Rotary Car Club - Remote mount turbo?

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Originally Posted by jerd_hambone (Post 50400)

I wasn't trying to make a comparison. I just wanted to see if someone had done it.

And has already been answered.

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I stated that it would be an effective way of giving an NA engine a bit of extra go. I said nothing about trying to get the most power out of an NA.

But then what about the turbo, manifolds, wiring harness, sensors, an exhaust to mate with the turbo manifolds, TII hood for going top mount, or a big front mount?

Nickle and dime, nickle and dime.

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But look at it this way. Everyone used to say there was no way of getting power out of an NA FC. Everyone said it was impossible to turbo one without it blowing up within a few hundred miles.

But people still tried it and did it successfully.

Maybe the remote mount is the same way?

No one's saying that it won't work. It's the difference between less effective and effective. This exact thing was covered quite in-depth on my local forum.

Link Unfortunately you need to sign up to see that. For what it's worth here are some excerpts from it:

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Obviously I'm going to say I'm not a fan, but they work. For a smaller engine like I have it wouldn't make much sense, but with a large engine it is allowable to have some loss, I'm sure it's still better than a supercharger. I guess I have a hard time believing things couldn't be shifted around to put the turbo up front, but I can't really say. I don't see how you can say they're super efficient though, depending on what you mean by efficient. You lose a lot of turbine-driving energy through the exhaust piping to the turbo which means you have to size the hot side smaller than normal to get the same spool, which therefore results in a more restrictive hot side. On the other hand, people report such good results with them that I can't down them.

HPBooks has a book out called "Street Turbocharging" written by Mark Warner, P.E. and it talks about rear mount turbos in a positive way. It's a decent book.

^Drives an SVO

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Exactly larger engines have less loss from flowing exhaust air back 8 feet to the rear of the car than say an itty bitty 1.6 liter honda engine that can barely displace enough to spool a turbo right off the header. About all Ill comment on the subject till the end of the month.

^did a 600whp rear mount on a Vetter (C5 I think)

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And where does this pressure differential pre-turbine and post-turbine come from? It come from expansion of the gasses.

Turbines are modeled as isentropic expansion devices. The energy in the exhaust is contained in the form of kinetic, heat (thermal), and a little bit of pulsations from each cylinder. Almost all the energy comes from heat--the expansion of the hot exhaust gasses in a turbine.

So maybe the turbine doesn't "care" if it is hot or not, but the energy spinning it's wheel is coming from the heat in the exhaust. Read a thermodynamics book instead of google.

^He's just an asshole... well, a smart asshole, but an asshole none-the-less

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Jebus are you really that dense? Are you really implying that we are saying that egts entering a rear mounted turbo are the same temp as air entering the engine???

air enters at say 100F, exits at 1400F. So it cools down to 400F at a rear mounted setup. Heat is still being used to spin the turbo (and yes the turbo takes advantage of expanding gasses as heat energy as you said). Heat in the exhaust drives the turbo, but it really just complements the pressure that is already there.

Fuck...come take a ride in my turbo. I can spin up the turbo on a cold engine (using your "windmill" or whatever-you-call-it joke). Heat does play a major role...I'm just saying don't discount big airflow from big engines to small rear mounted turbos to overcome a moderate heat loss in a rear-mounted setup.

^Response to asshole, but raises some points one would need to consider.

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I'm aware of that Semantics Man. What I was referring to was the fact that there's still a lot of free hydrocarbons in the exhaust that continue to burn (hence heating and expanding the exhaust) even after they've exited the exhaust ports. Some cars position the turbo so close to the head that there are still lots of free hydrocarbons in the exhaust even after it passes through the turbine, especially at higher rpm. This is wasted energy. Ideally you want to give the exhaust gas enough time to burn off all those hydrocarbons (hence "fully" expanding the exhaust) but not enough time to start to cool off, so the ideal place for the turbine inlet would be the hottest part of the exhaust stream where it would have the most available energy, both thermal and kinetic.

I'm not arguing this point anyway, all I'm saying is that if you can reduce the amount of heat lost through the piping, you can reduce the amount of energy lost by moving the turbo farther downstream. The turbo still works, and works well, just not AS well as having it at the optimum position farther upstream, but it's a compromise, just like everything else.

^He was the OP

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Depending on the application, there's enough exposed piping on the trip back up to the engine to sufficiently cool a moderately compressed (say sub 6 psi) air charge. Some applications (like TT rear mount vettes) use a front mount intercooler because they don't have enough pipe, and enough air flow around that pipe, to cool it, but a lot of the truck setups do because they're longer and the pipe is run usually right beside the frame rail.

^OP Again

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I'd take the faster spool over the increased top end any day, but if you have >3.0L chances are you have sufficient power until the turbo spools to start with.

Just to comment on the heat issue, the fastest spooling header setup for a WRX/STi is STOCK because of it being cast iron and maintaining heat better than any of the aftermarket designs. It doesn't make quite as much power up top as the equal length designs, but is does have much better spool (read: over 500rpm compared to some of the headers). So what have we learned children? In real life, where you burn engineering textbooks, heat effects spool, not overall power output. Now everybody go throw out your tampons and move on to a different aspect of this setup.

^2007 SCCA Prosolo National Champion- D-Stock in a 2006 WRX

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You make a good point, a lot of the vehicles this really works well on are ones that have sufficient grunt down low to flame the hides from a dig without having to have the turbo(s) spooled up already, unlike the four bangers a lot of us are used to, which means that the little bit of lag actually isn't such a bad thing, because you wouldn't be able to put it to the ground anyway. Once you're moving it's less of an issue and if you have an auto or flat shift the thing the turbo will stay spun up like a squirrel on coke.

I never said it was good for all applications, or ideal, I just wanted to get some opinions. The biggest concern I can see is keeping heat in the exhaust stream, which you can combat with coatings and wraps. Not ideal, but it helps. If you have 8 feet of piping going back up to the engine, what's the major difference between that and having four feet on each side of a front mount intercooler? Same amount of piping, possibly fewer bends, and you're getting effectively "free" charge cooling without the need for the front mount. Sure, the fmic is going to cool much more effectively, but it's also another restriction and the charge isn't as hot to begin with because the turbo is cooler and it's not passing through all kinds of heat saturated metal plumbing under the hood.

The biggest concern I had at first was the oiling issue, but that seems to have been resolved by using a scavenging pump setup with failsafe circuitry.

^OP Again

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I'll repeat it again, for the sake of all turbo systems, read a fucking thermo book. "The fluid velocities in most turbines are very high, and the fluid experiences a change in its kinetic energy--however, this change is usually very small relative to the change in enthalpy, and thus it is often disregarded (p188 thermo book)". So, what DRIVES a turbine is the change in enthalpy...which wiki explains nicely.

^A-hole again

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I'm speaking from in-car experience with an EGT gauge, temps of the actual exhaust gases as they leave the cylinder, they cool a good 500+ degrees F in just a few feet. Idle might be 900-1100, but under WOT for a few seconds at least you will see 1300, 1400, etc., in a turbo car anyway, in fact 1800 is not unheard of in a serious turbo engine but is pretty ragged and unsafe. Now if we're talking NA engine, it can be a lot lower, but still above 1000F under full load I would guess.

Proper EGT measurements are taken 1-2" from the cylinder head exit point.

Hydrocarbons definitely burn off as suggested, but max EGT should occur around 14-15:1 as this is the point where the most energy is extracted from the fuel. Any richer or leaner and EGT should drop off, which of course is necessary to keep an engine together. I'd say it's hard to determine just how much energy from excess hydrocarbons goes into spooling a turbo in normal operation. Even under a two step, yes you have lots of excess fuel burning in the exhaust but the main thing you've done is cause combustion to occur IN the exhaust in the first place so this is a totally different mode of operation, the limiting also allows you to get mass flow way up by holding the throttle open long enough to get the turbo spinning.

I don't know if that makes any sense.

^SVO Boy again

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Why is this discussion even going on? If there is room under the hood, place the turbo there. If you are itching to have a turbo system and there is no room for one under the hood, contemplate a rear mounted setup. It has been done and does work in certain instances. However, I believe the underhood location would be best, and the engine bay heat is minimal at best if precautions are taken. Certainly less heat coatings would be needed to keep engine bay heat down than there would be needed for a rear mounted system. An evac system would have to be plumbed into the turbine exit, seems a bit retarded to think about doing that with a simple rear mounted turbo (why did that even get brought up anyway?).

^His car runs on alcohol.

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Dumped wastegates usually sound terrible but whatever, maybe not on that. It does look cool, but on a road car, it's going to get trashed from road dirt and debris, I'm sure it's no problem on that polished to death car there. I've seen some setups with the air filter right behind the rear wheel, which isn't good. I'd definitely be running some heavy steel mesh under the turbo as a guard.

Also, as I alluded to earlier, it would be nice to understand how a nice setup like the long tube equal length turbo header I posted, is able to achieve backpressure equal to or less than boost (it is possible in some cases, but not easy), this is called crossover and basically you should picture 80s Turbo Formula 1 cars.

^SVO

Specifically for a 13B we have a higher rate of exhaust gases being pumped into the system, however we are not at all that big on displacement so our exhaust volume would not equal out to the V8 or the V6's hell we're smaller than most I4's. Where we are able to support larger turbos comes from the Temperature differential (which then equates to the pressure differential since the physical volume of the gases is limited to the pipe) and unburnt hydrocarbons.

Any questions? Don't make me look up Engineering papers on this stuff.

I'm not looking to argue, the questions been answered.

Like I said, I wasn't saying as if it were going to more effective than a front mounted turbo, just saying it would be an effective way to boost an NA engine. Not an effective way to get a rotary power house built around an NA engine.

I'll probably just set one up on my Isuzu, but I wanted to see if anyone had done it.

Vex you really like arguing haha.

I would actually probably try a mid mount, but even a mid mount is considered a remote mount. I was thinking having it placed about where the Pipes split into the Y pipe, with a small intercooler, and a small pump to pump the oil. And a small turbo. Maybe like a small Mitsubishi Starion turbo. I have one of those laying around along with a BOV and a manual boost controller, boost gauge and AFR.

I do know that on a Miata it produced very good results with a small intercooler.

too bad Vex and I don't disagree on almost anything, I'm sure we'd have epic arguments.

I just want someone to do it and show results.

One other thing to consider is how long will it take to pressurize that amount of intake plumbing, and what effect will that extremely long intake tract have on off-boost performance (a very valid question, given that everything about the remote mount setup increases the spool time).

The short answer: Shitty low down torque numbers until the turbo starts to spool, and even then, the boost will come on slowly, as it now has a fairly huge space to pressurize; and it has to re-pressurize it every time you let off and allow the BOV to vent the pressure to the atmosphere...

Which raises another question: What kind of monster BOV would you need to vent that volume of pressure -without- allowing it to back-spin the turbine? Probably you would want one very near the turbo outlet, and another post-intercooler.

Most people have a loss of power at the low end, but as soon as it spools, It boosts back up rather quickly. Or so the videos and people who have them say.

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Originally Posted by vex (Post 50409)

Any questions?

Yeah, what the hell are you saying?? lol

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Originally Posted by classicauto (Post 50553)

Yeah, what the hell are you saying?? lol

My E-Wang is Huge!!!!