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Location:
Gold Coast
Registered:
June 2004
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general turbo question
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Sun, 19 September 2004 12:58
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Ok so i went and read up about how a turbo works and after reading this i got to wondering, Is the power a turbo adds to your car relative only to the boost it supplys or does the size of the turbo also contibute to the power it makes, and if so how?
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Location:
Inside a giant turbo (syd...
Registered:
June 2002
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Re: general turbo question
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Sun, 19 September 2004 13:00
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simple. Bigger turbo flows more air at the same psi as a smaller turbo. Also turbo efficiency at said boost level comes into play as well.
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Location:
Potts Point, Sydney
Registered:
October 2003
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Re: general turbo question
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Sun, 19 September 2004 13:05
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yeh...size does matter. Smaller turbo's provide boost earlier, and the larger ones boost later on. That's what i've always thought anyway 
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Location:
Gold Coast
Registered:
June 2004
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Re: general turbo question
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Sun, 19 September 2004 13:05
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so running a larger turbo at the same pressure as a smaller one will result in more power, because it is moving more air at that pressure to the engine?
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Location:
Inside a giant turbo (syd...
Registered:
June 2002
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Re: general turbo question
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Sun, 19 September 2004 13:08
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hah, thats atleast what i think....
but also more peak power because generally a larger turbo will take longer to spool, so you will get a steeper power curve.
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Registered:
November 2002
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Re: general turbo question
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Sun, 19 September 2004 13:11
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Yep, a bigger turbo at the same boost as a small one will give more power.
BUT, bigger is not always better. The bigger it is the more lag it also has. So although you get more power you are also waiting for a higher rev range before the power really comes on.
Too big is not good for street use as the rev range is too high.
It really depends on what you want. I have a GT25 (320hp) on my 3T GTE and it comes on boost very fast at the expense of top end power. This is great for street use as I get maximum power from around 2500 to 5000rpm instead of a big turbo coming on around say 4500rpm to maybe 7000rpm.
Hope this helps,
Simon
http://users.chariot.net.au/~stmezz/celica.htm
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Location:
Potts Point, Sydney
Registered:
October 2003
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Re: general turbo question
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Sun, 19 September 2004 13:13
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| TA22 GT wrote on Sun, 19 September 2004 23:11 |
So although you get more power you are also waiting for a higher rev range before the power really comes on.
Too big is not good for street use as the rev range is too high.
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that's what im talking about.
Check out http://howstuffworks.com
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Location:
Gold Coast
Registered:
June 2004
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Re: general turbo question
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Sun, 19 September 2004 13:13
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but if your moving more air through the same space (intercooler piping) as the smaller turbo was using then shouldnt the pressure (psi) go up cause you have more air in the same volume ie higher boost? meaning the power IS relative only to the boost?
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Location:
Inside a giant turbo (syd...
Registered:
June 2002
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Re: general turbo question
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Sun, 19 September 2004 13:23
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that depends on where you are measuring the boost...
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Location:
Gold Coast
Registered:
June 2004
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Re: general turbo question
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Sun, 19 September 2004 13:26
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I see, my concept of boost measurment must be wrong. So where does the waste gate get its measurment of boost, because isnt that what governs maximum boost of the turbo?
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Registered:
November 2002
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Re: general turbo question
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Sun, 19 September 2004 13:27
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| tyottsoarer wrote on Sun, 19 September 2004 23:13 |
but if your moving more air through the same space (intercooler piping) as the smaller turbo was using then shouldnt the pressure (psi) go up cause you have more air in the same volume ie higher boost? meaning the power IS relative only to the boost?
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OK, you're missing a couple of important factors. Firstly small and big turbos push different amounts of air at different rev ranges. EG the small turbo will push MORE air early on and a big turbo will out puffa small turbo once the revs pick up. So there are trades offs either way, either you get low end power or more top end power.
In some ways Boost is just a measure of engine back pressure. Boost of 10psi with a small turbo doesn't mean the same air flow etc with 10psi with a bigger turbo, same can be said for ported heads, pipework restrictions etc. Turbo selection is not that easy and alot of factors need to be considered. So dont be fooled that bigger is better when it comes to turbos. So this also means that just talkign about boost alone doesnt mean that more boost = more power. Too much boost and you will start generating too much heat = less power. Theres no point pushing hot air into an engine.
Simon
http://users.chariot.net.au/~stmezz/celica.htm
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Location:
Gold Coast
Registered:
June 2004
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Re: general turbo question
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Sun, 19 September 2004 13:51
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I'm begining to understand
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Location:
Brisbane
Registered:
May 2002
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Re: general turbo question
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Mon, 20 September 2004 00:31
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What everyone is missing here is the exhaust side of the equation. The main reason a small turbo will make less power than a large turbo at the same boost pressure and the same rpm is the exhaust restriction. Look at the exhaust housings on a stock 1JZ turbo - they're TINY. You can pump as much boost as you like in the inlet side, but if you can't get the exhaust out the other side it's a big waste of time.
So yes it's all about flow, but you have to consider the overall flow from one end of the engine to the other, not just the inlet side.
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Location:
Perth
Registered:
October 2003
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Re: general turbo question
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Mon, 20 September 2004 05:12
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What norbie said 
Another way to look at it is if you had a supercharged engine with say 1" primary extractors running 10psi. You then put a bigger supercharger on, 10 psi but use 2" primary extractors = more power. More flow through the system as the exhaust side is freed up.
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Location:
Gold Coast
Registered:
June 2004
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Re: general turbo question
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Mon, 20 September 2004 11:31
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it is clear to me now  thanks a lot 
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