4 star fuel vs unleaded

[The Striker]

i have now fitted a 4-2-1 Non cat system to my 1600 ss, 1st would there be any benifit in putting leaded 4 star fuel in or would the eng management not like it. 2nd because of the higher octain would this increase power.

[Graham Sewell]

leaded 4* would be a complete waste of money @ £1.10 per litre! However, LRP is not leaded but does have an increased octane at similar or lower prices to Super Unleaded/Optimax/Ultimate.

 

Not sure how the Lead Replacement chemicals will react in a modern engine.

 

Forgot to say that higher octane fuel does not give more power, unless you modify the engine to take advantage of it by advancing the ignition or raising the compression ratio. Otherwise, even LPR/Optimaxultimate/etc are a complete waste of money.

 

Low tech luddite - xflow and proud!

 

Edited by - Graham Sewell on 6 May 2004 15:03:37

[V7 SLR]

Agree that you only get more power IF the engine can be tuned to use it, but it's not a waste of money. It gives you a larger safety margin before self-detonation when the car's being used hard. Most people will recommend it for track use.

[Simos]

There's possibly a case for using it on track days when you're thrashing your motor but otherwise there is no real benefit.

 

Octane value gives an indication of the burn rate of the fuel not its energy content.

Of course the higher octane fuel might have a higher energy content but not necessarily, and octane doesn't tell you.

 

Perversely higher octane is LESS likely to burn. This is good only in more extreme conditions such as hot / high revs / high compression etc.

The reason it's good is that if you use lower octane fuel it can start to burn to early (before the spark) when the piston is still on the way up on the compression stroke (pinking) which gives the piston a kick and robs you of power, both by not providing the energy in the power stroke but also slowing the engine by burning on the wrong stroke.

 

If you can run 95 octane there may be a case for mapping it for 97 Super and sticking to that - but I'm not sure the return is worth the investment.

[simonstevens]

in case anyone doesent realise, if you have a catalytic convertor fitted then dont use the unleaded. this may be bull**** on behalf of fuel companies who want more money from you as ive never tried it myself. worth checking out though!

 

but hey, what do i know?

[Simos]

Think you mean't to say don't use leaded rather than unleaded.

 

Both the lead in leaded and the potassium in LRP will poison the platinum and rhodium in your catalyst so that they don't catalyse any more. Your cat will be dead in a very few miles, well within one tankful....

 

Actually neat fuel will kill the cat albeit more slowly, hence carbs don't get catted etc etc.

[Mick Day]

Don't use leaded fuel if you still have a lambda sensor:

 

http://www.picotech.com/auto/lambda_sensor.html

 

"A lambda sensor's normal life span is 30,000 to 50,000 miles. But the sensor may fail prematurely if it becomes clogged with carbon, or is contaminated by lead from leaded petrol or silicone from an antifreeze leak or from silicone sealer."

 

Not too sure whether LRP would damage a lambda sensor.

 

 

[simonstevens]

soz yep, meant leaded in cats is a no no

 

but hey, what do i know?