About backpressure : intake pressure...
Jul 12, 2006, 03:12 AM
#31
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Originally Posted by trinydex
for the first point... i don't understand why wasting comes into the picture because once you're wasting you've reached desired boost level in which case it no longer matters.... or so i was believing.
does it matter once you hit target boost?
does it matter once you hit target boost?
The second point about choke flow is probably more important. Once a smaller nozzle reaches choke flow, it should become very inefficient and may simply not flow enough gas to power the turbine wheel as well as a larger nozzle.
Jul 16, 2006, 06:38 PM
#32
Originally Posted by ItalianEvo
My 3071r .63 comp housing
The GT30 turbine wheel should be fine for the application and should not create the excessive backpressure problems. Can you list the setup from the engine back? Header, turbo, dp, exhaust.
You do not want to see more than 1.5:1, backpressure vs. boost and this is the max value. Exhaust restrictions, a/r too small, turbine wheel undersized, and Exhaust manifold restrictions can all be causes.
Jul 16, 2006, 07:18 PM
#33
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[QUOTE=trinydex]i don't agree with (or see) the reason for larger turbines making more power at a given boost.[QUOTE]
A larger, higher inertia turbine wheel could make more power at a given boost level by significantly reducing exhaust back pressure. In certain hybrid, TO4 custom turbos, a larger, clipped H2 turbine wheel, is fitted into a fully ported housing, producing a high-inertia, low back pressure configuration , which results in a turbo with extremely good transient response although it becomes virtually impossible to control boost with an integral wastegate alone, and remote gates must be used.
A larger, higher inertia turbine wheel could make more power at a given boost level by significantly reducing exhaust back pressure. In certain hybrid, TO4 custom turbos, a larger, clipped H2 turbine wheel, is fitted into a fully ported housing, producing a high-inertia, low back pressure configuration , which results in a turbo with extremely good transient response although it becomes virtually impossible to control boost with an integral wastegate alone, and remote gates must be used.
Last edited by sparky; Jul 16, 2006 at 07:31 PM.
Jul 16, 2006, 09:20 PM
#35
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Good point! I guess I'm gonna have trouble saying exactly what I mean. Perhaps I misused the term, transient response.
A smaller turbine wheel accelerates, or spools more rapidly, however it also loses rotational speed more rapidly when you take your foot off the gas pedal. The larger wheel although it may be a bit slower in initial spoolup doesnt lose rotational velocity as easily.
High inertia-low backpressure. I guess I'll move back to the Newbie forum
A smaller turbine wheel accelerates, or spools more rapidly, however it also loses rotational speed more rapidly when you take your foot off the gas pedal. The larger wheel although it may be a bit slower in initial spoolup doesnt lose rotational velocity as easily.
High inertia-low backpressure. I guess I'll move back to the Newbie forum
Last edited by sparky; Jul 16, 2006 at 10:15 PM.
Jul 17, 2006, 12:43 AM
#36
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Originally Posted by 240Z TwinTurbo
I assume you mean .63 a/r turbine housing and not compressor housing. Are you running a 3071R or the 3076R as the 3076R is the one that uses the anti surge housing. Also, are you using the GT turbine housing, 5-bolt non GT, or 4-bolt non GT?
Hi 240Z TwinTurbo,
it's a GT3071, turbine housing is non-GT, a T31 4 bolt ar .63, 2.5" exducer;
compressor housing is a T04S .70.
The GT30 turbine wheel should be fine for the application and should not create the excessive backpressure problems. Can you list the setup from the engine back? Header, turbo, dp, exhaust.
HKS tubular 4 in 1 manifold,
dp is 2.5" to 3",
exhaust is full 3", no cat.
You do not want to see more than 1.5:1, backpressure vs. boost and this is the max value. Exhaust restrictions, a/r too small, turbine wheel undersized, and Exhaust manifold restrictions can all be causes.
Thank you.
Jul 17, 2006, 01:06 AM
#37
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Originally Posted by trinydex
i don't agree with (or see) the reason for larger turbines making more power at a given boost.
I'm just supposing, in my total ignorance...
maybe larger turbines give less backpressure, and less backpressure allows a better/faster in cylinder exhaust gas emptying and fresh mixture filling at high rpm ( less time to complete the processes )
Jul 17, 2006, 01:41 AM
#38
Originally Posted by SaabTuner
As I understand it, it's just more efficient to take a little energy from ALL of the gas, then a lot of energy from a LITTLE of the gas.
The second point about choke flow is probably more important. Once a smaller nozzle reaches choke flow, it should become very inefficient and may simply not flow enough gas to power the turbine wheel as well as a larger nozzle.
The second point about choke flow is probably more important. Once a smaller nozzle reaches choke flow, it should become very inefficient and may simply not flow enough gas to power the turbine wheel as well as a larger nozzle.
let's say we had a turbine compressor combo that provided 20psi in an otherwise all the same evo and there was no wasting because it was operating without a wastegate all together.
then any bigger turbine compressor combo would have to waste in order to create that same 20psi (assuming hte compressor is bigger)
if the compressor was the same size and only the turbine was bigger then it'd simply be a more efficient version of the aforementioned "just right" setup. have i just answered my own question? cuz i took wasting out of the equation and arrived at the original conclusion... but for a different reason.
oh yeah i don't disagree with you saab, takin' a little from a lot is better than taking a lot from a little... but i do have to ask this also. are we takin' a little from a lot when we put on the bigger turbine (only)? i'm not quite sure, and i must suppose we are because we've lowered the pressure ratio and we've increased the engine delta which then increases the mass flow through the system. this makes taking less from more.... so hard to isolate these characteristics... always have to analyze the entire system.
Jul 17, 2006, 01:42 AM
#39
[QUOTE=sparky][QUOTE=trinydex]i don't agree with (or see) the reason for larger turbines making more power at a given boost.
A larger, higher inertia turbine wheel could make more power at a given boost level by significantly reducing exhaust back pressure. In certain hybrid, TO4 custom turbos, a larger, clipped H2 turbine wheel, is fitted into a fully ported housing, producing a high-inertia, low back pressure configuration , which results in a turbo with extremely good transient response although it becomes virtually impossible to control boost with an integral wastegate alone, and remote gates must be used.
this quote was taken a bit out of context... i just didn't agree that the bigger turbine made more power because of wasting.
A larger, higher inertia turbine wheel could make more power at a given boost level by significantly reducing exhaust back pressure. In certain hybrid, TO4 custom turbos, a larger, clipped H2 turbine wheel, is fitted into a fully ported housing, producing a high-inertia, low back pressure configuration , which results in a turbo with extremely good transient response although it becomes virtually impossible to control boost with an integral wastegate alone, and remote gates must be used.
Jul 17, 2006, 01:46 AM
#40
Originally Posted by sparky
Good point! I guess I'm gonna have trouble saying exactly what I mean. Perhaps I misused the term, transient response.
A smaller turbine wheel accelerates, or spools more rapidly, however it also loses rotational speed more rapidly when you take your foot off the gas pedal. The larger wheel although it may be a bit slower in initial spoolup doesnt lose rotational velocity as easily.
High inertia-low backpressure. I guess I'll move back to the Newbie forum
A smaller turbine wheel accelerates, or spools more rapidly, however it also loses rotational speed more rapidly when you take your foot off the gas pedal. The larger wheel although it may be a bit slower in initial spoolup doesnt lose rotational velocity as easily.
High inertia-low backpressure. I guess I'll move back to the Newbie forum
i think the answer comes from thinking about both instantaneouses and averages of the two systems of operation.
the small wheel with accel and decel faster. this creates and loses boost faster. this takes less from the exhuast flow work to operate instantaneously but at any sustained point uses more to stay at a certain level (rpm) because it's constanly (wanting more) to change.
the bigger wheel is slower to accel and decel. this creates and loses boost slower. this takes more flow work instantaneously but less average work to sustain...
make sense?
the end call on this situation is that smaller turbos are ideal for acceleration dominant environments (road racing). it becomes important to get the right size and the sustaining at one rpm range isn't that much of an issue because you're always accelerating and that takes a lot of work (chemical) anyway.
a larger turbo would be more suited for sustained environments where the turbine wheel stays at one point all the time coasting along using little flow work. the fact of the matter is that this is no fun at all.
this is the same analogy as big wheels of diameter get better gas mileage (cruising) and smaller diameter makes you horsepower nad gets you down the strip or everywhere faster. racing is not about saving gas... so... go small... driving on the freeway is all about getting good gas mileage so get big wheels.
Last edited by trinydex; Jul 17, 2006 at 01:52 AM.
Jul 17, 2006, 07:21 AM
#41
Originally Posted by ItalianEvo
it's a GT3071, turbine housing is non-GT, a T31 4 bolt ar .63, 2.5" exducer;compressor housing is a T04S .70.
Jul 17, 2006, 07:48 AM
#42
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Originally Posted by 240Z TwinTurbo
I would recommend, if possible, to switch to the GT turbine housing, but if that is not feasible then you should consider getting a .82 4-bolt housing to replace the .63.
To tell the thruth I have already home a .82 4 bolt housing that I bought in USA...
BUT
1. I'm not sure it's really a true Garrett one as I requested
2. it's HPC coated even INSIDE... and I think this is not a really good thing...
so it's still on the table...
Do you think a GT .63 could be better ?
I went for a T31 because they told me is shorter than GT, so more space for the 90 deg. pipe at the turbine exhaust...
I am not sure if the spool will be affected too much, but it is safe to say the topend power will be increased.
I heard about 400/500 rpm later.... mmmm... if true, too much for the intended use of my car...
As told me by TedB, and with his help, yesterday I was finally able to lower EGTs a bit, advancing the timing.
I think that now I should make again the backpressure test to see if that changed it.
You can't always get it right the first time so this is not that big of a deal.
I thought it was interesting that you took the time to measure backpressure as most folks do not.
Thank you.
Jul 17, 2006, 07:55 AM
#43
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[QUOTEthe small wheel with accel and decel faster. this creates and loses boost faster. this takes less from the exhuast flow work to operate instantaneously but at any sustained point uses more to stay at a certain level (rpm) because it's constanly (wanting more) to change.
the bigger wheel is slower to accel and decel. this creates and loses boost slower. this takes more flow work instantaneously but less average work to sustain...
make sense?
[/QUOTE]
Yup...thanks. I think I got it now.
Sorry, for quoting you out of context.
the bigger wheel is slower to accel and decel. this creates and loses boost slower. this takes more flow work instantaneously but less average work to sustain...
make sense?
[/QUOTE]
Yup...thanks. I think I got it now.
Sorry, for quoting you out of context.
Jul 17, 2006, 11:09 AM
#44
Originally Posted by ItalianEvo
Do you think a GT .63 could be better ?
I went for a T31 because they told me is shorter than GT, so more space for the 90 deg. pipe at the turbine exhaust...
As told me by TedB, and with his help, yesterday I was finally able to lower EGTs a bit, advancing the timing.
I went for a T31 because they told me is shorter than GT, so more space for the 90 deg. pipe at the turbine exhaust...
As told me by TedB, and with his help, yesterday I was finally able to lower EGTs a bit, advancing the timing.
The non GT 4-bolt is shorter as the GT has the extension that tapers from the wheel to the 3" discharge.
Yes, retarded timing will raise EGT's. Timing is placed ADC will cause the fuel to ignite in the exhaust and spool the turbo. I used to see ~1600F(before the turbo) on my street car and pump gas. This is, of course, for WOT. Let us know how it works out.
Jul 17, 2006, 12:10 PM
#45
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Sorry 240Z,
one question....
I have 2 egt sensor, one for a Greddy gauge is 3" from the 3rd cyl. exhaust valves, and the other one is the one for the ecu logging and is just before the turbine inlet....
Do you know how much difference should I see at WOT ?
I found that the Greddy one is hotter at low to mid rpm, but it's 270 F. cooler at WOT,
so now I'm reading 1560 F max on the Greddy, and 1830 F on the other one...
one question....
I have 2 egt sensor, one for a Greddy gauge is 3" from the 3rd cyl. exhaust valves, and the other one is the one for the ecu logging and is just before the turbine inlet....
Do you know how much difference should I see at WOT ?
I found that the Greddy one is hotter at low to mid rpm, but it's 270 F. cooler at WOT,
so now I'm reading 1560 F max on the Greddy, and 1830 F on the other one...