Do they have the ability to eliminate the top speed restriction as well?

 

Just a couple of 4.2s have been done with the twin screw kit so this limitation might not be well explored.

Cambo, I'd also be interested in any documentation you have about this "feature". Is it outwardly apparent when this limit kicks in?

 

There is no "kicking in" it's just the engine will not put out more than 600Nm of torque, if you could notice it just feels like the car is holding back at WOT, because it's not actually at WOT.

And sorry no, it's not documented anywhere public.

 

There is indeed a limiter in the ECU for the STR, but I have not witnessed this in the 4.2 XKR, where a dyno pull showed 470rwhp and a nice power/torque curve. But who knows, it may be there as well, but at a higher level.

The STR does kick in earlier, and as far as I know it is the ECU itself that does it, as it can be programed out. The ecu doesn’t need to have torque sensors, based on the rpm/airflow it will know what sort of torque it produces.

I have had this when I installed a kit on a range rover sport with the same 4.2 engine (though with newer version of the Denso ECU), where at a specific point, when the there is more airflow then expected by the ecu it will throttle back to a table with stock values by closing the throttle. My tuner was able to program this out, so expect this can be just as well for the STR.

 

Wow so even if you had nitrous you'd be stuck at those power levels. Hopefully that can be programmed out. I see in the xfs the tunes yield 30hp if its around the same for the str ill buy the tune right away.

 

No, nitrous gets around the problem by adding oxygen & fuel after the MAF. The MAF doesn't see any higher airflow, and the ECU is putting in the same amount of fuel, so it can't tell that the engine is putting out more power. It's pretty sneaky.

Ah derrrrrr....so it can't be the TCM that limits the torque. Never mind me!

 

Under the presumption that your electrical diagrams are similar to those for the X308 ... broad hints about what information is passed between the modules and in which direction can be found at the very end of the pdf in the appendices. While the format is not called out, the message list is fairly comprehensive.

 

Mods on the XJR you witnessed hitting this limiter? I guess it was witnessed on a dyno when you say it "flat lined'?

Based on avos' post, it sounds like the limiter is within the ECU calibration. wish we had more info on this, what triggers the limiter exactly, is it based on several factors, is there a specific map in the calibration that determines "instantaneous torque", perhaps through Air Flow Rate at the MAF x RPM? Probably more complex than that though...

I'm wondering if there is any way to datalog this occurrence. Will throttle position sensor show the ECU pulling back throttle? Or could the ECU 'throttle-back' power through other means, including through ignition timing?

Where did you get the 600nm/443ft/lb torque figure though?
Indeed, I want to see that torque curve too, wouldn't mind seeing it 'flat line' however briefly at some point too.
That may be difficult, as the torque peak is below 4,000rpm, and it is difficult to go WOT on the dyno below 4,200rpm without it downshifting to third.

The figure itself is somewhat arbitrary; hard to say what that would translate to in terms of torque measured at the wheels by the dyno.
Which is why I'm curious whether or not in my particular case, I will even hit this limiter with my current mods... I would love to identify it though whether through datalogging or dyno read-out.

With that said, assuming we even trigger the torque limiter, it would happen only briefly around torque peak. torque starts falling off again after 4,000rpm, so it is possible the limiter would only come into play at a very narrow part of the band; kiss the limiter around torque peak, and then hover just below it from then on.

Now that you mentioned it, I will start observing much closer for the ECU throttling back power briefly around torque peak....

I will also contact Jerry at Eurocharged again, and ask him about this limiter, and whether or not his tune addressed it at all.
Certainly a VERY important selling feature if it stands to be proven that you can hit this limiter with the stock eaton...

Oddly enough, I didn't ask about this specifically. Maybe because I haven't come close to reaching the factory 155mph limiter (where do you guys take your cars up to such speeds, lol?)
With that said, I know for a fact they advertise a limiter increase for many other models, including the XFR cars they tune.
Would imagine this tune would have done the same for the STR. Another follow-up question regarding limiters I'll have to pose to Jerry at Eurocharged for sure.

 

It’s a very rudimentary system in these early denso ecu’s (nothing like the limiters/behavior on the 5.0 ecu’s), once you go above the threshold the ecu will control the TB in order to get the stock airflow. This is very noticeable, and drops your performance back to a stock car, and it stays in this mode until you stop your wot session.

But you already must have some serious airflow to hit this “switch back to stock power” threshold, a 3lb puley with an eaton will not get you there. You can monitor this with a standard obdii meter, just look at the % throttle opening if you suspect you are hitting the limiter. But the throttle is also used to lower power during shifts, so don’t confuse that with the limiter!

Tip: I think you have to search for the stock airflow map, adjust that to higher values and you’re done.

 

Wow! I could have sworn I saw a small bird come flying out of your exhaust. I thought perhaps that was your secret to the wonderful sound of your car LOL. Had to replay it a few times just for laughs

 

My thoughts exactly; not certain if the factory eaton will ever blow enough air to hit this '600nm" figure, or even if it does, may be very briefly at peak torque <4,000rpm,
Now on a twin screw kit... different story, I was looking at your twin screw dynograph, and you are making 600nm at the wheels STEADY past torque peak,
Which is why I was wondering about that XJR cambo351 talked about hitting this limiter, what mods it had, and under what conditions it was active...

LOL! I think it was a moth or something actually... noticed that too!

 

Isn't the PCM torque-based (from jag's docs) so applying a limit should be trivial for it. But let's see before & after dynos...

 

So i'd guess, it's probably something basic, like a table for mass airflow & rpm with a value for fuel.

And when the airflow goes "off the chart" it can't keep up so it winds back the throttle. All it would need is extending the table to include the higher airflow with a fuel value. If this can be added as part of the tune.

It's no coincidence that the ZF 6HP26 transmission is rated for 600Nm / 443ft-lbs, and the torque curve was a flat line at the same number...

Not everyone wants to run a stock eaton though...if you know what I mean.

 

Maybe it will, maybe it won't, now is the time to find out.

Do I really have to spell it out?

 

What would happen if you put a larger maf (calibrated) in the mix?

 

Old Supra trick ...

run a bigger MAF and bigger injectors

the ECU never knew the difference.

 

Tell us more Obi Wan

 

Man, I'd love a copy of those definition files...

 

The idea is a MAF that in effect lies to the PCM (says there's less air than there is) and at the same time injectors that let in more fuel to match the extra air. So the PCM can't tell and is happy but meanwhile you've more fuel & air so more power. I'd guess that matching MAF & injectors across a wide range of power will be hard but I stress "guess".

If the current MAF will physically allow enough air then you can likely just adapt its readings with a few resistors rather than fit a different MAF (but do what's easy for you if resistors are already sound hi-tech LOL).

I think you'd "only" need to get fairly close to matching injectors to MAF because the PCM will fine-tune anyway. But expect codes to flag if you're not close enough.

 

For the MAF trick to work you need to scale the injectors at pretty much the same rate. At WOT the ECU switches to open loop, so the fine tuning goes out the window and it's just a lookup table.

To really pull it off well you could use bigger injectors and then a MAF where you could adjust the calibration curve yourself and dial in the A/F mixture.