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Old 10-23-2015, 01:03 AM   #4761
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Originally Posted by aidandj View Post
Toyota COPs and some plug gap that someone recommended. It's probably somewhere in this thread. Interesting. I haven't even considered messing with timing because I'd rather it be conservative.
I always attributed the unsteady rpm to timing belt scatter or something.
Interesting that Curly and the tuner didn't catch it on the dyno.
I'd start by check the plug gap. If you don't want to upgrade to a hotter ignition system, just drop the gap until the problem goes away. How strong are the toyota COPs you are running? For reference, IGN1A and the GM coils are both around 100mJ at normal dwell, and both are capable of running more dwell. I can get >200mJ out of the IGN1As by cranking the dwell up, but I keep it at 3.0ms / ~100mJ with a .030" gap and that works at 28 PSI no problem. It took 5.5ms to get it run clean, no misfire at .040" gap for reference. I went back to 3.0ms dwell for coil reliability.

EDIT: I see people post logs all the time that have misfires, somehow people just look over it. Miatas have weak ignition systems from the factory.
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Old 10-23-2015, 01:11 AM   #4762
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Good info. Thanks pat.

I'll look into it soon. Last track day of the season is on Saturday so I'm not messing with anything because I know it works for now.
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Old 10-23-2015, 01:13 AM   #4763
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No problem. Also just thought of this, but the low timing causes high EGTs, might explain your manifold cracking on ya.
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Old 10-23-2015, 01:18 AM   #4764
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Good point. An egt bung was supposed to go in when we welded up the manifold but yank forgot to grab it. I'll put one in over the winter.
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Old 10-23-2015, 02:30 AM   #4765
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Originally Posted by patsmx5 View Post
Yes, RPMs dropping while WOT is a misfire. Think about it, when you're wide open, is the RPM going up, down, or staying the same? Going up of course. If a cylinder misfires, the engine suddenly slows down for a tiny moment in time because that cylinder didn't produce any power, it just wasted power doing nothing.

Other tell tale sign is AFR will be wavy too. Note your AFR bouncing around when it happens and compare to mine. Mine is a dead flat line.

That's a CYA timing table. I wouldn't run it that retarded, it's probably what's causing the misfire. Rich and retarded is how to make a motor misfire.

What plug gap and ignition system do you run?
Ping will also make RPM drop while WOT, as will the car losing and regaining traction (although the latter is much more likely on the street than on the dyno).

Theoretically, cam belt stretch could produce erroneous RPM readings on a motor without a crank angle sensor, but in order for it to go up and down the belt would have to be oscillating and I haven't heard of it doing that.

And yeah, that spark table is massively retarded.

You really can't tune timing on the street, you need a dyno so that you can tell when it's approaching MBT. Ideally you want it to be 1-2 degrees short of MBT, or as high as it will go without pinging. MBT is totally motor-dependent, for example in my dyno tuning today, substituting a test pipe for the cat moved MBT to a point 4 degrees less advanced.

--Ian
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Old 10-23-2015, 03:39 AM   #4766
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No way its ping. I've pushed this motor way too hard. If it was pinging the pistons would be vapor by now.

How do you tune for MBT? I wish dyno time wasn't so damn expensive. Also how do you tune all areas of the spark table? Pulls at different boost levels?

We touched timing once. And didn't gain any power
But that was low boost and before we turned on boost control.
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Old 10-23-2015, 03:58 AM   #4767
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Originally Posted by aidandj View Post
No way its ping. I've pushed this motor way too hard. If it was pinging the pistons would be vapor by now.

How do you tune for MBT? I wish dyno time wasn't so damn expensive. Also how do you tune all areas of the spark table? Pulls at different boost levels?

We touched timing once. And didn't gain any power
But that was low boost and before we turned on boost control.
It's not ping, no way in hell that little boost and low timing, fat AFRs. Pretty much impossible. He was just saying that ping and wheel slip can cause RPMs to do various things in a datalog. Neither of those are present in the log you posted.

Tuning to MBT is another thread, and there's probably already one here. I do it by reading plugs and checking mph at the 1/8 mile. It's a very slow process vs using a dyno, but it works. Reading plugs is its own thread too, and nobody does that on here anyway.
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Old 10-23-2015, 04:22 AM   #4768
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Originally Posted by aidandj View Post
No way its ping. I've pushed this motor way too hard. If it was pinging the pistons would be vapor by now.

How do you tune for MBT? I wish dyno time wasn't so damn expensive. Also how do you tune all areas of the spark table? Pulls at different boost levels?

We touched timing once. And didn't gain any power
But that was low boost and before we turned on boost control.
If you were to graph horsepower vs timing for a given cell, you'd see that as you advance the timing away from 0, the power goes up pretty quickly initially. At some point the curve noses over and becomes mostly flat, and will then slowly decline. MBT is the peak of that curve. Shamelessly swiping a graph that I found on the internet:



(note that the X-axis is degrees relative to MBT, not relative to TDC).

As I understand it, stress on the engine components continues to go up past MBT, so most people recommend tuning the engine to 1-2 degrees below MBT for an optimal ratio of power to engine life.

As for finding MBT, in principle it's simple. You do a dyno run and look at the power, then you advance the timing and compare it. IME, when you're at the left part of the graph, you're gaining 3-4 hp per degree of advance, then when you get close to MBT it's only 1 to 1.5. I typically do it in 2 or 4 degree jumps.

If you somehow wind up *past* MBT, you'll find that adding timing either doesn't change power, or can actually result in less power. If that happens, you want to take a BUNCH of timing out to get back to the (much safer) left side of the graph, then work your way up towards MBT.

Since you're looking at differences in the single digits of horsepower, you need to keep as many of the other variables constant as possible. One major problem here is that as you change the timing, you will change how the turbo responds. If you're using open loop boost control, this means that you'll change MAP by a few percent, and that can totally mask the timing-related power change. In particular, advancing the timing tends to give less boost, because you're expanding the combustion gasses more in the cylinder (thus extracting more work), but that leaves less energy in them for the turbine to use, so to do the same work on the compressor wheel it will need the wastegate to be more closed. Good closed-loop EBC will make this much, MUCH easier to do. If you've seen Jason's post about why the dyno should display torque/MAP instead of just torque, this is why.

Another variable that you need to pay attention to is the air intake temps. Since you're not actually moving on the dyno, the intercooler tends to heatsoak, and if you do two pulls too close to each other then you'll get significantly higher air intake temps. If you have the AIT trim table set to pull timing at higher temps, then you could potentially end up with less actual timing even though you've dialed in more in the spark table. Coolant temp can have a similar effect, although it reacts more slowly.

So you'll want to datalog each run on the dyno in the MS, and review it and the dyno output together.

Obviously if it pings before it hits MBT, you have to stop there. In fact, you probably want to back off a couple degrees from that point, because when running on the street (or even worse, the track) the engine spends a lot longer at a given load value than it does in a dyno sweep, so it's more prone to ping.

There's no real rocket science to it but there are a lot of things to keep track of, and when you're sitting in the car on the dyno you tend to be very aware that it's costing $2/minute, so there's a tendency to rush. It's easy to miss stuff when you're doing that. My first dyno session for the current motor I had been validating the base timing just before strapping it down, and had forgotten to set the MS3 back to using the timing table. I did 4 or 5 runs at a fixed timing of 10 degrees, puzzling over why the motor wasn't responding to ANYTHING I did before I realized what was going on.

--Ian
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Old 10-23-2015, 01:28 PM   #4769
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Thanks Ian. I'll be doing a lot more reading soon.








Thanks Brian!
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Old 10-23-2015, 01:47 PM   #4770
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Quote:
Originally Posted by codrus View Post
...MBT is totally motor-dependent, for example in my dyno tuning today, substituting a test pipe for the cat moved MBT to a point 4 degrees less advanced.

--Ian
Curious, what is your timing at 5K and 7K? Also at what boost pressure and fuel type/octane?

I'm finding my motor doesn't want as much timing as other miata motors running E85. And I'm not even running that much boost (just 16-18 PSI).
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Old 10-23-2015, 03:31 PM   #4771
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Originally Posted by patsmx5 View Post
Curious, what is your timing at 5K and 7K? Also at what boost pressure and fuel type/octane?

I'm finding my motor doesn't want as much timing as other miata motors running E85. And I'm not even running that much boost (just 16-18 PSI).
24 pounds of boost, 100 octane. I'll post the spark table in my build thread, rather than cluttering up Aidan's (well, OK, that battle was lost a long time ago, but still).

posted here:
Ian's 99 post-TB screw re-rebuild.

--Ian
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Old 10-23-2015, 05:12 PM   #4772
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Thanks Brian!
Nice! Glad it got there in one piece!
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Old 10-24-2015, 07:19 PM   #4773
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Quote:
Originally Posted by aidandj View Post
Interesting that Curly and the tuner didn't catch it
on the dyno.
Couple of things:

1. If that's a misfire it's miniscule.
2. We went to 220 once, never tuned timing because it was already in rod bending territory.
3. Don't listen to a damn thing patmx5 says, he's a moron.4
4. Do #3 again.
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Old 10-24-2015, 07:26 PM   #4774
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Did not mean any disrespect on your tuning Josh. Just was interesting because I know you have quite a bit if experience and Kris is very knowledgeable. Conservative timing is probably what has kept my motor alive for a while. I just got an EGT bung and will be installing it soonish. That will tell me more about the timing.
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Old 10-24-2015, 07:44 PM   #4775
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I'd focus more on knock control, that'll tell you more about what kind of timing your engine can take. EGTs is mostly theory, but in practice every engine is different.

I'd tune for knock, and use that as your max, then tune timing to please your EGT gauge.
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Old 10-24-2015, 07:45 PM   #4776
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Couple of things:

1. If that's a misfire it's miniscule.
2. We went to 220 once, never tuned timing because it was already in rod bending territory.
3. Don't listen to a damn thing patmx5 says, he's a moron.4
4. Do #3 again.
1. Yes, agreed it's not a major misfire. It is a misfire though.

A moron? Seriously? I'm not attacking you, or the OP. Or anyone.

If you think I'm a moron, perhaps you could be more civil and explain whatever I've said that leads you to that belief. OP posted a log with a misfire in it under high load, I told him it had a misfire. I don't think that makes me a moron.
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Old 10-24-2015, 07:54 PM   #4777
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Did not mean any disrespect on your tuning Josh.
Same for me, I have no disrespect either. Keeping the tune safe is the best way to tune it, especially if you're tracking the car.
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Old 10-24-2015, 07:57 PM   #4778
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I had a feeling it weren't just me.

The things you do are pretty solid evidence, the things you say. Its pretty clear you've got a thin grasp on this stuff, but you run around as if you're the primo authority on anything and everything.

If I went and found all posts of yours for proof I'd be here forever. Basically anytime you say someone is attacking you is a pretty solid contender, because that's all you focus on rather than considering why you might actually be wrong.
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Old 10-24-2015, 08:02 PM   #4779
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I had a feeling it weren't just me.

The things you do are pretty solid evidence, the things you say. Its pretty clear you've got a thin grasp on this stuff, but you run around as if you're the primo authority on anything and everything.

If I went and found all posts of yours for proof I'd be here forever. Basically anytime you say someone is attacking you is a pretty solid contender, because that's all you focus on rather than considering why you might actually be wrong.
I'm not an authority on anything, just a guy with a miata. I do have a thin grasp on some things, that's true. I don't know everything. I have my car apart right now making design changes to my SC system because the first design wasn't good enough. And found a brace I welded that cracked too, a testiment to my less-than-great welding skills.

I guess that makes me a moron. Oh well.
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Old 10-24-2015, 08:32 PM   #4780
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Knock sensor is on the list. I have one on my VVT block. Need to get a knock module and some det cans.

Egt is easier to install and monitor. But its all going to happen eventually.

Please no arguing in my ramble thread. People might have trouble finding things about my build if you argue too much
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