Morris Minor Owners Club

octane boosters allow higher pressures without pinking - i.e. allowing more advanced ignition, giving more power.

An octane increase on its own slows down the burn rate and will therefore reduce power without a corresponding change in the spark timing.

Probably far to technical for VBH though. That's probably why they completely overlooked any technical issues in the program. From a scientific point of view, without explaining the engine timing advance (I guess there wasn't any?) it was a pointless excercise.

Even so, I'd still agree that it's daft to spend money on expensive fuel additives - the ones I used for VSR protection were extremely good value for money.

that was very intresting

Modern engines (like this one in the test) automatically advance the ignition timing until 'knocking' is sensed -to take full advantage of any available octane rating in the fuel. I think the point is - the addition of the additive actually dilutes the fuel slightly - hence ~2% drop in power - despite 'possible' octane boost from the additive..
At least one of the additives used claims to give 'valve protection' too!

The valve protection is probably there to protect them from the harsh ingredients in the additive, That are causing the negative power level

If you have an engine with a high compression ratio and suitably advanced timing you need a certain octane 'level' to prevent pinking. You can knock your timing back a bit to lessen/avoid the pinking but will of course experience a drop in power.

I found an interesting situation on MoTUK recently when towing my caravan using my modified car with a 1380 A-series having a 10:1 compression ratio.

Using Total Excellium (plus Castrol Valvemaster Plus) there was no pinking at all. Using Shell VMax (plus Castrol Valvemaster Plus) there was no pinking at all.

Now, when I was running low on fuel I headed for a BP garage and filled up with BP Ultimate (plus Castrol Valvemaster Plus) and the pinking was AWFUL.

Luckily, on the way home I was running out of petrol so called at a Total garage and put a tenner's worth of Total Excellium (plus Castrol Valvemaster Plus) and shortly afterwards the pinking disappeared, so I learnt something. Mostly that there IS a difference between the 'super' unleaded fuels.

Now, I COULD have stopped and adjusted the timing and lost some power but using the correct octane fuel (& additive) I was able to enjoy the power without pinking!

Saw a similar test by a tuning mag but using a highly turboed engine in which they did advance the ignition to get a maximum power reading and they did gain a few BHP. But all this test did was prove that on a road engine with an ecu that keeps the engine away from detonation (with safe parameters that give the superchippers space to work by increasing advance and fuelling) the products are a waste of time and money (most modern engines don't have det sensors).

Now, when I was running low on fuel I headed for a BP garage and filled up with BP Ultimate (plus Castrol Valvemaster Plus) and the pinking was AWFUL.

That's assuming that they'd not filled the ultimate pumps up with 94!


I didn't see any mention of automatic timing advance on this TV test - and as an engineer, you learn every day that the devil's in the detail. Testing means nothing unless all the conditions are spelled out fully.

All modern engines have 'knock sensors' that constantly advance the timing till sensed and then retard - many times per second!
But certainly interesting to hear of the BP experience. You should ask BP for an explanation Cam !

that they'd not filled the ultimate pumps up with 94!

Heard about a guy (tanker driver, but not any more) that dumped 32000 ltrs of derv into a petrol tank on one of the services on the M6.

My supercharged moggy can run about 2 degrees more advance with octane booster in 97 fuel than it can on 95 fuel. And power wise its a noticeable difference.

You do have to pick your 97 fuel wisely there are different qualities out there.

And obviously there are huge differences in octane boosters, avoid little expensive retail bottles and buy the gallon can types that racers use with simple labels.

bmcecosse wrote:All modern engines have 'knock sensors' that constantly advance the timing till sensed and then retard - many times per second!
But certainly interesting to hear of the BP experience. You should ask BP for an explanation Cam !

Hmm I might stand corrected (just had a quick look at the modern mg owners forum). It mentions about ecus being preset to allow for lower octane ratings in other countries and the knock sensor pulling back from detonation with 95 octane fuel when it occurs. It does not say anything about advancing ignition to take account of higher octane fuel. In a lot of ways an ecu is a rather stupid slave that sticks to its task of providing 14.9 air fuel for the cat and emissions probe and giving open loop emissions when on full throttle or cold (when no ones checking). Getting the best out of the fuel is not really one of its priorities.

That's what the 'knock sensor' does! ECUs mostly adjust mixture (although they do hold a basic ignition timing map - which is fine tuned by the knock sensor) depending on temperature and throttle position and lambda reading at idle. Hence the 'booster' resistors you can buy on ebay which promise extra 10 bhp - they simply adjust the temperature the ecu sees - and it richens up the mix accordingly. More power - but poorer fuel economy!!

It's a shame they didn't put some super duper (expensive) petrol through the same test.
Maybe their lawyers warned them off?

bmcecosse wrote:That's what the 'knock sensor' does! ECUs mostly adjust mixture (although they do hold a basic ignition timing map - which is fine tuned by the knock sensor) depending on temperature and throttle position and lambda reading at idle. Hence the 'booster' resistors you can buy on ebay which promise extra 10 bhp - they simply adjust the temperature the ecu sees - and it richens up the mix accordingly. More power - but poorer fuel economy!!

So you are telling us that a modern engine runs at maximum pre detonation advance all the time (all right we will take that as full throttle). I can't see this being correct as there is a point of optimum advance where maximum power occurs which is before max advance (ref Dave Walker). The basic ignition map is fixed (eg Fords eec1v zetec allows for the different induction of the 115 and 103ps variants with different ignition curves) for the required octane (in most uk cases 95)and the knock sensor protects the engine against use of lesser fuel by detecting detonation and retarding ignition. If there are manufacturers who produce an accurate enough knock sensor to risk advancing timing for use of higher octane fuel I would be interested to know who they are.

^^^ I think it depends on how much you pay for the car

PSL184 wrote:^^^ I think it depends on how much you pay for the car

I would suggest you are quite right. I'm strictly down the lower end of the market when it comes to car budget (£2000 car scrappage allowance thats my total funds). Self tuning exotica is way out of my reach (a car that self adjusts between meths and avgas thats what I want)..

I know this will be a bit of an odd thing to say on a morris forum (the a-series being all about home maintenance), but how hard would it be to fit a knock sensor (assuming one can be found to fit Arnie's most valid spec) to an A-series? ... i'm not saying tht I would do this - my whole reason for having a minor is that it takes me away from my IT day-job, but it would be an interesting point.

Even the mega-jolt kits don't run knock sensors - just a fixed timing map with additional vacuum advance of course. Be a pioneer!

We looked into using a knock sensor with a Ms2 (ie using the knock sensor as advance control) since it can take the input. But because of the optimum power not being at max advance and choice of sensor and positioning being very important just making it a secondary sensor. Because a Megasquirt has no adjustment limits it is possible to wreck things very quickly so a knock sensor is a good safety option. Actually I think a range of 90-105 octane would be my most valid spec.