vdo boost gage adjustment

[fredmeister]

i have a clock mounted vdo boost gage that reads about 0.2 bar low.
HOW CAN I REZERO OR ADJUST IT FOR BETTER ACCURACY? i dont see an adjustment screw on the back of the gage housing......hmm.
I have compared it to a map sensor reading from my auxbox LM-1 unit which should be deadnuts accurate.

[kycarguy 935]

You need the reset key that fits over the little triangle in the center of the gauge.

[cole930]

Mr, Fred,

As far as I know North Hollywood is the one place you can get it cleaned and calibrated. Give them a call. If you need one in the interim you can come across the border and get mine.

Cole

[les_garten]

Originally Posted by fredmeister

i have a clock mounted vdo boost gage that reads about 0.2 bar low.
HOW CAN I REZERO OR ADJUST IT FOR BETTER ACCURACY? i dont see an adjustment screw on the back of the gage housing......hmm.
I have compared it to a map sensor reading from my auxbox LM-1 unit which should be deadnuts accurate.

Are you sure it's not the difference in the Pick Off points for your manifold signals? I have the 934 Boost gage and it picks off the Brake booster. It lags and reads lower than the stock sender off the IC.

Les

[fredmeister]

Originally Posted by les_garten

Are you sure it's not the difference in the Pick Off points for your manifold signals? I have the 934 Boost gage and it picks off the Brake booster. It lags and reads lower than the stock sender off the IC.

Les

i thought it could be this, since mine is hooked up off the booster while the mapp sensor reads from the intercooler outlet. but the pressure difference is 0.2 bar or 3 psi which is a large error. is the pressure drop across the throttle body 3psi then?
that means i could run my wastegate setting higher to really see 0.8 bar at the intake manifold or the brake booster.

how many bar or psi does yours lag so i can compare?
Fred

[fredmeister]

Originally Posted by cole930

Mr, Fred,

As far as I know North Hollywood is the one place you can get it cleaned and calibrated. Give them a call. If you need one in the interim you can come across the border and get mine.

Cole

thanks for the offer. i was hoping to avoid a bill and do it myself.....
just call me Fred, you make me feel old with "Mr. Fred'' , bad enuff with my grey hairs and i am only 43.

see ya

[les_garten]

Originally Posted by fredmeister

i thought it could be this, since mine is hooked up off the booster while the mapp sensor reads from the intercooler outlet. but the pressure difference is 0.2 bar or 3 psi which is a large error. is the pressure drop across the throttle body 3psi then?
that means i could run my wastegate setting higher to really see 0.8 bar at the intake manifold or the brake booster.

how many bar or psi does yours lag so i can compare?
Fred

Mine is laid up at present, but Your findings seem to be inline with what I had. The lag was irritating. I was also talking about the time lag, not just the pressure difference. I think you must be seeing that also. But most likely the booster location is more accurate being behind the TB. When I work on mine again, I'm going to get the signal back up directly off the manifold.

[cole930]

Fred,

43 "Old"; I have shoes older than that !!!!

I had the same issue as you and Les when attached at the brake booster. I moved to a T at the wastegate and my telltale needle started showing a consistent .96-.99 with a 1Bar spring. I figured at the wastegate was a good bet because that was the place where the boost pressure was actually used to open the wastegate, consequently , the exact point where I wanted to make sure the boost reading was correct.

Several years ago I made a power bleeder from a lawn sprayer and had put a gage on the sprayer bottle. I attached the sprayer hose to the boost gage and pumped it up while comparing the gage readings, it was nearly dead on up to 1.5 Bar. You can do the same thing with an air compressor if the compressor has a decent gage.

Cole

[fredmeister]

thanks cole, good idea, but what worries me is if there is truly that much pressure loss across the throttle body. that means in reality could we install a 1.1 bar spring knowing that the engine actually sees only 0.9 bar to the valves? this takes the 0.2bar loss into account.
i may run this test and post results once the cut ligament in my hand heals up.

[les_garten]

Originally Posted by fredmeister

thanks cole, good idea, but what worries me is if there is truly that much pressure loss across the throttle body. that means in reality could we install a 1.1 bar spring knowing that the engine actually sees only 0.9 bar to the valves? this takes the 0.2bar loss into account.
i may run this test and post results once the cut ligament in my hand heals up.

Hi,
Cut Ligament, Bummer! Jim2 had that Cessna Gauge plumbed before and after the TB to experiment with TBs to get his loss down. You may want to touch base with him. I would approach your Boost "calibration" carefully here. The Facto Boost gauge was plumbed at the IC. I don't know if they took that into consideration or not. I totally understand what you're saying, but you're making me wince a little.

Les

[cole930]

I assume your logging boost with your Innovate and the MAP sensor. Can you temporally move the Map to the intake and get a couple readings there. Might give us some answers. We can always use .2 Bar of extra "safe" boost.

I'm going to give you some OLD SAGE advice here as I have lived long enough I have made every mistake possible and, thankfully, learned from many of them. Don't screw around with the cut ligament. When I was young, about 43, I cut the tendons and a ligament in my right hand. After a couple weeks I cut the cast off and replaced it with an Ace bandage because it interfered with pulling the ripcord while sky diving. I now have a thumb that looks like a foot and I keep poking myself in the eye when I smoke. Seriously, true story, do what they tell you and take care of that hand until it completely healed. Do the rehab and listen to what the Doc tells you.

Cole

[fredmeister]

i hear ya, but 6 weeks in the middle of summer in a cast really sux. has killed my de dreams this year and i had hopes of running my turbo around a few tracks with some friends. now i cannot even back the car out of the driveway.
doc fixed the tendon to my right thumb last week, now i can hitch hike or give the thumbs up once again....once the physical therapy is finished in 6 weeks.
yeah i am assuming the innovate gage is accurate as hooked up to my bov housing under the intercooler outlet. basing all my findings on this assumption.
i saw video of jim2 and that crazy boost gage but cannot see the gage numbers to tell what kind of pressure drops he was encountering.
this is an interesting discussion.

Originally Posted by cole930

I assume your logging boost with your Innovate and the MAP sensor. Can you temporally move the Map to the intake and get a couple readings there. Might give us some answers. We can always use .2 Bar of extra "safe" boost.

I'm going to give you some OLD SAGE advice here as I have lived long enough I have made every mistake possible and, thankfully, learned from many of them. Don't screw around with the cut ligament. When I was young, about 43, I cut the tendons and a ligament in my right hand. After a couple weeks I cut the cast off and replaced it with an Ace bandage because it interfered with pulling the ripcord while sky diving. I now have a thumb that looks like a foot and I keep poking myself in the eye when I smoke. Seriously, true story, do what they tell you and take care of that hand until it completely healed. Do the rehab and listen to what the Doc tells you.

Cole

[billjam]

Originally Posted by les_garten

Are you sure it's not the difference in the Pick Off points for your manifold signals? I have the 934 Boost gage and it picks off the Brake booster. It lags and reads lower than the stock sender off the IC.
Les

Originally Posted by fredmeister

i thought it could be this, since mine is hooked up off the booster while the mapp sensor reads from the intercooler outlet. but the pressure difference is 0.2 bar or 3 psi which is a large error. is the pressure drop across the throttle body 3psi then?
that means i could run my wastegate setting higher to really see 0.8 bar at the intake manifold or the brake booster.
Fred

Guys, you're not alone out there.
I have had similar issues with different boost readings at different tapping points. The brake booster connection gave me significantly lower readings than the outlet side of the IC and the TB.
This recent thread Strange/Conflicting boost readings is also on same subject.

[les_garten]

Originally Posted by billjam

Guys, you're not alone out there.
I have had similar issues with different boost readings at different tapping points. The brake booster connection gave me significantly lower readings than the outlet side of the IC and the TB.
This recent thread Strange/Conflicting boost readings is also on same subject.

Glad to know it's not isolated to me. I bought one of those Cessna MAP Gauges with the Dual pointers like Jim2. Haven't put it in yet because I'm busy with a ton of other crap but It's on my plate. I really think you want to pick it off the manifold off the Plenum. It would be nice to know how Porsche intended it, when they setup the tuning from an Engineering standpoint. Where it's at now may be a manufacturing convenience, or maybe not.

.

[Jim2]

Fred, I was seeing 2.5"hg pressure drop across the stock throttle body (little over one PSI). This was with 10 psi boost measured inside the intake manifold. After building the 76mm throttle body and opening the mating port on the intake manifold the loss was reduced to about .5 psi. This difference is small but the restrictive effect compounds with increased boost.

Was the larger TB worth the effort? Nah, probably not.

I'd be cautious installing a 1.1 bar spring in order to make up the loss difference from your throttle body since you could be near detonating. However, having an actual reading of boost within your intake manifold is nice versus reading it upstream of a restricitve point. Since the brake booster is tapped into the intake manifold it's a convenient source.

I have no idea why different readings are seen when tapping into the brake booster line. I plumbed a few vacuum lines in permanently so I could do tests, and I dedicated a couple lines for measuring boost.

This, somewhat balding, chipped toothed, pot bellied, grey haired, 43yo needs to go do a rear wheel alignment so he can start driving his car again!

[les_garten]

Originally Posted by Jim2

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I plumbed a few vacuum lines in permanently so I could do tests, and I dedicated a couple lines for measuring boost.

This, somewhat balding, chipped toothed, pot bellied, grey haired, 43yo needs to go do a rear wheel alignment so he can start driving his car again!

Hi Jim,
That's my Plan for the future. I didn't like tapping off the one way valve to the booster and wanted to get a Plenum MAP reading. I'll plumb in my Cessna gauge at the same time! It has white needles and I'm thinking about Coloring the needles, either one or both and possibly marking the face a little for REF points if I can get it open without destroying it, and come up with a marking scheme that doesn't look Hokey. No offence to Hokies intended!

.

[fredmeister]

Originally Posted by Jim2

Fred, I was seeing 2.5"hg pressure drop across the stock throttle body (little over one PSI). This was with 10 psi boost measured inside the intake manifold. After building the 76mm throttle body and opening the mating port on the intake manifold the loss was reduced to about .5 psi. This difference is small but the restrictive effect compounds with increased boost.

Was the larger TB worth the effort? Nah, probably not.

I'd be cautious installing a 1.1 bar spring in order to make up the loss difference from your throttle body since you could be near detonating. However, having an actual reading of boost within your intake manifold is nice versus reading it upstream of a restricitve point. Since the brake booster is tapped into the intake manifold it's a convenient source.

thanks jim for responding.
looking at my findings, i am seeing about 3psi difference in gage pressure between the 2 units at 13.5psi boost measured at the intercooler outlet. part of this could be inaccuracy of the vdo gage, i plan to remove it and calibrate it using my mityvac brake bleeder as a source of pressure. will post results when done.

[les_garten]

Originally Posted by fredmeister

thanks jim for responding.
looking at my findings, i am seeing about 3psi difference in gage pressure between the 2 units at 13.5psi boost measured at the intercooler outlet. part of this could be inaccuracy of the vdo gage, i plan to remove it and calibrate it using my mityvac brake bleeder as a source of pressure. will post results when done.

I'm thinking your gauge is accurate. Is the difference less in 3rd and 4th?

.

[fredmeister]

i think it is consistently the same 3 psi in either 3rd or 4th gear. i cannot pull full boost in the lower 2 gears. i have checked this while running full load down the backstraight at mid ohio, so i am on boost from 80-135mph for a few seconds.
what is your line of thought?

[les_garten]

Originally Posted by fredmeister

i think it is consistently the same 3 psi in either 3rd or 4th gear. i cannot pull full boost in the lower 2 gears. i have checked this while running full load down the backstraight at mid ohio, so i am on boost from 80-135mph for a few seconds.
what is your line of thought?

I noticed on mine that the Facto gauge would show full in 1st and 2nd but the VDO wouldn't or would lag further behind depending on mass flow. It seemed to close the gap as mass flow increased, ie higher gear. Where the Gap was the closest was 4th gear. Just musing out loud.

.