cheftrd

It really depends on what you intend to do with the car, as well. If you truely intend to stay around 450 (smokin' in an S30), and it's just a cruiser with a little track duty, there's nothing wrong with the RB25. You'll need cams to make it breath beter, though. You can also get away with a T3/T4 hybrid that will bolt to the stock exhaust manifold, too (you may need an additional flange and longer bolts as a spacer, though). Above this level, though, and you really have to squeeze this motor for minimal gains. The last Rb25 I tuned was running TEC3, 272 cams, GReddy intake w/Q45 throttle, and T66 Garrett turbo on a Trust manifold. It made 501hp at 1.5 bar. This is the absolute limit for the stock bottom end. Any ping at this level, and the piston ring lands are going south for the winter (25 and 26). By comparrison, another of my customers has a 26 with close to the same mods, 272's, SDS EFI, and pistons (stock bore and compression) and rods for abuse insurance. Stock throttles and modified Nismo GT LeMans turbos on Veilside manifolds. 1.5 bar put this engine at over 700hp. That's the 25/26 difference. If you do intend to go higher, 200hp for $2000 is CHEAP.

Ditto. I would run the turbo on the motor, as is. Watch your EGT. As far as HKS head gaskets go, they seal combustion up to 1300hp in the RB26, which is right at the limit of the best head studs ARP can produce. However, holding pressure has less to do with the gasket and more to do with the clamp. In the event that you have to reduce compression, stay with the thin gasket and remove compression via enlarging the combustion chamber. Diesels try to pack the air into a very small area and raising the head COULD have disastorous results as far as power production.

No. All the exhaust has to go through one turbo. Then as boost builds up, a valve opens, letting the exhaust into a second turbo. As the boost from the second turbo comes on line, another valve on the compressor side opens to let the air from the second turbo enter the piping. When it's fully on-line, it operates just like a regular twin turbo, with both turbos working. For the sequential to see any bennifit, the exhaust on the first turbo has to be quite small. This will create a severe restriction in the exhaust flow as rpm's climb, and the engine won't make any power unless the excess pressure is fed to the second turbo. It's very complicated and hard to get all the valve timing and pressures right. A better option is to use a VATN turbo like the ones on the Ford Power Stroke. You can have a large turbo and lots of power. With proper sizing, full boost can be achieved by 1500-1800 rpm.

The Nissan auto trannys won't hold any type of power. With custom mods, I've had the clutches hold through 500hp, but the stock planetary gear carriers are weak and will break.

Summit Racing sells a relocater kit with universal adapters that will fit the Nissan filter threads. You can put a cooler in there, but it's wise to also have a thermostat. The expensive Japanese blocks, like the one in Clints pic, have a built-in thermostat. I use a block adapter from the non turbo RB20. It's straight, short, and gets rid of the stock cooler mess. They run about $50 from Nissan.

The HKS pump is the best on the market. The quality is awesome and the drive lug is extra long for reliablilty. 6000 rpm produces 53.1 liters/minute at 4kg/cm (58.8psi) of pressure. Stock is also 4 kg/cm at 6000, but will supply less volume if needed. That said.....There is no problem with the stock pump. The only difference between the stock and Nismo pump is that the Nismo rotor and scroll are hardened. This is the exact pump that Nismo uses in their engines for the Super Endurance race series. These cars are fast. I don't know the hp specs, but I've personally seen them hit over 300 km/hr in the straight at Fuji Speedway, lap after lap.....With a straight 33 or modified crank, I've never had a problem through 8000 rpm with the stock pump. I use the Nismo pump for 9000+ engines just "because" (I have engines using the stock pump that tap 9,000 once in a while with no problems to date. I'm not saying it couldn't happen, but the only pumps I've ever had break were at high rpm (7500-8000) and using the stock 32 crank. A good machine shop may be able to heat treat the gears in the stock pump. There's plenty of oil pressure up there with the stocker. The #1 cause for bearing failure in the RB26 is oil temp. With the stock cooler, a 500hp engine will hit over 220F in 1 quarter mile pass! Sustained rpm racing or pass after pass with no cool down will kill it quick. I once saw a guy pull the ATTESA fuse and go drift his GT-R (right after I told him not to do it). The engine came down with a nasty bearing knock in less than 5 minutes. I saw a video of a new, stock R32 that didn't even complete 1 lap of the Nurburgring and wasted the engine because of oil temp. A mid sized Earls type oil cooler will keep the temp in check and should be considered a mandatory upgrade. I have no Idea why Nissan didn't put one in from the factory. If you have the means, buy the HKS or JUN pump; they're good insurance, but don't abandon your project because you think you must have one. The guys running these pumps than NEED them are turning up to 13,000 rpm and making HUGE power. That's what they were designed for.

With those cams and the T88/34D 16cm you want to be looking for around 7000. When trimmed correctly, that engine will want to turn close to 10K with peak HP at about 9K. I'm going with the complete ATI adapter and converter on Jon's S15. He's headed to Fla. in about a month and will box and ship the tranny when he's there. We're also thinking about the Ford 8.8 IRS because HKS says the rear end has to remain IRS or the car goes to "PRO". Whatever....

If you can't get the bolt from the guy, let me know and I'll send you one w/washer.

The 26 head is a direct replacement for the 25. So is the RA. There are lots of people that do swaps like this in Japan when putting a 26 in a RWD car that previously had an RB. 25 block and oil pan with 26 head and internals. I don't because I like the rigidity of the aluminum pan and 26 pan rail.

What about going to Richard?

Sure, Cusco, Nismo, and a host of others. They are all chromoly steel and very light weight between 4-6kg. Price is probably around $400.

I've only had one stock RB25 tranny failure, ever. I think it had a lot to do with the rear end failure. The car puts down just over 700whp and likes to tear up R200's in third gear. That's the first gear to get any kind of "traction" at all in this car (275/15 555R's). Anyway, the latest failure locked up the rear hard, just for an instant, probably shocking the hell out of the tranny gears and knocked off a couple of teeth. I've had several OS failures in 700+whp GT-R's, but it's always the main drive gear, which stays stock in the OS (and most other) sets. Keep in mind that a 700hp GT-R leaving at 9,000 RPM with a tripple is a very traumatic experience for the gear. I've also seen the stock trannys live for quite a long time under severe abuse. Another weak point (it isn't) is the input shaft on very high power, high traction vehicles. OS sells an aftermarket one. The final weak point is the center plate. It takes a tremendous thrust load in high power cars and sometimes cracks. There are aftermarket ones available. The gears are the same in the GT-R, RB25, and Z32, so If you're using the Z32 diff, it's not a problem. The 2.6 first will make the gear a little long, but if you have near 500hp+, and are not on drag slicks, it may be a benifit. With a 4.1 or 4.3 on street tires, you ain't goin' nowhere in first or second.

3.7 on a 2.6 first is going to be loooong.

OS Gear Set for GT-R/Z32/RB25 ($2000) 1. 2.695 2. 1.703 3. 1.236 4. 1.000 5. Optional 0.826 ($750) Stock is: 1. 3.214 2. 1.925 3. 1.302 4. 1.000 5. 0.0752

I've been looking to relocate to the LV area and need to go see some friends out there, this year. Might be a good time to take this trip.

When I was talking about surge, I meant a system with no BOV. I should have been more specific. Where there is no BOV, the high pressure air has nowhere to go but back out the turbo. On super high boost apps. with no BOV, I've seen the shaft twist in two, wheels slip on the shaft, and compressor nuts come off (Mitsubishi). closing the throttle on 30 psi at 80 lb/min can cause a 100+ psi spike. No apologies necessary. Always question everything, especially that what you read on an internet forum.

Same as what you'd run for NA, but with less overlap.

A large single with big plenum combo that's large enough to be no restriction to the intake runners will make the most power. Throttle blades in the intake runners create a restriction and turbulance. johnc mentioned MOI or "moment of inertia". When you snap open a big throttle/big plenum combo, ambient air accelerates from a dead stop and has to fill the entire plenum and move all the way down the runners, which was a huge vacuum a second ago, before the engine "sees" any of this air. ITB's, on the other hand, have ambient air part way down the runners. When the throttles are snapped open, the air only has to accelerate and move a very short distance before entering the engine. Better throttle responce. It's a give and take depending on what type of racing you do. Most manufacturers don't use the ITB because of cost and drivability. Six very small (40-45mm) throttles makes for a huge throttle area. Six 40mm throttles is worth 75 cm2 where a 70mm single is only worth 38 cm2. The single makes for a much smoother transient throttle response, where the ITB's make for a kind of on/off switch. You and I don't mind driving a car with snappy throttle, but most normal people don't.

Any fluid (air is a fluid) moves from high pressure to low pressure. When the throttle closes, the pressure in the pipe spikes. If the BOV is next to the turbo, the pressure drops there first. The high pressure at the throttle then tries to go where there is less pressure (the turbo), reversing flow. When you hit the acceleerator again, the air must then reverse flow again. Compressor surge (whoop whoop whoop) is just that, airflow reversed. The difference is that it tries to go out the compressor inlet instead of the BOV and stalls the compressor. The main performance reason behind using the BOV is the fact that the lag time after an off throttle shift is less, due to the compressor not being stalled. I understand what you're trying to say about water, but it's different in that a fluid with the viscosity of water (liquid) is uncompressable. When a relief valve is opened in a closed, pressurized pipe containing water, there is NO FLOW because you can not have more water than the volume of the pipe. The pressure in the pipe decreases at the same rate everywhere in the plumbing at the same time. Air, on the other hand, is compressable, and we can have more than the volume of the pipe in the pipe. When the valve is opened, the pressureized air will flow to the area with less pressure (ambient outside). The cooling effect of cooler air going back into the intercooler vs. hot air that has to go into the intercooler anyway, is insignificant compared to keeping the air flowing in the correct direction concerning acceleration. This applies to a manual transmision vehicle that has the clutch released and trailing throttle between shifts. If you hold it to the floor for an entire quarter, where the BOV is makes no difference.

Any single large BOV like the GReddy R or Tial 50 mm will work fine. The 50mm valves will pass more air than the two stock ones. There is not a BOV for each turbo, BTW. A single outlet from the surge tank inlet pipe dumps to a common plenum to the two valves, and they discharge into a single return pipe that splits and re-enters the suction pipes between the AFM's and the turbos. It's a common BOV found on other cars and I believe they use two instead of redesigning a larger one; mass produced parts are cheaper. The BOV should be placed as close to the throttle(s) as you can get it. This keeps air moving in the direction of the intake when the throttle is closed. When mounted close to the turbo, the air in the pipe has to reverse direction when you lift, then reverse direction again when you come back on throttle. This causes a little more lag after the upshift. Either way is bennificial for the life of the turbo. Many BOV's that are placed by the turbo are because of packaging restrictions. Along this same line of thinking, I also run the wastegate and actuating port to a pressure/vacuum port like the one used for the BOV. When you lift, it pulls the gate shut, keeping the exh. gasses on the turbine, and opens the BOV, giving the air somewhere to go. This makes for awesome boost response between shifts.

Steel and bronze are ferritic and non-ferritic metals respectively. They won't bond and no errosion (valve-seat recessione) will occur. That's why high end race engines use beryllium seats. Bronze can be super hard. Lead in gasoline is used as a "lubricant" (in addition to being an octane booster) for the valve seats for the reason I gave above (it keeps the valves from sticking to the seats. Oil lubricates the valve guides. As for the E31 head; so the seats were cut right into the aluminum and that's what the valves closed against? I think not. They had inserts installed. The inserts were not machined out of soft cast iron. They are made of a steel or bronze alloy, either of which does not require lead to keep them from erroding. This is not opinion, it's fact. SAE stands for Society of Automotive Engineers (of which I am one). Of course, you're free to disagree Check it out: http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=5635342