can someone cast an eye over my VE table

[jonfx4com]

My engine idles at 800 RPM with MAP at 43kpa (is this unusually high?) and the redline is 6200RPM.
It is 139CI (2300cc) 4 cylinder with individual TB's. I have no real idea of torque or BHP. The standard figures are 130 BHP at 5500 and 144Lbft at 3500Rpm. The VE table generated by Megatune seems a little strange, starting in low forties at idle which seems strange. I have tried to run it and its very rough.

Thanks
Jon

[efahl]

My engine idles at 800 RPM with MAP at 43kpa (is this unusually high?) and the redline is 6200RPM.

Jon,

No, my engine idles at about that, too. Some people have better, in the 30s, and some have lots worse, in the 60s. It all depends on the condition of your engine, its static CR and the cam.

It is 139CI (2300cc) 4 cylinder with individual TB's.

In which case, the 43 kPa is quite good.

The VE table generated by Megatune seems a little strange, starting in low forties at idle which seems strange. I have tried to run it and its very rough.

Yes, did you read all the caveats? The generated table is just a (very) WAG, especially for an I4 with ITBs. It looks way too flat to me, mine ranges from about 17% at idle up to about 100% under boost...

Eric

[Cairb]

I have a 2.3l with ITB's and found that the VE table had a profile that rose slowly up to 90kpa then rose steeply from 90-100kpa.

I ended up changing over to hybrid Alpha-n which gave better control of fueling at high MAP. I believe that this is a characteristic of ITB's.

I have included VE table examples for SD and hybrid Alpha-n. Ignore some of the rogue values and that the table that goes to 179 is shown as kpa, it's not it's raw TPS.

[maztah]

is there a version of megatune that generates a 12x12 ve table?

[whittlebeast]

Here is from the CRX. I assigned a high percentage of the VE to the high KPA side of the table.

AW

[Cairb]

Here is from the CRX. I assigned a high percentage of the VE to the high KPA side of the table.

AW

I see that your SD VE follows a similar pattern to mine, where the VE virtually doubles from 90-100kpa.

I don't think that increasing the resolution in this area really helps much as the reason for increasing resolution is to reduce non-linearity errors.

I think that having this steep VE wrt MAP is not good as it can result in large changes in fuel for a small change in MAP, and MAP is a signal that by it's nature in an ITB setup is going to be pulsing. It would be interesting to see the AFR ratio from every fire cycle as I have a feeling that the AFR is varying significantly from one cylinder fire to another but we only see the average.

When I had my car on a rolling road I noticed occasional puffs of black smoke when operating in the 90-100kpa region yet my wb O2 was indicating between 12.5 & 13. I haven't repeated the exercise since changing to hybrid alpha-n but it feels much better at 90-100kpa.

I use the MAP input from the ITB's as I think that it is good to include engine load rather than pure alpha-n but I don't think that it is correct to have it just proportional, maybe a lookup table is needed, I need to do some more data analysis.

Colin

[jonfx4com]

Thanks for the VE table, they at least confirm that I have something badly wrong. The inbuilt generator does not seem to be ideal for my setup, in fact it seems a very long way off target.

I told it I have a 2300cc engine with bhp of 130 at 5500 RPM and torque peak of 144 at 3500 rpm with a idle MAP of 37 and a redline of 6200 RPM and got this very flat table. The parameters I gave are about right acccording to the manufacturer. My only modification is a head with valves like dinner plates and a four branch exhaust header with 2 1/4 system. So maybe my BHP is a little more than the standard but I chose to put in the standard published figures as a known fact. The figures don't seem unreasonable for an old technology 8v engine but the VE table that came out seems very strange and flat. Even if I was using a single TB setup I would still have been dubious about ths table.

So with hybrid do I use map at low throttles and move to alpha N at higher throttles? I don't really understand how the two systems integrate and where the switch points should be. A brief description might save me a lot of reading if anyone has time. Would a more progressive (non linear) throttle linkage help or am I looking for an over simplistic solution?

Jon

[whittlebeast]

Ok guys, this is whats messing with your head. ITBs act (from a physics standpoint) like a pipe organ. The problem is at low throttle angles this all acts like a closed end pipe and at higher throttles the math starts behaving just like an open end pipe and the resultent resonent frequencies.

see http://www.bgsoflex.com/intakeln.html but this math assumes the throttles are wide open

The ricers and thair cold air intakes and moving around the powerband is all related to this math. What you are seeing on the bend in the VE table is this transition that most if not all ITB installs have to deal with at some point in the VE table.

Hope this helps

AW

PS: to All you sensitive ricers out there ... I read those magizines and love them. I own 4 Hondas (two that spin over 8000 rpm) and a Nissan 240sx

[Jedrik]

IF one of you ITB people could take a datalog and plot Throtle position vs. MAP and post it here (or send datalog to me) I would be most grateful.
I think this could be helpful in setting up Alpha-n blending and I would like to comepare it to a single throtle body setup for some AE testing.
Like this:
(It is a bit hard to see on this graph, but the difference between low rpm and high rpm is interesting. Maybe sort the data and make one series for the lower 25% rpm and a second for the upper rpm.)

[jonfx4com]

Whittlebeast,

an excellent reply! Makes sense to me, not sure how to fix it but at least now I can visualise the problem which is good start. Anyone have any comments on the alphaN blending part of my question.

Jon