AV Gas vs. Petrol

[Disciple]

I live in CHCH and the only place I know to get AV is the waimac. So instead of making the out of the way trip to get some there what difference would petrol really make? Some say the plug will blow constantly while others will say you just dont get any power. i am new to most of this, so would like some opinions. Anyone have some wisdom into this?

I currently run AV with motul premix - but want to change...

[Scouse]

I live in CHCH and the only place I know to get AV is the waimac. So instead of making the out of the way trip to get some there what difference would petrol really make? Some say the plug will blow constantly while others will say you just dont get any power. i am new to most of this, so would like some opinions. Anyone have some wisdom into this?

I currently run AV with motul premix - but want to change...Twostrokes dont need high octain gas what do you think happens when you add oil to gas it lowers the octain 95 or 98 will do but if you still want to raise the octain get some Tolulene dont mix to much in advance though as Tolulene evaporates more rapidly than gas
Cheers
Steve

[digsaw]

AV gas V petrol,no contest,petrol wins hands down.
Why,you may ask well just look at it this way, planes are low revving, constant speed motors,and your bike is high revving,hi compression non constant speed motor,AV gas will burn too fast and hot causing detonation with some bad things going on inside your engine if you run it hard for a long time.:beer:

[speedpro]

avgas is avgas is avgas. Buy some today, buy some tomorrow, buy some next month, it's all the same. Pump gas, , , welllllllllllllll, maybe not, in fact definitely not. Unless modified however your bike won't notice any differance. There's threads here already on this topic.

[DEATH_INC.]

AV gas will burn too fast and hot causing detonation with some bad things going on inside your engine if you run it hard for a long time.:beer:
No, you got it all back-to-front..............:slap:

[cheese]

Well, I ran 96 or higher in my bike and it ate plugs like crazy (one every ride!) and that started to really piss me off. So I got some 100 octane fuel and no probs now. Also "AV gas" is leaded (well mine is) which I've found runs better in my bike. Also starting is easy too.

But then again, I've got local places for the race fuel, and it ranges from $1.90 - $2.50

If you find it makes it run better, use it, otherwise go for 96 octane +

I think it's more important to make sure you use good oils.

[Jantar]

Av Gas is slower burning, high octane, making it more suitable for high compression low reving motors. This is exactly the opposite to what your engine needs. If you have a high compression V8 in you bike then certainly use Av Gas. Otherwise forget it. The only reason some people reccommend Av Gas is a throw back to the days of leaded fuel, and some engines do still need lead. However lead is a killer to spark plugs in a two stroke.

[bobsmith]

I agree with Jantar.

Avgas has octane rating of 100/110 which is slower burning (more detonation resistance) so it will reduce the chance of detonation.

However on an engine which is not tuned for avgas, it will tend to burn too cold and the lead in the fuel will be likely to cause plug fouling. (The reason why we try not to idle the engines in our aircraft for long - to prevent plug fouling) If you have a automotive engine which is not specifically tuned for avgas, run normal petrol.

[digsaw]

Oh death,in away you are right as i was thinking methanol which will burn slower still,after using av gas and having big problems i wouldnt use it again,but proper race gas should be better than av gas:drinkup:

[scott411]

i ran 50/50 avgas in all my two strokes,
both sides of this argument are correct, avgas is slow burning, misng this with 95 helps this, also avgsa is very stable and will store better than pump gas

[Ivan]

We run AV Gas in the Honda RS125's and it is perfect I premix it with Spectro Marine PWC 2 Stroke Oil it burns perfect no crap no damage my piston was in mint condition

[sugilite]

Av gas has a slow burn time, and as a consequence, using it at 100% you lose bottom end power.
91 has a very fast burn time, so by running a brew ratio of 70% av gas and 30% 91 you do not lose any power down low and still gain the benifits of running the avgas. (being cooler running and allowing one to run higher compression)

[cowpoos]

Oh death,in away you are right as i was thinking methanol which will burn slower still,after using av gas and having big problems i wouldnt use it again,but proper race gas should be better than av gas:drinkup:
no...death is completly right.....the higher the octane the slower the burn....does not alter explosive force of the reaction at all though.....91 and 95 have the same energy output when burnt...just different rates of burn...

[cowpoos]

Av gas has a slow burn time, and as a consequence, using it at 100% you lose bottom end power.
91 has a very fast burn time, so by running a brew ratio of 70% av gas and 30% 91 you do not lose any power down low and still gain the benifits of running the avgas. (being cooler running and allowing one to run higher compression)

so u reckon run about 98-101 octane then?

most those bike just need normal pump gas...best run 95 in the summer...and up to u in the winter really....as bike will run cooler anyway...

[R1madness]

Interesting comments chaps,

When we run Stroudys bikes they run on 91. Why? Well it burns faster and easier than 96 or avgas or 100 octane (which is just old derated av gas anyway).
You only need to up the octane rating if you increase the compression ratio or it is detonating on the gas you are using.
If you run 91 it burns completely at high revs (fast flame spread).
If you run 96/98 it burns slower and may not burn all fuel before the valves open at high revs
100 octane is worse you, will definitly not get complete burnoff at high revs.
Av gas is worse still.

[cowpoos]

Twostrokes dont need high octain gas what do you think happens when you add oil to gas it lowers the octain 95 or 98

it raises the octane....oil is a very slow burning....much slower than diesel....and deisel is up around [dont quote me on this] about 170-180 octane.

[IronicCapers]

Theres a differrence between diesal and petrol. In diesal engines they use compression to light the fuel, so the diesal engine will detonate every single time hence why diesal engines look bigger than petrol engines of the same size. Petrol burns slowly and it shouldnt detonate at all in the combustion chamber, if it does theres something wrong with your engine or fuel.

Some people mix av gas and 98 octane dont know the ratio but apparently it works nicely. Not sure on performance gains but do you really need it if your just a trail rider or a clubman.

Diesal isn't rated the same way as petrol is there is a different rating because it burns quicker i think. THE HIGHER THE OCTANE THE SLOWER IT BURNS!!!

My advice is to use a good quality 98octane fuel with a good oil i recommend motorex or mobil 1 two stroke mix.

[Krusti]

Years ago the old man had a newish honda accord..filled it up with deisel at the farm by mistake,prob half tank petrol allready in the tank. Car was on LPG as well so he'd start it and warm up on LPG then switch to the tank. Smoked like shit but used it.

That car did 300,000km before he sold it! A true story!

[sugilite]

so u reckon run about 98-101 octane then?

most those bike just need normal pump gas...best run 95 in the summer...and up to u in the winter really....as bike will run cooler anyway...

Yep, I'm really only thinking racing purposes, anything else, just stick with pump gas.
When I supermoto'd the KX500 I learnt the hard way that I needed decent fuel.

Most of my info came from Robert Taylor. He seemed to have a shit load of knowledge on the subject.

[speedpro]

My current bucket is a 2-stroke and revs to 11,000rpm, the sidecar which had a similar 2-stroke ran to 14,000+rpm. They were tuned for 100 octane and would damage pistons in a short time on pump gas. If the compression hadn't been so high we probably could have gotten away with 96. If you want more consistency than pump gas then use either mega $$$ racing fuel or avgas/100octane. If the engine isn't tuned for it don't waste your time or money. Bucket guys with tuned motors using pump gas will every now and again have a piston fizzle away. Even if the motor has previously been just fine. The only variation has been a new can of gas from the petrol station. Ideally you'd want to change your ignition mapping putting in more ignition advance in the midrange. I played round with that on the dyno with good results. Big gains in the midrange with the same top end.

[cheese]

shit, I always thought the higher the octane the better for the bike I'll go back to normal pump stuff.

[vifferman]

shit, I always thought the higher the octane the better for the bike I'll go back to normal pump stuff.
Common misconception.
I guess people go, "Ooh! Higher numbers, must be more powerful!"

[Ivan]

I know of a guy who mixes Methanol with Wairarapa pump fuel 96??? and runs it in his scooter and in his RM250

[MSTRS]

I know of a guy who mixes Methanol with Wairarapa pump fuel 96??? and runs it in his scooter and in his RM250
Hmmmm...never heard of that. Does he have a problem with corrosion esp in his carbie? Methanol is veeery corrosive & has a high water content - not good to leave it sitting in the 'works'

[IronicCapers]

Hmmmm...never heard of that. Does he have a problem with corrosion esp in his carbie? Methanol is veeery corrosive & has a high water content - not good to leave it sitting in the 'works'

For sure. I think metanol has bad effects on rubber hoses and plastic tanks 2(not sure).
And why bother screwing round with the expensive stuff when your engine isn't tuned to it. Cause dam aint fuel fukin expensive.

Funny how the fuel price goes up quickly and stays high but goes down very slow....wait im wrong very very very very very very very very slow. Greedy fukers!!!!

[speedpro]

Methanol "might" mix with the new pump gas but not with the old leaded pump gas and 100 octane without a little help from something like acetone. I think the current pump gas has a lot of toluene/toluol in it which might help blending but even with that in my turbo bikes fuel it still needed about 500ml of acetone for every 20L of mixed fuel for everything to blend properly. It is a total pain in the arse on the race bike mixing it all, I can't imagine why anyone would bother on a road bike. I used to add Toluol to 96 octane and methanol and then blend it with acetone. Mixing methanol and petrol can play merry hell with seals and fuel lines as generally rubber is EITHER methanol OR petrol proof.