burn4005

agreed, what garret have managed to get out of a 49mm turbine exducer (21% less cross sectional area than a GTX3076) is remarkable. although their compressors are very impressive as well am looking forward to seeing what they can manage with something >70mm.

Yes, I think that's now accepted wisdom. The point of this thread is to show some evidence as to what is happening, and how bad it actually is.

I'd certainly be interested! the Mag is certainly the ideal, and capable of keeping up with a very small tooth pitch/module. I don't think i'd get away with a 60 tooth at the wheel diameter I'm using, but would have been fine with a mag. I am using the motec 36-2 wheel and Motec supplied hall sensor (its actually a ZF/Cherry).

12 on the crank is plenty. honda K series engines were only 12 tooth, and they're a pretty revvy engine! that debate can be settled very easily with a timing light, video camera and a high power pull on the dyno.

I did the maths on trigger errors at high rates of crank acceleration: one thing I haven't been able to account for as I don't have any data is changes in crank velocity over a cycle due to combustion pulses, if anyone has some please do share it! but in a reasonably steady state engine, the tooth window where the reset comes in should have the pretty much the same angular velocity and acceleration cycle to cycle. (and we're talking about a complete cycle time of between 60ms at 2000rpm, and 15ms at 8000rpm) so if you smoothly accelerate an engine from 2000-8000 in 1 second (a tough ask!) that is a constant rate of 100rev/s/s or 0.1rev/s/ms so at 2000rpm the engine is rotating at 33.3333rev/s with 10 degrees per tooth, a single tooth takes 0.83333333ms to pass. so the speed of the crank by the next tooth will be 33.3333+0.1*0.8333333 = 33.4166rev/s at this speed a single tooth (on a 36 tooth wheel) takes 0.831255138ms so for a 10 degree tooth, at 2000rpm the change in time between teeth is 0.00207813ms. and at 8000rpm the change in time is 0.00013ms which equates to: degrees at 2000/8000rpm: 90deg per tooth: 1.98044/0.12726 30 per tooth: 0.22/0.014 10 per tooth: 0.02/0.00156 5 per tooth: 0.00624/0.000391

it would depend where the crank trigger edges were placed relative to the desired ignition events. if you had a falling edge at 20deg BTDC on cylinder 1, you would have best case timing accuracy at a desired event at 19deg BTDC and worst case accuracy at 21deg BTDC. so your timing would be excellent at 19 BTDC regardless of 1,4,12,36,60 teeth, but would get progressively worse at 21 BTDC as you reduced the tooth count. but that is splitting hairs a bit. I just re-read this I get the feeling we're trying to convince each other about totally different things here? to clarify, I have not done any tests using 12 crank teeth.. i am using the 24+1 disc only so i can use the single window for my 720 degree reset, so CAS1 is wired to the 36-2 crank trigger, and CAS2 is wired to the pin in the nissan optical CAS that sees the single window of this disc. i am NOT looking at the other 24 windows in this disc at all, nor have i done any testing with it. trying to find some correlation, the sync position seems to be some component of engine speed (moves the position around, but an sync position band of 2.5 to 4 degrees exists everywhere, but rpm rate of change doesn't seem be correlated.

36-1 by a factor of 3 60-2 by a factor of 5 etc the shorter the interpolation window between trigger events is the less error can accumulate over that period if the conditions (crank accelerates) differ from the assumption (crank maintains angular velocity)

with timing locked at 25 degrees and a light on cylinder 1, crank timing is bang on (within 1/4 of a degree) whether steady or revving or rough idle, so the ECU certainly knows where the crank is. rough idle is actually going to show up triggering issues the most as the crank is turning so slowly. (2ms per 10 degrees at 800rpm vs 0.2ms at 8000rpm. or for a 12-1 it would obviously be 6ms/0.6ms per 10 degrees instead.

I can certainly do that test easily, both under no load (revving) and under load (standing on the brake) but at ~6000rpm, and rate of change being in the 100s of rpm/s, the cranks change in velocity over 10 degrees is going to be negligible. as the reset event occurs at the same point in the 720 degree cycle, give or take a few degrees for reasons we are trying to work out, the cranks angular velocity and acceleration should be very consistent under reasonably steady state conditions.

any 75W90 GL-5 will be fine, you don't need the friction modifiers, but you can use an oil that contains them (as most already do) I've always used Amsoil severe gear or Redline oils, but anything fully synthetic would be fine.

have now installed a 36-2 trigger wheel on my RB26 and for interest sake, I have installed a 24-1 wheel in the stock nissan CAS and am only using the single window as a phase reset. I have an Emtron KV8 which shows something called sync position that tells you where the CAM signal comes in relative to the Crank signals (so 50% would be half way between two crank triggering events) this gives a very accurate display of how much variability there is between the crank and the cam signals. this is on an R34 gtr type CAS, HKS timing belt, kelford Beehive springs and tomei type B cams. I am using Hall effect triggers and a falling edge trigger threshold of 2v for both. under some load (but not extreme, this is only 10psi of boost) you can see over the course of less than a second there is a variance of 36.6% in sync position. because there are 10 degrees between trigger events on the crank, this ends up being a variance of 3.6 crank degrees! I will post more once I have data where the engine is under heavy load (30psi) to see if it gets worse. so you may say, well the keyway in the cam is to blame, not the timing belt. well here is the result at very low engine loads (idle) if there was play in the cam keyway this should still show up here as variance. but the sync position is only 4.2% which is only 0.4 crank degrees! I would like to get a very fast scope to verify the trigger edge slopes are remaining the same, as that is the only other factor here that I have not controlled for (but at a steady RPM, the slope should be consistent for each trigger event regardless.

As much as precision not having compessor maps available pisses me off, the proof is in the pudding and Simon your setup is remarkable.

My car is tuned with EMAP compensation and my ignition table has the load axis in g/cyl so I'd really love to play around with a few combinations to see what happens with very minimal tuning required. shame the 1.45 is so physically large. I think the dump pipe would need a fair amount of rework compared to the 1.05 i have on there now. (and for some reason the 1.45 housing on its own is massive dollars (~$1300 just for the housing!) but based on that info you've posted, yea I reckon if you're shooting for over 500awkw a 1.45 9174 would be unbeatable, but a sequential box certainly hides away a turbos lack of response.

450awkw

if you want it to bleed effectively when cold, then yes plumbing in behind thermostat will provide circulation at all times, but once the engine is hot and the thermostat opens, it'll circulate then and that's when you really want your cooling system to be working properly. where i circled in red is where you'd plumb it instead of lower rad hose: putting it in lower rad hose, it means you have to wait for it to get hot before you can bleed the system after a coolant change, but that's also the case if you're doing it with half a coke bottle jammed in the radiator and its only once in a blue moon, so not a big deal so i put it in the rad hose. if you wan't to be technical about it, yes ideally it should be plumbed back in behind the thermostat. but the main reason for using a seperator other than as a bleed assistant is to evacuate any vapour/steam from the head or block, which only happens when it's hot. when i first installed mine with clear hoses nothing much happened until the engine hit 70ish degrees, then a heap of bubbles started coming through to the separator when the thermostat opened.

I've got an 8374 supercore with a small chip on one of the turbine blades you can have for cheap. chip occured during assembly and hasn't been run since, bearing CHRA is perfect, no play. going cheap, would need a balance.

use the shittest oldest compressor design you can to maximize the surge.

No, that is not the case. ARP recommended torque is 325-345ft.lb (440-467Nm) as per pdf in link: https://arpinstructions.com/instructions/102-2501.pdf

an update here, JHH engines in brisbane are doing a trigger kit with a 1000hp ATI balancer using motec trigger wheels and sensors. 12 or 36-2 options.

I now feel vindicated about my decision. thanks Aquaman.

looking at a few dyno sheets (from some manufacturers) it appears on some they correlate directly, and on others torque lags MAP by a little bit. I'm guessing that is more to do with torque calculation/smoothing and retarder control than reality? I can't think of any reason why torque and MAP wouldn't correlate directly. why would torque lag it?

Full boost at 5k on stock turbos? That's a bit lethargic

Yea came to that conclusion and ordered one today. Cheers!

Hi Guys, I'm going to be installing an ATI 1000hp balancer this weekend on my ~800 flywheel horsepower RB26 has a steel trigger wheel welded to it adding about 600 grams. will torque to 450Nm with oil as per manual, is the OEM nissan crank pulley bolt the correct option for this damper or should I be using an ARP (102-2501) version? cheers

I'm confused, a tomei rb26 oil pump is a spline drive. What Harmonic damper were you using when the snout snapped?