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whats your boost gage at when when cruising

i have been battling some air leaks and one thing i have thought was not right is my boost gauge would be pegged at -.5bar even at speeds of 80-90.

i think i may have finally fixed my air leaks.
usually when i drive about 65, the boost gauge is pegged at -.5bar. when it has run good, it has been just above that. well this morning at a steady 65, it was about -.4 or -.45bar.
i have just replaced my WG which had a LOT of play in the valve guide and i have also been messing with my DV.
i just pulled it out of recirculate mode and vented it to atmosphere. i dont see how the latter would help, but the WG would. i know i was losing boost through it.



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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
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Old 06-14-2013, 03:03 AM
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Crotchety Old Bastard
 
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Where your boost gage sits at cruise depends on many many things, most influential is your speed and turbo threshold. The goal range I use to tune is -10 to -17 psi of vacuum @ 70MPH in 4th gear (-0.8 to -1.2 bar). If you are seeing boost you are wasting fuel.
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Old 06-14-2013, 03:58 AM
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is that 10-17 inches of vacuum?
my gage does not go that far into vacuum to measure.

how or what are you doing to tune it doing this?

i think this could be a big help since my car runs bad at cruising speeds.

also,, right now i have my timing a little retarded and my CP is at 3bar with my AFR at 13.8 at 2500. i realize that is too rich, but retarding my timing richened it up and i dont want to change my CP to correct it. afr at idle is 12.5.
i retarded the timing to see if it would reduce that "miss" i still have.

i will bump my timing back up today.

brian
i am thinking about pulling the motor to fix some little things and was thinking of putting in some cams. what do you have as far as a cam i can put in and how much?
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 06-14-2013, 05:52 AM
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Quote:
Originally Posted by T77911S View Post
is that 10-17 inches of vacuum?
my gage does not go that far into vacuum to measure.
1 bar is 29.52 inches of mercury (in/hg) @ 0C.

So 0.5 bar is nearly 15 inches of mercury (in/hg).

I also see vacuum at cruise. Which converts to boost pretty quickly as you apply throttle and it spools.
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Old 06-14-2013, 10:18 AM
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My measurements are taken at 70 mph. The faster you go the more wind resistance and higher rpm which reduce vacuum. ID say 0.5 bar is about right at 80-90mph.
Cams follow the turbo. Both SC and 964 give good results without sacrifice to vac or fuel mileage.
Yes the transition from vac to boost should be instant if you are in good tune and BOV is working optimal.
Old 06-14-2013, 10:30 AM
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How do you tune to boost - is this more a function of timing than fuel?
Are there general timing or fuel spec's that would put us in the right ballpark?
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Old 06-14-2013, 10:53 AM
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With part throttle at 70 to 80 mph i am also around -0.6 bar. It is generally about the same as at idle. My max boost is 0.8 Bar.
Old 06-14-2013, 01:01 PM
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I'm +0.2 BAR at 80-mph on level grade and constant speed... I run 14.9 AFR at 80-mph.

It's not enough to richen my mixture [boost threshold], but certainly helps with fuel economy!
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Old 06-14-2013, 04:29 PM
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That's where mine is at 80-mph and steady level cruise:
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Old 06-14-2013, 04:32 PM
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Mine is at 0.2bar cruising at hwy speed as well.
Old 06-14-2013, 05:08 PM
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Mooney/Jesper, what is your boost threshold? Full boost rpm? Gears stock?
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Old 06-14-2013, 06:02 PM
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Brian, I am not sure I have for a data lo on it, and my car is still in AL, me in Cali. - moving.
By memory: Boost threshold is very low 1700-1800 I won't give a number for full boost. At that time I ha e until now been hanging on trying to monitor afr.
Old 06-14-2013, 07:48 PM
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Quote:
Originally Posted by RarlyL8 View Post
Mooney/Jesper, what is your boost threshold? Full boost rpm? Gears stock?
Boost threshold is set to about 0.4 BAR - - that's when enrichment begins to occur.
Full Boost RPM is about 3,600 under WOT
Currently Stock Gears. I used to have 8:41 and my boost [and engine noise] at 80 mph was a bit higher...

The only way I'd have negative MAP while cruising would be if I was decelerating...
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Old 06-15-2013, 04:49 AM
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By threshold I mean at what RPM do you first see positive pressure while accelerating in 4th gear. I would anticipate that to be ~2400rpm if you are seeing 1bar at 3600rpm.

Enrichment of the boost circuit on the WUR occurs ~0.4bar, however enrichment of control pressure occurs the moment positive pressure is seen by the WUR (this is the differential between the vac line signal and the ambient pressure port). If you have an AFR meter on board you should see the AFR drop in the absence of vacuum.
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Old 06-15-2013, 06:45 AM
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Also where are they taking the boost reading from.. before or after the top side of the throttle butterfly or directly from the intake manifold or brake booster hose?

That makes a big difference.
Old 06-15-2013, 09:53 AM
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Mine is at 1.5bar...
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Old 06-15-2013, 04:04 PM
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Quote:
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Mine is at 1.5bar...
Boosting to the moon
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Old 06-15-2013, 06:32 PM
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i dont understand this "threshold".

i feel a kick around .5bar. is this the threshold?

80mph and +.2bar vs rarely8's minus .8bar at 80? thats a big difference.

my boost reading is manifold. i want to use one of my DOD hoses to connect another gauge to read boost above the plate. i am curious to see what it does when i close the throttle. i also want to do this with my DV not connected.
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86 930 42kmiles [__] RUNNING:[__] NOT RUNNING: ____77 911S widebody: SOLD
88 BMW 325is 200K+ SOLD
05 BMW 330CI 130K:: [__] RUNNING: [__] NOT RUNNING:
08 VOLVO V70 190K:: [__] RUNNING: [__] NOT RUNNING:
90 B2200[__] RUNNING:[] NOT RUNNING:__2000 MER E320 WAGON [] WRECKED:[]RUNNING:
Old 06-15-2013, 06:38 PM
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Threshold is exactly the rpm that you notice positive boost.
For example, mine starts to move past the 0 boost or out of vacuum at 1900 rpm. I start to really move though at .4 bar and full boost(.8 bar) is 3000rpm for my car.
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Old 06-15-2013, 06:46 PM
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Boost threshold is the point (rpm) where boost is first observed when accellerating on a flat surface in high gear (3rd is good). The point where the boost needle first lifts off of zero.
For example, my old red rocket would move off of zero at ~1700rpm in 3rd gear and reach 1.0bar at ~2700rpm. Boost threshold 1700rpm, full boost 2700rpm. The last 500rpm of that range went by very quickly. If cruising above the full boost rpm, such as 70mph @3400rpm (915 tranny) the transition from vac to boost was instant with the movement of my big toe. I could adjust my driving habits for optimal fuel mileage by watching the vac/boost gage.

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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
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Old 06-15-2013, 06:54 PM
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