Any Thoughts Please Guys and Gals ? :smile: my 1997 900SS has a 944 bore kit, Sil Moto headers, loud exhasts, Dynojet Stage 2, with cut down air box and K&N filter. The oil temp guage runs at 110 when fully warmed through, even in the cold -ish weather. I know that gauges are notoriously inaccurate, but I also remember ( I think) reading on a certain now-defunct Forum, that the ignition timing should be changed by a few degrees when the motors have these sorts of mods bestowed upon them - anybody got more knowledge ( just about all of you) or a better memory (ditto) than me - best regards dave p :wink:
If you want some more info try digesting this BikeBoy.org - Ducati 2V Carb Model Ignition – Reducing advance, Ignitech TCIP4 and stuff it may help.
I fitted a 600SS flywheel, LOTS lighter for quicker acceleration/engine braking and easier starting, less wear & tear on the battery, soleniod & starter? Here's my guide: Lighter flywheel(600SS) on a 900SS - Ducati.ms - The Ultimate Ducati Forum The 600SS flywheel carries 32° advance instead of the 36° the 900SS flywheel has, PERFECT for running hi-comps! My motor is behaving just as it did before the rebuild heating-wise with a normal 900SS oil cooler? Result! *** I have found another 600SS flywheel and may have it with me soon - it will be machined to fit 900SS cases and listed on eBay!
Hi Guys, I have retarded the timing by around three degrees, and she runs a good 10 degrees cooler, which is good news. I feel that she lost a bit on the top end. I used to get 130 on the long straight, but only ( only !) 120 today. What I failed to do ( muppet ) was to check the actual timimg, I just retarded 3 degrees from the as found position, but it has had the desired effect - bring on Cadwell and Sunshine on the 27th !!
Flywheel has been delivered, will be machined to suit the 900 cases and listed over the weekend, watch this space...
Ok this is going to be more of an answer than you bargained for, but it may provide more background to the subject of ignition timing. The extra 2 degrees retard answer you got earlier should work pretty well but you may have pre-ignition detonation issues on hotter days at Wide Open Throttle. Recently I got asked by a motorcycle dyno operator why I had twin sparked the FastBikeGear project Ducati 900SS? His belief is that twin sparking doesn't provide a performance advantage and he is probably right! ...and I am guessing he has probably done back to back test on his dyno with a twinspark engine in both single and dual plug mode to confirm. I am hoping to do some back to back tests on a dyno with my engine in both single spark and twin spark mode in the near future, (with optimized ignition curves to suit both modes). But here's the theory for doing it. A bit of a brain dump really. Hopefully it will stimulate some thinking and debate (always a good thing!) Ducati normally sequentially fire the two plugs in their twin spark heads one after the other. I think their primary aim is to improve emissions, whereas I fire both plugs at the same time and my primary aim is to increase performance. A petrol engine can be thought of as just a self powered air pump. The pumps efficiency, can be tuned for economy or performance. When modifying an engine to gain performance you are trying to increase the efficiency of this pump. There are many ways to improve the power output efficiency of a pump that has been designed for fuel efficiency, especially if we no longer care about fuel efficiency, e.g. increase valve size, increase valve overlap, increase compression, increase valve lift, increase the size of the inlet and exhaust ports, increase the number of valves, relocate the spark plugs, use multiple spark plugs, reduce frictional losses, reduce pumping losses, etc. Many of the above items increase the charge density (the number of air and fuel molecules in the compression chamber). However increasing the charge density can create significant difficulties in managing temperatures and preventing pre and post ignition detonation of the fuel air charge. Ideally the spark plug ignites the mixture and the fire starts burning before the piston reaches top dead centre. Due to the geometric relationship between items such as pistons, conrods and cranks, to develop maximum power, starting the fire need to be timed so that the maximum combustion pressure occurs somewhere between 15 and 20 degrees ATDC. To achieve this means that the fire must be started sometime BTDC. As the piston is coming up on the firing stroke the fire is lit. This causes some extra increase in cylinder pressure over and above that caused by compression due to piston movement alone. This extra compression causes pumping losses. Retarding the ignition reduces the pumping losses as the inertia of the engine must fight the force of this increased pressure trying to reverse its direction. This fight between conflicting energies also increases heat build up dramatically. Because of this retarding the ignition also reduces the heat build up and consequently reduces the chances of both post ignition detonation and pre ignition detonation due to hot spots setting fire to the fuel before the spark plug. [Pre ignition is when the fuel air mixture explodes at some point after the spark plug has fired, post ignition detonation is when it explodes at some point after the spark plug has fired.] Using a twin spark set up allows less advance to be used and still have maximum combustion pressure arrive at between 15 and 20 degrees ATDC for the simple reason it reduces the distance the flame front has to travel from each spark plug in order to set fire to all of the mixture. In engines with a greater distance between the plug and furthest point of mixture (e.g large bore engines, engines with high domed pistons, or two valve engines with non centrally positioned spark plugs ) converting to a twin spark set up is even more of an advantage. Charge density affects the gas burn rate. A higher charge density burns faster. Charge density is a function of gas pressures and gas temperature. As charge density increases, burn rate also increases. The speed of the flame front depends on how many air and fuel molecules are packed together in the combustion chamber. The closer they are packed together in the same volume, the easier it is for the fire to jump from one set of molecules to the other. The burning speed is also dependent on the air-fuel-ratio. At about 12.5 to 13 air-fuel-ratio the mixture burns fastest. A leaner mixture than that burns slower. A richer mixture also burns slower. That's why the maximum power mixture is at the fastest burn. Source for this paragraph What If Dyno.com - Combustion Dynamics for Poor Man's Dyno Low Budget Engine Test Stand for testing of HHO, ION, Water Vapor. A really good resource of info on combustion dynamics and the source of much of the information in this rant. Even though raising the compression increases charge density, Kevin Cameron noted recently in an article that raising the compression can sometimes slow combustion as there is less room in combustion chamber for turbulence and even mixing of air and petrol vapour. This uneven fuel mixture also increases the chance of post ignition detonation. With high compression there is also a tendency towards detonation due to hotter temps. In addition with the consequent smaller combustion area in a higher compression engine some experts believe that you may also get more uneven (poor homogenous) mixing of petrol and air that can also increase the probability of detonation. Optimizing squish bands improves fuel air mixing and helps counter poor petrol air mixing. There seems to be near universal agreement that 40" or 1 mm is the ideal squish gap to achieve this for a number of complex reasons. Because petrol has about twice the specific heat (heat absorption ) capacity of air, richer fuel mixtures allow more energy to absorbed and not transmitted to the cylinder walls pistons and exhaust valves etc. etc. A really good resource of info on combustion dynamics and the source of much of the information in this article. Even though raising the compression increases charge density. Raising the compression can sometimes slow combustion as there is less room in combustion chamber for turbulence and even mixing of air and petrol This uneven fuel mixture also increases the chance of post ignition detonation. With high compression there is also a tendency towards detonation due to hotter temps. In addition with the consequent smaller combustion area in a higher compression engine some experts believe that you may also get more uneven (poor homogenous) mixing of petrol and air that can also increase the probability of detonation. Optimizing squish bands improves fuel air mixing and helps counter poor petrol air mixing. There seems to be near universal agreement that 40" or 1 mm is the ideal squish gap to achieve this for a number of complex reasons. Because petrol has about twice the specific heat (heat absorption ) capacity of air, richer fuel mixtures allow more energy to absorbed and not transmitted to the cylinder walls pistons and exhaust valves etc. I am beginning to better appreciate why higher performance engines are usually water cooled. I have read that some engine builders decrease maximum I am begging to fully appreciate why higher performance engines are usually water cooled. I have read that some engine builders decrease maximum compression to allow them to get higher performance. At some point further reducing the advance to enable higher compression must have negative gains. I have read that some engine tuners forego higher compression to allow them to get higher performance. Maybe lowering the compression, advancing the spark and running cams/timing that allows higher revs is a better way to go. Without hours on a dyno with multiple engine configurations, it's like trying to solve simultaneous equations without knowing what values to plug in for x and y!?
