Out of Curiosity

[TheShow50h]

I'm wondering what the advantage of converting an mkIV supra into a single turbo. I ran a yahoo search, looked for about 15 minutes and didn't find anything. Logically speaking, it doesn't seem to be beneficial to have 1 rather than 2, is there a simple explanation for this popular upgrade?

[Kirk]

:)

[Kirk]

no setup can be justified as "better" than the other. both have their advantages, and disadvantages. twin turbos in a sequential setup where one turbo begins to spool, then a few hundred, or in some cases thousand rpms later the other begins to spool up, generally offer a more linear power curve. the idea is to mirror a naturally aspirated power curve, where the majority of the power delivery falls over a wide range of the power band, to give the most "usable power" to the driver. the downside to this, is that most sequential applications are complex, and most aftermarket tuners have not tried to duplicate the stock setups to create big power* this means sequential setups are for the most part, limited to the maximum flow of the stock twins which come with the car. so in this application, around generally around 450-500 rwhp. it is this reason which drives many to "go single."

by switching to a single turbo which can flow much more cfm into the engine than the stock twins, more horsepower can be created. again, with regard to supras, this figure ranges anywhere from about 450-1000+ historically, the downside to a single turbo setup is that they generally tend to have a much sharper power curve than a sequential setup. in other words, though the turbos are making more power, because they are larger they tend to be more efficient than their smaller counterparts, and this makes their spool characteristics often very off/on. power will often jump two or three hundred horsepower in the space of 500-1000 rpms. this also tends to happen later in the rpm range because it takes more air to turn a larger turbine, and more rpms to create that spool. so after all is said and done, the single will create a huge jump of horsepower later in the power band than the smaller sequential setup. also, not that most aftermarket twin turbos are run in true twin, or parallel operation. this means they spool simultaneously, and operate like one big turbo. these usually follow the characteristics of large singles, don't be fooled into thinking they are "better" or "worse" than a single.

however, recently smaller single turbos have began to creep into the market which offer a compromise, in an attempt to give stock-like spool, eliminating the lag introduced by a large single, but ultimately at the cost of top end power. there are many diffrent turbos out there, so poke around and look at some dyno sheets of those who have the turbos you might be interested in. also, keep in mind, a lot more affects power, and driving characteristics of the car than just the turbo. manifold type, plumbing, and all sorts of other aspects of a car relate directly to it's performance. with proper research, it's easy to see what combos and setups work well. find out what you want out of your car, and look at other's setups which produce the results you are looking for. good luck

[flubyux2]

neither makes more power than the other... one of the most famous street MKIV's on this side of the pone still has twins... not stock, but still twins.

twins give you more linear power where a big single is kind of like nothing and then everything. idle to 4000rpm might take a long time and then after 4000 rpm, the rev limiter will hit before youre ready.

twins usually cost more money though... twice the stuffs to buy and more stuff to install/fabricate/engineer.

[riddlemr2]

Originally posted by SupraKid
no setup can be justified as "better" than the other. both have their advantages, and disadvantages. twin turbos in a sequential setup where one turbo begins to spool, then a few hundred, or in some cases thousand rpms later the other begins to spool up, generally offer a more linear power curve. the idea is to mirror a naturally aspirated power curve, where the majority of the power delivery falls over a wide range of the power band, to give the most "usable power" to the driver. the downside to this, is that most sequential applications are complex, and most aftermarket tuners have not tried to duplicate the stock setups to create big power* this means sequential setups are for the most part, limited to the maximum flow of the stock twins which come with the car. so in this application, around generally around 450-500 rwhp. it is this reason which drives many to "go single."

by switching to a single turbo which can flow much more cfm into the engine than the stock twins, more horsepower can be created. again, with regard to supras, this figure ranges anywhere from about 450-1000+ historically, the downside to a single turbo setup is that they generally tend to have a much sharper power curve than a sequential setup. in other words, though the turbos are making more power, because they are larger they tend to be more efficient than their smaller counterparts, and this makes their spool characteristics often very off/on. power will often jump two or three hundred horsepower in the space of 500-1000 rpms. this also tends to happen later in the rpm range because it takes more air to turn a larger turbine, and more rpms to create that spool. so after all is said and done, the single will create a huge jump of horsepower later in the power band than the smaller sequential setup. also, not that most aftermarket twin turbos are run in true twin, or parallel operation. this means they spool simultaneously, and operate like one big turbo. these usually follow the characteristics of large singles, don't be fooled into thinking they are "better" or "worse" than a single.

however, recently smaller single turbos have began to creep into the market which offer a compromise, in an attempt to give stock-like spool, eliminating the lag introduced by a large single, but ultimately at the cost of top end power. there are many diffrent turbos out there, so poke around and look at some dyno sheets of those who have the turbos you might be interested in. also, keep in mind, a lot more affects power, and driving characteristics of the car than just the turbo. manifold type, plumbing, and all sorts of other aspects of a car relate directly to it's performance. with proper research, it's easy to see what combos and setups work well. find out what you want out of your car, and look at other's setups which produce the results you are looking for. good luck

The above translated: "Single turbo supras make great dyno queens."

[MR2driver]

Originally posted by SupraKid
no setup can ...... produce the results you are looking for. good luck

That was sure a lot said by a guy who isn't even turbo :D

[TurboJZA70]

Originally posted by riddlemr2
The above translated: "Single turbo supras make great dyno queens."

:lol: :lol: :lol: So true.

[Muddy]

Originally posted by MR2driver
That was sure a lot said by a guy who isn't even turbo :D
I think he copied that from somewhere, I have never seen Kirk write that much or that well. I think flubyux2 is referring to Keith Ta's twin t66(?) car.

[TheShow50h]

Originally posted by SupraKid
no setup can be justified as "better" than the other. both have their advantages, and disadvantages. twin turbos in a sequential setup where one turbo begins to spool, then a few hundred, or in some cases thousand rpms later the other begins to spool up, generally offer a more linear power curve. the idea is to mirror a naturally aspirated power curve, where the majority of the power delivery falls over a wide range of the power band, to give the most "usable power" to the driver. the downside to this, is that most sequential applications are complex, and most aftermarket tuners have not tried to duplicate the stock setups to create big power* this means sequential setups are for the most part, limited to the maximum flow of the stock twins which come with the car. so in this application, around generally around 450-500 rwhp. it is this reason which drives many to "go single."

by switching to a single turbo which can flow much more cfm into the engine than the stock twins, more horsepower can be created. again, with regard to supras, this figure ranges anywhere from about 450-1000+ historically, the downside to a single turbo setup is that they generally tend to have a much sharper power curve than a sequential setup. in other words, though the turbos are making more power, because they are larger they tend to be more efficient than their smaller counterparts, and this makes their spool characteristics often very off/on. power will often jump two or three hundred horsepower in the space of 500-1000 rpms. this also tends to happen later in the rpm range because it takes more air to turn a larger turbine, and more rpms to create that spool. so after all is said and done, the single will create a huge jump of horsepower later in the power band than the smaller sequential setup. also, not that most aftermarket twin turbos are run in true twin, or parallel operation. this means they spool simultaneously, and operate like one big turbo. these usually follow the characteristics of large singles, don't be fooled into thinking they are "better" or "worse" than a single.

however, recently smaller single turbos have began to creep into the market which offer a compromise, in an attempt to give stock-like spool, eliminating the lag introduced by a large single, but ultimately at the cost of top end power. there are many diffrent turbos out there, so poke around and look at some dyno sheets of those who have the turbos you might be interested in. also, keep in mind, a lot more affects power, and driving characteristics of the car than just the turbo. manifold type, plumbing, and all sorts of other aspects of a car relate directly to it's performance. with proper research, it's easy to see what combos and setups work well. find out what you want out of your car, and look at other's setups which produce the results you are looking for. good luck

Ty, this question isn't to put turbo's on my car (although I wouldn't rule anything out :) ), but to just be more informed on the subject because I have a friend who just went to a single turbo in the t60 size, but that's not exactly what his turbo is, just the relative size of it. I just figured logically that the single wouldn't have near the power that the twin sequential had down low which is very important for a daily driver, but I guess when you start from a 70mph roll it doesn't really matter, :lol:

[Muddy]

Check out t04r.com to see some dyno sheets of big single turbo supras. They make about 200 rwhp up to ~3.5k, then the power curve goes up about 90*.

[93supra]

Well to shed a little light on the subject of wether stock twins or single is better. The stock twin turbos do an awsome job for a factory turbo that was never really meant to run more than 12psi-+ . Now as far as how they compare to a single turbo(60 mm p trim .58 a/r on up)the single turbo will smoke the stock twins.

Now you have to extend your rpm's so you have a more usuable power band(if you try to take off at low rpm's on a single turbo supra you don't need to be driving it).What I'm trying to say is that you drive these car's diffrent.

Also just like any high horsepower car when you start making more than 500 rwhp traction will be an issue but with the proper tire and suspension set up you can make more use of your new found power.:D

I do own a single turbo supra MKIV and have owned stock twin supra both auto and 6-speed.;) I would rather have a small single turbo over the stock twins.

[Mr 2]

Aftermarket parallel twins are actually less efficient than a single with the same potential outputs. The reason being is that there is more disturbance in 2 exhaust housings than one. The disturbance which causes velocity losses is the inside surface area of the housing. Air hitting the housing is slowed and since twins have twice this area there is more exhaust velocity lost.

[TheShow50h]

Originally posted by Mr 2
Aftermarket parallel twins are actually less efficient than a single with the same potential outputs. The reason being is that there is more disturbance in 2 exhaust housings than one. The disturbance which causes velocity losses is the inside surface area of the housing. Air hitting the housing is slowed and since twins have twice this area there is more exhaust velocity lost.

That's a very good point. I never thought of it like that.

[Slash]

so how does the stock supra regulate boost to the engine? Is it through a flapper gate system like on the RX-7?

Sorry I just thought that on the MKIV that both turbines were exactly the same size and fed 3 cyls each with the same boost.. thus being in sync.. not sequencial.. so at 3K rpm both turbines being exact sizing are at the same rpm producing the same boost, not that one was helping it to 3k-4k and then the other (larger turbine) was taking over...

I figured that they were both the same size and 2 of them because toyota

A: Has a ton of CT's already, didnt have to change much in their ordering cept maybe wheel trims and stuff (not sure on the size of the supra twins compared to the MR2 or something, might be the same i dunno)
B: Twin turbo sounds cooler than a big single (which they coulda gone for a T3-T4 sized turbine stock and gotten the same results... or maybe a T4 of some kind..) Also since the 300ZX was already Twin Turbo (since it has to be) and the skyline as well (prob for cheapness reasons kinda like the supra) were all TT.. having the supra be not Twin Turbo would hurt sales due to less coolness factor.....

I just thought that turbos on the supra were in tandem like on the 300zx / skyline

Not in sequence (1 then 2 after more RPM) like the RX-7 with its flapper gate switchover..

[Slash]

Originally posted by Mr 2
Aftermarket parallel twins are actually less efficient than a single with the same potential outputs. The reason being is that there is more disturbance in 2 exhaust housings than one. The disturbance which causes velocity losses is the inside surface area of the housing. Air hitting the housing is slowed and since twins have twice this area there is more exhaust velocity lost.

Could you not make up for this with smaller housings on the twins? to some extent? I figure this is exactly what they did....

[Kirk]

Originally posted by MR2driver
That was sure a lot said by a guy who isn't even turbo :D

I've owned a big turbo setup in the past and I will again within weeks......... I didn't buy my car because it was NA... :lol: It was the only black/black for sale under 20 at the time... and it was in Texas. So keep your smartass remarks to yourself.

[Kirk]

Originally posted by Mr 2
Aftermarket parallel twins are actually less efficient than a single with the same potential outputs. The reason being is that there is more disturbance in 2 exhaust housings than one. The disturbance which causes velocity losses is the inside surface area of the housing. Air hitting the housing is slowed and since twins have twice this area there is more exhaust velocity lost.

When you go parallel twins, you have to remember you've only got three exhaust ports per turbo as opposed to the six ports for the big singles. Obviously, six ports create more exhaust energy than three, but the bigger heavier big singles offset this somewhat. With twins, two smaller turbos are doing the job of one large turbo and, apples to apples, the twins should spool quicker and, together, generate as much top-end power as the big singles.

[Kirk]

Originally posted by TheShow50h
Ty, this question isn't to put turbo's on my car (although I wouldn't rule anything out :) ), but to just be more informed on the subject because I have a friend who just went to a single turbo in the t60 size, but that's not exactly what his turbo is, just the relative size of it. I just figured logically that the single wouldn't have near the power that the twin sequential had down low which is very important for a daily driver, but I guess when you start from a 70mph roll it doesn't really matter, :lol:

To answer the original question.. a small/big single turbo setup would produce more efficient power than a STOCK twin setup. I believe your question was leaning towards why people with a stock twin turbo would convert to a single turbo.

[Mr 2]

Originally posted by SupraKid
When you go parallel twins, you have to remember you've only got three exhaust ports per turbo as opposed to the six ports for the big singles. Obviously, six ports create more exhaust energy than three, but the bigger heavier big singles offset this somewhat. With twins, two smaller turbos are doing the job of one large turbo and, apples to apples, the twins should spool quicker and, together, generate as much top-end power as the big singles.

Could you elaborate. That makes no fucking sence. Now you are saying 2 smaller turbines are easier to spin than one larger one. Come one. The larger one weights less and has less surface area than the 2 smaller ones combined.

[Slash]

IF turbo A is one size and turbo B is (A*2) then its prob safe to assume that....

Twins of turbo A would have the same results as a single of turbo B..

This is a rough gestimate, but I dont see why it would be different...

[Slash]

Someone answer my questions..

Do MKIV supra turbos run in tandem like the 300ZX and Skyline..

OR are they Sequential like the flapper gate system on the TT RX-7..

Personally I think they run in tandem and aer the same size... Someone clue me in cause up above people were hinting at them being different size and sequential...

[Kirk]

Do you mean Parallel or Sequential? They run sequential...

1. how does the ssts (sequential twin-turbo setup) work?
first off, the is no #2 wastegate. there is only one wastegate and it comes off the #1 turbo because that turbo is always on line, therefore you always have a wastegate. there are 4 sets of vsv's, actuators, and control valves for the sequential turbo system. each vsv is simply a solenoid that is either 100% open or closed, allowing manifold pressure to pressurize the different actuators that open/close the four different valves.
wastegate: when the manifold reaches 11#'s of boost, the ecu sends a signal to the wastegate vsv, that allows manifold pressure to build in the wastegate actuator which opens the wastegate.
exhaust gas bypass valve (ebv): somewhere around 3500 rpm, the ecu sends a signal to the exhaust gas bypass valve vsv, which allows manifold pressure to build in the exhaust gas bypass valve actuator which opens the bypass valve. this is a small opening inside the #2 turbine housing which allows some exhaust gas to go through the turbine of the #2 turbo which makes it start spinning, and dumps the exhaust gas out the exhaust piping coming off of #1 turbo. since it is a small amount of exhaust gas, it pre-spools the turbo and does not get it up to full operating speeds. this will smooth out the transition from 1 to 2 turbos. This valve is similar to a wastegate in design, but is located after the turbine wheel instead of in front of the turbine wheel like a wastegate would be. this is not a wastegate!
exhaust gas control valve (egcv): this valve is located in the exhaust piping downstream of the #2 turbo. when this valve is closed, all exhaust gas must go through the #1 turbine wheel to get out through the rest of the exhaust system. at around 4000 rpm, the ecu sends a signal to the exhaust gas control valve vsv, which allows manifold pressure to build in the exhaust gas control valve actuator which opens the control valve. this allows exhaust gas to go through #2 turbo and out the exhaust system which brings the #2 turbo up to full operating speed.
intake air control valve (iacv): this valve is located in the intake tract coming off of #2 turbo. it is closed below 4000 rpm so that boost pressure coming off of #1 turbo cannot backup through the #2 turbo and back out the air cleaner/suction of #1 turbo. there is also a 1 way reed valve within the same housing of the intake air control valve. as the #2 turbo starts to pre-spin at 3500 rpm, it will build some boost. if it builds enough boost, it will open the 1 way reed valve to allow this boost into the intake tract to join with the discharge boost pressure coming off of #1 turbo. at somewhere over 4000 rpm, the ECU sends a signal to the intake air control valve vsv, which allows manifold pressure to build in the intake air control valve actuator which opens the control valve. this allows the full boost pressure coming off #2 turbo to join in with that coming from #1 turbo and you are now fully on line. Usually, the exhaust gas control valve will open first, which gets the #2 turbo spinning at full rate so that it is building good boost before the intake air control valve opens, allowing this boost to join in with that coming off #1 turbo. if the intake air control valve opens before the exhaust gas control valve, the boost pressure coming off #1 turbo will go backwards through #2 turbo, spinning it backwards if there isn't sufficient exhaust energy to keep it spinning forward. when the exhaust gas control valve opens, and the #2 turbo has to reverse the direction of the spin. this is a tremendous strain on the turbo shaft and bearings. if the sequential operation is not a well orchestrated symphony of motion, it is easy to see how the #2 can be prone to failure. for an alternate explanation including diagrams, see the new car features section. the appropriate pages are 91-95.

[Hella Slow]

on a tt supra 'A' turbine is a little smaller than 'B' turbine and 'A' spools up faster than 'B' there for 'A' helps 'B' to full boost....

[flubyux2]

i was actually referring to the Walser Supra w/ HKS GT2835's.

if you have twins w/ a .48 ar exhaust housings, that means you have 2 x .48 ar. its hard to say, cuz that number is a ratio, not an actual surface area. so i cant really say how much combined surface area twin turbos actually have. just like a big single might have an AR of like .80-ish.

i dont think the actual friction created by the exhaust gas inside the turbine housing is of as much importance than just flat out AR ratios and wheel weights. yes a ceramic impeller will increse response and yes smaller AR's will incresae response. but if we focus on the disturbance created by the sand-cast finish of the turbine housing, we will never get anything accomplished. i mean if it was such a big issue, we would see more talk about getting exhaust housings extrude-honed and polished. its more of nit picking than engineering.

a big single can create more power ultimately cuz you have every exhaust port feeding an exhast pulse into the turbine housing (regardless of frictional losses ;) ) and this can put all this work to use on the same wheel... remember the saying, many hands make light work? the downside is that hte power delivery on a big single is not as linear as most people would like for a daily driven car. the problem is that the exhaust housing AR ratio and turbine wheel have to be sized on the large side to accomodate the ultimate exhaust flow once the top end of the RPM's is reached and has an added 25-ish PSI added on top of that. you cant have a big single w/ a moderatly sized exhaust housing AR. itll choke off your top end and sacrifice your max HP potential. thats why big singles have alot more lag down low and less hp on the bottom end. the work-around is nitrous on a window-switch.

yea, twins will have better response and a more predictable power delivery since the exhaust AR's have to be sized much smaller than one single. theres only half the displacment of air flowing thru each turbo, AND half the exhaust pulses to push the turbine. twins have twice the frictional losses, half the force being applied to them, twice the complication, twice the hardware, twice the cost and twice the aggrevation. but it sure does sound cool to say you have a twin-turbo doesnt it?

i think twins are more for drivabilty and comfort than all out power. the Supra evolved from a single to a twin so it could have good torque just about anywhere in the RPM range and make a good street driver. the RX7 evolved from a single turbo so it too could have better street characteristics and more available power on a greater range in the RPM band. the 300zx evolved from a single turbo for the same reasons... not cuz it sounds cool.

(oh... and i typed all that myself ;) )

[Slash]

the 300ZX turbos are the exact same size and spool at the exact same time in parallel........ Its due to engine location and not being able to run the piping to be single turbine...

[1BFC]

Originally posted by TheShow50h
I'm wondering what the advantage of converting an mkIV supra into a single turbo. I ran a yahoo search, looked for about 15 minutes and didn't find anything. Logically speaking, it doesn't seem to be beneficial to have 1 rather than 2, is there a simple explanation for this popular upgrade?

A simple explanation is that the 2 stock turbos only flow enough air to produce on average 450rwhp at most. You CAN get more out of them by forcing the wastegate shut but they are then so far out of their effeciency range and turning far far more RPM then they were designed to that they don't last very long.

Most people keep the stock twins at a max of 18"ish" psi. Some people push them to 20-22 and seem to hold up for a "while". The best dyno I've seen was Andi B's car with quite a few supporting mods laying down 480+RWHP and 500+rwtq at 23psi on the stock twins.

Now, switch to a single setup in the 60+mm compressor range and that same 23psi would have you in the 550 RWHP range. The single is just far more effecient. Also, the stock twins fall off in the higher revs where the single has the power climbing still at the stock rev limit of 6800RPM.

This is a pretty basic explanation with some rough numbers as examples only. It's a far more complicated issue when you actually go to choose a turbo setup so please don't take these numbers as something to judge by.

Also keep in mind that X HP level doesn't equate to X psi. 10 psi on one supra with one turbo will produce a different amount of power than 10 psi on another supra with a different turbo. There's a hole mess of variables that ultimately dicate just how much power you pick up per psi of boost.

I know my own personal car picks up ~17 hp/psi. Every one will be different to some extent.

Also, don't believe the people that will tell you that single turbo supra = dog out of the hole. Or that singles = lag monsters. It's simply not true and all it requires is a modification to driving style. I have a single... I have 5psi at 3000rpm, 10psi by 3500 and whatever you feel like running by 3800+ rpm. To me.. that's not a bad range. In general I find my car produces a larger power range than most other cars I've seen dynos on. My power curve is very linear and controllable.

Updgraded twin turbos work like single turbos and are not sequential like the stock twins are. Upgraded twin setups are less popular due to increased cost (about 50% more money) and the fact that they are not as effecient due to losses from double the moving parts (among other things as well). The only reason to run a twin setup that isn't sequential would be if you couldn't find a single turbo that flowed enough air for your application. These days that's incredibly rare.... Single turbos can flow as much as 2000+HP worth of air thanks to modern technoledgy.

Hope that helps some :)

-BFC

[TheShow50h]

Definately helps, thanks everyone. I feel much better informed now :)