Hitting last column in maps bad/not good tuning?

[modulation]

I've read a few places that say you should have load scales adjusted so that you never hit the last column in the map.
This makes alot of sense for boosted cars since you can't be sure of the afrs/timing if you're off the map.

Is this statement correct? Or is it ok to hit it as long as the other cells interpolated into the results are all on the map still?
What about for NA cars?

The VE on my NA car is quite varied between rpms, between some columns it seems need really good resolution, but there is a large range of tp's to fit on the map so it's a tricky balancing act for me.
Right now mine is like this:
5 11 18 23 30 36 42 44 46 52 56 65 73 75 85 94
I wish I had a little more resolution between 65-73, but I'm already hitting the last column.

[DVS JEZ]

i try to keep mine in the 2nd last column at the highest load.
with the load or rpm rescaling once you have the higher load scaling set to where you need it work back down from there and try to keep the lattice (line in the scale) linear so there is no sharp spikes etc.

[PL]

It doesn't actually matter that much. I've seen lots of tunes where it pretty much slams against the last column and stays there. This isn't ideal cos you're pretty much running 2D fuel and IGN maps at high load. But lots of people do it. Mostly those tuning turbo engines who don't understand how the load scales work. But they get away with it.

The ECU is still using the TP value (the number representing load - calculated from AFM voltage and RPM) to do final injector pulsewidth calculations, so it's not quite as bad as it would seem.

I try to adjust the load scales so that the last column is *just* accessed. Often on turbo engines they'll hit the last column in the midrange and then start accessing lower columns as rpm rises.

Sometimes with turbo engines I'll leave them so they access the second to last column at max boost. But these are usually engines that are running lower boost than they eventually will. Like guys who wanna run low boost while running in. Or guys who have a small turbo but intend to upgrade later.

There are many techniques for setting up your load scales and each has its own merits.

You can even do what Mr. Nissan does on R33/34 Skyline engines - max load doesn't make it to the last column on std boost. But if boost is increased over std they will reach the last column. So Nissan fill the last column of the IGN map with very low values. Effectively saving the engine from damage if somebody turns boost up without doing any checks/tuning.

NA is much easier. Just set it up so the last column is accessed at full load.

PL

[ST240]

I try to adjust the load scales so that the last column is *just* accessed. Often on turbo engines they'll hit the last column in the midrange and then start accessing lower columns as rpm rises.

Not to hijack, but I'm a fan of not cluttering up forums :p.

Engine specs:
Stock everything RB25DE/30
Tubular mani
6262 (~gt35r :p)
740cc
Z32
etc

With the above, I noticed something in the logs. While doing a pull tonight I hit 12 psi at whatever rpm say 4000 at 10.3 AFR and 17* timing. She pulls hard at first but holding those same timing figures and AFRs the pull tapers off significantly and by 6500 its hardly pulling anymore! Anyways I noticed TP goes from 79 when i first hit 12 psi and its down to 65 by 6500 RPM. Thats damn near a 20% decrease in load. I'm assuming this decrease in TP and decrease in pull are a symptom of the same problem... I know its pig rich, but it doesnt get progressively richer, so why is TP dropping?

[PL]

TP = load = airflow@RPM. Usually if an engine is breathing well at high RPM you'll see the TP value remain pretty much constant once boost comes up. If TP is dropping off then you'll find that either boost is dropping off or else there's an airflow restriction somewhere that is stopping the engine from breathing at higher RPM. This could be something like cams or an intercooler/exhaust restriction.

PL

[ST240]

TP = load = airflow@RPM. Usually if an engine is breathing well at high RPM you'll see the TP value remain pretty much constant once boost comes up. If TP is dropping off then you'll find that either boost is dropping off or else there's an airflow restriction somewhere that is stopping the engine from breathing at higher RPM. This could be something like cams or an intercooler/exhaust restriction.

PL

Damn thats not what I wanted to hear... So leaning it out would not increase TP?

[PL]

Leaning it out will help but I doubt it's the only problem.

Then again at only 12psi you wouldn't expect to be having flow problems.

I'd probably trim your mixtures out to between 11.5 and 12:1 first. Then get some timing into it and see if things improve.

I normally wouldn't go jumping to conclusions before you've banged a rough tune into it. If you get good full load AFR's and you've spent some time on the IGN maps and it STILL drops off up top then I'd start to get concerned.

Is your VCT working alright? That would lose you some top end, although I was playing with an RB25DE+T last week - running an RB20 ECU. So no VCT control. Wired VCT on continuously. It still performed really well....

PL

[ST240]

Leaning it out will help but I doubt it's the only problem.

Then again at only 12psi you wouldn't expect to be having flow problems.

I'd probably trim your mixtures out to between 11.5 and 12:1 first. Then get some timing into it and see if things improve.

I normally wouldn't go jumping to conclusions before you've banged a rough tune into it. If you get good full load AFR's and you've spent some time on the IGN maps and it STILL drops off up top then I'd start to get concerned.

Is your VCT working alright? That would lose you some top end, although I was playing with an RB25DE+T last week - running an RB20 ECU. So no VCT control. Wired VCT on continuously. It still performed really well....

PL

Thanks for the replies man! Yeah it sure doesnt feel very fast right now. Cant be much over 300whp so i wouldnt expect flow problems either. The only culprit mayyybe is my ebay same side entry intercooler. Damnit because boy does she sure drop. 79 to 65 is quite a drop I'd say...

No VCT on this engine. R32 RB25DE head .

[PL]

I wouldn't worry too much. Is the boost dropping or is it a solid 12psi all the way?

PL

[ST240]

I wouldn't worry too much. Is the boost dropping or is it a solid 12psi all the way?

PL

Looks like a fairly solid 12 psi maybe .5 psi drop tops... Its strange because its flat for the first bit then begins to taper off quite a bit. Timing doesn't change. My fuel map is fairly lumpy though. Odd.

Edit: MAF volts increases parabollically quite a bit when TP is still level but then is dead level when TP starts dropping... I assume it should be a steady rise?

[PL]

Hmmm. Probably not airflow related so much then.

I just looked at a log from Matt's R34 (std RB25 NEO but with 3071 and cams) and his TP drops off quite a bit (216 @ 5000, 164 @ 7000) but his boost does drop a lot too (19psi @ 4750, 14psi @ 7000). Still makes 300rwkw though!

What timing figures are you running?

PL

[ST240]

Hmmm. Probably not airflow related so much then.

I just looked at a log from Matt's R34 (std RB25 NEO but with 3071 and cams) and his TP drops off quite a bit (216 @ 5000, 164 @ 7000) but his boost does drop a lot too (19psi @ 4750, 14psi @ 7000). Still makes 300rwkw though!

What timing figures are you running?

PL

I attached a pic. Aux1 is boost. 17* from 12psi onwards. I know it would make sense if boost was dropping... But it isnt!

[PL]

Sorry, didn't see that pic before.

That actually looks fine to me. I'd try leaning it out and see if it responds and then try adding timing. I'm not an RB guy but I'm guessing it'll want more than 17 degrees on 12psi.

PL

[ST240]

Well i took your advice and put in another cheap, yet better designed intercooler, and WOW did it make a difference!! For anyone using a same side entry intercooler on their RB, ditch it if its a horizontal flow for favour of a vertical flow!! It builds more boost/higher load for longer but now it is STILL tapering off . I guess I'm going to have to look at the intake manifold/TB now... Or something I donno. Lol.

[Fusion Ed]

See if you can get a differential pressure gauge. They have two pipe inputs, you can then put them on each side of something you're trying to test (say intercooler) and then see where a restriction lies...