience...

Midlana1
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Re: turbo mounting question

Postby Midlana1 » 19 Oct 2009, 19:49

You're correct - I'm not done yet. The turbo support can only be designed and built after the turbo, header, and wastegates are in place, right? ;)

Jagmandave
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Re: turbo mounting question

Postby Jagmandave » 20 Oct 2009, 13:18

The turbo is mounted as close to the head as possibile to get maximum efficiency from the heat, pressure and volume of the exhaust gasses. That's not to say it has to be there, but the closer it is the quicker and more efficiently it responds.

Most turbos these days are pretty lightweight, and hang from the bottom of the manifold - not straight out - so the load is in tension and not shear.

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Re: turbo mounting question

Postby Midlana1 » 20 Oct 2009, 15:26

Yeah that's what I read, but the same books also say the inlet tract should stay short, too. So the question is, which is more important? Rightly or wrongly, I went with the latter, which is why the turbo's where it is, and it's about 6" from the intercooler.

Jagmandave
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Re: turbo mounting question

Postby Jagmandave » 21 Oct 2009, 08:11

I'm not sure there's any real wrong way to do it, I've even seen turbo kits that are made to mount in the tailpipe just before the mufflers - they'd have long intake and exhaust runs!

Short intake tract means quicker response time, once the turbo spools up. Same with short run to the turbo's exhaust side impeller, short exhaust run means the turbo spools up quickly, but with a long intake run it takes time to fill the pipe so to speak. However, on my 2009 Cooper S, the turbo is mounted directly to the exhaust manifold, just inches from the head, where the pressure side meanders all over the engine compartment - thru the intercooler and so on. And there's virtually no detectable lag, but I think that's mostly because they use a tiny impeller that spools up almost immediately - but then that limits the ultimate boost and doesn't let the engine breathe well at high RPM's. Every design has it's compromies I guess. Then there's the heat to deal with too.....

WickedOne
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Re: turbo mounting question

Postby WickedOne » 21 Oct 2009, 12:13

With the proper wheel you can mount your turbo wherever you want. You just have to have the right wheel for the flow conditions of your mounting point. With the proper sizing they even mount the turbo at the end of the exhaust. Those don't really have a perceptible difference in response time because they don't use an intercooler.

Jagmandave
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Re: turbo mounting question

Postby Jagmandave » 21 Oct 2009, 12:43

Yes, to use my MINI Cooper example, the intake air for the inlet side of the turbo comes from the aircleaner mounted on the back of the engine, then goes down thru the intercooler then back up the other side thru a muffler (!) and then into the intake manifold. That's a long damn way to push the air, yet it has no perceptible turbo lag.

However I got one thing wrong, the turbo sits on top of the exhaust manifold, not under it.
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xero_xero
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Re: turbo mounting question

Postby xero_xero » 23 Apr 2010, 19:11

the best way to describe this scenario is the title of a great article called "Doing it from behind". This introduced the rear mounted turbo under the rear bumper of the 05 Mustang.

as far as bracing, never put much thought into it because i have always assumed that the turbo manifold was deigned to withstand the strain of the turbo. this may not be true with some ebay competitors.
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coyoteboy
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Re: turbo mounting question

Postby coyoteboy » 07 Oct 2011, 03:10

FWIW turbo's utilise the heat energy contained within the gas as well as the kinetic, mounting the turbo too far from the ports means you've lost some of that energy, the cooled gas has become more dense and slower moving (so you need to change your turbine) and if the pre-turbo exhaust tract is too long you're going to have a large column of "cold" gas to push through the exhaust and turbine which is notably less efficient than pushing a short column of hot gas (this is part of the reason for wrapping exhausts). OEMs place the turbo as close to the head as possible, at the expense of additional water cooling jackets and short service intervals, for a reason. You can ignore that reasoning if you can justify it I suppose! Having said that, the midlana position isn't very far from the head at all so not a massive issue.

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Re: turbo mounting question

Postby Midlana1 » 07 Oct 2011, 07:05

All true, but keep in mind what the turbo's used for - to pull air in through the intake tract, compress it, and push it into the engine. If the turbo inlet tract is long, that extra power gained by mounting the turbo close to the head is wasted on pushing the inlet air through the various bends.

Also keep in mind that OEMs have to deal with very tight engine compartments and simply don't have the option to put the turbo where they want. In many cases, the only place it can go is right next to the exhaust ports, so it being there isn't necessarily due to the efficiency aspect alone.


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