we all remember this thread, right?
http://www.bimmerboost.com/showthrea...ed-N54-630rwhp
ok so I have been studying this and I think it is totally possible Brian May's numbers are achievable on RB turbos according to thermodynamic equations and compressor maps for 15T turbos.
by the way, all these equations are from Garrett's website, advanced expert white papers, link below
http://www.turbobygarrett.com/turbob...Tech%20103.pdf
also there is an easy calculator garrett has to crunch all these formulas which I will use below. Here is the link to the calc so that you can crunch it yourself.
http://www.turbobygarrett.com/turbobygarrett/webadviser
So I was going to write all the equations here and show you how to solve for airflow and pressure ratio required to make 689hp with 100% E85 on our engine, but seems like a waste when we have a perfectly good Garrett calc to use above, so lets use it!
So let start first with the results reported by TFT/Brian May:
600whp @ 20.5 psi with 13% drivetrain loss is 689 crank HP
100% E85 at 7.8:1 AFR/lambda .8 as shown on log
so assuming the following:
VE = .95 as has been shown previously for the N54
BSFC = .6, common for E85 turbo engines
pressure drop across Intercooler and piping from turbo to manifold, 1psi at max power RPM
intercooler effectiveness = .7 (normal for air to air cooler as reported by Garrett)
Barometric pressure and temp the day of the Dyno - ok so I dont know this but lets assume it was an exceptionally high DA day so barometric pressure would be 14.94psia and ambient temp 61 deg F in the dyno bay and sucking into the intakes
a few more inputs to make sure you get the same result in the calc
mid range engine RPM 3500 (does not affect the answer at all)
peak power engine RPM 6500 (very important and does affect the number, this is taken from Brian May's Dyno chart showing Peak Power at around 6500 rpm)
plug and chug in the calculator and we get the following
![Click here to enlarge]()
From this result we get that required air flow is 26.26 lb/min (or 380 CFM) @ PR of 2.44 which gives 20.5 psi boost gauge pressure
Now lets take a look at the MHI published 15T compressor map and see where this point lands on the map. It lands in the 70% efficiency island at an optimal point in the map and at a PR of 2.44 the turbos are not being worked overly hard, everything checks out and the reported Dyno results looks credible according to the laws of physics and thermodynamics for turbo chargers. Not only that, the compressor map shows us that there is still more room for more HP which is why Brian was able to get up to 640 whp without running the turbos off the map at high inefficiencies.
*ignore the rpm lines, VEs and boost pressures on the graph in colors, they are for a twin turbo dodge stealth, sorry it was the only map I could find quickly with google.
![Click here to enlarge]()
So now some people may be scratching their heads and saying, "F*** that Garrett Calc, it dont know sh*t, I know RBs and the N54 cant do that sh*t bc no one else has done it with that same boost and timing curve"
Well if someone could provide me a dyno with a complete log for the 530 whp run that is the supposed limit of RBs, I would be happy to crunch and compare those numbers. Until someone posts that, I will make some assumptions about the 530whp Dyno run and why it was perceived to be the limit of Rb turbos.
So let begin with the assumed 530 whp run
530whp with 13% drivetrain loss is 609 crank HP
now lets assume this run was done on 93 octane pump gas
so assuming the following:
VE = .95 as has been shown previously for the N54
BSFC = .46, common gas turbo engines
pressure drop across Intercooler and piping from turbo to manifold, 1psi at max power RPM
intercooler effectiveness = .7 (normal for air to air cooler as reported by Garrett)
Barometric pressure and temp the day of the Dyno -assume the same 14.94psia and 61F as above (pretty high DA but common for high dyno numbers)
a few more inputs to make sure you get the same result in the calc
mid range engine RPM 3500 (does not affect the answer at all)
peak power engine RPM 5400 rpm
plug and chug and we get the following result:
![Click here to enlarge]()
WOW! this result says 28.46 lb/min (or 411 CFM) @ PR of 3.29 with boost pressure of 33.25 psi!
not only that, we need to adjust for the highly restrictive intake tubes as mentioned in Garretts white paper factored into P2c in the pressure ratio calc. If we assume a 2 psi loss in the pressure intake tubes vs the optimized TFT intakes Brian May used, than the adjustment to the pressure ratio is as follows:
PR = P2c / P1c
P2c = 33.25 + 14.7 = 47.95 psia
P1c = 14.7 - 2 = 12.7
PR = 47.95/12.7 = 3.78 !!
so lets see above on the compressor map where 411 CFM @ 3.78 PR falls...yeah, way off the map. Now more than likely the 530whp run was done with E50 and some meth for cooling which would bring it closer to the lowest efficiency circle on the compressor map but probably still pretty far outside and at the max of the turbos.
So what did we learn from all this:
1) Tuning with 100% E85 is awesome because it lowers required turbo air flow rate significantly for more HP
2) Improving the turbo intakes has a significant effect on the pressure ratio the turbo needs to run at and addressing the issue with the intakes (and any other restrictive part of the pipework) pays huge dividends at higher horsepower levels/PRs
Some other great features of 100% E85 tuning that contributed to Brian May's Dyno result:
1) Lowers EGT's. E85 will typically see EGT's 200c below pump gas at the same relative AFR (for instance 12.5:1 pump, 8.33:1 E85)
2) Octane rating of 105 with class 1 e85(raises detonation threshold significantly)
3) Very high vaporization cooling, much more than gasoline, which lowers mixture temps, thus increasing detonation threshold, along with increasing VE
4) Peak cylinder pressure are lower while maintaining a higher and longer overall cylinder pressure, thus raising detonation threshold and making more power due to increase in crank angle
5) E85 burns much more efficiently than gasoline, 27% more efficient
6) despite lower EGT's, E85 creates more exhaust gas volume, which helps with spool without added EGTs
7) E85 can take timing increases for days after max torque (peak VE). Lets say it takes 10* at max torque, after that it can ramp up to say 20* to redline and handle without a problem. On our engines it may not be so high due to CR and backpressure but I think somewhere between 17-20* at max rpm is very achievable with 100% E85.
I got this from evolutionm forum which has many tuners with many years of experience tuning their Evos to 100% E85 and getting awesome results
sorry for any Typos, It 2:41 in the morning!
By the way, in case anyone is wondering, I am a mechanical engineer so these equations and thermodynamic principals are all stuff I learned in school that Garrett reminded me of :)
I probably made some mistakes and or bad assumptions, so please I welcome any corrections or discussions regarding this post.
http://www.bimmerboost.com/showthrea...ed-N54-630rwhp
ok so I have been studying this and I think it is totally possible Brian May's numbers are achievable on RB turbos according to thermodynamic equations and compressor maps for 15T turbos.
by the way, all these equations are from Garrett's website, advanced expert white papers, link below
http://www.turbobygarrett.com/turbob...Tech%20103.pdf
also there is an easy calculator garrett has to crunch all these formulas which I will use below. Here is the link to the calc so that you can crunch it yourself.
http://www.turbobygarrett.com/turbobygarrett/webadviser
So I was going to write all the equations here and show you how to solve for airflow and pressure ratio required to make 689hp with 100% E85 on our engine, but seems like a waste when we have a perfectly good Garrett calc to use above, so lets use it!
So let start first with the results reported by TFT/Brian May:
600whp @ 20.5 psi with 13% drivetrain loss is 689 crank HP
100% E85 at 7.8:1 AFR/lambda .8 as shown on log
so assuming the following:
VE = .95 as has been shown previously for the N54
BSFC = .6, common for E85 turbo engines
pressure drop across Intercooler and piping from turbo to manifold, 1psi at max power RPM
intercooler effectiveness = .7 (normal for air to air cooler as reported by Garrett)
Barometric pressure and temp the day of the Dyno - ok so I dont know this but lets assume it was an exceptionally high DA day so barometric pressure would be 14.94psia and ambient temp 61 deg F in the dyno bay and sucking into the intakes
a few more inputs to make sure you get the same result in the calc
mid range engine RPM 3500 (does not affect the answer at all)
peak power engine RPM 6500 (very important and does affect the number, this is taken from Brian May's Dyno chart showing Peak Power at around 6500 rpm)
plug and chug in the calculator and we get the following
From this result we get that required air flow is 26.26 lb/min (or 380 CFM) @ PR of 2.44 which gives 20.5 psi boost gauge pressure
Now lets take a look at the MHI published 15T compressor map and see where this point lands on the map. It lands in the 70% efficiency island at an optimal point in the map and at a PR of 2.44 the turbos are not being worked overly hard, everything checks out and the reported Dyno results looks credible according to the laws of physics and thermodynamics for turbo chargers. Not only that, the compressor map shows us that there is still more room for more HP which is why Brian was able to get up to 640 whp without running the turbos off the map at high inefficiencies.
*ignore the rpm lines, VEs and boost pressures on the graph in colors, they are for a twin turbo dodge stealth, sorry it was the only map I could find quickly with google.
So now some people may be scratching their heads and saying, "F*** that Garrett Calc, it dont know sh*t, I know RBs and the N54 cant do that sh*t bc no one else has done it with that same boost and timing curve"
Well if someone could provide me a dyno with a complete log for the 530 whp run that is the supposed limit of RBs, I would be happy to crunch and compare those numbers. Until someone posts that, I will make some assumptions about the 530whp Dyno run and why it was perceived to be the limit of Rb turbos.
So let begin with the assumed 530 whp run
530whp with 13% drivetrain loss is 609 crank HP
now lets assume this run was done on 93 octane pump gas
so assuming the following:
VE = .95 as has been shown previously for the N54
BSFC = .46, common gas turbo engines
pressure drop across Intercooler and piping from turbo to manifold, 1psi at max power RPM
intercooler effectiveness = .7 (normal for air to air cooler as reported by Garrett)
Barometric pressure and temp the day of the Dyno -assume the same 14.94psia and 61F as above (pretty high DA but common for high dyno numbers)
a few more inputs to make sure you get the same result in the calc
mid range engine RPM 3500 (does not affect the answer at all)
peak power engine RPM 5400 rpm
plug and chug and we get the following result:
WOW! this result says 28.46 lb/min (or 411 CFM) @ PR of 3.29 with boost pressure of 33.25 psi!
not only that, we need to adjust for the highly restrictive intake tubes as mentioned in Garretts white paper factored into P2c in the pressure ratio calc. If we assume a 2 psi loss in the pressure intake tubes vs the optimized TFT intakes Brian May used, than the adjustment to the pressure ratio is as follows:
PR = P2c / P1c
P2c = 33.25 + 14.7 = 47.95 psia
P1c = 14.7 - 2 = 12.7
PR = 47.95/12.7 = 3.78 !!
so lets see above on the compressor map where 411 CFM @ 3.78 PR falls...yeah, way off the map. Now more than likely the 530whp run was done with E50 and some meth for cooling which would bring it closer to the lowest efficiency circle on the compressor map but probably still pretty far outside and at the max of the turbos.
So what did we learn from all this:
1) Tuning with 100% E85 is awesome because it lowers required turbo air flow rate significantly for more HP
2) Improving the turbo intakes has a significant effect on the pressure ratio the turbo needs to run at and addressing the issue with the intakes (and any other restrictive part of the pipework) pays huge dividends at higher horsepower levels/PRs
Some other great features of 100% E85 tuning that contributed to Brian May's Dyno result:
1) Lowers EGT's. E85 will typically see EGT's 200c below pump gas at the same relative AFR (for instance 12.5:1 pump, 8.33:1 E85)
2) Octane rating of 105 with class 1 e85(raises detonation threshold significantly)
3) Very high vaporization cooling, much more than gasoline, which lowers mixture temps, thus increasing detonation threshold, along with increasing VE
4) Peak cylinder pressure are lower while maintaining a higher and longer overall cylinder pressure, thus raising detonation threshold and making more power due to increase in crank angle
5) E85 burns much more efficiently than gasoline, 27% more efficient
6) despite lower EGT's, E85 creates more exhaust gas volume, which helps with spool without added EGTs
7) E85 can take timing increases for days after max torque (peak VE). Lets say it takes 10* at max torque, after that it can ramp up to say 20* to redline and handle without a problem. On our engines it may not be so high due to CR and backpressure but I think somewhere between 17-20* at max rpm is very achievable with 100% E85.
I got this from evolutionm forum which has many tuners with many years of experience tuning their Evos to 100% E85 and getting awesome results
sorry for any Typos, It 2:41 in the morning!
By the way, in case anyone is wondering, I am a mechanical engineer so these equations and thermodynamic principals are all stuff I learned in school that Garrett reminded me of :)
I probably made some mistakes and or bad assumptions, so please I welcome any corrections or discussions regarding this post.