Compound turbo possible?

[Graham]

I drive a Cummins Dodge ram 2500 as well as my sonic, its common to add a larger turbo after the stock one to shove pressurized air into the stock turbo for it to handle the high pressure. I feel its possible on our cars since the stock turbo is part of the manifold and good sized for drivability... let's throw a big one on to get into the next stage of power capable out of this motor. Then we wouldn't have to buy a exh manifold and loose the bottom end power.. it gives the best of both worlds. What do you guys think? I can't see a reason that it wouldn't be perfect for this car!
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[Graham]

In these setups the larger (low pressure) turbo is after the smaller (high pressure) turbo in the exhaust flow. The larger turbo dissent compress the air as high so its after the smaller turbo, this is handy for us since our small stock turbo is also the exhaust manifold and since its band outlet it would be possible to just mount another turbo where the primary cat/downpipe is and then pipe that into the inlet of stock turbo. I really think this will be very cost effective and lots of room For gains.

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[SONIC1.4]

hm

 

[cndctrdj]

Rear mount

 

[Swordsmith]

I looked into this a little as well, and I felt the same way, that this would be a way to increase overall power without losing the low end. If it works as some say, it would literally be like having exactly our engine most of the time, but one with a bigger turbo when we're really balls out WOT, and the only down side would be the added weight of the new system. Well, that and the expense and difficulty of the install.

Some, though, said that no, really you wouldn't get much added performance at all out of this rig, and that the difficulty of doing the install would actually be very high, and also that the internals would probably not be able to handle the added boost.

I know I've had bad luck with the clutch and possibly the transmission, with merely Red Pill E85, so they may well be right, not that it's impossible (there are too many dual turbo vehicles out there already for me to believe that) but that it's going to be very expensive to upgrade to this level.

Seems to me though, that even if that's true, that the same would be true of a straight "bigger turbo" upgrade, but that there would be much less downside with this idea.

 

[Preloader]

Any added air or air pressure you achieve must still exit through the turbine outlet of the stock turbo after combustion.

A second turbo doesn't change that. And what's worse is that the spent exhaust of the added air charge will begin to "back-up" inside the cylinders if it can't escape freely, causing EGTs to rise quickly, which will in turn cause knock issues.

If someone wanted to try it, they should install an EGT sensor in the stock turbine housing.

 

[Swordsmith]

I'm not following you at all there, Pre. Of course the added air has to go thru the turbo housing, but... how is that any different from what happens now? What difference does it make if that was supplied at 14 psi, 22 psi, or 28 psi? Are you saying that there's some level of overpressure at which the outlet is simply too small, and that that isn't being hit at stock or even with a trifecta tune, but will at some point not much higher?

I'm more concerned about the incoming air than the outgoing air, it seems one complaint is that on one rig, the system dumps all boost midway thru an RPM cycle, so it can kick in the second turbo and start all over. Holy double turbo lag, Batman! But I don't see why that's a necessary design feature, and it seems there are some other layouts that don't share it.

 

[Opticon]

That's sequential not compound. And the lag can be completely avoided if the two turbos are sized correctly. Also, your exhaust manifold can be as much a restriction as anything in your intake tract, especially if you are planning to spool a second larger compressor at high RPM.

Forget ever using the stock manifold in any performance application. It seems rediculous to even consider retaining stock equipment for cost savings when discussing a setup this complicated/expensive.

 

[sx sonic]

I'm not following you at all there, Pre. Of course the added air has to go thru the turbo housing, but... how is that any different from what happens now? What difference does it make if that was supplied at 14 psi, 22 psi, or 28 psi? Are you saying that there's some level of overpressure at which the outlet is simply too small, and that that isn't being hit at stock or even with a trifecta tune, but will at some point not much higher?

I'm more concerned about the incoming air than the outgoing air, it seems one complaint is that on one rig, the system dumps all boost midway thru an RPM cycle, so it can kick in the second turbo and start all over. Holy double turbo lag, Batman! But I don't see why that's a necessary design feature, and it seems there are some other layouts that don't share it.

Pre's point is the stock turbo manifold and turbo are getting very close to flow restricted on a current fully modded sonic. Cramming more air in is all well and dandy until you reach the choke limit of the 1st turbo and well you can't eat if you don't sh!t.

 

[Preloader]

Pre's point...... well you can't eat if you don't sh!t.

Well said. That would be the perfect "tl;dr" to my post.

Turbine housing outlet being the the clogged toilet..... The compressor housing being the next biggest problem.

A single, better power matched, turbo would be a less expensive/complicated solution to the input=output equation. And while the stock exhaust manifold obstacle sounds intimidating, the soon to come options won't be so costly/involved as they seem. Ex: modded mani + K03 ~ $500-700 (plus ~$300 of intake/dp parts)

Also, if "turbo lag" is such a concern, then one might consider a twin scroll turbo. But "turbo lag" is often confused with "boost threshold". Neither of which should be a problem with a frikken 1.4 liter engine with a reasonably sized turbo.

 

[Scot]

I'm already considering how to modify the twin-scroll turbo from the LTG (2.0L DI) to work with 1.4L

 

[Opticon]

But "turbo lag" is often confused with "boost threshold". Neither of which should be a problem with a frikken 1.4 liter engine with a reasonably sized turbo.

Heavy breather mods + a slightly larger turbo would make this car less peaky, more fuel efficient, stronger up top, and a general peach to drive.

Unless, you know, the owner was running E85 and aiming for 300hp. Then it would turn into a hot mess.

opcorn:

 

[Graham]

It would work as long as the engine can handle the back pressure. The stock turbine outlet on the he351 (Cummins) turbo is quite restrictive! Yet compound setups increase power capability up to well over 500rwhp reliably. Thanks in increase of over 30% over what the stock can do alone while keeping egts in check. Maybe doing the turbo upgrade from Vermont tuning and put that in a compound setup. Either way force feeding a small turbo makes it more capable. There's plenty of room and the secondary turbo would work!

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[Opticon]

Your truck ran fuel about as volitile as bathwater. The 1.4t is MANY times more prone to preignition than a diesel engine. The fuel in a 20psi charge will light off if you look at it wrong. That's why anybody trying to run even a reasonable amount of timing advance has to switch to E85.

The heat generated by a second compressor + the restriction of a stock exhaust manifold WILL melt pistons.

 

[Scot]

Your truck ran fuel about as volitile as bathwater.

 

[Preloader]

Unless, you know, the owner was running E85 and aiming for 300hp. Then it would turn into a hot mess.

opcorn:

 

[Opticon]

But don't go changin'.

Not for me. Not for anyone.

 

[Graham]

Yes diesel is much less volatile. I know they're different animals. How turbo chargers work is universal though. The ease of adding a secondary charger is there and modding our factory turbo and adding a secondary would support more in and more out. Obviously there will be a limit on the 1.4 and also on the fuel as well. E85 would be required at elevated boost levels.

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[Graham]

Bathwater doesn't have more energy density than gasoline like diesel does. Not volatile, yet.. its the most powerful of any fuel. And most reliable. Diesel is hard to get out of your system once you drive a performance one. I'm waiting for the Cruz diesel to come out in the manual... its got a lot of potential
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[$ub$onic]

Diesel is indeed highly addicting. My current diesel project is a slightly built Mercedes 5 cylinder In a ford ranger. So much addiction