Questions about remote mounted turbo

I need to move the turbo on my swap forward about three feet. I will then have to mount it to the chassis rather than the motor. So can I use flexible exhaust pipe on the hot side? I presume there will be not as much pressure as on the cold side, but more than a typical exhaust through a muffler. Or is there another way to isolate the turbo? Also, I will loose a bit of heat over the three feet. Is that important? I see that mentioned in turbo discussions, but I feel that it is exhaust velocity that provides the charge and heat is a byproduct and not a necessity. 

Lastly, I will have a three foot drain line. I have less slope than Cummins intended but it will still be over a foot. But I am wondering it there is a possibility for oil to back up when cold and blow the turbo seals. 

Thoughts? Anything else I should be considering?

Bump. 

No one knows remote turbos? I may have to go find a forum of people who build weird stuff in a grassroots kind of way. I'm sure there is one out there if I look. 

Since the rear mounted turbo kits seem to work well, this shouldn't be an issue what you are doing. I would look at using flex couplers, more durable than flex pipe is.

The drain shouldn't be an issue as long as there is a down slope. Don't think there should be an oil backup as long as the crankcase ventelation system works.

The heat is very important.  But you shouldn't have any trouble moving it a few feet.  Will it be optimal?  No.  Is anything besides a purpose-built race car running in an unregulated class optimal?  No.  Years ago a company called STS built kits to turbo C5 Corvettes at first and then branches out into other applications.  The twin turbos were at the very rear of the car.  All the "know it all" types on the internet had a field day with how it would never work because the exhaust gasses would be too cold by the time they went through 8 to 10' of pipe.  Guess what?  They worked REALLY REALLY WELL.  Maybe not as well as they would have under the hood with only several inches for the exhaust to travel, but it was a workable solution.  Not sure what ever happened to STS.

BTW, got that 12V swapped into the A-Team van yet?

I got nothing practical for you but the loss of heat does mean lost energy available for the turbo. The velocity of the exhaust stream comes from pressure that builds up because the hot and expanding gas is restricted by the turbine/nozzle. Less heat = less pressure = less power available to drive the compressor.

As 81cpcamaro says, it's done all the time and been done at least since WWII (B-17 and P-47 come to mind), so probably fine with less heat but I'd think about insulation just because I'm a nerd.

I think you'll find that the turbine will act considerably larger than its design; later boost, less turbine torque.

As long as you have adequate slope for the drain you should be OK.  If you have room, you can put a little sump below the bearings as a buffer and oversize the return.

I was going to wrap the pipe anyway, but thanks for the explanation of how the heat affects power.  I expect I will not notice a few less PSI anyway.  And flex couplers sound like just what I need! I did not know they were a thing. 

Is this a diesel? Usually high EGTs are the limitation on diesel performance, so moving the turbo away a bit might actually help, at the cost of maybe being a bit lazier to build boost. But unless you've got a crazy big turbo it should basically be making some amount of boost any time you're on the throttle, so maybe that even won't be too big of a deal.

Like mentioned above, the application is important. Generally, mounting the turbo farther away increases heat (energy) used to drive the turbine. At extreme lengths, like rear mounted, you would need a smaller than optimal turbine housing. But- hugging the block is not optimal either. Great for packaging, heat loss, and emissions. But it prevents an optimal header design, which can more than make up for the increase length. Look at the engine bay for any high powered turbo car, the turbo is usually mounted far from the engine to optimize the header design. And not just drag cars- rally cars need to have very responsive engines. I’d bet this turbo would be considered remote if you straightened out the header...

And 3 feet isn’t that long. I’d guess many factory turbo Subaru’s have the turbo mounted almost that far, at least from the passenger side head. Not optimal,  but it worked. They did mount the turbos lower down and closer to the exhaust ports later. 

This is for your motorhome right? 3ft isn't likely to see much of a drop in temp when the whole package is shoehorned into a tight engine bay. It's not ideal, but it's not going to be a night/day difference in feel or performance.

When mounting the turbo to the vehicle, could you have some rubber bushings on the mounts to provide a bit more compliance and help to isolate the turbo a bit from the vibrations of the body?

This is the turbo for my motorhome, yes. It is an ISM Cummins. I think the flex joint is the answer to my biggest question. I see now that they are quite common on some automotive applications, and certainly would be less prone to leaking. As for lag, not a problem. The main objective is to spend much less time on long grades so spool time is a rounding error.  Still a little concerned with the drain back.  Most remote applications seem to use pumps and I do not want that.  I think I will warm it up well before taking off. 

Turbo lag seems to be not a problem with a well done remote mount. They stick the after market turbos for the after market Toyoburu twins by the back of the car without undue lag, apparently.

I'm thinking with the exhaust volume of the ISM will help reduce the impact of the remote mounted turbo.   That's a big air pump.

As I recall, the clever loophole these setups exploit is that because they're downstream of the cat(s), they don't need to deal with getting an emissions exemption, which is a big deal.

Regarding the flex joint as a solution... If you're describing the thing that's a stainless bellows covered by stainless woven mesh, get a long one. In a different application, I attached one end to my header and the other end to the frame of the car, and the stainless bellows eventually work-hardened and cracked. A longer one would have less flex.

In reply to kb58 :

Noted, thank you.

bearmtnmartin (Forum Supporter) said:

I need to move the turbo on my swap forward about three feet. I will then have to mount it to the chassis rather than the motor. So can I use flexible exhaust pipe on the hot side? I presume there will be not as much pressure as on the cold side, but more than a typical exhaust through a muffler. Or is there another way to isolate the turbo? Also, I will loose a bit of heat over the three feet. Is that important? I see that mentioned in turbo discussions, but I feel that it is exhaust velocity that provides the charge and heat is a byproduct and not a necessity. 

Lastly, I will have a three foot drain line. I have less slope than Cummins intended but it will still be over a foot. But I am wondering it there is a possibility for oil to back up when cold and blow the turbo seals. 

Thoughts? Anything else I should be considering?

I've got an ISX (450hp and 1650 lb ft) in a different application and have really liked it a lot.

But, that doesn't help here :)  I also have a mid-mount turbo on a V8.  Total distance from each exhaust manifold to the single turbo is at least 3 feet, but probably closer to 5 without measuring it.  These are my answers to your questions, based on my personal experience:

My vehicle has a transaxle, so the transmission is in the rear, and I mounted the turbo to it.  That minimizes the movement between the turbo and the motor.  But, I still used a stainless steel mesh flex coupling in the pipe to allow for differing thermal expansion between the transaxle and the exhaust, and to ease installation.  My experience with flexible exhaust pipe is that it begins to leak and doesn't stand up well to repeated movement.  Maybe you'll have better luck, but I would avoid using it in a turbo system.  The mesh flex coupling, on the other hand, has been problem free so far.

Heat retention is very important.  If your exhaust gases cool, they will condense into a smaller volume, which means less velocity through the pipe.  The next effect is that the turbo will take longer to build boost, which affects your tune and when you have power available.  Initially, I started with all of my hot side exhaust components, including the turbine housing, ceramic coated.  I then tuned and dyno'd everything.  It performed well, or so I thought.  Then, I wrapped everything from the single exit pipe of each exhaust manifold all the way to the turbo, and put a turbo blanket on the turbo.  Retuned and re-dyno'd.  The difference was noticeable in regular driving and by the numbers.  Boost built sooner, quicker, and recovered quicker on down shifts.  The size of the pipes obviously has a huge impact, but wrapping the pipes and turbine also made a big difference.  I highly recommend it.  I don't have any direct comparison between cheap wrap and expensive wrap, but I went for the more expensive wrap and blanket, with no regrets.

Without knowing anything else at all about your system or setup, I can only add that if you're not already planning on it, you may want to get the signal for your wastegate from the intake manifold after the throttle plate, and not from the compressor outlet.  You will definitely lose some pressure between those two points, and the differential will change based on ambient temperature and air flow over the components.  The net effect will be that you'll have less boost in the manifold than the wastegate thinks that you're getting.

All other things being equal, and I know nothing about the draining requirements for your turbo other than the standard requirements for any oil cooled/lubricated turbo, I don't see any issues at all with a remote mount in your particular application.  Done right, you probably won't even notice the difference most of the time.

Good luck and let us know how it works out!

In reply to Bulsher :

Now that I think about it, all of the rear mount turbos that I've seen have a dedicated oil pump.  And cheaper ones tend to fail much sooner, so an in vehicle low pressure alarm for that loop is critical.  Even if you try to get away without the pump, you may want to consider a pressure monitor/alarm for the turbo oiling loop.

Mine is water cooled, using the engine cooling loop, so that was not an issue for my setup.

Bulsher said:

In reply to Bulsher :

Now that I think about it, all of the rear mount turbos that I've seen have a dedicated oil pump.  And cheaper ones tend to fail much sooner, so an in vehicle low pressure alarm for that loop is critical.  Even if you try to get away without the pump, you may want to consider a pressure monitor/alarm for the turbo oiling loop.

Mine is water cooled, using the engine cooling loop, so that was not an issue for my setup.

 

Turbos require gravity assist to drain.  The oil gets whipped into dirty mayonnaise in the bearing assembly, so they need a fairly large return and as close to a straight shot down to the oil pan as practical.  Even if you used engine oil in a remote setup you would still need the turbo to drain into a sump and use a scavenge pump to return that to the engine.

I think the setup being proposed would work fine without a scavenge, as long as the turbo was mounted relatively high up and the oil drain didn't have any long horizontal runs.

Boost_Crazy said:

 Look at the engine bay for any high powered turbo car, the turbo is usually mounted far from the engine to optimize the header design. And not just drag cars- rally cars need to have very responsive engines. I’d bet this turbo would be considered remote if you straightened out the header...

The tubes are that long on the WRCars because it gives the recirculated air enough time to mix with and combust with the exhaust gases, usually run over-rich just for this afterburner effect.

Note the small diameter tube over the radiator.  It connects to a computer controlled valve on the turbo compressor's outlet, and runs to ports on the underside of the header tubes as close as possible to the head.  They're dumping the some of the compressor outlet into the exhaust system to keep the turbo spooled when not accelerating.

I wonder if you could achieve this with a Diesel   Probably the EGTs are not high enough, and turbos destined for Diesels tend to not be very tough for temperature.

Pete. (l33t FS) said:

 

Turbos require gravity assist to drain.  The oil gets whipped into dirty mayonnaise in the bearing assembly, so they need a fairly large return and as close to a straight shot down to the oil pan as practical.  Even if you used engine oil in a remote setup you would still need the turbo to drain into a sump and use a scavenge pump to return that to the engine.

 

I think the setup being proposed would work fine without a scavenge, as long as the turbo was mounted relatively high up and the oil drain didn't have any long horizontal runs.

 Yes, exactly.  Sump, plus oil pump, for most rear turbos (not mine).  In those cases, the turbo drain is lower than the oil level in the main oil sump, so they require the pump to move the oil back to the main sump.

And I agree, the drop for this particular setup should be enough for the oil to drain out of the turbo.  Personally, I would still want the pressure gauge and/or alarm.  At least temporarily until I had confidence in it.  But, probably not necessary.

Try to keep the location the same distance from the engine for any EGT sensor used by the ECU. 

It may be in the exhaust manifold, which means you won't have to do anything with it, but if it's in a pipe  you'll want to try to keep it as close to the original distance is possible.