signature600

Yes but they will, they spool faster than stock, and make more PROVEN HP than ANY other system out there...just ask the people around here who KNOW

BTW, this is not a slam against the vendor who built the triple chargers. I've only met him once, and talked to him twice. These experts, are people who KNOW it is the end all because there are three turbos instead of two...and have no idea what a dyno is

I need to talk to him and get his theory on the subject...then maybe I can see where he's coming from??
Chris

GO 4LO

I just scrolled back up to see if I could figure out how to see the pics and saw that I mixed up my threads here. I was reading the triples thread - that's where the 35/35/S300 discussion occurred. The thread linked to this one, and I forgot what I was posting to haha.

Chris

GO 4LO

The twin 35's on the manifold would spool, but not until probably 26-2800. Going strictly by airflow, a pair of 35's would flow almost as much as the single I have on my puller, but due to the mods to this turbo, I doubt they'd spool quite as fast (and my pulling turbo doesn't light until 2450-2500).
The twin 35's would be fine up top if you wanted to run a monster primary (or maybe a pair of HT3B's for the primary stage, and do quads like Justin mentioned above), but now we're talking 1200 hp setups. An S300 on bottom just wouldn't work with 35's up top.
Now an S300 on top with twin 35's on bottom doesn't sound like a bad combo to me...

Chris

signature600

I've tried to explain the principles of twins, triples, and turbos in general to some of the people who "push" these setups. They have no idea that boost does not equal power, or that there are better turbos than factory shelf S300's and HX50's!!

Basically, they are clueless!
Chris

BTW, if I was going to design a triple charger setup, and deal with the extra complications involved with three chargers, they would be built like ATS' setup, and like most pullers setups. I wouldn't waste my time under the hood of a Dodge truck though...not enough space for the interstage cooling require for a setup like that

gman07

HOHN, post #25 is simply inspirational

This is an awesome discussion guys!

Artsi_L

I finally found two shots on BMW's twin turbo arrangement in a 3.0liter gasoline engine, model 335i. Two off turbochargers work in parallel, independent from one another.

The one with a worse resolution, I scanned from a magazine article (the pic was dang small anyways)

Timmay2

Anyone with compound twins ever measure their intake temps? Essentially they are pushing over 50 psi THROUGH the small turbo.. which is surely operating it well beyond its range..

Have yet to see a bypass valve to bypass the small turbo in any of the diesel twin turbo kits sold out there... wouldve thought if people didnt like the idea of pushing a small turbo that high, what makes using a bigger turbo to force even more air through the same tiny turbo any better?

Maybe im just full of hot air, but to me compounds seem completely ineffecient without a bypass valve to take the small turbo out of the loop once the large has enough to go off.

HOHN

A good twins setup isn't pushing 50psi to the small charger.


Notice I say TO, not THROUGH. The big turbo isn't trying to turbocharge the engine, it's turbocharging the smaller turbo. Which means all it has to do is provide a reservoir of pressurized air for the small turbo to draw from.

So if that small turbo is operating at constant pressure ratio, it can make a LOT more boost with the same efficiency by feeding it with, say, 40psia, instead of 14.7 psia.

Say you're running a 3:1 PR on the small turbo. By itself, it can make 29.4psi gauge, given atmospheric pressure of 14.7.

But if you force feed it with 40psia, now, it can make (theoretically) 105.3psi gauge pressure, at the same pressure ratio (and hence, efficiency).


Note that compressor maps for turbos go by pressure ratios, NOT BOOST NUMBERS. The compressor just multiplies pressure within a certain flow range.

Do not confuse pressure with flow. The big charger isn't trying to FLOW a certain amount of air through the small one, it's just providing a higher pressure reservoir of air for the small one to draw from and make higher boost (and, within reason, more air mass).

Ultimately, the only metric that matters is MASS-- how many POUNDS of air and fuel you can get into the engine. Pressure, density, flow, and such are just all means to this end.....

Justin

jon96ctd

jumping into this a little late, just saw it. why would you want to run parallels? yes, with smaller turbos you do have less inertia but the driving heat energy is also divided. you pretty much have the same thing as a single charger 5.9, but now it's a single charger 3.0. then you have more efficiency loss, as awesome as turbos are, they suck a lot of energy to drive.

if you look at turbine aircraft engines they're not rocket science, it's a turbocharger with a combustion chamber instead of a piston engine to drive it. on both the Allison 250 and Pratt&Whitney PT-6A when they go to bump up power they don't add more compressor and turbine wheels, they make the current ones bigger. especially the allison, used to have about a 7 stage axial compressor in front of the centrifugal compressor for about 300hp; now they're around 700hp and have a single stage centrifugal that's way bigger. the BIG PT6A-65 and -67 engines have two power turbines because they had to go well over 1,000hp and keep the physical outside size of the engine small; otherwise they would've just put a larger single wheel in there...even at that though, they two power turbine wheels are different sizes, the second stage is larger. the difference in power output on the big PT6 vs the small PT6 engines is about the same as running a single or sequential setup on our trucks.

now, the sequential setups that bypass the small turbo when the engine rpms are up are pretty cool, mercedes has been doing that for a while, I remember reading a very in depth tech article on a setup they were running in europe, that was about 2 or 3 years ago. complex? kinda, just another thing for the computer to monitor/adjust but not very difficult.

main reason parallels are run on cars are because of plumbing routing, especially with a V or opposed(pancake/porsche). it's easier to mount a turbo right on the exh manifold log and there's very minimal heat loss there as opposed to running a pipe across the engine compartment from one bank. plus, it's way easier to run two 3" exit pipes instead of one 5" exit pipe under a car.

if you look at most of the guys that upgrade the turbo'd supras(which are dang fast stock), they get rid of the bypassing sequential in favor of a single and they have no problem with a streetable 550-650hp range.

there's no practical reason to take a single charger off to replace it with smaller parallels. the efficiency loss wins. now, 'twins' when they're sequential and different sizes are great, like already mentioned, the big charger isn't for the engine, it's just to provide a higher baseline atmosphere for the little guy to start multiplying from. a large single charger is still more efficient than this setup BUT is less practical for street.

dodgeman01

If I had the money and the time I would make a 8 Turbo setup just for the heck of it. It would not fit but imagine 6 small turbos feeding 2of the same size (bigger) turbos then dumping into one huge monster of a turbo. would it make more power? most likely not but man would it look cool on a engine stand. I bet I could put it on a tractor just to hear how it would sound
DM01

jon96ctd

as ridiculous as that sounds, 8 turbos has already been done on a '57 chevy, it was done for the wow factor and the guy that did it knew before he even ran any numbers that it'd be near useless and pretty inefficient for a turbo'd small block. I guess it didn't turn out bad, still put down a respectable power number(though laughable when you compare power to cost). it wasn't a sequential style like you mentioned...I'd like to see it done, heck, I might even let someone pay me to do it. just to see the priceless, confused, stunned look of 'what the? why?' so many times that it wouldn't be funny to see anymore(that's a lot, by the way.)

Mike Holmen

If you run your secondary turbo with 30psi of inlet pressure and run it up to 100psi of outlet pressure, you drive pressure requirement would increase signifcantly. On my twins my secondary turbo is limited to 24psi of boost just for that reason. You need to balance the work between the turbos to reduce drive pressure, but on the other side using the lower part of compressor maps the turbos don't build as much heat as running them at the top of the there maps which are less efficient.

RowJ

Thanks for the PT6 example. Being familiar with that engine made it all clear...for me.
Before that, I could sense the parallel system was not the way to go, but could not find the words!!

Great Thread guys. Love it when all you engineering type thinkers kick ideas around. I try... but just come up with a headache

RJ

Artsi_L

I finally managed to stumble accross piece of information that will shed light into the very reason why indeed two small turbochargers are actually superior when comparing over to a large single turbocharger.

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Simulation of turbocharged SI-engines
- with focus on the turbine

Doctoral thesis - Fredrik Westin

KTH School of Industrial Engineering
and Management TRITA – MMK 2005:05
Royal Institute of Technology ISSN 1400-1179
SE-100 44 Stockholm ISRN/KTH/MMK/R-05/05-SE



1.3.2 Sequential systems
A more extreme case of variable geometry is sequential turbocharging. Instead
of varying the geometry of one charger the number of chargers is changed.
The reason for using sequential turbocharging is to widen the flow range for
the boost pressure required. Since still only one compressor stage is used it
does not necessarily increase the boost pressure.
Volvo tested sequential systems presented in an SAE paper in 1991 [1.26] as a
part of a methanol engine program. The engine was a six-cylinder unit and the
boost pressure target was as usual, slightly below 2 Bar abs. They state that a
parallel turbo system has around 30% lower inertia than a single turbo with the
same top end flow characteristics, and thus should have a benefit in terms of
response.

jon96ctd

where can I read more of that article you found? not sure why he talks about a parallel setup under the sequential section. yeah, the inertia or mass is reduced but so is the drive energy, you split it in half.