joshuaho96

For those that are interested in the original problem, I found some logs of a stock R32 GTR running Nistune and concluded that it's a roughly 23.5 or 23.6x factor that is hidden in the TP calculations. So instead of this: TP = (Kconst * VQ) / RPM It's actually something like this: TP = (Kconst * VQ * 23.6) / RPM Here's my work, gathered by going through this Nistune post: https://forum.nistune.com/viewtopic.php?f=8&t=3655 The header is not quite as helpful as I would hope but basically the first 4 columns are straight from the logs and TP less K is effectively the expected VQ/RPM value, while VQ and VQ/RPM headers are the interpolated VQ value measured from MAF voltage and VQ/RPM is that VQ value divided by the RPM in that part of the log. The two methods arrive at vastly different numbers, so the ~23.6x factor I mentioned is how I reconcile the two. Edit: What's remarkable about this is actually how close the TP index is to the total airflow to the engine, in grams per cylinder, just with fewer significant digits.

My understanding was that if you adjust K at all or changed the MAFs you've effectively rescaled the ignition and fuel maps, even if the math still works out such that the ECU stays within the OEM load scale. I really just want to ensure that I keep the factory fuel targets/ignition timing in real load + RPM, so that the behavior is going to be the same as stock if I don't modify them. Maybe pointless but I'm trying to make sure that I don't change too many variables all at the same time.

I’m aware that general practice is to not bother with trying to do this, I just want to make sure that messing with K and VQ that I rescale the maps correctly. Getting down to raw physical units helps because the VQ scale is not a linear factor.

I'm trying to understand how a stock BNR32 ECU calculates TP load on the primary fuel/ignition maps. I read through the Nistune manual to find the following equation: TP = (VQ * Kconst) / RPM TP load index = TP / 256 I looked up the MAF VQ (voltage quantifier) curve in the base BNR32 ECU's MAF table and referenced it against Haltech's RB26 stock MAF curve. From this I concluded that the VQ curve is such that 1 VQ unit is equal to roughly 0.005152 grams per second of mass flow. This constant produces a curve that makes the Nistune and Haltech curves agree almost perfectly. The only error I see with this method is below 1 g/s, so with two MAFs at roughly the same flow rate that's likely below the minimum airflow at idle: From there I tried to reverse the TP load index equation to get some sort of estimate for grams per cylinder. Something I noticed reading the tables is that there is a fuel cut that occurs above a load index of 160, which suggests to me that the load index of the OEM tables should never exceed 80 and the final load row of 88 is just a failsafe. I tried the following to convert this TP load index into grams of air per cylinder: TP_load * 256 * Kconst * 60 = VQ/RPS Where TP_load is 80, Kconst is 233 (defined by the ECU), and 60 is a constant to convert RPM to RPS. From there we can convert VQ into a grams per second value like this: TP_load * 256 * Kconst * 60 * 0.005152 = (g/s) / RPS The seconds cancel out, so this is actually a grams of air per revolution value. Every revolution half of the cylinders are intaking air because it's a 4 stroke engine, so we can divide this number by 3 to get grams of air per cylinder. The problem is that when I do this math I get a figure of ~27 grams of air per revolution. At the power peak of ~6800 rpm stock that implies the "peak load" limit corresponds to roughly 3000 grams per second of air mass metered by a single MAF. A single MAF can only meter about 150 grams of air per second before it maxes out. So I'm off by a factor of 20 which is definitely wrong. Anyone know if I just suck at math? Or if I'm missing a bunch of extra bits to how TP is calculated? If anyone has a Nistune log of MAF VQ, RPM, and TP on a stock RB26 + stock tune I would really love to see it.

Step one is probably sell the car and get an AWD variant because you need a big divot in the floor pan to fit the transfercase.

I flipped it backwards, -5s are too big, correct. But GT3-SS turbos are tiny, 0.54 a/r exhaust turbine which is tighter than any other turbo out there. They nose over hard on 2.6, so the concern is that a 2.8 will just shift everything down a few hundred RPM and make the engine feel like a Mazda 2.5T where the power falls off a cliff well before redline. The HKS turbos may be a waste of time/money but it's already too late, the turbos are bought for and installed so I'm just going to see how they go. The engine isn't at the point where the bottom end is going to be taken apart yet so it's going to just be a 2.6 for now. I have a VCAM step 1 sitting in the garage so that can be a first attempt to try and get the VE up earlier to spool the turbos. If that doesn't get the desired powerband then I'll think about a stroker or RB26/30. I'll post dyno charts and data logs as I work through this, if it sucks you guys can have some fun pointing and laughing.

No, but I'd rather not spend 5000 USD on a stroker kit only to discover that the engine peaks in power undesirably early. -5s are too small for 2.6L, but the GT3-SS is so small that it has trouble holding boost out to 7000 RPM even with 2.6L. I have a feeling that if you stroke it out to 2.8L it's going to be even worse in that regard.

Gran Turismo Sport seems to do a pretty good job of simulating the R32/R33/R34 GT-Rs.

I was under the impression that if a turbo is already choking the engine above a certain RPM, additional displacement would just shift the power curve down some amount of RPM. Is this not the case?

Yes, if you're going to go past a 2.8L stroker on an RB26 block it definitely makes sense to go to an RB30 bottom end instead, which has a much longer 152.7mm conrod. Even with a 3.4L, 94mm stroker kit on an RB30 you're still at 1.62 rod ratio which is roughly what the RB26 is at stock. More cubes is better for performance no doubt, my concern is that going to a 2.8L stroker on the RB26 means you might increase piston side pressure to unfavorable levels, and that going to a 121.5mm rod means you compromise the piston design. Shorter compression height means there's less room for the piston rings, either the top ring gets closer to the crown, the oil control rings get closer to the piston pin bore, or the rings have less spacing. Personally, I'm really hoping the turbo I selected is small enough to not require agonizing over this issue any further.

Stroker kits are either 119.5mm or 121.5mm, but the stroke in both cases increase to 77.7mm. So you're picking between a 1.56 rod ratio or 1.54 rod ratio. Either way it's on par with the B18 used in the Integra Type R, which seems to be pretty close to the edge of what is considered safe. The longer conrod length kits use a different piston design to get everything to work. Anyways, my plan has always been to target low power and focus on balance. I expect with the HKS GT3-SS turbos I selected it will already nose over well before 7000 RPM even with 2.6L displacement.

Is 2.8L stroker on the RB26 really a wise move to go for in a rebuild? I get the impression that the RB26 was already a stroker motor from the factory and was originally intended to be a 2.4L. 2.8L would cause the conrod/stroke ratio to get even more unfavorable. I'm currently planning out an RB26 build and this issue has made me go back and forth on whether a stroker kit is really wise.

doublepost

Base timing on an RB26 is 20 degrees BTDC. If you actually have your base timing at 10 deg BTDC then commanding 26-28 degrees means you're actually commanding 16-18 degrees of timing. As others have said, it's also possible that you're knocking and not hearing it. Is the OEM knock sensor particularly insensitive or something? I was under the impression that a properly set up knock sensing setup (bandpass set up with correct bandwidth + peak, crank window appropriately set) is on par with what human ears can do.

What kinds of compromises are involved in fitting an RB30 into the R32?

45M yen price tag. Well outside the budget of anyone that would be posting here I presume.

Are they ever getting around to the double VCAM setup they claimed to be working on?

The question is really more why do you want a billet block? They're designed for 1200+ hp builds. The liners are extremely thick and the water jacket doesn't do as much as it does in the stock block which is a closed deck that reduces coolant flow. You should really consider what this car is going to be used for. If it's going to be idling in traffic all day that means keep the power relatively low to reduce cooling load on the engine, keep the OEM water pump, big radiator, stock clutch fan with fan shroud, proper radiator ducting. All of those requirements point towards either OEM or N1 block. It would be cool to have some billet aluminum block tailored for say 600 whp max as a "street oriented" block but the people willing to put down 10-13k USD on a billet block usually want big power, not just removing ~30 kg from the front of the car.

Now that we've derailed this thread about billet blocks, does anyone know if the PPG or stock ratios are better for the stock 5 speed in the R32/R33 GTRs? I'm looking for a synchro transmission and I don't think I can afford the expense of doing a V160 swap properly.

If the car starts just with a normal key and no transponder/remote required there's no real security system.

I'm planning on putting in a step 1 VCAM, does it make sense to change the exhaust cam as well or just leave it?

Yeah, the first step is fine. I would just install a Nismo oil separator or comparable while you're in there. Low boost, tune, take it easy for a while and make sure the engine is healthy. Dipstick vent and oil cap vent are really last resorts, don't bother unless you're really having issues with blowby, which you shouldn't at low boost and an internally stock engine. If you're going to run a high flow oil pump you should go with an extended sump. The two go together, generally speaking.

More boost creates more blowby, which stresses the PCV system more. More blowby means more oil spitting out the breathers. The crankcase vent mods are really to solve that issue, track use just means spending more time at high boost. Street use just implies you're not spending very long at high boost. If you're going down the road of a built engine think carefully about the trade-offs there. 2618 forged pistons are very tough and make big power but they do not live long lives. For something that is street-first you probably don't want to have an engine that has quite a lot of piston slap and needs to be carefully and lovingly warmed up, it's better to have a piston that calls for a tight piston to wall clearance for street use. Don't wildly overbuild an engine for way more power than you want. Tight piston clearance also helps with reducing blowby, so for track use if you aren't too wedded to huge power it'll make oiling less of a headache. Really, every time I think about these issues with the RB26 the real solution is to sell the car and get a 996 Turbo but I have some kind of brain damage that keeps me from doing the obvious, cost effective solution. Does anyone know if the Tarmac Solutions sump is going to be enough with just 1.5L extra? I'd like to only bump up to ~6L of oil capacity instead of 8-9L but I'm not sure if it's a good idea.

Modifying engines is hard, if anything it's harder if you intend for this to be a street build that can survive track punishment. Deleting power steering/AC/etc is a much harder pill to swallow to go dry sump, ripping out your trunk liner to fit an Accusump is a lot less palatable for a street-first kind of build, etc. You have to decide what this car is going to be. If you want it to survive on the track with wet sump you want to turn down the boost, run less aggressive tires, etc. If you want to have 500+ whp for hard drag launches with slicks and hard track use but also street usability something has to give for practicality. The RB26 is really not a great engine in that regard, modern engines are amazingly better at doing what you want to do. Don't forget that to survive races with 600 hp the RB26 had swinging pickups and all kinds of other craziness for the oiling system, the stock RB26 has basically none of that.

Biggest thing to worry about with these engines is crankcase ventilation. You can have a huge pump pushing tons of oil on the oil feed but you'll ventilate the block if excessive crankcase pressure keeps oil from returning to sump fast enough. That's really what causes the "oil stuck in head" issue. Nissan figured this out with the R35 GTR, which is why the oil pump has both a scavenge pump and a pressure pump as well as significantly improved crankcase ventilation. The pressure pump is your usual oil pump, the scavenge side is on the oil return ports trying to forcibly suck air/oil down the return ports and force the returned oil into the pickup, so it's a "hybrid wet sump" in that regard: https://conceptzperformance.com/aam-competition-oil-pump-isr-treatment-nissan-gt-r-09-r35-aam-isr_p_7433.php In the context of a wet sump RB26, you can either try and improve the crankcase ventilation system as-is with more breathers. I haven't been able to examine the breather fittings/hoses yet but one "easy" mod may be to put in a checkvalve on the crossover tube and then drill out any restriction that may be present in the stock breather fittings. That would keep fresh air from bypassing the crankcase when on vacuum but allow for maximum flow when on boost. I suspect that you would ultimately need to add another crankcase breather directly off the crankcase though.