Boost pressure


SLF360

SLF360

GT Owner
Mark IV Lifetime
Sep 21, 2005
1,239
Italy but lately lot's of Shanghai!
Guys,
I have observed a worrying situation. I used to get good boost, then saw some fluctuation on the gauge, thought of heatsink as a cause, then had the Musclemotor Accufab K&N set installed, saw to my delight even better pump (full gauge, 15PSI), but now am around 7,5, sometimes only 5 PSI.. Naturally I feel the car is not as great in acceleration, but that might just be as I've grown accustomed to it too much (happens all the time).. Is it the gauge, the sensor, or something more worrying, no clue... Anybody else had gauge issues or pressure issues ?

Let's share the experience also on this item... Knowing Booost matters to all of us !
 
Dave, boost statistics please !

Had an idea,

maybe DBK can have a little box voting set up where people can anonymously click the boost they have on theirs. Something like the MPH voting box some time ago, that was great !

Wow, just saw the previous was my 1000'th post on the Forum...:cheers

stefan
 
Stefan

When I have been on the dyno, the dyno bost gauge reads higher than the cars and I believe the dyno gauge. I think all of our boost gauges are inaccurate based on seeing 12+ GTs on the dyno.

Dave
 
The stock boost gauge not high quality and is mechanical rather than electrical. Did you do a pulley upgrade and use a MAFIA? These will cause the readings to appear lower. Otherwise it may just be a gauge malfunction.
 
lthlvpr said:
The stock boost gauge not high quality and is mechanical rather than electrical. Did you do a pulley upgrade and use a MAFIA? These will cause the readings to appear lower. Otherwise it may just be a gauge malfunction.
Click to expand...

Did it before the pulley change and after also no MAFIA.

Dave
 
you can always do a quick test by tapping a mechanical boost gauge off of one of the fittings and running some vacuum line from that point to the passenger side door/windowand monitoring the boost gauge under WOT. My guess is that it's just the cheap electrical gauge not working properly. Did you use the steering pump spacer or larger idler pulley to pick up the slack in the belt. Belt slippage can cause some inaccuracies in boost measurements as well.
 
lthlvpr said:
you can always do a quick test by tapping a mechanical boost gauge off of one of the fittings and running some vacuum line from that point to the passenger side door/windowand monitoring the boost gauge under WOT. My guess is that it's just the cheap electrical gauge not working properly. Did you use the steering pump spacer or larger idler pulley to pick up the slack in the belt. Belt slippage can cause some inaccuracies in boost measurements as well.
Click to expand...

Belt was sized and custom made for the application.

Dave
 
The boost gauge is electronic and has 4 wires to it,
1. GND
2. Power (12v ?)
3. Power for LED light
4. PWM (pulse width modulation signal) for boost.

I didn't see a MAP sensor in the diagrams, so as others have stated, the boost pressure must be derived from MAF, RPMs and IAT.

For those people using a MAFIA or modified MAF the pressure reading with be off. Now here is another product idea for Analogdesigner, connect a MAP sensor and convert it to PMW for the stock gauge. It still will pin and 15 psi, but can be made accurate up until that point, or you can just have pressures scaled to fit within the 15 psi gauge limit.

BlackICE
 
Just take your GT to Ida Automotive in NJ and he can recalibrate your stock gauge to read accurately.
Thanks Bob you are the man!
 
TrackDay said:
Just take your GT to Ida Automotive in NJ and he can recalibrate your stock gauge to read accurately.
Thanks Bob you are the man!
Click to expand...

For those of us on the left coast, I would be interested in a recalibrated guage that works with my Mafia unit and goes beyond 15lbs. Has Bob Ida designed one, if so I need to hook up with him.
 
My understanding is the gauge is recalibrated for your car not the other way around.
So it's real accurate.

Several have had their GT trailered to his shop for a laundry list of things. He has close contacts with top Ford folks and has successfully worked out some real difficult issues for his customers.
Great shop, great guy, send your car to Bob and you won't be disappointed www.IdaAutomotive.com
 
TrackDay said:
My understanding is the gauge is recalibrated for your car not the other way around.
So it's real accurate.

Several have had their GT trailered to his shop for a laundry list of things. He has close contacts with top Ford folks and has successfully worked out some real difficult issues for his customers.
Great shop, great guy, send your car to Bob and you won't be disappointed www.IdaAutomotive.com
Click to expand...

I wish Ida was closer, I know his rep is the very best. To bad for me that I am in California.
Merry Christmas!
 
I came in to post on exactly this subject, and behold, it was already here. I love this place -- guess I better make a donation:wink

Anyway, once I got somewhat accustomed to my new thrust machine, (post Whipple) I started watching the boost gauage, AND BOY, IS IT ACTING WEIRD! It acts like its ten pounds off in both directions; the vacuum is now higher at idle, and its at zero while the car is pulling with some urgency. Max reading is 6 pounds, and I have the 17 pound pulley. I do have the Mafia installed, and I wonder if that's what it is? Any technical explaination for this?

I will say this: the car sure doesn't feel any slower:ack If the guage is accurate when it says 6 pounds, 17 pounds would have me orbiting Mars.
 
The Mafia scales the voltage from the MAF down. So what you are see is what I would expect. I don't know for sure though, just a guess based on what I read.

BlackICE
 
BlackICE said:
The Mafia scales the voltage from the MAF down. So what you are see is what I would expect. I don't know for sure though, just a guess based on what I read.
BlackICE
Click to expand...

Mafia this and mafia that. What's a mafia?? I keep reading references to it in various posts but I can't figure out what it is.:confused Please help.

Chip
 
http://www.diablosport.com/index.php?module=htmlpages&func=display&pid=4

It is just an electronic device that scales the MAF (mass air flow) sensors output voltage to some fraction of the MAF's original signal level. When the car is boosted more, the MAF's output voltage exceeds the ECU input voltage limit, and pegs it. So beyond some point the ECU doesn't see any more air flowing. The Mafia takes the MAF voltage as input and divides it (adjustable) so that it is a smaller voltage. Then the ECM can read the entire range of air flowing through the MAF.

BlackICE
 
ChipBeck said:
Mafia this and mafia that. What's a mafia?? I keep reading references to it in various posts but I can't figure out what it is.:confused Please help.

Chip
Click to expand...

we call dem da bunnies....
or MOTHERS AND FATHERS ITALIAN AMERICA club


but Mr. Ice is correct as it relates to the GT:biggrin
 
thanks for the good discussion and insights

lthlvpr said:
The stock boost gauge not high quality and is mechanical rather than electrical. Did you do a pulley upgrade and use a MAFIA? These will cause the readings to appear lower. Otherwise it may just be a gauge malfunction.
Click to expand...

Lthlvpr,
yes I have a pulley upgrade and a MAFia. Since I got a new setup with Accufab and stuff, I got a new tune that made me change from setting 1 to setting 2.

Thanks all for the great discussion, only point of worry is I think it deteriorated from what I had before. Based on your all input, I will reload the previous tune, go to setting 1, and recheck. Will also check if there is a 'hole in the charger' or somewhere a loss of pressure, or instrument inaccuracy.

let's see....

Stefan
will report back what's the story.
 
ChipBeck said:
Mafia this and mafia that. What's a mafia?? I keep reading references to it in various posts but I can't figure out what it is.:confused Please help.

Chip
Click to expand...

Chip,

MAFia stands for a Mass Air Flow signal corrector unit that allows to overcome the pegging of the potentiometer, with smaller pulley sucking in more air than the range of the standard setting. See DBK's line, 'boost gauge pegging' :biggrin ...meaning smaller pulley, more air, more boost. Even with a 2,8'' pulley the standard gauge setting will lead to the gauge to pegg
 
... with the whipples coming out and being optimized,
there soon will be a subline somewhere popping up
saying: 'speedometer pegging'...:biggrin
 
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