What Are The Keys To Turbo Response

[wegs]

I have tried searching using keywords +turbo +response +lag but can't find any posts that talk purely about improving response regardless of your turbo choice. I will try to narrow down the discussion using my example of an R32 RB26 but a lot of what i'm asking here is relevant for any turbo setup... just in varying amounts and results.

I set out on a simple Rb26 performance upgrade focussed on response. Peak power wasn't the priority but for reference let's say up to 300rwkw. I took a lot of advice from these forums and spoke first hand with guys running identical or very similar mods. The expectations/claims they gave are not what I'm experiencing.

My turbos of choice for response are HKS GT-SS. Was running stock R32 RB26 turbos before this which reached a max of 0.8 bar around 3500rpm using elec boost controller.

I already had a high flow cat-back setup. So at time of turbo upgrade I installed high quality dumps/fronts for increased flow, high HP BOV, hard piping kit for reduced flex and peace of mind, fuel/ECU upgrades to match turbos and rest remains standard. Had Nismo AFM's ready to go but factory ones didn't max out.

Idle timing remains @ 20deg and compression test of all cylinders is within 5 psi of each other. Car was tuned by one of Australia's most experienced RB26 tuners.

A comparable setup with built motor on SAU has reported 1 bar as early as 2700rpm! Others with built and non built motors vary between this & 3500rpm. Real world results for me.... postive boost starts around 2000rpm, 1 bar reached around 4000rpm. Changes in air intake temps (35-50deg) shifts the peak boost point a bit but not by much.

From here I experimented with different theories. I removed the water pump, clutch fan and A/C from the crank pulley. No noticable change on road or dyno. Installed popular RB26 Jap cams and Manifolds... slight change in midrange power but rest was identical. Boost points didn't change.

Things like head porting, intake manifolds, throttle bodies might help in other situations but at this power level on RB26 it wouldn't be worth it. The only thing brought to my attention recently is the FMIC - apparently changing to a high quality FMIC with less internal restriction is best thing i can do for my turbo response. But it's not like the GTR FMIC is known for killing response so how much can i expect to gain from this $1k investment? For all i know it could be a repeat of the cam/manifold story above which i have now removed and sold because they are wasted on my setup.

I have tried playing around with gain on the boost controller but the gap i'm trying to bridge is too big to be result of this. Boost doesn't drop off once it peaks, don't believe i have any leaks but can check.

Trying to steer clear of a brand name debate here as I can't see how this will prove anything. Are my results what they should be, have others embellished their results or have i overlooked something?

Wegs

Edited February 3, 2008 by wegs

[STATUS]

to start it is impossible for any 26 to have one bar at 2700, to achieve tis one would have to run a crazy dyno ramp load in top gear and even then i reckon it would be near on impossible. Based on your results and measurements (ie use the same dyno) i reckon the best you would get is a couple of 100 rpm for 000's of investment. Im presuming you mean Donnon as your based in SA? or simon as they are the two "guru" over there. Donnon is a killer tuner if you know him and get him on a good day. Simon is also very good and is the only person i ever let touch any of my cars tuning over there.

i would not compare road and dyno results either as the two differ extremely (if your not versed on all things dyno read the latest HPI, makes my choice of a purchasing dynapack all the more reassuring ), drive your car and map the boost response vs rpm via a laptop or boost controller (id III and E-01 can do this, im not sure what you use) then compare it to someone elses datalog.

[Roy]

I would be checking the exhaust system. If your R32 GTR is running a 14 year old performance exhaust the the mufflers could be stuffed/collapse. Ditto a poor quliaty cat converter. I would personally run std cams until you get a good benchmark of performance, only playing with cam gears

Then there is always the question of engine health. What is compression like, kms on engine etc.

But also consider that with the turbos you are running that you are still going to be makign about 500hp at the engine. Now it is only a 2.6L engine, so thats a hell of a lot of power from a 2.6L engine. And the fact that std turbo RB26s arent all that great in the response department. Dont get mislead by all the people that thing the Mines GTR is the way it is because it only runs "small" 2530 turbos. So with even smaller GT-SS it must be even more responsive. The Mines cars runs stupid diff ratios, carbon fibre driveshafts and weighs about 150kg less then your GTR

[rev210]

response is all about the ticking clock time between things happening.

You clearly missed the measurement you wanted. Seat of the pants won't help but, if you are on a dyno then map time VS rpm/speed or horsepower to see changes in response.

There are lots of things that can improve it.

Don't know what you are measuring but, generally less time taken to achieve 'x' is what I reffer to as a repsonse gain when power isn't necessarily on the increase. Boost insn't the be all end all.

How much boost you have at 2,700rpm is not really what you want to be measuring, in fact who cares? I think you want a car that accellerates faster and is quick to 'listen' to your right foot. Am I right?

You could bolt a baby single T15 or something on and have more than a bar of boost at 1,500rpm but, your car isn't going to be 'responsive' in terms of performance. Maybe towing another car out of sand.

If we talk just about the GT-SS turbo setup then 'response' improvement could be sensibly confined to the area that turbos works best in with regards to airflow. Removing airlfow restrictions naturally improves the efficiency and speed at which the turbo can pump air.

Can a better designed intercooler acheive this?

Yes. However core volume increases aren't necessarily good if you are chasing better low end/mid range characteristics.

Cams help?

Yep. If the right sized cams are setup with the right settings for valve timing you can bring airflow changes on faster in addtion to pumping more air at the same engine speed. With a reduction in airflow restriction and greater cranking compression if you go more advanced valve timing setting on the intake. You can measure the time it takes to achieve this on a dyno and also power increases are a dead give away.

Anything else that improves response with regards to rotational inertia helps. Light wheels , crank pulley, flywheel & clutch , tailshaft. Diff ratios etc..

[STATUS]

^ dyno is to hit and miss as ramp rates determine the relationship, a good boost vs rpm graph will tell you REAL life what is going on... a dyno can NEVER replicate this accuratley. do your mods and compare the before and after graphs.

[wegs]

to start it is impossible for any 26 to have one bar at 2700, to achieve tis one would have to run a crazy dyno ramp load in top gear and even then i reckon it would be near on impossible. Based on your results and measurements (ie use the same dyno) i reckon the best you would get is a couple of 100 rpm for 000's of investment.

Good to hear these things from a reliable source. It's starting to sound like my results are close to the norm. I'm happy with the power so it's probably more a matter of adjusting my driving style to get the most out of it.

Im presuming you mean Donnon as your based in SA? or simon as they are the two "guru" over there. Donnon is a killer tuner if you know him and get him on a good day. Simon is also very good and is the only person i ever let touch any of my cars tuning over there.

You presumed correctly in the first instance

i would not compare road and dyno results either as the two differ extremely (if your not versed on all things dyno read the latest HPI, makes my choice of a purchasing dynapack all the more reassuring ), drive your car and map the boost response vs rpm via a laptop or boost controller (id III and E-01 can do this, im not sure what you use) then compare it to someone elses datalog.

Will look at the HPI mag, thanks for the heads up. Am using the Blitz I-colour R and will have a look at rpm vs boost curve in more detail

Thanks Trent,

Wegs

Edited February 1, 2008 by wegs

[wegs]

I would be checking the exhaust system. If your R32 GTR is running a 14 year old performance exhaust the the mufflers could be stuffed/collapse. Ditto a poor quliaty cat converter. I would personally run std cams until you get a good benchmark of performance, only playing with cam gears

Will check out the exhaust system.

Then there is always the question of engine health. What is compression like, kms on engine etc.

Km's unknown as speedo was changed at some point. Compression test was 182-187 across all 6. Sounds high but could be the gauge, it was very consistent though. Same reading to +-1psi after repeating 2 more times.

But also consider that with the turbos you are running that you are still going to be makign about 500hp at the engine. Now it is only a 2.6L engine, so thats a hell of a lot of power from a 2.6L engine. And the fact that std turbo RB26s arent all that great in the response department. Dont get mislead by all the people that thing the Mines GTR is the way it is because it only runs "small" 2530 turbos. So with even smaller GT-SS it must be even more responsive. The Mines cars runs stupid diff ratios, carbon fibre driveshafts and weighs about 150kg less then your GTR

Always thought the GT-SS were about as small as you'd want to go.. kept hearing usual comments how they run out in top end. I guess the lesson is it's only relative to what you compare them to. Not true if compared to stock turbos.V Interesting comments about the Mines GTR... nothing is ever as it seems with marketing like that

Cheers Roy,

Wegs

Edited February 1, 2008 by wegs

[GTR31]

Dont get mislead by all the people that think the Mines GTR is the way it is because it only runs "small" 2530 turbos. So with even smaller GT-SS it must be even more responsive. The Mines cars runs stupid diff ratios, carbon fibre driveshafts and weighs about 150kg less then your GTR

I think this is particularly interesting Wegs as the Mines GTR is the "benchmark" car. Might be time to start stripping the GTR.

[BOOSTD]

1 bar at 4000rpm..I assume in 4th.. is a wee bit sleepy for GT-SS's. I have 1 bar at 4050rpm and +ve boost @ 1800rpm- you know the setup I am running.

Also your compression readings do seem high if that was an accurate reading. Though if true you should have even more response than expected and low ignition values up top...say 10-16 degree's ???? From my last car I bought from M***** I see his tuning has gone away from high ignition timing and rich mixtures to economical AFR's and less timing. May just be the way he tuned the ZOOM 4 door RB26 but I would be interested to see your tune.

Another check would be to see what you min boost level is....if your waste gate actuators are wound out to soft you will get average boost response no matter what. I set mine to just below the min boost I would run, which is 1.05bar.

I assume the BOV you bought is adjustable...I would screw it closed also for a quick check.

If your exhaust was blocked if would expect the difference to effect top end....... Your power level seems about right on the low boost level you are running.

I can understand the reasoning to run only 1.2bar as the mapped efficientcy level does drop off when looking at the compressor map at over 1.25 bar. However HKS recommend 1.4bar.......Probably because of the HKS housing. Which is much different to Garrett as I have had the two side by side. The dyno graph attached which I assume is at the engine does look how I would expect from what you have told me response wise. I have been in two different RB26's and they make 1bar by about 3800- 3900rpm on the stock turbos...the transient response however in much better than the larger turbos.. I really don't think there is a massive rpm difference to reach one bar off boost between stock, GT-SS and GT2530's ...maybe 500rpm.......as the other graph shows

Hope some of this blurb helps

[discopotato03]

Generally speaking by making the head breathe properly without losing trapping efficiency . I believe its a juggle between making some power pre boost and taking as much advantage as possible from the exhaust gasses pulse velocity energy .

It sounds silly but I think you need to seperate throttle/torque response from turbo boost response here . How you go about getting torque is tied to static and dynamic compression ratio and how boost pressure/turbine and housing restriction affects these two .

First things first what exactly are you trying to achieve and over what rev range ? I sort of get the feeling that the RB26's power characteristics don't suit you and you'd prefer it to pull hard without reving it .

[Leadfoot]

I would not rule out your EBC not to be the cause of the slow reponse.

I have the Blitz i-color and it took me ages to get it set up right.

Initially it took me days to figure out what I was doing but now I can get close to what I want in about an hour of solid road tuning.

I gained a massive improvement in response by changing from single stage manual to 4 stage manual.

If your using auto control or single stage manual control they are both very very lazy.

If your are already using 4 stage manual then try and increase the duty of the sub 3000rpm stage and see what happens.

If you are not using it in 4 stage manual control then you could easily be loosing 500 to 1000 rpm to full boost.

An incorrectly setup EBC is evident by results of 0.8bar at 3000rpm and 1.0 bar at 3500rpm.

If this is the case then 1.0 bar will still be achievable at 3000 rpm by correctly setting the duty cycle at lower rpm.

It will take a process of iteration however I would start with the 1st stage from 0 - 3000 rpm,

2nd stage from 3000-4000, 3rd stage from 5000-6500 and 4th stage from 6500 - 7500rpm.

You will then need to road tune each stage to find the right duty cycle for each. 4th gear of higher is best.

Some adjustment of the rpms may also be needed to keep the boost curve as flat as possible.

A good setup will actually give a small amount of overboost when the turbo first comes on boost.

In the first stage I bypass nearly all the pressure at the wastegate (70% duty cycle) to prevent wastegate creep.

This then quickly decreases down to 20% once the turbo is fully spooled.

Faster response will also be achieved by increasing the spring tension on the actuators so that the EBC duty cycle is kept low at all engine revs.

If the spring pressure is too low you will be getting waste gate creep costing you response regardless of EBD duty cycle.

Since you have 2 turbos on the GTR some care would need to be taken that each actuator is set correctly.

If one actuator opened before the other then all sorts of things could happen.

For piece of mind it is quite easy to use a compressed air souce and pressure regulator to ensure the actuators are behaving equally and in unison.

For a 15psi setting the actuators should be opening at around 12psi.

The most stable boost control is obtained by taking the boost supply directly off the turbo(s) and not from the cool side of the intercooler.

Whilst the idea of running cool air through the expensive solenoid sounds like a good idea it does not give the best result.

In fact, auto mode on the IBC wont even learn if this setup configuration is used. Not on my single anyway.

Pressure loss across the intercooler at higher rpms (pressure drop increases at higher flowrates) creates havoc on hot versus cold days and you will forever be fiddling with duty cycles.

[wegs]

How much boost you have at 2,700rpm is not really what you want to be measuring, in fact who cares? I think you want a car that accellerates faster and is quick to 'listen' to your right foot. Am I right?

If we talk just about the GT-SS turbo setup then 'response' improvement could be sensibly confined to the area that turbos works best in with regards to airflow. Removing airlfow restrictions naturally improves the efficiency and speed at which the turbo can pump air.

Can a better designed intercooler acheive this?

Yes. However core volume increases aren't necessarily good if you are chasing better low end/mid range characteristics.

Anything else that improves response with regards to rotational inertia helps. Light wheels , crank pulley, flywheel & clutch , tailshaft. Diff ratios etc..

Thanks for your reply Rev210. I can see what you mean about response. YOu are right about the engine listening to my right foot. I probably should take some focus away from boost but doing so doesn't leave me with much to work with on a stock engine. I will look at improving the efficiency of the intake system and making sure that is the best it can be.

I will look at what i can do to reduce drivetrain weight within my budget, thanks

1 bar at 4000rpm..I assume in 4th.. is a wee bit sleepy for GT-SS's. I have 1 bar at 4050rpm and +ve boost @ 1800rpm- you know the setup I am running.

Also your compression readings do seem high if that was an accurate reading. Though if true you should have even more response than expected and low ignition values up top...say 10-16 degree's ???? From my last car I bought from M***** I see his tuning has gone away from high ignition timing and rich mixtures to economical AFR's and less timing. May just be the way he tuned the ZOOM 4 door RB26 but I would be interested to see your tune.

Another check would be to see what you min boost level is....if your waste gate actuators are wound out to soft you will get average boost response no matter what. I set mine to just below the min boost I would run, which is 1.05bar.

I assume the BOV you bought is adjustable...I would screw it closed also for a quick check.

I can understand the reasoning to run only 1.2bar as the mapped efficientcy level does drop off when looking at the compressor map at over 1.25 bar. However HKS recommend 1.4bar.......Probably because of the HKS housing. Which is much different to Garrett as I have had the two side by side. The dyno graph attached which I assume is at the engine does look how I would expect from what you have told me response wise. I have been in two different RB26's and they make 1bar by about 3800- 3900rpm on the stock turbos...the transient response however in much better than the larger turbos.. I really don't think there is a massive rpm difference to reach one bar off boost between stock, GT-SS and GT2530's ...maybe 500rpm.......as the other graph shows

Hope some of this blurb helps

Matt, some great stuff here for me to get my head into. I'm starting to think my setup is pretty close to what it should be but starting to sound like there's a bit of improvements to be had which is the purpose of this thread. Would be good for you to have a look at my tune sometime. I'm pretty keen to come out with your mates on a cruise soon to see some other examples. I have another friend who's just about finished his GTR upgrade too and could join.

I tested my actuators before installing the turbos. They are HKS 1 bar actuators and using a regulator & compressor i could see they were starting to open at 12-13psi so i left them as is. Interestingly, my tuner didn't discuss or advise on boost at all. Nor did we talk about adjusting the BOV. Currently the BOV is set just above minimum so I will wind it to max and see what happens. As for boost i assumed my max was what was set on the dyno (1.1) and never to go above that? I haven't considered anything over 1.2 - makes me nervous.

Given the focus on actuators in these responses I want to retest/reset my actuators to make sure they are spot on - what pressure would you recommend I set them at to start opening and to fully open? Should i really consider upping my boost past the dyno tune max of 1.1?

First things first what exactly are you trying to achieve and over what rev range ? I sort of get the feeling that the RB26's power characteristics don't suit you and you'd prefer it to pull hard without reving it .

Discopotato03. I was only ever expecting what I was told to expect. The Rb26 is pretty damn good for torque and response in stock form and I never set out to improve on that as it would involve internals. This is why I focussed this thread on boost. I love jap engines and their ability to rev... but I want mine to last and that means keeping away from the factory rev limiter. I don't drive it hard much or in hot weather and always change gears before 7000rpm. If i was just focussed on 1/4 mile runs this whole response thing wouldn't be a discussion. I can launch and stay on boost no problems. But I want a fast street car that when cruising off power, is still quick to get onto boost. Not very technical way of putting it but that's what i wanted to acheive best I could given it's an Rb26.

I would not rule out your EBC not to be the cause of the slow reponse.

I have the Blitz i-color and it took me ages to get it set up right.

Initially it took me days to figure out what I was doing but now I can get close to what I want in about an hour of solid road tuning.

I gained a massive improvement in response by changing from single stage manual to 4 stage manual.

If your using auto control or single stage manual control they are both very very lazy.

If your are already using 4 stage manual then try and increase the duty of the sub 3000rpm stage and see what happens.

If you are not using it in 4 stage manual control then you could easily be loosing 500 to 1000 rpm to full boost.

An incorrectly setup EBC is evident by results of 0.8bar at 3000rpm and 1.0 bar at 3500rpm.

If this is the case then 1.0 bar will still be achievable at 3000 rpm by correctly setting the duty cycle at lower rpm.

It will take a process of iteration however I would start with the 1st stage from 0 - 3000 rpm,

2nd stage from 3000-4000, 3rd stage from 5000-6500 and 4th stage from 6500 - 7500rpm.

You will then need to road tune each stage to find the right duty cycle for each. 4th gear of higher is best.

Some adjustment of the rpms may also be needed to keep the boost curve as flat as possible.

A good setup will actually give a small amount of overboost when the turbo first comes on boost.

In the first stage I bypass nearly all the pressure at the wastegate (70% duty cycle) to prevent wastegate creep.

This then quickly decreases down to 20% once the turbo is fully spooled.

Faster response will also be achieved by increasing the spring tension on the actuators so that the EBC duty cycle is kept low at all engine revs.

If the spring pressure is too low you will be getting waste gate creep costing you response regardless of EBD duty cycle.

Since you have 2 turbos on the GTR some care would need to be taken that each actuator is set correctly.

If one actuator opened before the other then all sorts of things could happen.

For piece of mind it is quite easy to use a compressed air souce and pressure regulator to ensure the actuators are behaving equally and in unison.

For a 15psi setting the actuators should be opening at around 12psi.

The most stable boost control is obtained by taking the boost supply directly off the turbo(s) and not from the cool side of the intercooler.

Whilst the idea of running cool air through the expensive solenoid sounds like a good idea it does not give the best result.

In fact, auto mode on the IBC wont even learn if this setup configuration is used. Not on my single anyway.

Pressure loss across the intercooler at higher rpms (pressure drop increases at higher flowrates) creates havoc on hot versus cold days and you will forever be fiddling with duty cycles.

Really appreciate your response Leadfoot. Suddenly all of my attention has turned to your post about the amount of time I should spend setting up my EBC. I am currently running a single channel on manual duty cycle. My peak boost seems to keep changing depending on air temps so I find myself constantly adjusting the duty cycle of the channel to keep it under 1.1bar. I haven't even given any thought to 'tuning' it. The only advice i got form my dyno tune was to experiement with gain on the road... but even now i'm still not sure what that means. The Icolor manual recommends small ball bearing turbos should have gain set between 5 & 15 (factory turbos are 15-25)... and that's on a scale between 1 & 100. Doesn't give me much room to experiement hey. Do you think i can ignore this in my testing and try higher gain numbers? Are boost spikes the only thing to watch out for with gain increases? What is considered safe? I also need to approach this with the multiple channel manual setup.

Also i have been questioning the pickup point for my boost controller from the day i installed it. I wanted to take the pickup point after the turbos but there was no factory option to do this. I took it from the same point as the factory boost guage which comes off the back of the manifold. There's almost 1.5 metres of vacuum hosing bewteen the pickup point and the boost controller... i started to wonder if this itself would create delays in actuator response. After reading your post I am thinking about tapping a vacuum point into the hard pipe piece which is directly after the point where the 2 turbo chambers merge on their way to the FMIC.

Thanks again for everyone's input.

Wegs

Edited February 3, 2008 by wegs

[BOOSTD]

"Matt, some great stuff here for me to get my head into. I'm starting to think my setup is pretty close to what it should be but starting to sound like there's a bit of improvements to be had which is the purpose of this thread. Would be good for you to have a look at my tune sometime. I'm pretty keen to come out with your mates on a cruise soon to see some other examples. I have another friend who's just about finished his GTR upgrade too and could join.

I tested my actuators before installing the turbos. They are HKS 1 bar actuators and using a regulator & compressor i could see they were starting to open at 12-13psi so i left them as is. Interestingly, my tuner didn't discuss or advise on boost at all. Nor did we talk about adjusting the BOV. Currently the BOV is set just above minimum so I will wind it to max and see what happens. As for boost i assumed my max was what was set on the dyno (1.1) and never to go above that? I haven't considered anything over 1.2 - makes me nervous.

Given the focus on actuators in these responses I want to retest/reset my actuators to make sure they are spot on - what pressure would you recommend I set them at to start opening and to fully open? Should i really consider upping my boost past the dyno tune max of 1.1?"

-Your actuators sound to be set ok, I would leave them( adjusting up to 1.1 from .9 wouldn't make much difference to there response)

-BOV could be a leaking issue if it is set as low as you say....your boost pressure is not that high as yet though

-1.1 Bar !!! wow I'm quite impressed with your power level then

-I wouldn't increase boost without a wideband AFR and PFC hand controller for knock feedback. If you sold yours I have a PLX. But yes get the boost up!

[wegs]

-BOV could be a leaking issue if it is set as low as you say....your boost pressure is not that high as yet though

-1.1 Bar !!! wow I'm quite impressed with your power level then

-I wouldn't increase boost without a wideband AFR and PFC hand controller for knock feedback. If you sold yours I have a PLX. But yes get the boost up!

I don't think i'm telling tales about the boost but I should clarify... my EBC read a peak of 1.15 after coming off the dyno... but the dyno sheet shows it peaks slightly higher at 1.2 bar before falling back to 1.1bar for the remainder of the run.

Yep, sold my LM-1 before getting a chance to use it. I decided not to tune with it so it would've been a waste keeping it for a couple one off uses. I'll leave boost as is for now, might be an area we look at later on.

Thanks,

Wegs