Silvia Club of NSW
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Turbine A/R Ratio
https://forum.silviansw.com/viewtopic.php?f=1&t=24554		 Page 1 of 8
Author:  182Go [ Mon Oct 09, 2006 1:58 pm ]
Post subject:  Turbine A/R Ratio
Just thinking if a turbo uses an external wategate which dumps the excess gas prior to it going into the turbo, would you use a smaller turbine A/R since it doesn't have to cope with as much exhaust gas passing through it, or would it make no difference?
Author:  DumHed [ Mon Oct 09, 2006 2:34 pm ]
Post subject: 
it'll have the same effect as it does with an internal wastegate, but you could probably get away with a slightly smaller A/R with an external gate.

It will still reduce the peak power because the turbine won't get as much flow without producing too much restriction, so it won't be able to drive the compressor as hard.
Author:  182Go [ Mon Oct 09, 2006 2:51 pm ]
Post subject: 
Yeah I was just reading through the basics on the Garrett website and it got me thinking. I thought there might be a marginal gain but not massive.

This is from their website "However, the vast majority of gasoline performance applications require a Wastegates. There are two (2) configurations of Wastegates, internal or external. Both internal and external Wastegates provide a means to bypass exhaust flow from the turbine wheel. Bypassing this energy (e.g. exhaust flow) reduces the power driving the turbine wheel to match the power required for a given boost level. Similar to the BOV, the Wastegates uses boost pressure and spring force to regulate the flow bypassing the turbine."

I was thinking if all of the energy going into the turbine housing was being used to turn the turbine instead of some of it being lost out of the internal wastegate, this would have to result in a slightly faster spool... And maybe slightly more top end.

Just found this bit..."External Wastegates are added to the exhaust plumbing on the exhaust manifold or header. The advantage of external Wastegates is that the bypassed flow can be reintroduced into the exhaust stream further downstream of the turbine. This tends to
improve the turbine’s performance. On racing applications, this Wastegated exhaust flow can be vented directly to atmosphere."
Author:  DumHed [ Mon Oct 09, 2006 3:14 pm ]
Post subject: 
the internal wastegate is still before the turbine though.

The benefit of the external gate is that it can be larger, and it doesn't interfere with the flow through the turbo as much.
When the wastegate is closed there's not a lot of difference between internal and external, except that external gate housings will generate less turbulence due to a smoother shape.
Author:  182Go [ Mon Oct 09, 2006 3:24 pm ]
Post subject: 
Thanks for that...
Author:  QIK513 [ Mon Oct 09, 2006 10:40 pm ]
Post subject: 
182go u should give up now and buy a holden astra
Author:  splashman [ Tue Oct 10, 2006 2:46 am ]
Post subject: 
QIK513 wrote:
182go u should give up now and buy a holden astra


turbo astra?
Author:  QIK513 [ Tue Oct 10, 2006 8:13 am ]
Post subject: 
hah no turbo car ,, maybe a hyundai excel :evil:
Author:  mokompri [ Tue Oct 10, 2006 11:45 am ]
Post subject: 
DumHed wrote:
..and it doesn't interfere with the flow through the turbo as much..


ive always wondered how much benefit this really gave, the flow through the turbine housing would be better, but then every externally wastegated manifold ive seen has a wastegate pipe welded at 90 degrees to the runners for the wastegate, i cant see this being good for flow through the manifold. alot of the time it looks like it will cause turbulent flow through the collector as thats where its usually attached.
Author:  DumHed [ Tue Oct 10, 2006 11:58 am ]
Post subject: 
yeah they are usually still pretty ugly, but seem to work ok...

Not being in the actual turbo housing probably gives enough space for the flow to smooth out on its way in.
Author:  182Go [ Tue Oct 10, 2006 12:30 pm ]
Post subject: 
not sure how this would effect the grand scheme of things but I would have thought that once it hit the turbine housing it would be under the greatest amount of pressure, since before this point it has a full sized runners and a larger collector area.

The less volume of air going into the compressed turbine housing would have to result in less heat being transferred to the turbo??? maybe a greater life span of the turbo??? bleeding the air off in the collector area where it has a larger quantity of available air through a larger wastegate would have to relieve the pressure build up more effective... does this give a more accurate control and stop boost spiking???
Author:  mokompri [ Tue Oct 10, 2006 2:20 pm ]
Post subject: 
DumHed wrote:
yeah they are usually still pretty ugly, but seem to work ok...


much like internal wastegates :)

Quote:
Not being in the actual turbo housing probably gives enough space for the flow to smooth out on its way in.


i would expect the same to occur with the internal as well, as the wastegate flap is just at the start of the 'scroll' part of the housing, exhaust flow should become laminar a little further down the scroll before it hits the turbine wheel.

182Go wrote:
The less volume of air going into the compressed turbine housing would have to result in less heat being transferred to the turbo??? maybe a greater life span of the turbo??? bleeding the air off in the collector area where it has a larger quantity of available air through a larger wastegate would have to relieve the pressure build up more effective... does this give a more accurate control and stop boost spiking???


i dont think heat is really an issue anymore with ball bearing turbos in terms of affecting their life span, its not something i would take into consideration for the 'pros' of an external gate.

in regards to the pressure point your making, in theory it may be detrimental to flow, but like i mentioned before its a toss up between having flow interrupted there, or in the manifold. Im confident that any boost spiking/accuracy problems are a result of a poorly setup boost controller, rather then anything to do with the differences of external and internal gates.
Author:  DumHed [ Tue Oct 10, 2006 2:39 pm ]
Post subject: 
external gate setups do often seem to provide better response than a comparable internal gate setup, and better boost control, but it's hard to have a direct comparison when there are other differences involved.

For most cases I'd definitely use an internally gated turbo (much simpler, more reliable, cheaper, etc)
Author:  182Go [ Tue Oct 10, 2006 2:43 pm ]
Post subject: 
so at the end of the day.. does it simply come down to the external wastegate operating more efficently than internal? ok you posted while I was taking a phone call... so if there not more reliable then why does anyone go external?
Author:  mokompri [ Tue Oct 10, 2006 3:11 pm ]
Post subject: 
DumHed wrote:
external gate setups do often seem to provide better response than a comparable internal gate setup, and better boost control,


do you mean like spool up time, or transitional mid throttle response ?

i agree that it can be difficult at times getting exactly the sort of boost characteristics out of an internal, i have had such problems ! but they have always been because the boost controller wasnt effective enough, or setup correctly, or both
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