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Old 02-15-2004, 08:31 PM   #1
metoo
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Default 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?
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Old 02-15-2004, 08:37 PM   #2
subywrxwrblu
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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?
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Old 02-15-2004, 09:53 PM   #3
wac
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Default Re: Which to believe: Mechanical or Electronic boost?

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
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Old 02-15-2004, 11:29 PM   #4
metoo
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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.
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Old 03-23-2004, 01:18 PM   #5
ride5000
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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
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Old 03-30-2004, 09:42 PM   #6
samwY
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get some defi's
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Old 03-31-2004, 02:47 PM   #7
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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
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Old 03-31-2004, 04:42 PM   #8
kitbar
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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
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Old 03-31-2004, 06:44 PM   #9
Big Turkey
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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.
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