I think for sure I would stay stock size up front for my application. I could go 265's up front but it would probably would be of little benefit for a cruiser like me.

Here is a good thread about these tires and sizes.

https://www.jaguarforums.com/forum/x...n-97354/page2/

 

Matt - For street GT use the car is great I was really being picky and its my personal preference when it comes to suspension feel. I like my cars really stiff and brakes to feel like you're pushing on a 2x4. The brake fade I mentioned really isn't typical fade just an overly soft pedal after repeated hard braking, which the car recovered from quite quickly. I really hope the H&R springs are satisfactory and I'd love to find some stainless braided brake lines that may help with the pedal sponginess. Youve owned some similar cars to what I have had in the past and you can't argue with the great brake feel in the Porsche.

Based on the thread you mentioned I went with the Pilot Sports in 265 front and 305 rear since I had to replace all four tires anyway.

Going to send you a PM on the Euro Spec Clear Side Markers, I'd love to have a pair.

 

I think you're big on modifying the car because that's what you enjoy doing, and obviously have wasted no time modding your 2013! Whatever floats your boat is cool with me, but I have to say I can hammer on my XKR's brakes on the race track all day at 140 mph and not get fade or soft pedal, the suspension is tight and controlled under all conditions including hard transitions, and would be the same at 700 hp because the car is already running on the limits of grip and more power won't apply more load to the suspension. More power would put more load on the brakes on a race track because you'd be hauling down from higher speeds, but I can't see enthusiastic driving on the street coming close.

While over an inch of drop with the H&R may appeal visually, that's more than double what the factory does on its lowered versions, and I'd be more concerned about degrading handling from compromising the suspension's designed geometry, reduced suspension travel, mismatched spring rates and damper valving. And I don't know what affect that would have on operation of the DSC and eDiff which get inputs from many sensors. Did you determine what the factory spring rates are vs the H&R's, or figure out the other aspects I mentioned?

Bruce



,

 

Bruce - The degraded handling is what I'm concerned about but decided to give it a try for 400 dollars before going the 3k route on the Spires coilovers. I have a feeling I'm going to end up with the coilovers with properly tuned dampers and a ~.75 in drop. As far as going over the suspension geometry that will be done hopefully this week when the car goes in for the alignment at a local race shop. I know thats backwards but all the feedback I've heard on the H&Rs has been good so for 400 I'll give it try.

As far as the suspension and brakes again I'm not saying they are bad, I just feel there's room for improvement and that just my opinion.

 

I hope the H&Rs work out well for you...simple and inexpensive. And at 1.2" drop the car will definitely look lowered! Good luck

Bruce

 

UPDATE:

Car is driving beautifully and everything is great. Really love the new feel of the throttle and the car is very fast. If you are deep into the gas and shifting from second to third, the rear wheels will absolutely lose traction, as I found out yesterday. Temp was about 72 degrees outside and the traction control abruptly cut in. Looking to upgrade the tires soon, probably beginning of next year.

Gas mileage seems to have gone up a bit which is surprising...I was averaging 13 mpg and now I'm at 13.8 mpg. I reset it the day of the tune.

Hope everyone is doing well!

 

It's very possible that tune changed your A/F ratios to a bit more lean. That would help with mileage.

 

I'm not sure what it is, but my AFR's are basically identical to stock according to the dyno sniffer. Eurocharged said they prefer the AFR's to be "stock-like" for this tune.

Could be the cooler weather? I'll drive it more and keep and eye on it, who knows maybe I gained a little MPG somehow.

Still very happy with the tune. Glad I did it, car is a complete monster.

 

Glad to hear you're pleased with the results! The dyno only shows AFR at wide open throttle looking like stock. It's very likely that the tune they use has been leaned out a little in the part of the rpm band and throttle conditions that you mostly drive under. That would account for the more responsive throttle and the fuel savings.

Bruce

 

I'm reading the a/f curve. Is there not scope to lean it out a little. Is 10.5 not a bit rich?

 

Mine is also in that range and sure you can lean it out, but you need some safety margin in there. Bad gas, high ambient temps, altitude, etc can cause detonation . Why risk it for a few more HP on a daily driver.

 

I know that Bruce H. told me before that 10.5 AFR was "old school" but, that is where I set my own fuel curve when I mapped my twin turbo RX-7.

For normally aspirated cars you might be safe with 12+ AFRs at high RPMs. However, with cars with substantially increased boost over the factory levels, IMO, you will have to consider that extra factor.

In the fuel map, you set the fuel feed values according to both the engine RPM and the levels of turbo or supercharger boost. In my case that included entering 400 differing fuel values for the range of RPM and turbo boost. Since I am running as high as 19 psi boost and RPMs of 8000, I set the AFR to 10.5 between 7 and 8K RPM at full boost. Of course, I am running gradually higher AFR values as the boost and RPMs decrease. I am pretty sure, that 12+ would be very risky for my engine at these parameter.

So, with the increased boost rates of a non-factory tune, I can see 10.5 on the slightly rich end but, safe. Like MaximA said, I rather be safe than sorry. Blowing an engine is a HUGE deal in a Jag. Not worth the risk..

 

The reason tuning that rich is old school is because the fuel supply and monitoring has changed so much in the newer cars to make more safe power, improve fuel economy, and reduce emissions. The addition of a second oxygen sensor after the catalytic converters on new cars allows the ECU to constantly monitor and finely calibrate air fuel ratios, with the ECU constantly trying to lean it out, and also advance timing as much as possible. Older cars ECU couldn't monitor or control fuel as carefully, and had to run them richer to allow a greater safety margin from pre-detonation.

Your RX7 probably runs upwards of 19 psi of boost, Albert, perhaps double what the factory boost level was. Max is adding less than 3 psi with his pulley, and maybe no more than 1 psi in the mid-range where the torque limitters are reducing his power (compare to Matt's with XKR-S ECU and tranny). Where your RX7 was pushed hard, Max's isn't. The large safety margin you tuned into yours is not needed with his, and where you likely had no ECU anti-destruction knock response system, he has a sophisticated ECU with many sensors monitoring every aspect of operation, with the ECU ready to put itself into "limp mode" at the first sign of trouble. In addition to fuel mapping according to RPM and boost, it will additionally be mapped at least according to engine load.

But the tuning of the fuel map is just one part of a comprehensive tune to improve safe levels of power and performance. The other is the ignition map, with more advanced timing making more power, and bringing you closer to the threshold of detonation. Remember, the ECU will normally adjust operation so that the engine is running on the threshold of detonation, not a long ways away from it. The tuning procedure that is used is to adjust the fuel map first, and then the ignition map if necessary. AFR's would normally drop from lean at low rpm and engine loads to richer from peak torque to redline.

As Max mentioned, Jerry worked for hours on his AFR, and on Matt's I would assume as well. Where Jerry indicates he didn't want to risk running lean at higher rpm, the AFR plot indicates fuel running so rich it falls right off the scale at high rpm. You'll notice the same on Matt's plot, but in that case it appears a horizontal scale was set at ~10.5 AFR, and all readings below that disappear onto that line. Where you tuned yours to 10.5:1perhaps from mid-range to redline under full load and boost, these plots show what's called "fuel dumping". The stock ECU would normally do that only in extreme conditions, and if we were to see a dyno run with less than full throttle we would likely see an AFR plot closer to 13.0:1 I expect. What I would be asking is "why is the ECU fuel dumping under full throttle.

I has seen hundreds of dynos on different engines that have been tuned and they always are tuned to a pretty consistent AFR out to redline, and never richer than 11.0:1. Perhaps it's a limitation of the ECU, or perhaps the advance in the ignition map needed to be retarded to compensate for a better AFR, or perhaps the tuner just didn't try to optimize it. many tuners are reluctant to adjust the ignition map unless they are able to monitor the engine's knock sensor. That would likely have been impossible for Jerry to do when he was tuning from another location, and would have required a lot more work than just adjusting the AFR.

Why should anyone care if the AFR goes crazy rich if the customer is happy with his power gain? That depends on why it's going crazy rich on the dyno. Is it just something the ECU likes to do when it sees you going full throttle, is it a reaction to higher intake air temps caused by the intercooler's inability to cool the air charge at higher load and boost levels, is it because of higher coolant temps on the dyno, because you've been diddling with its fuel maps, removed a speed limitter that it didn't want you to, etc, etc. Should you be concerned in normal use with a high grade of fuel (unlikely), or worried under sustained full throttle and high load use like on a race track?

If you think it's a reasonable question to ask why the ECU is fuel dumping at high rpm, and I most definitely do, then you should look into it carefully. It might be easily explained, and be quite an acceptable operating condition, but at this point it looks more like a lack of tuning rather than an optimizing of one. And I'd be delighted to be wrong.

Bruce

 

Bruce

You are making good points in the above post. Indeed, my RX-7's aftermarket ECU has no anti-knock provisions where the stock ECU had it. I programmed both the ignition and the fuel curve on that engine and could not be happier with the results.

One of the dynos posted on these pages shows the AFR going to 10.5 at less than 4K RPM. That is too much fuel, no doubt. Max's only drops in that range above 6K, right before the redline.

Given my initial experience where my XKR violently jerked on a steep uphill acceleration near redline, I still suspect that it was either an octane number issue or a lean-AFR issue that caused the engine's anti-knock protection to likely cut ignition. Perhaps, after I get done with working on my XKR Monday, I'll take it back to that steep hill and test it again to see if I can pin-point the issue. If I can reproduce the jerking, I could add some 103 octane racing fuel from my RX-7 fuel supply and see if that stops it. Then, I will know that it was an octane issue. If it jerks with the 103 it would likely be a lean-AFR issue. The problem whenever you buy a used car, even one with 6K miles, you never know what was done to it. For all I know, someone may have flashed a tune into it that is running too lean under very high engine loads.

 

As I've mentioned before, I've had the same 'jerking' under hard acceleration (full throttle) from low speed on two occasions. The tune in mine is 'stock', i.e. it's unmodified from what Jaguar provided but the Jag tune is not the usual XKR one. It was tweaked for the 75 by Rocket Sports Racing, so who knows what it ended up like. I get my petrol pretty consistently from the same garage, and it's always 95 RON (91 US octane), so I don't think mine is octane-related, though it's not impossible. Hasn't happened for a while now, though.

Interesting tidbit I picked up from the original AutoCar article on the XKR 75 - Mike Cross said that they were running the development car at 545 bhp (553 PS) during testing. All the reviewers, from several magazines, commented at the time that the 75 felt like it had considerably more than 20 HP increase over the standard 510 (and it feels that way to me too, though I admit I haven't spent a lot of time in a stock XKR). Since I already know that the speed limiter is set to 186 mph rather than 174 as claimed, I suspect the power output is closer to 550 PS than 530.

 

Guys, according to the dynos, the stock AFR's are around 10.5 at WOT and upper RPM. This was before the tune was ever touched by Jerry. Jaguar must have done this for a reason, I would think. I assume Eurocharged agrees and wanted to keep upper AFR as close to stock as possible. I don't see a problem with this. The car has been running great for many months, makes amazing power, as is extremely responsive.

 

I do not mind a 10.5 on the principle of safety right at top RPMs and top accelerating loads. I will gladly give up 5-7 HP but sleep well. I blew one engine when my AFR went HIGH due to a weak fuel pump. Glad it was not a Jaguar V8. On the Eurocharged dyno shown on this page, however, 10.5 starts at less than 4000 RMP. That appears too rich, too soon.

Anyone knows how much it would cost to replace a blown-up SC 5.0 liter? I would guess around $45K. I'm confident that the warranty would be pulled if the dealer determined that it was a non-factory tune.

 

I don't think running a 10.5:1 AFR is a problem in any way, and if monitored on the road vs a dyno with good gas it may actually be leaner. The difference in dyno vs road AFR measurements is why final monitoring and tuning of AFR is typically done during road testing, not on the dyno.

In your case, I don't think your AFR plot shows how rich yours is actually running. It shows 3 very different AFR curves from three runs dropping fast as they hit the scale line drawn at 10.5:1 and then they simply disappear into that line as opposed to actually leveling off at an identical 10.5:1.

https://www.jaguarforums.com/forum/a...ine=1383669248



Here's an example of a 5L S/C dyno where four AFR curves are fully shown out to redline, and all four show gently fluctuating curves that become quite even through the higher rev range. The one run shows an AFR of closer to 12.5:1 to redline.



As an aside, when it takes so much extra tuning to get to the AFR's that you and Max have, it makes you wonder what the AFR curve would look like for those purchasing a standard flash tune without all the tweaking. I suspect the results would be much different, and it'd be worth any extra cost to have it done the way you both did.

Hopefully avos will chime in to give his thoughts as he knows infinitely more about Jaguar tuning than I do.

Bruce

 

I believe the AFR's at lower RPM are going to vary from run to run a bit because of throttle modulation by the dyno tuner as he tries to ease into the throttle to prevent the car from downshifting at the start of a run. Each run might be a hair different and I don't think it will be exactly repeatable from pull to pull because of this. The difference between 4000 and 4500 RPM is a hair of a second.


Also, I should make clear my car was not tweaked on the dyno at all. Jerry loaded in the tune, we ran the dyno a few times, and everything looked great. From what I understand, no adjustments were made to my tune after it was loaded in.


The AFR's look more gently fluctuating in the other graph you posted mainly because of the resolution on the axis. Eurocharged shows a range from 9-19, the other graph is shown from 0-20. That is basically double, so AFR fluctuations in the Eurocharged graph will look twice as large by comparison. I would be concerned for that person if my AFR were 12.5 at top of the RPM range when stock is around 10.5. I think it is probably an outlier or flawed measurement since none of the other runs are even remotely close to that.


I am also not sure about the assumption that 10.5 is a scale line that all data disappears at. Maybe I am confused, but I believe Jerry showed me in the tuning software that you can input AFR's and the engine will adjust air and fuel to match the AFR you have input into the system. Perhaps the bottom range from 4000 RPM to redline is 10.5? This I am not sure of.


Either way, my car must be a hair leaner somehow than before because my MPG has gone up about 1. My driving style is consistent and my routes are the same.


I cant help but think this whole conversation, although interesting, is basically making a mountain out of a mole hill.

 

Matt:

So happy to hear about your success with your Eurocharged tune. After 6 months I am completely happy with my results and would do it again without a doubt. Since having the tune done, I put new tires on my XKR and I have not had any slippage and I am impressed with the wet weather performance of my Vredestein tires. Ride safe.