VW 16v ITB vacuum and ISV question...

[Mike_Robert]

Damn!

What vacuum is normal on ITB's? Should it be 0 kpa at idle, and is it normal it drops to atm. very soon?

Unless you're a 2 stroke, a peripheral ported rotary or a 4 stroke with a radical cam, no, these numbers are not correct. That said, even without the above condictions the pressure fluctuations in each ITB tract are usually extreme and need to be combined and averaged out either mechanically, computationally or usually, both. For mechanical averagimg/smoothing, MIG jets or aquarium needle valves can serve as restrictors, cheap small engine fuel filters can serve nicely as capacitance vehicles. In MS-II, there are "lag" numbers that can be adjusted to provide statitical averaging of the MAP and other inputs. It'll work, you'll just have to try a couple of things. If this is an emissions restricted or daily driver type vehicle, Alpha-N is unlikely to work well.

-Mike

[JSchlappi82]

I have a 4-stroke engine, with other camshafts. I don't know what you mean by "radical" cams, i have the 2nd upgrade? We got 3 degrees of camshafts, sport, rally and race. I'll try to post the specs of the camshafts.

Can i built the megasquirt first, and then sort out my vacuum issues?
I'm now trying to sort out the issues first, but maybe i'll have to try to get the engine running on megasquirt first, and get my throttlebodies synchronized again.
Because of the bad injector i have to open the htrottleplates more for good idle, maybe they are opened to much for decent vacuum?

At idle my vacuum is about 80 kpa, when driving away it drops to atm., and when driving between 1000 and 3000 rpm it gets about 60 kpa, but a little more throttle and it drops to atm. again... At higher rpm it also drops to between 80kpa and atm.
At decelleration it gets 40 kpa...

My ride is a daily driver, but we don't have strict emmission rules here.. What about the combined alpha-n/speed density?

I find the time i'll post some pictures of the manifold with the vacuum plugs... (I have to get them off first..)

[Mike_Robert]

If you're able to idle below 1000 rpm, you should be able to get a decent MAP signal. I'd probably try to fix the bad injector problem before you do anything else. The thing with larger ITBs is that at low load, a small throttle opening angle can result in 100 kPa detected MAP so you need loads of AE. At higher load and high rpm, the need for AE drops off dramatically. You also have big changes in MAP in each intake tract during each engine cycle - especially at lower load. At higher load reversion becomes evident in some engines. All these can generally be managed by the averaging techniques I previously mentioned. The combined AN/SD mode may also be an option that may help you. For now, you need to get that injector fixed and hopefully clean and flow test all of them. Then balancing the TBs would be an excellent idea. Another thing to remember is that the MS logs' contents are a snapshot of what the sensors were seeing at that instant - there are usually several other engine cycles between log events and you're also not guaranteed as to when the log data was captured in relation to valve opening, etc. Get your machine running and post some logs and the operating msq, there's numerous people here on the forum who may be of tremendous help.

-Mike

[JSchlappi82]

Thanks Mike_Robert, it's a bit clearer to me now...

Bit i need to mention i still need to build the megasquirt setup, it isn't complete yet. I almost have all the components, and will be starting the setup soon...

Another question, i couldn't find info on the difference between the normal alpha-n and the hybrid alpha-n. Do you know them?

If i'm cruising the vacuum comes back, so is it possible to switch between speed-density and alpha-n, depending on MAP and TPS signals? When driving, and having some vacuum, you would be using SD, and when the throttle opens, and MAP-vacuum is lost, you would be using alpha-n. This would mean while cruising the engine can be lean, and when WOT you're using alpha-n for power, disregarding the economy and emission.

Is there target AFR possible with the alpha-n?

Thanks, Joris.

[Mike_Robert]

Joris, you described blended SD/AN quite nicely in your previous message. Were I you, I would probably start with trying to make straight SD work w/ MAPdot triggering your AE. You can get probably better consistent results for WOT power using SD - AN will only be correct for a certain temp, humidity and fuel. Very few people, especially car users, have to use AN. I'm not sure target AFR works with AN but would suppose so. It takes an eternity in injection events for the target to be converged upon but I would not recommend it to rely on for high performance vehicles in high load areas. It doesn't take long to melt aluminum or crack things with high RPM, high load operation running too lean. I'm very glad to see you doing research before starting your project, lack of doing so is the #1 reason for startup problems!

-Mike

[Uncle Bob]

well, depending on my cams and cam timing, my ITB's idle somewhere around 60 KPA (8-12 in/hg)

I'm sure its different for different motors, configs, etc. But you will see much higher numbers with ITB's.