This topic may be better suited to a more general forum here but has anyone had experience tuning Jags or other brands for that matter to use higher octane or race gas? I have been told by an Audi tuning shop they map the ECUs to use race gas which has 2 benefits they say. Keeps the motor running cooler, helping with wear and heat soak and increases horsepower and torque.

Any thoughts or experience?

 

some of these laptop tuners are a bag of gas themselves. And it is the most classic excuse they use. 'your car was tuned to run on low grade gas'

there is a British tuner here on these threads, totally trust him, he has been working on Jaguars for a very long time. he gets what is important

 

That's not how they put it. He, the Audi tuner who does NOT do Jags, suggested additional performance can be had just by writing the ECU map (timing, AFR, etc) to compensate for higher octane.

Who is the tuner you are referring to?

 

Half what your tuner is saying is absolute garbage. 'Race gas' burns pretty much the same as any other gasoline so it causing the engine to run cooler or with less wear and tear is b*llsh*t. I can give you lots of tech references from the fuel manufacturers themselves if someone tries to tell you any different.

There is sometimes a potential for more power but with a big, very BIG maybe. Race gas is usually of a higher octane rating which means solely and strictly by definition that it is more resistant to detonation.

All modern Jags are tuned for and achieve full rated HP on 95RON/91AKI gasoline. Filling the car with higher grade gas might and only might allow it to make more power if the engine was experiencing detonation on the recommended 95/91 fuel and the knock sensor/ECU was retarding the ignition timing accordingly.

I've seen no evidence that this actually occurs. Guys using 94 octane here don't go any faster than the guys using 91.

Your tuner is proposing to change the ignition timing map so that it advances the timing beyond what Jag developed. Doing so would most probably induce detonation, hence the requirement for higher octane fuel to compensate. In theory, the additional timing advance might produce more HP- but that all hinges on whether the engine was already at it's optimum setting or not. Contrary to myth, more is not always better.

It's very easy to demonstrate on a dyno that any engine will start to produce less power as timing is advanced past a certain point, even if detonation is not a problem. I've not seen any evidence that Jag got it wrong.

 

Without any mods or ECU re mapping, higher octane gas will make no difference, in fact you may be able to use lower than recommended as long as early detonation does not occur. The ECU retarding timing is what causes a loss in power/performance, not the gas itself, of course.

My question is can modifications to timing, such as advancing, yield greater power, particularly on a forced induction motor with high compression, requiring higher octane such as race gas at 112RON?

 

i don't think you quite understand what the tuner is saying. he is not saying run higher octane, he is saying tune it for higher octane but run 93 octane. there is some truth in performance gains, but some risks. thus the need to find a good jaguar tuner. Its less about timing and more about leaning out the engine. Their claim is that Jaguar is running too rich, they are right. but jaguar may have its own reason for that.

I can't remember the name of that great guy from Vancouver who has the tune and exhaust company. Good guy!

 

Stuart @ Velocity. I contacted him but he never responded.

 

Yes the Jag does run rich and no he said specifically they use 108 octane gas in their Audi's after remapping. He claims they run cooler and performance is increased by compensating for the higher octane. However going back to lower octane may not be possible due to increased risk of detonation. Whether this is true or not, I do not know and whether this would make any difference on a supercharged Jag, I know not either.

 

"Race Gas" is made for high-compression engines to keep them from blowing apart. HIGH COMPRESSION is in the order of 13:1. My drag car is 12.5:1 and if I don't use 105 or higher it makes a racket. The paltry little 8.5:1 (or whatever) isn't even CLOSE to requiring Race Gas, let alone Ultra-Super (95 octane) fuel.
R+M/2 ratings, of course.
High Octane is more stable, so if used in low compression engines it's actually LESS powerful unless it can be compressed more, or by increasing timing. That only goes So Far until it's no further benefit.
It smells cool though.

 

Yes Stuart. He is the master's master in this field. But i don't know if he takes on 4.2. He is very popular with the ftype guys and thus 5.0 xkr.
He was the guy who taught other tuners how to do a 4.2. keep trying.

 

That too is correct.

I have the AJ34S motor which does run at 9:1, the NA version is 11:1. According to my torque app I am at around 10:1 +/- but have been told with the smaller pulley and mapping I can get up to 13-14:1.

 

I answered that in last part of my response above.

"Your tuner is proposing to change the ignition timing map so that it advances the timing beyond what Jag developed. Doing so would most probably induce detonation, hence the requirement for higher octane fuel to compensate. In theory, the additional timing advance might produce more HP- but that all hinges on whether the engine was already at it's optimum setting or not. Contrary to myth, more is not always better.

It's very easy to demonstrate on a dyno that any engine will start to produce less power as timing is advanced past a certain point, even if detonation is not a problem. I've not seen any evidence that Jag got it wrong. "

Using the ubiquitous Chev Gen 1 V8 as an example, many of them came from the factory with very conservative timing curves, for a variety of reasons. An common trick was to advance the timing curve by resetting the distributor a few degrees which within certain limits boosted power but sometimes also brought on detonation which could be quelled with higher octane gas.

'60s Corvette owners sometimes tried the same thing but frequently got nothing in return or went slower, or sometimes blew up. The factory ignition timing was already at it's peak and further advancing was counter productive. Peak timing on the small blocks is around 36-38*, anything more is wasted effort.

Hope this helps.

 

Do you have anything to back that up? All my documentation shows more variability in energy content per volume in standard pump fuels than when comparing pump gas to race gas.

 

Thanks for encouraging me to try again. Spoke with him today and he is going to write a few different tunes for me to use standard gas as well as race gas. He says I will be able to increase boost, increase spark and lean it out more to use higher octane for increased performance. I'll be able to switch between the tunes as needed. Should be getting the equipment in a few days. Can't wait to see the results. I've only been waiting 5 or more years to get it done.

 

Glad to have been of some assistance. You are in the most competent hands in this field. He understands Jaguars. I am quite opposed to most tuners- they are not holistic, sure they can increase something, only at a cost of something else. The biggest problem is they apply a one tune fits all strategy, Stuart on the other hand actually has an Ex Jaguar Tech on staff, looking at hex code all day long to find a way of properly removing the limitations.

 

??????
Of course. Common sense, knowledge and science.
I don't have time go Google it for you.

 

Way ahead of you. There's nothing that support your statement. All gasoline contains roughly the same amount of energy- approx. 116,000 btu/gallon. It all has approx. the same flame front velocity.

 

I don't think the Jaguar ECU has been cracked, has it? For such a limited production car, I can't see serious effort put into it, but it would sure be cool to have access to all the engine maps!

 

There are some good gains to be had with leaning and advancing the spark on these 4.2 engines (as on the 5.0) as long as you run higher octane gas as a precaution. Stock these engines are rich and have a relatively conservative spark advance, but that’s all required for longevity (so enough safety margin) and the extra cooling from the fuel will also help to keep your cats for longer.

All ecus have been cracked, however I have not heard yet on a switchable setup for a 4.2 ecu, maybe for the later pan pag ones (which the 2008 has)?

 

Supposing for curiosity that "race gas" and a tune "work", what sort of HP gain on this engine might be achieved (without unduly compromising engine life)?