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Chain fence eating turbo
 
Join Date: Dec 2008
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Hp/tq increase going to 4" exhaust?

After asking about a high-flowing, moderately quiet muffler, I thought about 4" mufflers/exhaust pipe post turbine housing (I know, counterproductive to suppressing sound).

Why I ask is the turbo I have on hand has a 4" v-band turbine housing and never remember seeing anyone run such a big exhaust. Diesels run extremely large down pipes with small turbine wheels/inducer/exducers respectively. For reference, the turbo I have has around a 63mm minor with a 102mm (4") v-band outlet. Maybe this aids quick spool?

Then thought, this could guarantee you never have a restriction for the quickest spooling, least backpressure post turbine you could have.

Anyone seen any results or pondered?

Too, and on the other end of the turbo, newer compressors run say a 102mm (4") inlet with say only a 60mm minor compressor wheel. Of course this is due to the area required for surge ports but I'd imagine this bellmouth would a minor supercharging effect. I know this is opposite of the turbine side regards to physics but it seems to help.

I imagine having lots of extra volume for the exhaust could help overall performance of a turbo and there is some potential benefits to adapting the 4" piping.

Thoughts?

Old 05-23-2013, 12:42 PM
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Can't help you on the data, but my exhaust opens to 3.5" and I can't keep the headers from blowing up!!!
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Old 05-23-2013, 01:30 PM
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Chain fence eating turbo
 
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Yeah, that was a silly failure.
Old 05-23-2013, 02:08 PM
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Brando
 
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Think I read that anything over 3" is similar to open for these turbo sizes. 4" would look cool and sound cool but I'd doubt any change in power or boost onset.
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Old 05-23-2013, 02:51 PM
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Chain fence eating turbo
 
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Hmmm, so I guess some tests have been done? It's the diesel thing that has more than piqued my interest in this.

You're right though, I had an open turbine for a few months while I fixed my v-band flange and I don't remember any quicker boost onset.
Old 05-23-2013, 03:01 PM
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Chain fence eating turbo
 
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Another thing I guess would make sense is as the exhaust gases exit the turbo, it starts to cool. Cooler air contracts allowing for a smaller diameter exhaust/muffler ID than the turbo outlet in terms of maintaining total airflow I guess to an extent.

If I'm off based, let me know.
Old 05-23-2013, 03:06 PM
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Brando
 
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Quote:
Originally Posted by Tippy View Post
Another thing I guess would make sense is as the exhaust gases exit the turbo, it starts to cool. Cooler air contracts allowing for a smaller diameter exhaust/muffler ID than the turbo outlet in terms of maintaining total airflow I guess to an extent.

If I'm off based, let me know.
Don't know about that....or anything else for that matter, but I do know that turbo cars are not the same as NA cars with respect to velocity and back pressure value in a four stroke engine. NA cars need some back pressure to keep the intake charge inside the combustion chamber rather than escaping into the headers and turbos have back pressure built in with the turbo and so turbos try and remove back pressure with free flowing mufflers and such. Even then, turbos would not work well with 2+inch primaries but I don't know much about the dynamics of header design.
And diesel vs gas are lots different as well. It's a mistake to compare gas and diesel turbo tech as it would just mix you up as to what you want.
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Old 05-23-2013, 03:32 PM
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You sure your turbo outlet is 4.0"? Or just the v-band clamp's OD?
Haven't seen 4" make a difference until you get into big turbos -- like GT4202R.
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Old 05-23-2013, 09:54 PM
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Chain fence eating turbo
 
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Although I did not measure, it's huge and I assumed around 4". It's a diesel turbo my brother had lying around. The turbo would be maxed on my engine but I couldn't help to wonder if it's huge ~4" vband that's used with a tiny ~63mm minor turbine, would we see any benefits going with a lot larger exhaust to turbine minor relationship?
Old 05-24-2013, 04:06 AM
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Chain fence eating turbo
 
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So Chris, you have a rough hp limit for the standard fare 3" most seem to run (I assume) here?
Old 05-24-2013, 04:10 AM
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Bad LT
 
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Quote:
Originally Posted by Tippy View Post
Although I did not measure, it's huge and I assumed around 4". It's a diesel turbo my brother had lying around. The turbo would be maxed on my engine but I couldn't help to wonder if it's huge ~4" vband that's used with a tiny ~63mm minor turbine, would we see any benefits going with a lot larger exhaust to turbine minor relationship?
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Old 05-24-2013, 04:37 AM
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Quote:
Originally Posted by Tippy View Post
So Chris, you have a rough hp limit for the standard fare 3" most seem to run (I assume) here?
Over 600whp.
And there's plenty of Supras and other high VE, high power cars out there with a 3" exhaust front to back doing 700-750hp. Our tuner, Tony, did 760awhp on an Evo with 3" exhaust.
930s have a shorter exhaust, fewer bends... We just don't see it being the limiting factor for most Turbos.
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Old 05-24-2013, 08:23 AM
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Ditto. Our 3" mufflers dyno the same as a Zork. Going bigger did nothing more.
Old 05-24-2013, 10:04 AM
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Great, thanks

Old 05-24-2013, 10:59 AM
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