95 octane problems
 

Hi,
Just a quick question about running 6 cyl cars on today's petrol. I have just bought back my old vitesse engined Spartan kit car and am getting it ready for the road again after a 13 year layoff. I recall that the last time I ran it (1995) it was susceptible to pinking and needed the timing retarding a bit. Have any of you 6 cylinder sammio owners had the same problem and if so have you discovered a better solution?

I built a water/methanol injection system to raise the octane of the fuel, similar to that used on supermarine spitfires supplied to the Russians. Cost about £120.

Hi Towed

I remember reading that with interest. How effective has it proved. I remember having to be careful to use gentle throttle at lower revs in a higher gear to avoid pinking. Higher revs was ok though. Have you tried running for a while with it switched off to see if pinking occurs. Are you running standard static ignition timing and a standard distributor advance curve?

lots of questions, all answers greatly received

Andrew

isnt there a thing/stuff you can drop in the tank????

There are lots of claimed octane boosters on the market but a bit of browsing shows that the benefits are dubious. Water/methanol injection is based on scientific principles and as Mr Towed says in his epic build thread, looks really cool!

Hi Andrew, I'm running 13 degrees advance on the distributor as recommended by Triumph, and inadvertently ran it with 16 degrees advance for a while, which wouldn't be possible without the water injection system.

As for trying it without the system running, the original setup used a 35cc/minute nozzle that I'd calculated would deliver a suitable mist for my two litre mk1 lump with the 70psi fish-pond pump I was using. Unfortunately, despite having two filters in the system it clogged up on the run down to Goodwood last September. This resulted in the engine pinking like a can of spanners when pulling away from a standstill after running at 70mph for an hour, and the engine 'running on' after switching off the ignition when I arrived at the hotel.

Even after clearing the 35cc nozzle with an airline and flushing the system it kept blocking up in use, so I've switched to the next size up, which delivers 70cc/minute. This completely eliminates the pinking but with the triggering micro-switch set where it is at the moment the 3 litre tank empties in about 70 to 80 miles of driving, which is only about half a tank of fuel.

Plan is to alter the point at which the micro-switch triggers to make it kick in a little further into the throttle opening so it doesn't constantly feed the water in while cruising. That should conserve the contents of the tank but stop the pinking when pulling away or accelerating from low speed in a high gear.

The real test will come when I've got enough spare cash to upgrade the engine power - Ultimately I'm looking at fitting a mk2 cam, Witor flow balanced inlet manifold and raised compression ratio back to factory spec of 9.5:1. That should give me something like another 30bhp over the 79 it's got at the moment, and will be a much better test of the water injection's ability to prevent pinking.

Hi Towed,

thanks for all of your info. Sounds like the system prevents pinking really well. Now that you are using the larger nozzle to avoid blocking, could you reduce the delivery pressure to make the water/methanol mix last longer? A constantly variable system would be even better using some sort of pressure regulator linked to throttle opening (both rising together) or regulator linked to inlet vacuum (delivery pressure rising as inlet suction decreases).

Saab fuel injection systems have a knock sensor on the block that tells the ecu to retard the ignition when it detects pinking. This allows Saab to use conventional 10:1ish compression ratios on their turbo engines rather than a lower ratio. Rather than using it to retard the timing it might be possible to link such a sensor to your system in place of the microswitch?

Anyway, that's my tuppenceworth, thanks again,

Andrew

Hi Andrew, using a variable pressure pump wouldn't necessarily work - I had the same idea and contacted the (U.S.) nozzle manufacturer, who said they'd only guarantee it would mist the mixture above 50psi, and recommend 100psi (my pump is 70psi, so it's actually delivering about 70% of the nozzle rating).

At less than that the water just pi$$es out the end instead of fogging and could cause a hydraulic lock in the engine if it got sucked into the induction system, which would be bent rods bad. :(

Until I added a second solenoid with a return pipe back to the water tank to relieve the residual pressure in the line between the solenoid and nozzle I was getting two or three seconds of mixture piddling out of the nozzle on a closed throttle. Luckily there wasn't enough to cause a hydraulic lock, but it was pooling in the aluminium airbox, evaporating and keeping the engine idling for up to thirty seconds after the ignition was switched off. There can't have been a spark with no ignition on so it must have been dieseling on the fumes!

I could be wrong, but a knock sensor trigger sounds a bit complicated, not really the sort of thing an enthusiastic diy mechanic could just bolt onto a sixties motor. Anyone tried it? It would be a good idea on a high-po motor.

I did buy a vacuum actuated switch that I hoped would open the solenoid under acceleration but even at its lowest setting there wasn't enough vacuum in the inlet stacks to trigger it. That's when the simple and infallible micro-switch on the throttle lever got designed in.

So, current thinking is to modify the aluminium arm that the micro-switch sits on with a pivot, threaded bar and spring from a biro so that the arm rises up with the throttle lever and the point at which it triggers the switch can be adjusted. Ideally I want it to trigger after a couple of inches of throttle pedal travel, but not cut in during high gear cruising.

All good stuff! I am looking forward to giving this a try. That is after overhauling the brakes, suspension bushes and gearbox and diff mountings plus lots of other stuff.