New UK Subaru Sti - Due April/May
11 July 2014, 06:47 PM
#1501
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I think the difference here is scoobyclinic are looking to see what they can get out of the engine, where as John is thinking reliability and warranty.
11 July 2014, 07:00 PM
#1502
Former Sponsor
If each car is being setup individually, what fuel are you using. Are you stating one specific type or a broad range from 97 to 99 as this will have a big factor into the figures being lower than Scoobyclinics if your trying to go broad scale.
lower RON fuel you are no going to want huge amounts of torque from a 97 as it would most likely not take the timing so would det for fun...
lower RON fuel you are no going to want huge amounts of torque from a 97 as it would most likely not take the timing so would det for fun...
11 July 2014, 07:21 PM
#1505
Scooby Regular
Oh well. Here goes! I will try to show the effect of retarding the ignition on the temperature of cylinder head, cylinder wall exhaust, turbo etc.
If you forget the charge for a minute, and just consider the piston compressing and decompressing air, then you'll know that as the air is compressed, it's temperature rises.
The temperature and pressure traces would look a bit like this.
Igniting the charge earlier means the mixture is burning as the piston is still rising up the cylinder on the compression stroke. The burning increases the temperature, which increases the pressure, but at the same time the piston is also increasing the pressure which increases the temperature!
Here's how the temp and pressure traces look when the charge is ignited 45° before TDC.
We can see that the two effects combined increase the pressure and temperature dramatically. The fuel is still burning past TDC, so the temperature continues to rise even though the piston is now descending down the piston which expands and cools the gas slightly offsetting the increase in pressure and temperature from the fuel burn.
Now consider what would happen if we ignited at TDC. The piston is now descending down the cylinder, again expanding and cooling the gas. This effect works against the increasing temperature of the fuel burn, meaning although the temperature from the burn is still high (still the same energy going into the same mass of air) the overall pressure is dramatically reduced.
[/IMG]
You can see that the pressure and temperature are already dropping before the fuel burn really gets going so less of the energy can create work (power and torque). Notice also that because it takes longer for the burn to get going, there is more residual heat left at the end of the stroke, which increases Exhaust Gas Temperature and also transfers more heat to the head and cylinder walls, which in turn will go into the water jacket.
As for all the exhaust gases leaving the cylinder. If this were the case why bother flowing heads and headers or adding big bore straight through exhausts.
If you forget the charge for a minute, and just consider the piston compressing and decompressing air, then you'll know that as the air is compressed, it's temperature rises.
The temperature and pressure traces would look a bit like this.
Igniting the charge earlier means the mixture is burning as the piston is still rising up the cylinder on the compression stroke. The burning increases the temperature, which increases the pressure, but at the same time the piston is also increasing the pressure which increases the temperature!
Here's how the temp and pressure traces look when the charge is ignited 45° before TDC.
We can see that the two effects combined increase the pressure and temperature dramatically. The fuel is still burning past TDC, so the temperature continues to rise even though the piston is now descending down the piston which expands and cools the gas slightly offsetting the increase in pressure and temperature from the fuel burn.
Now consider what would happen if we ignited at TDC. The piston is now descending down the cylinder, again expanding and cooling the gas. This effect works against the increasing temperature of the fuel burn, meaning although the temperature from the burn is still high (still the same energy going into the same mass of air) the overall pressure is dramatically reduced.
[/IMG]You can see that the pressure and temperature are already dropping before the fuel burn really gets going so less of the energy can create work (power and torque). Notice also that because it takes longer for the burn to get going, there is more residual heat left at the end of the stroke, which increases Exhaust Gas Temperature and also transfers more heat to the head and cylinder walls, which in turn will go into the water jacket.
As for all the exhaust gases leaving the cylinder. If this were the case why bother flowing heads and headers or adding big bore straight through exhausts.
11 July 2014, 07:54 PM
#1506
Scooby Regular
Oh and the STI has variable exhaust and inlet valve timing. Which can also be mapped and might be a clue to how you get big torque figures! And possibly beyond the average mappers knowledge base. But if you understand the graphs you will get there!
11 July 2014, 08:09 PM
#1507
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Can see this getting rather boring for people haha but...
All you have quoted there is correct and makes total sense.
Those graphs are spot on, theories correct.
Now, look at the numbers, those graphs are talking 45 degrees difference in timing. The difference between a high comp turbo motor staying in 1 piece forever and blowing itself to million bits is about 3 degrees timing when set up to the optimum. I don't think 3 degrees swing has anything like the effect you're talking about. I'll shy away from mentioning MBT points as most high comp turbo motors don't hit them.
Those graphs are quoted clearly for a normally aspirated motor where heat is your enemy. We're talking turbos, the more heat and pressure in the manifold the bigger the expansion rate over the turbo and the more boost. We're limited by materials getting too hot and failing. Too much temp and you'll overheat the runners/head/valves/wheels etc etc which then rolls onto charge temp and you chase yourself in circles.
Porting and such does work, but the vast majority of gains are on the inlet side for that reason, opening an exhaust port up but then still trying to blow into a 900 degreeC 1 bar of pressurised turbo manifold makes it less important. You seen the internal casting on o.e. turbo manifolds? Flowed headers again are NA tuning orientated, a long length turbo manifold works well at high sustained rpm, but not for punchy fast spool when a short runner setup will retain heat and low rpm turbo efficiency.
Big bore exhausts reduce backpressure on the turbo so the difference in pressure across the turbine wheel is greater so faster expansion, so faster spool and greater efficiency. Big bore NA exhausts don't work as the absorb the pulses so you cant use them as a scavenge effect at the collector.
...Still unsure how you think the gases are being held in the cylinder?
WRX STI thread I thought this was... Great cars by the way, impressive, when would a white one be available John?
All you have quoted there is correct and makes total sense.
Those graphs are spot on, theories correct.
Now, look at the numbers, those graphs are talking 45 degrees difference in timing. The difference between a high comp turbo motor staying in 1 piece forever and blowing itself to million bits is about 3 degrees timing when set up to the optimum. I don't think 3 degrees swing has anything like the effect you're talking about. I'll shy away from mentioning MBT points as most high comp turbo motors don't hit them.
Those graphs are quoted clearly for a normally aspirated motor where heat is your enemy. We're talking turbos, the more heat and pressure in the manifold the bigger the expansion rate over the turbo and the more boost. We're limited by materials getting too hot and failing. Too much temp and you'll overheat the runners/head/valves/wheels etc etc which then rolls onto charge temp and you chase yourself in circles.
Porting and such does work, but the vast majority of gains are on the inlet side for that reason, opening an exhaust port up but then still trying to blow into a 900 degreeC 1 bar of pressurised turbo manifold makes it less important. You seen the internal casting on o.e. turbo manifolds? Flowed headers again are NA tuning orientated, a long length turbo manifold works well at high sustained rpm, but not for punchy fast spool when a short runner setup will retain heat and low rpm turbo efficiency.
Big bore exhausts reduce backpressure on the turbo so the difference in pressure across the turbine wheel is greater so faster expansion, so faster spool and greater efficiency. Big bore NA exhausts don't work as the absorb the pulses so you cant use them as a scavenge effect at the collector.
...Still unsure how you think the gases are being held in the cylinder?
WRX STI thread I thought this was... Great cars by the way, impressive, when would a white one be available John?
11 July 2014, 08:15 PM
#1508
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It's already been mentioned John's specified lower torque levels for reliability and so a warranty can be offered. Greater numbers are clearly easily attainable but they don't want to risk every one of their customers new cars.
11 July 2014, 08:41 PM
#1509
Former Sponsor
Oh well. Here goes! I will try to show the effect of retarding the ignition on the temperature of cylinder head, cylinder wall exhaust, turbo etc.
If you forget the charge for a minute, and just consider the piston compressing and decompressing air, then you'll know that as the air is compressed, it's temperature rises.
The temperature and pressure traces would look a bit like this.
Igniting the charge earlier means the mixture is burning as the piston is still rising up the cylinder on the compression stroke. The burning increases the temperature, which increases the pressure, but at the same time the piston is also increasing the pressure which increases the temperature!
Here's how the temp and pressure traces look when the charge is ignited 45° before TDC.
We can see that the two effects combined increase the pressure and temperature dramatically. The fuel is still burning past TDC, so the temperature continues to rise even though the piston is now descending down the piston which expands and cools the gas slightly offsetting the increase in pressure and temperature from the fuel burn.
Now consider what would happen if we ignited at TDC. The piston is now descending down the cylinder, again expanding and cooling the gas. This effect works against the increasing temperature of the fuel burn, meaning although the temperature from the burn is still high (still the same energy going into the same mass of air) the overall pressure is dramatically reduced.
[/IMG]
You can see that the pressure and temperature are already dropping before the fuel burn really gets going so less of the energy can create work (power and torque). Notice also that because it takes longer for the burn to get going, there is more residual heat left at the end of the stroke, which increases Exhaust Gas Temperature and also transfers more heat to the head and cylinder walls, which in turn will go into the water jacket.
As for all the exhaust gases leaving the cylinder. If this were the case why bother flowing heads and headers or adding big bore straight through exhausts.
If you forget the charge for a minute, and just consider the piston compressing and decompressing air, then you'll know that as the air is compressed, it's temperature rises.
The temperature and pressure traces would look a bit like this.
Igniting the charge earlier means the mixture is burning as the piston is still rising up the cylinder on the compression stroke. The burning increases the temperature, which increases the pressure, but at the same time the piston is also increasing the pressure which increases the temperature!
Here's how the temp and pressure traces look when the charge is ignited 45° before TDC.
We can see that the two effects combined increase the pressure and temperature dramatically. The fuel is still burning past TDC, so the temperature continues to rise even though the piston is now descending down the piston which expands and cools the gas slightly offsetting the increase in pressure and temperature from the fuel burn.
Now consider what would happen if we ignited at TDC. The piston is now descending down the cylinder, again expanding and cooling the gas. This effect works against the increasing temperature of the fuel burn, meaning although the temperature from the burn is still high (still the same energy going into the same mass of air) the overall pressure is dramatically reduced.
[/IMG]You can see that the pressure and temperature are already dropping before the fuel burn really gets going so less of the energy can create work (power and torque). Notice also that because it takes longer for the burn to get going, there is more residual heat left at the end of the stroke, which increases Exhaust Gas Temperature and also transfers more heat to the head and cylinder walls, which in turn will go into the water jacket.
As for all the exhaust gases leaving the cylinder. If this were the case why bother flowing heads and headers or adding big bore straight through exhausts.
Can see this getting rather boring for people haha but...
All you have quoted there is correct and makes total sense.
Those graphs are spot on, theories correct.
Now, look at the numbers, those graphs are talking 45 degrees difference in timing. The difference between a high comp turbo motor staying in 1 piece forever and blowing itself to million bits is about 3 degrees timing when set up to the optimum. I don't think 3 degrees swing has anything like the effect you're talking about. I'll shy away from mentioning MBT points as most high comp turbo motors don't hit them.
Those graphs are quoted clearly for a normally aspirated motor where heat is your enemy. We're talking turbos, the more heat and pressure in the manifold the bigger the expansion rate over the turbo and the more boost. We're limited by materials getting too hot and failing. Too much temp and you'll overheat the runners/head/valves/wheels etc etc which then rolls onto charge temp and you chase yourself in circles.
Porting and such does work, but the vast majority of gains are on the inlet side for that reason, opening an exhaust port up but then still trying to blow into a 900 degreeC 1 bar of pressurised turbo manifold makes it less important. You seen the internal casting on o.e. turbo manifolds? Flowed headers again are NA tuning orientated, a long length turbo manifold works well at high sustained rpm, but not for punchy fast spool when a short runner setup will retain heat and low rpm turbo efficiency.
Big bore exhausts reduce backpressure on the turbo so the difference in pressure across the turbine wheel is greater so faster expansion, so faster spool and greater efficiency. Big bore NA exhausts don't work as the absorb the pulses so you cant use them as a scavenge effect at the collector.
...Still unsure how you think the gases are being held in the cylinder?
WRX STI thread I thought this was... Great cars by the way, impressive, when would a white one be available John?
All you have quoted there is correct and makes total sense.
Those graphs are spot on, theories correct.
Now, look at the numbers, those graphs are talking 45 degrees difference in timing. The difference between a high comp turbo motor staying in 1 piece forever and blowing itself to million bits is about 3 degrees timing when set up to the optimum. I don't think 3 degrees swing has anything like the effect you're talking about. I'll shy away from mentioning MBT points as most high comp turbo motors don't hit them.
Those graphs are quoted clearly for a normally aspirated motor where heat is your enemy. We're talking turbos, the more heat and pressure in the manifold the bigger the expansion rate over the turbo and the more boost. We're limited by materials getting too hot and failing. Too much temp and you'll overheat the runners/head/valves/wheels etc etc which then rolls onto charge temp and you chase yourself in circles.
Porting and such does work, but the vast majority of gains are on the inlet side for that reason, opening an exhaust port up but then still trying to blow into a 900 degreeC 1 bar of pressurised turbo manifold makes it less important. You seen the internal casting on o.e. turbo manifolds? Flowed headers again are NA tuning orientated, a long length turbo manifold works well at high sustained rpm, but not for punchy fast spool when a short runner setup will retain heat and low rpm turbo efficiency.
Big bore exhausts reduce backpressure on the turbo so the difference in pressure across the turbine wheel is greater so faster expansion, so faster spool and greater efficiency. Big bore NA exhausts don't work as the absorb the pulses so you cant use them as a scavenge effect at the collector.
...Still unsure how you think the gases are being held in the cylinder?
WRX STI thread I thought this was... Great cars by the way, impressive, when would a white one be available John?
Because of the warranty I offer with the car, I have to ensure there are sufficient tolerances built in as do the factory, else my warranty company will prevent me from offering them anymore as both Chris and redace have already correctly said.
Subaru have already posted on their site that any modifications will invalidate their warranty, as they are well aware there are plenty of modified ones out there already, and if I am selling these as ...bhp increase and ...torque increase, then everyone we do has to hit that target as a minimum, else I would not feel comfortable putting mine or the companies name on them.
11 July 2014, 08:50 PM
#1510
Former Sponsor
11 July 2014, 08:54 PM
#1511
Scooby Regular
Oh well. I will hand my PhD back. But my original post did say both were running the same boost pressure! I am off to read up on Mass Fraction Burned.
If we cannot talk about tuning the new WRX STI then I will go quiet.
The injectors max out at 350bhp by the way.
If we cannot talk about tuning the new WRX STI then I will go quiet.
The injectors max out at 350bhp by the way.
11 July 2014, 09:17 PM
#1514
Former Sponsor
Yes, and no. Yes, as that was what was offered on the previous model, and that is what people were wanting on the new one, but Subaru said they would not be offering it on this car.
But no, I was lead totally by my engine tuner, who has worked on these for many many years, and both myself and my dealer principal (who has dealt with him for almost 15 years) trust him completely. If he says it is safe with safety built in, then we are happy, if he says it is on the edge, then we follow his advice. I have yet to meet anyone else who has the depth of technical knowledge he has, but that can also put it into plain English for me to understand as well
I wanted originally a 50-60 increase, but his advice was that this would leave very little margin for error, and increase the chances of a failure and I didn't want that.
Hope that makes sense
But no, I was lead totally by my engine tuner, who has worked on these for many many years, and both myself and my dealer principal (who has dealt with him for almost 15 years) trust him completely. If he says it is safe with safety built in, then we are happy, if he says it is on the edge, then we follow his advice. I have yet to meet anyone else who has the depth of technical knowledge he has, but that can also put it into plain English for me to understand as well
I wanted originally a 50-60 increase, but his advice was that this would leave very little margin for error, and increase the chances of a failure and I didn't want that.
Hope that makes sense
11 July 2014, 10:08 PM
#1516
Scooby Regular
11 July 2014, 10:14 PM
#1518
Scooby Regular
Yes, and no. Yes, as that was what was offered on the previous model, and that is what people were wanting on the new one, but Subaru said they would not be offering it on this car.
But no, I was lead totally by my engine tuner, who has worked on these for many many years, and both myself and my dealer principal (who has dealt with him for almost 15 years) trust him completely. If he says it is safe with safety built in, then we are happy, if he says it is on the edge, then we follow his advice. I have yet to meet anyone else who has the depth of technical knowledge he has, but that can also put it into plain English for me to understand as well
I wanted originally a 50-60 increase, but his advice was that this would leave very little margin for error, and increase the chances of a failure and I didn't want that.
Hope that makes sense
But no, I was lead totally by my engine tuner, who has worked on these for many many years, and both myself and my dealer principal (who has dealt with him for almost 15 years) trust him completely. If he says it is safe with safety built in, then we are happy, if he says it is on the edge, then we follow his advice. I have yet to meet anyone else who has the depth of technical knowledge he has, but that can also put it into plain English for me to understand as well
I wanted originally a 50-60 increase, but his advice was that this would leave very little margin for error, and increase the chances of a failure and I didn't want that.
Hope that makes sense
12 July 2014, 01:32 AM
#1519
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Just to say got my car back today ��thanks to some great service from crossroads dealership. Just got to run it in now.
Also passed its first MOT
Tony
Also passed its first MOT
Tony
12 July 2014, 08:37 AM
#1521
Former Sponsor
Absolutely agree terzoscooby. It is great having someone working with you that has the same goals and values as you have, knowing they are there for the long run not just a fast buck overnight.
12 July 2014, 08:37 AM
#1522
Former Sponsor
12 July 2014, 10:38 AM
#1523
Scooby Regular
If that represents the total number of failures then 2 out of 204 is less than a 1% failure rate after three years.
I'd say that's pretty good going.
Could just be the tip of the iceberg and all that but I doubt we'd have had the thread at the top of the page if we'd been given the 2011 spec from the start.
12 July 2014, 01:01 PM
#1524
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Me too Tony, glad you're back on the road.
If that represents the total number of failures then 2 out of 204 is less than a 1% failure rate after three years.
I'd say that's pretty good going.
Could just be the tip of the iceberg and all that but I doubt we'd have had the thread at the top of the page if we'd been given the 2011 spec from the start.
If that represents the total number of failures then 2 out of 204 is less than a 1% failure rate after three years.
I'd say that's pretty good going.
Could just be the tip of the iceberg and all that but I doubt we'd have had the thread at the top of the page if we'd been given the 2011 spec from the start.
There are issues and are oil usage related. And not ring ring land failure.
By next week I'll start a thread in technical with my views, concerns and issues. For experts to discuss.
so I'll not post anymore in here as not to spoil or over run this thread.
Tony
12 July 2014, 09:18 PM
#1528
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Have a quick look for your self, go to the comments at the bottom and let's just say the sti gives the bmw 235 a hard time.
http://www.topgear.com/uk/photos/BMW...WRX-2014-05-08
in case it's not obvious, you need to go through the pics one by one to read the full review.
http://www.topgear.com/uk/photos/BMW...WRX-2014-05-08
in case it's not obvious, you need to go through the pics one by one to read the full review.
Last edited by Carnut; 12 July 2014 at 09:27 PM.
12 July 2014, 09:38 PM
#1529
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Have a quick look for your self, go to the comments at the bottom and let's just say the sti gives the bmw 235 a hard time.
http://www.topgear.com/uk/photos/BMW...WRX-2014-05-08
in case it's not obvious, you need to go through the pics one by one to read the full review.
http://www.topgear.com/uk/photos/BMW...WRX-2014-05-08
in case it's not obvious, you need to go through the pics one by one to read the full review.
