Sydneykid

Size and brand of tyres please?

Need to know a few more things before I can work out the wastegate size; Is the engine capable of handling 700 bhp? What boost level are you intending to run? Will the engine handle that level of boost?

Get the angle grinder out and put a slice down one of the valleys, then hit it with a cold chisel. They usually come off after that. If not, put two angle grinder slices in it, 180 degrees apart and when you hit it with the cold chissel it will break in half. New pulleys are very cheap.

A couple of years ago I changed the rear spring rate on an R33 GTST from 6kg/mm (335 lbs/inch) to 3kg/mm (170 lbs/inch). I also did a rear wheel alignment, backed off the shocks a bit and it was 3/10th's faster over 1/4. It already had pineapples, so no change there. A drag strip is a lot flatter and better prepared than the roads you drive on every day.

I have no problem with people having their own choice, after all it is their money, their time and effort. All I do is point out things that need to be understood when making a decision, too many people make decisions without the data to do so. I may use race cars as an example because I have thousands of data samples to draw on. I don't have to guess, I have the data to back it up. Data for road cars is not such a priority, I have a lot but not anywhere near as much. Road turbo sizing for me is very easy, I cruise at 120 kph max and as pointed out it is better to do that with no boost. My Skyline does 37 kph per thousand rpm in top gear. So I don't want any boost until after 3,250 rpm. So if I choose a turbo that will make boost at 3,500 rpm I will have the best of both worlds. I only have to rev it to 6,500 rpm in first, so it drops to 3,750 rpm in 2nd and I still have plenty of boost. I don't understand, for a road car, anyone not wanting boost until 5,000 rpm, that's a 185kph cruising. I should point out that there are plenty of other factors involved in when the turbo makes boost, many more than simply the tubo itself. Camshaft timing and lift, compression ratio, porting, manifolds, igntion timing, fuel tuning boost controller etc etc. Hope that helps clarify:cheers:

Damn, I was hoping that Stageas didn't have the annoying RB25DET power dip around 5,000 rpm when you give them a mild tune. :zap:

I have a 650 bhp RB31DET (3.1 litres) and it doesn't make 300 bhp off boost, in fact it doesn't even make 200 bhp off boost. An RB26 (2.6 litre) would have no chance and we have 2 of those as race cars to compare with.:cheers

I was talking about road and track (circuit and drag). It is very frustrating waiting for the boost to come back after you change into second. And the lower rpm you use in first the worse it gets, ie; you wait longer for the boost to come back. A few examples might help; Change up at 7,000 rpm, drop to 4,000 rpm, wait for revs to rise 1,000 rpm for boost to come back Change up at 6,000 rpm. drop to 3,500 rpm wait for revs to rise 1,500 rpm for boost to come back Change up at 5,000 rpm, drop to 3,000 rpm and never get boost at all. On the road I like to be able leave the repmobiles behind without reving the crap out it.

What about the floor pan?

Ahhh plenty, when tyou change from 1st to 2nd gear the engine revs drop by 3,000 rpm, So if you change up at 7,000 rpm in first you will end up at 4,000 rpm in 2nd. That means no boost until it reaches 5,000 rpm. Oooops that's not good for a fast time or beating that ........

Obviously if the gearbox needs a new mainshaft, selector hubs or output shaft then the price is higher. But if it is genuinely synchros, bearings and seals then $500 is a working average. You really can't tell until you open it up and do a detailed inspection.

Hi Roy, we could go around on this one all day. The Jun GTR isn't 2.6 litres, the works HKS driver uses N1's on his R34 GTR for around 600 bhp. He could have a T51 if he wanted. Plenty of people have tried, but as far as I know the GTR lap record at Tsukuba is still held by the Mines GTR and it doesn't have a T88 or a T78 or more than 650 bhp. You might get more power from a monster turbo, but the driveablity goes out the window and as you know lap times are more about the total engine package than outright power.

An RB20 DET gearbox is pretty much the same as a VLT gearbox, they cost ~$500 to service in Sydney. If you go to a RB25DET gearbox there are a number of things you need to change as well that inflate the costs (tailshaft, speedo drive etc)

1. You don't have to "butcher the looms" I splice in the larger AFM wiring harness in parrallel tothe standard plugs. This means you can swap back to the std AFM easily. 2. ARC (and probably others) make an airbox that fits the 80mm AFMs. You can modify the standard airbox, basically you just cut out the 65mm flanges and replace them with aluminium sheet for 80 mm. Sounds hard/shonky but looks good when finished. I have some pictures somewhere of one modified, I will try and find them. 3. Yes 4. Yes, there a few Jpanaese tuning shops that used to make them, swap the Z32 hot wire in to the GTR AFM body. But they aren't very common, most people went for the cheaper and more effective 80mm option. Hope that helps

Replacing an RB20/25DET AFM with a Z32 AFM is a worthwhile upgrade if the RB20/25DET AFM is reaching its max voltage and causing tuning problems as a result. This seems to have flowed over to GTR's even though it isn't really necessary in most cases. After all why worry about spending a couple of hundred dollears extra on Z32 AFMS compared to RB20/25 AFM's? Many people spend tens of thousands on their GTR upgrades, so what's a couple hundy here or there? Plus why take a risk, they might make enough power to max out the RB20/25 AFM's. Just buy the biggest and baddest and not worry about it. Perosnally I prefer to buy the right size for the power target, this table may help; Rule of thumb for Air Flow meters RWKW & Engine BHP ------ ---- OD ---- RWKW ---- RWKW ---- BHP ------ BHP No of AFM's ---- ------- 1 -------- 2 -------- 1 -------- 2 RB26 ------ 65 ------ 149 ------ 299 ------ 271 ------ 474 RB20/25 --- 80 ------ 226 ------ 453 ------ 376 ------ 683 Z32 ------- 80 ------ 255 ------ 511 ------ 415 ------ 763 Q45 ------- 90 ------ 302 ------ 605 ------ 479 ------ 890 Please note that this is only an indication, every engine is different and tuning makes a big difference. For example, I have seen a GTR equiped with twin Q45 AFM's make 1100 bhp. RB20/25 and Z32 AFM's are all 80 mm OD, that's outside diameter, not ID that's inside diameter. There is no real difference between an RB20 and an RB25 AFM. On the other hand the Z32 AFM is calibrated differently, so at the airflow the RB20/25 AFM shows max voltage, ~5 volts the Z32 afm is only showing ~4 volts. This means when the airlfow gets higher the Z32 can still show voltage increases to the ECU. Q45 (Infinity) AFM's are 90 mm (OD), so they have the same calibration advantage but they are also larger in diameter for less restriction. Hope that helps:cheers:

The R34 GTT RB25DET Neo has solid followers, so Tomei have 260 degree Poncams for them. The 256's are for the R33 GTST R25DET (non Neo) which has hydraulic followers. As for the HKS dyno, I have yet to hear of anyone, anywhere in the world that has achieved that result. I don't know what HKS did on the engine dyno, but this is what I would do; 1. Run a highly oxygenated fuel with a high RON, like TurboMax (sold as HKS Drag Fuel in Japan) :idea: 2. Use a water to air intercooler with iced water :aroused: 3. Who cares about detonation, it only has to do one run 4. Don't worry about tuning for daily life, just screw everything up to the max. 5. Use a constant loss water cooling system (not a radiator) and maintain the perfect engine temp 6. No flywheel, alternator or water pump 7. Run the turbo inlet off the dyno room airconditioner outlet, with no restrictions 8. No exhaust, mufflers or restrictive pipe, straight off the tubo dumps into huge vacuum assited ducting This would give me a "true" result, but hardly what I would call "real world". But maybe I am just more devious than HKS.

Checking that all is well in the A/F ratio area would be my first priority. Then you could maximise the base ignition timing. That's about it.

A T78 on a 2.6 litre is not good for any type of circuit work. Have a look at the quick Japanese circuit Skylines and they run around the 650 bhp mark. Bottom line, there are more suitable turbos for your requirements. Hope that helps

PFC every time.

DB, wins a chocolate frog for the right answer

Pop into your local Repco,SupaCheap, Auto One, Auto Pro, AutoBarn and buy some of this

RB26 AFM's are 65mm ID, RB20/25/Z32 AFM's are 80 mm ID. What R32-GTS is saying is, the electrical connectors are the same on RB20 and RB26 AFM's so "they"plug straight in". The standard rubber hoses from the turbos will stretch to fit the larger OD. But the AFM's won't bolt up to the standard air box. If you have pods then just upgrade the bases to RB20/25 ones. Hope that helps

The first thing I would do is get a pressure test done on the coolant system including the radiator cap. Any good workshop will have the necessary equipment.

GTST pump is 135 litres per hour and supports 300 bhp at standard pressure.

I think you may have a boost leak.