Overall drivability I think suffers a very few percent. But new car manufacturers always stack the odds in the vehicles favor.

quick starts and highway passing etc. 40-60 sprints etc. one of those is going to suffer.

Its like tire pressure. Tires are designed to for multiple cars. So tire inflation guidelines are for NVH

 

Not sure I get the "yes and no" statement. You described in different words what I had to say. I never said that we control the "rate" of burn - I said that we (or the ECU) control the time given to the engine to burn the fuel. With the same fuel, you can time the engine for very poor power (timing somewhere ATDC), average power (2-12 degrees BTDC; or by the book), or lots of power (custom timing curve matched to a specific engine. My favorite method for old, carb'd engines: Vacuum Gauges | Diamondback Engines). I haven't been brave enough to get into a custom ignition curve with EFI yet.

What proof do you have that your computer gets more energy out of higher octane fuels? If you have some evidence, please share. This is what I was getting at - there are lots of experts out there with no proof. The octane of the fuel necessary for an engine is based on many items (CR, swirl, etc.)- octane's purpose is to reduce engine knock/pinging. If you have an engine that only needs low octane (or doesn't ping on low octane), putting high octane into it will not make more energy/power and only means wasted money.

It would be the same thing as using 87 octane at sea level. Low octane is low octane. What's your point? I grew up living at sea level (where 87 is the low octane). I now happen to live at 5850ft (where 85 octane is the low octane). I'd burn off that tank of 85 octane before ever reaching a low enough elevation to see any difference.
Since we're talking Discos, I didn't think there were any NAS Discos that came with the lower compression 3.9s/4.0s - I thought they all were 9.35 to 1 engines.

Given the numerous factors affecting MPG, the drop of MPG noted could have been due to something other than differing octane levels in the fuel. For me, it's not adequate evidence... but that's just me! I hold no ill will towards anyone who wants to believe that an increase in MPG equates to high octane/premium fuel is needed.

That's why I said someone would need a way to record the data, not watch it live. It better fluctuate! My point was whether or not one would see the computer using higher/more timing for higher octane - remember octane is only used to prevent detonation/pinging/engine knock and the more you have, the longer it takes to burn. It would be neat to see if the ECU treated a tank of high octane differently than a tank of low octane - if the engine monitoring devices (in this case, the knock sensor) detected engine knock with low octane, then the timing would be reduced and the engine would make less power. Then toss in high octane, and see if/how the timing curve changes. If it does, then point proven. If it doesn't, then money was wasted on high octane. I don't see anyone using adequate evidence (other than use what LR said to use in the owners manual/RAVE/workshop manual) to show that high octane is needed - I would LOVE to see some type of concrete evidence! You could make a sticky out of such evidence and just refer back to it whenever a low octane vs. high octane thread popped up. Hell, I wonder if some of the Rover V8 shop websites have some evidence posted... now I'm gonna have to go looking around.
It's not going cheap, it's going with what the engine needs. Buying higher octane fuel which an engine doesn't need is a waste of money. So, I can throw back at you that if you want to waste your money, that's your business. If you have proof (most quote the owner's manual) that you need high octane, then good for you. I just ask that if you are going to throw around "required octane rating" that you state your source. It'd be great if people understood why engines have a minimum octane rating, and have taken the time to determine what their engine needs beyond the owner's manual.
I got freaked out when it was being stated that our engines fire ATDC. It was nothing personal towards you. I get worried about the casual reader who will take what was posted and go spouting it off as fact.
As Spike already outlined, just buy the premium when possible given the math. In one sense, it's good that the station runs out often - you'll know the premium gas you do get from said station will be fresh. While I have my concerns over the high octane/premium vs. low octane/regular gas topic, you'll survive with a tank of mid-grade if the station is out of premium.

Oh, and my Disco passes emissions with flying colors each year running low octane. I'll step away from the keyboard now.

 

I ask these question using the average 1997 4 liter automatice with cats and 9.25 compression.

Help me with these questions. You seem to have lots of knowledge.

What do our knock sensors do, what do they control, how do they work?

How does air density (hot air and cold air) effect combustion, timing with high octane and low octane fuels.

Do higher octane fuels have more BTU's per gallon?

Do higher octane fuels enhance early or late combustion?

Does diesel fuel have more BTU's than Gasoline? How do we take advantage of it?

does more initial ignition advance produce a peppier car at a stop light?

Does more ignition advance allow for a cooler engine?

Does super unleaded fuel contain more fuel additives then low octane fuel from the same maker such as techron?

 

First off octane is an actual chemical part of gas, octane rating is the gases ability to resist detonation compared to a known sample of gas. A gas that has low octane can have its octane rating raised by adding different compounds, the most common is ethanol. So you can have a 93 octane rated gas that actually has no more octane than an 87. That's why I hate the 10% mixed gas you are getting less "power" aka octane, I'm sure I'm not the only one who noticed a drop in my mpg when they started putting ethanol in the gas.

 

Because you have to use more Fuel to produce the same power and efficiency. Thats the nature of ETOH. Thats also show the flexibility of your fuel system to handle E fuels

 

Just read in the rave, the knock sensor can sense if any cylinder is knocking aka preignition, when it senses knock it retards that cylinders timing then advances it to find the optimum timing for it and according to all the other inputs like tps, vss, maf. So I would assume that the higher octane you could put in the more the computer could addvance your timing giving you more power and efficientcy. Of coarse this doesn't apply to distributor models without knock sensors.

 

Bingo! Thus...to a certain extent typically more timing will produce more efficient combustion more power and economy. Doing less with more while maintaining the use of cats (ie getting them hot enough to produce the chemical reaction)

My bet is that we see less ignition advance on out ultra gauges in the summer plus we see less power.

 

Yes there was a low compression 3.9, very few were imported to the NAS market.

Here are the compression ratios for all of the Rover engines.

http://jimsrover.afraid.org/rover/gt...troduction.pdf

 

For background and more discussion, there is a tune select resistor that is used in various markets, depending on fuel quality and CAT requirements (CAT or no CAT).

From RAVE:


White wire, 3K9 Ohms, European catalyst

It is on C243 of the ECU. Most likely sets range of advance. Mercedes had a similar one, dash mounted, on Euro models, a selector switch you turned depending on quality of fuel you could purchase.

Here's a link to a write up of the GEMS system used on the Morgans, very similar to ours. http://www.gomog.com/allmorgan/GEMS/GEMSbyPoole.pdf

attached is a LR document set on types of fuel injection systems used

here's a link to the LR booklet on the Bosch engine management, has good write up on the way the various sensors operate and impact fuel economy, etc. http://www.google.com/url?sa=t&rct=j...hBObmeBccwHDUw

And then there is the book by Des Hammill that contains piles of data and pix of Rover engines with an attitude... http://books.google.com/books?id=gmS...page&q&f=false

 

My spidey sense is tingling. Don't think I'll bite.