Nistune Forums

Hi PL, sorry for a long time it took to write a reply.

Turbo and bearings - exactly what you say. Stock was ball bearing. Dealer told us the same thing - turbo CHRA is stuffed (had excessive axial play) and being ball-bearing can not be repaired, requires replacement. Local dealers' warranty policy is such that "professional installation" is required to get 1 year turbo warranty, otherwise warranty period is only 1 mounth or so. Professional installation means installation performed by an authorized dealer i.e. themselves. So we just asked for standard medium-size garret ball bearing section (GT25, GT28, GT30 and GT35 share the same central body, dealer recieves crates with spare parts and assembles them at their local facilities), GT28 turbine wheel and shaft and left the car at their place. They assembled the turbo and installed it, dont know if they had to change oil lines or not. Good thing is that when you repair/buy turbo with them, the installation is free. Another good thing is that they check oil flow and pressure that engine delivers prior to installation, so no leaking bearings and seals. Bad thing is the cost of a new BB central section - more then half of price of a new turbo.

Exhaust restriction. Matt's example clearly shows just how important turbine section and its flow and size characteristics is for good power. GT3071 is a bit extreme in this case - a lot of turbine for the compressor, a bit unusual for gasoline engine these days, but advantages of spacious turbines and housings are very well seen on power vs. boost dyno prinouts. Stock turbo makes more boost and makes boost earlier but still produces equal or less power everywhere. Torque range with 3071 is nice, progressive and broad, car is fun to drive and does not shock you with sudden surges of power. This car is really fast - in OEM kind of way. It is fast but not nervous and does not require top driving skills to be fast.
Also note how easily full compressor flow potential has been released - you do not see this often nowadays on turbos like T3/T4's, GT28's, GT3076's/GT3582's these days. All these turbos have too little turbine for their respective compressors hence the necessity to use the biggest A/R turbine housing to achieve all the power available from compressor and necessity to play with housing A/Rs to get either acceptable boost response or top end power, but rarely both at the same time. Even more extreme examples of turbine and compressor imbalance are GT3040R
- 82mm compressor capable of 600+hp worth of air mated to GT30 60mm turbine equal to that on Matt's car, which have never shown any more HP than original 520hp GT3076 unless water/methanol injection or some 110-115 octane fuel have been used, and all this with the biggest available 1.06 AR housing (but it have shown pathetic mileage, compressor surging and generally unusable street manners) - or popular several years ago GT2876R
- where even the smallest 48 trim 76.2mm compressor is just an overkill for 53.8 GT28 turbine and that is

Garrett wrote:Best suited for unique applications such as asymmetric turbo installations
Not recommended for general performance applications

On the other hand when we have adequate size on turbine size, we see turbos that are easily producing all the HP provided by compressor - like your GT3071 and ours so-called GT2867. No huge boost, no comp surge, no big thermal and mechanical stress - all this is direct consequence of enough (not big, but enough) turbine and its flow for a given compressor.

I've desided to split the above post.

Cams. Directly related to the above subject and road manners. Obviously too small a turbo or A/R - and you have to reduce valve overlap and stick to short duration/high lift cams. I'm not an expert by any means but pretty much every source or info calls this combo at least less then optimal and not promoting broad torque range. Like you say, we are lucky that we now have modern multi-valve free-flowing heads with efficient chambers. Corky Bell's statement that "It is hard to find a better cam for turbo engine than a stock cam" definitely got old. Remember that at the very beginning of multivalve era 4 valvers were considered unable to deliver good low-end performance due to lack of intake charge swirl. Fortunately, OEMs proved these statements wrong. Now we enter even more wonderful era - manufacturers investigate means of infinitely variable valve events. Although no directly applicable to our SR20's and RB25's, these investigations more often than not give us some really interesting data as to the influence of varying valve events on 4 stroke combustion process.
Regarding turbo engines - among the info I read lately, there was a description of an engine outfitted with variable valve lift mechanism that was used to emulate VGT action and to broaden useful turbo range. The idea here is that on a really geometrically effective and flow-optimized manifold it was found useful to employ long duration/little lift exhaust valve event to impart substantial momentum to outflowing gasses during spoolup period (i.e. pre-boost). Results seem quite promising - turbo lag was reduced significantly and this allowed the use of bigger turbine housing and lower engine backpressure and also reduced fuel consumption. It makes me think that it will be nice to experiment with (possibly custom-ground) low lift and long duration cams on the exhaust side to aid turbo spoolup, intake side can have oversized valves and generously lifted/timed lobes to help cylinder filling and reduce boost pressure requirements.
The other cool thing I saw lately is continental/siemens electric variable valve train actuator. I'm trying to gather more info now, because although having switched two-position VTC on intake is nice, the ability to infinitely control cam angles and overlap is still nicer

Unfortunately implementation of and experimentation with all these ideas requires HUGE amounts of time and expertise and even bigger amounts of money. But I'd like to do it some day.

Petros.

I can segway the off topic discussion back on topic...

Matt, which set of cams are you going with?

Thats good what Pedros has posted, found it quite interesting. Currently its running standard cams but that will probably change eventually

Hi Petros,

Very interesting post. I totally agree with your thoughts. The 3071 seems to be a real sweet spot on a NEO RB25. I gotta say I was amazed to see the power it made before boost came up. And 280rwkw - I never would have thought it possible with the 71mm wheel.

My experience has generally been that going to a larger turbine side adds unacceptable lag - so seeing extra HP at less boost has come as quite a revelation.

I've been speaking to local tuners who are using the GT3071 (with the cut down 56.4mm turbine wheel and machined out T25 turbine hsg) on SR's and they're loving them. Supposedly full boost only a couple hundred rpm later - and they're seeing 280rwkw. From and SR!! Admittedly at higher boost (20psi).

Cams. Yes, once again I concur. It seems that we can go to "hotter" cams than factory and get good gains but if using small turbine sides then overlap needs to be minimised because the usual benefits are offset be the high backpressure. This explains why I've never seen any decent gains from fitting larger cams and/or adjusting overlap on SR's - nearly all the SR's I play with run 0.64 AR T25 turbine housings.

So unless we start using larger turbine sides on SR's then any camshaft improvements are a waste of time. But most people steer clear of the 0.86 T25 ex hsg due to poor response. Turbo sizing on SR's is a bit of a problem in this regard. ) .64 too small, 0.86 too big. Chris mentioned that he's modified a 0.64 to make it flow a bit better. Maybe this is the answer...

I guess, as always, it's a matter of deciding what you want from the engine. SR's go great with the old trusty T28 (GT2560) - to a point (around 200rwkw). Above that the 2871 is good but whether to go 0.64 or 0.86 is a problem, with 90% of owners ending up with 0.64 - and presumably quite high backpressure. Maybe the answer is to just go T3 pattern...

I wonder how a 3071 would go on an SR with your long duration ex cam idea to try to improve boost response. This turbo:

http://www.turbobygarrett.com/turbobyga ... 0382_3.htm

with a Poncam inlet cam (short duration, high lift at 256 degrees and 11.5mm) and one of the HKS 264 degree/10mm ex cams. HKS tend to run more duration and less lift than Tomei. I guess you could go to a 272 degree ex cam but the off-the-shelf cams tend to go to larger lift when you go to larger duration - requiring aftermarket springs, lifters etc. Running the Poncam inlet and HKS 264/10.0 ex cam would be "drop in" and valvetrain friendly.

Sorry to bang on about SR's all the time, but they are the main engine I deal with. How these RB's snuck into my life I'll never know...

Pete L

yeah my bad

Hey guys anyone run into this issue with R34 GTT's, we have a few making over 300rwkw and running 22-odd psi. Any boost over 19ish seems to bring on the check engine light on these cars (3 cars same deal).

Disconnecting the boost sensor fixes the warning light but means a full re-tune as the A/F leans out by 1-1.5 afr accross the range. The light seems to make no detrimental effects but is bit of a pain, and i like the map sensor to be functional so atm i put up with the light.

Am i missing something or is there no way of stopping the light once the map sensor hits peak voltage?

I've heard of this before once going over 17psi the boost pressure I belive hits max voltage and then the ECU triggers the DTC code but also pulls the check engine light

When we were running my car on 17 it was triggering the DTC code but no more problems than that

I've been looking at the ER34 code lately in regards to the boost pressure sensor (and boost solenoid)

The boost pressure sensor value is reported using Consult-II but we dont show that right now (I will eventually once I do some rewrite of the existing consult code without breaking stuff like logging which I've been doing recently )

Trying to understand the code is the major issue. Its very complicated compared to earlier code bases and I havent got much to go from

If I can work out what causes the CEL to trigger when DTC goes too high and eliminate that then we can get rid of it

One think you can try...

On the DTC Filter 2 - Boost Pressure Sensor - untick this one. Let me know if you still get the DTC code and check engine light when going over 19 psi

This is a filter for turning off codes but I dont know how far it goes as far as CEL lighting up is concerned

STATUS, by disconnecting the sensor do you mean disconnecting its plug or disconnecting boost signal hose from it?

If reaching peak voltage on map sensor does not cause any side effects other than CEL, then you may try to reduce voltage that comes from MAP back to ECU by putting some kind of voltage divider inline with MAP signal wire.

Petros.

I might do a log of the raw voltage from the sensor on my next dyno run to see what voltage levels its getting to (or monitor the consult memory address which might be easier)

@ 6000rpm we were seeing the BOOST SENSOR DTC code raised

Matt wrote:I might do a log of the raw voltage from the sensor on my next dyno run to see what voltage levels its getting to (or monitor the consult memory address which might be easier)

@ 6000rpm we were seeing the BOOST SENSOR DTC code raised

phew im kinda glad im not alone

i will have a play with the dtc filter and let you know.

LEGIONAIRE; i have fitted a ball bearing in the vac line to the sensor to see its effects on tuning and it has a major effect on AFR's so we removed it. I understand we canjust fit a voltage clamp on the signal line like we do with emanage ultimates on the r34 but im sure the setting will be hidden somwhere inside ecu.

Im totally useless to anyone when it comes to code so i have to sit that out. Maybe oneday ill read up on it.

Mine comes on also


not a great pain in the ass
but I was hoping that checking the DTC flag option would get rid of it



ahh well im sure matt will come up with something to combat this

Any news on this?

nothing yet. i've been incredibly busy lately that both cars have been ignored. still going to look at it through

Another dyno run and testing on the R31 ...

After last night we established that knock count works but the connection to the sensor is dodgy and keeps falling off. I need a proper connector for the hose type knock sensor. Also for some reason knock count isnt on the wideband trace so wasnt very useful

I need to add innovate back as a second sensor so we can log boost with the DLP and AFRs with the Innovate at the _same_ time. Also the DLP and Type 1 working together freezes up the entire laptop after not long. (Some kind of FTDI driver issue since both devices use this chipset and doesnt freeze up my desktop)

With the new exhaust system, loom rewiring we are now getting consistent results and a better curve. Dyno graphs to come