Out of curiousity...(Intercooler/Turbo question)

[MrMazda92]

Out of curiosity, since I haven't found out much online... Why exactly don't people run a small intercooler(pre-cooler, if you will) between their exhaust and their turbo, and then a second intercooler(after-cooler if you will) between the turbo and the intake?

It would cool the air from the exhaust before compressing it further, and the exhaust pressure should be enough to push it through the pre-cooler without significantly slowing the charge. This would better allow the air to compress, without any drawbacks that I can see... In addition, you should be able to run smaller intercoolers, which should reduce the losses of intercooling in the first place.

Thoughts, opinions, ideas?

It just came to me when I was reading through a ZE-T worklog, and it reminded me of the idea of a downstream turbo...(brilliant btw, utterly brilliant!)

[Inodoro Pereyra]

Hmmm...you seem to be confused.

There are 2 different circuits on a turbo.

The exhaust from the engine goes to the turbine, and, then (through whatever exhaust setup you have), to the atmosphere. You want the exhaust gases to be as hot as possible, when they reach the turbine.

The intake air comes from the air filter to the compressor (the "low temperature turbine" if you will), then to the intercooler (if you use one), and from it, to the intake manifold.
If your question is why don't you put an intercooler between the air filter and the turbo, the answer is simple: the intake air is pretty much at room temperature at that point, so an intercooler (or "precooler" as you called it) wouldn't do much to cool it down. You could use a refrigeration system (like the second A/C we talked about), but even that would be much more efficient if put after the turbo, as the temperature differential (between the intake air, and the environment) is much greater.

[RS_OBD'oh_2]

^
exactly.

People drop lots of $ to ceramic coat the turbo mani, hot side of the turbo and down pipes (including heat wrap) to ensure the heat stays in the components. The hotter the exhaust, the better (to an extent). Exhaust velocity and thermal eff' is key.

[Josh]

IMO - Ceramic coating and header wrapping your Turbo mani and DP is not a good idea.

Why do you want your Turbo HOT? I am not understanding this concept. It does not matter. the cooler the better.

A Procharger is gear driven Turbo and it sees virtually no heat compared to exhaust driven Turbocharger. Why would turbochargers come water cooled if you needed them hot? HEAT KILLS THE LIFE of your turbo, as well as your engine. The covers and wrap's in many cases are to reduce the heat in the engine bay and surrounding areas when next to other components. many use heat or "header" wrap because they don't want people to see their crappy welds. Heat will kill your turbo and your engine, that's why most Turbo motors use Sodium filled valves like in the BPT and GTR motors, also another good reason most OE turbos are oil and water cooled vs majority of aftermarket turbos only being oil cooled.

What about the remote turbo kits?
the turbo is located at the end of your exhaust system, to maximize space and reduce heat. you don't even need an intercooler with many of these kits. They will see 500 to 800 degree reduction in heat even more from that of a "normal" turbo set up.

I think understand what the OP is after, and i dont think a intercooler for the exhaust would work, a nice tubular equal length turbo manifold is your best option, and a log style turbo mani run much hotter than an equal length mani will.

[MrMazda92]

IMO - Ceramic coating and header wrapping your Turbo mani and DP is not a good idea.

Why do you want your Turbo HOT? I am not understanding this concept. It does not matter. the cooler the better.

A Procharger is gear driven Turbo and it sees virtually no heat compared to exhaust driven Turbocharger. Why would turbochargers come water cooled if you needed them hot? HEAT KILLS THE LIFE of your turbo, as well as your engine. The covers and wrap's in many cases are to reduce the heat in the engine bay and surrounding areas when next to other components. many use heat or "header" wrap because they don't want people to see their crappy welds. Heat will kill your turbo and your engine, that's why most Turbo motors use Sodium filled valves like in the BPT and GTR motors, also another good reason most OE turbos are oil and water cooled vs majority of aftermarket turbos only being oil cooled.

What about the remote turbo kits?
the turbo is located at the end of your exhaust system, to maximize space and reduce heat. you don't even need an intercooler with many of these kits. They will see 500 to 800 degree reduction in heat even more from that of a "normal" turbo set up.

I think understand what the OP is after, and i dont think a intercooler for the exhaust would work, a nice tubular equal length turbo manifold is your best option, and a log style turbo mani run much hotter than an equal length mani will.

This is almost exactly where I went with this idea... And a remote turbo kit is the same thing as a "downstream turbo", sorry if I used the wrong name.

I just don't see why you would want to superheat the air, right before you have to compress it... I can't get my head around that You want to compress HOT air, and then run it through an intercooler, which slows it down, and robs you of power? Something about that just doesn't fit. I understand that Turbos are DESIGNED to tolerate the temperatures, but that doesn't necessarily mean they LIKE the temperatures...

I may be off on this you guys, but I really can't grasp the idea of it... Compressing HOT air vs compressing cold air... That alone makes it look like a no-brainer to me.

[MrMazda92]

I just grasped something that makes me feel like a complete idiot. The exhaust gas isn't forced back into the engine, and I knew that already. Still... A turbo is made of metal, so I can understand why you wouldn't want to cool the air too much beforehand(it loses velocity, and won't power the turbine as well), but there will still be heatsoak into the intake charge.

[Josh]

Downstream turbo, remote turbo - tomato, tomado..

Now correct me if I am wrong here guys, but the hotter the air the less dense it becomes. The colder the air the more dense, basic principles from flight school. So, if the air entering the turbo is hot you can cram more into it to be compressed. Then when it passes through the intercooler becomes colder and more dense it increases the volume of air into the intake mani?

If that is correct the same principle would apply if you ran colder more dense air into the turbo, then cooling it even more before it hits the intake mani.

Truth is at 700 to 1400 deg F coming out of the exhaust ports at the manifold, does it really matter that much at these temps

700 to 1400 deg at the motor is a big difference to the 300 to 500 you would see at the tail pipe. When measuring the EGT after the turbo vs before, on average, you will see a reduction in exhaust temps of 500 deg F. I for one will always want it cooler vs hotter. A cool running engine makes for a happy one

[RS_OBD'oh_2]

I read up on this every day. Hotter air has more velocity and thats what you want in your exhaust. If there was a cooler before the turbo, the back pressure would be stupid and counter productive.

Down stream turbo is another story all together. They can be a great idea if engine bay space is limited.

[Inodoro Pereyra]

The exhaust gas isn't forced back into the engine, and I knew that already. Still... A turbo is made of metal, so I can understand why you wouldn't want to cool the air too much beforehand(it loses velocity, and won't power the turbine as well), but there will still be heatsoak into the intake charge.

Exactly! That's the point I was trying to make.
You want the exhaust side to be as hot as possible (like RS accurately said, within reason) for a very simple reason: heat is energy. And you want all the energy from the exhaust (or most of it) to move the turbine, not to be dissipated into the environment.
Of course there are downsides to that, but there are also other things to consider, and, all in all, that's the best compromise.
For example, you could make the shaft longer, and get the 2 sections of the turbo farther apart from each other. But that would make the setup heavier, and harder to install (in a place where typically, you have serious room constraints), and, most importantly, would make the resonant frequency of the shaft lower. That may not be important on a crankshaft, for example, but, on a shaft that's spinning upwards of 150 000 rpm, it becomes critical. Also, a longer shaft would have a higher rotational inertia (because it's heavier), which would increase lag.

Remote turbos are, like everything else, a compromise. They allow you to install a turbo setup when you don't have the room for it in the engine compartment, but, in exchange, you get less power from a given setup, and higher lag times, precisely because of that extra distance between the engine and the turbine (the hot side of the turbo). Then again, if you look at remote turbo setups, you will see all of them use standard, short shaft turbos (which goes to my previous point about shaft length).

Bottom line, turbos have been around for more than a century, and a big deal of engineering has gone into them. Besides that, the hot side of the turbo is precisely what makes it expensive (because manufacturers have to use expensive, exotic alloys, like inconel that are, also, difficult to machine), so, if there was a way to make the exhaust gas work cooler, they'd jump on it immediately.

[Josh]

Makes complete sense, very informative guys!

[MrMazda92]

This is the kind of thing that should be stickied, I haven't seen much of this on the internet... Granted, I never put a lot of time into studying FI, It's still been very informative.

[RS_OBD'oh_2]

I subscribe to a car mag (I know this is not for everyone). Other than being sick and tired of seeing evos and sti's, you really can't go wrong. There is a lot of information out there, and I feel better paying for tried and true info (including parts tesing on the dyno) than trusting the net. I do not plan on plugging the mag, but brand has already won one of our members an LSD. This type of thing is a little basic for forced induction, so I would suggest a little outside reading (while on the crapper).

[Evo_Spec]

I subscribe to a car mag (I know this is not for everyone). Other than being sick and tired of seeing evos and sti's, you really can't go wrong. There is a lot of information out there, and I feel better paying for tried and true info (including parts tesing on the dyno) than trusting the net. I do not plan on plugging the mag, but brand has already won one of our members an LSD. This type of thing is a little basic for forced induction, so I would suggest a little outside reading (while on the crapper).

i assume DSport? i just subscribed to that a couple days ago after buying like 6 issues, they're super awesome and last months engine issue was fantastic

[RS_OBD'oh_2]

mmmmmaybe

but you've been to my place.. you may have already seen some here. That's cheating

[Evo_Spec]

mmmmmaybe

but you've been to my place.. you may have already seen some here. That's cheating

actually no i didn't >.<
why didn't you show me! i've been missing out!

sorry, went off topic.
uhhhhh turbos do spinny stuff and makes heat and magic unicorns that you put into the combustion chamber and blow up to make power =D