Out of Curiosity
THE HAMMER
Joined: May 2002
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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...
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...
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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.
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.
Elitist Supra Asshole :)
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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 )
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
)
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THE HAMMER
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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...
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Re: Out of Curiosity
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?
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?
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
