Warpspeed

He he, thanks Phantom. Golly, I never thought anyone would actually do that. But the figures seem about right. I wonder how big the battery is, and how much it weighs? As soon as you say mil-spec on anything it means big $$$$. I am just in the final stages of completing my third airflow test bench at home. The centrifugal blower generates just over 2psi, at around 480 CFM, and it is driven by a 7.5 BHP three phase electric motor. The motor amps are right up at full rated load as well.......

Thanks Joel, I have learned a fair bit from this thread. It has been many years since my own unfortunate adventure with forgies, and things seemed to have changed a lot since then. It is quite possible that the thermal expansion of more modern forging alloys are considerably less, as well as forging technology generally. I would still be guided by the recommended piston to bore clearance, and try to stay with pistons that have as small a clearance as possible. Sorry if I misled anyone, but I try to pass on what I have learned the hard way over the years, and some things DO change. Most of my engineering reference books, like me, are getting old and they are quite clear about the problems associated with forged pistons. Compression ratio is the total maximum volume at BDC divided by the total minimum volume at TDC throughout the stroke. So its stroke volume + gasket volume + chamber volume, divided by gasket volume + chamber volume. A lot of people get confused with this. If the stroke volume is 500cc, and the chamber plus gasket volume is 50cc, then the compression ratio is 11:1 (550/50) Measuring this on an RB engine is not that easy because of the domed piston, but it must be done.

Thinking about this a bit more, with evaporative cooling in cooling towers and such, you try to keep all the cooled surfaces completely wet. So you spray heaps more water than is actually evaporated. So how about catching the water under the intercooler and returning it to a storage reservoir underneath, and using a decent pump to really keep evey fin on that cooler seriously wet. Some sort of scavenge pump (like with a dry sump) might also work if it comes on with the main spray pump. I realise this may not be practical for several reasons, but it would be the theoretical ideal. But it would certainly solve the water on the road problem. As far as water injection goes, what about using a second set of suitably sized fuel injectors, and powering them off the main injectors via a suitable electronic drive circuit. This would keep the petrol/water ratio near constant, and you could easily arrange to switch off these extra injectors below a certain boost threshold. If your aftermarket computer has a spare PWM output you could map the water injection easily enough. This should conserve water as well as get the most benefit. There might be some problems though with corrosion if you feed water through an EFI pump, injectors, rail and regulator ? It would not surprise me if some of these were made with stainless steel components, but have no idea if this is the case. Anyone know for sure ? Hey....... I just think up these ideas, it is up to you to make them work.

I would use the n/a RB30 pistons. I believe that this will give you about 8.5:1 cr which is not a bad compromise. If you have any trouble at all it will be broken ring lands through detonation. This is not going to be the fault of the piston though. On an RB25 I would prefer stock GTR pistons (plus crank, rods, and oil pump). There is the belief that high power requires stronger pistons. I have never been able to understand this. High power comes more from high BMEP, which is AVERAGE gas pressure on the piston. Peak combustion pressures are going to be limited by detonation anyway, so you cannot go much higher there. So what breaks the pistons ? I doubt very much it is just gas pressure. If RPM are limited by piston speed, it is the conrod that breaks under tension, not the piston. A heavier forged piston is probably not the answer if you are snapping rods due to a severe accidental over rev. If someone tells you to fit forgies because they are stronger, ask why the stock pistons break. What actually fails and why. This is a perfectly valid question.

Lower compression will reduce torque pretty much evenly throughout the whole range at any given boost level. But that is the price you have to pay to stay out of detonation. Forgies are stronger, no argument, but there are also some disadvantages that go with it. Engine builders are only interested in two things, making money, and getting results. Results are measured on the dyno, not by overall engine life. So forgies and an agressive high lift cam, with super strong valve springs will get the job done. A year later you have massive ring blow-by, a rooted valve train, and the engine clatters at any speed, and uses rather a lot of oil. But the engine builder did his job. It made the power (when it was fresh) and it has not blow up. A lot of top professional drag racers dismantle and inspect their engine after only minutes of full throttle operation down the strip. To expect a similar engine to last months or years on the street is silly. So you read in the magazines how Joe Bloggs is running 35 psi and making 1000+ BHP, and he probably is. The guy reading the magazine thinks he can put an identical engine in his Commodore to drive to work in it every day. Some things are just not practical on a street engine, even if they are possible. But it all depends on your point of view I suppose. I expect many will not agree with me. It is not right or wrong, just an opinion.

The biggest problem with stock RB25DET pistons is the compression ratio they give, not the piston material. People tweak up the power to detonation and then say the stock pistons are crap, the ring lands are weak. Stock GTR pistons do not give nearly as much trouble because the compression ratio is lower, they are actually no stronger. But in the end it all comes down to money and engine life. If you want high power it is going to cost you, and that powerful engine is not going to last 100,000Km to the next rebuild. So what is reasonable ? Would you spend fifty grand building a racing engine that was worn out junk after only 10,000Km on the street? A lot of people would. Been there, done that. I think we all need to do it at least once in our lives to get it out of our system. So go ahead, have fun.........

Don't know exactly how much N1s cost, but I recall someone here mentioned that new from Nissan in Japan they are not much more than standard GTR pistons. Try doing a search ? Not sure what factory clearance is on standard GTR pistons, but I have a set of six here that were removed from a low mileage R34 GTR donk. Four are .001 under correct standard bore size, one is .0015 under, and one is .0005 under. The stock pistons are a snug fit. I run about .0015 clearance with cast pistons on my Laser turbo. When I ran the Arias forgies those were set to the recommended .007 under, and they were pretty loose and rattly when cold.

The Autospeed article is a good one. The biggest problem is using the water efficiently. If you spray on heaps it just runs down the cooler onto the ground, and you need gallons of the stuff. If you just mist on a pissy little bit, it is not going to do much. Probably the best and most efficient way to use water is with a water injection setup. This will help with detonation, but it is not going to increase power potential much, if at all. If you are happy to cart around a couple of gallons of water, a air/water setup has some real advantages on a street car.

I agree with Tony 100% If you are building a long life street motor, factory pistons are going to give you a good strong tight well sealed quiet running engine. If you simply must run forgies N1s would be my first choice. Aftermarket forgies are HEAVY, and they usually expand more depending what they are made from (silica content). So you must often run loose pistons. This is not good from the aspect of blow-by, oil control and piston rattles. Some of the short skirt slipper pistons are reasonably light, but piston rock adds to the loose piston syndrome to make ring sealing an even bigger problem. Pistons rarely break except through detonation. If you have detonation it will break anything you can put in there, and so will a dropped valve.. Oil spray is very good at keeping piston temperature within bounds, but it depends on how long you plan to hold full throttle. The aluminium alloys all lose strength at elevated temperatures to a greater or lesser degree. I would rather run sprays and stock pistons than no spray and rattly old forgies on the street. The last forgies I used were a set of Arias blower pistons and I was not at all happy with them. Forgies would be o/k in an all out drag motor though, but not on the street.

Joel, the consensus seems to be that you should aim for about thirty thou squish clearance with steel conrods. Any less and you might be in trouble, any more and you quickly lose squish effectiveness. So you juggle deck height and head gasket thickness. How you do this is up to you, but decking the block after a trial assembly is the most usual way. Also there is a pretty good choice of head gaskets if you wish to go aftermarket. If you are after 8.5:1, just order replacement (forged) GTR pistons, how about some factory N1 pistons? These will have the internal oil passage around behind the rings for the squirters, other aftermarket forgies most probably will not have this feature.

All the whole Garrett T04 range optionally come in split scroll, the N flow being the smallest. Toyota have a fairly small split scroll turbo on the MR2. There is plenty of choice available.

It can be extremely accurate ! There are a few things to watch though. First make sure the degree wheel is centered properly on the crank pulley. If it wobbles around when you turn the engine, TDC and BDC may be correct, but the ninety degree points can be a fair bit out. Turn the engine and make sure the edge of the degree wheel runs true under the wire pointer. Also make sure the dial indicator is parallel with the valve stem. This can be judged by eye. And lastly make sure the dial indicator is solidly mounted. A scrap of aluminium or steel angle with a couple of holes makes an excellent dial indicator mounting. The first time you do this it will probably take most of a day to get set up. After that you should be able to get accurate valve opening and closing points repeatable within one or two degrees in typically an hour. Plug the numbers into Dyno 2003, and see what you get. Try moving things around in the software and see the results instantly in the torque and power curves on the screen. Then go and do it on the engine. The software does not lie. I think you will be truly impressed, and you will have done it all yourself as well.

Ok here is how to degree your cams. The first and very important step is to know exactly where top dead centre is. The factory mark on the crank pulley may be o/k and it may not. But checking this is a vital first step. Now you cannot just measure piston movement around top dead centre through the spark plug hole, because the piston slows down, stops, then changes direction. Over a very few degrees around top dead centre, piston motion is minute and unmeasurable, and things like con-rod bearing clearance can make it more inaccurate anyway. So what you do is make yourself a mechanical metal stop that you can screw into the spark plug hole that stops the piston about half way up the stroke. This might be a bolt epoxied into a stuffed spark plug base, after you have removed all the ceramic. It does not have to be exact length, but somewhere around half piston stroke will work fine. You then attach the degree wheel to the end of the crank pulley somehow. Strong magnets, double sided tape, bolts, children's silly putty, whatever. The zero degree TDC mark on the degree wheel should roughly line up with the factory TDC mark on the crank pulley. Fix a pointer to the engine made from coat hanger wire, or welding wire, so it points exactly at TDC on the degree wheel. Next you slowly and carefully rotate the engine with a long spanner through BDC until the piston comes up firmly against the stop (gently does it). Note the reading on the degree wheel. It might be 98 degrees, or some other reading. Then gently rotate the engine back the other way through BDC until the piston again goes up firmly against the stop. The reading might for example be 88 degrees. Split the difference, and bend the wire pointer to 93 degrees (in this example). Go back and re check a few times to ensure that the degree reading when the piston hits the stop is identical both ways. You can now be certain TDC on your degree wheel corresponds exactly to TDC at the crankshaft. Next you make a fixture to hold the dial indicator against the flat surface of the hydraulic cam follower. This may take a bit of ingenuity, because the cam lobes always get in the way. The end of the dial indicator will have a small ball that screws in. If you unscrew this you can fit a flat piece of metal drilled with a small hole, held in place by screwing back the ball. The flat metal sticks out at right-angles like a foot from a leg. This flat section can rest on top of the cam follower at the side of the cam lobe, and the lobe will not strike the shaft of the dial indicator as it goes past. Mount the dial indicator rigidly to the cylinder head, it must be parallel to the valve stem for accurate results. A magnetic stand works o/k, or you can make up something better and more rigid that bolts onto one of the cam cover studs. Turn the engine so the valve is shut, and zero the dial indicator. Slowly turn the engine until the valve just begins to move. With a hydraulic cam, movement will be very sudden. You may have to do it a few times to get the exact spot. You can then read the exact valve opening point on your degree wheel. Valve closing is very similar. You pick the spot where the valve just seats, and your dial indicator returns to zero. It is not difficult, but you need patience and practice, and setting it up for the first time can be bothersome. But once you have all your bits of metal prepared, pointer, and a method worked out, it can be repeated pretty quickly. You know the readings are accurate if they repeat. What surprises me is how far the cams can move when you increase or decrease the timing belt tension. Also do not be surprised to find the factory cams five or more degrees away from the proper factory spec. Knowing where the cams really are is vital, do not trust those factory dots either, they are only supposed to get you within one whole tooth. If the cams are miles out, or unsuitable, moving them around blindly is not going to help you much. When you have everything pretty well optimum, small changes can be easily detected by how the engine goes.

Steve, one thing you can do yourself for minimal cost is go out and get yourself a degree wheel and a cheapie dial indicator. Without actually changing anything, find out exactly where the inlet and exhaust valve opening and closing points are. I still think the engine is not producing enough exhaust flow. Excessive advance requirement strongly suggests a serious combustion problem. The two biggest influences here are compression ratio and exhaust dilution from reversion.

Actually the 2 x boost pressure is not a bad turbine inlet pressure to aim for on a tractable everyday road car. Most of the factory turbo systems run about that amount. Any less and the boost threshold stats to get a bit high, any more and the top end power starts to suffer. I believe measuring the turbine inlet pressure and dump pipe pressures are just as important as knowing what boost you are running. A surprising number of turbo guys have not a clue what is going on in the exhaust side of things.

o/k Steve, I understand what you are saying. Something is not right, and you have made more than one change, so you need to go back to what you had that worked, and then try a few things. My gut still tells me that the exhaust flow is just not there. The smaller housing will almost certainly be better, but it may, or may not be the best solution. The exhaust cam change is guaranteed to work and be completely non critical. The inlet cam phasing is far more critical than you probably realise. It is extremely easy to stuff up the inlet valve timing with only small change either way. I suggest you fit a degree wheel and measure the exact opening and closing points of inlet and exhaust. You might be in for a surprise.

I believe a lot also depends on the circumstances and how fast you are going. If its at low speed in the wet, and you suddenly hit an oil patch or something turning at an intersection, or going around a traffic island, I would think backing off pretty smartly might be best, especially if you have an LSD and both rear wheels suddenly break traction. On a fast sweeper in the dry at high speed, if you feel the rear starting to go a bit wide, I think you might be a bit more cautious, and just slowly ease off. Both are an oversteer condition, but the situations are totally different.

Hi again Steve, sorry it took so long to get back. Disconnecting the VVT is not a fair test. I am not sure if it goes to the fully advanced or fully retarded position when disabled. If the cam fully advances, the overlap will be rather large, possibly enough to cause a lot of reversion. Also the cams you now have probably open and close a bit more aggressively than stock. So both valves will be at higher lifts as well as open together longer. If the cam fully retards, inlet closing will be extremely late, and this will really reduce low end and mid range torque. You really should not be using VVT with that cam, it will go a lot better at a fixed position. The engine must make enough torque off boost to generate enough exhaust flow to start the fun in the turbine. If you cripple the engine with excessively low compression, or a highly unsuitable valve timing it will not be able to light up the turbo, and it is no fault of the turbo. Try putting the stock inlet cam back in, if it helps, then go back to the 256, disconnect the VVT and set it to a suitable position. If it is still crook with the stock cam, at least you will then know the problem is definitely in the exhaust side of things. With an untried combination of parts, sometimes some completely unexpected mode of operation can trick you. The only way you can narrow it down and figure out what is actually happening is to try changing a few things.

Very nice read Steve. One thing I discovered was that too much valve overlap also does what you are experiencing. It feels like it really wants to go off boost, but as soon as you floor it, it dies in the bum. You might be right, or you might be looking at the wrong end. If its not too hard, can you put the stock inlet cam back in ? Leave the long runners and the big exhaust housing fitted, and see if the boost threshold drops back down. If it does, it might be an exhaust reversion problem, and not caused by low exhaust gas velocity. What inlet cam did you finally decide on ?

The thing to realise with the Nissan ATESSA system is there is no centre diff. Most other 4WD cars have full time 4WD where a fixed proportion of torque is split front/rear. The ATESSA system has the gearbox output shaft continuously driving the rear diff through the tail-shaft, and it is fixed 100% solid drive, just like a normal RWD car. Also on the gearbox output shaft is a multi-plate wet clutch that drives a front "tailshaft" via a chain in the transfer case. Now normally, this clutch is fully disengaged so the rear wheels only are driven. The ATESSA computer can apply hydraulic oil pressure to the clutch and feed torque to the front wheels. The clutch can go smoothly from open, to fully locked, or any degree of slip in between. As said above, the ATESSA computer is pretty smart. It looks at front and rear wheel speeds, and has lateral and longitudinal accelerometers. It may also look at throttle position, but I am not absolutely sure about that. The computer in the R32 GTR reacts more slowly than the similar computer in the R33 GTR. So the R32 is a bit notorious for being slower to respond. The R33 GTR V spec also has a similar electronic clutch in the rear diff, whereas normal GTRs have a conventional LSD. To disable the 4WD you can remove a fuse which supplies power to the hydraulic pump that operates the clutch pack. I do not know which fuse, but the hydraulic pump is located behind the right hand rear wheel. With the FWD clutch disabled the car becomes 100% RWD.

Haha. There is an old saying............. Understeer is when the driver wets his (her) pants. Oversteer is when the passenger wets their pants.

I would arrange to do two things. First go with the guy to your bank, and check with your bank manager that the check is genuine and o/k. Phone through first and make an appointment. If its o/k give the guy back his check. Then both of you visit motor reg, and transfer the registration. He will then be sure you own the vehicle, and that side of things is o/k. If you are still nervous about this, take a large friend along with you.

Well it depends on how much gain in noise you want. A three inch will certainly give you some gain, but a four inch pipe will make much more noise. A five inch pipe will gain you even more noise still, especially if you run no muffler.

Here in oZ the only real Australians are Aboriginal, the rest are foreigners living here. And America has been going down hill ever since it left the British Empire. Exclusivity is not what Nissan need anyhow. They are in business to make money by selling cars, no other reason. The more cars they can sell, the better the profit. The HRT427 was an exclusive car, only one ever built. You cannot get more exclusive than that. I doubt if that one car is going to keep Holden profitable all by itself though. What are the technical reasons against a dry sump for road use and emissions ? I would really like to know.