[Rowant]

I was recently in a discussion with a person and we agreed to disagree about fuel for a p38.

As I understand the fuel/ignition situation these settings were designed so the engine will digest low grade fuel ok. I am also under the impression that feeding it ´the good stuff´ (eg genuine 98 octane) will not make any difference in performance or economy as the settings are controlled by the ecu chips.

The other person reckons that the system can detect what it is being fed and so adjust fuel and ignition settings to give a proper set of readings and thus a distinct performance and economy increase.

If the later is correct then people like Mark Adams must have it all wrong. Is anybody able to help with some info regarding what really happens when it is fed top grade fuel vs crap.

Cheers
PS The other person is my brother in law and I don´t want to start any sort of fued or ill feeling but sometimes he reckons that he knows it all.

 

[bonnychoo]

Doesn't the Owners' Manual specify min RON95 fuel.
Going below that would merely be foolhardy.

 

[Rich998a]

A standard fuel map takes into account the likelyhood of running a RV8 on poor fuel over the long term. It has to for obvious reasons.

If you call Mark and ask for a pair of chips, his first questions will be 'Are you presently running or likely to run on LPG?' and 'What sort of grade of fuel do you use - Are you travelling to East Europe?'. Why? Because a fuel map can be customised to run the RV8 more efficiently.

 

[Chris X]

I equate the premise to what you eat. Stuffing down a double Whopper from Burger King will fill your stomach and you can survive, but your gastrointestinal system will likely be unhappy with you and there will be some side effects. Whereas you eat a nice protein rich low fat chicken salad with fresh veggies and the like, you'll feel better for it.

Replace the above double Whopper with "low octane cheap gas" and chicken salad and veggies with "93 octane" and stomach with "vehicle" and see how it works.....

 

[kmagnuss]

Yes...the ecu will adapt to lower grade fuel (which I've been running exclusively for over 4 years now)
Will there be more/less power? Theoretically, yes. Is it noticeable... not to me or my wife. IIRC Dennis said in a post awhile back he got better fuel mileage with the better stuff.

 

[dutchfrompredator]

my understanding of it was what kmag said. the higher quality the cleaner and longer it burns. that's why i try and use premium. filling up more often at a cheaper cost kinda is a wash in my mind, when you can spend a little more to get a little further. with that said, the first thing i look at is the price, like many of us. when it's pushing $3 a gallon for 91 or 93 i say screw it and get 89. if it's within reason, i go premium. times when i go regular, i top off a quarter or half tank with premium a few days later. car seems happy either way. all i can give you is anecdotal evidence that premium does appear to last a little longer in my experience. i hope i'm not confusing the crap out of the fuel system...

 

[RRToadHall]

I ran Safeway low grade in mine for a couple years on a high compression 9.6:1 / 4.6. I never had any knocking or poor performance and did quite well on the dyno. After my engine rebuild I ran premium for a little while as I have slightly higher compression than before. I have since gone back to low grade fuel with no changes in performance. Our engine have knock sensors that tell the ECU adjust the timing should any pinging occur. THe slight difference in timing would only account for a few horsepower which wouldn't be noticed by even the most sensitive butt dynos. :mrgreen:

 

[shupack]

Sorry Rowant, I have to agree with your BIL on this one

I did an experiment long ago, with a 4 cyl carb equipped toyota truck. 10 tanks on cheap, 10 tanks on regular. $/mile was cheaper on the good stuff because of the increased milage. plus with that weak engine, the power change was noticeable, to get up on the highway needed full throttle, not so in the RR.. the power shift may not be noticeable, but you'll use a bit less loud pedal for the same acceleration, which helps with the increased milage. I rarely need more than 1/2 throttle...

the maps on the stock chips are designed to cover a wide range of operating conditions, from sub 0 arctic to 130 deg dessert, from cheap, dirty fuel to high-grade clean stuff you pay a premium for. From fresh, clean oil and filters to the owner that just gasses and drives, 10k on low oil, clogged filters etc.... the mapping has to handle it all.

A Mark Adams (or others) chip will narrow those bands, and specify you use high grade fuel and change your oil/filters regularly. By narrowing the expected operating ranges and maintenance conditions, more power can be safely coaxed from the engine.

 

[996TURBO]

Here in France we have access to 95 or 98. 98 gives better economy

 

[Rowant]

Thanks one and all for the comments and experiences.

My BIL seems to be of the opinion that the standard ecu will give the same performace (ignition, fuel etc) that a complete remap will. Apparently not. The standard settings still seem to be somewhat cautious and restrictive.

I might look at running the highest octane available here to see if the price is really worth it.

Once again thanks all.
Rowan

 

[paul.adshead]

My BIL seems to be of the opinion that the standard ecu will give the same performace (ignition, fuel etc) that a complete remap will. Apparently not. The standard settings still seem to be somewhat cautious and restrictive.

That's the case with every manufacturer's chips. The last thing the manufacturer wants is to start having engines failing, by going to the limits and wringing an extra 5% power out of them, when they can back off slightly and not loose any.

I might look at running the highest octane available here to see if the price is really worth it.

That'll be LPG then - 99 Octane!
http://www.rockgas.co.nz/4-automotive-lpg.asp
It also costs only 60% of the price of petrol (if you buy it the 'right' way).
Come and join the club.....

 

[viperover]

I use 95 with great results...

I have a Rangie in for major repairs that has the tornado chip in it, after all the work has been done Im curious to see if its really that good compared to my standard 4.6, the bet is its not but we'll see.

Power gains can be achieved by sorting out fusebox problems if old, soldering cable end lugs on earths and supply ends, making sure a good battery is present etc.

The issue of more power and where to get can go on forever, for a kick adding a octane booster can broaden your smile for not much money if everything is in order

 

[Gemmiti]

I've tried different grade gas in my Rover. I feel she most definitely likes the premium gas. Better fuel economy and a smoother running feel to the engine. More power? I'm not sure but a smoother purrr for sure! Honestly the difference in price for 87 octane to 93 octane is never more than $0.30 here so an extra $5-$7 per fill up is a no brainer.

 

[81stubee]

I'm surprised no one has mentioned compression ratios yet.

My understanding is that the higher the CR the more efficient the firing stroke due to the stored kinetic energy, however the downside is there is more risk of pre detonation due to the increased temperature. Therefore the engine fires at an optimum position for the given fuel by listening to the knock sensors and retarding/advancing the timing accordingly.

Therefore a low compression engine as sold in Oz and some other countries (8.23:1) will be able to run on lower octance fuel, but will not have the same kinetic energy per firing stroke but is less likely to detonate. The higher octane fuel is more efficent in a high comp engine such as sold in europe ( CR of 9.23:1).

In summary, if you have a High comp engine you will get much more benefit of 98RON fuel than a low comp engine running on the same fuel. Or something like that.

Stu

 

[NachoMan77]

I'm surprised no one has mentioned compression ratios yet.

My understanding is that the higher the CR the more efficient the firing stroke due to the stored kinetic energy, however the downside is there is more risk of pre detonation due to the increased temperature. Therefore the engine fires at an optimum position for the given fuel by listening to the knock sensors and retarding/advancing the timing accordingly.

Therefore a low compression engine as sold in Oz and some other countries (8.23:1) will be able to run on lower octance fuel, but will not have the same kinetic energy per firing stroke but is less likely to detonate. The higher octane fuel is more efficent in a high comp engine such as sold in europe ( CR of 9.23:1).

In summary, if you have a High comp engine you will get much more benefit of 98RON fuel than a low comp engine running on the same fuel. Or something like that.

Stu

Interesting point 81stubee.

Apparently my Rangie is an Euro Export model for the Arabian markets (according to my mechanic). Long time ago the some dealer imported a big batch of them. Looking at Microcat I found the following: low comp (8.37:1) non catalyst engine (067AL) / lo octane leaded (103AB).

My milleage is not as good as many posted here (even taking into account unit conversion, driving habits, tire pressure, etc. and I recently had the top end redone). I always used premium fuel, which in reality should be on par of regular fuel in the rest of the civilized world. I do it mostly because regular fuel here is dirty junk. Now I think the low comp engine has something to do with it. So, excuse me for my ignorant question, but do you suggest these low comp engines don't have knock sensors ? Is that even possible ?

N.

 

[Rowant]

So it seems that the system can´t actually tell what it is drinking - it just runs as far up the engine map as possible until it detects the onset of detonation and then backs off a little - sounds logical.

My machine is a Jap import but I have not been able to find any label/plate anywhere that tells what grade of fuel to run or what the compression ratio is for mine. I will have another look but I don´t read Japanese too well.

 

[NachoMan77]

So it seems that the system can´t actually tell what it is drinking - it just runs as far up the engine map as possible until it detects the onset of detonation and then backs off a little - sounds logical.

My machine is a Jap import but I have not been able to find any label/plate anywhere that tells what grade of fuel to run or what the compression ratio is for mine. I will have another look but I don´t read Japanese too well.

Look it up in Microcat. That's where I found the info on mine.

N.

 

[Rowant]

Microcat? Is that the same as Rave? I searched for microcat and ended up at The Green Oval and Rave.

 

[AMcK]

Microcat? Is that the same as Rave? I searched for microcat and ended up at The Green Oval and Rave.

Nope Microcat is the parts system the dealers use. You can enter VIN and it will show info on vehicle and correct parts for your Rangie.

Go back to mentioned web site and just use your scroll button and you will find what you seek

 

[81stubee]

We stumbled across something recently on the AULRO forum in OZ.

In Oz, the early (95/96) p38's had no oxygen sensors. One of the guys here was going to hook some up as the looms were already there and enable them with testbook. As he found out the option has been disabled, and upon further investigation it was revealed that the early Oz ones had a fixed fuel map. Therefore they run in open loop all the time. This also means that the ECU can't adjust the mixture to compensate for different fuels, because it has no way of knowing how rich/lean the exhaust is.

This would probably be the case for south america and africa where fuel quality is very poor.

Stu