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Location:
Sydney
Registered:
July 2002
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Bigger turbos
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Thu, 27 March 2003 10:04
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Reading a few mags, and from having a T04E on my old 7M, I've been wondering.
Why do people put a bigger turbo on, but still run at the same boost pressure?
And from what I can see, you get more power. I don't understand. People put a bigger turbo on, run it at the same boost, but get more power.
I know theres a flow curve in turbos, and that turbos can't flow more than the flow curve.
It just seems weird, as I've seen a reconditioned 3T turbo run consistantly (and reliably) at 24psi. But the T04E on my old engine was only running 8psi (yes, the controller wasn't working properly).
I always figured the point of putting a bigger turbo on, would be for more boost.
No, don't start a war between ballbearing turbos etc. Just generally BIGGER and ability to produce more boost, but not using it.
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Location:
Montrose, VIC
Registered:
May 2002
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Re: Bigger turbos
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Thu, 27 March 2003 10:13
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Easy one - restriction.
Boost is in no way reflective of power - there's only 2 ways of getting more power from an engine, namely making it more efficient or getting more air through it. That said, the 2nd one is always the easiest...
Bigger turbos will have a bigger exhaust housing and wheel, which means a lot less backpressure strangling the poor old engine, as well as a bigger compressor generating less heat.
Remember, boost is only air building up against the restriction of the engine, so a restrictive, small turbo will always make little power with a lot of boost compared to a big one.
The difference is response - the bigger and freer flowing the turbo, the more air it lets pass through without spinning itself, thereby taking longer to come onto boost.
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Location:
Sydney
Registered:
July 2002
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Re: Bigger turbos
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Thu, 27 March 2003 22:16
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So with a bigger turbo running the same boost level, the actual amount of air going through the engine is increased (through less restrictive exhaust housing)?
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I supported Toymods
Registered:
February 2003
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Re: Bigger turbos
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Thu, 27 March 2003 22:27
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yup, works less, but pushes through more..
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Registered:
June 2002
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Re: Bigger turbos
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Fri, 28 March 2003 01:02
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And then this is where poeple get into trouble building hybrid turbo's!!
For example: They strap a big mutha t04 comp wheel onto a tiny t25 turbine. You get heaps of flow into the engine but it gets stuck coming out.
1. the turbine can't flow enough so it starts to use the wastegate alot more to keep flow up (if you've looked at an internal WG you'll know they aren't designed for the best flow characteristics).
2. The WG isn't big enough to flow the extra and the turbine spins faster to try and get more flow, thus increasing flow and inturn Boost and you watch the boost gauge go around the dial.
One option to solve this is to have the turbine wheel clipped, which increases flow or have the WG ported to flow more (then you are back to 1.)
The other option is to run an external WG which is bigger and flows more effiecently.
I think I got a bit carried away there.
O'well you can never have too much info can you.
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Location:
North Sydney
Registered:
May 2002
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Re: Bigger turbos
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Sat, 29 March 2003 09:20
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You've just stumbled on the key to "smart" big power there Pete.
I'm cranking out alot more herbs now running only 10psi compared to when I was running 14psi with 300rwhp because I have made improvements to make the engine flow better. My aim is to have the turbo only running at 7psi to make my peak power and so it won't even be working hard.
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