Our last articles about combining supercharger performance with turbocharger top end seems to have found some online appreciation. So, I’ve decided to write up a step by step on how to do the math for twin-charging your own car.
I’m going to start with a typical compact car engine, such as the Toyota Celica 2.2 liter 5sfe engine. The engine makes 135 hp at 5200 RPMs with a 6200 RPM redline.
For starters, every horsepower requires about 1.5 CFM of air (depending on the air density).
So 135 naturally aspirated hp requires a flow of 202 CFM at pressure ratio of 1.
The pressure ratio is the ratio of turbocharger or supercharger boost pressure divided by atmospheric pressure. Each 1 atmosphere is equal to 14.7psi of pressure… thus:
PR = (14.7 + Boost pressure)/14.7
So for a normally aspirated car: PR = (14.7 + 0) / 14.7 = 1.
Supercharger calculations:
Using 14psi as our target boost (and the maximum safe boost we’d want to extract out of a roots style supercharger) we get the following pressure ratio:
PR = (14.7+14)/14.7 = 1.95
New expected horsepower level: old HP * pressure ratio
New HP = 135 * 1.95 = 263 HP
New CFM = 227 * 1.5 = 395 CFM.
So now, we have our supercharger flow requirements, we need a supercharger able flow 395 CFM at a pressure ration of 1.95 (or 10psi).
Going through different Eaton supercharger maps I had available I find one available option:
1- The third generation M62 or the fourth generation MP62 are capable of producing 395 CFM @ 1.95 PR @ 13,000 RPMs.
|
Criterion |
Eaton M62 |
|
CFM @ PR |
395 @ 1.95 |
|
RPM |
13,000 |
|
Horsepower required to drive the supercharger at peak RPM |
35 hp @ 13,000 RPM |
|
delt T (temperature increase at supercharger outlet) |
160 * F @ 11,000 RPM |
My final expected hp is going to be less than the original estimate263 for two reasons:
1- The supercharger requires 35 hp to drive it at 13,000 rpms.
2- The outlet temperature (if not managed through a proper intercooler) is going to be 88*C higher than the inlet temperature, and with every 13*C by rule of thumb costing us 1 hp of power, then 88*C would equate to a power loss of 7 hp.
Our final supercharged power figure (with no intercooler and no other bolt-ons) is
Final hp = (original hp * pressure ratio) – supercharger drive power – (delta T (Centigrade) / 13)
Final hp = 263 – 35 – 7 = 221 HP
Hello from Greece.
I own a Mercedes CLK 200K 11/2003 with the M271 supercharged engine. I am trying to find many months now if i can twincharge my car. The only tuning that i have try is the K1 Kleemman kit which rise the power to 212Hp. Do you have any suggestions for my plans; Is it to complicated to set up a twincharged system for the M271. That set up has already done on VW 1.4 engine. Whish is the better setup sc into turbo or turbo into sc, considering that the M271 is already supercharged. Your posts are fantastic and the only one in the internet. Keep on going.
Best Regards
Anagnostopoulos George
Thanks for the question George, and thanks for the kind words.
I own a 2005 M271 and believe me I’ve thought about the twin-charged M271 often.
The way I would twincharge the M271 is by using a custom exhaust manifold or a shory 4-1 manifold off the older ~2003 SLK. On that manifold I would custom weld a mounting bracket for the turbo of my choice. I would choose a turbo capable of my target power goals (say 260hp worth of air @ 15psi of boost) … which is around a medium sized T3 or a TDO4-15G, which is not that large a turbocharger.
Since this is a twin charger setup you’re going to need a turbo with a wider compressor map, what you are realistically looking for is peak compressor efficiency around 260hp @ 7psi (rather than 15psi) because the pressure ratios will multiply and so the turbocharger is actually working on that point on the map even though the total manifold pressure is higher.
I would feed the intake system into the turbocharger, and then feed the turbo outlet into the supercharger inlet.
If the turbocharger has a higher efficiency at that point , than your supercharger does, I would uninstall the kleemann overdrive pulley bringing boost back down to stock and use the turbocharger to feed more of the air since it is more efficient and will give a cooler and safer mixture.
One of the advantages of the M271 setup is that the supercharger isn’t part of the intake manifold, but rather has an outlet feeding the factory front mount intercooler.
Now that the air mixture is doubly compressed and doubly as hot (having selected the most efficient turbo i can find at that demand point to keep things as cool as possible), I would upgrade the factory front mount intercooler, and charge piping for the added cooling requirements and added flow…. and return that and feed it to the factory throttle body.
This part of the build up is actually the ‘simple’ part.
The hard part is now making the setup work with the factory ECU. The factory ECU runs a very aggressive air to fuel ratio below 4000 rpms, and has built in boost cut features using the stock electronic bypass valve and the drive by wire throttle body if you exceed its expected Mass Air meter or Manfiold Pressure sensor readings.
Furthermore, if you scale down these 2 sensor voltages (as is typical on older cars) it will detect so using the on board wideband primary oxygen sensor when it exceeds the factory expected range of fuel trims …
Short of going to a full standalone engine management system, the only piggy back controller that I know of capable of pulling this off would be the AEM F/IC …
with the AEM FIC (as far as I know since I’ve never owned one), you will be able to do all the following:
* Clamp the factory MAP sensor signal to prevent boost cut
* Clamp the factory MAS sensor signal to prevent fuel cut
* Control the larger injectors required to reach the higher power figures (the kleemann kit already uses an upgraded fuel pressure regulator, but this isn’t enough if you go for even more power)
* Fine tune your wide open throttle air fuel ratios to a more power friendly 12.5:1 or richer as needed
* Use the O2 sensor skew feature of the AEM in current mode (since the mercedes uses a current based wideband sensor) to make the ECU think that the fuel trims are 0% when your air fuel ratio is where YOU want it to be for this setup
Since the AEM can do minor fuel trims based on IAT , i would wire up an extra intake air temp sensor after the intercooler before the inlet to the throttle body… This way if there are any boost leaks, any heat soak from the intercooler, any nonlinearities between the switchover between the two chargers, the AEM will be able to tell the final temperature (and density) of the mixture after both chargers and the intercooler and you can make a more accurate tune based on exactly what is going into the motor (since you have a temp sensor right at the throttle body, and a boost line from the manifold going to the AEM on board MAP sensor).
From then on, it’s just taking the time to dyno tune it and fine tune it.
You see this is not an impossible setup but it is not cheap.
But the question that I carry with me now, is :
“Why would you twin-charge and go through with that complexity when a twin screw supercharger, such as a lysholm, will be able to give you the instant boost that a positive displacement roots charger will, and still will have good efficiency (of over 65% which is comparable to lots of turbochargers) up to 18psi of boost?”
You could take off the M45, get yourself the right size lysholm and get to the same power goals, with the same kind of power band (good low end and good top end) without really having to go to the complexity of a twincharger….
I guess there’s always more than one way to do things.
First off all I want to thank you for all these precious guidelines. You are right about the complexity of the twincharged setup. It is pitty from the other hand why there isn’t any bolt on twin screw kit or even a twincharged one. We are hundredes of MB owners with the M271 seeking for some power. If you estimate the cost of my setup (Kleemman K1) + custom headers + free 200 holes cat + workshop expence is about 2.600 € (3.750 USD). My car was stock 183,2Hp and reach 212Hp now, measured on a bright new DynoRace before and after. I gain 28,8Hp and pay 130 USD for each one Hp. I will check the twin screw option like Lysholm and I will let you know.
Thank you again for your time and your advises. Congratulations for your professionalism.
Wow i have been dreaming about this for a long time and finally i find a website that is talkingabout doing it.. Do you think a h22 Will hold up with twincharging? I plan i getting a standalone ECU before i do it so i can tune it. And a bunch of other goodies to
Yeah the H22 is a good engine and should hold up well to boost so long as the tune is safe.
Some H22′s are open deck, others are close deck. If you have an open deck, then going with a block guard is going to be a must pretty much to do this safely.
Take it easy and do your research… one advantage to twin charging is that you can stage it. Do a basic turbo (or supercharger setup) … get that tuned… later on add in your other charger…. redo your plumbing to compound the boost… and retune.
It’s not too complicated, but there is a lot to do.