mk1-forum.net

Hi everyone,
Does anyone add Toluene to pump petrol in increase the octane rating? I have heard it can be done but I have no idea of the quantity required. Here in NZ, only 95 is available in lesser populated areas and 95 is barely enough for my car. In the bigger centres, I can get 98 (BP only) and that is fine.

Regards
Al

From memory, both toluene and xylene (methyl and di-methyl benzene) have high octane numbers. Off the top of my head, I think it comes out around the 105 MON mark.

Conveniently, cellulose thinners are a blend of tol and xyl and you can by colour tainted thinners "brush thinners" which are no good for paint at a knocked down price. Industrially, this was cheaper than a lot of pump fuel.

Both Tol and Xyl are "aromatics" which means they contain benzene rings. These affect "lead response" which is how lead improves the octane rating of your fuel. So, if you are using lead additive, you will kill some of the octane boost from that by adding celly thinners.

So, I'd look at it this way. If you have an unleaded engine, consider adding cellulose thinners. (if you can get it, I'll run through the calculations with you for how much you need) and if you have low grade "alkylate" (which means petrol consisting mostly of chain hydrocarbons - like spaghetti) this responds to leading very well indeed. About the maximum you can get away with is 4% TEL and 1.5% methyl aniline (which boosts things up a nadge). You could also look into di-cyclopentadiene compounds which have octane numbers well over 200 (IIRC).

It's something I was very interested in for a time. You can brew your own avgas if you can be bothered. What's the other stuff....? Tertiary butyl ether. Have a look into that.

Thankyou for your response but much of what you are saying seems to be beyond me. I can see that you have studied the matter quite closely. I have access to Toluene and all I really need to know is the effect of adding a percentage of Toluene to 95 octane fuel. If one could say I need to add say 20% Toluene to 95 to lift the Octane to 98 RON, that would be what I am looking for.

Regards
Al

A friend of mine has a US market MGB with a very high compression ratio. We went through a difficult period here where even 95 RON was hard to find. He was having trouble so was adding toluene. Unfortunately he can't remember how much was needed (it was about 8 years ago), he found the information on the internet.

We can get 95 pretty much everywhere and 98 in most places now, 100 RON is available in the major cities. I've been using 98 which contains 10% ethanol in the Moke, with good results.

Tim

The wonders of google

Toulene has RON+MON/2 of 118, so when you average it out with pump gas, this is how you obtain the final octane rating.

Pump gas has 9% toulene by volume, and 8% xylene. Race gas has 27% toulene and 1% xylene.

Pump93/Toulene ratio----Gallons----------Octane
95%/5%------------------17.575/0.925-----94.05
90%/10%-----------------16.65/1.85-------95.10
85%/15%-----------------15.725/2.775-----96.15
80%/20%-----------------14.8/3.7---------97.20
75%/25%-----------------13.875/4.625-----98.25
70%/30%-----------------12.95/5.55-------99.30

Entire article here:

http://www.supramania.com/forums/showth ... ane-rating



Mark F

Thanks Mark, exactly what I wanted. I carried out a Google on that but never turned this post up and it is the most useful !! If I add 20% to 95, it looks like it will pretty much do the trick and without any risk to anything.

Regards and thanks again

Al

Sounds good, but keep an eye on your hoses, some modern stuff isn't up to the solvency of all that extra toluene!

Worst case you might get some rubber break up inside the hose and block a jet or something?

Look forward to hearing how you get on....

And how the exhaust smells! Love that race car smell (probably very bad for you!)

Hi Graham,
I don't plan on adding any more Toly than what would be in 98 anyway, so I don't think it will cause problems. I am quite aware of the problems one might encounter but thanks for the warning anyway.

Regards
Al

I have just been sent a graph from a friend who used to work for Shell and it is saying that adding 10% Toluene to 95 RON will increase the octane to 98 RON. The document seems to be protected so I can't post it here. The amount suggested is about half of what the quantity suggested in the artical Mark clipped from a forum, so I might try 10% and see how the car feels. Thanks to all who responded. You may like to see if you can open the attachment below, I think I've got it to work.


Regards
Al

66 s's chart