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brontosaurus
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Discussion Starter #1 (Edited)
I figured I'd post this here as it's relevant towards ITB tuning.

http://electromotivetec.freeforums.org/erratic-map-t907.html

I am going to be installing these on a turbocharged engine eventually. The fact I keep finding people repeating it's a pain to tune because of erratic map signals has kept me from even bothering to fiddle with it. Although I suspect much of this banter is people repeating what they've been told.

Well on this thread it would seem someone smarter than I has logged a solution to the erratic MAP signal. Running a larger vacuum block and longer lines has smoothed out the MAP signal significantly. Another member on that board had success with it too. This is the first time I have read about someone solving the erratic MAP signal in another way than running a TPS based tune or doing a hybrid alpha-n setup.

It would seem a large vacuum block+longer lines makes the signal workable. It is within the range that a small bit of MAP filtering in the EMS could create a perfectly clear signal which is easily done in megasquirt or the AEM unit.

So here is my question to you guys, do any of you know which vacuum blocks have a larger internal volume? It's not something advertised. Whats your thoughts on running two vacuum blocks? This info could get my project off the ground. Any help is much appreciated.
 

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brontosaurus
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7,236 Posts
Discussion Starter #3
Right now I have ATD racing 1.6 cams in the engine. I cannot find the exact specs off hand at the moment, but they were around 252 duration and .340" lift if memory serves me right.

Heres the specs for their 1.8 cams

Intake: 252 degrees duration @ .050
Lift: 0.340" @ .010" clearance (so 8.63mm lift)

Exhaust: 250 degrees duration @ .050
Lift: 0.335" @ .010" clearance (so 8.5mm lift)
 

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was looking into this before deciding which route to go down longer lines will help a bit since you are adding a small amount of volume but with the vacuum block I would imagine it would be a custom job easier maybe as well? Hard to say how much bigger it needs to be bit of experimentation is needed until you find the right amount before the signal goes all funky on you.

In regards to the vacuum blocks not seen any bigger than the golden eagle etc mind you could easily connect 2 of them together
 

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Supporting Mamber
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I machined my own using A golden eagle unit as sort of a template, modified the ID to accommodate more volume. Works great for me.
 

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I'm using a small fuel filter on my map line to help smooth it out.
 

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brontosaurus
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Discussion Starter #7
I figured custom was going to be the answer. What setups have you guys been using with the vacuum blocks? Was the MAP signal smoothed out a good deal when switching to a larger volume vacuum block?

I have read of physical MAP filters, I would assume these do the same as the small fuel filter. So was this filter needed along with the filtering on the EMS or in place of it? A standalone has the ability to "filter", or smooth, the map signal. Was this used in conjunction with the fuel filter in your case?

I'm glad a few of you guys have messed around with this before. I was under the impression I was going to need to tune by TPS which is less than ideal with a turbo. I'm hoping through some ingenuity I can circumvent the erratic MAP signal.
 

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Multiple problems here, but using enough filtering (pneumatic or electronic) to smooth out
idle MAP variation will have an impact on tip-in fuelling/spark, so it's not a great solution. If you have individual throttle plates and they're slightly out of alignment things get even worse.

The right approach is to use synchronous sampling of the MAP signal, that is, to measure the MAP signal at the same piston position, every cycle. This need not be the IVC point, although that is the best approximation of cylinder pressure you're going to get. In fact, other crank angles can be preferable if you choose a point where the pressure is changing slowly, so it's easier to measure it precisely.

An ideal system might use 4 MAP sensors on an I-4, sampling each cylinder in turn, so you can do individual cylinder trim. Even if your ECU does not support that, summing the 4 sampled MAP signals is better than using a non-sync'd system, plus the 4 MAP signals can be used to align your throttles by balancing the measurements.

If you can't stand all the expense & complexity however, I gather a MIG welding tip in each vacuum line to a mini fuel filter does the trick 'til you change your mind :)

HTH,
Rod
 

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combine all the port signals into the Golden Eagle manifold. Then run a slightly larger, say 1/4" vac line to a vac canister with the appropriate volume and 2 ports. Use the second port to feed the map sensor.
 
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