MAP sensor install with triple Webers

[bajcsi]

Hi,

 I'm planning to add a MAP sensor to my current setup; this includes 3.1L + Triple Webers + Electromotive HPX ignition.  If you take a look at the attached photos, you'll see how I plumbed PCV and the brake booster.  I've read that it's not advisbile to pull vacuum for a MAP sensor directly off the same vacuum line as the booster.  My DCOE 40-151's have a vacuum port that I use to balance the carbs using gauges.  Would this be a sufficient vacuum source for a 1 bar map sensor?

 

Thanks,

Bajcsi

[Tony D]

Depends on what you want to do with it.

To get a smooth signal instead of he strong spiky pulse inherent in individual runner manifolds you can add a restrictor jet, or a small- engine fuel filter in-line between the tap in the runner and the MAP sensor.

 

Look what the Megasquirt guys did, generally cheap and effective.

[bajcsi]

Depends on what you want to do with it.

To get a smooth signal instead of he strong spiky pulse inherent in individual runner manifolds you can add a restrictor jet, or a small- engine fuel filter in-line between the tap in the runner and the MAP sensor.

 

Look what the Megasquirt guys did, generally cheap and effective.

 

Cool, thanks. I'll take a look at that.

[madkaw]

Could you not just tap into the Cannon "runner " that's there now? In the center would give you a good signal.

[bajcsi]

Could you not just tap into the Cannon "runner " that's there now? In the center would give you a good signal.

That was my plan but doing random reading on the internet some people had warned not to do it off it because of the brake booster.  I may well give it a try regardless...

 

Thanks.

[SleeperZ]

That was my plan but doing random reading on the internet some people had warned not to do it off it because of the brake booster.  I may well give it a try regardless...

 

Thanks.

 

I do not understand the concern.  Obviously you have to be on the manifold size of the booster valve, but the booster is an excellent vacuum reference

[Tony D]

The booster is a big source of capacitance...if you are using the brakes there is a draw in the line which can affect the readings.

 

Better to take it direct so no skew whatsoever enters the system. Watch what happens with a MAP straight on the runner, then with a Briggs & Stratton or McCulloch fuel filter in the line. The capacitance changes how the MAP reacts.

 

Same for the brake booster which is indirectly a vacuum using device.

[SleeperZ]

The booster is a big source of capacitance...if you are using the brakes there is a draw in the line which can affect the readings.

 

Better to take it direct so no skew whatsoever enters the system. Watch what happens with a MAP straight on the runner, then with a Briggs & Stratton or McCulloch fuel filter in the line. The capacitance changes how the MAP reacts.

 

Same for the brake booster which is indirectly a vacuum using device.

 

The large reservoir can hurt or help I suppose.  But it seems like it can help smooth the vacuum better than the constant pulsing of the six venturis.  If you are on the brake with the engine dropping the vacuum further, does it matter?  Doesn't the booster get overwhelmed at that point?

 

Probably the best implementation is a separate reservoir drawn from a different tap on the common source, but I'm just pressing keys behind a screen on the interwebz, I know nothing about ITBs, and I'm sure it shows.

[Tony D]

The Megasquirt guys did this a decade ago.... the consensus was the ONLY capacitance necessary was provided by a small engine gas filter. Anything more and the MAP started getting sluggish in response.... and if you have sluggish MAP response then you get hesitation.

 

There IS such a thing here as "Too Big" and the brake booster is it!

 

You DO NOT want a separate reservoir with the MAP taken from it!!! That is TERRIBLE and when you put a megatune on it and datalog you start seeing the disconnected lag that results in longer larger TPS Dot enrichments to cover the lag that you normally wouldn't have if you piped it properly.

 

Let me put it this way: Look at a GM MAP sensor, or the old Honda PGM FI MAP sensor and see how they are plumbed. Yeah, I know, a common plenum manifold, but the MAP sensor is RIGHT THERE with maybe a 6" hose. 

 

The impulse spike from a dedicated runner manifold can be mitigated somewhat by using a BALANCE TUBE, and taking your MAP there but if you are running Carbs it becomes a BITCH to synchronise and mixture adjust the carbs properly then unless you make it easily isolated... Really that's the best compromise, and most people run the balance tube as it makes a vacuum tap easy for A/C etc...  But if you are running without one, then you want a dedicated line and a variable orifice which you trim for best response using your datalogs. WOT vs MAP change, %Throttle Angle Change vs MAP change, etc. As stated, most guys found sticking a Briggs & Stratton or Weed Whacker fuel filter in the line worked out just right to dampen the pulses but not add so much volume that MAP Lagged.

 

"BEEN HERE DONE THIS!"

[SleeperZ]

Sorry, that's sort of what I meant when I said "reservoir", I meant balance tube.  Sounds like you need just enough volume to make the reading constant without affecting it's time response.  I've said way too much, sorry for muddying the thread.

[Tony D]

You consolidated it exactly: you want only enough capacitance to dampen the spiking, but not cause a delay in response!

 

(Edit: "captivity nice"? C'mon, Apple pull your head out!)

Edited September 26, 2013 by Tony D

[bajcsi]

Sorry, that's sort of what I meant when I said "reservoir", I meant balance tube.  Sounds like you need just enough volume to make the reading constant without affecting it's time response.  I've said way too much, sorry for muddying the thread.

 

Actually, I think it's great that such discussion occurred.  This thread has been quite informative for me and I hope it helps someone else.  I got my MAP sensor wired up, vacuum plumbed and timing reset this evening.  I tied into the psuedo-balance tube and added the inline fuel filter per Tony's suggestion.  I'm going to be heading out for a test drive once the wife gets home and can watch the boys.