NA is best - 3.1L M20 w/ ITB's

[CorvallisBMW]

Damn, not sure how I missed this thread, but sub'd!

[nando]

Even if it's electric it still needs to be referenced to intake pressure somehow in order for the injectors to behave in a linear fashion. I don't think I've ever heard of such a thing on an M20.

Also, going electric seems like a lot of hassle - I think a vac distribution line would be a better effort, and maybe that's why you couldn't get the "Blended" Alpha-N/SD mode to work. The blended mode should actually be easier to tune, since it factors relative pressure into the equation and not just your TPS, which isn't necessarily linked 100% to engine load. But it's not going to work very well with just one referenced cylinder for MAP.

FYI lower vacuum makes no difference to the effectiveness of a FPR. It just needs to provide a constant 3 bars of ambient pressure relative to manifold pressure - so if the intake vacuum is lower, the FPR automatically compensates by increasing pressure to stay at a 3 bar equilibrium. But by tying it to just one cylinder, you'll get pressure spikes every time the valve opens and closes on that cylinder..

[jeenyus]

if you're that concerned though, why not just go with a electronic FPR that's manageable through MS?

[ForcedFirebird]

Might not be a good idea, though. With it hooked up to one cyl, it will pulse vacuum every time that cylinder pumps. It's interesting to watch a mechanical vacuum gauge hooked to just one. I have been leaving the FPR open on open trumpet cars and using a manifold when they have them.

[Raxe]

Do you have the regulator to a vacuum manifold, or a single cylinder?

I have it hooked up to a single cylinder with no splices. Ditched the original vacuum block idea in favor of simplicity.

[ForcedFirebird]

Do you have the regulator to a vacuum manifold, or a single cylinder?

[Raxe]

I know that Bosch rates their injectors at a fuel pressure of 43.5 psi, or 3 Bar. What is your pressure at the rail? The higher the pressure, the more they will flow.

It's the stock 3 Bar FPR, I haven't actually measured the pressure but I'm assuming it's working properly...

I've considered the effect that the lower intake vacuum may have on how the regulator works at low load, perhaps that's contributing to a rich idle but I have no idea how you'd tune that out besides just getting the vacuum as strong as possible and adjusting the fuel table as necessary.

[Phoenix]

Yeah that first picture was set up very very wrong, I've spent the last two afternoons fixing it little by little as I figured out what needed correcting.

- Switched the pins on the TPS connector (whoops) and I'm actually getting a decent ADC range now.
- Changed to alpha-n and disabled all of the MAP input.
- Changed the ignition timing to a proper table and redid all of the table scaling for alpha-n.
- Actually wired my wideband to the MS and set it to read from there vs the narrowband O2.
- Mechanically synchronized the throttles a bit better with a feeler gauge and set a reasonable idle but I still need to do a proper vacuum sync now that it runs.

I've been playing around with the VE and AFR tables and managed to get a decent idle mixture of 13.5-14.5 at 1100rpm, I'm still having a hell of a time with anything under load but it's baby steps... I'm pretty much starting from scratch with no experience and learning along the way.

Is this looking better?



I don't think the scaling is off? Otherwise I'm really not sure what to do about the pulsewidth.

I know that Bosch rates their injectors at a fuel pressure of 43.5 psi, or 3 Bar. What is your pressure at the rail? The higher the pressure, the more they will flow.

[Raxe]

In general big cam with overlap has more contamination of exhaust into intake due to reversion at low load and rpm so it burns alot slower therefore you need to light the fire a little earlier. of course this assumes the setup is correct and if you ask for X* you are actually getting X*. If the thing is offset then..........

The other thing is if the throttle isn’t sync'd then a couple cylinders could be running too lean and this slows the burn down so it happens very late and can even continue into the exhaust. if you get lean enough it will still be burning by the time the inlet valve opens and you can get backfires and popping in the inlet.

You should invest in a sync tool they are so easy to use rather than screwing around with pressure tapping’s etc that require tiny restrictors to dampen all the pulses and it tells you actual airflow instead of vacuum



yeah the problem with ITB is the fuel curve is very steep at low throttle position so you need more load point down there.

also this thread is back alive, Fporro has a map that might interest you there

http://www.e30tech.com/forum/showthr...=33028&page=12

Man, thanks again for the advice. You're really helping me along here and I appreciate it. I have an STE synchrometer lined up for the weekend to hopefully get them dialed in as close as possible now as per Ramas guide and I'm thinking I'll aim for 900rpm as an idle.

Hadn't even realized e30tech is back, I was just browsing the archived pages until now... Franks map and info looks like it's going to help me tremendously! Very excited. :D

Will report back with results when I get the new numbers entered.


A picture for anyone just looking at pics:

[digger]

In general big cam with overlap has more contamination of exhaust into intake due to reversion at low load and rpm so it burns alot slower therefore you need to light the fire a little earlier. of course this assumes the setup is correct and if you ask for X* you are actually getting X*. If the thing is offset then..........

The other thing is if the throttle isn’t sync'd then a couple cylinders could be running too lean and this slows the burn down so it happens very late and can even continue into the exhaust. if you get lean enough it will still be burning by the time the inlet valve opens and you can get backfires and popping in the inlet.

You should invest in a sync tool they are so easy to use rather than screwing around with pressure tapping’s etc that require tiny restrictors to dampen all the pulses and it tells you actual airflow instead of vacuum



yeah the problem with ITB is the fuel curve is very steep at low throttle position so you need more load point down there.

also this thread is back alive, Fporro has a map that might interest you there

http://www.e30tech.com/forum/showthread.php?t=33028&page=12

[Raxe]

Look at others' timing maps in this thread. They are in the ballpark.

http://www.r3vlimited.com/board/showthread.php?t=390283

This is great, thank you. Hadn't seen that thread before.

mine idles fine anywhere between 15-20, gives a bit better vacuum as you need the throttles to be closed further to pull the idle speed down, in general mine likes a heap of timing at light load no doubt due to the cam and combustion chamber characteristics

i'm sure some other member could share their fuel and ignition MAP and you could scale from there? it would streamline the process

Good to know, I'm finding it's running too retarded at light load 2500-3000rpm right now (evident by the super hot exhaust and afterfiring), yet the numbers apparently work well on less modified engines. More cam = more advance?

Any tips on how to scale for ITB's? Most of these boosted maps start at 10-30% load and go past 200%, obviously I need to start at 0% and end at 100%. I've read that the first ~30% is more important than the last 70% because of effective WOT and lack of IAC, and that they need relatively little fuel at idle vs much more as soon as they open.

[ForcedFirebird]

Look at others' timing maps in this thread. They are in the ballpark.

http://www.r3vlimited.com/board/showthread.php?t=390283

[digger]

mine idles fine anywhere between 15-20, gives a bit better vacuum as you need the throttles to be closed further to pull the idle speed down, in general mine likes a heap of timing at light load no doubt due to the cam and combustion chamber characteristics

i'm sure some other member could share their fuel and ignition MAP and you could scale from there? it would streamline the process

[nando]

Sweet thanks, 19 was a guess and didn't kill it so I left it alone. I'll try lowering it a bit.

I'm also thinking now might be a good time to give VEAL a try and see what it can do to help ease things along.

if you look at a factory ignition map, the idle area is more like 8-10 degrees. A modern BMW engine is like 6.. lol. :)

with the cam you might need a little more, but not 19. Also, with the cam, you will probably find that it doesn't like to idle at 14.7:1. Instead, focus on trying to get a smooth idle with a high vacuum, rather than trying to hold a specific AFR (will probably end up being high 13's low 14's). Should be able to idle at ~800-900 just fine which is a little more comfortable than 1100.

[nando]

right, what I said was if you fire twice in a cycle (one crank revolution), your pulse width gets cut in half, it doesn't double. I'm not really sure that you want to fire twice in a cycle anyway, sometimes that's used as a form of AE, but even factory sequential tunes only fire each injector once per cycle. Instead you use an injection timing map to trigger them based on load an RPM, to like you say, hit the back of a valve or target an open valve when appropriate.

If he was using 1 / simultaneous (all 6 fire at once) or 2 / alt (basically just 2 banks, but each one still only fires once per cycle) and then changed to sequential without changing anything else (like the # of pulses per cycle), then his base PW would remain the same, because in all 3 modes the injectors still only fire once.