Compound turbos on a MB

OM617

OM617

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Apr 7, 2007
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Has anyone tried compound turbos on a mercedes? This setup is common for diesel pickups to increase the pressure ratio above 3bar.

I've got a GT2256V mounted to my engine right now and a stock KKK K26 leftover from the conversion. I'm not looking for more than 30psi of boost, but the GT22 won't make much more than 22psi on my OM617 without choking.

Compounding would allow me to get to 25psi quickly while keeping the GT22 in it's efficient range and getting the K26 off my shelf. 12psi fed to the GT22's inlet plus 14psi from it could net me 26psi without extreme exhaust pressure and intake heat.

I know I could do this with a GT2359V or GT2559V but they are still rare
 
Compounding doesn't work by adding boost pressures together. It ends up multipling the pressure ratios together. Is it intercooled? Why is it important to have 30psi? How will you keep the head from lifting?

Having said all that, I think it's an awesome concept!

brnaodn.
 
12psi feeding and 14psi on top of that is really 41psi

it's not a multiplication, you just add another atmosphere on top of the boost from the first turbo.

instead of 12psi you are really feeding it 12 + 14.7 = 26.7psi then add 14psi to that and the resultant boost would be ~41psi(40.7psi)
 
In a compound configuration, one turbocharger is used to pressurize the air coming into the inlet of the other, resulting in a multiplication of the pressure ratios. (Notice it's not pressure as in PSI, it's the pressure ratio).

For example if both turbochargers are running at pressure ratios of 3.0 and the atmospheric pressure is one bar the resulting pressures will be three bar absolute pressure at the inlet of the second turbocharger and nine bar absolute pressure (eight bar gauge) at the inlet manifold of the engine. The pressure ratio in this example becomes nine because of the compounding, not 3 + 3 + 1.

brandon.
 
Interesting.

That takes out that idea. I was just looking for an easy way to 30psi since that about all thats needed to get into the 300hp range.
 
yeah joe, ur right. and after realizing what turbo(s) he has there...the compounding of those turbo's would probably not be a good idea. the ideal for compounding is a 2:1 size ratio meaning the primary should be twice as large as the secondary. that K26 is no where near twice the size of the GT22.

Compounding turbochargers is only effective to acheive very high pressure ratio's that a single could not acheive on it's own. I would recomend to sell both turbo's and get a larger unit that can support the 30psi you want to acheive.

ps: I'm a huge fan of proving me wrong though! :)
 
Ken in AZ said:
yeah joe, ur right. and after realizing what turbo(s) he has there...the compounding of those turbo's would probably not be a good idea. the ideal for compounding is a 2:1 size ratio meaning the primary should be twice as large as the secondary. that K26 is no where near twice the size of the GT22.

Compounding turbochargers is only effective to acheive very high pressure ratio's that a single could not acheive on it's own. I would recomend to sell both turbo's and get a larger unit that can support the 30psi you want to acheive.

ps: I'm a huge fan of proving me wrong though! :)
Click to expand...

Sorry about the cranky post, not a good day on my part. :bang I've tried a 58mm hx40 and a 64mm s400 on a 5.9l before. You're right about 2:1 ratio, but I still haven't found the math to back it up. I think it has something to do with the efficiency of the turbine housing/wheel. The 58mm/64mm setup was quick spool, but didn't have any top end at 60psi of boost like you would have thought. I believe it to have something to do with the 64mm being out of it's efficiency range too soon as a primary?

bnraond.
 
I think that both the turbine and compressor size of each have a large to do about efficiencies of the whole. you have to get the gas out to get the gas in otherwise you'll choke. I am taking a big gamble here and saying that the math isn't difficult, but rather the changes in variables that make it difficult to produce suitable results on paper. the real proof is in testing, obviously I haven't done the testing, but seeing what everyone else does is fairly convincing.
 
You loose about 30% of your primaries hp potential by compounding it (this differs slightly depending on the engine too. CR's are less and 12v's can be more). The size of the secondary also plays a role here. 50% of the primary is a little small for a secondary.

So Brandon your 64mm S400 realistically probably only flowed about 75-80lbs/min max. On a 12v I wouldn't expect it to be able to make more than 550hp. If it was a small turbine wheel version S400 it might choke before that even.
 
I'm pretty sure the 64mm version was a small turbine...it made a nice, cool, quick spooling 500hp on a VP44 24v...I think it would be very lucky to crack 500hp with toasty EGT's on a 12v!

Chris
 
The 58mm/64mm compound set was on a 24v. It went 511 on fuel, but that truck has other problems.

brandon.
 
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