MAP swings at high rpm, what can i do.

[martin2day]

Hello,

my engine is a small block chevy 350 with a composite manifold from AFR.
With 5000rpm and more the map begin to swing.
Today i drive Alpha-N with the option Multiply MAP so intact of this my PW is also swinging.
At 5000rpm and more i see change in PW from 5% and more. (swing)
Please see the short LOG.

modified.msl

(80.47 KiB) Downloaded 38 times

My MAP Averaging Lag Factor is set to 25.

What do you think is the better solution for my performence car and motor?
1. lower the Lag Factor... but than the MAP is slower as the TPS change (slow response time)
2. Change to pure Alpha-N
3. Let the PW swing

Thank you very much for helping.

Regards Martin

[billr]

Can you give more detail on the manifold, maybe post pictures?

[martin2day]

6A7603AC-BE64-42D5-9BA9-293D045F03F6.png (237.57 KiB) Viewed 774 times

This is the manifold.
All 8 intakes are connected to 1 plenum. The source of the map signal is also connected there.
You see this little black pipe right.

Martin

[elutionsdesign]

If you plot PW vs. MAP in megalogviewer you have a perfect 45 degree line, no reason to change to alpha-N. I wouldn't lower MAP averaging either, probably already too low. There isn't much swing in that log, maybe 1 KPa out of 75 which wouldn't bother me unless you notice issues. Your AFR is pretty constant in the 13's, maybe try lowering that a bit?

[billr]

That was kind of my impression, too, the swings are really only +/- 1 to 2%; not enough to be much problem considering other compromises with a typical V8 head.

[spitnl]

Are you running staged injection?
Hope you are, because in this log with less than 50% TPS the injectors are already over 85% Duty cycle.

Also how many primary injectors?

[martin2day]

Hello,

please also have a look at the PW. Here i see up to 5% different from step to step.

Yes i run staged injection. It is a TBI Setup. Up to 49% i drive only with the front 2 throttle blades and the 2 fron injectors.
Over 49% TPS the rear blades begin to open and the rear 2 injectors cum in.

Martin

[billr]

5% peak-to-peak, but that is only +/-2.5% deviation from "perfection".

[spitnl]

Hi Martin,

Had another thought about your issue.
Was this log made with or without EGO correction on?

You didn't post an msq, but I had a look an earlier one you posted and one thing caught my eye.
In the "EGO Control" menu, you had set the "ignition events per step" set to 8.
This is very low for an 8 cylinder and could cause the AFR swings you're seeing.
For an 8 cylinder the recommendation is to set this to at 33.
So I would try 33 and test if you're still seeing those swings.

Fred

[martin2day]

Good afternoon,

no, my EGO is deactivated. I set the rpm active to 8000rpm.
Today i think i find the solution.

My map is swing a little bit. So the "normal" PW is think also a little bit.
But please have a look at the EAE... my setup is to high... so the EAE multiply the little PW noise to big noise.
I set the ear_AWC is set to about 80% in that area.
I want the EAE to react very quick...
I think i have to lower the value and then the noise is gone.

Thanks for helping.
Martin

[kjones6039]

Up to 49% i drive only with the front 2 throttle blades and the 2 fron injectors.
Over 49% TPS the rear blades begin to open and the rear 2 injectors cum in.

Seems to be a bit odd to an old school guy. How in the world do you keep from starving the other 2 cylinders??

Or did I not understand your post? Which is more than likely! lol

Ken

[martin2day]

Hello Ken,

sorry, but i don't understand what you mean.
Can you say it in other word's... my english is not so good.

Martin

[whittlebeast]

You could always try ITB Mode. I would think it would improve the situation that you are looking at.

See https://www.youtube.com/watch?v=_GDZxUVTplk

Andy

[martin2day]

Andy,

thank you for your hint.
But if i use ITB i must shut off "multiply map" to have pure Alpha-N at WOT?
If multi Map is on i have the same situation as now, or?

Martin

[whittlebeast]

Try it, it is free.

Use multiply MAP.

Andy

[kjones6039]

Hello Ken,

sorry, but i don't understand what you mean.
Can you say it in other word's... my english is not so good.

Martin

You are running independent throttle bodies, correct? If you shut off 2 injectors you are running on 2 cylinders, correct? Won't the other cylinders starve for fuel?

Your English is fine. I think I don't always ask my questions properly!

Ken

[whittlebeast]

I think you are over thinking this.... Just try ITB Mode. Use Ignition Cut for rev limiting. Get a log and post it up.

Your Fuel pressure concerns me more than the PW.

Andy

[martin2day]

Hello Ken,

thank you for your answer.
No i don't drive independent throttle bodies. I "only" have got a TBI.
I use my "old" MSD Atomic EFI body and connect the MSQ.
I also rework the throttle cable. Original the front and rear blades open at the same time, but now only the front open up to 48%TPS.

Martin

[martin2day]

Andy,

thank you for your answer.
I connect the original MSD Fuel pressure sender. I do not use shielded cable. I only what to have a approx value to adjust my fuel pressure.
I think you mean the swing of the signal, or do what concerns you?

I think you are right... i over thinking this. That's my big problem.

Martin

[kjones6039]

Got it!

I do something similar with my Holley TBI. Except I use staged injection combined with table switching.

Ken