Photo Archive
Building: confidence and miles with smiles
posted on 13/5/13 at 07:23 PM
running extra octane, hi high can I go?
My last track day included me doing a rush to the local garage with an empty jerry can to get some more fuel. I normally use 95 Ron (normal?) but this
time grabbed some higher stuff, 98?
It did feel a little faster, I think. Mainly at the higher end, it just sounded a little more eager but either way has got me thinking.
On my next track day I will be going all high octane, some garages do 99 or more "super dooper" stuff. What is sensible to run? Can I put
high in and octane boost and have 110RON or something stupid? That would be approx 15% more bang, right?!?
Engine is 1.6 20V 4age with Omex 710 including Lamber sensor so I would like to think the ECU will adjust something to take advantage of the extra
saucy juice.
Thoughts?
Track days ARE the best thing since sliced bread, until I get a supercharger that is!
The only parameter that an ECU can adjust to take advantage of higher octane fuel is ignition timing, and then only if the engine is detonation
limited. To do this it would need a knock sensor.
An oxygen sensor simply helps to maintain the correct air/fuel ratio, and this shouldn't be impacted by octane to any significant degree.
In short, if you don't have a detonation problem running on 95, it's unlikely that bunging 99 in is going to help much. It will lighten
your wallet giving a small increase in power/weight though
Photo Archive
Building: Sold turboblade, back to tin tops
posted on 13/5/13 at 07:50 PM
It will only really benefit you when you go forced induction, I like optimax anyway as it keeps the engine nice and clean and I feel my TIn top is
smoother with it although the book says 95 Ron is fine.
My little car has to have optimax as I stuck the turbo on a stock engine.
If you decided to run a higher octane fuel ALL the time it would be worth getting the car mapped on that fuel to take advantage of the higher octane
rating.
Otherwise just use what the car was mapped on, Although having said that mine was mapped on standard un-leaded but when i did drop the occasional
optimax in it it did feel a bit 'cleaner' on the throttle.
Worth noting that the higher the octane the harder it is to light off and the lower the burn rate so without sufficent compression ratio and
appropriate combustion chamber shape you will find that it actually makes less power!
NA engines are actually very octane sensitive as it's all about getting the optimum amount of gas generation done in the cycle time available.
Some trick fuels are oxygenated so you will see gains here but generally speaking pump fuel is pump fuel and burn rates are similar. Going 95 to 98 on
a good 4V chamber engine with a nice amount of compression will generally move MBT by 1.5 - 2 degrees which can be worth useful power.
Your Omex has no ability to adjust for Octane rating and if your lambda is narrowband then it won't be using this past very low throttle.
With regards octane boosters etc. anything you buy in Halfords is pointless. You want Toluene or a very similar aromatic hydrocarbon really, this will
allow you to brew fuels to suit your application (as we do with the F1 Turbos) but be careful it's nasty stuff and if it gets to the point where
you're running pre heaters in the fuel tanks to get the burn rate up you've probably gone too far
Photo Archive
Building: not sure, i'll know when its done
posted on 13/5/13 at 08:19 PM
higher octane fuel basically allows the compression to be higher before the fuel self combusts (without the use of the spark plug) if you have a
really high compression engine and use 95 fuel then it will self combust under the pressure and start putting rods through the block and cracking
liners.
higher octane fuel also 'explodes' quicker when ignited, which will allow quicker revving (better acceleration).
i work for a race team and we use high octane fuels in some of our cars.
if i was you i would your car on 99 octane (tesco Momentum) and octane boost it to between 102 and 105 when on track and the rest of the time (road
use) just run it on 99 octane.
octane boosters are okay but boosting your octane level with it to 105 for example isn't the same as using 105 octane fuel. 105 octane fuel has
been special developed.
RON has nothing to do with the calorific content of the fuel, as mentioned above, its only an indication of its resistance to knock.
I had a similar argument with a guy at work, he thinks 98 RON fuel must give more power than using 95 RON.
Dutch bears have terrible skin due to their clogged paws
higher octane fuel also 'explodes' quicker when ignited, which will allow quicker revving (better acceleration).
Gasoline fuel only explodes when something has gone horribly wrong. It's a combustion process with a steadily propagating flame front not any
sort of rapid uncontrolled explosion. Also the higher the octane the lower the burn rate, if you think about it the measure of octane is related to
resistance to pre-ignition i.e. how hard it is to light off. A modern road car based engine with very little cam overlap, poor rod ratio (as many OE
engines have) and low sub 11:1 compression ratio will not really benefit at all from fuels in excess of 100 octane as there simply isn't enough
squeeze in the combustion chamber to reach the temps and pressures required to impact MBT timing.
Modern 100+ octane race fuels are oxygenated i.e. they decompose to release o2 during the combustion process - however quite often we find teams
utilising fuels which are far higher octane than ideal/required but making the power back due to the o2 release during combustion i.e. the slower burn
rate reduces loading on the piston crown but the oxygenated mixture allows a higher in cyl fuel burn rate which makes back the difference or even a
touch more.
The CA06 engine went to 20,000RPM in race trim and was one of, if not the highest reving V8 engines ever made. It ran crazy LOW octane fuel purely
because at these engine speeds the combustion cycle time was so low we needed extremely quick light off and burn rate.... also the peak cylinder
compression occurred so rapidly that we'd have delivered the spark and got the burn going before anything had chance to light off on it's
own..... even more impressive and this really gives some idea of how perfect the chamber was we were running no more ignition timing than most people
here run on Pintos.... at 20K RPM
Photo Archive
Building: confidence and miles with smiles
posted on 13/5/13 at 10:04 PM
The blacktop has a ratio of 11:1 anyway and being Jap import only may be designed to run on 99+.
Interesting reading and conflicting advice at times. Especially on something quite basic. By basic I mean a decision we all take when filling our cars
up.
Track days ARE the best thing since sliced bread, until I get a supercharger that is!
You need to be around 12.2+:1 to really see any real benefit on 100+ octane with the rod ratio, bore size and cam profile you are running (assuming
standard cams?). JDM "Plus" fuel was 100 octane with a high aromatic hydrocarbon content due mainly to their persuasion for boost (lots of
boost) The 4AGE is actually a really nice engine though, the earlier 16V were for all intense and purpose a mass production optimised BDA, as such
the combustion chamber is nice and small so flame front propogation speed becomes less of an issue.
The bottom line here is that without optimising the engine calibration to the fuel you are using AND ensuring that the fuel used is appropriate in
terms of burn rate for the chamber size and operating regime you're unlikely to see any real difference in the load on the piston crown i.e
power produced. If you aren't able to quantify your ignition timing is essentially at MBT for most operating loads (obviously outside of any
KLSA areas) on your current calibration then you're better off investing time in optimising this for lowest common denominator fuel and working
from there first..... and that's before you start to question what the crank accuracy actually is on an 20 year old ECU design at 8000RPM and as
such if you can actually achieve consistent MBT timing in the first place.
It's not rocket science but it's still combustion in a pipe and there's quite a lot to that For the most part if you stick 98
octane Super/Fancy branded unleaded in a road car on a stock ECU or MBT/below MBT calibrated aftermarket ECU it's going to be so far clear of
the knock threshold it definitely won't fail from det... which is nice to know.
quote:Originally posted by Dooey99
higher octane fuel basically allows the compression to be higher before the fuel self combusts (without the use of the spark plug) if you have a
really high compression engine and use 95 fuel then it will self combust under the pressure and start putting rods through the block and cracking
liners.
You are describing pre-ignition (which can be reduced/eliminated with higher octane fuel). Detonation is a separate issue that can be caused by
pre-ignition or it can occur after the spark.
