Boost Spike

[JANNETTYRACING]

No one said it was spinning out of Sync.

The boost spike comes when the bypass closes suddenly.

The Bypass responds to Throttle input or the change over from Vacuum to boost, and boost to vacuum.

Ted.

Originally Posted by ayousef

rotor speed is always in sync with crank speed so there is no way the rotor is spinning out of sync causing the boost spike.

What im saying is if at 4000rpms the blower is spinning at 8000rpms (just for the sake of the argument) it should compress enough air to pressurize the manifold 5psi, there is no way the blower is spinning 16,000rpms at 4000rpm engine speed to cause such a HUGE boost spike.

plus if you look at one of his logs the boost was spiking DURING the run.

[JANNETTYRACING]

Originally Posted by ayousef

the bypass valve IS opening between shifts and is very obvious in the printscreens on the first page, notice how MAP drops to a very low value and then jumps and keeps on going up.

I did find that desired throttle position isn't equal to actual throttle position, and ive seen this exact phenomena cause spike even though I dont know how to explain it well, im thinking the throttle body opens up flows alot of air gets to the point where it cannot hold blade position due to the large amount of CFM flowing through the motor shuts partially and causes a spike of pressurized air between the throttle and the cylinders on a decelerating motor, notice how the spikes are happening when the throttlebody is OPEN but rpms are steady or in some cases going down.

This is just a theory.

The bypass lags behind but does follow what the throttle is doing in the opposite direction.

Closed Throttle Open bypass
Open Throttle Closed bypass.

IF he is Flat foot shifting then the bypass is out of the equation.

NOW You also must consider that Air flows like a Slinky, So When the Engine goes from High RPM To a Lower RPM Suddenly Like on a shift, the Air Builds up in the intake as Load is pulling the Motor Down in RPM.

Remember also that Boost is a Product of Restriction, If you suddenly put a load on the motor the Slinky of Air will Spike the Boost.

This really has nothing to do with the Throttle.

This is All very hard to explain in Text, but it's Real.

Ted.

[mikepage0007]

Originally Posted by PMJ

How much boost are you making? Was your stock TB a bottleneck? Whipple says my TB is a bottleneck...i should be making 16+ psi, but only making 15. So if the TPiS lets the air flow, i should get another pound out of it...which should be good for 20+ hp easy. At least that's the theory.

I'm also seeing ridiculous IATs, my coolest run at the track tonight got up to 172 degrees (hotest was 199) ; Ted posted he saw a 25 degree drop in IATs...I'm thinking that and the RX Super CHiller i have ordered should knock out my IAT issue.

I have some work to do, but I'm determined to get into the 10s my next trip to the track.

i was running 15lbs boost. my poblem is. i was overspining he whipple a 18lbs boost wih he 9.5 to 1 compression..so i changed pullies. also iats were 200f back to back pulls...installed a dual whipple he and that go me to 140

[ayousef]

Originally Posted by JANNETTYRACING

The bypass lags behind but does follow what the throttle is doing in the opposite direction.

Closed Throttle Open bypass
Open Throttle Closed bypass.

IF he is Flat foot shifting then the bypass is out of the equation.

NOW You also must consider that Air flows like a Slinky, So When the Engine goes from High RPM To a Lower RPM Suddenly Like on a shift, the Air Builds up in the intake as Load is pulling the Motor Down in RPM.

Remember also that Boost is a Product of Restriction, If you suddenly put a load on the motor the Slinky of Air will Spike the Boost.

This really has nothing to do with the Throttle.

This is All very hard to explain in Text, but it's Real.

Ted.

Not trying to start an argument, but you really seem to be missing my point here, his MAP readings SPIKE while in boost as well, when the bypass valve was shut long before that. Look at the first page in the second set of images and you will see what im talking about, I can also show you a log of another whipple car spiking the MAP reading through a 4th gear pull on the dyno right in the middle of the pull (will post a screenshot later since im using my Macbook now), we also made sure that the bypass valve wasnt moving at all at WOT and remained shut, the only thing that differed was desired vs actual throttle position.

Again, waiting to hear back from Pat on what happens after he swaps to a different and not necessarily larger throttlebody just a different throttlebody.

[PMJ]

Originally Posted by ayousef

Not trying to start an argument, but you really seem to be missing my point here, his MAP readings SPIKE while in boost as well, when the bypass valve was shut long before that. Look at the first page in the second set of images and you will see what im talking about, I can also show you a log of another whipple car spiking the MAP reading through a 4th gear pull on the dyno right in the middle of the pull (will post a screenshot later since im using my Macbook now), we also made sure that the bypass valve wasnt moving at all at WOT and remained shut, the only thing that differed was desired vs actual throttle position.

Again, waiting to hear back from Pat on what happens after he swaps to a different and not necessarily larger throttlebody just a different throttlebody.

Mohamad, Sounds like my TPiS is still a few weeks out... as mentioned, i'm running a vmax cnc ported LS3 TB. I still have my stock LS3 TB...but i'm assuming if my VMAX TB is having an issue, then the stock will have the same issue? Or should i change it out and see what happens?


Ted, my tuner (Bill) and I had already planned to change to a speed density tune based on trouble i've had with tuning around my meth on the MAF tune. He says that will address your recommendation. I do have some hesitation moving to a speed density tune. What is your preference on a whipple/meth car?

In the end, i think if i fix my lean spike, the boost spike may not be an issue...currently the result of both of them together is causing knock and obviously pulling timing. My theory is if i can fix 1 of the 2, my problem (knocking) will go away (i.e. I know when i have the lean spike w/o the boost spike, i don't knock...and i think i've seen atleast 1 boost spike w/a minor lean spike that also did not cause any knock). We'll see if my theory hold true once i fix one of the issues.

I was at the track last night...this run in particular scared me w/ the high knock going to 2nd gear. This was after Ted suggested power shifting...i clearly need driving lessons (as I didn't power shift to 2nd or 3rd...and i'm not sure what i did to 4th would be considered power shift or not), but i think i avoided the bypass from closing going into 4th...no boost spike.

So my path forward is:
- 1 upgrade TB
- 2 fix my tune to remove the lean spike (either SD or Ted's suggestion w/the MAF tune)
- 3 learn how to drive

While i'm at it, i think i'm going to do a cat delete too...

BTW, any suggestion on preventing belt slip? I have a 10-rib belt and still seeing slip...looks like belt conditioner is a short term fix?

thanks,
Pat

[ayousef]

Oh didnt know you still had the stock throttlebody give it a try its a very simple swap, wont loose anything.

Ps. You can see how actual TPS drops while desired was at 100% in the first spike on the latest printscreen. Second time it didnt fall on its face but seemed like it took more time than it should have to match the desired you can see the actual sloping upwards.

Try the stock throttle

[PMJ]

Will give it a shot when I get 20 min...

[JANNETTYRACING]

Originally Posted by ayousef

Not trying to start an argument, but you really seem to be missing my point here, his MAP readings SPIKE while in boost as well, when the bypass valve was shut long before that. Look at the first page in the second set of images and you will see what im talking about, I can also show you a log of another whipple car spiking the MAP reading through a 4th gear pull on the dyno right in the middle of the pull (will post a screenshot later since im using my Macbook now), we also made sure that the bypass valve wasnt moving at all at WOT and remained shut, the only thing that differed was desired vs actual throttle position.

Again, waiting to hear back from Pat on what happens after he swaps to a different and not necessarily larger throttlebody just a different throttlebody.

Neither am I, We are sharing a common goal to Resolve and explain Boost Spikes with a PD blower.

There are Several Things that will cause a boost spike

Sudden load on an engine, for example slipping then grabbing of clutch or tires.

Detonation, causes sudden slowing of the engine.

Bypass Valve on the closing event.

Rotational inertia of the blower not being controlled by the belt because it goes in to a slip on Decel.

This is a big one most people never even consider.

Also Sudden Throttle Opening at High RPM but I don't see this under these circumstances.

Years ago we built a Vortech YSI equipped 347 AOD manual shift, with a Cog drive.

The rotational Inertia of the blower would Clean the Teeth off the cog Drive belt on the 2-3 Shift every 3rd Run because of the sudden RPM Drop in the motor.

A loser converter fixed the problem.

Originally Posted by PMJ

Mohamad, Sounds like my TPiS is still a few weeks out... as mentioned, i'm running a vmax cnc ported LS3 TB. I still have my stock LS3 TB...but i'm assuming if my VMAX TB is having an issue, then the stock will have the same issue? Or should i change it out and see what happens?


Ted, my tuner (Bill) and I had already planned to change to a speed density tune based on trouble i've had with tuning around my meth on the MAF tune. He says that will address your recommendation. I do have some hesitation moving to a speed density tune. What is your preference on a whipple/meth car?

In the end, i think if i fix my lean spike, the boost spike may not be an issue...currently the result of both of them together is causing knock and obviously pulling timing. My theory is if i can fix 1 of the 2, my problem (knocking) will go away (i.e. I know when i have the lean spike w/o the boost spike, i don't knock...and i think i've seen atleast 1 boost spike w/a minor lean spike that also did not cause any knock). We'll see if my theory hold true once i fix one of the issues.

I was at the track last night...this run in particular scared me w/ the high knock going to 2nd gear. This was after Ted suggested power shifting...i clearly need driving lessons (as I didn't power shift to 2nd or 3rd...and i'm not sure what i did to 4th would be considered power shift or not), but i think i avoided the bypass from closing going into 4th...no boost spike.

So my path forward is:
- 1 upgrade TB
- 2 fix my tune to remove the lean spike (either SD or Ted's suggestion w/the MAF tune)
- 3 learn how to drive

While i'm at it, i think i'm going to do a cat delete too...

BTW, any suggestion on preventing belt slip? I have a 10-rib belt and still seeing slip...looks like belt conditioner is a short term fix?

thanks,
Pat

I would not go Strictly Speed Density, Keep it MAF and Tune the Coefficient tables, this is the Best Case Scenario.

Ted.

[PMJ]

I'm pretty sure I have belt slip...I saw an extra # when I used belt conditioner and the belt is sticky after a run.

It's raining at the moment, but now I'm curious if belt conditioner will help the spike? I'm going to look through some logs at 16psi and see if I see spike. If not, I'll do some more tests when the streets dry up.

[PMJ]

i checked my logs and no luck...at my next opportunity, i'll condition the belt...make sure i'm seeing 16psi vs. the high 14s i typically see and then try to reproduce the boost spike.

The 10 rib pulley kit sure is expensive to still have belt slip...

[Whipped416]

U have the wrong belt or something
10 rib here and no slip at 17 psi just the tensioner coming up and hitting the top idler pulley got some custom machined pulleys from adm that should fix this problem.
Send me a pic of your belt setup u can pm me for cell number if u wanna send that way

[mikepage0007]

also ran at 18psi overspinninmg the whipple to 22500 and no belt spin. now running 15psi at 18600 and no belt spin

[PMJ]

Originally Posted by Whipped416

U have the wrong belt or something
10 rib here and no slip at 17 psi just the tensioner coming up and hitting the top idler pulley got some custom machined pulleys from adm that should fix this problem.
Send me a pic of your belt setup u can pm me for cell number if u wanna send that way

So Whipped416 helped me with rerouting my belt to prevent belt slip. (Thank you!) See pic below. I think this may have solved my belt slip issues (based on feel of the belt after the run), but did not address the boost spike.

I also tried a run power shifting which seems to remove the boost spike...something about engaging the clutch at 6000+ rpms with the pedal on the floor just scares me...visions from Days of Thunder even though I know i have a rev limiter...the RPMs still seem to go higher than the limiter a little bit...

I also added my last boost spike...pic. This seems to clearly show Ayousef's theory of throttle body issues. You can actually see the throttle position opening, get sucked back a little as the spike occurs and then finally open up. I hope the TPiS resolves that.

So i think i'm down to just fixing the lean spike and heading back to the track to finally break into the 10s .

[PMJ]

I haven't posted in a while, so not sure if anyone will be looking, but I think i solved what has been causing my boost spike. I think Mike TexaSS was close to right saying "Ive seen boost spike on CTS-V's when you hit a lean spot."

My lean spike, caused detonation...the detonation causes a pressure spike that i think is occuring while the intake valve is not sealed resulting in a "boost spike" that has nothing to do with the mechanics of the blower. The log attached below made it crystal clear to me... or so i think.

Why this happened is a longer story...but needless to say i had an issue w/my tune that i have sense fixed, but i started easing into the throttle and went lean, engine had detonation and all of a sudden boost went from 5psi to 20+psi.

So i've concluded this is 100% a tune issue, although my TPiS should finally be here this week...i was planning the TPiS regardless of this issue.

I've been waiting to get my TPiS before i got a new tune...i was actually testing using the VE coefficients from a ZL1 stock tune when i ran into the issue with the attached log...i think it was because the Dynamic Airflow High RPM Disabled is set at 3800rpm on the ZL1...i moved back down to 2000 and the lean issue seemed to go away. I haven't tested thoroughly, but currently the problem appears to be much better.
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