ITBs, large cams, speed density and altitude change

[ethergore]

I’m having trouble understanding what is going on with my setup. I am running a 16v 4age with ITBs and 280 degree camshafts. ITBs are plumbed into a vacuum manifold. Car is running speed density and I am trying to make it a daily driver.

Here is the issue:

Car was tuned by a friend at sea level (100 kpa) and runs great at that altitude. Once the car was brought back to my house at ~2000 ft above sea level (96 kpa) the car does not run well.

The altitude change prevents the fueling from reaching the top WOT (100) kpa table rows and is stuck down on the lower rows when at WOT (96 KPA). This causes extreme lean conditions as my VE table is extremely non-linear because of the cams.  96KPA is something like 50% of the fuel needed. This also changes depending on what RPM the engine is at.

The problem is temporarily remedied by using ECU calibration and simply adding 4 kpa to the map sensor offset. The problem is that when I try to drive up a local mountain the same problem occurs again as altitude increases and the VE drops.

I attempted to configure an external map sensor for barometric correction however this does not remedy the problem as it only adds a percentage of fuel.

Is there something fundamentally incorrect with my system I do not understand? Can ITBs be run with speed density and still have the ability to make large altitude changes?

If the external baro would just offset the actual load value on the main VE and ignition tables, I think this would fix my problem.  right now it is just adding fuel on top, which seems to be the less effective way to implement the correction.  The ignition map doesn't seem to be corrected with external baro adjustment as well so I'm likely running too lean and too advanced at my altitude.
Thanks!

[MWfire]

You are doing wrong. With itb and that cams you need to map alpha/n. Also map sensor should measure the atmospheric pressure.

[Grant]

Alpha-n on a street car is really not good when I tried it with VEMS in 2012.   Any reason he should try alpha-n now?  MS guys have no problem doing SD and ITBs with alpha-n blending.

[VEMS]

Hello Grant/Ethergore,

On an ITB setup with large cams Alpha-N is recommended, there are no problems mapping a street car this way. When you are in an area with big altitude differences, it is imperative to enable  barometric compensation, either Dynamic Mode (preset compensation curve) or Barometric Correction with Anytrim control (fully mappable).

Speed density will not work accurately on a setup like this and is therefore counter recommended.

Since everything is fully configurable any problems you might have with setting it up are mapping problems, not VEMS software problems. Do not expect a non-tuned fully mappable barometric compensation to magically work without tuning it:). More information about barometric compensation is available at its help page: http://vems.hu/vt/help/v3/v3_engine_setup.html.

Best regards, Dave

[ethergore]

Thanks for all the responses everyone. I was afraid I would hear people say alpha N is the only way as I have heard lots of negative comments on its use in a street car. Do you all disagree when people say it is difficult to get alpha N to run smoothly on a street car? It seems the biggest criticism is in low speed off idle condition like parking lots and traffic.

Is there a blended map option supported in VEMS? Would it even work on my setup?

[Grant]

Dave,  I did see the scalar.  Even with the fueling correct the ignition timing won't be able to be compensated for correct?  He is having too large of timing change because of the perceived lack of load by the MAP sensor. 

Ethergore, maybe you can figure out a way to upload a screen shot of your VE and spark table so people see how non-linear the map is? 

I'm thinking blended alpha-n might be the only other option.  The problem I had with Alpha-n on my own came 4AGE was that throttle tip in is terrible as a small opening in the throttle would not be picked up by the TPS sensor, causing the car to be very jerky in daily use.  Also the TPS reading would change slightly depending on the temperature of the sensor. 

My own car is 270 duration cams so the map isn't quite as drastic, but I was still able to make it work with speed density with great results.

Thanks for any of your input...we are so close to wrapping this up for Ethergore!

[MWfire]

alpha/n + map sensor configured before throttle will make very good results(so you don't need to turn on the baro correction). I mapped that way many cars for hillcimb(race are from 0m from see level to 1000m) without problems.
You can also use anytim for ign correction depending on atmospheric pressure.

And alpha/n will run smooth with problems with good mapping(also for DD car). But for good alpha/n mapping you need a dyno with brake.

[Grant]

MWFire,

I'm currently trying to upgrade my old vems box (serial number 560 or so) from 1.1.44 to current.  After that I'll try out blended alpha-n/MAP and see if I can get that to work well with ITBs.  If not I'll be seeking advice for Alpha-n only.  Thank you.

[Sprocket]

I had no problems with Alpha N on a high power road car, but it does require a little more thought mapping. Make sure there is a high resoltion on the rpm scale, say, 100 rpm increments around idle regions, widening gently to 200, 500 and then up to 1000rpm increments or more at the higher end of the map. The same for throttle, start with a high resolution at idle and gently widen from about 50% throttle up to 100%. Race cars don't need this sort of resolution low down the map but a road car works better with the high resolution in those low map areas for idle and cruise. The map end up looking very different, mountainous for want of a better description.

Later firmwares have more features that will allow ignition advance based on coolant temp so you can now add a chunk of advance on a cold engine to help with warm up, that however is never a substitution for more air if you can, a choke cable or other actuator on the throttles for simplicity perhaps.

[ethergore]

Thanks for all the comments everyone. I have learned a lot from this experience. I understand that alpha n can run almost as good as speed density but it seems that speed density tuning is still superior overall in terms of daily driving if not all aspects.

Maybe this is a question for a different forum as I don't expect a special software function to be made for my setup but I still want someone to help me understand something.

Is there any reason that a load-based barometric correction is not a way to effectively run ITBs on speed density? Like I stated in my first post, my car runs great with a simple ecu calibration to correct for the change in altitude where the car was tuned. If this could be done through software, I would have an effective way to run my car on speed density, and so would many other people with ITBs.

Technically the car would still slightly lean out as it climbed in altitude but this could still be corrected in the traditional baro correction in addition to the load based correction.

Am I missing something because this seems like a great way to tune ITBs if its possible?

[VEMS]

Hello Ethergore,

You seems to have drawn the wrong conclusion from the hints we provided, let me repeat my recommendation:

On an ITB setup with large cams Alpha-N is recommended, there are no problems mapping a street car this way.

All other tuners with experience tuning ITB + large cam setups on small engines will confirm.

Best regards, Dave

[ethergore]

Hello Ethergore,

You seems to have drawn the wrong conclusion from the hints we provided, let me repeat my recommendation:

On an ITB setup with large cams Alpha-N is recommended, there are no problems mapping a street car this way.

All other tuners with experience tuning ITB + large cam setups on small engines will confirm.

Best regards, Dave

I fully understand this recommendation and will be doing this on my setup. With that said I am just asking a theoretical question to help me understand this concept. Would it be possible to run ITBs with large cams by using a load based barometric correction? I prefaced my question on my last post by saying I was not sure if these types of questions are appropriate for this forum. If so I can find a more broad based forum as I am simply trying to expand my understanding here.

Thank you so much for the help and recommendations you have provided.

[Sprocket]

THE problem with speed-density tuning on an engine with wild cams and ITB's is that it becomes almost impossible to get a manifold pressure reading that does not fluctuate significantly even when the engine is running at a steady state. I've heard all sorts of weird ways to 'filter' out the pressure fluctuations but all you end up with is an average reading at best, and as such you will only ever achieve an average tune.

Bottom line here is if you really really don't like the idea of Alpha-N on a road car with wild cams and ITB's then you need to sit down and ask yourself what it is you really want from your engine. Wild cams and ITB's do not necessarilly make for the best road car to begin with (in my opinion) and that is not the fault of whatever fueling system you care to use.

I'm pretty sure that an engine with soft cams and a single large throttle with alpha-n would be much more refined in a road car. The fact of the matter is that Speed-density is piss poor with wild cams and ITB's, I know, I tried all sorts at the very begining, it just didn't work. Something also to consider is where fuel pressure is refferenced to......... same problem here. I just left the reference port on the regulator open to atmosphere giving a steady, all be it varying fuel pressure.

Tiny engine, wild cams, ITB's, Vems tuned in Alpha-N, MAP sensor measuring barometric preasure used in heavy trafic.

[Grant]

I'm also wondering what would be wrong with having baro correction change the actual load value on the VE and Spark table.  That way, fueling and ignition would be corrected in one go.

Anyways I have really tried to steer this project away from alpha-n as on my own 4AGE on alpha-N I had poor drivability at cracked throttle openings.  Basically, there was not enough TPS resolution at the 1-3% range to keep the car from being jerky, no matter how I changed the x-axis on the tables. The TPS reading would also change depending on the engine temp...just 1% would cause issues with fueling.   If there was map/alpha-n blending that allowed the engine to run SD below 50kpa, and TPS above it, I think we would be done. 

Anyways we will stop beating a dead horse, I will try and set him up alpha-n and report back.  thank you for your comments. 

[Grant]

Also wanted to mention that some other systems allow blended maps for MAP low load/TPS high-load for ITB installs and people are happy with it.  We seem to only allow TPS low load/MAP high load, which is great for boosted cars.