Lynn E. Hanover

Let me speculate (because I have no experience tuning a turbo engine).



Racing Beat recommends 12 degrees both leading and trailing for turbo engines with timing checked at 6,000 RPM. I would regard this as a hint, and probably the maximum advance used.



They also recommend that torque for case bolts of boosted engines be 32 pounds. Apparently in an effort to develop more clamping power to resist the dowel shearing and iron breaking problem.



They have built a 900 HP turbo airplane rotary, so they know about most of these problems.



I notice that rotors for turbo engines are 8:1 or 8.5:1 compression ratio for racing. So the effective compression ratio under boost is a big factor.



I read in a Patent for a controler for turbo rotary boat engines that leading timing was 5 to 18 degrees BTDC and trailing timing was 5 ATDC to 3 BTDC.



One of the rotarie's advantages over the piston engine is Dwell time As Smokey used to say.



He did things like move the crank centerline away from the cylinder centerline and install the pistons backwards (when stock pistons were required) to extend the Dwell time. Dwell time is the period of time when the piston is at or close to TDC. Because you can burn more of the charge with less ignition advance, if you have a longer period with the piston not moving. This is important because if you light the fire well before TDC, then the pressure generated, Brake Mean Effective Pressure (BMEP) must be subtracted from the BMEP from TDC on to exhaust valve open point. So it is to reduce the power lost because of ignition advance BTDC.

Simple.



Another advantage is that the length of time the burning charge is heating the head and piston crown is reduced. So, lower charge temperatures, and then you can run higher compression before detonation starts.



So the rotary has a very long Dwell time, and therefore requires very little ignition advance.

And that is true of NA rotaries. Boosted rotaries require even less advance than NA rotaries.



For several years the SCCA forced us rotary people (and all others in open engine classes) to use racing fuels. We had to have the specs for the fuel we ran, and a fuel sample was taken after each race, and random cars were checked after qualifying.



With racing gas, 107 Octane, you get less power because it has fewer BTUs per pound than does street gas (no alcohol). So just about anything worked better than racing fuel. Daryl Drummond gave them dyno sheets using both fuels, and convinced them that rotaries made more power on street gas than on racing fuel, and eventually they let rotaries go back to street gas, and everything returned to normal for us anyway. Racing fuel (high Octane) just has a bunch of lead salts and other compounds in it to make it insensitive to autoignition due to pressure. So, you can have higher compression with no detonation.



High Octane fuel may also burn (Flame front velocity) just a bit slower than low Octane fuel. So you use more advance to get the highest cylinder pressure at about 50 degrees ATDC.



Two factors to think about.



When boost is high, effective compression is high. The bits that burn heat each other at a rate inverse to distance. So, in the NA engine the burn rate (Flame front velocity) is low, and a long smooth combustion takes place, and nobody breaks anything. In the boosted engine, the bits that burn are very close together, (the effective compression ratio is higher) and the flame front velocity is very high. So the combustion is quick and peak pressure at the ideal 50 degrees ATDC requires that ignition be retarded compared to the NA engine.



Now review the Detonation definition, and note that the trailing plug igniting starts to look like a detonation event if the time after the leading plug firing is too long. Note Racing Beat says no split timing.



One of the airplane guys shuts off his trailing ignition during nitrus injection to eliminate detonation. Mmmmm.......Think about that.



A detonation event in a NA rotary might go unnoticed due to the limited amount of mixture left to burn late in the combustion event. In the boosted engine, a detonation event would include more mixture in the same area, it is likely to be at higher temperature than in the NA engine. It will not go unnoticed as it may result in damage the very first time it happens. The rattle in the muffler is the apex seals.



The detonation events are likely to happen right beside the apex seals...........



Early rotaries used the front case as the engine mounting point. So you end up torque loading the whole stack during hard use. The engine is being twisted in opposition to and in the exact same amount as the torque output.(Newton) So in later years the engines were mounted by the center iron, cutting the load to only half of the stack. Some folks picked up on this fact and mount the engine with only a plate between the rear iron and the bell housing. I figured this out far too late. So all of the torque loads on the stack are just those produced by the torque of the engine. No torque loads from downshifts, upshifts or misfires must use the stack to travel into the chassis. Duh............



So the higher case bolt torque makes more sense. Also the object of the extra dowls and the oversized case bolts is to carry the torsion loads from the housings into the rear iron where it is accepted by the bell housing. Ever crack a bell housing? I have.



So, 500 HP at 6,000 RPM requires 437.8 foot pounds of torque. That torque is twisting the stack and is prevented from twisting by the dowels and the friction caused by the case bolts squeezing the stack against the rear iron. Like a deck of cards held between your palms, when you twist the stack the pieces end up at slight angles to each other. In the rotary the pieces put the dowels into single shear, and that microscopic angle change puts the same section of dowl in a bending

load. So if the dowel does not shear off, it cracks the hole out of the iron.



When you see a drag racing rotary come off the line with the whole body torqued over in one direction what part of the engine is twisting the whole car that much? Would you mount that engine with the front cover, the center iron, or the rear iron?



So I suggest backing off the ignition advance a bit, shorten the split, spraying water into the intake, spraying water onto the radiator and intercooler, and oil cooler. Run the fans manually.

use all high Octane, use a bit extra ash free synthetic premix (to keep the apex seals cooler).



Use a monster ignition system at least on the leading plugs. Use inductive secondary plug wires.

Keep the wires well away from low voltage wires, and away from each other. No full throttle until the revs are up........





Just a guess though....



Lynn E. Hanover

rotaryinspired

Thanks for the informative post Lynn. I appreciate you taking the time to share your knowledge and experiences. After taking the time to review everything I believe I had a misfire due to leading and trailing plug wires touching and not being shielded from each other appropiately. I was also running the car too hard too early without making sure everything was completely ready. I can be impatient, which explains the plug wires. We all spend too much time and money on these cars to let little mistakes side line us. Lesson learned.

j9fd3s

i was gonna suggest that. firing the trailing 180 degrees early will break things

Lynn E. Hanover

Quite true. If your failure involves the top dowl hole breaking out of the front iron, there has been a cross fire.



Induced by secondary wires from the front housing being too close to rear housing wires, or, early igniters talking to each other. For other than stock operations, most folks discard the igniters (points eliminating SCRs) and use an aftermarket system triggered by the stock pickup coils. Wires from a crank trigger system can also cross talk, as output at speed can exceed 100 volts.



Lynn E. Hanover

j9fd3s

Here's something interesting. - TeamFC3S



food for thought...

rotaryinspired

Some good reading and information there. Thanks for the link.

Lynn E. Hanover

More accounts of heartbreak due to broken engines. In those accounts I see several points that might be usefull.



I suggest that 2MM seals have 1/3 less strength than 3MM seals. Mazda knows how to make seals.



Other people make seals because seals are expensive. Like crack cocain expensive, so there is lots of money in making seals. Ceramic seals are incredibly strong and unaffected by heat. They are available with stock like corner pieces, so whining about a good compression seal is no longer valid.



Apex seals need top oil to keep them cool. Premix an ash free synthetic 2 cycle oil even if the OMP is still running. Racing Beat was mixing large amounts of top oil to keep the 900 HP airplane rotary alive.



Breaking a front iron just about requires a cross fire or a very early preignition, since the front housing has little torque load on it.



Real racing engines use crank triggers, because distributors/ crank angle sensors are gear driven and subject to harmonic disturbance that alters timing in harmonic sympathy with various RPM.



Unless the system you choose is designed to work with a flying magnet, like the really big MSD systems mounting a magnet or magnets to trigger a more conventional management system may need a rethink. The magnet will trigger the pickup as a function of speed and air gap. The pickup or trigger circuit may not be happy with voltages from the trigger going into the hundreds of volts.



There is also the problem of ignition advance caused by magnet speed. In small diameter trigger wheels the speed is just not a problem. In a trigger magnet mounted on the edge of a flywheel or front pulley not the same. Just a screw head standing proud of the surface is all that is needed. Or go to the hot rod shop and copy the MSD trigger wheel.



A pickup with a magnet bias does not need a magnet flying by to excite it. Just a chunk of ferris metal is fine.



About 100 years ago when I raced Karts, we had a button on the steering wheel that was a normally closed switch. It was in series with the points wire. So when the revs got to be above about 12,000 you push the button in and that opened the points circuit. But the magnet on the flywheel was going past the coil so fast that the coil would fire directly from the secondary windings, and this gave about 7 degrees more advance that went up with more revs. It was called Maveric ignition.



At high boost it takes a hugh amount of voltage to get an arc across the plug gap. At least two Mallory HiFires or MSD6ALs would be required. Hell I need them for a NA engine to get to 9,600RPM.

With never a misfire.



A lost spark system is firing a plug gap at both ends of the coil. Smell any problems? That is the same as doubleing the plug gap on a single plug.



An MSD can fire two coils at once. You could have a coil for each plug, and fire both front housing plugs from one MSD, and both rear housing plugs from the other MSD. The plug wires should be as short as it is possible to make them. The wires need to be inductive. That Monel coiled stuff. It keeps the radio output to a minimum so reduces cross fire.



Triggering wires need to be run through Dash 4 braided stainless fuel hose. The braid needs to be grounded at both ends. If you have two pickups they need to be run in separate hoses. The hoses must be run well away from each other.



The spark plug heat range needs to be just the coldest there is. Probably a surface gap plug with no ground electrode at all, or as close as you can get your hands on.



The lower the RPM where you demand power from a boosted engine, the less ignition advance you need. The object is to attain maximum cylinder pressure at about 50 degrees after TDC. With high boost, the burn rate is so fast that I suspect timing close to zero will get max pressure at 50 ATDC.



Years ago the Nissan GTP car had two huge turbochargers mounted. Seldom did they make a race start. They changed the people running the car for them,



Nissan GTP ZX-Turbo - Wikipedia, the free encyclopedia



Electromotive took over and the cars started to work. I noticed the exhaust had a huge amount of black smoke from then on. They used excess fuel to cool the pistons, as they kept turning up in the oil pan.



So don't be bashfull about the F/A ratio. Extra fuel (low F/A numbers) burn slower, are cooler, and cools the mixture to hold off detonation. If you premix, there is extra oil moving over the apex seals.



Keep in mind I know nothing about turbowcharged engines.



Lynn E. Hanover



The picture shows two versions of a lost spark layout on each rotor housing. One with a coil for each plug, (best) and one with a double ended coil for both plugs (Good).

indio84

good thread

boprotary

its all in the tune guys ,