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PMJ 05-27-2013 10:30 PM

Boost Spike
 
1 Attachment(s)
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...itís 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?

Whipped416 05-27-2013 10:36 PM

I have logged mine and I see nothing higher then 17-18 all the way through .

old motorhead 05-28-2013 07:37 AM

Centrifugal blower with A6?

PMJ 05-28-2013 08:06 AM

No, PD blower w/M6.

realcanuk 05-28-2013 10:23 AM

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.

PMJ 05-28-2013 10:50 AM

Quote:

Originally Posted by realcanuk (Post 6598001)
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.

carlos@redline-motorsport 05-28-2013 11:46 AM

Looks like a little clutch slip at engagement.

PMJ 05-28-2013 02:26 PM

Quote:

Originally Posted by carlos@redline-motorsport (Post 6598310)
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.

PMJ 05-28-2013 10:34 PM

4 Attachment(s)
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 :facepalm:, 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:facepalm:.

These snaps are all before Meth and engine mods.

.

Supercharged SS 05-28-2013 10:37 PM

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.:cry:

PMJ 05-28-2013 10:56 PM

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.

Supercharged SS 05-28-2013 10:58 PM

Quote:

Originally Posted by PMJ (Post 6601183)
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.

PMJ 05-28-2013 11:16 PM

Quote:

Originally Posted by Supercharged SS (Post 6601191)
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. :mad: Was hoping someone else has seen and solved this, but not looking good.

Supercharged SS 05-28-2013 11:19 PM

Quote:

Originally Posted by PMJ (Post 6601246)
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. :mad: 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.

PMJ 05-29-2013 12:33 AM

Quote:

Originally Posted by Supercharged SS (Post 6601261)
Try pm'in Ayousef. That guy knows quite a bit of stuff. He may have an idea.

Thanks. I pm'd him.

ayousef 05-29-2013 08:44 AM

Quote:

Originally Posted by Supercharged SS (Post 6601261)
Try pm'in Ayousef. That guy knows quite a bit of stuff. He may have an idea.

Thanks!

Quote:

Originally Posted by PMJ (Post 6601513)
Thanks. I pm'd him.

Well I have an idea in mind already based on the print screens but cant be too sure, can you send me the log and the file by email? I want the log from where you got the initial printscreen from.

Also, to get correct boost readings always make sure you subtract the Barometric pressure in PSI from MAP PSI, this is the only correct way to do it.

Using a static number such as 14.7 or 14.5 to estimate barometric pressure may only be accurate 10% of the time.

But thats not the problem. Ill send you my email address as a PM :)

carlos@redline-motorsport 05-29-2013 12:07 PM

Quote:

Originally Posted by PMJ (Post 6598888)
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.

Yeah, looking at it again looks like tire spin.

Would be nice to see throttle blade position and pedal position to see what you are actually telling it to do vs what it's doing.

What happens if you go WOT in say 3rd or 4th gear, let off completely around the top of the gear and stab it again without shifting really quick? Also, what happens if you stab it from a high 3rd or 4th (somewhere that you get traction) gear roll? Also, rescale the speed and rpm in order to show more drastic changes in the graph.

Also, does this car have cats or cutouts?

ayousef 05-29-2013 12:50 PM

Quote:

Originally Posted by carlos@redline-motorsport (Post 6602884)
Yeah, looking at it again looks like tire spin.

Would be nice to see throttle blade position and pedal position to see what you are actually telling it to do vs what it's doing.

What happens if you go WOT in say 3rd or 4th gear, let off completely around the top of the gear and stab it again without shifting really quick? Also, what happens if you stab it from a high 3rd or 4th (somewhere that you get traction) gear roll? Also, rescale the speed and rpm in order to show more drastic changes in the graph.

Also, does this car have cats or cutouts?

Carlos, clutch slip or tire spin could not possibly cause a boost spike at all on a blower car, there is absolutely nothing that should cause boost to go up unless you're spinning the blower much quicker at a given RPM and even thats not possible unless the blower's carrying momentum from being spun at a high speed and over boosting at a lower rpm, even this doesnt make sense.

I do have some weird ideas however especially since MAF frequency isnt as high as it should be when the spike occurs.

PMJ 05-29-2013 01:29 PM

Quote:

Originally Posted by ayousef (Post 6602142)
Well I have an idea in mind already based on the print screens but cant be too sure, can you send me the log and the file by email? I want the log from where you got the initial printscreen from.

Also, to get correct boost readings always make sure you subtract the Barometric pressure in PSI from MAP PSI, this is the only correct way to do it.

Using a static number such as 14.7 or 14.5 to estimate barometric pressure may only be accurate 10% of the time.

But thats not the problem. Ill send you my email address as a PM :)

Fantastic! I'll get that e-mail sent out ASAP.


Quote:

Originally Posted by carlos@redline-motorsport (Post 6602884)
Yeah, looking at it again looks like tire spin.

Would be nice to see throttle blade position and pedal position to see what you are actually telling it to do vs what it's doing.

What happens if you go WOT in say 3rd or 4th gear, let off completely around the top of the gear and stab it again without shifting really quick? Also, what happens if you stab it from a high 3rd or 4th (somewhere that you get traction) gear roll? Also, rescale the speed and rpm in order to show more drastic changes in the graph.

Also, does this car have cats or cutouts?

The car has OBX Hi-Flow Cats...I have considered that as one possibility, but i would think it would occur all the time, not just some of the time.

I am hopefully Ayousef finds something, but i like some of your suggestions...I'll see if getting off the throttle and punching it will reproduce it. I'll also see if i can add logging for throttle and pedal positions.

Thanks,
Pat

yonson 05-29-2013 01:30 PM

Has this calibration been scaled? You might have missed something during scaling...

carlos@redline-motorsport 05-29-2013 03:19 PM

Quote:

Originally Posted by ayousef (Post 6603039)
Carlos, clutch slip or tire spin could not possibly cause a boost spike at all on a blower car, there is absolutely nothing that should cause boost to go up unless you're spinning the blower much quicker at a given RPM and even thats not possible unless the blower's carrying momentum from being spun at a high speed and over boosting at a lower rpm, even this doesnt make sense.

I do have some weird ideas however especially since MAF frequency isnt as high as it should be when the spike occurs.

I wasn't implying that was the cause, just pointing it out.

Like I said, hard to figure out what's going on without seeing what position the throttle blade is at. This is why I was asking him about quickly interrupting a pull pre-gear shift. Also, because the PD blowers make instant boost and it's not really dependent on RPM, the only thing that would cause boost to legitimately go up would be a restriction down stream. That is, if it's not the MAP showing pressure backed up behind the throttle blade and the bypass isn't reacting fast enough, as the MAF doesn't seem to be on the same page, like you just mentioned.

Mike TexaSS 05-29-2013 03:44 PM

Ive seen boost spike on CTS-V's when you hit a lean spot.

Id bet your tune is off. If you look at your logs the 02 voltage is extremely lean when the boost spike occurs!

Mike TexaSS 05-29-2013 03:47 PM

Also are you 2.5 bar SD? Or OL MAF? CLMAF.. Details buddy details!

ayousef 05-29-2013 04:49 PM

Quote:

Originally Posted by Mike TexaSS (Post 6603775)
Ive seen boost spike on CTS-V's when you hit a lean spot.

Id bet your tune is off. If you look at your logs the 02 voltage is extremely lean when the boost spike occurs!

You're saying the lean spike is causing the boost spike, hes saying the boost spike is causing the lean spike :noidea:

hes running a MAF closed loop tune

PMJ 05-29-2013 05:30 PM

Quote:

Originally Posted by Mike TexaSS (Post 6603790)
Also are you 2.5 bar SD? Or OL MAF? CLMAF.. Details buddy details!

3 bar ZR1 MAP. Stock MAF.


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