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Old 05-27-2013, 10:30 PM   #1
PMJ
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Question Boost Spike

For a while I've been working on "reducing" the lean spike after a gear shift. Occasionally it will cause knocking so avoiding is ideal to avoid timing to get pulled (or something worse). After much review, I had an ah ha moment today...the lean spike isn't the issue...it’s a "boost spike".

I never noticed this before, but on a gear shift, i will occasionally see a "boost spike" like pictured below. The boost spike is significantly higher than my "normal" max boost (i'm running 15-16psi, and the boost maxes out my MAP sensor at 22.3psi). As a result I get a lean spike and ultimately detonation.

Any others with a super charger seeing this boost spike on gear shift? Has anyone solved it?
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Old 05-27-2013, 10:36 PM   #2
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I have logged mine and I see nothing higher then 17-18 all the way through .
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Old 05-28-2013, 07:37 AM   #3
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Centrifugal blower with A6?
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Old 05-28-2013, 08:06 AM   #4
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No, PD blower w/M6.
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Old 05-28-2013, 10:23 AM   #5
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What kind of blower ? Some PD blowers do a spike like that right at the top of a run, but mine is .5 to 1 lb.... yours seems excessive.
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Old 05-28-2013, 10:50 AM   #6
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Quote:
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What kind of blower ? Some PD blowers do a spike like that right at the top of a run, but mine is .5 to 1 lb.... yours seems excessive.
I have a whipple 2.9l.
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Old 05-28-2013, 11:46 AM   #7
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Looks like a little clutch slip at engagement.
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Old 05-28-2013, 02:26 PM   #8
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Looks like a little clutch slip at engagement.
Are you saying I got on the gas before letting off the clutch? Or the clutch slipped after I engaged it and hit the gas? It is a mcleod RXT, so I wouldn't expect slip. I think I see a little tire spin as well.

I'm going to post another example prior to my engine mods and new clutch when I get home tonight.
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Old 05-28-2013, 10:34 PM   #9
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So looking back at old logs, i've had this "problem" since day 1. The first shot shows a tuning log right after the whipple install on a stock motor (4" pulley). No AFR gauge at the time.

The second snap is from a texas mile run and shows a double spike! Only one of those i found. This was while running race gas. I had a 3.75" pulley getting a little over 11psi. Street tires.

The 3rd is at the track w/drag radials. Also getting 11psi. This should have been my best run ever, but no doubt the knock made me lose a few hundredths (was a better launch than my all time best that same day).

Last was another run at the texas mile. This was going into fifth gear...as you can see i had trouble getting there , i'm hoping this was resolved with my upgraded clutch, but i could never shift cleanly to 5th at 145 mph... anyway, this one surprises me the most because the blower had spooled down prior to getting in gear, but still see the spike.

Am I the only one experiencing this w/a Whipple or PD blower? Or am i the only one that keeps all his logs.

These snaps are all before Meth and engine mods.

.
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Old 05-28-2013, 10:37 PM   #10
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I don't have any boost spike. I've never had it in 3.5 yrs of pd blower.


And I have no idea what's causing yours. Maybe the belt just grabs better at that moment. I have boost dips do to some slipping though.
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Old 05-28-2013, 10:56 PM   #11
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BTW, my defined "Boost" value is off in all of these by .2 For some reason my defined value had MAP.PSI - 14.7 instead of -14.5. So add .2 to the boost to = the MAP.
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Old 05-28-2013, 10:58 PM   #12
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BTW, my defined "Boost" value is off in all of these by .2 For some reason my defined value had MAP.PSI - 14.7 instead of -14.5. So add .2 to the boost to = the MAP.
I know. I posted about that last night but deleted because I didn't want to crap up the thread with a moot point.
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Old 05-28-2013, 11:16 PM   #13
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I know. I posted about that last night but deleted because I didn't want to crap up the thread with a moot point.
I'm guessing a manual transmition has something to do with it. I'm also assuming it may be something i'm doing...but talking to Mike at Whipple, I'm the first to report this...doesn't sound like i'm going to have a solutions any time soon...or maybe ever. Was hoping someone else has seen and solved this, but not looking good.
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Old 05-28-2013, 11:19 PM   #14
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I'm guessing a manual transmition has something to do with it. I'm also assuming it may be something i'm doing...but talking to Mike at Whipple, I'm the first to report this...doesn't sound like i'm going to have a solutions any time soon...or maybe ever. Was hoping someone else has seen and solved this, but not looking good.
Try pm'in Ayousef. That guy knows quite a bit of stuff. He may have an idea.
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