25 replies to this topic

[Bradley Gaunt]

I am running flat top forged Cosworth pistons in my 1380 and when on the rollers the guy had to retard back to 15 degs advance instead of the normal 30(ish) which he proposed was the usual advance for a mini engine. I imagine the compression ratio must be high for him to have to do that as pinking was occurring. I was using normal 95 octane fuel which for the moment is fine as I'm running the engine in but eventually want to get the most out of my engine and therefore was considering using 98 or 99 octane from the pump and maybe adding octane booster to get over 100. I have read that most 'octane' boosters are simply kerosine and don't contain any octane but in a cheats way they still reduce the 'bangyness' of the fuel and therefore allow for more compression before pinking. Does anyone have any advice and / or can suggest a quality octane booster?

[jaydee]

To be honest I still have to find one that is thrusty..
Best deal would be adding toluene but thats usually available in a solution with meth/ethanol, its a paint thinner though.

[summs116]

millers ctv turbo seems to the best ive found to use with my race engine, im using 94/95 octane 4 star petrol tho.

[Artful Dodger]

Yeah we run the CVT in our classic racing engines, works the best in our opinion.

If this is a racing engine (you wouldn't need to run a comp. ratio that high on a road car?!) then could you not run on Sunoco 105 octane?? That stuff is awsome!

Edited by Artful Dodger, 09 November 2012 - 11:29 PM.

[carbon]

Must be some compression ratio if you're having to retard it back to 15 degrees on the RR!

Why run in on 95 octane? Shell VPower is 99 and not much more expensive...

[Bradley Gaunt]

Must be some compression ratio if you're having to retard it back to 15 degrees on the RR!

Why run in on 95 octane? Shell VPower is 99 and not much more expensive...

The 95 ron was in the car at the rollers before he or I knew just how high the compression was and hence he had to retard that much.

I initially bought the half engine from FleBay only to find that the block was cracked between pistons 2 and 3. The Cosworth pistons were in this block already so I asked a so called expert form this forum to build me a new engine using my existing pistons and crank assembly. I asked him to deck the block and do the head to give me 10.5:1 compression. Without ranting on about how utterly incompetent said builder was (everything was wrong and had to have engine rebuilt after it blew up and this guy refuses to help / re-emburse me), unsurprisingly he obviously took no notice and built it with a very high compression ratio anyway.

I plan to use the on the fly switchable ignition map facility on my Megajolt so I can use 95 octane fuel for when Im feeling tight and also at the flick of a switch be able to use the 99 octance VPower fuel to get more power.

[jaydee]

How much high the CR is?
Mines 11:1 and theres no way to run it with 95RON no matter the advance (which retarding cost performace though and not very reccomendable as you'llend up with burnt exhaust valves).

[racingbob]

mines about 11.1 220 on compression gauge

i run shell v power timing at around 30 seems fine

[Bradley Gaunt]

I reckon based on guestimating the chamber cc, the very slight rebate in the pistons cc and the above deck height that the compression ratio is in the region of 12:1

[jaydee]

The max timing at 30° gives just the optimal power, its the timing between 2500-3000 that gives the most trouble
With a 12:1 CR i wouldnt even think of 95 RON, V-power + additive sounds a good idea.

[Bradley Gaunt]

yes it is really bogging down between 2.5k to 3.5k... I thought it was the emmulsionn tubes that need changing, it could be the compression and timing causing the problem?

[jaydee]

More likely just too litle advance, the RR operator had to 'retard' the timing a fair bit from its optimal timing to make it run on 95RON.
There could be about 5 deg difference in the optimal timing between 95 and 100 octane on a high CR engine.

[tiger99]

Neither kerosine not toluene are octane boosters, in fact they are the complete opposite.

The ideal answer to your problems is something that is rarely seen these days, water injection. I expect that someone has fitted it to a Mini at some time. Not only can it allow safe running at higher compression, but it can, if properly implemented, improve combustion, fuel economy and emissions, and it may help to prevent carbon build-up in the combustion chambers. I think the only reason that it never became common on mainstream cars is that Joe Public could not be bothered to fill up with water as well as petrol.

[dklawson]

The ideal answer to your problems is something that is rarely seen these days, water injection.
and it may help to prevent carbon build-up in the combustion chambers.
Joe Public could not be bothered to fill up with water as well as petrol.

+1 for that. It was exactly what I was going to suggest.

I have not installed water injection on a Mini but I did install it on a Toyota 18RC engine. I had shaved the head to boost compression way up and shortly thereafter the fuel companies lowered the octane of regular pump gas. I bought a very inexpensive Spearco kit and tweaked it to achieve a very functional solution to get power without pinging and knocking.

You did have to keep an eye on the water level so I customized the reservoir to have a float switch and light on the dash to give me advance warning. The other issue was winter. During winter I used windshield washer fluid instead of water to avoid freezing.

When I had to pull the head two years later to address some issues with the distributor drive I found that there was ZERO carbon in the head and combustion chambers.

There will be nay-sayers who tell you that adding water to the combustion process will only rob you of power. The power lost by adding the water is more than offset by the power gain you retain by running more advance and the higher compression that is possible. The downside today is that Spearco no longer makes cheap kits like I bought. The components available now are frequently much more sophisticated and designed for turbo systems. They are very well engineered and priced accordingly.

[mini13]

Care to elaborate on this? I know Kerosine is crap, but toluene and xylene are supposed to be very good at boosting octane ratings.

Neither kerosine not toluene are octane boosters, in fact they are the complete opposite.