Single spark plug housings
Hey guys
Is there anyone out there running single spark plug housings on their engines? I just bought one of a member on this forum. And Im wondering a little about tuning it, is there anything I need to do differently than if I was running regular housings with leading and trailing? |
You might be referring to the "anti detonation" mod that some have done. It basically deletes the trailing plug. In contrast, all the old Audi/NSU rotaries ran on trailing plugs only (believe it or not).
I don't have firsthand experience with tuning these but I would expect a decrease in fuel economy at the very least. |
Arghx check this out,
https://www.rx7club.com/3rd-generation-rx-7-1993-2002-parts-99/stage-3-ported-motor-dowell-pinned-balanced-coated-oil-coolant-mods-3mm-polished-966223/ In the description Allrotor93 claims single spark plug housings. I guess they do exist John |
Renesisfd nailed it. That engine is currently on the way over the pond (to Norway).
Arghx, trailing plugs only?? This one is the other way around. Leading only. |
Interested in this as well since I don't want to run my giant trailing coil pack (FC ignition)
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2 Attachment(s)
Running leading-only could prevent detonation in modified turbo applications. That's really the only potential benefit. There's nothing else to gain from running it, and the engine will lose some efficiency.
I just double checked some stuff. The NSU KKM 502 engine used a single trailing plug. This was a single rotor, peripheral ported engine found in the Wankel Spider which was the first production rotary-powered vehicle. At the time NSU found that running dual spark plugs was superior but they couldn't figure out an affordable way to do it. https://www.rx7club.com/attachment.p...1&d=1322079913 Here's some data from their early tests. The crude triangle-looking plots are from the experimental 2 plug system, and circle plots are from the trailing-only system used in the KKM 502. You can see that specific fuel consumption ("SFC") is lower, the mixture is leaner (lambda is a higher value), and engine load/output (brake mean effective pressure, BMEP) is higher with the two-plug system. Later Audi/NSU switched to a dual plug system in the KKM 612 engine, which was a 2 rotor peripheral ported configuration found in the Audi Ro80 luxury car. The dual-plug system didn't need as cold of a heat range so the plugs lasted longer. Mazda investigated leading-only, trailing-only, and dual spark plugs when they were developing the 10A engine. They used combustion chamber pressure sensors to generate the pressure-volume indicator diagrams commonly used in engine development: https://www.rx7club.com/attachment.p...1&d=1319142990 The problem with running leading-only plugs is that the flame must work against the gas flows traveling along the trochoid path of the rotor. The problem with trailing-only is that the flame can encounter quenching effects. The dual spark plug system has superior output. Mazda used 3 spark plugs per rotor on the R26B 4 rotor engine in the 787B LeMans race car: https://www.rx7club.com/attachment.p...1&d=1322079913 |
In actual day-to-day use, it is certainly conceivable that deleting the trailing plugs reduces detonation. The reason why it reduces detonation is because most detonation typically occurs in the trailing portion of the combustion chamber due to the squish flows. Squish flows are concentrated pockets of air/fuel mixture that are also found on piston engines.
https://www.rx7club.com/attachment.p...1&d=1318823469 https://www.rx7club.com/attachment.p...1&d=1318823469 When you eliminate the trailing plugs there's much less flame propagation into the trailing portion of the chamber, thus the chance of knock in that area naturally decreases. There are legitimate reasons why it works, but overall engine efficiency will undoubtedly decrease even if it's not obvious on the dynojet at Billy Bob's Mustang Shop. |
So would running 3 plugs help prevent det and give more power ?
Rix |
Originally Posted by RIX-7
(Post 10873381)
So would running 3 plugs help prevent det and give more power ?
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Originally Posted by arghx
(Post 10873359)
Running leading-only could prevent detonation in modified turbo applications. That's really the only potential benefit. There's nothing else to gain from running it, and the engine will lose some efficiency.
Hopefully the loss of efficiency will be outweighed by the benefit of less detonation. Im using a t88 34d and aiming for 500+rwhp. I was thinking of buying some mercury IGN-1A coils, looks like they are the bees knees these days. Although i have been considering msd 6 or 7 series ignitors with coils. |
Originally Posted by arghx
(Post 10873404)
Theoretically yes (at least on the power part, not sure about detonation) but how many sets of 3 plug housings are out there? To my knowledge only the R26B had them, and those housings were meant for a peripheral ported n/a race engine application.
Raymond, I think I need to get my dad to get his drill and tap set out :). Easy to drill and tap a third hole. Time for some R&D I think. Did you pull any info on the wiring for a third plug. |
I think rx7specialties can modify for a 3rd spark plug.
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Originally Posted by arghx
(Post 10873404)
Theoretically yes (at least on the power part, not sure about detonation) but how many sets of 3 plug housings are out there? To my knowledge only the R26B had them, and those housings were meant for a peripheral ported n/a race engine application.
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Originally Posted by Bryan Jacobs
(Post 10873443)
I think rx7specialties can modify for a 3rd spark plug.
Rix |
i'd be curious about trailing only if it was timed correctly. ran a TII on the dyno which wound up having a incorrectly installed leading coil pack that was put on afterwards. i know the timing was correct before so i didn't recheck it.
the car made about 247whp with trailings only but came up about 50 horsepower with the leadings working with a different leading coil pack. of course the trailing timing is severely retarded in comparison to the proper leading timing. many people have ran with just 1 plug per housing in the leading position and have had decent results but probably could have had better with both functioning. |
When I spoke to Adam(rx7specialties) he said that these housings are uber rare and were used in rotary generators
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got any pics of these 1 plug housings?
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Originally Posted by Karack
(Post 10873458)
i'd be curious about trailing only if it was timed correctly. ran a TII on the dyno which wound up having a incorrectly installed leading coil pack that was put on afterwards. i know the timing was correct before so i didn't recheck it.
the car made about 247whp with trailings only but came up about 50 horsepower with the leadings working with a different leading coil pack. of course the trailing timing is severely retarded in comparison to the proper leading timing. many people have ran with just 1 plug per housing in the leading position and have had decent results but probably could have had better with both functioning. I would highly speculate on lower chance of detonation in leading only design. As the burn rate is even worse than normaly, for same output from same airflow (which wonīt even happen) it would call for more advanced timing, which on its own defeat its purposse. From above graph we can also see that leading only has higher blowdown pressure so higher EGTs without making good power. Still there are some thing which I donīt understand. Like a fact that zero split is fine even in high boost engine in spite of opinions that it would cause annihilation of human race but trailing firing just small bit ahead at high load will cause immediate engine death:( Barry Bordes testing so far shown that burn rate in rotary engine is without excuse sh*t and peak pressures are extremely delayed resulting in poor HP/airflow and high EGTs. Making it worse by running leading only?:scratch: |
1 Attachment(s)
Originally Posted by Liborek
(Post 10873538)
Still there are some thing which I donīt understand. Like a fact that zero split is fine even in high boost engine in spite of opinions that it would cause annihilation of human race but trailing firing just small bit ahead at high load will cause immediate engine death:(
Barry Bordes testing so far shown that burn rate in rotary engine is without excuse sh*t and peak pressures are extremely delayed resulting in poor HP/airflow and high EGTs. Making it worse by running leading only?:scratch: https://www.rx7club.com/attachment.p...1&d=1322089655 Speaking of burn rate... I know we're jumping around a little bit here, but if you're wondering how combustion phasing/burn rate is measured in engine development see the above data from a study on a prototype Ford Ecoboost V6 engine. The engine was used to evaluate E85 injection. E85 was sprayed through direct injectors while E0 pure gasoline was sprayed in the conventional port configuration. In this case Ford engineers were trying to tweak the timing and the amount of E85 injection. The whole point was to find a balance between spark retard and E85 use for purposes of good torque output without too much E85 consumption. Looking at the graph I boxed, you can see a combustion phasing plot. Y axis is the degrees ATDC at which 50% of the mass in the cylinder is burnt. X axis is load. As load increases, spark is retarded, and the mixture burns later. The ratio of E85 to gasoline decreases and the mixture richens up to keep the exhaust temps from getting too high. |
i don't doubt it, which is why i always run the stock 2 plug system.
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Originally Posted by Karack
(Post 10873458)
i'd be curious about trailing only if it was timed correctly. ran a TII on the dyno which wound up having a incorrectly installed leading coil pack that was put on afterwards. i know the timing was correct before so i didn't recheck it.
the car made about 247whp with trailings only but came up about 50 horsepower with the leadings working with a different leading coil pack. of course the trailing timing is severely retarded in comparison to the proper leading timing. many people have ran with just 1 plug per housing in the leading position and have had decent results but probably could have had better with both functioning. the NSU is a P port too.... |
Very nice, as always:icon_tup:
Their burn rate must be really fast, so low EGTs at stoichiometric AFR (granted its partly due to E85). On rotary it would be over 1000°C:lol:
Originally Posted by arghx
(Post 10873572)
I haven't seen a comprehensive overview of his testing. Normally when testing burn rate there are a few metrics used, such as the crank angle at which 50% of the mass in the combustion chamber is burnt.
Mazda did research of "pilot flame ignition system". Whole paper is called "Research and Development of a Direct Injection Stratified Charge Rotary Engine with a Pilot Flame Ignition System" Todays development seems like joke compared to what these folks were doing decades ago:blush: |
Let me add this to the conversation.
Since I am doing the ignition timing and split testing I thought I would revisit Mazda's papers on the subject. My favorite is the somewhat confusing chart on flame front. I think it is time to decipher it better. (See Attached) At first it makes little sense because the legend's symbols and traces are not well marked and seem to be mislocated. One symbol in the legend had to be interrupted as -15 degrees (or ATDC) for trailing plug to make the chart work correctly. It also helps to know that the actual ignition point is about 5 degrees before the points that were initially shown ( I added extension lines to the actual location). Now you know how I like to color.... it helps to simplify it for me. It looks like the biggest split burns the fastest because it allows the leading plug to spread furthest before the collision with the trailing flame front. What thoughts do you guys have? Raymond, are you going to DGRR this year? I would to talk with you and some of our other thinkers. Barry http://i287.photobucket.com/albums/l...ametravel3.jpg |
When I first bought my rx7 it had the anti-det mod done by KDR. My arm was twisted by several folks so I took out the faux plugs, added a coil pack, & re-tuned. I still have the faux plugs & pfc map if anyone is interested.
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Originally Posted by Barry Bordes
(Post 10915864)
It looks like the biggest split burns the fastest because it allows the leading plug to spread furthest before the collision with the trailing flame front.
What thoughts do you guys have? |
Originally Posted by Liborek
(Post 10873538)
As in other thread, even with timing advanced to reach MBT, it would be poor, as majority of air fuel mixture is pushed to the leading side, no matter if rotor recess is MDR or LDR design. Maybe it could work "ok" if you had rotor with trailing deep recess, but still, it wonīt match dual plug system.
I would highly speculate on lower chance of detonation in leading only design. As the burn rate is even worse than normaly, for same output from same airflow (which wonīt even happen) it would call for more advanced timing, which on its own defeat its purposse. From above graph we can also see that leading only has higher blowdown pressure so higher EGTs without making good power. Still there are some thing which I donīt understand. Like a fact that zero split is fine even in high boost engine in spite of opinions that it would cause annihilation of human race but trailing firing just small bit ahead at high load will cause immediate engine death. Some people do this in the idle and no boost range. Barry |
Originally Posted by Barry Bordes
(Post 10915864)
Let me add this to the conversation.
Since I am doing the ignition timing and split testing I thought I would revisit Mazda's papers on the subject. My favorite is the somewhat confusing chart on flame front. I think it is time to decipher it better. (See Attached) At first it makes little sense because the legend's symbols and traces are not well marked and seem to be mislocated. One symbol in the legend had to be interrupted as -15 degrees (or ATDC) for trailing plug to make the chart work correctly. It also helps to know that the actual ignition point is about 5 degrees before the points that were initially shown ( I added extension lines to the actual location). Now you know how I like to color.... it helps to simplify it for me. It looks like the biggest split burns the fastest because it allows the leading plug to spread furthest before the collision with the trailing flame front. What thoughts do you guys have? Another big factor here are overlap and exhaust pulse interference effects. This is going to depend on engine speed, port timing, and exhaust manifold design (twin scroll should have little interference between the two rotors). I have been studying exhaust pulse interference effects on piston engines, specifically 4 cylinders and the current Ford Coyote 5.0 which has an oddball firing order. On those engines, overlap and exhaust pulse interference contributes to the amount of residual exhaust gas blown back into the cylinder. This affects combustion phasing, pumping work, and the tendency to knock. Ford has published an extensive analysis of 5.0 twin turbo prototypes that deals with this issue. I have not seen full details of the various tests you have been doing. I know you have been using some kind of pressure transducer equipment. Have you generated indicator diagrams from your tests? Do you have specs on peak combustion chamber pressure and indicated mean effective pressure? Raymond, are you going to DGRR this year? I would to talk with you and some of our other thinkers. |
Originally Posted by arghx
(Post 10917030)
The color does help but it's still a very crude diagram with a lot going on. It appears to be hand sketched, as was typical back then. All the newer literature uses 3d solid modeling and visualization which is much easier to understand. I don't have a whole lot to add about that diagram. As I mentioned in an earlier post, I would like to see statistics on combustion phasing--crank angle at which 10, 50, and 90% of mass fraction is burned. Then we could benchmark it to known piston engines.
The program does combustion burn rate. I usually compare runs at the 70% point. It also does peak pressure and location, max rate increase pressure and burn location, horsepower, torque, and IMEP. Getting clean data is essential for the comparisons. I try to get air, water, and oil temps the same for each run. This requires driving for about 5 miles after each stop to check logged data, and then adding a new map for the next test. The real problem is that after a 3rd gear run to 8000 rpm I may or may not have good data. I would estimate my success rate at only about 20%. We think that my old PCIA card equipped computer is the problem. Another big factor here are overlap and exhaust pulse interference effects. This is going to depend on engine speed, port timing, and exhaust manifold design (twin scroll should have little interference between the two rotors). I have been studying exhaust pulse interference effects on piston engines, specifically 4 cylinders and the current Ford Coyote 5.0 which has an oddball firing order. On those engines, overlap and exhaust pulse interference contributes to the amount of residual exhaust gas blown back into the cylinder. This affects combustion phasing, pumping work, and the tendency to knock. Ford has published an extensive analysis of 5.0 twin turbo prototypes that deals with this issue. I have not seen full details of the various tests you have been doing. I know you have been using some kind of pressure transducer equipment. Have you generated indicator diagrams from your tests? Do you have specs on peak combustion chamber pressure and indicated mean effective pressure? Barry http://i287.photobucket.com/albums/l...alignition.jpg |
so in the above screenshot I am seeing 50% mass fraction burnt at about 50 degrees ATDC? That does seem to be occurring late compared to some of the numbers I have seen on piston engines, but those tests are all done on engine dynos. What are the pressure units here? It says IMEP 251... 251 psi? That's about 1.73 mPA/17bar which passes a sanity check at least.
I'm not completely clear what the arrow is pointing to. |
still no pictures of these unobtanium housings...
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Allrotor posted a picture in a forsale thread i believe, i will check.
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It just looked like a plug but I was told by Adam that it is just a stamp in the casting of the housing...only one plug per housing inside
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Originally Posted by arghx
(Post 10918625)
so in the above screenshot I am seeing 50% mass fraction burnt at about 50 degrees ATDC? That does seem to be occurring late compared to some of the numbers I have seen on piston engines...
Most piston engines have highest burn rate around TDC - its logical, very compact and dense space - very short distance for flame to travel. Also burn rate itself has much higher value. Consequently, peak pressure is much higher and much better positioned to make work. 90% of mass fraction is usually burned before 40° ATDC or earlier... We can fiddle with timing, but it still will be poor. Direct injection and stratification of charge is way to go. Or fuel which burns ridiculously fast and is not practical at all - hydrogen:lol: |
puts hand up
have been running leading only wastespark HEI ignition system daily for several years i idle at lambda , i cruise at lambda and at wot under medium boost i run low 13 AFR so would be suffice to say my engine efficiency is UP with single leading plug there is a mitigating factor---- fuel of choice is LPG propane/butane vapour ,, and lambda is 15.7:1 so why is it i am the only rotary i know of that idles at lambda ? and why am doing so with a supposedly lesser single location ignition system ? here is the curveball --- homogeneous mixture charging -something LPG vapour does naturally that petroleum does not- it has a positive effect on flame propogation and burn efficiency ,, burning more completely with stability at lambda ,,, even in the long narrow chamber what happens when i put back in that trailing spark? -nothing positive in terms of running mixtures , still idles and cruises at the same lambda - under medium ( up to 15 psi ) boost with hot soaked inlet manifold with a NGK 10 plug the trailing spark will introduce a light preignition timing revision is then required to push back that preignition threshold quite a lot,, more than 5 degrees off the total timing when done on the microtech ( the dizzy proving a little crude to quantify and the microtech was installed to test various ignition configs ) my current daily config is back to the modded dizzy,, with BIM024 modules with HEC 715 coils and leading only wastepark |
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