Discussion
Can anyone tell me a bit about the turbo's in the 3.0l ? Are they t25 or gt25, what boost are they running, and what A/R ratios are they using for the compressor and turbine wheels ?
Are the exhaust manifolds lagged and if not what are the engine bay temps like ?
I have had a passenger ride in the 2.5l and it was pretty impresive but does the 3.0l have any vices - i.e. bad turbo lag or sudden boost surges.
What compression ratio is the engine running ?
Are the exhaust manifolds lagged and if not what are the engine bay temps like ?
I have had a passenger ride in the 2.5l and it was pretty impresive but does the 3.0l have any vices - i.e. bad turbo lag or sudden boost surges.
What compression ratio is the engine running ?
Ken,
I can't comment about the technicals cos I know nuffin about that. What I can say in my very limited period of ownership is that the turbo seems very smooth and progressive. No lag that I am aware of. I have to admit here that my only other Turbo car was an all White Montego Turbo, which I used not to own up having owned, but I now reckon it was a classic, turbo lag and all. Should have kept it.
Come on England!
Chris.
I can't comment about the technicals cos I know nuffin about that. What I can say in my very limited period of ownership is that the turbo seems very smooth and progressive. No lag that I am aware of. I have to admit here that my only other Turbo car was an all White Montego Turbo, which I used not to own up having owned, but I now reckon it was a classic, turbo lag and all. Should have kept it.
Come on England!
Chris.
kenmorton said:
Can anyone tell me a bit about the turbo's in the 3.0l ? Are they t25 or gt25, what boost are they running, and what A/R ratios are they using for the compressor and turbine wheels ?
Are the exhaust manifolds lagged and if not what are the engine bay temps like ?
I have had a passenger ride in the 2.5l and it was pretty impresive but does the 3.0l have any vices - i.e. bad turbo lag or sudden boost surges.
What compression ratio is the engine running ?
Compressor and Turbine are usualy measured in "trim", trim is basicaly a value that describes inducer and exducer size. A/R Ratio is the measure of the turbine/compressor housing.
The exhaust manifolds are wrapped, underbonnet temps are low anyway due to the design on the engine bay and rather large vent present across the rear of the car.
Lag is virtualy non-existant, even though the intake - TB length is very long. Partly due to the low boost pressure employed and partly due to the volume of air the V6 pulls through during each revolution.
matt_t16 said:
The exhaust manifolds are wrapped, underbonnet temps are low anyway due to the design on the engine bay and rather large vent present across the rear of the car.
I'll check when my car is back from serive but I'm sure the manifold isn't wrapped. Vent is for intercooler, not cooling.
m12_nathan said:Turbo's and surrounding pipework are wrapped in heat tape.
The exhaust manifolds are wrapped, underbonnet temps are low anyway due to the design on the engine bay and rather large vent present across the rear of the car.
I'll check when my car is back from serive but I'm sure the manifold isn't wrapped. Vent is for intercooler, not cooling.
J
joust said:
Isnt it a sequential turbo system? If so are they both really T25s?
Yes, and yes AFAIK.
J
Really, sequential? Are you sure about that? Sequential turbo systems are very complex (the mk4 supra's has 1 extra wastegate, 2 extra butterfly valves, 1 pressure tank and 5 electronic solenoid valves to control all that stuff) and I guess I'm sceptical that Noble would engineer that into their V6.
matt_t16 said:
Compressor and Turbine are usualy measured in "trim", trim is basicaly a value that describes inducer and exducer size. A/R Ratio is the measure of the turbine/compressor housing.
Well, trim is the turbo's major diameter squared divided by its minor diameter squared times 100. Compressors usually have trims in the 50s, and turbines in the 80s. So a 2 turbos can be different sizes and have the same trim.
In my experience, T25s are a small turbo on a 2.0L car (ie a factory-equiped turbo for zero percived lag). I know some people use twin T25s or T28s on 3.0L cars, but I've never ridden or driven such a car. Personally if I were going to build a motor and turbo it, I'd go for larger turbos than T25s or T28s. If I remember correctly, they aren't very effecient at the more "fun" boost levels. But lots of people hate turbo lag, so I can see why Noble would choose those turbochargers.
>> Edited by GrantB on Sunday 28th March 06:59
GrantB said:Err - you lost me
Really, sequential? Are you sure about that? Sequential turbo systems are very complex (the mk4 supra's has 1 extra wastegate, 2 extra butterfly valves, 1 pressure tank and 5 electronic solenoid valves to control all that stuff) and I guess I'm sceptical that Noble would engineer that into their V6.
If you mean "do they come on and off sequentially" - i.e. one after another so that the boost on and off is controlled, then yes, that's exactly what they do.
If that means what you wrote above - sorry - no idea, but I can tell you there are solenoids all over the place, along with rather a lot of plumbing!
J
A typical sequential turbo setup like the MKIV Supra has 1 turbo with a smaller A/R ratio than the other. This is the one that spools first. Once this is spinning, the larger one starts to spool, thus eliminating most of the lag. The problem is that the smaller turbo becomes a bottleneck to the exhaust gas, and so a valve is used to re-route all of the exhaust gas to the larger turbo once it’s spooled up.
I have helped with the removal of the turbos on a MKIV Supra and can confirm it is extremely complex.
I wasn’t aware that such a system could be used on a V engine as each bank has its own turbo. Using a small turbo of one side and a larger one on the other would cause a difference in backpressure between the two banks, and I’d imagine this would cause problems!
I may be completely wrong and the Noble may well use a sequential setup – haven’t actually had a real good look under the engine bay. It’s all good discussion though.
I have helped with the removal of the turbos on a MKIV Supra and can confirm it is extremely complex.
I wasn’t aware that such a system could be used on a V engine as each bank has its own turbo. Using a small turbo of one side and a larger one on the other would cause a difference in backpressure between the two banks, and I’d imagine this would cause problems!
I may be completely wrong and the Noble may well use a sequential setup – haven’t actually had a real good look under the engine bay. It’s all good discussion though.
matt_t16 said:
A/R Ratio is the measure of the turbine/compressor housing.
This is not quite right.
A is the area of the port used to send the exhaust gas into the turbine housing, and R is the radius of the turbo, measured from the centre of the turbine shaft to the centre of the exhaust gas port.
Ah. I see. Sorry - we may be talking cross purposes then.
Each bank has it's own turbo fed by just three cylinders of exhaust gas. Each one then feed the compressed air through a common intercooler (the air to air has two inlets and a single outlet) into a single throttle body which is then split back into two sets of inlet manifolds.
However they are programmed to come "off" at different times with the dump valves blowing sequentially, one after the other. Looking at the dyno plot I have I'd guess they come "on" one after the other as well as there is no massive spike in the power curve, just a smooth increase around 3000rpm.
However, it sounds like a sequential setup has two turbos in sequence?
Does that make sense?
J
Each bank has it's own turbo fed by just three cylinders of exhaust gas. Each one then feed the compressed air through a common intercooler (the air to air has two inlets and a single outlet) into a single throttle body which is then split back into two sets of inlet manifolds.
However they are programmed to come "off" at different times with the dump valves blowing sequentially, one after the other. Looking at the dyno plot I have I'd guess they come "on" one after the other as well as there is no massive spike in the power curve, just a smooth increase around 3000rpm.
However, it sounds like a sequential setup has two turbos in sequence?
Does that make sense?
J
Personally I prefer a parallel setup, waaay less to break, usually less restrictive piping.
Actually the MKIV Supra's TTs are both the same size with the same AR. Depending on throttle position and RPM, the computer can decide to use either one or both turbos. I owned a Supra for 5 years, and spent more time than I'd like to think diagnosing problems with my and others sequential turbos (as we all ran 18+ psi of boost).
I believe the RX7's sequential turbos are the same size as well, but I am not sure about that.
>> Edited by GrantB on Sunday 28th March 23:42
LaurenceFrost said:
A typical sequential turbo setup like the MKIV Supra has 1 turbo with a smaller A/R ratio than the other. This is the one that spools first. Once this is spinning, the larger one starts to spool, thus eliminating most of the lag. The problem is that the smaller turbo becomes a bottleneck to the exhaust gas, and so a valve is used to re-route all of the exhaust gas to the larger turbo once it’s spooled up.
Actually the MKIV Supra's TTs are both the same size with the same AR. Depending on throttle position and RPM, the computer can decide to use either one or both turbos. I owned a Supra for 5 years, and spent more time than I'd like to think diagnosing problems with my and others sequential turbos (as we all ran 18+ psi of boost).
I believe the RX7's sequential turbos are the same size as well, but I am not sure about that.
>> Edited by GrantB on Sunday 28th March 23:42
LaurenceFrost said:
A/R Ratio is the measure of the turbine/compressor housing.
This is not quite right.
A is the area of the port used to send the exhaust gas into the turbine housing, and R is the radius of the turbo, measured from the centre of the turbine shaft to the centre of the exhaust gas port.
Thats correct but both those values on their own are a of little use (to the end user) when comparing one housing to the next. In order to produce a meaningful value that can be compared housing to housing R is divided into A to give you the A/R Ratio.
Matt
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