Feeding the Turbo Rotary: Horsepower, Airflow, Fuel Injector Sizing w 2014 turbos
02-22-10, 03:22 PM
#1
Racing Rotary Since 1983
Thread Starter
iTrader: (6)
Feeding the Turbo Rotary: Horsepower, Airflow, Fuel Injector Sizing w 2014 turbos
Much of this post can be found scattered around this board but i thought it would be a good idea to put it all together and add in alternative fuels such as E85, ethanol, methanol and that non-fuel water..
The rotary is unique. It would be a big mistake to use piston metrics when planning setup.
How unique?
Let's talk airflow:
A piston engine can generally make ten hp for every pound per minute of air, so a 70 pound per minute turbo can make 700 piston rwhp. As we navigate the web looking at turbos we often see a hp tag... for instance a 73 pound per minute TO4Z/GT500/PT67 is often rated at 730 hp. If you are looking for 730 you'd best look elsewhere because they are talking PISTON lingo.
Should you wish to translate to rotary you'd take the pounds per minute, or the estimated HP number, and divide by 1.3.
73 pounds per minute of air is 561 ROTARY rwhp.
BTW, that doesn't mean the rotary takes a back seat to the piston engine. While it does take a discount due to lower volumetric efficiency (VE), it more than makes up by flowing more air versus displacement.
O K, let's get into it starting with airflow and hp.
FDs are all about airflow from turbos.
Most turbos have a compressor map which sets forth maximum airflow in pounds per minute and other metrics such as efficiency as well as airflow at differing boost levels etc. (see Sean's “How To Read a Compressor Map” thread sticky in the Single Turbo Section).
This thread is about properly sizing the fuel system(s) so let's just focus on the maximum air as set forth on a commonly used GT3582R compressor map.
Airflow is represented in pounds per minute. The standard GT3582r makes approx 62 pounds per minute max.
Rotaries require 1.92 CFM (cubic feet per minute) to make one rear wheel hp.
62 pounds per minute times 14.471 equals 897 cubic feet per minute.
Now that we have CFM we divide by 1.92 to get rear wheel rotary hp.
897/1.92 = 467 max rotary rwhp.
TO4Z, GT500, PT67, Borg Warner S300 63, the newer GTX3582r turbos make approx 73 pounds per minute.
73 X 14.471 = 1056 CFM/1.92 = 550 max rotary rwhp
moving to the 80 pound+ turbos…
GT4094r makes 80 pounds, 1157 CFM, 603 rw rotary SAE hp
BW S300 64 FMW makes 80 pounds, 1157 CFM 603 hp
GTX4088r makes around 84 pounds, 1215 CFM, 633 hp
GT4294 puts out 85 pounds, 1230 CFM, 641 hp
Now that we have an understanding how to get CFM from pounds per minute and then rw rotary hp let's move on to solving for fuel requirements from air generated.
AFR
Air Fuel Ratio... 10 to 1, 11 to 1, 12 to 1. These ratios are for air and fuel measured in POUNDS.
11 to 1 is 11 pounds of air and one pound of fuel.
Back to the standard GT3582r. Let’s calculate fuel injector sizing.
We need some "givens."
"Given" we want to have enough fuel to run 10.0 to 1 AFR if necessary. A small amount of overkill in the fuel department is prudent. We won’t be tuning 10.0.
"Given" we want to run our fuel injectors at no more than 85% capacity (expressed as duty cycle). Injectors run at more than 85% become unhappy.
Assuming 62 pounds per minute of air, at a 10 to 1 ratio we need 6.2 pounds per minute of gasoline.
62 pounds air
6.2 pounds gasoline
The 6.2 pounds is NET into the engine.
When sizing injectors there are two deducts to get to NET that need to be added back to get to GROSS which is the common number used when referring to injectors by size.
The two deducts are duty cycle and lag.
We wish to limit our fuel injectors to 85% duty so we divide 1 by .85
1/.85 = 1.1764
another adjuster that needs to be recognized and added to the calculation.... LAG.
Fuel injectors are sold based on max flow output such as 850 or 1600… this is measured when the injector is open continuously.. in the real world, our world, injectors open and close.
It takes time to open fully. During this time and the duration of the closing time the injector is not flowing as much as if it were wide open. This is called “lag” or “deadtime” and it costs flow. The amount is somewhat variable based on voltage and other variables.
The delivery cost of lag varies and I will use 13%.
My method of injector sizing starts w a known, the airflow in pounds and the AFR, which gives us fuel in pounds. We now can convert pounds to cc per minute and we know the NET Fuel Needs.
In order to select the correct injectors we need to calculate the Gross Fuel Needs.
Which is now easy…
Back to the 62 pound GT3582r
Adjusting for 85% duty and 13% lag we find we need to multiply our 6.2 pounds by 1.352 to get to GROSS Injector requirements.
6.2 X 1.352 = 8.382 gross pounds of fuel.
The next step is to convert the pounds of gasoline to gallons. Gasoline weighs 6.35 pounds per gallon.
8.382 pounds / 6.35 = 1.320 gallons per minute
Google now does conversion so Google “1.32 gallons per minute to cc per minute” and you get 4996 call it 5000 cc per minute.
5000 GROSS injector capacity will properly service 62 pounds per minute or 467 rotary rwhp..
Given the above calculations we can now easily calculate Gross Fuel Injector delivery requirements for other turbos based on max air output.
TO4Z, GT500, PT67, BW S300 63, the newer GTX3582r turbos make approx 73 pounds per minute.
550 max rotary rwhp/467 = 1.177 X 5000 = 5888 Gross Injector
moving to the 80 pound+ turbos…
GT4094r 603/467 = 1.291 X 5000 = 6456 CC Gross Injector
BW S300 64 FMW 603 = 6456 CC
GTX4088r makes around 84 pounds, 633/467 = 1.355 X 5000 = 6777 CC
GT4294 641/467 = 1.372 X 5000 = 6863 CC
Yes, you can make the above power w slightly less injector because I am wanting you to have enough to run 10.0 if need be. Further, you can up the rail pressure from 43.5 psi for more net flow. The newer Bosch EV14 injectors can run at 8 BAR (116 psi). Just remember that you get the square root of the pressure increase.
As example, let’s say you raise static pressure 26.4% from 43.5 to 55 psi.
You would get a 12.4% flow increase.
howard
The rotary is unique. It would be a big mistake to use piston metrics when planning setup.
How unique?
Let's talk airflow:
A piston engine can generally make ten hp for every pound per minute of air, so a 70 pound per minute turbo can make 700 piston rwhp. As we navigate the web looking at turbos we often see a hp tag... for instance a 73 pound per minute TO4Z/GT500/PT67 is often rated at 730 hp. If you are looking for 730 you'd best look elsewhere because they are talking PISTON lingo.
Should you wish to translate to rotary you'd take the pounds per minute, or the estimated HP number, and divide by 1.3.
73 pounds per minute of air is 561 ROTARY rwhp.
BTW, that doesn't mean the rotary takes a back seat to the piston engine. While it does take a discount due to lower volumetric efficiency (VE), it more than makes up by flowing more air versus displacement.
O K, let's get into it starting with airflow and hp.
FDs are all about airflow from turbos.
Most turbos have a compressor map which sets forth maximum airflow in pounds per minute and other metrics such as efficiency as well as airflow at differing boost levels etc. (see Sean's “How To Read a Compressor Map” thread sticky in the Single Turbo Section).
This thread is about properly sizing the fuel system(s) so let's just focus on the maximum air as set forth on a commonly used GT3582R compressor map.
Airflow is represented in pounds per minute. The standard GT3582r makes approx 62 pounds per minute max.
Rotaries require 1.92 CFM (cubic feet per minute) to make one rear wheel hp.
62 pounds per minute times 14.471 equals 897 cubic feet per minute.
Now that we have CFM we divide by 1.92 to get rear wheel rotary hp.
897/1.92 = 467 max rotary rwhp.
TO4Z, GT500, PT67, Borg Warner S300 63, the newer GTX3582r turbos make approx 73 pounds per minute.
73 X 14.471 = 1056 CFM/1.92 = 550 max rotary rwhp
moving to the 80 pound+ turbos…
GT4094r makes 80 pounds, 1157 CFM, 603 rw rotary SAE hp
BW S300 64 FMW makes 80 pounds, 1157 CFM 603 hp
GTX4088r makes around 84 pounds, 1215 CFM, 633 hp
GT4294 puts out 85 pounds, 1230 CFM, 641 hp
Now that we have an understanding how to get CFM from pounds per minute and then rw rotary hp let's move on to solving for fuel requirements from air generated.
AFR
Air Fuel Ratio... 10 to 1, 11 to 1, 12 to 1. These ratios are for air and fuel measured in POUNDS.
11 to 1 is 11 pounds of air and one pound of fuel.
Back to the standard GT3582r. Let’s calculate fuel injector sizing.
We need some "givens."
"Given" we want to have enough fuel to run 10.0 to 1 AFR if necessary. A small amount of overkill in the fuel department is prudent. We won’t be tuning 10.0.
"Given" we want to run our fuel injectors at no more than 85% capacity (expressed as duty cycle). Injectors run at more than 85% become unhappy.
Assuming 62 pounds per minute of air, at a 10 to 1 ratio we need 6.2 pounds per minute of gasoline.
62 pounds air
6.2 pounds gasoline
The 6.2 pounds is NET into the engine.
When sizing injectors there are two deducts to get to NET that need to be added back to get to GROSS which is the common number used when referring to injectors by size.
The two deducts are duty cycle and lag.
We wish to limit our fuel injectors to 85% duty so we divide 1 by .85
1/.85 = 1.1764
another adjuster that needs to be recognized and added to the calculation.... LAG.
Fuel injectors are sold based on max flow output such as 850 or 1600… this is measured when the injector is open continuously.. in the real world, our world, injectors open and close.
It takes time to open fully. During this time and the duration of the closing time the injector is not flowing as much as if it were wide open. This is called “lag” or “deadtime” and it costs flow. The amount is somewhat variable based on voltage and other variables.
The delivery cost of lag varies and I will use 13%.
My method of injector sizing starts w a known, the airflow in pounds and the AFR, which gives us fuel in pounds. We now can convert pounds to cc per minute and we know the NET Fuel Needs.
In order to select the correct injectors we need to calculate the Gross Fuel Needs.
Which is now easy…
Back to the 62 pound GT3582r
Adjusting for 85% duty and 13% lag we find we need to multiply our 6.2 pounds by 1.352 to get to GROSS Injector requirements.
6.2 X 1.352 = 8.382 gross pounds of fuel.
The next step is to convert the pounds of gasoline to gallons. Gasoline weighs 6.35 pounds per gallon.
8.382 pounds / 6.35 = 1.320 gallons per minute
Google now does conversion so Google “1.32 gallons per minute to cc per minute” and you get 4996 call it 5000 cc per minute.
5000 GROSS injector capacity will properly service 62 pounds per minute or 467 rotary rwhp..
Given the above calculations we can now easily calculate Gross Fuel Injector delivery requirements for other turbos based on max air output.
TO4Z, GT500, PT67, BW S300 63, the newer GTX3582r turbos make approx 73 pounds per minute.
550 max rotary rwhp/467 = 1.177 X 5000 = 5888 Gross Injector
moving to the 80 pound+ turbos…
GT4094r 603/467 = 1.291 X 5000 = 6456 CC Gross Injector
BW S300 64 FMW 603 = 6456 CC
GTX4088r makes around 84 pounds, 633/467 = 1.355 X 5000 = 6777 CC
GT4294 641/467 = 1.372 X 5000 = 6863 CC
Yes, you can make the above power w slightly less injector because I am wanting you to have enough to run 10.0 if need be. Further, you can up the rail pressure from 43.5 psi for more net flow. The newer Bosch EV14 injectors can run at 8 BAR (116 psi). Just remember that you get the square root of the pressure increase.
As example, let’s say you raise static pressure 26.4% from 43.5 to 55 psi.
You would get a 12.4% flow increase.
howard
Last edited by Howard Coleman; 02-02-14 at 08:34 AM.
01-21-12, 10:01 AM
#4
Racing Rotary Since 1983
Thread Starter
iTrader: (6)
"Does that 1.92 to 1 rwhp include drivetrain losses?"
yes...
"we divide by 1.92 to get rear wheel rotary hp."
howard
yes...
"we divide by 1.92 to get rear wheel rotary hp."
howard
Last edited by Howard Coleman; 12-21-13 at 07:23 PM.
07-17-12, 10:58 AM
#5
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I'm curious about where this number comes from (not saying it's wrong, btw). Specifically, what RPM is this at? What compression ratio? What kind of ports?
The reason I ask is that I'm trying to guesstimate the amount of airflow needed throughout the rev range (I'm trying to produce a specific torque curve). I know that it's way more complicated than a few numbers plugged into a simple equation, but I figure if I can get it close, I can smooth it out later during tuning.
I wish I had a Ricardo WAVE model of a 13b and could do this properly.
The reason I ask is that I'm trying to guesstimate the amount of airflow needed throughout the rev range (I'm trying to produce a specific torque curve). I know that it's way more complicated than a few numbers plugged into a simple equation, but I figure if I can get it close, I can smooth it out later during tuning.
I wish I had a Ricardo WAVE model of a 13b and could do this properly.
07-24-12, 04:27 PM
#6
Senior Member
".., it makes up for lower VE by being able to flow more air V displacement."
isn't "able to flow more air V displacement" mean higher VE.
Did you mean to say instead "due to a lower thermal efficiency" aka BSFC?
Last edited by Clubuser; 07-24-12 at 04:29 PM.
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11-30-13, 10:05 AM
#8
12-27-13, 04:13 AM
#10
" Adjusting for 85% duty and 13% lag we find we need to multiply our 6.2 pounds by 1.352 to get to GROSS Injector requirements.
6.2 X 1.352 = 8.382 gross pounds of fuel. "
Maybe my math is wrong but is that "1.352" the right number? I don't get how he's getting that number.
6.2 X 1.352 = 8.382 gross pounds of fuel. "
Maybe my math is wrong but is that "1.352" the right number? I don't get how he's getting that number.
02-02-14, 08:28 AM
#11
Racing Rotary Since 1983
Thread Starter
iTrader: (6)
"is "1.352" the right number?"
to get to Gross from Net....
first max injector duty cycle of 85%...
100 X .85 = 85
only .87 of gross gets to net because of opening and closing slippage (Lag)
85 X .87 = 73.95
100/73.95 = 1.352
after figuring the net engine fuel needs you multiply that number bt 1.352 to get to gross which is the number to use when buying your fuel injectors.
howard
to get to Gross from Net....
first max injector duty cycle of 85%...
100 X .85 = 85
only .87 of gross gets to net because of opening and closing slippage (Lag)
85 X .87 = 73.95
100/73.95 = 1.352
after figuring the net engine fuel needs you multiply that number bt 1.352 to get to gross which is the number to use when buying your fuel injectors.
howard
02-20-14, 06:14 AM
#12
Which I believe puts me at 6220 max injector if ID's site is correct @100% duty cycle (85% would be on 5287). Would this setup still be sufficient to provide the fuel requirements of the turbo or should I look to downsize? I lost 260cc of injector by downsizing from ID1000s to ID850s (tuner recommended it for Power FC) and was wondering if that will realistically be a limiting factor as I progress with my build. I don't necessarily mind going the the s300sx fmw 61.8mm but the attraction to the 64.5mm should be obvious.
Thanks and sorry for the rather elementary questions.
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