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The mkiv Supra Owners Club

Fuel chemistry


Adam W

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Right, the Supra isn't my daily driver any more so I can go a bit crazier with it. My big-ass hairdryer is just about waking up at 1.2 bar or so, I'd like to run it harder to get my moneys worth. Now I'm not doing 400 miles a week in it I suppose buying race fuel is a possibility, but I'm an organic chemist and I work in a lab so I can get hold of most stuff and I have the proper facilities for handling nasty shit, so I'd like to have a go at mixing my own. Plus it beats working, right? :D

 

For high boost, I need high octane. I could run 20% toluene, which would give me around 102-103 octane I think. If 98 octane optimax is good for around 1.2 bar boost without detonation on a standard-ish timing map, can anyone give me any idea how much extra boost I could run on the toluene mixture? I'm aiming for a safe 1.5 bar or so, would 103 octane be enough?

 

Even if it is enough, more octane would allow more timing advance, and therefore give more power, right? And give me a greater safety margin at the same time I guess (as long as I don't get too happy with the advance!).

 

All of the really high octane (116RON or so) race fuels are leaded, and use lead compounds to raise the octane instead of (or maybe as well as?) toluene-type hydrocarbons. I have really struggled to find any info about these fuels on the net though. I know the old-style leaded petrol used low concentrations of tetra-ethyl lead (TEL) as a lubricant and an anti-knock additive. Do these race fuels just use higher concentrations of TEL to raise the octane further, or entirely different lead compounds? Plus, TEL is really horrible stuff, a more user-friendly option would be nice :)

 

On a different tack, I know you can use Ether compounds, like MTBE, as an oxygenation agent in fuel. This is kind of like having nitrous oxide mixed into your petrol, as the MTBE or whatever burns, it liberates more oxygen from its own makeup than it requires to combust - you have a net gain of oxygen within the combbustion chamber. I can see how this would be useful on an N/A engine where you desperately need all the oxygen you can get in the chamber, but on a turbo car you can just turn the boost up right? And also, if you have more O2 in the chamber, you're going to run leaner and hotter (just like having a small dry shot of nitrous) which is not going to be conducive to high boost by my reckoning. So is oxygenated fuel a good idea on a turbo car or is it counterproductive?

 

I know a few guys on here have played around with race fuel etc so I was hoping someone might have some input :thumbs:

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Bob - engine is in 1000 pieces again so it's unlikely - sorry!

 

Gaz: yes I do have an ITC, but plugging it in gives me a nice misfire at 3000rpm and major starting issues. No idea why, but several other Mk3 owners have reported similar. Therefore, I'm hoping to avoid my original plan of using that to back the timing off, instead I want to give the engine the octane it's crying out for.

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OK, I feel very inadequate in asking this but... What kind of octane rating is normal pump 4 star or LRP these days?

Secondly, would it hurt a de-catted Supra to run on this stuff?

 

Please excuse my ignorance, reading Adams post made me feel like I'm back at school in a Chemistry class that I know nothing about... Where's my rubber bands and ruler... :stupid: :zzz:

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I asked out of curiosity really, firstly, a friend of mine that does hill climbing in older cars, said he thought 4 star would be a better fuel. This was ages ago, when I first got the car, so I dismissed it as it would damage the cats. Adams post just reminded me.

Secondly, in Adams post he mentioned leaded fuel, I know it was race fuel he was refering to, but as I said, just curious... :)

 

I'll stick to Optimax then... If I can find any in Maidstone today! :D

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they were selling that cool76 hi octane fuel at dragstrip last time i was there

 

10 liter of 106 ron for £39 and they had some 118ron stuff too

 

was talking to the cortina guy with big power, he said he buys aircraft aviation fuel and mixes it with optimax. another drag racer i know has a propper drag car and he said he uses same stuff. is 106 ron overkill for us little fish running 1.4bar

 

will be nice to see yours go

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Mark, you need to be a bit careful with fuel. I used the 106 cool blue on the higher power dyno runs, and it worked well, but I would have made more power by using a dedicated turbo fuel, as this would have special anti-det ingredients, so whilst only being say 102 Ron, it would allow more boost without detonation.

 

Does that make sense?

 

BTW the 118 is leaded and will trash your O2 sensor in no time.

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Originally posted by Terry S

Mark, you need to be a bit careful with fuel. I used the 106 cool blue on the higher power dyno runs, and it worked well, but I would have made more power by using a dedicated turbo fuel, as this would have special anti-det ingredients, so whilst only being say 102 Ron, it would allow more boost without detonation.

 

Does that make sense?

 

BTW the 118 is leaded and will trash your O2 sensor in no time.

hi terry i know nothing :)

but thought 118 octane is overkill. you seem to have gone into every aspect of getting your car tuned and running perfect.

will be good to see it go. i will stick to silkolen octane booster for a bit of added peace of mind

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Originally posted by Thorin

http://www.albionchemicals.co.uk/

 

I think if you buy a big drum it works out cheaper than optimax.

 

It does but getting the stuff delivered is a pain.

 

They won't from my investigations deliver to private addresses so unless you have a suitable business address for delivery and then a way round the problem of moving a 45 gallon barrel to your house......

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Originally posted by MONKEYmark

was talking to the cortina guy with big power, he said he buys aircraft aviation fuel and mixes it with optimax.

 

Working with aircraft i know that the piston aircraft fuel is very good if mixed with normal fuel (for all the addivitives (sp)) not that i would ever do that, :innocent: just might know someone that has :conf:

 

shame i only work on jets now only good for feeding diesels :(

but it is free, and doesn't have that red colour that farmers have in there sruff :D

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adam, they wont let u transfer it in the same cabin space as the driver. and the 45 gallon drum is very very very very heavy.

 

ive read that aircraft fuel is not good for turbo engines, in fact, that its very bad. i cant remember the ins and outs, i'll try and dig out the article.

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They won'tlet you put it into an enclosed car, you need something liuke a trailer or Pick Up :D

 

Matt H' found a place that delivers. 55 litre drum is all you really want to be lifting, but then I am little.

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