Which to believe: Mechanical or Electronic boost?

metoo · 02-15-2004, 08:31 PM

I have a new Autometer Z-series mechanical boost guage and a new Greddy Profec B Spec 2 EBC, which is also a boost gauge. The mechanical gauge shares the intake manifold pressure line on the BOV. The Profec B is Tee'd of the intake manifold nipple coming off the front of the manifold. I would think location wouldn't matter as long as it is manifold pressure ( sampled after the TB and before the TGVs) The Autometer gauge always reads 2+ psi more than the EBC while driving. When driving and the Auometer reads 0 psi, the EBC reads around -2.3 psi. Which the engine off, but accessories powered, the EBC reads a perfect 0 psi. The Autometer may be showing just a tad less (this is not 2+psi more, I know).

According to a local tuner, the Profe B Spec 2 reads nearly identical to the unit he uses on car to tune them on the dyno. So I would assume my gauge sucks, and/or not all intake manifold lines are not equal (I doubt that though).

Thought?

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subywrxwrblu · 02-15-2004, 08:37 PM

FWIW, I had a mechanical Autometer boost gauge and it read identical to my SBC-id. Maybe its your Profec B and not your gauge that is reading wrong.

Do you have any other way of checking how much boost you are getting? ie. Deltadash or something like that?

wac · 02-15-2004, 09:53 PM

Quote:

Originally posted by metoo
I have a new Autometer Z-series mechanical boost guage and a new Greddy Profec B Spec 2 EBC, which is also a boost gauge. The mechanical gauge shares the intake manifold pressure line on the BOV. The Profec B is Tee'd of the intake manifold nipple coming off the front of the manifold. I would think location wouldn't matter as long as it is manifold pressure ( sampled after the TB and before the TGVs) The Autometer gauge always reads 2+ psi more than the EBC while driving. When driving and the Auometer reads 0 psi, the EBC reads around -2.3 psi. Which the engine off, but accessories powered, the EBC reads a perfect 0 psi. The Autometer may be showing just a tad less (this is not 2+psi more, I know).

According to a local tuner, the Profe B Spec 2 reads nearly identical to the unit he uses on car to tune them on the dyno. So I would assume my gauge sucks, and/or not all intake manifold lines are not equal (I doubt that though).

Thought?

I wouldn't trust any Autometer boost gauges to be more accurate than +/-2 psi. I've compared my Phantom series boost gauge to two different industrial pressure sensors and the OBD-II readings from the ECU, and the Autometer is always +2 psi high, even with the engine off. I've seen some gauges that read 0 psi with the engine off, so mine somehow made it past quality control. Who knows how many others did?

-WaC
Wayne

metoo · 02-15-2004, 11:29 PM

New info:

Maybe the mechanical gauge just needed a little break-in(?). I put some more miles on the gauge. If anything, it now lags to Greddy unit. The at Idle, my EBC reads -9.9 psi. This is equal to -21.16 in-Hg, which is pretty much what my Autometer reads.

Also, with Autometer being a mechanical gauge with surge protection (very tiny hole for the air to enter) that it takes time for the needle to reach the actual reading of the boost. If I accelerate quickly while short shifting, the needle will never indicate the peak boost numbers I hit between shifts.

The B2 is all electrical. There is no mass to swing, so it's readings are as close to real-time as it gets. I could have it at 14 psi and lift the throttle. The B2 almost imediately reads -9ish, while it takes the needle on the mechanical gauge over a second to fall to -21ish. I did a test to simulate a situation like some would see in auto-x in 2nd gear where you hit the throttle quickly then get off. The autometer gauge needle didn't pass 6psi before I gt off the throttle. The EBC read 11+ each time.

I'll believe the Greddy, but keep the Autometer gauge because it looks nice.

ride5000 · 03-23-2004, 01:18 PM

my autometer sportcomp manifold pressure gauge reacts instantly to presure changes.

yours taking a second to register vacuum doesn't sound right at all.

are you sure your lines aren't kinked or ruptured?

ken

samwY · 03-30-2004, 09:42 PM

get some defi's

vtecTHIS · 03-31-2004, 02:47 PM

sorry, a little OT,butcould a leak in the line cause high idle vacuum pressures,and low boost? i installed my b2 and i think i have a leak somwhere. my stock gauge and b2 read the same. i know my boost is not hitting cuz it feels slow as hell. max psi i get is 4.5

kitbar · 03-31-2004, 04:42 PM

My autometer boost gauge is +3 from what my UTEC shows

autometer -12 vacumm 19psi
UTEC 16.5 PSI

I think the autometer is prob wrong

Big Turkey · 03-31-2004, 06:44 PM

My AVCR is reading a little bit off from the UTEC. I hit a peak of 19.8psi and I had a peak of 1.43 kg/cm^2 on my AVCR. Now if you do the math on kg/cm^2 converted to psi, it is 14.2 = 1.00 kg/cm^2. If that's the case, then the math says it's supposed to be 20.3. But nowhere on the log did it show that. I'm thinking maybe UTEC didn't catch the split second that it spiked to 1.43, or I have a leak in the system somewhere. But mine holds boost all the way to redline. So that should rule out the leak.

02-15-2004, 08:31 PM	#1
metoo Scooby Guru Member#: 4764 Join Date: Mar 2001 Chapter/Region: TXIC Location: Houston Vehicle: 2004 STi sold :( forizzle	Which to believe: Mechanical or Electronic boost? I have a new Autometer Z-series mechanical boost guage and a new Greddy Profec B Spec 2 EBC, which is also a boost gauge. The mechanical gauge shares the intake manifold pressure line on the BOV. The Profec B is Tee'd of the intake manifold nipple coming off the front of the manifold. I would think location wouldn't matter as long as it is manifold pressure ( sampled after the TB and before the TGVs) The Autometer gauge always reads 2+ psi more than the EBC while driving. When driving and the Auometer reads 0 psi, the EBC reads around -2.3 psi. Which the engine off, but accessories powered, the EBC reads a perfect 0 psi. The Autometer may be showing just a tad less (this is not 2+psi more, I know). According to a local tuner, the Profe B Spec 2 reads nearly identical to the unit he uses on car to tune them on the dyno. So I would assume my gauge sucks, and/or not all intake manifold lines are not equal (I doubt that though). Thought? * Registered users of the site do not see these ads.

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02-15-2004, 08:37 PM	#2
subywrxwrblu Scooby Newbie Member#: 9332 Join Date: Aug 2001 Location: hello..shiela...nice tank lady	FWIW, I had a mechanical Autometer boost gauge and it read identical to my SBC-id. Maybe its your Profec B and not your gauge that is reading wrong. Do you have any other way of checking how much boost you are getting? ie. Deltadash or something like that?

02-15-2004, 11:29 PM	#4
metoo Scooby Guru Member#: 4764 Join Date: Mar 2001 Chapter/Region: TXIC Location: Houston Vehicle: 2004 STi sold :( forizzle	New info: Maybe the mechanical gauge just needed a little break-in(?). I put some more miles on the gauge. If anything, it now lags to Greddy unit. The at Idle, my EBC reads -9.9 psi. This is equal to -21.16 in-Hg, which is pretty much what my Autometer reads. Also, with Autometer being a mechanical gauge with surge protection (very tiny hole for the air to enter) that it takes time for the needle to reach the actual reading of the boost. If I accelerate quickly while short shifting, the needle will never indicate the peak boost numbers I hit between shifts. The B2 is all electrical. There is no mass to swing, so it's readings are as close to real-time as it gets. I could have it at 14 psi and lift the throttle. The B2 almost imediately reads -9ish, while it takes the needle on the mechanical gauge over a second to fall to -21ish. I did a test to simulate a situation like some would see in auto-x in 2nd gear where you hit the throttle quickly then get off. The autometer gauge needle didn't pass 6psi before I gt off the throttle. The EBC read 11+ each time. I'll believe the Greddy, but keep the Autometer gauge because it looks nice.

03-23-2004, 01:18 PM	#5
ride5000 Scooby Guru Member#: 32792 Join Date: Feb 2003 Chapter/Region: NESIC Location: lincoln, ri Vehicle: 2003 GGA MBP 12.9 / 105+	my autometer sportcomp manifold pressure gauge reacts instantly to presure changes. yours taking a second to register vacuum doesn't sound right at all. are you sure your lines aren't kinked or ruptured? ken

03-30-2004, 09:42 PM	#6
samwY Scooby Specialist Member#: 31816 Join Date: Jan 2003	get some defi's

03-31-2004, 02:47 PM	#7
vtecTHIS Scooby Guru Member#: 48048 Join Date: Nov 2003 Chapter/Region: International Location: Japan Vehicle: . Nasioc, serious Bidnazz	sorry, a little OT,butcould a leak in the line cause high idle vacuum pressures,and low boost? i installed my b2 and i think i have a leak somwhere. my stock gauge and b2 read the same. i know my boost is not hitting cuz it feels slow as hell. max psi i get is 4.5

03-31-2004, 04:42 PM	#8
kitbar Scooby Newbie Member#: 41411 Join Date: Aug 2003 Location: Kansas City, MO Vehicle: 2004 WRX Sedan Java Black No Spoiler!	My autometer boost gauge is +3 from what my UTEC shows autometer -12 vacumm 19psi UTEC 16.5 PSI I think the autometer is prob wrong

03-31-2004, 06:44 PM	#9
Big Turkey Scooby Specialist Member#: 32118 Join Date: Jan 2003 Location: Houston, TX	My AVCR is reading a little bit off from the UTEC. I hit a peak of 19.8psi and I had a peak of 1.43 kg/cm^2 on my AVCR. Now if you do the math on kg/cm^2 converted to psi, it is 14.2 = 1.00 kg/cm^2. If that's the case, then the math says it's supposed to be 20.3. But nowhere on the log did it show that. I'm thinking maybe UTEC didn't catch the split second that it spiked to 1.43, or I have a leak in the system somewhere. But mine holds boost all the way to redline. So that should rule out the leak.