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I always see these things about running MSD in DIS form, but why not just run it through the cap? I know it's more efficient to run it straight to the coils, but does that apply when running it to two coils? Seems to me that having the voltage split is less efficient than having it run through the cap.

Jeff20B

iTrader: (13)

Should I tell him the obvious answer, or let him figure it out for himself?

Siraniko

iTrader: (13)

let him experiment. thats the only way to prove it.

REVHED

A lot of people run it through the cap and it works great.

FB II

yep, it's true. may not be as good as dlfis idjfiajsfjajf, but still works better than stock.

Jeff20B

iTrader: (13)

I guess I'll tell him.

You'll have to buy caps and rotors more often. There, I said it lol.

Ahem. The CDI output of the MSD takes your car's stock 12-14 volts and converts it to around 400 volts and a lot less amps. What happens when you apply two (more or less) equal loads in parallel? The voltage stays basically the same, but the amperage is reduced 50%. The result is a 'colder' spark. Several thousand volts can jump great distances, but accomplish very little work if the amperage is low. Infact, you know that static discharge that you feel from walking on a carpet and then touching a light switch? One amp through the heart can kill you, but those little static sparks aren't anywhwhere near that.

I guess what I'm trying to help you understand is that the single primary inside a DIS coil is better suited to the CDI output of an MSD than two seperate coils are. This would account for the better performance experienced by both addicted_2_drpepper and a hyper4mance2k when they switched from blaster coils to a DIS coils.

A nice feature of the 2nd gen leading coil I noticed while bench testing, was when I increased the resistance substantially on one of the spark plugs, the other was happy to keep sparking away. This shows that if one plug becomes fouled in the engine, the other will continue to spark. This means the 2nd gen coil contains two secondary coils rather than simply connecting both to one secondary, and would cause problems if one plug became fouled.

I'm probably getting a little more detailed than was necessary, but when it comes to ignition, I don't mess around. I feel that I can safely say an MSD connected to two coils is inferior to a single DIS coil. That's the theory, anyway. Two so far have proven this theory, and I can't wait to try it on an engine myself. Of course we need more to try it and report their findings.

By the way, if I didn't already have a 2nd gen leading coil, I'd go out and get an MSD or Accel brand DIS coil (the color choices are red or yellow; whichever color matches the rest of the car, hehe).

FB II

i thought he was referring to running an msd box thru the cap?

BigJim

i have my msd to my coil then my coil to my cap and cap to plugs and i have about 3000 miles on that setup with no issue and the cap and rotor show no signs of burning or wearing

Blake

I know and like Jeff20B, but I respectfully disagree with his belief that there is any legitimate performance improvement that can be attributed to a "hotter" spark.

The ignition system in a rotary engine (or any internal combustion engine, for that matter) only serves to initiate combustion. Either it does or it doesn't. It can't make the A/F mixture burn faster or hotter or whatever. The power output is entirely attributable to the chemical energy of the fuel burned, not the means of ignition. The only time you need a "hotter" spark is when you get misfire, such as when running a turbo car pig rich for the benefit of charge cooling or when you are running race gas. You generally do not get misfires in any "normal" circumstance on the street. I can tell you for a fact that my peripheral port 13B engine could go up to 11,000 rpm under full load without a hint of misfire, and that was with a 100% stock 1st gen ignition system fired through the distributor cap.

There is a ton of power lurking in ignition tuning but all of it relates to TIMING of the spark to result in the Peak Pressure Pulse of the combustion occurring at the point of maximum mechanical advantage over the eccentric shaft.

Just my $0.02. It's your car, so do as you wish.

steve84GS TII

Im surprised no one mentioned the fact that you can not run a wasted spark setup when running juice through the cap.
Wasted spark is how the stock FC ignition works,with no distributor,just wires drirectly from the coils to the plugs.
Normally,on a piston engine,wasted spark is just that,wasted.The spark plug fires at the top of the exhaust stroke,when there is no compression and no fuel present.Its just a convienient way to cut a DIS system in half.
On a rotary,there can be actual gains to be had from wasted spark,due to the long power cycle,sliding motion of the rotor,and the rotaries thirsty nature.
Because its heavier than air,much of the fuel will congregate at the back of the rotor,near the trailing apex seal as each working surface of the rotor moves by the plugs.Thats why we have trailing spark plugs,to ignite the trailing fuel left in the back.By firing the leading plugs again in a wasted spark setup,the leading plugs get another spark in that mass of fuel(for a total of 3 between the 2 sparkplugs) to ensure a more complete burn.Depending on RPM and load,this may mean more economy,power,reduced emissions or a combination of all three.
Plus by using an MSD box,you get multiple sparks for both leading hits at lower engine speeds(like idle) where we tend to get a lot of misfires.

Blake

Unburned fuel does accumulate at the trailing apex seal but the timing of the combustion (what little there may be) is such that it will add no power. It happens very late in the stroke. It is possible that such a late burn could help expel combustion gasses more efficiently, but that's not something I have seen any evidence of.

The trailing ignition is there because the gas flow in the chamber is faster than the flame front of the combustion, so the "burn" would not otherwise go past the minor axis of the engine. This is well documented in "Rotary Engine" by Kenichi Yamamoto ©1969. Even so, the trailing combustion event is also mainly about "cleaning up", though it can contribute to power with proper ignition timing.

Hyper4mance2k

iTrader: (40)

the cool thing about this thread is that my name was mentioned. hahah I'm cool.... not really,but. Honestly If i honestly didn't thing it made a difference then I wouldn't have changed it. About 2 years ago I had 83 gs with a blown oil seal that would start on one crank. and a 83 gsl that didn't allways want to start until i took the msd out of the gs and put it in the gsl. My ignition has had a very positive effect on my engine. And I think its the contributing factor in the fact that I hold the bhp record for a stock port gsl-se engine.... 140bhp.... If there is someone with a dyno sheet that has done more I havent seen one and I'll stop braging.

steve84GS TII

I kinda approach it like this.....if Mazda did it,there must be a reason.Either power,effeciency or emmisions must be somewhat affected by running wasted spark direct fire ignition or why would Mazda(who has more R&D time on the rotary than anyone), make it standard on all 86-up engines.

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So I know the advantages of running the DIS setup. I just don't have money for the coil right now, so I might as well run the MSD through the cap while I'm waiting for cash to come, that's why I asked the question. So onto question two, will the MSD run with the stock wires? I know that an MSD is supposed to run with MSD wires and the true benefit of running the MSD won't come until I get the wires; but they're waiting for me when I get back to california on the 12th of march.

Siraniko

iTrader: (13)

Bring it to me on ur next trip to SOCAL. I can save you $$$$. Forget about MSD.

Blake

Next time you're in Portland, go visit Pineapple Racing and ask to see the dyno chart on the stock-port GSL-SE engine that put out 186 whp. BTW, if that's really BHP, then you don't have much to brag about...a 5 bhp gain over stock!

Blake

Yes...emissions, cost, simplicity. The real breakthrough was computerized ignition timing, which is leaps and bounds better than distributors (just as EFI is so superior to carbs). Once you have that, it's actually easier and cheaper to have a direct-fire, wasted-spark leading ignition than it would be with distributor setup (which was easier and cheaper to run non-wasted-spark).

steve84GS TII

One thing I found in abundance when running MSD direct fire was energy leakage.Even if you run the MSD power through the cap,youll want to use good quality wires.Not neccesarily 10MM Magnacores or $150 monster cables,but at least something new and equivelant to stock.
And packing the plugwire boots with dielectric grease makes a big difference.My Magnacores would put on a lightshow in the dark at the sparkplugs before I packed them.After the grease,its all contained inside the boot,plus the wires are easier to remove since theres no corrosion.

puntorotary

Im running 2 MSD6al thru the cap and dont have a single problem with anything,just make sure you have good wires.

Directfreak

iTrader: (2)

Same here.

680RWHP12A

same here....

680RWHP12A

what happens if you use the waste spark setup on a bridgeport?
there is overlap wich is the exhaust port and intake port are open at the same time.... waste spark fires..intake port/exhaust port is open.... then what?

i know alot of guys with 3rd gen cars that couldnt get a bridge to run .....and they are GOOD engine tuners....

Siraniko

iTrader: (13)

I've tried a MSD direct fire (2 MSD 6A boxes) on a bridgeport...I went back to dizzy cap set up.

Jeff20B

iTrader: (13)

That would be fine. You could pick up a 2nd gen coil for next to nothing at a wrecking yard, or maybe somebody here could sell you one for cheap.

Blake, 11k on J-109s? I'll have to mess with the dwell settings on my MS and see if I can get spark that high (it's just for testing purposes as I don't plan to run my engine that high).

I'm not sure exactly why the engine in my red REPU ran as well as it did with a direct fire ignition system compared to through the cap on a 1st gen distributor and coils. It was my test vehicle for a few years (the ignition setup you saw in the white truck was based on the succes of red truck's). I tried an MSD hooked to two coils in the red truck and it improved a fair amount, but it still backfired now and then, just as it did when stock (there was a leak in the exhaust). Then when I switched to DLIDFIS, it improved the power and driveability further and there were no more backfires. The real kicker though was when I had removed the MSD to switch over to DLIDFIS, I realised I needed to get some small female quick disconnects for the backs of the ignitors, so before the short drive over to a local car stereo shop to pick some up, I switched back to the stock 1st gen ignition system since it was quicker to set up than reinstalling all the MSD's paraphernalia (I was also curious to see how it would run since I was now used to the MSD). Oh man, it was weak! It was as if I'd installed several clutch fans or other power robbing junk to the engine. You once said to go back to stock after driving on an upgraded ignition system for a while, to see if there really were any benefits. Heh, there certainly were some.

It's really odd. Switching from the MSD/stock to DLIDFIS made a big difference and yet the only things changed were routing the leading spark from the cap to the plugs directly, the addition of late leading sparks 180°ATDC, the deletion of the leading coil to cap wire (whixh wasn't damaged or leaking any more than the trailing coil to cap wire), and moving the trailing wires over to the leading part of the cap. The available voltage to everything in stock mode was actually more than with DLIDFIS because stock mode only has two coils to charge instead of three (less voltage drop and load through my old ignition switch and wires).

It was oddities like these that hardened me into the ignition guy that I am today.

Robert, I know the stock leading coils of 3rd gens are not a good as 2nd gens. I also know that there are a lot of people with half bridgeports running all sorts of ignition systems (they mostly hang out on nopistons) with turbos and what not on their 2nd gens. Since the anti-det device was originally intended for 3rd gens, I suspect there is a lot of misinfo out there. I'd need to look into it further to be able to give you an answer.

Steve, thanks to the exhaust leak in my truck, and the general free-flowing nature of its Rotary Engineering glass packs, I was very easily able to hear the difference when I changed ignition systems. Stock through the cap sounded liek a 4 cylinder. It was like putt, putt, putt, putt. The MSD sounded a lot smoother, but also a bit choppier. DLIDFIS sounded the most like a 2nd gen. Like you said, that late leading spark does ignite the fuel in the trailing edge of the rotor, producing the FC-like exhaust note. The logic I'm using here is: if it wasn't burning any fuel, it couldn't produce any sound, so it's definitely doing something above and beyond a stock system.

As Blake says, it's pretty late in the cycle for the extra spark to produce any power, but I'm still at a loss to understand why my engine's power improved so much. Also, what about at full advance? Isn't it still early enough in the cycle to have some influence over the engine's power? Well, whatever the case, direct fire certainly doesn't reduce power as far as I know.

purple82

Sorry, this is incorrect. Simply reading a passage from Yaw's website states:

"This may be true in simple laboratory tests, with homogenous mixtures, but it ignores the dynamic nature of internal combustion engines. The fact is, that not only does the mixture quality in the spark gap change from one cycle to another, it is also changing during the cycle. For this reason, long duration, or multiple sparks are very beneficial to combustion efficiency. This is especially true in rotary engines where the air fuel mixture is traveling past the spark plug at a high rate of speed when it fires."