rb26dett with single turbo and twin maf?

[GAWDZRA]

Hello guys,

im fairly new with skylines and just had a couple questions regarding turbo setups and advice to what works and what doesnt. i do have a automotive background but even though vehicles might share the same principles and basic function i do understand that some applications might apply better than others ~differences on how a vehicle reacts to mods.

So here's my situation, since the rb26dett's have stock twins, everything is doubled, maf, chargepipes, plumbing , etc. kind of a pain in the bummmm..

A single setup not only makes plumbing easier it might actually be a little lighter than a tiwn setup and easier to diagnose as far as leaks of isolating a problem in the future.(i know a lot of 2j people that did single setups and been very happy)

BUT.....THERE'S one thing from stopping me..

I DON'T want to run an EM. or i refuse to buy one..

Mainly for one reason, i want to keep the motor setup as stock as possible since i need reliability and longevity.

But since the motor originally was wired/came with 2 mafs, is it possible to run a single without needing an EM? i dont mind not having big power/numbers i just want to eliminate the old and tired stock twins and in the same process have a cleaner/easier to work on engine bay.

to make this happen what do i need to do?

*find out how much max CFM the stock twins on a stock tune/boost can push?
*find a single turbo that has the same CFM output as the stock twins combined?
*keep boost levels relatively conservative, As if the car has stock twins?

would the car act up if i decided to eliminate the other maf? of do i have to run it like so..



Chances are everythings going to be homebrew except a single turbo manifold for the rb26.

***My goal is to run a simple single turbo setup, stock fuel, stock everything, runing pumpgas 93oc. to keep the car reliable and relatively simpler

any info regarding this matter would be greatly appreciated! Gurus/experts/seasoned builders/tuners all welcome.

Thanks for reading!

[GAWDZRA]

no one?

[Super_Dude]

Your asking a lot of questions that have been discused a lot. Search around this forum and check out gtr.co.uk and skylinesaustralia.com aswell.

[DJ]

why dont you keep the twins but swap them for newer garrett items...

If you want to run a single set up with a stock system well then forget about big power cause your limiting yourself on many aspects, stock fuel system is one , the mafs...etc.

You can run a single with a y pipe going to both mafs,i've seen it done here in town.

[Phastwon]

I am going to generalize a bit and say you can't convert to a different turbo setup (twins or single) without some sort of engine management. Any other turbo(s) you put in will have different flow characteristics at different RPM. They will change hte timing and fuelling requirements of your engine regardless. MAF versus MAP is a debate that has been discussed many times and I won't get into. However if you want to remain fairly reliable but want more power you are much better served by getting intakes, exhausts, high flow cats, and a boost controller.

[cortexx]

I agree with Phastwon , reallly the only compelling reason to change the turbos you have is that the originals will have ceramic exhaust wheels that tend to break orbit into the cat if you run more than the factory boost. If you want to keep the car stock then look around for a pair of n1 turbos that had steel exhaust wheels , or remove the ones you have and buy the conversion cartidges that are available and get them rebuilt.

I would then add a EBC and run around 1 bar if the engine is healthy (do a compression test and look for the difference in compression of no more than 12 psi betwen the lowest and highest cylinder).

As far as adding an engine management system goes , and i'm going to go against alot of opinions here , you only need it when the stock ECU has to run larger injectors due to larger flow rates on aftermarket injectors. On alot of turbo platforms this comes into play when the boost is increased from factory specs and the turbos are asked to hold this to redline which they do under factory boost , but not on a higher boost limit. This is where the factory ECU and injectors max out.

The stock setup comes with 440cc injectors (i think) , and as a rough guide you can support 1 HP per cc of injector used on a 6 cylinder engine(assuming the furl pump, FPR and injectors are in good shape) , i would err on the safe side and restrict total power to 375 .

(the next paragraph is what goes against most turbo opinions on these forums)

On a factory setup designed to run at 12 psi you can run whatever turbo you like , , 12 psi is 12psi and it doesnt matter weather its a tiny 9b turbo (6g72 3000gt platform) or a masssive scania transport turbo, the engines cylinder capacity and volumetric eficiency dictate how much fuel/air mixture you can stuff into it per charge at 12psi , the turbos flow rate is irrelevant. However when you start upgrading exhaust, intakes , cams to aftermarket items and changing the engines VE so that it scavenges exhaust gasses more efficiently and increases its ability to take more fuel/air mixture per charge then the turbos do flow more cfm for the same 12psi boost level and THIS is where your fuel system has to be able to keep up. And this is where upgraded injectors and MAFS require a reprogrammed or programmable ECU to drive them properly come into play.

The volume of air entering the engine is measured by the MAF's and this amongst a few other sensor parameters is how the engine knows how much fuel to add , as long as you stay within the safety range of the factory MAFS, injectors, fuel pump the factory ECU will calibrate itself to mild mods.

I'm also going to add at this point that i'm also fairly new to the RB26 platform , but the theory is the same for pretty much most turbo platforms. my comments are based on my own experiences of 8 years tuning the mitsu 6G72 platform and various other setups over the last 25 years ( yea im really that old ) .

[GAWDZRA]

You can run a single with a y pipe going to both mafs,i've seen it done here in town.

Good to know that it has been done. thats the answer i was looking for.

I am going to generalize a bit and say you can't convert to a different turbo setup (twins or single) without some sort of engine management. Any other turbo(s) you put in will have different flow characteristics at different RPM. They will change hte timing and fuelling requirements of your engine regardless. MAF versus MAP is a debate that has been discussed many times and I won't get into. However if you want to remain fairly reliable but want more power you are much better served by getting intakes, exhausts, high flow cats, and a boost controller.

I totally understand the concept behind EM's but you can't say you can never swap turbos without doing an EM. (ex: supras have been doing it for ages, same concept) Yes, i agree with the flow characteristics through out the rpm's but if anything theres nothing to worry about when converting to single since its a larger turbo and itll take longer to get going meaning fuel trims would most likely be the most aggressive on WOT where the bigger turbo shines anyways. If the single turbo and the stock twins have the same exact amount air forced into the motor i just dont see it causing any problems. I am not doing this for POWER. im doing this to keep things simple/cleaner setup. If by doing this it'll yeild me stock numbers but be reliable then so be it.

Thank you for the input buddy! i really appreciate it!

I agree with Phastwon , reallly the only compelling reason to change the turbos you have is that the originals will have ceramic exhaust wheels that tend to break orbit into the cat if you run more than the factory boost. If you want to keep the car stock then look around for a pair of n1 turbos that had steel exhaust wheels , or remove the ones you have and buy the conversion cartidges that are available and get them rebuilt.

I would then add a EBC and run around 1 bar if the engine is healthy (do a compression test and look for the difference in compression of no more than 12 psi betwen the lowest and highest cylinder).

As far as adding an engine management system goes , and i'm going to go against alot of opinions here , you only need it when the stock ECU has to run larger injectors due to larger flow rates on aftermarket injectors. On alot of turbo platforms this comes into play when the boost is increased from factory specs and the turbos are asked to hold this to redline which they do under factory boost , but not on a higher boost limit. This is where the factory ECU and injectors max out.

The stock setup comes with 440cc injectors (i think) , and as a rough guide you can support 1 HP per cc of injector used on a 6 cylinder engine(assuming the furl pump, FPR and injectors are in good shape) , i would err on the safe side and restrict total power to 375 .

(the next paragraph is what goes against most turbo opinions on these forums)

On a factory setup designed to run at 12 psi you can run whatever turbo you like , , 12 psi is 12psi and it doesnt matter weather its a tiny 9b turbo (6g72 3000gt platform) or a masssive scania transport turbo, the engines cylinder capacity and volumetric eficiency dictate how much fuel/air mixture you can stuff into it per charge at 12psi , the turbos flow rate is irrelevant. However when you start upgrading exhaust, intakes , cams to aftermarket items and changing the engines VE so that it scavenges exhaust gasses more efficiently and increases its ability to take more fuel/air mixture per charge then the turbos do flow more cfm for the same 12psi boost level and THIS is where your fuel system has to be able to keep up. And this is where upgraded injectors and MAFS require a reprogrammed or programmable ECU to drive them properly come into play.

The volume of air entering the engine is measured by the MAF's and this amongst a few other sensor parameters is how the engine knows how much fuel to add , as long as you stay within the safety range of the factory MAFS, injectors, fuel pump the factory ECU will calibrate itself to mild mods.

I'm also going to add at this point that i'm also fairly new to the RB26 platform , but the theory is the same for pretty much most turbo platforms. my comments are based on my own experiences of 8 years tuning the mitsu 6G72 platform and various other setups over the last 25 years ( yea im really that old ) .

I agree with everything BUT with highlighted section of your post.

Also, Psi is not just Psi. Psi is directly correlated to the volume of air thats being moved. So are you telling me that 29 psi on a passenger tire and a much bigger truck tire at 29psi have the same amount of air? This is the same exact reason why when running a bigger turbo that flows more CFM's you need to run bigger injectors because theres much more air resulting to running lean if the upgrade is not performed.

Also volumetric effiency is just a percentage value. In this case, its somewhat irrelevant because technically All boosted cars both supercharged/turbocharged are already considered 100%+ volumetric efficient since as soon as theres "boost" theres positive pressure in the cylinders making it 100% volumetric efficient. kinda like stuffing a 10lbs potato bag with 15lbs of potatos.

volumetric efficiency is normal used for Naturally aspirated vehicles that depend on athmospheric pressure to take air into the combustion chamber. anyways, i just wanted to clear that out.

Over all, A lot of great info shared! thank you very much.. i think this is a very interesting idea and would like to learn more about it as we go along. Thanks again guys!

[cortexx]

See , this is my point , the PSI or preassure under boost can only flow a certain amount of fuel air into a certain cc , your comparison with 2 different tire sizes is not a good comparison because both tires have different volumes , the tire volume directly correlates to the volume of the cylinder you are trying stuff full of fuel/air mixture running different turbos with different flow characteristics does not alter the volume of the cylinder. Once a certain fuel/air volume has been reached the psi rises to 12 psi then the wastegate vents any remaining exhaust gasses to stop further volume of fuel/air from being pushed into the cylinder.

The turbos flow capacity comes into effect as the engine revs to redline and still requires the same PSI of boost to remain constant. This is usually where the smaller turbos cant keep up and the larger turbos have the higher CFM to keep the boost 12psi until redline is reached.

[GAWDZRA]

See , this is my point , the PSI or preassure under boost can only flow a certain amount of fuel air into a certain cc , your comparison with 2 different tire sizes is not a good comparison because both tires have different volumes , the tire volume directly correlates to the volume of the cylinder you are trying stuff full of fuel/air mixture running different turbos with different flow characteristics does not alter the volume of the cylinder. Once a certain fuel/air volume has been reached the psi rises to 12 psi then the wastegate vents any remaining exhaust gasses to stop further volume of fuel/air from being pushed into the cylinder.

The turbos flow capacity comes into effect as the engine revs to redline and still requires the same PSI of boost to remain constant. This is usually where the smaller turbos cant keep up and the larger turbos have the higher CFM to keep the boost 12psi until redline is reached.

I think we are in the same page actually, just said it differently. haha

also, the tire analogy/comparison was not for the engines cyl cap. its for comparing a big to small turbo thats why i used tires as an example.

Anyways, in theory.. what im trying to accomplish here is very plausible correct? it will be a little laggy-er than the twins but as far as fueling goes it should be fine as long as the turbo used is kept under the limits of the factory injectors/factory tune. forget about twins yeilding me more power or whats right and whats wrong..since im not doing this for efficiency or power, my ultimate questions is...it would work and run just fine. yea? i already know the answer but i just wanted to see what people have in mind.

whatcha think?

[archaeic_bloke]

based on the question you asked and your reason for wanting to do so, I'd say 2 things.

1) sell your GTR
2) buy a damn nice GTS

heres why: the GTS is lighter, and easier to work on, and for the money you'd sell your GTR for you can get a top of line baller GTS thats more reliable than your GTR ever could be. it has one turbo instead of 2... and if you really want the AWD.. then get yourself a GTS4.. you have options man, just gotta look around.

[NismoS-tune]

You should get an EFR (borg warner) turbo in my opinion. One of the fastest EVOs uses one of those

[GAWDZRA]

based on the question you asked and your reason for wanting to do so, I'd say 2 things.

1) sell your GTR
2) buy a damn nice GTS

heres why: the GTS is lighter, and easier to work on, and for the money you'd sell your GTR for you can get a top of line baller GTS thats more reliable than your GTR ever could be. it has one turbo instead of 2... and if you really want the AWD.. then get yourself a GTS4.. you have options man, just gotta look around.

agreed. that would be the smart thing to do.

2 things..

- i like the challenge of trying new things /experiment / learning

- i like the rb26

Thanks for the input but i like working with what i have.

You should get an EFR (borg warner) turbo in my opinion. One of the fastest EVOs uses one of those

?

[cortexx]

Basically as long as your turbo setup does not push more air into the engine than the fuel system has the capacity to deliver for your fine.

at a factory boost setting the turbo will not create a lean condition period no matter how heavy you mash the go pedal

On WOT as the turbos/turbo spool up the ECU switches to openloop and ignores the oxygen sensors and takes its reading from the MAFs. The factory ECU is dialled in to match the factory mafs and it adds or reduces fuel depending on the ECU's fuel map and makes small adjustments based on MAF readings.

If you want to be safe the 2 best tuning tools are these :-

http://www.theknockbox.cc/

http://www.innovatemotorsports.com/products/db.php

One more thing that alot of people overlook when cranking boost is heatsoaking the intercooler and the problems that causes.

As you preassurize air it raises the temp alot and once under that preassure your intercoolers job is to reduce the temp of that charge back down to the ambiant temp.

The factory intercooler is designed to handle the heat exchange coming from a set boost for a given volume over time. By upping the boost you up the temp of the charge and also the velocity as you keep this boost throught the rev range until you reach a point where the cooler ability of the intercooler is overwhelmed by the heating ability of the hot air.

Hot air entering the combustion chamber sucks, it's less dense and cannot combine with as much fuel so produces less power , it also causes dotonation.

I remember years ago tuning my 3000gt and gradually upping my boost and logging a 1/4 pull up to 4th gear . I reached a point at 14.2 psi where i hit a knock sum of 25 at around 5500rpm in 4th gear but didnt have this at the same rpm in 2nd or 3rd. I thought it was leaning out but the IDC the EGT and the O2 readings didnt really agree with this and What we eventually found by trial and error is that the 2 small intercoolers where getting too hot by the time we were in 4th gear that the system started pushing hot air into the engine causing the detonation. We ditched the stock intercoolers and modifed a pair of eagle talon coolers to fir the car. This fixed the problem and allowed us to boost up to 15.1 psi on a pair of 13g turbos all the way to redline with no further probs, all on the factory ecu and mafs btw .

[GAWDZRA]

Basically as long as your turbo setup does not push more air into the engine than the fuel system has the capacity to deliver for your fine.

at a factory boost setting the turbo will not create a lean condition period no matter how heavy you mash the go pedal

On WOT as the turbos/turbo spool up the ECU switches to openloop and ignores the oxygen sensors and takes its reading from the MAFs. The factory ECU is dialled in to match the factory mafs and it adds or reduces fuel depending on the ECU's fuel map and makes small adjustments based on MAF readings.

If you want to be safe the 2 best tuning tools are these :-

http://www.theknockbox.cc/

http://www.innovatemotorsports.com/products/db.php

One more thing that alot of people overlook when cranking boost is heatsoaking the intercooler and the problems that causes.

As you preassurize air it raises the temp alot and once under that preassure your intercoolers job is to reduce the temp of that charge back down to the ambiant temp.

The factory intercooler is designed to handle the heat exchange coming from a set boost for a given volume over time. By upping the boost you up the temp of the charge and also the velocity as you keep this boost throught the rev range until you reach a point where the cooler ability of the intercooler is overwhelmed by the heating ability of the hot air.

Hot air entering the combustion chamber sucks, it's less dense and cannot combine with as much fuel so produces less power , it also causes dotonation.

I remember years ago tuning my 3000gt and gradually upping my boost and logging a 1/4 pull up to 4th gear . I reached a point at 14.2 psi where i hit a knock sum of 25 at around 5500rpm in 4th gear but didnt have this at the same rpm in 2nd or 3rd. I thought it was leaning out but the IDC the EGT and the O2 readings didnt really agree with this and What we eventually found by trial and error is that the 2 small intercoolers where getting too hot by the time we were in 4th gear that the system started pushing hot air into the engine causing the detonation. We ditched the stock intercoolers and modifed a pair of eagle talon coolers to fir the car. This fixed the problem and allowed us to boost up to 15.1 psi on a pair of 13g turbos all the way to redline with no further probs, all on the factory ecu and mafs btw .

agreed.

i do have an aem wideband waiting to go in! knockbox reminds of those old school turbo xs tuna units! this brings me back!

[cortexx]

turbo xs lol i used to use one of their blue anodized manual boost controllers , and even that replaced the original manual one i made out of some brass fishtank fittings lol. And my knockbox looked like a radioshack DIY kit , didn't look as flashy as the new ones lol