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post #1 of 44 (permalink) Old 12-30-2004, 10:12 PM Thread Starter
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Twin-turbo potential...

I know using twin turbo's by having two turbo's of the same size is less efficient than using a single larger turbo. I've also heard using two turbos, one of a larger size and a smaller size has potential to increase performance. I know this is the prefered setup to create astronomical boost levels in diesel applications. Does anyone have information on using two turbo's of a dissimilar size on a gas engine? Could it offer an advantage over a single turbo... potentially with the smaller turbo coming to boost faster and the larger turbo providing more boost at higher rpms?

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post #2 of 44 (permalink) Old 12-31-2004, 02:35 AM
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"the smaller turbo coming to boost faster and the larger turbo providing more boost at higher rpms"

That's the advantage right there, if of course they're sized properly.
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post #3 of 44 (permalink) Old 12-31-2004, 05:58 AM
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A single will make a crapload more power, the twins are typically more streetable for the reason BlackCat mentioned, less lag.
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post #4 of 44 (permalink) Old 12-31-2004, 08:30 AM Thread Starter
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Quote:
Originally Posted by SanDiegoLXBird
A single will make a crapload more power, the twins are typically more streetable for the reason BlackCat mentioned, less lag.
A single large turbo will make more HP... But isn't this kind of like the debate between a screw type supercharger and a centrifugal? Yeah, the centrifugal might have more HP in the upper RPM range but the screw type will be faster, especially on the street.

Do supra's have two equal sized turbos?

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post #5 of 44 (permalink) Old 12-31-2004, 08:32 AM Thread Starter
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Quote:
Originally Posted by BlackCat94
"the smaller turbo coming to boost faster and the larger turbo providing more boost at higher rpms"

That's the advantage right there, if of course they're sized properly.
How would the pipe routing look on something like that?

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post #6 of 44 (permalink) Old 12-31-2004, 01:29 PM
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Quote:
Originally Posted by Stoltz13
How would the pipe routing look on something like that?
I wouldn't know for sure, all of the trucks & heavy equipment I've driven only had a single turbo.

Do they run the exhaust through the small, then into the big one?
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post #7 of 44 (permalink) Old 12-31-2004, 04:07 PM Thread Starter
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Quote:
Originally Posted by BlackCat94
I wouldn't know for sure, all of the trucks & heavy equipment I've driven only had a single turbo.

Do they run the exhaust through the small, then into the big one?
I would assume it to be the opposite... but either way wouldn't the smaller turbo be a restriction at higher RPM's that way? Could they somehow run them parallel or bypass one?

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post #8 of 44 (permalink) Old 12-31-2004, 04:13 PM
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Quote:
Originally Posted by Stoltz13
A single large turbo will make more HP... But isn't this kind of like the debate between a screw type supercharger and a centrifugal? Yeah, the centrifugal might have more HP in the upper RPM range but the screw type will be faster, especially on the street.

Do supra's have two equal sized turbos?

If twins are quicker, why is it that Outlaw Street and several other Drag Racing classes are dominated by big singles? Riddle me this.
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post #9 of 44 (permalink) Old 12-31-2004, 04:38 PM Thread Starter
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Originally Posted by SanDiegoLXBird
If twins are quicker, why is it that Outlaw Street and several other Drag Racing classes are ted by big singles? Riddle me this.
Oh, I don't disagree... but they are purpose built cars rarely driven on the road. I'm just wondering if a twin setup would offer more for your daily driver by delivering more lower end power. And using two unequal size turbos could give you the best of both worlds.

Answer this, why do you think high performance diesels use twins (ie: pulling tractors)... they build more than 100lbs of boost by using two unequal size turbos in a series.

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post #10 of 44 (permalink) Old 12-31-2004, 05:42 PM
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Quote:
Originally Posted by SanDiegoLXBird
If twins are quicker, why is it that Outlaw Street and several other Drag Racing classes are dominated by big singles? Riddle me this.
Class rules for one thing. Twin turbo's are generally considered to be dual power adders. Most of the time only a single power-adder is allowed or you go into a higher class.

Complexity for another. If a single turbo will get the job done and turbo response time is not an issue, then the single is the superior choice. Once you add the requirement of fast response to big power that's when twins begin to look good.
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post #11 of 44 (permalink) Old 12-31-2004, 06:37 PM
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just use a larger single.. to reduce lag time.. add nitrous injection to spool the turbo up quicker at low rpms while racing... i know a few people who do that with much success..
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post #12 of 44 (permalink) Old 12-31-2004, 06:58 PM Thread Starter
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Quote:
Originally Posted by Parker Dean
Class rules for one thing. Twin turbo's are generally considered to be dual power adders. Most of the time only a single power-adder is allowed or you go into a higher class.

Complexity for another. If a single turbo will get the job done and turbo response time is not an issue, then the single is the superior choice. Once you add the requirement of fast response to big power that's when twins begin to look good.
Probably would make more sense to using nitrous and a single large turbo... but I would be interested in seeing how they set up a sequential twin turbo...

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post #13 of 44 (permalink) Old 12-31-2004, 07:01 PM
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yeah, a hole shot would spool the turbo faster, as well as cooling the air charge, and adding more hp.

a twin turbo setup in series has the smaller turbo closest to the exhaust, then leads to the larger turbo. When the smaller one spools up sooner, it throws faster exhaust at the larger turbo, spooling that one up as well. But the smaller turbo can be a restriction, as the exhaust impeller is smaller than the larger turbo's.

Drag turbo setups are way different than street setups would ever be. Have you ever seen the size of drag turbo's? They're huge. The gearing in the transmission is set up for drag race, as is the motor. The boost comes in at high rpm because they have time for it to. On a street setup, you'd want power at the lower rpm's, which a properly spec'd single turbo could very well do. These days a twin turbo setup is more wood factor than anything else. That, and two smaller turbos are easier to come by, and sometimes cheaper than one large one.

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post #14 of 44 (permalink) Old 01-04-2005, 09:18 AM
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*sigh*

(digs out his turbo knowledge)

A number of you are on the money on some things. A number of you are not.

A single biggie turbocharger will have lots of topflow but lots of lag. Drag cars don't care so much about that, because they already spin off the line, so the lag is helpful. By the time they get traction, they are also getting boost. Now, the lag would be so bad that it would take longer than that, except for the fact that bigie turbos are often paired with biggie exhaust.

See, something that is very different with turbocharging from natural aspiration is that a naturally aspirated engine needs some backpressure in the exhaust piping. A turbocar does not. In fact, you want it as wide open as possible. Why? Well, the exhaust manifold sees the turbine housing as a major restriction, and creates more backpressure than you will ever need.... so having a wide open exhaust after it is ideal.

Using nitrous to spool a turbo is for the really crazy tube chassis drag setup or for the inexperienced. Running the proper exhaust pipe size is how you *should* be doing it.

Now, in the case of twins versus single, you have to be more specific about what turbos are being used in a twins setup. Sure, if you run twin T25's, a huge T66 will outflow them still. Of course the twin T25's will outspool it.

But what if you are running twin T3 turbos? This changes things dramatically, and now you have to consider that, while a T3 cannot flow as much as a T66, two T3's can.

Here is why: Consider a car with a T3 single vs. twin T2's. The T2 is only good for about 14 psi, after that it's overspun (meaning it has to spin so fast that it generates enough heat to cancel out the comression with heat expansion, meaning it makes no more boost). The T3, on the other hand, is good for about 18 psi properly tuned.

Bare minimum on most external wastegates is 7psi (that's what the spring is tensioned to). SO... imagine TWIN T2's. Running the minimum boost, they are each pushing 7psi, in parallel, into the same piping, for 14psi. At 7 psi they arent making much heat, so are well within their efficiency range. Yet have superior spool to the T3, and less crazy exhaust pipe requirements. As you push them to 10 psi, you are now still within their safe zone, but now pushing *20* total. Now you outflow the T3, still in efficiency range of the T2 flow maps, and still with superior spool. See?

Of course, it's not actually 7psi + 7psi = 14. You lose a pound or two. But still the strategy works better.

NOW, finally, there's the issue of compression. Look guys, these V8's aren't low compression like built turbo V8's, or even like factory four and six cyllinder turbocars. Typically those cars run anywhere from 7.5:1 to 8.5:1 and no higher. Some carefully prepped engines run 9:1 but they don't run alot of boost, only about 7-10psi, and generally are more torquey than big HP numbers. Big HP cars run lower compression, high boost, big exhaust. I don't see many of you ordering 8:1 pistons any time soon for a turbo project, I see many of you interested in bolting something on. IN that case, expect to run 7psi, not the biggie 20 psi of the OEM turbocars. Trust me, 7psi is alot! You have to consider that before you reach positive pressure, you first have to defeat the vacuum an engine generates. So 7psi is alot! 7psi on something like even a '94 Romeo will probably make it haul like no tomorrow. If anything it might even be the better choice of engines for it, since the smaller ports would act as velocity stacks durring turbo spool time.

If I had the time I would do it. Twins are easier on a V8 than running a crossover pipe for a single. Actually for the same reason, twins are probably going to be cheaper. Twin T2's. I can pick up a T2 for 50 bux a piece in perfect condition. They are small so they should find easy room under the side of the head. Together they have the potential, without intercoolers, of safely putting out 14psi (7 each), and WITH an intercooler (or twins, come cheapo DSM sidemounts, one for each), can put out 12-14psi each for a total of well more than I will ever need.

I think you'd see this undesirable '94 engine wake up and run good numbers.

Say, anyone have any pictures of a '94 exhaust manifold?

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post #15 of 44 (permalink) Old 01-04-2005, 04:43 PM Thread Starter
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Quote:
Originally Posted by Arro
*sigh*

(digs out his turbo knowledge)

A number of you are on the money on some things. A number of you are not.

A single biggie turbocharger will have lots of topflow but lots of lag. Drag cars don't care so much about that, because they already spin off the line, so the lag is helpful. By the time they get traction, they are also getting boost. Now, the lag would be so bad that it would take longer than that, except for the fact that bigie turbos are often paired with biggie exhaust.

See, something that is very different with turbocharging from natural aspiration is that a naturally aspirated engine needs some backpressure in the exhaust piping. A turbocar does not. In fact, you want it as wide open as possible. Why? Well, the exhaust manifold sees the turbine housing as a major restriction, and creates more backpressure than you will ever need.... so having a wide open exhaust after it is ideal.

Using nitrous to spool a turbo is for the really crazy tube chassis drag setup or for the inexperienced. Running the proper exhaust pipe size is how you *should* be doing it.

Now, in the case of twins versus single, you have to be more specific about what turbos are being used in a twins setup. Sure, if you run twin T25's, a huge T66 will outflow them still. Of course the twin T25's will outspool it.

But what if you are running twin T3 turbos? This changes things dramatically, and now you have to consider that, while a T3 cannot flow as much as a T66, two T3's can.

Here is why: Consider a car with a T3 single vs. twin T2's. The T2 is only good for about 14 psi, after that it's overspun (meaning it has to spin so fast that it generates enough heat to cancel out the comression with heat expansion, meaning it makes no more boost). The T3, on the other hand, is good for about 18 psi properly tuned.

Bare minimum on most external wastegates is 7psi (that's what the spring is tensioned to). SO... imagine TWIN T2's. Running the minimum boost, they are each pushing 7psi, in parallel, into the same piping, for 14psi. At 7 psi they arent making much heat, so are well within their efficiency range. Yet have superior spool to the T3, and less crazy exhaust pipe requirements. As you push them to 10 psi, you are now still within their safe zone, but now pushing *20* total. Now you outflow the T3, still in efficiency range of the T2 flow maps, and still with superior spool. See?

Of course, it's not actually 7psi + 7psi = 14. You lose a pound or two. But still the strategy works better.

NOW, finally, there's the issue of compression. Look guys, these V8's aren't low compression like built turbo V8's, or even like factory four and six cyllinder turbocars. Typically those cars run anywhere from 7.5:1 to 8.5:1 and no higher. Some carefully prepped engines run 9:1 but they don't run alot of boost, only about 7-10psi, and generally are more torquey than big HP numbers. Big HP cars run lower compression, high boost, big exhaust. I don't see many of you ordering 8:1 pistons any time soon for a turbo project, I see many of you interested in bolting something on. IN that case, expect to run 7psi, not the biggie 20 psi of the OEM turbocars. Trust me, 7psi is alot! You have to consider that before you reach positive pressure, you first have to defeat the vacuum an engine generates. So 7psi is alot! 7psi on something like even a '94 Romeo will probably make it haul like no tomorrow. If anything it might even be the better choice of engines for it, since the smaller ports would act as velocity stacks durring turbo spool time.

If I had the time I would do it. Twins are easier on a V8 than running a crossover pipe for a single. Actually for the same reason, twins are probably going to be cheaper. Twin T2's. I can pick up a T2 for 50 bux a piece in perfect condition. They are small so they should find easy room under the side of the head. Together they have the potential, without intercoolers, of safely putting out 14psi (7 each), and WITH an intercooler (or twins, come cheapo DSM sidemounts, one for each), can put out 12-14psi each for a total of well more than I will ever need.

I think you'd see this undesirable '94 engine wake up and run good numbers.

Say, anyone have any pictures of a '94 exhaust manifold?
Is it possible the inherent efficiency of one single turbo out weigh the reduced lag of two singles?

Does compounding, a larger turbo and smaller turbo in a series, provide realistic and bigger HP potential? And would it be streetable or would it only work for a drag car?

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post #16 of 44 (permalink) Old 01-04-2005, 04:56 PM
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[QUOTE=Arro]I can pick up a T2 for 50 bux a piece in perfect condition. They are small so they should find easy room under the side of the head. Together they have the potential, without intercoolers, of safely putting out 14psi (7 each), and WITH an intercooler (or twins, come cheapo DSM sidemounts, one for each), QUOTE]

look under your hood again and tell me you can fit a turbo on each side and you are going to stir something up here to drive people insane

the 4.6s footprint is as wide as a Ford 460

it barely fits... slap headers on, and there is even less room... now way you are going to fit extra plumbing right there for a turbo

on the driver side there is this nifty thing called a steering column that further reduces clearance

Please please please look carefully before posting stuff like that dude.. i don't care how small a t2 may be... thats why SirWill is trying his setup with a front mount near the bumper
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post #17 of 44 (permalink) Old 01-04-2005, 07:12 PM
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yeah on a mustang there is a lot more room on either sides of the heads for turbos, or in the fender wells because those are roomy too. For the mn12...aint gonna happen. Way too tight of an area in there. The mid-length headers for the 4.6 nearly touch the side wall. Down by the cats there is more room than beside the heads, but probably still not enough to fit turbos there, its still a very tight spot. On the v6 and 5.0 there's room down by the cats for turbos, and I bet you could do something with that, but the 4.6 practically fills the entire engine bay of the mn12.
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post #18 of 44 (permalink) Old 01-04-2005, 08:07 PM
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JamesD, you're close but mine is in the rear....near the bumper.

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post #19 of 44 (permalink) Old 01-04-2005, 09:28 PM
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I'm looking at it more closely and thinking of more southward.... low. No extra plumbing, just using the present collection points, and intercepting it. As much as you may feel I am underestimating the space problem, I am not entirely certain it can't be done.

This engine was rebuilt in my buddy's shop, and put back into the Bird. I've had some quick glances at it, I admit nothing serious but nothing from memory seems out of possibility. I might have to have them low slung, but so what? Again they are T2's and mayb you don't realize how small they really are...??

I'm not spouting off I promise, I just think it may very well be possible the way I envision it.
I won't be able to lift it and snap pics any time soon but my biggest concern is the orientation of the turbos. But anything is doable with enough ingenuity.

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post #20 of 44 (permalink) Old 01-04-2005, 09:38 PM
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quick question, whats your vw sportcoupe? Is it a g60 corrado? My roommate has one.

Anyways, if you're going to go twin turbo with t2's it might not be too bad for power actually, seeing as how twin t2's pushed a stock motor split-port 3.8 mustang into the 11's. But on a heavier car and larger displacement they might not be as efficient. Should be interesting to say the last. I think it might be easier to mount them in the fender wells. t2's are small enough to fit there on an mn12. Plus less pipe routing for the intake tubing. if you put a turbo back behind the motor you'll need your exhaust in/out and intake in/out pipes all running back there, which could be very cluttered. But hey, if you think its doable go for it. I'd like to see it done.

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post #21 of 44 (permalink) Old 01-04-2005, 09:44 PM
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Yeah it's a G60, yellow, and for $ale if you're interested. Please, help me get rid of it!
lol

Fenders might be a better choice of location, so noted.

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post #22 of 44 (permalink) Old 01-04-2005, 10:37 PM
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Arro

You can't add pressures like that. Each turbo is suppling a flow of air (flow rate, cfm whatever) The flow rates will relatively add creating a higher pressure after both turbos.

Maybe I am taking the wrong thing away from your post. But you can't have 7 psi after each turbo and then dump them into a tube with a pressure greater than 7. It would flow back to the turbos.

Just use flow instead of pressure it will make me feel better.

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post #23 of 44 (permalink) Old 01-04-2005, 11:16 PM
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that and saying a turbo supplies such and such pressure is innacurate since boost is a measure of backpressure and the amount of displacement, mods, intercooler, etc will change it.
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post #24 of 44 (permalink) Old 01-04-2005, 11:51 PM
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Yup...so will pinhole leaks in your tubing from the turbo to the motor......don't ask how I know.

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post #25 of 44 (permalink) Old 01-04-2005, 11:58 PM
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Quote:
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JamesD, you're close but mine is in the rear....near the bumper.
bah.. i knew it was ONE of the bumpers heh

and i just saw a lot of plumbing in the front
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post #26 of 44 (permalink) Old 01-05-2005, 12:24 AM
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Quote:
Originally Posted by Arro
*sigh*

See, something that is very different with turbocharging from natural aspiration is that a naturally aspirated engine needs some backpressure in the exhaust piping. A turbocar does not. In fact, you want it as wide open as possible. Why? Well, the exhaust manifold sees the turbine housing as a major restriction, and creates more backpressure than you will ever need.... so having a wide open exhaust after it is ideal.
To clarify...

True, you want an open exhaust system on a turbo car, but not simply because the turbine is the restriction...the turbine extracts energy from the exhaust based on a difference in temperatures and pressures. The greater the pressure drop accross a turbine, the more energy is extracted from the exhaust and is transfered to rotational power, which we all know causes much fun to be had on the compressor side of the turbo.

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post #27 of 44 (permalink) Old 01-05-2005, 02:58 PM
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Quote:
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Arro

You can't add pressures like that. Each turbo is suppling a flow of air (flow rate, cfm whatever) The flow rates will relatively add creating a higher pressure after both turbos.

Maybe I am taking the wrong thing away from your post. But you can't have 7 psi after each turbo and then dump them into a tube with a pressure greater than 7. It would flow back to the turbos.

Just use flow instead of pressure it will make me feel better.
That's not what Turbonetics said. Granted, as I said earlier, it's not actually 7+7=14. It's less. But it's certainly more than 7. And of course as Thomas stated, there are other factors to consider, such as overall airpath volume, port size, intercooler volume and flow properties and heat exchange efficiency, intake air temps, etc. etc. My comments establish a baseline concept, certainly not a final word on the real world results.

As far as pressure backing outward in reverse through the turbocharger, that's actually called "stacking", and it's very hard for that to happen when the exhaust is pushing the turbine at high speeds. There's alot more pressure in the exhaust manifold than in the induction path, even boosted. No way that will defeat the spin of the exhaust side, the shaft would twist itself sooner. Which sometimes happens on old, small turbochargers. But not usually.

How else do you think parallel systems work? Or even sequential setups that utilize a smaller turbo in the lower RPM ranges, and then transition it to a bigger one for the upper end? It would flow right outta the little one if that was true.

Stacking generally occurs when you let off the throttle quickly, the throttle plate shuts, the RPM's drop, the turbine sees a sudden reduction of pressure, and suddenly there's a compressor wheel spinning allthis boost into a short, closed system (terminating at that closed throttle plate), and it starts to halt the shaft assembly in the turbocharger, so it can indeed vent out the pressure backwards through the turbo compressor inlet. If you have a blow-off valve, properly tensioned, that doesn't happen (or happens very little in much higher boost). Of course, stacking on a MAP based system is no big deal (well, it does put alot of stress on the turbocharger's thrust bearing and shaft), but on an airflow metered setup, it can cause some erroneous data to be sent to the ECU. Bad. So just run a BOV. Or two.


Now as far as the Bird goes, I'm going to the shop it's resting in later this evening (still waiting for the lien sale to complete). I'll bust out the biggie floor jack and get a good look underneath, take some measurements with my handy-dandy tape measure, and get a good, solid feel for the feasability of what I have in mind. I'm taking many of you serious when you worry over space constraints, but I'm confident there's a likely solution other than locating them in front. Actually I like the fender idea but it means custom manifolds. I am hoping to ghetto-style this thing, using modified stock manifolds. The airflow plumbing from turbos to intake mani is actually the least of my concerns.

Why am I toying with this idea? I know there are easier ways to make power, I've read quite a bit on here, but I love turbocharging, and why make the T-Bird my only nonturbo? Twin turbo V8? It just has an awesome sound to it (Sir William will agree I'm sure).

I also have to figure out intercooler location and choice, based on a 94/95 front bumper with a Xenon front lip (I hope I find a decent used one soon).

So yeah, it's not easy stuff, I get that. I wouldn't even be able to do it now anyways, maybe come summer. Still, I want to look into it.

-J. Arro
1994 Ford Thunderbird 4.6L LX V8
Bone stock engine, *partial* Xenon Body kit.
http://www.cardomain.com/ride/750285
PLZ HELP ME FIND A XENON FRONT LIP

I also own some Turbo Dodges, a couple turbo DSM's, a few turbo Nissans, a Toyota pickup, and a supercharged VW sportcoupe.

Last edited by Arro; 01-05-2005 at 03:07 PM.
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post #28 of 44 (permalink) Old 01-05-2005, 11:33 PM
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That's not what Turbonetics said. Granted, as I said earlier, it's not actually 7+7=14. It's less. But it's certainly more than 7.
I am very surprised they would say that. I would assume them to be reputable.

I just kind of skimmed the rest of your post, but what you are calling stacking is not what I am refering to, and that seems to be correct.

There are 2 ways to look at it, and maybe I misread before, hell I probably did, sequetion turbos would do that, one builds 7 psi boost and dumps that to a larger one that makes another 7psi of boost and then yes you end up with 14.

But two in parrallel (sharing a single outlet) will be seeing the same pressure before and after each turbo. That is all I was trying to get across. Everything else looks pretty dang good.



I have always wondered if it would be beneficial to run sqeuntial IC's after each turbo in a squential turbo setup, if you will. That would be a nightmare to plumb, but 2 stage compression like that in refrigeration gains efficency (power) or single setups.

Julian

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post #29 of 44 (permalink) Old 01-05-2005, 11:40 PM
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As far as pressure backing outward in reverse through the turbocharger, that's actually called "stacking", and it's very hard for that to happen when the exhaust is pushing the turbine at high speeds. There's alot more pressure in the exhaust manifold than in the induction path, even boosted. No way that will defeat the spin of the exhaust side, the shaft would twist itself sooner. Which sometimes happens on old, small turbochargers. But not usually
If a tube sees 7 psi at one end and 14psi at the other, the fluid WILL flow from the high to low pressure. I agree it wouldn't go back through the turbo, but I said back TO the turbo previously. It is all physics, get guitarmaestro to post from the audio forum, he is a physics major.

Julian

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post #30 of 44 (permalink) Old 01-06-2005, 12:37 AM
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Looked at my Bird tonight.

Yeah, that 4.6 is damned wide! SHEESH!

What a coincidence, a 5.0L Vortec-fed late 90's Mustang was there too. Yeah, HUGE difference.

So yes, that engine bay wall is too close to the side of the head. If I were to do this, I would need to run a four to six inch length of steel tube from the manifold, straight down. THERE, a T2 WILL FIT. Barely but it will. To be safe and avoid smacking the turbos into the chassis, I need some solid engine mounts. Who makes them?

I am not sure I can use the stock T2 O2 housing. I think I will have to make my own, using a T2 flange on the output side.

Otherwise it still seems very doable.

-J. Arro
1994 Ford Thunderbird 4.6L LX V8
Bone stock engine, *partial* Xenon Body kit.
http://www.cardomain.com/ride/750285
PLZ HELP ME FIND A XENON FRONT LIP

I also own some Turbo Dodges, a couple turbo DSM's, a few turbo Nissans, a Toyota pickup, and a supercharged VW sportcoupe.
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