I thought i would start a thread about detonation. Im looking for any info and opinions on the subject, or rather how to avoid it.
So far i know that the fuels octane level has a lot to answer for, for example 98 will make more power safelly than 91 or even 95 when they are all tuned to there individual limits. So if the engine was tuned for 98 and you ran 91 it may suffer detonation. Race fuels again have higher octanes.
From my basic understanding of detonation it is an unstable combustion that takes place resulting in two explosions that smash into each other, or one that ignites first without a spark occuring yet or am i thinking of pre-ignition?
Ive always heard a lot of talk about compression ratios being too high causing detonation, however people like to turbo na srs, 2jzs due to the added compression and extra tourque given, it is not uncommon to here of turbo motors running 9:1 compression and na motors of 11:1 on pump fuel, but how much of this has to do with the combustion chambers shape/design?
Which would be a better design head the open chamber head or the heart/peanut type to avoid detonation, is this the same for na and turbo engines?
Timing i no makes heaps of difference, add a bit too much advance and tink, tink, tink! Also air temp for boosted engines!
The reason i want to no more about this is my l20b turbo has started detonating since ive changed the headgasket and got it up and running again, the boost has crept up to 10psi as i noticed the wastgate actuator was loose when its suppost to be shut/tight so i adjusted it up. Ive had to back the timing out a considerable amount to the point were i cant get wheelspin at all unless im rough with the clutch, its really killed the engines performance and resposiveness. I have a fuel/air meter and its not running lean up top although its lean at idle (hunting and stalling a bit). The engine itself isnt over heating. It was only pinging when under load and high in the revs or on the limiter in 2nd and above. I also filled up with a fresh tank from another sevo and made no difference, its annoying because it never used to detonate. Im hoping im not at the limit of the standard engine as far as safe power without detonation goes. i am seriously considering building a fresh engine up with one goal in mind, to avoid detonation as much as possible. Still using cast pistons but try and find some with a bigger dish to drop compression, the best type of l head either open or closed/heart chamber, modified if need be and of course new bearings, quality gaskets etc. That way i can just crank boost and timing into it, or is it not that simple, im probably missing heaps, anyway enough rambling, thanks guys/girls

Lower compression ratio help alot with boosted engines.
Also people run water injection to reduce detonation on boosted engines.

what happened to stock and home made stuff

yes i forgot about water injection, ive found this which im going to have a go at, only trouble will be sourcing the jet as i cant find anything on the net from spraying systems, and no doubt it will be $100+. Anyone had diy experience with water injection? I wonder if an old spraygun could be modified, may require too much pressure though.

Boost Pressure Water Injection
A good quality boost-pressure controlled water injection system can be built using off-the-shelf components. The system gives an extremely fine spray and can be used with water/methanol as well as pure water. While the injection of water is not proportional to load (it is proportional to boost pressure), there is a variation in the supply of water which is still better than many systems provide. The best part of the system is that it is maintenance-free, other than requiring the refilling of the water tank as required and the occasional cleaning of the filter.

The nozzle used is an air atomising design produced by US company Spraying Systems. It has two connections - one for compressed air and the other for water. The compressed air is directed out of two orifices so that it collides with the water stream, scattering it into the tiny droplets. The pressure to supply both the water and the compressed air comes from the turbo or supercharger. The part number for the nozzle is SUE18A and it is available from agricultural irrigation and spray suppliers.

Unlike many air atomising nozzles, the SUE18A works effectively at pressures below 50kPa (7psi). Around 200 ml/min flows through the nozzle when it is supplied with water and air at around 20 psi (1.4 Bar) boost. If this flow is too great, a ball valve can be placed in the water supply hose to allow easy adjustment of the flow. If the ball valve is closed down to restrict the water supplied, the remaining water will then be even better atomised! If more than 200 ml/minute of water is required I suggest that you use two or more nozzles.

The water supply for the nozzle should be through a small water filter to avoid filter blockages occurring. An appropriate filter is available from the suppliers of the nozzle or a small garden irrigation filter can be used. The nozzle must be mounted so that it flows into the intake system before the compressor and the water should be injected after the airflow meter (if present) to prevent the water droplets upsetting the air metering.

The fluid storage container must be pressurised if the water is to be forced through the nozzle. A custom tank can be made or a large pressurised radiator header tank pressed into service. Preferably the tank should be at least 5 litres in volume for each nozzle used. Note that the tank must be capable of handling the constant cycling of internal pressures up to the peak boost level. A low fluid warning buzzer should be fitted.

Plumb the system using a ball valve to adjust the supply of water and a boost-pressure triggered solenoid (pictured) to give a positive starting and stopping behaviour. An alternative to the use of the solenoid is to install a vacuum-operated valve (such as the EGR valve) to vent the tank back to the inlet system, causing the tank pressure to more closely follow boost when the throttle is lifted. However, the solenoid valve is the safer of the two approaches: if the water ever flows into the intake when the engine is stopped, very major engine damage can be caused when it is attempted to be re-started!

well to help reduce the pinging and still run the same timing i run a nulon octane booster it increases the octane by up to 7 points and it practically works. when i had it tuned on the dyno i even observed the run before the octane boost was added then the one after and all of the massive amounts of ping were no more hope this helps the bottle is like 22 bucks at supercheap auto and like 27 elsewhere so good luck and try it but make sure that you get the pro strength booster and not the boost and clean
cheers kurt
also this thread is a champion idea

does the one bottle do more than one tank? 7 points is a lot of an increase, that would make 98 into 105

ive got the bottle in my hand and it says "this product is so powerful using half strength may well achieve the disired result. one bottle (500ml) will treat 60 litres of fuel"
so for our datsuns its like a cheap insurance but experiment with different "dosage levels" until you find the right one that suits you that is how i did it, for my worked A15 with 220psi compression i use 250ml for 20litres of fuel
-boosts octane by up to 7 numbers (70 ron points)
-stops engine pinging (detonation)
-increases performance and acceleration (again on the dyno i whitnessed this and it really does increase horsepower )
-protects valves and valve seats from wear
-prevents engine damage caused by detonation
safe for catalytic converters and oxygen sensors.
hope this helps

Good thread idea sikdatto1200,
Here`s some thing to check and some remedies,
-ENGINE CONDITION, piston damage, ring wear, poor oil control .(will cause mixture contamination and lower octane rating)

-BLOCK PRESURE, water pump must be making fairly good block presure (about 25lb)
never run an engine without a thermostat or suitable restrictor to maintain good block pressure. otherwise you will be getting localised boiling (Hot spots) around exhaust valves and combustion chambers leading to higher combustion temps and detonation. Even tho the temp guage is reading normal!!!

-INTAKE AIR TEMP. This is probably the the most important one for turbo engines. I cant recall the exact figures but something like for every rise of ten degrees c in air intake the fuel octane requirement goes up by one point..(feel free to correct my figures here) Realising that a turbo compressor at at 65% eff. making 20lb boost on a 20 deg. day has a discharge temp of 120degrees!! This is where intercooling comes in!!
Draw through carb setups are the most handycapped here.. Increase the fuel octane or a very good water injection set up might get these setups out of strife unless you lower the compression, which can give you a sluggish engine off boost.

-OTHER CONTRIBUTING FACTORS, mixture quality, the shape of the combustion space(plent of squish).Igntion curve and total advance, plugs, the cars gearing, engine size v car weight ..

Or something like that,
Simon.

Hmmmm, detonation eh?
Here's the way I remember it from my old days on the tools, & keep in mind, this is digging back about 35 to 40 years into my memory.
Accurate corrections are invited.

Definition.
Detonation is when the charge of fuel/air, or a portion of the charge of fuel/air, spontaneously combusts [explodes] or 'detonates' The fuel charge is supposed to 'burn'. It does in fact burn, almost at the same speed as the powder in a rifle round.

How does it happen?
This is when the fuel charge in the cylinder, compressed by the rising piston, is set alight by the plug. It starts to burn in a flame 'front' across the compressed charge, & as it burns, the rising pressure of the consumed fuel compresses the unburned fuel even more. There comes a time when the unburned charge simply reaches the point of self ignition & the whole thing just goes bang.

The fuel.
Fuels are like rifle powders, they are made with different burning rates. This is measured with an 'octane' number. The lower the number, the more volatile the fuel [the quicker it burns] & the more chance that it will detonate. Higher octane fuels burn more slowly. Low octane fuels are less costly to produce as they don't have as many additives to control the burn rate.

How do we control it?
Back in the days when petrol/gasoline was little more than kerosene, a brilliant engineer named Ricardo discovered that if you could agitate, or swirl the gas mixture, it would propagate the flame much faster & burn the fuel before it could explode. Up until then combustion chambers were little more than bowls over the piston & valves.
By placing a portion of the combustion chamber so that it covered a portion of the piston, leaving a very small gap between them [the thickness of the gasket in many cases] a portion of the charge would be squeezed in there, & it would jet out into the chamber causing a great deal of swirling. This allowed an increase in compression from something like 4 to 1 up to as high as 6.5 to 1 in some engines. This was on improved kerosene remember.
So high swirl can be a great help.

Fuel quality.
During the 50's fuel companies started adding Tetra Ethyl Lead to fuel & this slowed the burn rate noticeably, thereby raising the octane rating by a fair amount, but at a price. This is when 'Super' grade fuel was introduced & the increased octane rating allowed the Dodge hemi to go from 7.5 to 1 compression in '55 to 9.5 to 1 in 1956. That's two full points in one year. Other manufacturers did the same.

Timing
If the fuel is set on fire [ignited] too soon, with the piston still rising, it is trying to compress the fast rising gas pressure in the cylinder. This pressure can still rise high enough to cause the unburned portion of the charge to 'detonate'
Clearly, we want enough advance to ensure that the charge is lit & burning, but not so much as to overdo it. The faster the engine revs, the sooner in the cycle we need to light it as the burn rate stays fairly constant, but the time available to get it burning right becomes less.

Boost
Now this is where we have problems.
By cramming more air/fuel charge into the cylinder then it would normally hold, we push compression PRESSURES sky high, so we are already looking at the possibility of detonation by virtue of the higher cylinder pressures even as the spark plug sets it off.
The fixes for this are the same as before, but some are more practical.

REDUCE THE C.R.
By reducing the compression ratio, we actually get more fuel into the cylinder [more combustion chamber volume], but we do not face the potentially astronomic compression pressures that we would at standard C.R. The extra fuel in the cylinder still gives us more power, but with reduced chance of detonation. The lower the CR, the higher the permissible boost, but the more the engine becomes a slug when 'off boost'

HIGH SWIRL
While modern fuels have much better burn rates, the old high swirl rate still adds its measure of protection by propagating the flame front more quickly through the volume of the charge rather than needing to burn across it.

HIGH OCTANE
The higher the octane, the less chance of detonation.

BOOST RETARD
As the boost comes on, the compression pressures rise & the likelihood of combustion pressures rising too far during combustion also increase, so we need to set fire to it later than before to avoid excessive pressure rise & detonation.
We need to find a way to RETARD the spark from the position it would be in when normally aspirated while it is running & tie the amount directly to the boost pressure. This is the hard part & is, in my view, the single biggest killer of your carbureted, blown engines. With EFI, the timing map is tied directly to M.A.P. [Manifold Absolute Pressure] & the computer controls the timing, so all is well.
When the timing is right, the rise in pressure is also controlled by the fact that the piston will have gone past TDC before the critical pressure is reached & is moving away from the head, thereby increasing the volume in the cylinder & controlling pressure rise. [to a degree]

SUBSTANCE ABUSE.
Water injection is used to help cool the intake charge & also to slow the rate of combustion. The steam created assists in this regard while contributing to the pressure rise overall. Methylated Spirit also works I'm told, but I don't remember why. Octane boosters do the same thing, they slow down the burn rate [were talking milliseconds here] & allow a more controlled combustion.

CONTROL THE BOOST PRESSURE.
Yeah, I know, everyone wants 30 pounds of boost & an A15 becomes a V8 killer, for a few seconds. If your engine isn't built for that kind of power, then perhaps we should screw down the boost pressure.
The lower the boost, the fewer the problems & the longer it will live, so you need to strike a balance between power & engine life. That will be your call, but 5 to 6 psi is often a good starting point in a home built application, & work up from there.

Hopefully this overlong tome will provide some of the basics

Sikdatto1200 - if you read the fine print on any bottle of octane booster it states that they are using a different points system. It's very sneaky but they somehow get away with it. Nulon Pro Strength octane booster is the one I use and, presumably, the one Wodie uses too and it is a very effective product but there is no way it lifts the octane rating of the fuel to 105.
Matty