Which fuel for Superlight R?

[clarkey]

Does everybody use Super Unleaded? I always would on the track, but is it needed on the road?

 

Thanks

[murph7355]

You should use Super.

 

The odd amount of normal unleaded won't kill it though.

 

C7 AJM

[clarkey]

Thanks

[Richard Ince]

I always use my Superlight R on normal unleaded. Racing included. Suggest you ask G Fuller at Minister.

 

Richard

[murph7355]

Wouldn't be the first time I've been wrong...

 

But I'm sure the Caterham owners manual mentioned that the Supersport k's should be run on Super...I would have thought the 'R' to be running a higher compression ratio than these and I thought this is what dictates which fuel to use to some extent...

 

 

 

C7 AJM

[CHRIS CLARK]

I agree with Richard on this.

I think 'std.' unleaded is fine for the engines, but don't use the cheap stuff from TescSainsAsda etc. This (I have been reliably informed) stuff comes in from dubious sources and has a high sulphur content. Can give some problems that just don't seem to occur when using the 'better' fuel from the big retailers. I know some people use it OK, but why chance it for a couple of quid!

[clarkey]

I've also been told that pretol degrades fairly quickly, and the octane rating falls over time (not a very technical description, sorry), so that SUL can be of a lower octane rating than UL when you buy it as it tends to sit in the tanks at stations for longer. So try to find a station that sells a lot of SUL as it should be fresher.

 

Not sure is this is a load of old b*ll*cks, but seems to make sense.

[V7 SLR]

All you need to know about Octane explained....

 

High-Performance Gasolines

by Scott Parkhurst

from Popular Hot Rodding / January 1998

 

It all comes down to fuel. You can build the hottest, most

throw-down thumpin' big block that ever existed, but it's

gotta have good gas.

 

What is good gas anyway? What separates the killer stuff

for your NMCA Pro-Streeter from the slag your lawnmower

barely runs on? After consulting experts in the field, we

decided to check into the various street fuels available,

various types and grades of octane booster, aviation

gasoline (AvGas), and racing fuels. By comparing the

different options available to you, it may be easier to

choose the best grade for your ride.

 

What is octane anyway? Octane is a measurement of a fuel's

resistance to ignition. Ideally, the air/fuel mixture will

ignite at the proper time and burn smoothly through the

power stroke, The idea is, one powerful combustion is

better than several, randomly-ignited small flame fronts.

When you can precisely control the point at which the fuel

will ignite, maximum performance of the engine can be

achieved, and power-robbing knock and ping will be

eliminated. Knock and ping are a result of abnormal

ignition, or multiple flame fronts colliding within the

combustion chamber during the compression stroke.

 

All reputable fuel manufacturers determine the octane

rating of their gasoline in the research lab using a

special, dedicated single cylinder engine. Comparing the

gasoline to a series of standard reference fuels in the

test engine results in either a research octane number

(RON) or a motor octane number (MON) depending on a set of

operating conditions. The RON is determined with the test

engine operating at 600rpm, at standard barometric

pressure, and the intake air temperature set at 125 degrees

Fahrenheit. RON is primarily used to address part-throttle

knock and ping problems. The MON addresses wide open

throttle operation and is determined with the test engine

spinning at 900rpm, also at standard barometric pressure,

and the intake air temperature pumped up to 300 degrees.

 

The best predictor of a fuel's performance in a

street/strip machine is the Anti-Knock Index (AKI). This is

simply the average of the RON and MON numbers, or

(RON+MON)/2. Most all octane ratings posted at the pumps

are determined by this AKI formula, and are the minimum

values you could expect to see. The minimum octane

requirement of your engine is determined by several

variables besides the compression ratio. The engine and

cylinder head configuration, air/fuel mixture, timing,

coolant temperature, atmospheric pressure, relative

humidity, and ambient air temperature will also affect the

octane required to make your mill produce maximum power.

 

The burn rate of a fuel is a measurement of the time

required for complete combustion of the air/fuel mixture.

The notion that octane ratings affect the burn rate of fuel

is about 180-degrees from reality. Burn rate is a function

of several variables, and the two are completely

independent, although there is generally a correlation

between octane ratings and burn rates.

 

To give you a good example of this, we contacted Jim Wurth

from Sunoco Race Fuels. He explains, "A perfect example is

Sunoco Maximal, which is our fastest burning fuel, and

coincidentally one of Sunoco's highest octane fuels at 116

(R+M)/2. A lot of Pro Stock teams rely on Maximal for those

sub-seven second runs. When they are turning 9,000rpm or

more, the fuel has to burn pretty quickly to achieve

complete combustion."

 

Octane boosters offer little help in the quest for higher

octane. Most popular street-legal octane boosters claim

increases in octane ratings up to five points, and those

boosters intended for off-road use only claim up to seven

points, That's a lot of octane to hope for simply by

pouring an additive in a tank. Sunoco told us that before

they launched their GT-100 Unleaded retail pilot program,

they wanted to be sure that a 100 (R+M)/2 octane street-

legal fuel would be of value, and that enthusiasts would

not be able to get the same (or better) results using an

octane booster. Nine of the most popular retail octane

boosters were put through a series of tests to determine

where the consumer could get the most bang for the buck,

The test results were verified by an independent testing

facility, using several brands of regular unleaded and

premium gasolines, just to make sure everything was legit.

 

According to Mark Borosky, Vehicle Test Engineer for

Sunoco, "Of the nine octane boosters tested, none showed a

significant increase, and one actually lowered the octane

number of the test gasolines." Testing repeatedly showed a

maximum increase in octane of 3.5 points by only two of the

six street-legal octane boosters when the recommended

treatment rate was blended with lower base 87-octane

gasoline. The best the remaining four products could muster

was less than a one point increase. "While clearly no one

would actually use an octane booster in a low base octane

fuel, we wanted to give the manufacturers the benefit of

the doubt relative to their claims of five-to-seven point

increases" explained Borosky.

 

When tests were performed using 98 and 94-octane fuel, even

the two best products from the previous tests produced a

disappointing 1.5 to 2 point maximum increase. The

remaining four street-legal octane boosters showed less

than a .5 point increase. Those products designated for off-

road use only didn't fare any better than the street-legal

products. Subsequent tests where the dosage of octane

booster was doubled, tripled, and even quadrupled produced

only minimal improvements in octane, regardless of the base

octane hum-ber of the test gas. In fact, quadrupling the

treatment rate of the most powerful additive produced only

a 3.5 point increase in octane when added to 98 premium,

resulting in a cost of $3.25 a gallon.

 

An alternative path to octane euphoria is to blend

gasolines of different octane levels yourself. It's easier

than you may think, safe, and the results are predictable.

The formula for mixing gasolines of the same type is pretty

straightforward. When you mix a 50/50 blend of two unleaded

fuels, simply average the two octane ratings to determine

what's in the tank. If you mix 94 and 100, you get 97. The

same generally holds true for leaded gasolines, assuming

the lead content is nearly equal.

 

Blending a leaded fuel with unleaded, however, pushes the

octane up a bit more than the math would suggest, due to

the effect of the lead. Just a gram or two of lead blended

into the unleaded fuel will raise the octane number

significantly. Commercial leaded racing fuels contain

anywhere from a trace to six grams of lead per gallon. If

you were to mix 50 percent 110 octane leaded fuel with 100

octane unleaded, you would actually end up with an octane

number around 106 to 107. Keep in mind that even the

smallest amount of lead or leaded gasoline with unleaded,

could spell the end of your catalytic converter or oxygen

sensor. The same holds true for using octane boosters

intended for off-road use only. A word to the wise, check

for any lead content in all the additives you might mix

with your unleaded gasoline. And check with your state

emissions regulations for street use.

 

We asked Sunoco's Wurth about using aviation fuel in an

automobile engine. He was emphatic when he said, "Don't do

it. Even though Sunoco is a major producer of aviation

fuel, this fuel is specifically blended for aircraft

engines. Aircraft operate under very different conditions

than automobiles, and the fuel requirements are quite

different as well. Aircraft engines generally use very

small pistons and run with- in a very narrow rpm range.

There's no need for transient throttle response in an

airplane because after the pilot does the initial engine

run-up, the throttle is set in one position and the rpm

doesn't normally change until landing. Also, airplanes fly

where the air is cold and thin, and the atmospheric

pressure is low. These are not even close to the conditions

your street machine will see on the ground. Also, since

most piston-driven aircraft cruise at 3,000rpm or so, the

burn rate of aviation gas is much too slow for any high-

performance automotive applications."

 

What is it that makes race gas so different? What's it made

of? Sunoco tells us their GT PLUS 104 octane unleaded race

gas is only 15-20 percent traditional gasoline, and about

85 percent additives! Actually there are about 120

different chemicals in GT PLUS. One reason it isn't street

legal is the high oxygen content. The EPA requires that the

oxygen content of a street legal fuel cannot exceed 2.9

percent. GT PLUS is about 3.5 percent oxygen. This fuel is

light in weight at only 6.14 1bs-per-gallon. The high

oxygen content improves the octane, and when the induction

system is properly calibrated, this fuel will help make

additional horsepower. The high oxygen content has a

supercharging effect, since 3.5 percent oxygen is the

equivalent to about 17 percent more air. Different fuels

can actually alter horsepower 5-to-10 percent or more.

 

We wanted to know more about the different types of race

gas Sunoco had, and didn't realize there were five

different types of racing fuel alone.

 

GT-100 Unleaded, is a clear fuel with a pump octane of 100,

and will handle compression ratios of up to 12:1, and is

street legal in all 50 states.

 

GT PLUS, is also unleaded, and is rated at 104 octane. It

is suitable for compression ratios up to 14:1 and is

colored light blue. It will not harm oxygen sensors or

knock sensors in computer controlled engines, It is not

street legal.

 

STANDARD, is a leaded fuel rated at 110 octane, is colored

purple, and is intended for drag racing, road racing, and

race boats.

 

SUPREME, also a leaded fuel, rated at 112 octane, is dark

blue. It was developed to help resist vapor lock and meet

the demands of sportsman, modifieds, offshore powerboats,

and endurance racing where engines regularly run in excess

of 7,000rpm.

 

MAXIMAL, we mentioned earlier, is colored red, has 116

octane, and is leaded. It is intended for exceptionally

high performance applications like Pro Stock where

extremely high cylinder pressures are common, Its extremely

fast burn rate is satisfactory where rpm exceeds 10,000.

 

Now that you're an expert on gasolines, you probably would

like to know where to buy and store the stuff. If you are

fortunate enough to live in the mid-Atlantic states, you

can take advantage of Sunoco's GT-100 Unleaded retail pilot

program and get 100-octane race fuel at pumps located at

select service stations, The rest of us have to purchase

from local speed shops, at race tracks, or directly from

Sunoco distributors.

 

When you plan on buying fuel in quantity, say a 55-gallon

drum, you'll be happy to know that racing fuel has a shelf

life of about a year, if you store it properly, The

container must conform to all safety standards, and should

be made from metal or polymer. Make sure the container is

opaque and solid in color, The white plastic jugs we see at

the track should be used for short-term storage only. They

let in sunlight, which will affect the fuel The lead in

leaded fuel and other chemicals in unleaded fuel are

photosensitive, and will dissipate if they are exposed to

the sun. Keep any container tightly sealed to prevent

evaporation.

 

Good gas is a great thing, and we learned a lot from the

Sunoco guys. They have been at this a long time (remember

Mark Donahue's Camaro?) and we hope you learned as much as

we did. We couldn't talk them out of a tankful of the

killer stuff for Project X, but we had fun. C'mon guys!

It's research!

[Marius]

Jesus Christ!

[Red SLR]

V7 - just for that you should be promoted to "I ought to get out more"

 

X777CAT

[V7 SLR]

Err... I didn't write it.

[clarkey]

I wish I hadn't started this one now....................

[murph7355]

Chris - I don't believe the comments you've heard about supermarket fuels are necessarily true...there was a thread on this some time back, but I'm sure it comes from similar sources to "branded stuff" and it's just that the additives are different (which may or may not be a bad thing) - I used to work for an oil company and saw tankers from other companies filling up at the same refineries. The economics involved in refining and shipping fuel mean that sharing like this is commonplace (or at least it was 6yrs ago. I can't see this having changed).

 

Busy petrol stations are your best bet for any fuel as it sits in the tank for less time (theoretically. I suppose they could also have bigger tanks!) as Clarkey noted.

 

I'm going to stick with Super in mine (as I did on the old 1400SS engine), but then I have a higher cr than SLRs anyway. And it was mapped on Super.

 

C7 AJM

[Geoff Dixon]

Chris Clark in this stream refereed to Tesco/ASDA/Sainsbury fuel as not to be used as it is not to the quality of the oil majors.

I work for Texaco and we supply a huge quantity of fuel to them.

Take it from me - there is absolutely nothing wrong with the quality of their fuels.

[Maccers]

I was gonna ask the same question for Cross Flows. I guess the basic idea is the same, fuel/air mix, burnt, piston goes down, then up, out goes waste gas.

 

I have an unleaded 1700 Super Sprint. I use 95RON at present, but wandered if there was any gain to be had using 97 RON. Used 97 once in my GTi, only cos there was no 95, and there was no difference at all.

 

RM.

[Blatman]

As no-one else mentioned it..............

Doed the SLR have a catquestion.gif If so, normal 4 star will kill that, as will LRP.

[Powderpuff]

Nigel, have you been taking those tablets that Peter C gave you question.gifwink.gif

 

Al.

[Gary Furst]

I use 95 Octane unleaded and Millers CVL in my Xflow which produces about 185bhp and during last season raced about 700 miles and did a further 500 road miles. I get my engine stripped and rebuilt at the end of each racing season and Roger King who did the work, said that there was no visible deterioration in the valves or head. The head has not been converted to have the harder valve seats. If the above article is right it would suggest that i could use ordinary unleaded without additive, but I am not convinced. The increased octane fuel would only have a beneficial effect if the engine had been calibrated for 95 octane fuel originally and was recalibrated for 98, or had been calibrated for 98 and had a knock sensor to retard the ignition for "poorer" fuels.

[CHRIS CLARK]

Geoff.

 

Didn't I read recently on (I think) the se7ens net about a guy with engine problems due to using some 'duff' fuel ? Guess where that came from ? You may know the Co quite well. !!!!!!!!!!!!!

 

[Peter Carmichael]

SUL burns slower than premium. If you map on SUL, you will end up with too much advance somewhere in the map for premium.

 

High duration (performance) camshafts are more tolerant of CR than short duration. The breathing of a gas-flowed big valve head will increase the cylinder filling and bring back the worry of pinking. This generally doesn't seem to be a worry with the k-series (pent-roof combustion chamber), but if the mapping was matched to SUL then running with premium will cause problems.

 

Sounds like the SLR is mapped on premium.

 

When you run at full throttle for long periods (track use) everything gets hot (exhaust valves particularly) which can lead to detonation. SUL will resist these effects.

 

Hence, premium is OK for road use if the engine is mapped for it, SUL is a good insurance policy for track use. An engine mapped for premium will get less power on SUL. An engine mapped for SUL running on SUL may survive in a more extreme state of tune and therefore generate more power.