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Old 11-05-2007, 01:44 PM   #21
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Its great for grasping tuning concepts. Thats where you need to start.
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Old 11-05-2007, 01:45 PM   #22
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tuning fuel is pretty cake, its the timing that will generally make or break you.
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Old 11-05-2007, 01:47 PM   #23
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What exactly do you want? A manual for specifically tuning a Miata? Isn't generic what you are after, being that you want the theory behind tuning?

You aren't looking for being on the bleeding edge of things, sounds like you are more worried about being safe. Safe numbers should be pretty easy to arrive at at the cost of ultimate performance.

Maybe you should just ask your questions here, lots of good experience with <gasp> Miatas and the MegaSquirt. What is it that you want to know?
Sorry. I'm still unsure on the relationship of AFR, EGT, and spark. I know all 3 are independantly variable. How do I know what EGT is safe if I have to roll timing back to reduce knock, since adding fuel won't add anything to cool egt. Also, I don't know what parameters for AFR based upon load are safe.

And with all this talk about safety, how do I determine a happy medium between safety and fastness? I guess with knock I just roll timing forward until it stops making power...right?
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Old 11-05-2007, 02:13 PM   #24
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I agree with WOT- the book is good for explaining the basics, though I don't think there's anything in there that I haven't found on the internet. I think anybody with a standard car IQ can put a safe reasonable tune on the car. It's building a safe powerful tune that's difficult. Then you really have to examine all the parameters. And I think at that point is when a load based dyno is going to make the job a lot easier. I personally wouldn't want to own a project car without understanding the tuning process.
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Old 11-05-2007, 02:42 PM   #25
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I might install my mspnp and play with it on the stock 1.6. Maybe that will help me inspire some confidence.
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Old 11-05-2007, 02:43 PM   #26
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Buddy of mine was telling me about his experience tuning on a load based dyno. He said at 4000 rpm he found the timing advance that he made the most power at, he then increased it by one more degree and found that it dropped his power output by 1. There is a point where you will make the most power and you can advance it too much the poing where you actually make less.

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I might install my mspnp and play with it on the stock 1.6. Maybe that will help me inspire some confidence.
You really should. Mess around road tuning, you instantly start understanding things better when you can see how things affect the cars drivability.
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Old 11-05-2007, 02:55 PM   #27
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Buddy of mine was telling me about his experience tuning on a load based dyno. He said at 4000 rpm he found the timing advance that he made the most power at, he then increased it by one more degree and found that it dropped his power output by 1. There is a point where you will make the most power and you can advance it too much the poing where you actually make less.



You really should. Mess around road tuning, you instantly start understanding things better when you can see how things affect the cars drivability.
Can I leave the AFM plugged in and still see MAP values? I want to play with it, but I still don't understand what tells you to fatten up the AFR as load increases. What is the indicator for that curve?
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Old 11-05-2007, 03:02 PM   #28
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The MAP values come from a vacuum line you attach to your intake manifold. So yes you can see them the MAF has nothing to do with it. The indicator for you AFRs is your wideband and datalogs. You can drive it under all different load conditions and datalog it everytime. Then go back and analyze what is going on. Autotune will adjust your VE tables for you as well, if your table is lean it will fatten it up for you based on your VE targets you set.
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Old 11-05-2007, 03:09 PM   #29
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The MAP values come from a vacuum line you attach to your intake manifold. So yes you can see them the MAF has nothing to do with it. The indicator for you AFRs is your wideband and datalogs. You can drive it under all different load conditions and datalog it everytime. Then go back and analyze what is going on. Autotune will adjust your VE tables for you as well, if your table is lean it will fatten it up for you based on your VE targets you set.
****, I'm a dumbass. I was thinking IAT, and duh, the AFM will report that. How do I know what AFR's are appropriate for each load cell? I still have to set the parameters for EGO correction, but how do I know what is appropriate at each load cell for AFR?
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Old 11-05-2007, 03:17 PM   #30
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just keep in mind that 12-12.5:1 is ideal for boost, and 13-13.5-is ideal for WOT N/A and 15.5-16.5:1 is ideal for cruise. Fill in the gaps.
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Old 11-05-2007, 03:20 PM   #31
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just keep in mind that 12-12.5:1 is ideal for boost, and 13-13.5-is ideal for WOT N/A and 15.5-16.5:1 is ideal for cruise. Fill in the gaps.
so those are safe too? I assume AFR is solely load based, and not rpm? Does the AFR need to increase consistantly with kpa, or some funky ratio?

Am I over-thinking this?
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Old 11-05-2007, 03:29 PM   #32
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you are over thinking it some. afr needs to increase more or less linearly with load. I think its a good idea to go richer at the very top (11-11.5:1), at say 14-16psi, especially on our cars if you don't have a dual feed rail. that's just supposition though.

remember that rpm and load depend on each other in that you won't be revving 7k and have 70kpa load, and you wont be boosting 15psi at 2k.
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Old 11-05-2007, 03:34 PM   #33
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and dont forget 14.5-14.7 for idle. otherwise I agree with John C Al Hounous.

you can't really increase AFR with kPa or you'll end up at 30 psi with 5:1 AFR or something silly. I do run 12:1 out at 10 psi though.

if I had to pick an order for factors that alter engine combustion, I'd do them in this order:

1. Fuel (AFR)
2. spark timing
3. boost

In that order of priority, you can narrow in on a "perfect tune". That doesn't mean you'll make the most power, but you'll make the most efficient power.

Beyond that, efficient power is knock limited.

So basically:
1. dial in your AFR
2. dial in your timing (so that advancing more doesn't add power anymore)
3. repeat 1 and 2 until you make the most power per psi.
4. run as much boost as you can before knock.

I didnt mention EGT because 1 and 2 will take care of it for you basically. properly timing the ignition event will prevent burning charges from going out your exhaust valves and keep EGT under control.

matt
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Old 11-05-2007, 03:47 PM   #34
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Thanks guys. I'm still confused on kpa and AFR. I understand the maxima and minima relationship with kpa and rpm. I only understand the maximum and minimum figures, I don't understand what ratios make sense, and what indicates a "good" afr at partial load percentages. I think this is very important considering TPS-based boost control on large tracks where I'll be using lots of maintenance throttle.

After you guys answer this question, I promise to let the thread die.
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Old 11-05-2007, 03:53 PM   #35
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ITs cool to go back to the MS forums and realize how much I've learned over the last year. I never could read stuff over there because it was like another language. Now I see that only a few threads over there even belong. Apparently no one reads the megamanual before posting.
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Old 11-05-2007, 04:29 PM   #36
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Quote:
Originally Posted by hustler View Post
Thanks guys. I'm still confused on kpa and AFR. I understand the maxima and minima relationship with kpa and rpm. I only understand the maximum and minimum figures, I don't understand what ratios make sense, and what indicates a "good" afr at partial load percentages. I think this is very important considering TPS-based boost control on large tracks where I'll be using lots of maintenance throttle.

After you guys answer this question, I promise to let the thread die.
below atmospheric, the numbers are pretty well mapped by doods everywhere. you can re-find this on a dyno with your car now if you want but you'll probably come back to around 13.2-13.5:1 AFR. at part throttle it doesn't matter as much as long as you're in the ball park.

you really want to stick around the rich side of stoich between idle vac and approaching WOT. for simplicity, I do a straight interpolation between 13.3ish and 14.7ish from WOT to idle and it works fine.

but since you bring up boost and part throttle, remember that the base fuel map doesn't actually know what your TPS is. it knows MAP and RPM.

100% TPS @ 5000 rpm and 10 psi is going to use the same amount of fuel as 30% TPS @ 5000 rpm and 10 psi.

what was the question again?
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Old 11-05-2007, 05:26 PM   #37
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Originally Posted by hustler View Post
Thanks guys. I'm still confused on kpa and AFR. I understand the maxima and minima relationship with kpa and rpm. I only understand the maximum and minimum figures, I don't understand what ratios make sense, and what indicates a "good" afr at partial load percentages. I think this is very important considering TPS-based boost control on large tracks where I'll be using lots of maintenance throttle.

After you guys answer this question, I promise to let the thread die.
For turbo cars with a MAP sensor load is always determined via KPA, it's not really a 100% accurate for measuring mass air entering the combustion chamber so you pretty much map the increase assuming that the load increases linearly which means that you often will increase the AFR as you get higher in load.

At idle and in vac conditions (light load on a turbo motor) you will go with AFR ratios as lean as possible without causing knock or rough running. So the process here is to start around 13.5-14:1 and advance the timing as far as possible without knock. Then you want to pull fuel until power falls away or EGTs start to rise significantly. At this point you might want to add a small amount of fuel and remove maybe a degree of timing to get the best power.

Under boost (Above say 2 PSI) you want to start with about 13.5:1 AFR and then tune timing and fuel for best power. As boost increases you should quickly move to your optimum A/F ratio. This can be anywhere from 11:1 to 13:1, depending on your vehicle. The important thing is to tune to what the engine whats, not what you think it should be.

As others have said, start with the basic fuel curve and then move back to timing. Start with a conservative timing curve and then add more timing as needed. Once you get to best timing for power without knock you should be in the neighborhood. I would initially shoot for around 12-12.5:1 and see if you can run less fuel with the same timing after you dial in the initial curve. You may need to add some extra fuel at the torque peak. You may also add fuel to see if additional fuel provides more power, it usually won't, occasionally it will but only because it's suppressing knock usually.

Mark
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Old 11-05-2007, 05:32 PM   #38
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you guys are making it harder than it is:

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Old 11-05-2007, 06:49 PM   #39
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BHAHAHA, tuning fork FTMFW!!!!!
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Old 11-05-2007, 07:03 PM   #40
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+1 for installing the MS on the stock motor, and screwing with it. If you try to understand every nuance of tuning before you even make any changes, you're never gonna do anything. Start with the raw basics: take someone else's base map, and start tweaking it. You will learn far faster by just taking those initial steps.

I found it really easy to dial in my fuel map, based on everything I've heard from various people. Spitfire EFI (the guys who taught me what I should be doing to start dialing in the MS they built for me) said to shoot for 10-15% rich at high load. Watching the green cursor on the fuel tuning UI gave me a good idea of what kpa ranges were "high load" based on what my right foot was doing, and how hard the car was working. I also then discovered through trial and error, that the car seemed to like being closer to stoich at low RPM high loads (like <2000rpm). When I installed my turbo, I just tried to taper the boost to hit around 12:1 at 5psi and like 11.5:1 at 10psi.

Lately I've been learning through trial and error what kind of changes make the car behave differently at idle, and startup, etc. (god, f'ing startup is going to make me insane).

All the while I've been running on the MSPnP base timing map. Some day I'll hit a dyno and learn how to tune timing.

I learned what detonation sounds like by having 20+ degrees of timing at 90+ kpa 1000-2000 rpm.

I'm certainly nowhere near being a "good tuner", but you definitely sound like me, in that you want to know all the details before you start working. You just gotta grit your teeth and jump in.

-Mike

EDIT: BTW, the most useful tuning I've done for anything other than start/idle has always been when someone else is driving. Find someone with steady feet (sometimes left foot braking to hit and hold load cells is required), while you sit in the pax seat with the laptop, watching what's going on, and making changes on the fly.

Last edited by grippgoat; 11-05-2007 at 07:14 PM.
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