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Thread: help 15psi stable with no boost controler

  1. #21
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    Quote Originally Posted by Millbank View Post
    Your right I shouldn't make the mistake of saying stage 3 as a custom map is nothing like a stage 3 chip. Was just tring to say that as much as people say you need this and that for stage 1, 2 and 3 it all depends on what condition those parts are in as well. Just because you bolt on some 444cc injectors it doesn't mean they are pushing the right fuelling.

    You did kind of jump the gun a bit lol

    The generic maps stage 1-3 are mapped specifically for certain mods

    You can't put any size of injector on any map. The 444cc might show safe afr's when on full boost but cruising around will run really rich on that stage 2 generic map which will eventually lead to worn rings and no compression.

    As above unless that t25 your running has a ball bearing core that turbo will die quickly, I would also suggest tweaking it to 1.1-1.2bar even then it won't last long. Also the boost dies way early with t25, why not put a gt28r on there and enjoy 320bhp all day with quick spooling.

    I have to note that I had a stage 2 ca that made 280bhp at 1bar but the best thing about using the t28 was that my power didn't die till 7200rpm. So instead of wasting 1500rpm changing early to stay in the power I could use all the revs through the gears. Felt good, better than my current sr20det running 330hp at the wheels

  2. #22
    Guest M.D.'s Avatar
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    Quote Originally Posted by croustibat View Post
    It still wont last long at 1.5bar though ... a T28 starts becoming unreliable past 1.2bar. Yours is a hybrid, so should not go higher either.

    Fact is, if you want you turbo last a little bit, lower the boost to 1~1.1bar ... yes it will be less enjoyable. but there is no joy in breaking a turbo either.
    I'm not sure how to read compressor maps yet but I do find your responses very closed minded.
    The Renault 5 boys running t25s are running in the region of 30psi in some cases due to very restrictive carbs. That's 2 bar boost. Much much over what your saying is max for the turbo. I'm guessing that the engine size has a fair bit to do with it so having a larger engine will mean the turbo will have to work harder to achieve the same boost hence lowering the safe boost level.

    The cosworth boys run silly boost through there t28 sized turbos too. It's only over here on the Nissan sites that running more than 1.2 bar from a turbo seems to be slated immediately. And I'm still not sure why that is.

    Anyway to reply to the OP.
    if you have a STOCK stage 2 chip you need to remove the injectors for a start and fit standard ones before you bore wash the engine. Or get the stage 3 chip.
    As for the boost have you got washers behind the bolts for the actuator? Or is the arm bent in any way?

  3. #23
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    Quote Originally Posted by M.D. View Post
    I'm not sure how to read compressor maps yet but I do find your responses very closed minded.
    The Renault 5 boys running t25s are running in the region of 30psi in some cases due to very restrictive carbs. That's 2 bar boost. Much much over what your saying is max for the turbo. I'm guessing that the engine size has a fair bit to do with it so having a larger engine will mean the turbo will have to work harder to achieve the same boost hence lowering the safe boost level.

    The cosworth boys run silly boost through there t28 sized turbos too. It's only over here on the Nissan sites that running more than 1.2 bar from a turbo seems to be slated immediately. And I'm still not sure why that is.

    Anyway to reply to the OP.
    if you have a STOCK stage 2 chip you need to remove the injectors for a start and fit standard ones before you bore wash the engine. Or get the stage 3 chip.
    As for the boost have you got washers behind the bolts for the actuator? Or is the arm bent in any way?
    Ok, here is how to read these maps:
    vertically you have the pressure ratio, ie the difference between turbo air inlet and outlet. Watch that sheet of paper, and tell me what you see on the 2.5bar line (which is 1.5ar boost).

    Horizontally you have the flow of your engine, which depends on its displacement, volumetric efficiency, the boost you are running and the rpm. As it is approximate, use 90% VE, it works ok.

    The closed forms in the middle are called islands, and are the efficiency (remember it is a compression), and the "somewhat horizontal lines" are at iso turbo shaft speed. You never want to be on the left of the islands, which is surge domain, nor over it, which is overspin domain. And you dont want to be anywhere OUT of the islands in fact, because that is unefficiency domain (but that last one does not break turbos, it just kills performance)

    Basically you want to stay in the center island most of the time.

    On the pic i posted, someone has already drawn the flow of a CA18DET on various pressures.

    The oem turbo on a CA18DET should not be run past 1bar, because it simply becomes unreliable and unefficient there. 1.5bar is just completely out of the map, so thats a no no.

    R5 turbos dont run a T25, they run a T2, and they use a 1.4L engine; you cant compare them just because they have "somewhat the same size". It does not work like that. Finally, if many people do the same stupid thing, it does not make it good; it makes them stupid. If they truly run 2bars on a CA18DET turbo, that makes them completely stupid.

    A GT2871r is still a T28 sized turbo, and it can nearly run 2bars ... of course you can make it produce 2.5bars. But it wont be efficient; a gt3076r will produce way more power at the same pressure (efficiency), and surely the same power at 2.1bar.


    A turbo is not a magical device; it produces flow at a given pressure, and it can only do that if it is powered in some way (there comes the usual "there is no replacement for displacement"; if you want a lot of flow, you need a big engine, or you will have a very narrow boost range).

    A T28 has around the same map as a gt2560r ; you can see the maps on turbobygarrett.com . It can barely flow up to 1.5bar . His is a hybrid between the 2, so limits are somewhere in between.

    It is not a question of ball bearing or not, ball bearing turbos tend to be less tolerant to overboost / overspin too.

  4. #24
    Guest Millbank's Avatar
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    Thanks for sharing you knowledge. I run the car at0.9 bar for normal driving as his produces 270 bhp. I turn it up to full boost which is 1.5 bar for shits and giggles.
    Also if my turbo stops producing extra power a lot less than 1.5 bar why would jez keep turning it up past that point. The man knows his stuff so I'll trust what he's done with my car thanks :-)
    Last edited by Millbank; 11-12-2012 at 07:15.

  5. #25
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    Funnily enough I was down there after this dyno run, I remember seeing it on the screen...

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    I think people are just trying t o give you some useful/sensible advice i wouldn't throw it back in their faces because you never know one day you may just need them.

    Oh but hang on you know what your doing so you won't be needing no advice! Lol

    I am actually very interested to hear what Jez has to say and why he hasn't posted on this thread yet (if he's seen it) Yes Jez is highly recommended and knowledgable but so are others!!!

  7. #27
    Guest M.D.'s Avatar
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    Quote Originally Posted by croustibat View Post
    Ok, here is how to read these maps:
    vertically you have the pressure ratio, ie the difference between turbo air inlet and outlet. Watch that sheet of paper, and tell me what you see on the 2.5bar line (which is 1.5ar boost).

    Horizontally you have the flow of your engine, which depends on its displacement, volumetric efficiency, the boost you are running and the rpm. As it is approximate, use 90% VE, it works ok.

    The closed forms in the middle are called islands, and are the efficiency (remember it is a compression), and the "somewhat horizontal lines" are at iso turbo shaft speed. You never want to be on the left of the islands, which is surge domain, nor over it, which is overspin domain. And you dont want to be anywhere OUT of the islands in fact, because that is unefficiency domain (but that last one does not break turbos, it just kills performance)

    Basically you want to stay in the center island most of the time.

    On the pic i posted, someone has already drawn the flow of a CA18DET on various pressures.

    The oem turbo on a CA18DET should not be run past 1bar, because it simply becomes unreliable and unefficient there. 1.5bar is just completely out of the map, so thats a no no.

    R5 turbos dont run a T25, they run a T2, and they use a 1.4L engine; you cant compare them just because they have "somewhat the same size". It does not work like that. Finally, if many people do the same stupid thing, it does not make it good; it makes them stupid. If they truly run 2bars on a CA18DET turbo, that makes them completely stupid.

    A GT2871r is still a T28 sized turbo, and it can nearly run 2bars ... of course you can make it produce 2.5bars. But it wont be efficient; a gt3076r will produce way more power at the same pressure (efficiency), and surely the same power at 2.1bar.


    A turbo is not a magical device; it produces flow at a given pressure, and it can only do that if it is powered in some way (there comes the usual "there is no replacement for displacement"; if you want a lot of flow, you need a big engine, or you will have a very narrow boost range).

    A T28 has around the same map as a gt2560r ; you can see the maps on turbobygarrett.com . It can barely flow up to 1.5bar . His is a hybrid between the 2, so limits are somewhere in between.

    It is not a question of ball bearing or not, ball bearing turbos tend to be less tolerant to overboost / overspin too.
    Thankyou that was very informative actually. And Thankyou for taking the time to write that too.

    As much as I can see what your explaining you are also going against what people have been doing for decades. The whole concept of engine modification is to push the boundaries of what's possible. Back in the 80s when f1 were running turbocharged 1.6 v6 engines they were running KKK turbos. Nothing massive either. And we're running 4 bar boost! As you say things like flow etc of those little F1 engines would have been fairly immense but I'm putting a lot of there 1000bhp down to the fact they had so much fuel and boost rammed through them.

    Also my local engine tuner has been winding gt30-35 style turbos on scoob and evo engines (both 2 litre) to well over 2 bar for a long time with excellent success. How else would you get 700bhp from an impreza engine without having such a big turbo that the lagg would be obscene.

    Just because the flow map says you "shouldn't" do it doesn't mean it's stupid to try. And this guy with only a very very mildly modified turbo has got more power than many have on his engine and turbo set up. It may well be peaky and the turbo may spit its guts out before long. But then every tuned engine has a massively reduced lifespan anyway. So it's no different to deciding that you want to rev to 8k rather than 7k. It's less safe but its the choice you have decided to make to get more from your engine.

    Don't take this as me questioning your knowledge on the subject as you obviously know a lot more of the technical side of things than me. But im more into actually trying things rather than theorising the outcome.
    For me. When a turbo stops making power increases. That's when I'll stop turning the boost up.

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    @ Milbank you may know about cars but can't tell apples from pears. A T25 with a T28 comp wheel IS NOT A T25. If it was a T25 you would have been very upset at the result. You have a turbine that spools the comp earlier than a T28, boost like a T28 but it runs out of puff early hence the 5750 rpm peak power, somewhat lower than stock 6400 rpm.

    A 1.4L Renault 5 engine has 0.77 of the gas flow kg/sec compared to a 1.8. That will just about stick it straight up the middle of the boost map. While a 1.8 falls way off to the right and at about 15psi hits the choke line - that's where the constant speed line is plummeting towards zero pressure ratio. At 2.2 bar and 20 lb/min it's nicely on the map at 154000rpm and 71% effy, take it to 25 lb/min and it needs to go over 168000rpm with less than 60% effy. It like

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    Turbo'ed F1 where design to last 1 race, or considering qualification engines, 3 laps. I dont want my car to last 3 laps. You dont wan either.

    And yes, when the flow map tells you will be overspinning, surging and at a 60% efficiency at best, it IS stupid to try, unless you dont care if the turbo dies very fast, produces no power, and heats your charge so much it will need a 50L intercooler to get it at an acceptable level. A T25, or a T25 hybrid, being used at 1.5bar on a CA18DET is just plain stupid, and just made so its owner can say "OMG I HAZ 1.5BAR BOOST" . Get a small gt2871R, boost it at 1.2/1.3 bars, and you will have just the same power with more reliability than ever, turbo and engine wise.

    Sometimes it is stupid to try, that is why people pay engineers: to know exactly when it becomes stupid, unreliable, costy or just not what you actually want. I will make some runs when my S13 is out from the shop. It just uses a gt28r, and i bet i get more power out of it at 1.2bar than he is making at 1.5. I was already doing ~290 at 1bar, with leaky injector gasket (aka "no fuel pressure"), maxed injector duty, a reversed exhaust gasket (it blocks half the flow of a cylinder) and stock exhaust mani...

    Local engine tuners around here like to tell that EFI is shit and nothing beats a pair of WEBER 40 DCOE. While they were right 40 years ago, things have changed, and i would not trade my EFI system against any number of carbs. But these people did not evolve, and are still stuck with the same talk. Too bad.

    Now GT30/ 35 turbos are NOT T25, nor T28. These are made to sustain high pressure boost on a 2L/2.5L engine. Just look at their compressor map, what more can i tell you ? The problem is not boosting an engine to a high level, the problem is trying to reach a boost pressure and flow that a particular turbo cannot output reliably. Stock T25 ? 1bar max. T28/gt28r ? 1.2bar max. These are the acceptable reliability limit; going higher is going to wear the turbo fast without producing much more power. Of course it may produce an extra bit, but it really is not worth the damage it makes. Unless you get an unlimited free turbo supply of course.
    Last edited by croustibat; 11-12-2012 at 11:13.

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    I have to agree with what Croustibat is saying here and, as already mentioned, its good that he took the time to explain his reasoning in a clear, non-confrontational way.

    One minor point I would make is that what you set the boost controller at is not necessarily what you get. It only sets the maximum and stops you going over.

    My T25/Stage 1 S13 was making 240 bhp and 245 lb/ft with the controller set to 16 psi (1.1 bar) but the turbo was only producing 16 psi at around 2.5 to 4K rpm. Once above that rpm range, the boost dropped off steadily to around 9 psi (0.6 bar) at 6K rpm. There was no boost leak, no lean running or anything else. I was told this was simply down to the turbo not being able to move enough air into the inlet to keep the pressure up as the cylinders took the air out.

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    Quote Originally Posted by Jonny Wilkinson View Post
    I have to agree with what Croustibat is saying here and, as already mentioned, its good that he took the time to explain his reasoning in a clear, non-confrontational way.
    thanks for noticing it

    Quote Originally Posted by Jonny Wilkinson View Post
    One minor point I would make is that what you set the boost controller at is not necessarily what you get. It only sets the maximum and stops you going over.

    My T25/Stage 1 S13 was making 240 bhp and 245 lb/ft with the controller set to 16 psi (1.1 bar) but the turbo was only producing 16 psi at around 2.5 to 4K rpm. Once above that rpm range, the boost dropped off steadily to around 9 psi (0.6 bar) at 6K rpm. There was no boost leak, no lean running or anything else. I was told this was simply down to the turbo not being able to move enough air into the inlet to keep the pressure up as the cylinders took the air out.
    That is due to the turbo being out of puff. Report your flow on the map on the previous page (you can extrapolate from the 8psi line, just double its height), you will see that you should be out of the map somewhere near 5500/5800rpm. Solution : use a T28 and you will get that boost till redline :d

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    Guest M.D.'s Avatar
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    Christ this actually seems like a decent discussion not a slagging match. Makes a nice change for a forum lol.

    I was just thinking while sat in the car. I'm sure I remember polo running his gt2871r .64 turbo at something like 2.2bar boost to get well over 400bhp on his bone stock SR.
    Would this be considered "outside" the map for that turbo?
    Because he ran it like that for a hell of a lot of hard drift miles.

    I'm getting where your coming from with the stock t25 etc turbo as I know that they drop off boost very quickly.
    But my argument to your reply of "why didn't he just get X turbo and run it at less boost more reliably" is lagg.
    A larger turbo = more lagg. So although his power may drop off faster due to the turbo not being able to sustain that boost pressure. He will have a much more responsive engine that performs better lower down the rev range. And I know from experience this is exactly what I require when drifting or using the car in the lanes. Higher revs really are not desirable for some situations so keeping small turbos can actually be a benefit.
    Although as you say. It may not last as long.

  13. #33
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    Quote Originally Posted by M.D. View Post
    I'm sure I remember polo running his gt2871r .64 turbo at something like 2.2bar boost to get well over 400bhp on his bone stock SR.
    Would this be considered "outside" the map for that turbo?
    Because he ran it like that for a hell of a lot of hard drift miles.
    Probably close to the limit.

    If it was bone stock (cams and all) then you can run a slightly higher boost pressure as the engine flow would be less than an identical engine with cams and various other intake/exhaust mods.

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    The trade off between having a tubbie with enough puff and having it be responsive in the lower rev range is why I'm fitting a GT2560R....unless I spend so long getting round to it that I get interested in a GTX2863R and fit one of those instead.

    I'm just waiting for someone to do the pioneering for me as I don't know anyone that's fitted it to a CA yet. There are a few SRs out there with the GTXs now but the SRs have enough cc difference to mean they don't behave the same.

  15. #35
    Can't tell the difference cleanhands's Avatar
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    One of the things I've noticed since moving into the Japanese tuning scene is the almost obsessive interest in boost pressure at the redline.

    This is only the same as normally aspirated tuning where long duration, high lift cams are specified and has exactly the same result. i.e. a loss of low-mid range torque. It's horses for courses really. Personally I'd prefer a smaller turbo working hard low down.

    Compressor maps are just to give you an idea of where a turbo is most efficient, as with any tuning it's a trade off. Using Polo's example no one could say categorically which would break first, a stock SR running 400bhp or a 2871 pushing 2.2 bar. Bet it was fun while it lasted.

    Jonny, I want to look at an IHI vf38 one day, I'll have to get Rapid to dust of the TIG welder.
    Last edited by cleanhands; 11-12-2012 at 18:09.

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    Quote Originally Posted by bigluke View Post
    right i fitted a boost gauge today and found that it's hold 15psi with no problem i have 444incjectors turbo back stage 2 chip pod filter and thats it the actuator id black not gold by the way is this right ?
    feel sorry for this guy as hes probably no where nearer the resolution to is problem..

    shouldnt be using 444s on a stock stage two map

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    Welll, yes it has gone a bit off topic but TBH, there is something not quite right.

    If you really had a T25, 444 injectors, a cone filter and an exhaust, you'd struggle to get the car to start let alone pull 15 psi with no actuator. Add to it a Stage 2 chip that is written for a different turbo and different injectors....

    The only thing I can think is that the OP is going off what he was told was on the car when he bought it and the reality is somewhat different.

    His best bet is to take good quality close-up pics of the injectors, the actuator and surrounding area and removing the ECU and photos of the inside.

    He could then get suggestions as to what his spec really is, what he should think about removing straightaway and what he can change to get to a matching set of tuning goodies.

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    Quote Originally Posted by Jonny Wilkinson View Post
    The trade off between having a tubbie with enough puff and having it be responsive in the lower rev range is why I'm fitting a GT2560R....unless I spend so long getting round to it that I get interested in a GTX2863R and fit one of those instead.

    I'm just waiting for someone to do the pioneering for me as I don't know anyone that's fitted it to a CA yet. There are a few SRs out there with the GTXs now but the SRs have enough cc difference to mean they don't behave the same.
    I cant remember which one it is (2867 or 2863), i'll ask. My tuner has one on his CA, and i will see him on saturday. Although his CA is really highly developped, so it might not exactly compare to yours... but i can tell these turbos have come a long way since the old GT28R / 2860/2871. You can now get gt28r spool time with gt2871r power level (the big 450HP ones). His car is insane and it goes fast, so cant really tell how fast it spools. But it spools fast, and i kind of already went in stupidly fast cars. He has a (already blown) Z32 gearbox, but it nearly feels like a close ratio, he can make the speedo go at the max it can between two not so distant roundabouts, and then brake enough to stop. unrestricted, tuned 1000cc bikes dont accelerate nor go that fast

    But in a way it "lacks something". It is too efficient, the "boost kick in the face" is not there. It feels like a very strong and smooth push. The car is fast but does not show it... i remember saying "hmmm ... i am not impressed by the braking", which he answered by "watch the speedo next time". The thing goes fast so smoothly my mind somewhat did not record we were going at around 270.

    Anyway he is done playing with small turbos and is building something even more stupid, with an enormous twinscroll turbo system. I might convince him to use nitrous to spool the beast though. I think he is planning to run between 2.5 and 3 bar boost.

  19. #39
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    I ran my old t28 (s14) at 1.3 /1.4 bar in an attempt to see its life expectancy.

    It snuffed it rather pronto.

    I suspect this t25/t28 or whatever will also be pushing up the daisys soon, well ok maybe blowing out the oil seals...

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    Opened a can of worms here...lol
    Come on guys it's all in the fun of pushing it. As I said earlier I drive it at 0.9 bar so as not to kill it too quickly. But it has been mapped to run 320 bhp so god damn it I'm gunna run it sometimes ;-)
    My limiter has been mapped in to 7250 rpm so I don't over rev and destroy.
    Also tubby is brand new so should last a bit.

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