Exhaust Size vs HP & TQ
Dec 22, 2009, 07:14 PM
#76
Here is an example of a GT35R turbine map:
Basically what it shows that with a .82 A/R T3 housing, once the difference in exhaust manifold pressure vs. turbine outlet pressure builds up to around 22psi or so, it's flowing all it can. It sure doesn't seem like much, but don't forget that the WG is flowing considerable air mass around the turbine, which accounts for the balance.
Last edited by Ted B; Dec 22, 2009 at 07:18 PM.
Dec 22, 2009, 08:03 PM
#77
There is one VERY important word on that chart.
"CORRECTED"
There is an equation that goes along with that axis. 30 lbs/min on that chart IS NOT 30 lbs/min of actual airflow under operating conditions. Once you apply the correction, 60 lbs/min of exhaust at 1300F and 60 PSI is a MUCH lower corrected airflow on that chart. Like 30-35 pounds/min depending on the pressure ratio and EGTs.
Without having accurate EGT and exhaust back pressure (before and after the turbine wheel) you really can't use that chart, other then for approximate comparisons like what affect switching housings have. That chart isn't even close to a complete turbine map anyway though. All that line represents is the average airflow, with no regards to shaft speed or efficiency other then the peak efficiency.
I do have another excel spread sheet that uses an energy balance method to approximate exhaust back pressure based on the compressor and turbine performance parameters. That spread sheet also gave a value for excess airflow, or in other words, approximated the flow out the wastegate.
Again though, I've never had a setup that I was able to chart it out and verify it produces reasonable numbers. I've alos only come across a very few number of true turbine maps, so it's really not accurate without that information anyway.
"CORRECTED"
There is an equation that goes along with that axis. 30 lbs/min on that chart IS NOT 30 lbs/min of actual airflow under operating conditions. Once you apply the correction, 60 lbs/min of exhaust at 1300F and 60 PSI is a MUCH lower corrected airflow on that chart. Like 30-35 pounds/min depending on the pressure ratio and EGTs.
Without having accurate EGT and exhaust back pressure (before and after the turbine wheel) you really can't use that chart, other then for approximate comparisons like what affect switching housings have. That chart isn't even close to a complete turbine map anyway though. All that line represents is the average airflow, with no regards to shaft speed or efficiency other then the peak efficiency.
I do have another excel spread sheet that uses an energy balance method to approximate exhaust back pressure based on the compressor and turbine performance parameters. That spread sheet also gave a value for excess airflow, or in other words, approximated the flow out the wastegate.
Again though, I've never had a setup that I was able to chart it out and verify it produces reasonable numbers. I've alos only come across a very few number of true turbine maps, so it's really not accurate without that information anyway.
Last edited by 03whitegsr; Dec 22, 2009 at 08:20 PM.
Dec 22, 2009, 08:14 PM
#78
Yep, those maps are more of a 'mean' map. A true turbine map shows several curves with the speed of the turbine and the efficiency. You use the speed that you would get from your compressor map to match it to a turbine that is efficient at that speed.
The mass airflow (as shown in the map above) can be thought of more as what pressure ratio pre and post turbine is required to reach higher efficiencies.
The mass airflow (as shown in the map above) can be thought of more as what pressure ratio pre and post turbine is required to reach higher efficiencies.
Last edited by l2r99gst; Dec 22, 2009 at 08:18 PM.
Dec 22, 2009, 09:30 PM
#80
Dave did you do a timing sweep on the 3.5" to 4" test? Did you log your delta P pre and post turbine? How was your transition from turbine housing to downpipe? Do you have a picture of the downpipe? Can you quantify the difference you saw dave? 5whp? For you Engineers out there... might you consider what would be significant in terms of an MSA?
I ran a test and varied back pressure at different engine speeds and measured torque/horsepower and hundreds of other channels with a Horiba A/C Engine Dyno with the AVL control.... Not surprising the engine lost power with the exhaust pressure raised.
So by all means... increasing exhaust pressure reduces power.
I cannot test the actual diameter change due to our test cell's exhaust system already having a pre-determined length (plumbing in the test cell) We get 4" until the step to 12" up and out of the building
IF THE SMALLER EXHAUST SIZE THEORY IS TRUE...
The test would be to have Dave take his 3" exhaust and shorten it by a few feet and overlay the dyno charts.
Heat soak car
Run 1, 2, and 3.... full 3" exhaust
Run 4, 5, and 6.... weld or clamp on a 5 foot long 3" diameter exhaust extension on the end of the exhaust
Run 7, 8, and 9.... un bolt rear section leave test pipe
Average the 3 runs and overlay the data.
If it IS in fact resonance related you'll see waves in the power that peak at different engine speeds. If there are no waves or shifts in the powerband then there are no measurable affects from the wave tuning of the exhaust length.... or SOMETHING else in the engine system is restricting the engine besides the exhaust. If it's Dave's car... I find that hard to believe.
Since I know Dave has done lots of intake manifold testing.... he can attest to the shift in power attributed to runner length... (which diameter is a contributing factor to the effective length of the runner as well as the taper) I would expect to see similar results with the exhaust length IF IT'S EVEN QUANTIFIABLE.
I ran a test and varied back pressure at different engine speeds and measured torque/horsepower and hundreds of other channels with a Horiba A/C Engine Dyno with the AVL control.... Not surprising the engine lost power with the exhaust pressure raised.
So by all means... increasing exhaust pressure reduces power.
I cannot test the actual diameter change due to our test cell's exhaust system already having a pre-determined length (plumbing in the test cell) We get 4" until the step to 12" up and out of the building
IF THE SMALLER EXHAUST SIZE THEORY IS TRUE...
The test would be to have Dave take his 3" exhaust and shorten it by a few feet and overlay the dyno charts.
Heat soak car
Run 1, 2, and 3.... full 3" exhaust
Run 4, 5, and 6.... weld or clamp on a 5 foot long 3" diameter exhaust extension on the end of the exhaust
Run 7, 8, and 9.... un bolt rear section leave test pipe
Average the 3 runs and overlay the data.
If it IS in fact resonance related you'll see waves in the power that peak at different engine speeds. If there are no waves or shifts in the powerband then there are no measurable affects from the wave tuning of the exhaust length.... or SOMETHING else in the engine system is restricting the engine besides the exhaust. If it's Dave's car... I find that hard to believe.
Since I know Dave has done lots of intake manifold testing.... he can attest to the shift in power attributed to runner length... (which diameter is a contributing factor to the effective length of the runner as well as the taper) I would expect to see similar results with the exhaust length IF IT'S EVEN QUANTIFIABLE.
Last edited by R/TErnie; Dec 22, 2009 at 09:45 PM.
Dec 23, 2009, 01:28 PM
#82
I did some searching, here is the single muffler to two muffler test thread, dyno sheet is in the very first post:
https://www.evolutionm.net/forums/ev...r-testing.html
Here is the 3" to 3.5" exhaust testing, dyno sheet also in the first post.
https://www.evolutionm.net/forums/ev...5-exhaust.html
Yes, I have taken back pressure test readings but always before the turbine wheel. I do not have the data any longer (sorry) it was all given to Robert at FP as when I was doing it I was testing back pressure for him. I deleted the logs some time ago.
My point I was going to get at was the back pressure in the turbine housing. My belief on all this is that yes, reducing back pressure in the exhaust will absolutely, 100% increase horsepower BUT when the turbine wheel/turbine housing end up being the actual largest restriction in the system THEN that is when increasing the size of the exhaust no longer has an effect. I hope that makes sense.
40, 60, 80 psi of exhaust back pressure in the turbine housing is not unheard of, when the engine is that backed up anyway there has to be a point that putting a larger exhaust on is not going to have an effect until you also reduce the back pressure in the turbine housing. In other words, it seems that until you are flowing more exhaust through the turbine/turbine housing a larger exhaust will have no effect. Go from a 35r turbine wheel to a GT42 turbine wheel and then it makes sense that going from a 3" to a 3.5" is will have an effect.
https://www.evolutionm.net/forums/ev...r-testing.html
Here is the 3" to 3.5" exhaust testing, dyno sheet also in the first post.
https://www.evolutionm.net/forums/ev...5-exhaust.html
Yes, I have taken back pressure test readings but always before the turbine wheel. I do not have the data any longer (sorry) it was all given to Robert at FP as when I was doing it I was testing back pressure for him. I deleted the logs some time ago.
My point I was going to get at was the back pressure in the turbine housing. My belief on all this is that yes, reducing back pressure in the exhaust will absolutely, 100% increase horsepower BUT when the turbine wheel/turbine housing end up being the actual largest restriction in the system THEN that is when increasing the size of the exhaust no longer has an effect. I hope that makes sense.
40, 60, 80 psi of exhaust back pressure in the turbine housing is not unheard of, when the engine is that backed up anyway there has to be a point that putting a larger exhaust on is not going to have an effect until you also reduce the back pressure in the turbine housing. In other words, it seems that until you are flowing more exhaust through the turbine/turbine housing a larger exhaust will have no effect. Go from a 35r turbine wheel to a GT42 turbine wheel and then it makes sense that going from a 3" to a 3.5" is will have an effect.
Dec 23, 2009, 04:33 PM
#84
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So let say the Evo is tuned and making 600whp with 3in then you put 3.5? Not fair comparison right? Why not tune it w 3.5 then put 3 inch without re-tuning it let see if the results will be the same?
Dec 23, 2009, 05:13 PM
#85
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Here is the 3" to 3.5" exhaust testing, dyno sheet also in the first post.
https://www.evolutionm.net/forums/ev...5-exhaust.html
My point I was going to get at was the back pressure in the turbine housing. My belief on all this is that yes, reducing back pressure in the exhaust will absolutely, 100% increase horsepower BUT when the turbine wheel/turbine housing end up being the actual largest restriction in the system THEN that is when increasing the size of the exhaust no longer has an effect. I hope that makes sense.
40, 60, 80 psi of exhaust back pressure in the turbine housing is not unheard of, when the engine is that backed up anyway there has to be a point that putting a larger exhaust on is not going to have an effect until you also reduce the back pressure in the turbine housing. In other words, it seems that until you are flowing more exhaust through the turbine/turbine housing a larger exhaust will have no effect. Go from a 35r turbine wheel to a GT42 turbine wheel and then it makes sense that going from a 3" to a 3.5" is will have an effect.[/quote]
I agree 100% that at some point the turbine housing/turbine wheel will restrict the exhaust flow more than the exhuast so that a bigger size pipe isnt going to gain any power.
But in the test of the 3" vs 3.5" was the car retuned for 3.5"?
https://www.evolutionm.net/forums/ev...5-exhaust.html
My point I was going to get at was the back pressure in the turbine housing. My belief on all this is that yes, reducing back pressure in the exhaust will absolutely, 100% increase horsepower BUT when the turbine wheel/turbine housing end up being the actual largest restriction in the system THEN that is when increasing the size of the exhaust no longer has an effect. I hope that makes sense.
40, 60, 80 psi of exhaust back pressure in the turbine housing is not unheard of, when the engine is that backed up anyway there has to be a point that putting a larger exhaust on is not going to have an effect until you also reduce the back pressure in the turbine housing. In other words, it seems that until you are flowing more exhaust through the turbine/turbine housing a larger exhaust will have no effect. Go from a 35r turbine wheel to a GT42 turbine wheel and then it makes sense that going from a 3" to a 3.5" is will have an effect.[/quote]
I agree 100% that at some point the turbine housing/turbine wheel will restrict the exhaust flow more than the exhuast so that a bigger size pipe isnt going to gain any power.
But in the test of the 3" vs 3.5" was the car retuned for 3.5"?
Dec 23, 2009, 05:50 PM
#86
The car didn't require a retune for the exhaust swap. AFR's and timing remained the same and nothing showed up that made the car need any adjustments. That's kind of obvious from the sheets, not being a smart ***, but you can see by the sheets the power/curve is nearly identical on both. A re-tune isn't needed for minimal hp/tq increases when the curves stay the same too.
Dec 23, 2009, 08:58 PM
#87
My point I was going to get at was the back pressure in the turbine housing. My belief on all this is that yes, reducing back pressure in the exhaust will absolutely, 100% increase horsepower BUT when the turbine wheel/turbine housing end up being the actual largest restriction in the system THEN that is when increasing the size of the exhaust no longer has an effect. I hope that makes sense.
40, 60, 80 psi of exhaust back pressure in the turbine housing is not unheard of, when the engine is that backed up anyway there has to be a point that putting a larger exhaust on is not going to have an effect until you also reduce the back pressure in the turbine housing. In other words, it seems that until you are flowing more exhaust through the turbine/turbine housing a larger exhaust will have no effect. Go from a 35r turbine wheel to a GT42 turbine wheel and then it makes sense that going from a 3" to a 3.5" is will have an effect.
Just like on FSAE... everything downstream of the restriction has a very small effect on power compared to when you make improvements to the restriction.
good information though dave. Thank you for taking the time to look that up.
Dec 23, 2009, 10:44 PM
#88
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This maybe a little off topic but I see evos doing side exhaust on front bumper. Are they just doing it for weight purpose or is there any hp gain/faster spool up running shorter exhaust? What Turbo size do you suggest to consider using side exhaust? Bigger than 67mm?
Last edited by evovin; Dec 23, 2009 at 10:48 PM.
Dec 24, 2009, 10:18 AM
#90
Damn it, I had a nice long response typed up a lost it......this one is going to be a lot shorter.
evovin, side exit exhausts are done for ease of fabrication, weight, straightness and we have done them as far back as the mid-90's for safety. Blow a head gasket or have something happen to an engine and the water/oil get shot out the side of the car rather than under it where you have to drive through it.
R/T, I know you know this, I am just typing. While a 1:1 ratio of boost vs back pressure sounds great and is great for top end power it sucks to drive it. The HTA86 in the single scroll .82 housing has a good mix of response and top end. I wish I had the datalogs from the testing but I want to say at 40 psi of boost somewhere around 6,000 rpm the back pressure gets to be higher than the boost pressure. That is just a best memory of what we saw. Since then the header design has been changed, the 02 housing and the turbine housing. The real Garrett GT housing is absolutely the best T3 housing I have tested, our FF kit uses a custom machined housing with a 3" V band outlet and out 02 housing on that kit is 3". The turbine wheel though is only about 2.5" on the exducer.
evovin, side exit exhausts are done for ease of fabrication, weight, straightness and we have done them as far back as the mid-90's for safety. Blow a head gasket or have something happen to an engine and the water/oil get shot out the side of the car rather than under it where you have to drive through it.
R/T, I know you know this, I am just typing. While a 1:1 ratio of boost vs back pressure sounds great and is great for top end power it sucks to drive it. The HTA86 in the single scroll .82 housing has a good mix of response and top end. I wish I had the datalogs from the testing but I want to say at 40 psi of boost somewhere around 6,000 rpm the back pressure gets to be higher than the boost pressure. That is just a best memory of what we saw. Since then the header design has been changed, the 02 housing and the turbine housing. The real Garrett GT housing is absolutely the best T3 housing I have tested, our FF kit uses a custom machined housing with a 3" V band outlet and out 02 housing on that kit is 3". The turbine wheel though is only about 2.5" on the exducer.