Plus or Premium gas for 95

[BullDogSix]

Honestly none of those motors qualify as high compression to me lol....

That's what I was thinking.

[ArmyRover]

So I guess I will not acknowledge the existence of a high compression 3.9 rover motor

Going off those figures any RRC that needs premium to run right probably needs a tune up

[BullDogSix]

Check this link...http://www.bajajusa.com/High%20Octane.htm

[p76rangie]

Originally Posted by BullDogSix

from RangeRovers.net:

8.1:1 (to 1988), 8.13:1 (1989-92), 9.35:1 (93-95), 8.95:1 LWB

My motor is a 1994 4.2ltr-8.95:1 comp. I don't think that 8.95:1 compression requires premium...now a 3.9ltr specs out at 9.35:1...more than likely it could use a higher octane gas.

Those figures are not correct. Landrover built both compression motors at the same time and has been an option since the 1980's.
How hard is it to look at the motor and see what is stamped on it.

[ArmyRover]

Originally Posted by p76rangie

Those figures are not correct. Landrover built both compression motors at the same time and has been an option since the 1980's.
How hard is it to look at the motor and see what is stamped on it.

oh hell here we go again.....

hmmm rangerrovers.net one of the largest resources for RR owners is wrong now hmmmmmm

how about the parts listings

3.9 Litre
Standard Size
Low Compression (8.13:1 cr) - (1) - RB7485KLC
High Compression (9.31:1 cr) - (1) - RB7485KHC

Single Piston;
Supplied with rings & gudgeon pin.
4.2 Litre - 8.94:1 cr - (8) - STC1191S
4.0 Litre Series 2 Range Rover type
Offset gudgeon type - standard size only.
Low Compression (8.13:1 cr) - (8) - ERR5555
High Compression (9.35:1 cr) - (8) - ERR5553
4.6 Litre Series 2 Range Rover type
Offset gudgeon type - standard size only.
Low Compression (8.13:1 cr) - (8) - ERR5556
High Compression (9.35:1 cr) - (8) - ERR5554


All of that jives with what bulldog said. None of those are high compression engines to me so I still don't have to acknowledge it P76. There is a higher compression engine but neither are pushing any serious compression.

oh here's the website I pulled my information from.

Rover V8 Engine Pistons & Conrods - Parts Spares Accessories - Rimmer Bros

[p76rangie]

ArmyRover, you are splitting hairs. Whether you class 9.35 as high compression or not is largely irrelevant. From Landrover's point of view it is. The compression ratio is high enough to run better on a higher octane fuel than standard. But as we all know, nearly all modern motors have knock sensors and therefore can run the lower octane fuel, but just don't expect the power out of the motor.

[SafariDave]

My engine is a CR 8 . 13. 1 (Low Compression) I guess I can use both 87 or 92. What will make my Rover get more MPG's? And Not clog it up?

[ArmyRover]

So would you consider a 1.5 L honda civic motor high compression? It was used in the late 80's in the cheap fuel economy cars.

No you wouldn't and it's running the same compression as a high compression rover (ok it's .09 less)

Your not going to sway me with the argument that Land Rover thinks it's high compression. I thought when I was 6 that I was going to be the starting center fielder for the Chicago cubs. Both are wrong. Reality is that neither of those things are right 9 to 1 compression is not high compression.

You have not shown me anything that proves my rover needs 93 octane. All the facts are to simple to me it's not needed. Low compression 6 years with low octane and no pinging and no difference that can be felt seen or heard ='s waste of money on premium fuel.

It's to easy it doesn't need the high test and it's not going to get it so I have a warm fuzzy feeling that I spent 6 dollars more on gas so my car will run for ever.

[p76rangie]

Some independant views:

Howstuffworks "What does octane mean?"
If you've read How Car Engines Work, you know that almost all cars use four-stroke gasoline engines. One of the strokes is the compression stroke, where the engine compresses a cylinder-full of air and gas into a much smaller volume before igniting it with a spark plug. The amount of compression is called the compression ratio of the engine. A typical engine might have a compression ratio of 8-to-1.
The octane rating of gasoline tells you how much the fuel can be compressed before it spontaneously ignites. When gas ignites by compression rather than because of the spark from the spark plug, it causes knocking in the engine. Knocking can damage an engine, so it is not something you want to have happening. Lower-octane gas (like "regular" 87-octane gasoline) can handle the least amount of compression before igniting.
The compression ratio of your engine determines the octane rating of the gas you must use in the car. One way to increase the horsepower of an engine of a given displacement is to increase its compression ratio. So a "high-performance engine" has a higher compression ratio and requires higher-octane fuel. The advantage of a high compression ratio is that it gives your engine a higher horsepower rating for a given engine weight -- that is what makes the engine "high performance." The disadvantage is that the gasoline for your engine costs more.

7. What parameters determine octane requirement?
7.2 What is the effect of Compression ratio?

Most people know that an increase in Compression Ratio will require an
increase in fuel octane for the same engine design. Increasing the
compression ratio increases the theoretical thermodynamic efficiency of an
engine according to the standard equation

Efficiency = 1 - (1/compression ratio)^gamma-1

where gamma = ratio of specific heats at constant pressure and constant
volume of the working fluid ( for most purposes air is the working fluid,
and is treated as an ideal gas ). There are indications that thermal
efficiency reaches a maximum at a compression ratio of about 17:1 for
gasoline fuels in an SI engine [23].

The efficiency gains are best when the engine is at incipient knock, that's
why knock sensors ( actually vibration sensors ) are used. Low compression
ratio engines are less efficient because they can not deliver as much of the
ideal combustion power to the flywheel. For a typical carburetted engine,
without engine management [27,38]:-

Compression Octane Number Brake Thermal Efficiency
Ratio Requirement ( Full Throttle )
5:1 72 -
6:1 81 25 %
7:1 87 28 %
8:1 92 30 %
9:1 96 32 %
10:1 100 33 %
11:1 104 34 %
12:1 108 35 %

Modern engines have improved significantly on this, and the changing fuel
specifications and engine design should see more improvements, but
significant gains may have to await improved engine materials and fuels.

[SafariDave]

All this info is quite fantastic. ArmyRover you have been driving your 1991 for 6 years on Regular Unleaded 87 without any problems, that's great! I guess I will do the same my Rover has 186500 miles how long can it last. When it dies it dies. And then I'll upgrade to a 4.6 engine short block on LPG or better a Turbo Diesel converted to cooking oil that would be the best!

[ArmyRover]

156k and counting. Runs like a champ!

Keep it tuned up and your fine on the low octane.

P76 nowhere in that huge article do you prove that the Rover engine requires premium fuel. It is a good article on how a combustion engine works and what octane is about that's it.

[p76rangie]

Originally Posted by ArmyRover

You have not shown me anything that proves my rover needs 93 octane. All the facts are to simple to me it's not needed.

By your post, as to what compression ratios were available in the US in what years, your motor is most likely a low compression motor and you are completely correct in running standard fuel in it. So I am not sure what we are debating?

[p76rangie]

Originally Posted by ArmyRover

P76 nowhere in that huge article do you prove that the Rover engine requires premium fuel.

The second article stated that you should run 96 octane in a 9:1 compression motor and 100 octane in a 10:1 motor. So in a 9.35 you should run something around 96 or a little above. I know that they use different rating systems in the states, but here the base fuel is 92, the middle is 95 and the top is 98. All I have been suggesting is that you need to go above the base unleaded fuel if you run a 9.35:1 rover motor.

[SafariDave]

So whats best for you fuel injectors?

[ArmyRover]

Originally Posted by SafariDave

So whats best for you fuel injectors?

gas and the occasional fuel injector cleaner of your choice.