Is there a top limit for acceleration enrichment?

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gtmdriver
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Is there a top limit for acceleration enrichment?

Post by gtmdriver »

I am experimenting with the TPS.dot based enrichment curve and there seems to be an upper limit in the values although I can't find a reference to it in the documentation.

I can't seem to set these values higher than 25.5. If I submit a higher value in the table or on the graph it just drops back to 25.5 when I press 'enter'.

Image

Have I set something wrong somewhere.

I was watching one of the Tech Session videos on AE by Scott Clark and the values they were using for alcohol fuel were much higher than this.
LT401Vette
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Re: Is there a top limit for acceleration enrichment?

Post by LT401Vette »

firmware?
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gtmdriver
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Re: Is there a top limit for acceleration enrichment?

Post by gtmdriver »

Sorry.

MS2/Extra 3.4.1 release 20151223 14.04 GMT
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Re: Is there a top limit for acceleration enrichment?

Post by jsmcortina »

The video may have been using MS3?

On MS3 the number is a percentage of ReqFuel.
On MS2 it is a raw pulsewidth adder.

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gtmdriver
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Re: Is there a top limit for acceleration enrichment?

Post by gtmdriver »

Aha.

Yes I'm using MS2.

So is there an upper limit to the pulse width adder depending on the pulse width settings for normal running?
slow_hemi6
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Re: Is there a top limit for acceleration enrichment?

Post by slow_hemi6 »

The maximum time available for pulsewidth is 25.5ms. That is the same as 100% injector Duty Cycle.
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gtmdriver
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Re: Is there a top limit for acceleration enrichment?

Post by gtmdriver »

OK.

That explains it.

Thanks very much.
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Re: Is there a top limit for acceleration enrichment?

Post by whittlebeast »

Do you have a data log off this motor? What are you seeing that is leading you to that much AE?
gtmdriver
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Re: Is there a top limit for acceleration enrichment?

Post by gtmdriver »

As I said in the original post it's purely experimentation.

The aircooled VW engine seems to need a lot more fuel than a modern engine in most circumstances so I was just seeing what the effect of extra AE would be.

I haven't run it yet as I wanted to clarify the issue outlined in the post.
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Re: Is there a top limit for acceleration enrichment?

Post by whittlebeast »

If you are going to have the injectors at the original VW Carb location, AE and DE may wind up fairly extreme. If the injectors are located close to the heads shooting down on the intake valves, AE and DE will be almost nothing.

Have fun designing, building and tuning.

Andy
gtmdriver
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Re: Is there a top limit for acceleration enrichment?

Post by gtmdriver »

I have a single throttle body but port injection.

I'd better back it off a bit then!
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Re: Is there a top limit for acceleration enrichment?

Post by whittlebeast »

I would guess you will be closer to 2 milliseconds
gtmdriver
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Re: Is there a top limit for acceleration enrichment?

Post by gtmdriver »

2ms at what sort of TPS.dot?
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Re: Is there a top limit for acceleration enrichment?

Post by whittlebeast »

In the neighborhood of 200 pct per sec. What that implies is you go from 0 throttle to full throttle in a 1/2 sec. This is all a "What this motor wants" type thing.

This is how I look at AE.

http://www.nbs-stl.com/CRX/CRX%20AE%20Testing.png

On the top I always have RPM, MAP and TPS

The next trace is the Engine code, MAPdot and TPSdot.

The next trace is MAPxRPM that is essentially MAF in most motors. It is an optional calculated field in MLV. I compare that to Duty Cycle as that is essentially fuel flow. Notice the bump up in Duty Cycle compared to the MAPxRPM.

In the next trace I use MAP vs Pulse Width. It tends to look just like the trace above.

I have accelerators in my car but you will feel this as push in the back.

It happens that it is a little sketchy to watch widebands at this level as they have trouble responding fast enough to huge changes in heat and flow.

Hope this helps

Andy
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Re: Is there a top limit for acceleration enrichment?

Post by whittlebeast »

I just looked and at this point in the tuning process, I am only using TPS based AE. This motor has only been on the road two weekends and I had not even got to looking at AE.

This happens to be a ITB motor with the injectors mounted in the Throttle bodies. As I have to wet up lots of intake wall on every transition, I would expect it to take a considerable amount of AE. I did not have any driveability issues that lead me to AE issues, so I simply had not got to there yet.

http://www.nbs-stl.com/CRX/CRX%20Engine.jpg

Andy
gtmdriver
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Re: Is there a top limit for acceleration enrichment?

Post by gtmdriver »

I'm at just about the same stage as you.
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