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Frozen Lake Driver
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1,292 Posts
Discussion Starter #1
Ok so before attempting to screw around with my AEM EMS Anymore than I already have I decided to maybe try and learn some basics about tuning.

So now I'm completely stuck on VE Or Volumetric Efficiency. I understand what it is and how it contributes to the overall equation, but the part I can't wrap my mind around is how you calculate the actual VE. Since this is one of the essentials to tuning I wanna understand it completely and properly.

Any help would be greatly appreciated.
 

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Madd Tyte JDM yo ®
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7,014 Posts
Are you asking this because you want to write a base map from scratch? If so... There is a big problem here. Especially since the arm tables are shown in either raw numbers, percentage or something else. The ve table is indicative ofthe raw airflow the engine can pump at any given rpm/load(pressure) point. The highest ve cell is where the peak tq can occur. Calculate it against the rpm
And thats where the hp comes from. And the fuel necessary for that ve load cell is directly related. More ve = more fuel. I haven't looked at an aem in yrs so I hope someone else can add more info.

Idk what you wanna do but I'd start with a base map as close to your setup as possible. Then turn on auto tune, use small/lightly weighted values so it makes Gradual changes, and use the o2 feedback feature with logging turned on. That way you can dictate what o2's you'd like to achieve in any given load cell with your rough base map as the starting point. If you try to make too drastic of changes with heavily weighted Adjustments, its likely the corrections will overshoot/overcorrect and it wont be successful at honing in on your pre-selected o2 targets.
 

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Frozen Lake Driver
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1,292 Posts
Discussion Starter #3
Ok Maybe i wasn't clear On what I was actually looking for.
The supra was tuned by one of the pro's here on the coast and is running pretty good (A bit rich with 720 injectors on batch fire). What I'm trying to do is understand how VE is calculated so that I can understand the basics of tuning and then tune the motor myself once the ECU comes back from getting some Injector drivers repaired (was giving an improper sequential wiring Diagram).

I got a few equations off the net on how to calculate it but most of them were using a MAF to calculate the VE which I'm running a MAP sensor which throws me off. I Think I've got some of the basics down to it and I understand how it takes place in the whole tuning world. But i feel if I understand how it's properly calculated and taking into consideration with the whole outlook of tuning I'll get to where I wanna be a lot sooner.
Hopefully this makes a bit more sense lol.
 

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Frozen Lake Driver
Joined
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1,292 Posts
Discussion Starter #4
Are you asking this because you want to write a base map from scratch? If so... There is a big problem here. Especially since the arm tables are shown in either raw numbers, percentage or something else. The ve table is indicative ofthe raw airflow the engine can pump at any given rpm/load(pressure) point. The highest ve cell is where the peak tq can occur. Calculate it against the rpm
And thats where the hp comes from. And the fuel necessary for that ve load cell is directly related. More ve = more fuel. I haven't looked at an aem in yrs so I hope someone else can add more info.

Idk what you wanna do but I'd start with a base map as close to your setup as possible. Then turn on auto tune, use small/lightly weighted values so it makes Gradual changes, and use the o2 feedback feature with logging turned on. That way you can dictate what o2's you'd like to achieve in any given load cell with your rough base map as the starting point. If you try to make too drastic of changes with heavily weighted Adjustments, its likely the corrections will overshoot/overcorrect and it wont be successful at honing in on your pre-selected o2 targets.
After reading your post a second Time I see what you mean as far as getting where I wanna be with tuning, But is it also so that VE isn't as big a factor here as I think it is as the ECU will calculate it for me and then I have to work with that or will I need to calculate that first and then start from there?
 

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Madd Tyte JDM yo ®
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7,014 Posts
Oh I see.

Then yes, the map sensor assumes you ALREADY know the ve curve of your particular app. Tyats why you'll have difficulty with it. A maf sensor is required to build an accurate ve table to begin with. This is the basis for building a boost comp map. If you think you need to recalc your ve table, reinstall your maf and log everything under all driving conditions. Try to keep it out of boost. Once you can build a ve table usin the maf inputs (which actually determine how much air the engine really is ingesting) under 1 atmosphere of pressure, buildin a fuel map for TWO atmospheres of pressure is simply a matter of extrapolating the ve curve from 1atmosphere of pressure. The ve of the motor always stays the same. The pressure is the only thing that changes.

At least, thats my loose grasp on ve and boost comp
 

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Frozen Lake Driver
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1,292 Posts
Discussion Starter #8
Oh I see.

Then yes, the map sensor assumes you ALREADY know the ve curve of your particular app. Tyats why you'll have difficulty with it. A maf sensor is required to build an accurate ve table to begin with. This is the basis for building a boost comp map. If you think you need to recalc your ve table, reinstall your maf and log everything under all driving conditions. Try to keep it out of boost. Once you can build a ve table usin the maf inputs (which actually determine how much air the engine really is ingesting) under 1 atmosphere of pressure, buildin a fuel map for TWO atmospheres of pressure is simply a matter of extrapolating the ve curve from 1atmosphere of pressure. The ve of the motor always stays the same. The pressure is the only thing that changes.

At least, thats my loose grasp on ve and boost comp
That's the thing, Nothing on my engine is really stock anymore, there is no way I could hook the MAF back up since I'm running a T67 turbo and also I sold it. I'll see If i can find some way to measure the actual input of air. Otherwise I guess i'll have to see If i can find another way to calculate this (or maybe the guys who tuned my car already did, So I should ask them)
Thanks for your input.

In another thread didn't you say you bought a megasquirt2? Now you have a aem?
Nope I've never even contemplated buying megasquirt lol
 

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Madd Tyte JDM yo ®
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7,014 Posts
You could always hook up a maf. Just find a 4" to 3.5" reducer and stuff it in there. Just idle and drive around nicely. You don't really need to hit any positive manifold pressure. In fact, pullthe spring out of the wg and let it blow open. Then you'll be able to hit wot and not worry about fuel cut. That should map your ve across the entire rpm range and everything below 1psig
 

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Moderator
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Volumetric efficiency is different for every single engine. For every engine, a different modification will affect volumetric efficiency further. There is no real way to calculate volumetric efficiency without removing the engine and having it flowed/measured at a specialty shop, you can only assume what it is. That's what makes tuning so 'mystical', because stupid people can't grasp the idea of 'the car is at x, it will run better at y, do whatever I need to do to get it to y such as (insert stuff)'. Uh oh, new symptoms, how can I fix that? Continued on...

Given your the run of the mill non-idiot (I have faith!) you'll be fine, but you need to research what is/isn't a good estimation of volumetric efficiency and whether or not it changes with boost/rpm.

flux: How would the maf map VE? Using the air output signal?
 

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Madd Tyte JDM yo ®
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7,014 Posts
The maf "counts" every piece of air coming in. The base map for a 7m assumes the stander pumping losses. But if you rewrite the map and use the stock maf as the measuring device, it can tweak the load cell values. The algorithm in the basemaps already uses the stock karmann maf log with it's factory cross sectional area. So the formula already exists with the stock maf measuring device as a "constant". Pressure and temp will be a known variable in a certain range. Rpm is also a known Input value. So using all the known values, the ve of the engine will dictate how much air is ingested or pulled past the maf. So let's say, 1000rpm, 72*f, 100% tps, 0psig shows 190hz on the fuel map load cell. If you ported the head, went ffi, long tube exh mani, or otherwise changed airflow values, the only indicator will be the maf signal. All the inputs being the same as before, perhaps the karmann output shows up as 210hz. If you're rewriting the base map with the stock maf in place, it will slowly change that load cell every time you're in it. If you weight the values lightly, it may change to 192hz next time. Then the next time you're driving, it'll rewrite to 195hz. And so on until the karmann maf input value matches the value on the load cell on the base map. So this can be how you compensate for new cams or head work.

The map sensor would already assume your ve is a known constant. Which it's Not if you change any part of the engine which affects pumping losses. A turbo is not though. As it was explained to me, 2 atmospheres can only force its way into an engine so fast, regardless of what is producing that pressure (61mm, 76mm, m190, another planet). So at 2atm, your ve can only double. It can't flow ingest more than 2x it's ve that it had at 1atm.

But thats just my interpretation. I might be way off. Lol
 
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