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RX7 tuning questions (low compression post break in)

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I've been watching HPA videos for a while and I have a similar build RX7 that I've been tuning to the one HPA did their RX7 series on. I wanted to know, what spark plugs did you guys use during the tuning process? I saw it looked like the 393hp WOT pull was on the base map AFR and Ignition tune from Adaptronic?

I'm using a very similar setup, Adaptronic Modular ECU, 500hp Turbosource kit with IGN 1-A coils, but with an EFR 8374 IWG turbo and 4x 1700cc injectors on US 93 pump gas. At 1100 miles when I finished the break in process, I had around 90 PSI compression, both rotors and all faces, using a normal piston compression tester. After that I started doing quick pulls at full boost 15PSI (my turbo currently spools to 10psi at 3k rpm and quickly ramps up to 15psi from 6000-6500rpm), and now, at 1500 miles I have around 60 PSI front and 70 PSI rear where all faces of each rotor are very close to each other. I can't figure out why I've lost so much compression in 400 miles.

I have a half bridgeport FD with OEM Mazda seals using a similar map to the Adaptronic and Turblown base maps, but I have taken around 1-2 degrees of timing out everywhere to be a little safer, and added a little more target fuel (around .2 AFR throughout the target AFR table). My engine builder says the pictures I sent him of my spark plugs show detonation (due to the center electrode being burned back a little and rounded at the tip on my trailing plugs, however my leading plugs, that I changed a couple 100 miles before my 90PSI compression check, look normal on the electrode), but I can't see how it was detonating unless it's due the heat range of the 4x Bur9eq spark plugs I've been using. I was planning to switch to race plugs this week so I could push the engine harder and thought the plugs would be fine for light street pulls and driving. I've been hitting 15psi of boost, but only for a few seconds at a time on quick pulls through 2nd and 3rd gear and most of my MAP in high rpms where it hits 15psi has been running below target (in the 10 AFR range) since I haven't finished dialing the MAP in.

As far as knock sensor readings, I just can't really tell what's noise and what's knock. All I can say is generally when I'm off throttle I'll see anywhere from 0 to .03 plus sometimes random spikes into .1x, when I get around 0PSI I'll see more elevated levels around .05 and maybe spikes higher, and when I get more into boost I'll see random spikes into the .1x values. But it would also randomly spikes to .3x in the middle of fuel cut after a few seconds being off throttle. Sometimes I'll see periods of 0 on both rotors as well in all pressure ranges, but I haven't really found a pattern, and these spikes happen a lot of the time when my AFR's are richer than targets.

I also wonder if maybe it's a result of wear due to carbon buildup from running rich or premixing 1oz/2gal plus using the OMP that could have worn down the apex seals? It's awfully quick though...

If you guys can provide any advice about what I should do or any help it would be greatly appreciated.

You can bow seals with too much heat on the exhaust stroke but I wouldn't have thought that would be a problem. I assume you are throttle open plug out on the other rotor for the compression test?

If the side seal clearance was a bit loose to start with and they have bedded onto the corner seals that could be a problem.

2 stroke oil should be helping if anything.

Is it a secondary bridge only? Not something sill like it's more warmed up and warm up throttles are open letting more air push back on the late port timing? Is it cranking at the same speed?

Might be worth trying to have a look at the apex seals with a bore cam in the leading plug holes or exhaust ports.

Yeah I know heat is usually what bows seals, but I really thought the tune was safe enough if I added a little more fuel to cool it down and lower the timing a little, especially because I was using the Bur9eq plugs, which most people say not to use past 10PSI. And I figured if I kept the amount of time on WOT down it wouldn't hurt anything. I also let it run rich as I'm coming off throttle to help cool down the combustion chamber. Really wish I had just swapped to race plugs as soon as I finished break in to eliminate that as a potential problem.

So I only removed the plug on the rotor that I was testing, but I did try both throttle closed and open, but it didn't seem to make a difference. I'll probably try doing another compression test though and maybe give that a shot. I think normally it's done with only the one spark plug removed for the tester though.

The 2 stroke oil I know, but I'm using the OMP as well and I'm using Adaptronic's OMP table. I don't really know how if they're injecting more or the same amount of oil as stock, and I know if too much crank oil is injected it can build up carbon plus lower the octane rating of the fuel. I'm thinking of the SPM (spark plug mountain) where carbon builds up if your spark plugs are too hot. Supposedly a cooler plug is supposed to reduce this along with reducing the chance of detonation.

The bridge is actually on the primary port. I didn't know the half bridge was normally done on the secondary ports, and didn't find out until I had already told my engine builder I wanted them on the primaries. But I believe even on a full bridgeport people see 100+ compression numbers on fresh rebuilds.

I do believe the cranking speed is the same. It sounded the same speed, and when I recorded the slow-mo videos of my compression tester I tried to calculate the speed using the time stamps on the video from my iPhone and it came out to 250 rpm. Not sure exactly how accurate it was, but that was one of the things I was thinking of though. Wish I had a real rotary compression tester.

You might find there is someone nearby who has one. I actually took mine to help a guy I went to primary school with a couple of weeks ago. If there a Facebook group or state forum that's active in your area on rx7club?

Carbon deposits are normally a problem with too-cold plugs.

As was mentioned, you really need to use a proper wankel compression tester to see if it's all faces or just one. If all are equally low on only one rotor, it suggests it may be a housing issue, all low on both rotors maybe a build or tune problem. If it's only one or two rotor faces, it suggests a rotor seal problem.

It sounds like you're both doing the OEM oiling system and pre-mix? From what you said, the pre-mix is 1:32, most good quality 2 stroke oils are good for closer to 1:50 for 2 stroke engines, so if both used you may have carboned up the seals, causing them to stick?

Well I'm sure it's all faces are even and low. You can tell the pressure difference by removing the schrader valve on the piston compression tester and viewing it with a slow-mo camera like what the iPhone has. But if the cranking rpm's are low then it would generate overall lower pressure readings on the piston tester and a proper rotary tester would normalize the readings based on rpm.

And yeah, I talked to the engine builder earlier and he says the seals wouldn't be sticking. I don't know though, I still want to try disconnecting the OMP and see if I can get any compression back if it's carbon buildup or something. Plus I want to see if the knock readings change in the Adaptronic logs since conventional oil reduces the octane rating of the fuel.

Nearly everyone making half decent power on a single does go to 10, 11, 11.5 heat range iridium plugs and IGN01A, GTR or similar coils.

That is a LOT of 2 stroke, I used to run 100:1 premix on my NA 12a without OMP (flow tested when we got it running and it wasn't working). Even e85/methanol drag guys with the poorly treated "mild steel" housing eaters are only running about 80:1 premix from memory. I would back off a bit.

And going to colder plugs this week was my plan. I just hadn't ordered them yet. But I was hoping to hear from anyone with experience running 4x of the Bur9eq plugs and if they had any problems with light street driving, or if anyone could confirm that those plugs would cause detonation at even the shortest periods of time in WOT with my setup. I'm definitely regretting not buying colder plugs sooner so I could eliminate that possibility. =(

I ran 9s in mine on factory s8 turbos, exhaust & tune, didn't have any problems, did free practice track days in it.

Have 9 equivalent Denso iridium in it now but will go colder in NGK with the single setup.

I wouldn’t think they are a big risk for a squirt on the street.

I'm not sure what is going on with your compression there Derek but you should be pretty safe with the stock adaptronic map, particularly if you've pulled a little timing. A couple of things to point out:

1. 1100 miles is very much overkill for a brake in on any engine, rotary or piston. After the first 100 miles it's about as run in as it's getting - get out there and enjoy it.

2. If you'd suffered detonation then you'd know about it because you'd likely be missing an apex seal or parts there of. This is why I don't believe in knock control/detection on a rotary - If the engine knocks it's usually already damaged unless you've been incredibly lucky.

3. Our engine is about 420 whp on pump gas and 15 psi. We run the NGK 10.5 plugs which i feel is a little better suited to the power levels. Your 9's 'should' be ok but I prefer to err on the side of caution, particularly if it's likely to see a race track.

4. Your pre mix is very rich compared to what we run, however I've yet to hear two rotary engine builders or tuners agree on the 'correct' amount of premix. All I can tell you is that we run 150 ml per 20 litres (about 130:1) and we don't run the factory OMP either. If you're running premix then there really shouldn't be much reason to retain the OMP unless you want to use over run fuel cut off.

5. You can get a lot of variation in your compression readings depending whether the engine is hot, cold, or warm. Make sure it's always done from the same condition.

Keep us in the loop with what you find.

I'd be curious what your EGTs were. While Reduced timing and more (sometimes too much) fuel is great for combustion event safety it can/will tend to increase EGTs as well. Since you've got such an even drop in compression I'd suspect a heat related stress on a sealing part; also since they're OE seals - which I don't see bow very often - I'd look at the springs first.

That said, just about everything Andre just said I'd agree with, and I'd reiterate that cold compression almost always reads higher so don't fall into that trap.

Thanks a ton for the advice guys. I will keep you updated soon. Unfortunately I went to check the timing yesterday and my front rotor IGN-1A trailing ignition coil went bad. It started smoking like crazy a few seconds after I started the car. Thankfully it didn't happen when I was out for a drive last week.


This is the dwell settings table I'm using from a thread I found in RX7 club, but converted to ms for adaptronic. Can anyone confirm if this is too much dwell time? I'm currently using the wasted spark configuration because I haven't put in an extra wire for direct fire yet.

Also I did do a cold compression test yesterday just out of curiosity. I know it's not the same reading as warm, but I did see around 80psi across the board which is strange to me considering there was a 10psi difference between front rotor and rear rotor when the engine was hot.

But after talking to my engine builder again, I saw what he meant about the spark plugs. I thought he was referring to the trailing spark plugs being rounded but smooth, which I've seen other people have issues with that with IGN 1-A plugs eating the electrode, but my leading spark plugs were burned back on the electrode at the tip. It was rough and bumpy and that's what he was talking about. So I guess I have had some detonation and I got lucky that it hasn't broken off an apex seal.

At this point I'm going to change the plugs, and get a new ignition coil, and try driving the car without the OMP operating. I want to see if the knock readings drop if I inject less conventional motor oil and put in colder plugs. Hopefully I can confirm the cause of detonation and eliminate it before I have to rebuild the engine. Then I'll try another compression check after driving for a little bit to see if it changes at all. I don't have high hopes because I know it's unlikely to get any compression back, but fingers crossed I can clear out carbon build up and get some use out of the engine before I pull it out.

Pic of my rotor when I pulled my turbo the other week. It looks like there was a good bit of carbon built up. Curious if it's alarming to anyone.

Carbon Buildup?

Rotor looks clean. That's way too much dwell for wasted spark. At 15 psi you shouldn't need more than 3.5ms to light off even methanol.

Odd that a trailing coil cooked they are sequential, it's the leading which is waste spark. I have a dwell vs duty cycle for waste and sequential table in a spreadsheet I can email you if you would like.

You should probably be fine with 2.5ms.

Those dwell numbers are around 1.5-2MS higher than I've found needed for clean combustion almost across the board, and on the verge of what I've seen as the 'rule of thumb' for them as far as safety. I haven't, however, roasted one personally from anything other than a single bonehead wiring mistake so don't take what I'm saying as gospel.

Also, I've never used and what your engine builder is describing as a marker for detonation on a rotary engine though he may know something I don't.

I've ordered a rotary compression tester so hopefully I can get that soon, and get a new coil too.

So you can see it here, the trailing plug electrodes look pretty normal, like they're just being worn down and rounded at the tip. But the Lead electrodes look bumpy, which I guess means it's being burned down unevenly. I mean I've never heard of this happening before either, but that's what the owner of Pettit Racing says is happening. Might be something only seen on these type of spark plugs. You can also see oil in the threads and on the crush washers.

Attached Files

I like and respect Dan/Pettit but I still don't see that as a detonation indicator on a boosted engine. He's got far more experience in the naturally aspirated race world than I do though, potentially there's some odd low load high timing based wear that can be caused. I'm not certain.

That looks like a new electrode with carbon deposits, which would be expected with the big premix and OMP. It still has a really clear perpendicular edge. If they are worn/melted they round off. I'd say you may have gummed the seals up a bit with carbon. EGT monitoring would definitely be a good thing. A bit of water injection on boost and some revs and load with less oil might clean it up.

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