Rear Turbocharging the W123
Rear Turbocharging the W123
So I'll pose this question: why not rear turbo our cars?
There are a few benefits to doing so over the traditional manifold mounting. One is that the turbo itself is going to be cooler mounted in the back underneath the car than it will in the engine compartment. And vice versa, the underhood temps will be far cooler than they would with a hot turbo adding to the sauna, which doesn't do any good for the long life of anything in the compartment, including the motor and turbo themselves.
The second is that if you have your piping up to the turbo underneath the car made out of aluminum, there is an intercooling effect produced without the need to actually use an intercooler. Due to the cooler turbo, which is itself being cooled while the car is in motion by the air passing underneath the car, while the intercooling offered by by pipe is likely to be less than a FMIC, it won't need to cool the charge air as much in the first place.
The third is that moving the turbo to the back is much the same as relocating the battery to the trunk as concerns weight distribution.
The fourth is that charge cooling no longer takes cooling potential away from the engine's radiator, and that AC can be retained if desired.
The challenge is really just packaging, and I think there's enough room for a turbo plus a standard 'rice' muffler afterwards. On the west coast it would be easy to run a cone filter underneath the car, people living in areas with heavy rain would have to find a way to not inhale water.
There is a company called STS turbo who does this for a variety of vehicles, and I think they've had some decent amount of success. Their kits don't seem like they scream 'oh, this is the cheapest, easiest route to go' either, as far as comparing them to 'standard' turbo kits. I figure this makes about as much sense on an already-turbo'd car as it would to convert an NA car.
Anyway, I think it's worth looking into. Depending on how you routed it you could even have the charge tube go up the driver's side, through a FMIC under the bumper,, over to the inlet of the intake manifold (double cooled if you include the pipe). Making the post-turbo exhaust as low backpressure as possible is suddenly cake. Likely you'd adapt the stock exhaust to an NA 617 manifold and just run a straight perforated muffler afterward.
If one were willing to remove the spare tire well, you'd have all the room you'd need to do whatever. Weld a flat, stiff steel sheet into the top first, then cut the well out.
Someone needs to run with this, and maybe I'll be the guy, who knows...
- CID
CID Vicious
11-18-2009, 03:27 PM #1So I'm looking at the various methods of obtaining more power and/or lower temperatures out there...A/W ICs, A/A ICS, FMICS, and I've seen some people having difficulty adapting the turbo to the flange on our manifolds, etc.
So I'll pose this question: why not rear turbo our cars?
There are a few benefits to doing so over the traditional manifold mounting. One is that the turbo itself is going to be cooler mounted in the back underneath the car than it will in the engine compartment. And vice versa, the underhood temps will be far cooler than they would with a hot turbo adding to the sauna, which doesn't do any good for the long life of anything in the compartment, including the motor and turbo themselves.
The second is that if you have your piping up to the turbo underneath the car made out of aluminum, there is an intercooling effect produced without the need to actually use an intercooler. Due to the cooler turbo, which is itself being cooled while the car is in motion by the air passing underneath the car, while the intercooling offered by by pipe is likely to be less than a FMIC, it won't need to cool the charge air as much in the first place.
The third is that moving the turbo to the back is much the same as relocating the battery to the trunk as concerns weight distribution.
The fourth is that charge cooling no longer takes cooling potential away from the engine's radiator, and that AC can be retained if desired.
The challenge is really just packaging, and I think there's enough room for a turbo plus a standard 'rice' muffler afterwards. On the west coast it would be easy to run a cone filter underneath the car, people living in areas with heavy rain would have to find a way to not inhale water.
There is a company called STS turbo who does this for a variety of vehicles, and I think they've had some decent amount of success. Their kits don't seem like they scream 'oh, this is the cheapest, easiest route to go' either, as far as comparing them to 'standard' turbo kits. I figure this makes about as much sense on an already-turbo'd car as it would to convert an NA car.
Anyway, I think it's worth looking into. Depending on how you routed it you could even have the charge tube go up the driver's side, through a FMIC under the bumper,, over to the inlet of the intake manifold (double cooled if you include the pipe). Making the post-turbo exhaust as low backpressure as possible is suddenly cake. Likely you'd adapt the stock exhaust to an NA 617 manifold and just run a straight perforated muffler afterward.
If one were willing to remove the spare tire well, you'd have all the room you'd need to do whatever. Weld a flat, stiff steel sheet into the top first, then cut the well out.
Someone needs to run with this, and maybe I'll be the guy, who knows...
- CID
'78 300D, OM617.912: 4spd manual, TB03 at 10PSI, 26*BTDC, DV's turned, HVAC, emissions system removed, e-fan, short ram, 3" downpipe to straight exhaust, W126 Bendix brakes, MR2 Spyder seats. 2890lbs
A turbo is an efficiency device that relies on the hot exhaust gases to achieve its efficiency. With all the boost piping, and not to mention the nightmare of routing the system, turbo servicing, oil lines, an exhaust mount that will support the weight of a turbo, all you would gain is monster turbo lag, extra weight, hard to access and more venerable turbo, and dirty air filter. Good idea at first glance, but in reality the benefits of remote turbo systems cant outweigh their drawbacks.
'78 300D, OM617.912: 4spd manual, TB03 at 10PSI, 26*BTDC, DV's turned, HVAC, emissions system removed, e-fan, short ram, 3" downpipe to straight exhaust, W126 Bendix brakes, MR2 Spyder seats. 2890lbs
(11-18-2009, 03:27 PM)CID Vicious why not rear turbo our cars?Rear turbos are a marketing gimmick. They are very inefficient on g@ssers and would be ballast on a diesel.
Most of the heat and velocity energy in the exhaust is dissipated well before it reaches the turbo. By the time it gets there, the turbo is working more on the pressure differential across the turbine than the exhaust's energy. Thats why you see that STS's kits use much smaller turbines than kits that mount directly on the engine.
They also require a scavenge pump to return oil to the sump, or their own oil supply.
Quote:There is a company called STS turbo who does this for a variety of vehicles, and I think they've had some decent amount of success."Success" is relative. Like K&N, the "tornado", fuel line magnets and HHO "generators", you don't have to make a product that is actually good or works effectively to sell a lot of them and make big money, you just have to market it in a way that convinces a lot of people to buy it.
The only advantage I can see to the system is not using engine bay space.
Personally, I'd rather cut out a firewall section and mount the turbo next to the transmission in a doghouse at the passenger's feet.
ForcedInduction
11-18-2009, 05:02 PM
#3
(11-18-2009, 03:27 PM)CID Vicious why not rear turbo our cars?Rear turbos are a marketing gimmick. They are very inefficient on g@ssers and would be ballast on a diesel.
Most of the heat and velocity energy in the exhaust is dissipated well before it reaches the turbo. By the time it gets there, the turbo is working more on the pressure differential across the turbine than the exhaust's energy. Thats why you see that STS's kits use much smaller turbines than kits that mount directly on the engine.
They also require a scavenge pump to return oil to the sump, or their own oil supply.
Quote:There is a company called STS turbo who does this for a variety of vehicles, and I think they've had some decent amount of success."Success" is relative. Like K&N, the "tornado", fuel line magnets and HHO "generators", you don't have to make a product that is actually good or works effectively to sell a lot of them and make big money, you just have to market it in a way that convinces a lot of people to buy it.
The only advantage I can see to the system is not using engine bay space.
Personally, I'd rather cut out a firewall section and mount the turbo next to the transmission in a doghouse at the passenger's feet.
I guess what I'm saying is that it'd be worthwhile on a turbo conversion for a car with already decent hp - a Chevy V8 truck, for instance, has the ride height, undercarriage room, etc to allow for a fairly problem free installation, and it isn't hard to get hp out of a boosted LS V8 that already has at minimum 290hp. Our motors, on the other hand, are still an unknown quantity for the most part, at least if you live west of the Baltic. Meanwhile, the closest I've seen anyone come to claiming V8-ness in their power delivery is running cut DVs with ridiculous EGTs, or Forced but he's got the most tuned 617a that I've seen. Maybe I'll try that when I have a few 617s just lying around but since I only have one I'll pass for now.
Meanwhile, a Goodwrench truck 350 makes 260hp and 350lb-ft with a wimp cam, crap heads, etc. It's just a starting point, whereas unless you're going Myna that's about the plateau of the 617a that I see without huge investment. And I'm thinking that for less than it would cost to get one of those running with a 5 speed Toyota trans behind it, I could get a pulled LT1 or even LS1 with a 6 speed and call it a day. I'd just have to have it all at once...I'll probably end up with a used engine at first, to be honest, in any case, but the Goodwrench is a decent benchmark - new longblock and 350 lb ft for 1500 bucks.
I'm still going to mess with the 617 but I realized that I quite enjoyed the 240D as-is, and that even a stock 617/manual will probably be quite enough for a daily driver, and the V8 car would be for just going fast. I want to be able to have some fun on four wheels more than I feel like being some kind of pioneer, I guess.
Anyway, if I want to even keep what I got, better get back to work...
CID Vicious
11-19-2009, 04:27 PM #5I think it's probably a better idea for conversion to a stock block NA gasser. A light pressure turbo at 5psi is going to be at least as powerful as a 5psi centrifugal SC. One of those wouldn't be worth shit on our turbo motors - maybe on the NA versions though. Meanwhile, a 5-6psi Vortec turns a 250hp 5.0l V8 into a 375hp engine, we're running 9-10psi and getting hp levels that could be bested by a twenty year old DOHC 2.0l NA gasser. It really doesn't make much sense for our cars, come to think about it. maybe as a way of compound charging?
I guess what I'm saying is that it'd be worthwhile on a turbo conversion for a car with already decent hp - a Chevy V8 truck, for instance, has the ride height, undercarriage room, etc to allow for a fairly problem free installation, and it isn't hard to get hp out of a boosted LS V8 that already has at minimum 290hp. Our motors, on the other hand, are still an unknown quantity for the most part, at least if you live west of the Baltic. Meanwhile, the closest I've seen anyone come to claiming V8-ness in their power delivery is running cut DVs with ridiculous EGTs, or Forced but he's got the most tuned 617a that I've seen. Maybe I'll try that when I have a few 617s just lying around but since I only have one I'll pass for now.
Meanwhile, a Goodwrench truck 350 makes 260hp and 350lb-ft with a wimp cam, crap heads, etc. It's just a starting point, whereas unless you're going Myna that's about the plateau of the 617a that I see without huge investment. And I'm thinking that for less than it would cost to get one of those running with a 5 speed Toyota trans behind it, I could get a pulled LT1 or even LS1 with a 6 speed and call it a day. I'd just have to have it all at once...I'll probably end up with a used engine at first, to be honest, in any case, but the Goodwrench is a decent benchmark - new longblock and 350 lb ft for 1500 bucks.
I'm still going to mess with the 617 but I realized that I quite enjoyed the 240D as-is, and that even a stock 617/manual will probably be quite enough for a daily driver, and the V8 car would be for just going fast. I want to be able to have some fun on four wheels more than I feel like being some kind of pioneer, I guess.
Anyway, if I want to even keep what I got, better get back to work...
The hotter turbos run, the more efficient they run. Putting them on the end of a 4m long heat shedding exhaust is just dumb.
In California, you can't cobble together a junkyard turbo system together and just waltz through inspection with it. This isn't a problem for our cars, but I already said the idea of rear turboing a 617 is dead. A car that does have to get inspected, however, you'd need a turbo kit with a CARB number compatible for the application. For many applications these kits don't exist. However, this does not apply if the turbo system is downstream of the cat.
If the motor sees 5 psi out of a turbo that would be running 10psi otherwise, it will still make a lot more power than it would without the boost. 5psi is safe for most applications without internal modifications, whereas 10psi is often pushing it anyway.
This would be easy to use on a pickup truck to get more power, the packaging is a challenge in cars because of the vastly reduced underbody area.
There is an advantage when you can cut a 5.0l+ truck engine's single rear exhaust and find a turbo adequate to get 5-6psi in this rear mount application. It's relatively simple to accomplish and the piping to the TB can be accomplished by any exhaust shop. It's an advantage when you can get turbos good for this application for practically nothing because they're too big to be used by the smaller motors that make up the majority of the 'performance turbo' crowd, or they're too old and out of date. A V8's exhaust, especially in a single pipe, will be more than enough to spin a correctly sized turbo.
Meanwhile, what's the comparable system? Duals on flipped manifolds? Larger single turbo mounted in the engine compartment (that's a joyous mount and piping job, I'm sure). Turbocharging any engine that wasn't configured for it from the factory is a challenge, period. I wonder if all of those STS customers feel ripped off, seeing as how, even with a lack of 'efficiency' all of the cars would still be more powerful than stock, regardless...
CID Vicious
11-19-2009, 04:59 PM #7It's easier for a couple of reasons:
In California, you can't cobble together a junkyard turbo system together and just waltz through inspection with it. This isn't a problem for our cars, but I already said the idea of rear turboing a 617 is dead. A car that does have to get inspected, however, you'd need a turbo kit with a CARB number compatible for the application. For many applications these kits don't exist. However, this does not apply if the turbo system is downstream of the cat.
If the motor sees 5 psi out of a turbo that would be running 10psi otherwise, it will still make a lot more power than it would without the boost. 5psi is safe for most applications without internal modifications, whereas 10psi is often pushing it anyway.
This would be easy to use on a pickup truck to get more power, the packaging is a challenge in cars because of the vastly reduced underbody area.
There is an advantage when you can cut a 5.0l+ truck engine's single rear exhaust and find a turbo adequate to get 5-6psi in this rear mount application. It's relatively simple to accomplish and the piping to the TB can be accomplished by any exhaust shop. It's an advantage when you can get turbos good for this application for practically nothing because they're too big to be used by the smaller motors that make up the majority of the 'performance turbo' crowd, or they're too old and out of date. A V8's exhaust, especially in a single pipe, will be more than enough to spin a correctly sized turbo.
Meanwhile, what's the comparable system? Duals on flipped manifolds? Larger single turbo mounted in the engine compartment (that's a joyous mount and piping job, I'm sure). Turbocharging any engine that wasn't configured for it from the factory is a challenge, period. I wonder if all of those STS customers feel ripped off, seeing as how, even with a lack of 'efficiency' all of the cars would still be more powerful than stock, regardless...
(11-19-2009, 01:31 PM)dervdoc seen an m5 twin tubo'd using this method, made sick bhp no problem
M5 engine and OM61x have so many things in common
That engine makes over 500hp and "enough" torque stock, so it requires only a minimal boost to produce that 700hp (small turbos). As it has nice power even before boost and is a high revving engine, the lag is not consired a problem. The turbos would be mounted in the engine compartment if there only were space. So it works "ok" in that application.If it would have been a good idea, it would have been used..
(11-19-2009, 01:31 PM)dervdoc seen an m5 twin tubo'd using this method, made sick bhp no problem
M5 engine and OM61x have so many things in common
That engine makes over 500hp and "enough" torque stock, so it requires only a minimal boost to produce that 700hp (small turbos). As it has nice power even before boost and is a high revving engine, the lag is not consired a problem. The turbos would be mounted in the engine compartment if there only were space. So it works "ok" in that application.If it would have been a good idea, it would have been used..
(11-19-2009, 04:59 PM)CID Vicious Meanwhile, what's the comparable system? Duals on flipped manifolds? Larger single turbo mounted in the engine compartment (that's a joyous mount and piping job, I'm sure). Turbocharging any engine that wasn't configured for it from the factory is a challenge, period. I wonder if all of those STS customers feel ripped off, seeing as how, even with a lack of 'efficiency' all of the cars would still be more powerful than stock, regardless...
The only reason to fit a turbo on the tailpipe is because it can't physically fit in the engine bay.
Remember turbo setups that can work on a petrol which throws a massive amount of waste heat out the exhaust don't work well on a diesel with much cooler exhaust. Diesels run smaller turbine housings than petrols (based on compressor size) for a very good reason.
Those customers would feel ripped off if they were shown how much better performance and fuel economy they'd get with the same boost from a manifold mounted turbo.
(11-19-2009, 04:59 PM)CID Vicious Meanwhile, what's the comparable system? Duals on flipped manifolds? Larger single turbo mounted in the engine compartment (that's a joyous mount and piping job, I'm sure). Turbocharging any engine that wasn't configured for it from the factory is a challenge, period. I wonder if all of those STS customers feel ripped off, seeing as how, even with a lack of 'efficiency' all of the cars would still be more powerful than stock, regardless...
The only reason to fit a turbo on the tailpipe is because it can't physically fit in the engine bay.
Remember turbo setups that can work on a petrol which throws a massive amount of waste heat out the exhaust don't work well on a diesel with much cooler exhaust. Diesels run smaller turbine housings than petrols (based on compressor size) for a very good reason.
Those customers would feel ripped off if they were shown how much better performance and fuel economy they'd get with the same boost from a manifold mounted turbo.
(11-20-2009, 04:15 PM)Kiwibacon Those customers would feel ripped off if they were shown how much better performance and fuel economy they'd get with the same boost from a manifold mounted turbo.
People that buy fuel line magnets don't feel ripped off?
ForcedInduction
11-20-2009, 06:24 PM
#10
(11-20-2009, 04:15 PM)Kiwibacon Those customers would feel ripped off if they were shown how much better performance and fuel economy they'd get with the same boost from a manifold mounted turbo.
People that buy fuel line magnets don't feel ripped off?
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