Different Fuels

[Geoff Johnson]

Does anybody know what is good and bad at the moment. I am finding it increasingly difficult to find 97 octane, petrol. 95 & LRP aplenty. I take it that LRP is not good, what about Optimax & other named fuels?

 

Cheers

 

Geoff

[Casbar]

Depends what engine you are running.

 

If you have a xflow, has hardened valve seats, it can run on unleaded, but super or LRP is the preferred option.

 

If its a xflow and is more highly tuned, ie around 155 bhp, you should only use super or LRP regardless of hardened valve seats.

 

If you have a K, then I understand from other owners, that they tend to use Super.

 

 

[Blatman]

LRP is not good if you run a catalytic converter, but it is 97 octane. I use it for track days days if I can't get 97UL in my 185 bhp Vx XE. I use the same fuel in my N/A cossie on the hills and sprints, with no harm in two seasons. I have heard some very good things about optimax, and some scepticism too. I am currently trying it in my motorbike, which is a fairly fine instrument for "performance" testing. IE I'll notice an increase in performance and/or decrease in fuel consumption quite easily, as I use it every day, and I'm very used to how it feels on normal unleaded.

[James Arnold]

Does anybody know whether there is anything behind the hype around Optimax? A TVR owning friend is convinced that he not only got better mpg, but it was also more responsive.

Me, I'm a complete cynic, Tesco's is cheaper....

James

[EFA]

I'm running it in the Seven, my F(i)at Coupe and getting better MPG in both.

 

In the Fiat the engine is smoother at the top end and teh car feels more responsive.

 

In the Seven its hard to tell.

 

Fat Arn

The NOW PROVEN R500 Eaterid=red>

See the Lotus Seven Club 4 Counties Area Website hereid=green>

 

[Geoff Johnson]

Sorry, I forgot to say the car is a HPC Vx Carb, no cat. Looks like I have to try Optimax. The only downside with that is, that I have noticed I am turning into my father/Victor Meldrew & I got bad service at the shell garage not so long ago....time to swallow the pride & stop the pinking then.....

 

Geoff

[Eugene]

What are peoples thought on standard UL with an addative to improve octane rating and provide lead substitute? I am told that this is preferable to LRP and I have to say that the tests I have run would seem to agree. I have used Castrol's addative and Redex (can't remember exactly which ones asI'm in the office and the car isn't).

 

Small Boy - with Big Toy!

See Eugene here

[Big Brother]

If you have a xflow, has hardened valve seats, it can run on unleaded, but super or LRP is the preferred option

Please forgive my ignorance but can any one tell me why?

 

 

Steve

 

cool.gifScream...if you want to go faster!!!id=limegreen> cool.gif

[Casbar]

Its something to do with how hot the fuel burns.

 

This advice was given to me by Roger King, when I rebuilt my xflow with forged pistons, 244 cam etc.

 

He told me not to run on unleaded at all, he said I must use, either super or LRP.

 

So as he knows hell of a lot more about xflows than me, job done!!!

[Big Brother]

Casbar / All,

 

Do you know if this is for engine protection or performance - consumption?

 

Steve

 

cool.gifScream...if you want to go faster!!!id=limegreen> cool.gif

[Asklepios]

Steve,

I expect this advice was because in this advanced state of tune,Casbar`s engine needs protection from pre ignition.A relatively high reving,modestly raised compression engine running a reasonably advanced ignition curve can detonate to oblivion quite quickly if a poor fuel is used. So a low anti knock fuel(nominal),which was of a below batch spec.initially,and which goes off in storage -either in the suppliers or your tank,has eaten into the safety margin which existed with fresh fuel. Result ---tuned engine blows up. Solution,build in a safety margin by spec.ing higher octane fuel.

 

Some people talk of adding anti-knock products to 97 oct fuel as an addition safety margin.I suspect this is not a good idea unless your c/r is very high,and you are pushing the safety margins as above.I reason that the Millers,(why is beer so often a subject in these pages?) or whatever, (used to be lead),is merely a passenger in the combustion process,and if say represents 1% of combustible volume,the engine would produce 1% less "bang" as it sees that bit less explosive.The additives will permit a higher c/r and greater efficiency up to a point,but with a fixed c/r ,a higher octane should have an adverse effect on power.

Comments?

 

[fastforward]

FWIW I use Castrol valvemasterplus and get it at Halfords, I add it to UL and it gives an octane boost and is a lead substitute. This was on the advice of Ian Smith of GRL in Woking who tuned my car after a couple of tankfuls had gone through. He was clear that this was superior to LRP. The car is on song and the engine is a 1600 x/flow

 

Brian

 

brianfyfe@ema.org.uk

[Gary Furst]

I have run my 185bhp X-flow for the last two racing seasons on 95Octane Unleaded with Millers CVL with no apparent damage to the valves/head.

My engine is also a RK unit and he checked it over after last seasons races. The engine does not have hardened valves and has I think a 12:1 CR.

[Michael Peterson]

My X-Flow seems to be quite happy on 100 octane low lead aviation petrol. Not cheap, but works a treat! thumbsup.gif

 

X-flow equipt Yankee

[V7 SLR]

The low-down on fuel, according to this author...

 

******************************************

 

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!

[cskip]

V7 SLR,

 

Is that the longest post ever??????

 

 

Clive.

 

Crossflow - Loud and Proud!

 

[sparkey]

I run a 130bhp crossflow on super unleaded and Castrol valvmaster plus, and it has been fine for 2 years with losts of hard use. I run a Formula Ford (crossflow again)with unleaded and Millers CVL and it's fine as well. Neither have hardened valve seats.

 

Sparkey