patsmx5

iTrader: (16)

Ok, so what is everyone running for MAT based timing retard? Please post what fuel you're running. We know you guys with E85 probably don't even have a table, but the rest of us on pump gas need this feature.

Here's my current table.


93 Octane:


I think this is conservative. To the point I'm tempted to make it less-conservative as it really hurts power as AITs climb, though I'm also trying to improve the AITs too.

codrus

Here's mine. It was originally a lot more conservative than this, but we pulled it back some. It's a long way from being well-tuned, though. I'm using straight 100 octane.



--Ian

patsmx5

iTrader: (16)

Ian- Yours is almost identical to mine. I did all the conversions from C to F and we're very similar curves.

EDIT: I also just read online some systems simply pick a number, (say 120*F for example) and then subract X timing per degree above that temp, flat and linear. I read 2 people with a miata used ~40*C (~104F) and then every degree C above that, minus 1/8 degree.

That would look like
40C = 0
45C = .625
60C = 2.5
80C = 5
90C = 6.25

That's similar to mine below 60*C, but above 60*C, mine is more conservative, as I'm pulling about 1 degree more timing up top.

ihiryu

ihiryu

I'm still pretty noobish, but I run 93 octane here. I driven around with my det cans and haven't heard any knock.

But looking at your timing retard, I might have to pull some timing on mine. What's your IGN map looking like?

Stock MSM on 10 psi for reference

patsmx5

iTrader: (16)

Yeah your setup does nothing until 180, then only pulls 1 deg at 200*F!!! Seems like it's essentially off on your setup.

Here's my timing table. It's not ideal, I pulled 3 deg out of the upper boosted cells and it cost me 52whp... But I saw a tiny amount of metal on the plugs (det) so I pulled timing until I could get the spark tuned better. I actually think the det was happening at high load/low RPM/high AITs but I pulled across the entire table to be safe.

ihiryu

Oh yeah, our timing tables are way different. I only go up to 188 KPA (I actually don't hit this, more along the lines of 180 KPA). I'm only running 17 degrees of timing here.

patsmx5

iTrader: (16)

Ok here's a thought I just had that I'd like to get some feedback on.

When the air temps go up, this basically means that the fuel/air charge is going to be hotter during compression and during the early parts of ignition. Thus more likely to detonate.

I believe a colder mixture burns slower, and a hotter mixture burns faster. So I can kinda see the need to pull timing with higher temps due to this, even if detonation was not an issue. Just to keep peak pressure in the right spot. But I doubt it's much because while it burns faster, hotter air is less dense too so they kinda cancel each other out to some extent.

But in the miata's case, the problem is too hot = detonation. And pulling timing doesn't directly cool the charge, it just shifts peak pressure to the right to prevent it from detonating at the expense of power. Less peak pressure solves the detonation but hurts power.

So.... What about just setting up a fuel enrichment at high AITs and NOT pull timing? This would more or less treat the problem (air is hot) instead of masking it (pulling timing to reduce peak pressure/chance of det but at the expense of power). You would be relying on the extra fuel to help cool the charge. This is well accepted that more fuel helps prevent detonation.

My gut feeling says going from say, 11.0:1 AFRs to 10.0:1 AFRs would make more power than pulling 5-6* of timing and keeping the 11.0:1 AFRs. And I believe both would "fix" the problem of detonation. Thoughts? I think this idea has promise!

codrus

First off, I don't think 1 point of fuel is equivalent to 5 degrees of timing in terms of knock safety.

Second, the existing tables in the MS3 won't do this, because the air density table is a 2d table and you'd want a 3d one. There's no point in running 1-2 points richer when cruising down the freeway just because you're in Las Vegas and the ambient air temp is 116F.

--Ian

patsmx5

iTrader: (16)

Yeah, I just made up some numbers for discussion. I really don't know what the numbers would be either, but they're something. I just wonder if it's a better approach?


You can sort-of do it though, at least well enough to test it. MS3 has the MAT air density correction, and also has time based fuel enrichment option called "high power time enrichment" that would essentially do the same thing, though it would be based on time not temp.

But I'd probably do it based on MAT. And not have it kick in until air temps are pretty high, say +130 for example. That way it only kicks in when actually boosting around.

patsmx5

iTrader: (16)

As an example, you could play with the MAT fuel correction and have it begin adding fuel above 120*F, and by 150*F it's enriching AFRs from say 11.0 to 10.0. And at the same time, you're MAT based timing retard pulls say 1* at 140 and 2* at 160.

So comparatively, with 160*F air temps, I'd be only pulling 2* of timing instead of 4, but adding 1 point of fuel too. The question is, would this make more power? I think it would. My car gets slow when you start pulling lots of timing.

ihiryu

It makes sense, but my fear would be that you'd lose a whole bunch of power that way. Forcing more fuel down the cylinder should help keep it cooler, but it's much easier to pull a bit of timing. I'm interested in results though

patsmx5

iTrader: (16)

Both are easy, I just need a few minutes and a laptop.

I don't know how much power I'd "loose", but virtual dyno shows 3* of timing cost me 52whp on my setup. Thus why I'm curious what would happen if I could keep more timing in it and use fuel to help control detonation. Neither of these are new ideas, we all tune rich in boost to control det, and pulling timing with high AITs is nothing new either.

The question is, would more of one and less of the other make more power? Based on loosing 52whp pulling 3* of timing on my setup, I'm thinking that adding fuel and keeping the timing higher could be a better approach.

EO2K

iTrader: (37)

I agree, I was thinking about this at lunch and it seems like a much better way to go. Certainly better than pulling fuel as does the as-delivered table.

Honestly, I wouldn't be screwing with this as a "make more power" feature, I'd be looking at it as a "make it safer" feature.

codrus

If you're seeing 160F, I think you need a better intercooler. 160F is 70C, I don't even see temps that high on the dyno with pitiful airflow through the intercooler. Looking at my datalog from fuel pressure testing a week or so ago, a 3rd gear pull (at 27 psi!) took the AITs from 27C/80F (which was about the ambient temp) up to 40C/104F.

--Ian

DNMakinson

iTrader: (3)

<p>&nbsp;</p><p><img src="https://cimg4.ibsrv.net/gimg/www.miataturbo.net-vbulletin/576x504/80-mat_timing_retard_dab02c5ea210e69f6150e81ee60c47fc 2faeabba.png" title="" />&nbsp;</p><p>&nbsp;</p>

EO2K

iTrader: (37)

The only time I see temps this high is idling in traffic after the fan kicks on and heatsoaks the hell out of everything under the hood.

But I agree, while you should never see IAT's this high, it would be nice to know that something is watching your back should you loose significant airflow through the heat exchangers or you heatsoak sitting on a grid/in the pits/staging area/burnout box.

patsmx5

iTrader: (16)

Just using 160*F as a number for discussion. Though my air temps aren't as good as yours I will say. Also this blower makes air wayyyyy hotter than any turbo I've ever run.

patsmx5

iTrader: (16)

Well I'm doing it for both I suppose. Make it safer, and while making more power if possible.

Like I mentioned above, this blower makes realllyyy hot air. I'm working on getting my intercooler to work better. Currently it's around 10-15 over ambient in cruise, and will climb an additional 40*F in a 1-2-3 pull to 8,500. It's an ebay bar/plate, maybe it sucks but I ran this same IC with a turbo and it was beast then, more like Ian's numbers.

codrus

Right, I'd forgotten you were running a blower. I have a GTX2863, which is one of the super fancy, new-tech efficient compressors that Garrett is turning out. My intercooler is a standard FM2 unit, nothing all that elaborate.

--Ian