Rear mounted turbo...

[JGTurbo]

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Sorry for the slow reply. It's dead week for me (week before finals). I'm working on four projects and also cleaning up a little TD03 turbo (~60-140hp) that arrived on Monday.

Cooling of gases does decrease pressure.

But not if you run the cooler gas through a smaller hole.

You can obviously size the machinery to work as a rear mount, it has been done. But if you were to take that same turbo and mount it under the hood where it belongs, you would see more boost and less lag.

Along with less lag, you would see a restricted top end of the powerband. It would be like running too small an A/R. As far as seeing more boost, I'd say more boost sooner, yes, but I believe a rear mount turbo can still run the pressure ratio up to a level where the compressor efficiency is the limiting factor. I see your point on efficiency, but I've never heard of a properly sized turbo running out of exhaust energy.



I think I'm done disagreeing with you two (for the moment ). I am very impressed by your responses. I'll read your posts again and do some more thinking on the subject. If I find something that I can't pass up I might dig into this again.

Thanks again for the great discussion guys!

 

[JGTurbo]

Sorry Falcon Ranch, it's about all I can do to keep up with these engineers! I'll try to answer some of your questions soon. I've got to get back to work at the moment.

 

[tjnavyblue]

Just put the turbo under the hood where it belongs.

Or on the the roof.

 

[80broncoman]

I've went over this whole thread in the last 30 mins and I can't belive you guys that have been around turbos missed this completly.

That turbo in the pics he has, has NO wastegate!! is this not really really needed on a gas engine to limit boost pressure?

 

[StrangeRanger]

IIRC T03s do not have an integral wastegate like the T04s do.

Actually a wastegate isn't necessary.
If you use what used to be called a blow-off valve but is now usually called a pop-off valve to avoid confusion with the anti-surge device that is now called a blow-off, you don't need a wastegate.

The wastegate senses output pressure from the compressor and when the setpoint is reached, it dumps the exhaust causing the turbine to spool down. The pop-off simply acts as a safety valve to dump the compressor output but does nothing to dump the exhuast flow or slow down the turbine.

 

[80broncoman]

I just remember seeing turbos on diesels and that they had nothing contol boost at all.

 

[wallaka]

IIRC T03s do not have an integral wastegate like the T04s do.

Actually a wastegate isn't necessary.
If you use what used to be called a blow-off valve but is now usually called a pop-off valve to avoid confusion with the anti-surge device that is now called a blow-off, you don't need a wastegate.

The wastegate senses output pressure from the compressor and when the setpoint is reached, it dumps the exhaust causing the turbine to spool down. The pop-off simply acts as a safety valve to dump the compressor output but does nothing to dump the exhuast flow or slow down the turbine.

Still need a wastegate IMO. If the turbo overspeeds, bad things happen.

 

[JGTurbo]

I've went over this whole thread in the last 30 mins and I can't belive you guys that have been around turbos missed this completly.

That turbo in the pics he has, has NO wastegate!! is this not really really needed on a gas engine to limit boost pressure?

I believe that issue was addressed earlier. I recommended that he install a wastegate flange but hold off on the wastegate until he can see how the turbo works. The turbo he has is fitted with a small compressor and large turbine, so there's a chance that a wastegate will not be needed.

 

[Falcon Ranch]

As much as I want to start this turbo install, the only thing holding me back is the oil return pump...over $200 bucks for one...be patient guys, I will install this monster!

I so much appreciate every ones interest in my RMT install.

 

[Mrbrink]

I just remember seeing turbos on diesels and that they had nothing contol boost at all.

diesels also don't have butterfly valves to control the engine speed. they can take as much air as you wanna shove into them and won't rev unless the injector pump is putting fuel to it

 

[TCIC 300ci superbeast]

is that why they dont have waste gates? i all ways though it was strange that they didnt have one.

 

[Mrbrink]

delete

 

[CobraSix]

FR,

I found this:

http://www.rbracing-rsr.com/oilsystems.htm

They have a lot of options for you to look into. There is even a remote twin turbo install shown on a 95-98 mustang (not sure which) towards the bottom of the page. I was looking for a 'boost' pump for my truck since it's oil pump is dieing and with 320k miles on the engine, it isn't worth pulling and fixing it (gotta pull the whole engine).

 

[rust collector]

Just for fun, I figured I could add a little comment about that turbo.
Kamaz is one of the bigger russian truck makers, who also makes engines for...other stuff...like gensets, pumps, and ural trucks.

Anyway, most of the older v8 turbo diesels they made had was 10.8liters, and around 200-250hp.
(I am just guessing they would get an "old" turbo if they fitted it to an unimog)

Or maybe they just swapped in the kamaz engine too???

Anyway, back to the topic!

 

[I66coupe]

No trurbo experience here at all. Reading this thread has been great!

So, what I'm getting from this is that the front mounted turbo is going to be more efficient and more responsive. Some of that can be retreived by careful selection of the A/R (ratio?). Not all but some. The rear mount is not the choice for fast response drag racing but should work fine for street driving.

So, If i'm looking for a decent increase in driving power but I'm not too concerned with fast launch from a dead stop, the rear mount should work just fine (not optimal, but should work fine anyway). This will clean up the engine compartment and likely reduce under hood temps. I would guess that the pressure pipe leading to the carb might cool the charge somewhat but probably not much as the air would moving through it quickly and the pipe would heat up under use and would reach a point where it just can't reduce the charge temp anymore. Seems at higher boost, an intercooler would be needed anyway. Steel is more effective at radiating heat than AL, so using a steel pipe might be better. You could also weld on some strapping to act as cooling fins and perhaps make it more effective.

Why would a return pump for the oil be needed? Seems to me the oil would have no choice but be forced back to the engine by the oil being pumped from the engine to the turbo. It has nowhere else to go.

 

[StrangeRanger]

No trurbo experience here at all. Reading this thread has been great!...Why would a return pump for the oil be needed? Seems to me the oil would have no choice but be forced back to the engine by the oil being pumped from the engine to the turbo. It has nowhere else to go.

Any backpressure on oil draining out the turbo's center cartridge will cook it in nothing flat. The oil has to be removed. If you have an underhood turbo, you can usually mount it high enough that a gravity line will drain to just above the liquid level in the sump or to the timing cover. With a rear mounted turbo, it is impossible to get it high enough for gravity to work and a scavenge pump is required

 

[tjnavyblue]

There are virtually no reasons to do a rear mounted turbo on these cars aside from trying to do something unique. Which is a fair enough reason I guess. If you wanna clean the engine compartment, hide the wires and trunk mount the battery. For many, HAVING a turbo under the hood would be considered "cleaned up". 8)

 

[I66coupe]

The reason I would do a RMT is that I don't want that turbo under the hood. I want the engine compartment as stock looking and open as possible.

I still don't get the need for an oil return pump. You mention the oil draining out. It just drains out? Wouldn't the oil pressure force it out? If so, it would be forced back to the engine. Any back pressure would be minimal. There should be no restriction in the return line.

 

[StrangeRanger]

ANY BACKPRESSURE WHATSOEVER will destroy the center bearing cartridge of a turbo. The turbo has to be either mounted high enough that it can be fitted with a return line which drains by gravity to a level higher than the liquid level in the sump or it has to be equipped with a scavenge pump. The turbo is spinning at something like 30-40,000 RPM. At the shear rates that those sorts of RPMs produce, the oil breaks down instantaneously if it is not flowing freely and radiply. Once the oil breaks down the center cartridge is cooked.

 

[tjnavyblue]

I think the issue is that there are currently no sealed bearing designs that can withstand the RPM of a turbo shaft. So they make do with a sort of semi-sealed shaft that gets a steady supply of oil. If the oil is forced to stay in the bearing cartridge for any length of time (as Ranger said) it is compromised, (and so is the turbo most likely). Many recommend oil return drain lines in excess of 1/2 inch from the turbo to the engine.