the gt3071r would be best,in the majority of cases 20psi from a small turbo means far less peak power than 20psi from a bigger model, its down to compressor efficiency and turbine restriction. a larger compressor side can flow more air and is also able to flow the same air as a smaller turbo more efficientiy,there for cooler. a bigger turbine side can let more exhaust gas out without resrition,which allows more air in increasing power and lowering the chances of detonation.;-)
I've not rolling roaded it to give figures but it changes the way the car come on boost and you get more of a kick. On my car at 1.4Bar, almost as soon as the turbo comes on boost the boost controller is opening the waste gate to slow it down. At 1.9Bar it starts to open the waste gate past 1.6bar.
This immediate surge in torque I find handy for overtaking on the road. When driving normally on the road, the extra torque of 1.9Bar means I rarely use full throttle. For trackdays I think it puts too much strain on the engine and as I'm not trying to win races a smoother power delivery is more enjoyable so around 1.6Bar is better for me.
Just my opinion
P
pulsarboby
Guest
haha youve hit the nail on the head there jim.
this is why i said 1.4 bar:lol: as the 3071 will be underperforming but a t28 with a 360 thrust would be probably at its optimum as would a 2871r be coming up to its optimum which makes it not quite so clear cut in my book!
i reckon at that boost level the 2871 would be the fastest car over the 1/4 as the charge temps will be down over the t28 but it should beat the 3071 due to it not being at its optimum spool rate for size of turbo.
spool time should be quicker with the smaller tubby and what it would lack in sheer out and out grunt could surely be made up for with going through the box quicker!
this is why i said 1.4 bar:lol: as the 3071 will be underperforming but a t28 with a 360 thrust would be probably at its optimum as would a 2871r be coming up to its optimum which makes it not quite so clear cut in my book!
i reckon at that boost level the 2871 would be the fastest car over the 1/4 as the charge temps will be down over the t28 but it should beat the 3071 due to it not being at its optimum spool rate for size of turbo.
spool time should be quicker with the smaller tubby and what it would lack in sheer out and out grunt could surely be made up for with going through the box quicker!
Jobi on here was running 11.5 or 11.7 on the HKS GTRS (basically it's a 2871) he swapped to the 3071 and was running 11.3s. I don't know what boost level he was running, but I think it was either 1.5 or 1.7.
Makaveli_se7en
Member
Hard question to answer based on the information Garrett are willing to give out about the performance of their turbos. The 2871 and 3071 have the same compressor wheel so if we assume the housing used on both turbo to be the same they will have identical compressor stage performance.
The performance of the turbo then comes down to turbine stage performance to differentiate between the two setups, and this is where we run into issues. Garrett only release what are called swallowing capacity curves to define the performance of their turbine stages. These are basically a plot of the flow at peak efficiency for a given expansion ratio (or pressure ratio depending on which way you look at it) and are ok for basic matching work to the chose a suitable size turbo for a given displacement but that’s about it.
What is required is a 'proper' turbine map, which basically looks a bit like a compressor map, only the horizontal axis is turbine speed, the vertical axis is mass flow and lines of constant expansion ratio are plotted. Then the amount of shaft power can be calculated for a given flow and the running points on both the comp and turbine map can be calculated. The other factor that can then be ascertained is quality of the match between the compressor and turbine by examining the U/C ratio for the turbine. This can be approximately thought of as how closely the most efficient speed of turbine matches the most efficient speed for the compressor and hence how efficient the turbocharger is as a unit.
The engine breathing lines as plotted in the link to VWVortex don't really tell you a lot other than for basic matching work and cannot really be used to judge when the turbo will spool or not. I also think the guy knows sod all about the Holset range of turbos, but I don’t blame him as it’s not the easiest thing in the world to grasp.
Therefore we are stuck looking at antidotal evidence. Although my gut feeling would sway towards the 2871 at 1.4Bar swaying to the 3071 by 1.6bar but have nothing to back that up with.
Sorry for the long post.
The performance of the turbo then comes down to turbine stage performance to differentiate between the two setups, and this is where we run into issues. Garrett only release what are called swallowing capacity curves to define the performance of their turbine stages. These are basically a plot of the flow at peak efficiency for a given expansion ratio (or pressure ratio depending on which way you look at it) and are ok for basic matching work to the chose a suitable size turbo for a given displacement but that’s about it.
What is required is a 'proper' turbine map, which basically looks a bit like a compressor map, only the horizontal axis is turbine speed, the vertical axis is mass flow and lines of constant expansion ratio are plotted. Then the amount of shaft power can be calculated for a given flow and the running points on both the comp and turbine map can be calculated. The other factor that can then be ascertained is quality of the match between the compressor and turbine by examining the U/C ratio for the turbine. This can be approximately thought of as how closely the most efficient speed of turbine matches the most efficient speed for the compressor and hence how efficient the turbocharger is as a unit.
The engine breathing lines as plotted in the link to VWVortex don't really tell you a lot other than for basic matching work and cannot really be used to judge when the turbo will spool or not. I also think the guy knows sod all about the Holset range of turbos, but I don’t blame him as it’s not the easiest thing in the world to grasp.
Therefore we are stuck looking at antidotal evidence. Although my gut feeling would sway towards the 2871 at 1.4Bar swaying to the 3071 by 1.6bar but have nothing to back that up with.
Sorry for the long post.
So, does this mean that for a given displacement engine (let's say 1998cc for argument's sake), there should be a sweet spot in the turbine housing/size that give you the best transfer of power to the compressor, or is it not nearly as simple as that? - You need to find the spot where the turbine most efficiently spools the compressor: a large compressor is no use if the turbine can't even spin it, but equally a small one is no good if the turbine keeps pushing it past the effective range for it.
I know that you've mentioned before that the Holset units in cars are a little unknown because that's not the original application, and they've been modified for this use; so any mention of diesel engines is misleading.
Do turbines have inertial mass? Does a larger turbine spin-down less than a smaller one; and in which case, does that mean they 'loose' less on gear changes... but you have to put more work (physics) into spinning them up in the first place.
As you can tell, I don't really know shit about turbos... but I'm eager to learn.
I know that you've mentioned before that the Holset units in cars are a little unknown because that's not the original application, and they've been modified for this use; so any mention of diesel engines is misleading.
Do turbines have inertial mass? Does a larger turbine spin-down less than a smaller one; and in which case, does that mean they 'loose' less on gear changes... but you have to put more work (physics) into spinning them up in the first place.
As you can tell, I don't really know shit about turbos... but I'm eager to learn.
Interesting stuff. I was planning on running 1.6bar day to day with 1.9 for the strip. What your saying with the boost controller makes alot of sense from what ive seen aswell. Below 1.4 i see spikes and then the controller struggling abit especially in lower gears as the boost comes in very quickly. Once it gets to 1.4 and above theres very little spike. I havent tried yet but i rekon i'll be able to get better response as the boost goes up aswell by adjusting the gain and start boost without suffering from the same spike issues. All points to the 3071r coming into peak efficiency past 1.4bar.
Does the difference between 1.6 and 1.9 effect how soon your hitting full boost at all?
Fusion Ed
Active Member
Not sure exactly. Its a HKS one. Ill pay more attention when I'm back in the workshop.
Makaveli_se7en
Member
There's a little bit more to it than that George but that’s a good way of thinking of it. The U/C ratio is the ratio of the blade tip velocity to isentropic spouting velocity or how fast the turbines spinning to how quickly the exhaust gas is going into the turbine wheel. Basically there is a golden ratio where the turbine is most effective, which 0.7 (no one seems to know why, it just is lol). If the turbine wheel is a poor match to the compressor you start to move away from this golden ratio which results in poor turbo efficiency.
*A little off topic but in reference to VWVortex post:
Before I start ranting for those that don’t know I work for Cummins Turbo Technology (formerly Holset)
This is where I think Cummins Turbo Technology has an advantage over some of its competitors and where I think a lot of confusion comes from with regard to the product range. For a start a HX30/HE300 or HX40/HE400 is not a turbo, it’s a frame size, bit like saying GT30 or GT28, it means next to nothing. As a company Holset works very differently, in that there’s not a range as such, what is offered is a more bespoke solution for client. So if we take the HX50 (I know it’s a bit big for a 2l pulsar but it’s my frame size so the one I know the most about) as an example there are 2 impeller and 2 turbine wheel diameters which fall under that frame size. If we look at the impellers we offer 10 different options depending on the design and manufacturing process/material (from cast aluminum to machined from solid titanium) each of those 10 impellers could have one of 6 trims. Then the comp covers we offer I lose track of as they are often bespoke to an engine manufacturers requirements depending on inlet/outlet connections, A/R etc. The same is true of the turbine end. So when I see someone on the internet saying I have a HX-whatever map it does make my blood boil a little as it just means bollocks all.
*gets off soap box to go back to his drinking coffee*
Does that mean I would a Holset turbo on my car over a Garrett one, in a word no lol
*A little off topic but in reference to VWVortex post:
Before I start ranting for those that don’t know I work for Cummins Turbo Technology (formerly Holset)
This is where I think Cummins Turbo Technology has an advantage over some of its competitors and where I think a lot of confusion comes from with regard to the product range. For a start a HX30/HE300 or HX40/HE400 is not a turbo, it’s a frame size, bit like saying GT30 or GT28, it means next to nothing. As a company Holset works very differently, in that there’s not a range as such, what is offered is a more bespoke solution for client. So if we take the HX50 (I know it’s a bit big for a 2l pulsar but it’s my frame size so the one I know the most about) as an example there are 2 impeller and 2 turbine wheel diameters which fall under that frame size. If we look at the impellers we offer 10 different options depending on the design and manufacturing process/material (from cast aluminum to machined from solid titanium) each of those 10 impellers could have one of 6 trims. Then the comp covers we offer I lose track of as they are often bespoke to an engine manufacturers requirements depending on inlet/outlet connections, A/R etc. The same is true of the turbine end. So when I see someone on the internet saying I have a HX-whatever map it does make my blood boil a little as it just means bollocks all.
*gets off soap box to go back to his drinking coffee*
Does that mean I would a Holset turbo on my car over a Garrett one, in a word no lol
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Bearing in mind that 1.9 bar is a higher full boost than 1.6 bar then it will always hit 1.6Bar faster ;-). If Ross were around he'd tell us to stop talking about boost level anyway and start talking about air flow.
If I put the engine under a high load in 5th then the rate of change is slower so the controller is less of an issue. The boost level becomes a function of the turbine speed and on my car 1.4 bar, 1.6 bar and 1.9bar ramp up at repeatable rpm and load points. This is just talking about boost though and as 1.9Bar generates more torque than 1.6bar its "faster"
If you are in 2nd gear holding 3.5Krpm in a typical 40mph overtake, you can pull out check its safe and when you accelerate it goes staright to 1.9Bar missing out everything in between. When you look at the logs of this you see the load cells going vertical. (It does ramp but again its mS)
So as well as the raod/engine conditions, there is also your setup which plays a huge part. I use a .64ar turbo with an appropraiately sized pace intercooler through a short pipe run. A smaller turbo with a larger ar using a bigger intercooler would probably be less responsive.
@bobby, it depends what you mean by faster. Most people with a 3071 can make 380hp around 1.4Bar without too much effort. A 2871 might potentially be more responsive but it would also be more strained when producing 380hp. A T28 isn't in the same league as a GT turbo, my 3071 starts generating 0.7Bar of boost from 2.5krpm then surges again at 3k.
@Chris, if you want drag racing and street then just get whatever maximum you can and use it for both. When on the street, use your right foot to modulate power.
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LOL. Might be best to drop boost then like you said ;-)