Boost Spike

[PMJ]

Originally Posted by ayousef

I concluded that ill forget half of the stuff I wanna say by tomorrow so im typing this now.

- Disabling transient fueling MIGHT cause a change, transient fueling is basically a fuel adder/subtractor based on throttle position changes whether you are getting onto the throttle or off of it, and its purpose is to estimate the amount of fuel injected that will NOT end up in the combustion chamber yet stick on the intake port wall and evaporate from heat (simple definition). There is a master disable switch which could turn this off for some experimenting.

- Regardless of what tuners say I always put my wideband after the x-pipe or in the y-pipe if applicable, yes putting it that far isn't that accurate for part throttle and idle which I never use my wideband for but its spot on for WOT infact a reading at the collector could be 0.2:1 richer than having it far back, so its conservative.

- The FPCM is an electronic device that controls the fuel supply by changing the pulsewidth signal to the pump, when fuel demand increases it starts pulsing the pump quicker etc... The problem with this is the small delay between the ECU sensing an increase pump speed demand, increasing the pump speed, flowing the fuel to the injectors which is why you can clearly see a fuel pressure dip when you floor it. I was taking the injector delta thing you got on your log too seriously but it looks like its way off!

Injector pressure delta is basically (fuel pressure - manifold pressure), if manifold pressure is below barometric pressure (vacuum) then use a minus so the injector essentially becomes "bigger" and vice versa. Now the problem I see here is when you're going WOT, fuel pressure drops momentarily to about 45psi and you're instantly making 17.5psi of boost, so your injector pressure delta is about 27.5psi which is very bad itself. This is exactly why we have 1:1 boost referenced regulators because say on my car with a base fuel pressure of 60psi, the pressure delta is ALWAYS 60psi etc...

- On a Whipple I guess you're bound to seeing one side being richer than the other, I would like to think its because one rotor spins 66% faster than the other one but im not sure. Instead of moving the wideband just log narrowband readings from both cylinder banks because AFR is dipping past 14.6 so the narrowbands show a lean reading as well.

- Your IATs went crazy high on the last pull in the last screenshot however increased steadily on the WOT run before the last one, I think it has something to do with the detonation cause it really spiked. I think you should richen the mixture a bit or reduce spark advance just to be safe, make the IAT vs spark table more aggressive on higher IATs.

- So my conclusion here is restrict the bypass valve in the blower like Ed suggested, slow down the throttle transition rate and if you still have the fuel pressure drop at the WOT stab you can use it to your advantage, you should do a few runs and measure the fuel pressure delta at this very spot then goto the Injector vs flowrate table in the tune and at the same pressure delta spots REDUCE the injector size, this will trick the ECU to think the injector is smaller and force it to command higher duty cycle for this short moment only and your problem might as well be gone!

This is all theoretical of course >.<

believe it or not I did one 2-3 shift in my ZL1 and saw a lean spike as well, I haven't duplicated it yet however since im fixing my fuel heating issue first.

I'll give the transient fuel disabled a try tonight (I hope).

Yes, from what I've read and heard, the SS ECU does not acknowledge boost (despite the 3 bar MAP), so inj delta is nothing more than fuel pressure when in boost.

I don't think I buy the comment on the whipple pushing more boost on one side than the other...it is all connected, so pressure should be distributed relatively equally...nice try though

The detonation definitely raises IATs quick. I was running race gas above, so I don't pull any timing below 200* on my race tune (even w/o detonation, running the whipple on a 2.75" pulley in Houston results in very high IATS). My street tune is more conservative...

Slowing the throttle definitely works to reduce the boost spike...when it works like it's supposed to...the spike to 50%+, drop 30%, spike back to 100% irritated me greatly... I think the jet Ted recommended will have the same effect mechanically instead of electronically...so if it works, i'm going to move the throttle back to 100% and try to keep the damn computer out of it!

So I just looked at my friends log...I ran his car twice the last time I was at the track (his 2 fastest runs in his car ever ). He has a similar build with a Maggie vs. my whipple. He is running less boost, but I had this problem at 9# of boost as well. He doesn't have a wide band, and looking at his fuel pressure, he is still on a stock SS fuel pump (it dropped to 46# by the end of the pull & 38# on the stab). Based on the narrowband, he had what I would guess is a lean blip...but nowhere near the spike I have.

[PMJ]

OK, I just made 2 pulls w/transient fuel disabled...I hope this made it worse, because I knocked both times. I made one pull w/it enabled again and didn't knock...but that's not enough sample set to conclude i'm good at the moment.

The thing that's frustrating is I saw a boost spike w/the slow throttle...this goes back to my original theory of detonation causes a boost spike. I'm thinking I have multiple things causing a boost spike.

I do see when I have the lean spike, it is on both sides based on the narrowband.

I would like to get one more track night in before prepping my car for the mile...

[ayousef]

shit okay that didn't help but what you do next SHOULD definitely fix the lean issue which might fix the boost spike?

your injector delta will never ever reach 42psi except in this lean spike, infact it will never drop below 45psi SO:

- goto the injector flow rate vs pressure table and select all the cells from 44.7psi until the lowest cell which in my tune at least is 18.6psi and multiply them by 0.9, then select from 44.7psi to 50.5psi and click interpolate between horizontal bounds so it smoothens the transition, this will only edit the cell in the middle which is the 47.6psi cell.

Keep transiet fuel ON this time since your saying its better with it turned on.

Then, goto the throttle opening rate table and right click >> column axis >> edit.

make the values 1250, 2500, 3750, 5000, 6250

and for the in-gear from 1st to 6th gear values enter:

5 for 6250
4 for 5000
3 for 3750, 2500 and 1250

Do both changes the same time and log, look at how throttle position rate responds to those values cause it might be a trial and error thing.

im positive you will come back with better news the next time!

[PMJ]

Originally Posted by ayousef

shit okay that didn't help but what you do next SHOULD definitely fix the lean issue which might fix the boost spike?

your injector delta will never ever reach 42psi except in this lean spike, infact it will never drop below 45psi SO:

- goto the injector flow rate vs pressure table and select all the cells from 44.7psi until the lowest cell which in my tune at least is 18.6psi and multiply them by 0.9, then select from 44.7psi to 50.5psi and click interpolate between horizontal bounds so it smoothens the transition, this will only edit the cell in the middle which is the 47.6psi cell.

Keep transiet fuel ON this time since your saying its better with it turned on.

Then, goto the throttle opening rate table and right click >> column axis >> edit.

make the values 1250, 2500, 3750, 5000, 6250

and for the in-gear from 1st to 6th gear values enter:

5 for 6250
4 for 5000
3 for 3750, 2500 and 1250

Do both changes the same time and log, look at how throttle position rate responds to those values cause it might be a trial and error thing.

im positive you will come back with better news the next time!

Good call on the injector settings! This definitely helped...I still have some tweaking to do, but definitely helped. So any ill side effects I should be concerned with?

Your throttle settings seem to be a little more complicated than needed.

I started w/all set to 3 and clean as can be. Then I got greedy and set it all back to 100 ...that didn't quite work out the way I hoped. I settled on 8 and looked like I was in good shape from 3rd to 4th, but then I tried 2nd to 3rd...can't do it WOT on street tires, and it knocked pretty bad. 4th to 5th also at WOT knocked bad (practice for the mile ).

So, I think my conclusion is the flow vs. pressure solution definitely worked...now I just need to get to the track so I can test different rates for injectors and throttle.

The 90% was just a starting point...correct? Any concerns or ill effects if I go smaller?
Thanks Mohamad!

BTW, after many tweaks and runs tonight, I've gone back to the theory that detonation is causing the boost spike. I did see a boost spike w/out logged KR, but I heard the knock...some reason the sensors didn't log it.

I still think I can benefit from slowing down the bypass valve, so still plan to test that when I get the jets I ordered.

[PMJ]

BTW, I just noticed something else I think is contributing...my timing doesn't get down to where it is supposed to be fast enough...for example at 5013 rpm, 1.42 CylAir my timing is still at 22, coming down from 30+...no wonder I'm knocking!

I'm thinking I need to lower my timing in the high RPM low Cylinder Air range...so it doesn't have so far to come back down???

[ayousef]

Originally Posted by PMJ

BTW, I just noticed something else I think is contributing...my timing doesn't get down to where it is supposed to be fast enough...for example at 5013 rpm, 1.42 CylAir my timing is still at 22, coming down from 30+...no wonder I'm knocking!

I'm thinking I need to lower my timing in the high RPM low Cylinder Air range...so it doesn't have so far to come back down???

wohooow it worked, how awesome is that. there is 0 downside to what you're doing, your car will NEVER ever get into this range of the injector flow rate table except in this specific scenario, there isn't any other time injector delta would go down to 37psi.

Now 0.9 was not only a starter it was also nothing but a guess, you can see how injector duty cycle now goes UP during the dip, I think you should now try to multiple that range by 0.95 but again you need to smothen to make sure the changes are not abrupt. Keep doing small steps until the it doesn't get lean enough, a little lean during the shift is fine, I confirmed that my car does it as well yesterday but I cant use this trick to fix my lean spike unfortunately lol.

Also I did notice the timing thing, lower the timing in that portion of the table by a few degrees and I think your problem is gone for good even if you don't restrict the blower bypass valve. Now put the MAF sensor back on!

[ayousef]

also don't get too greedy on the throttle thing, use the injector trick as the main solution and back it up by slowing down the throttlebody slightly, you wont even feel it being slower if im not mistaken and this way you could bang the shifts without worrying either since it will ramp in the power more linearly.

[PMJ]

Originally Posted by ayousef

wohooow it worked, how awesome is that. there is 0 downside to what you're doing, your car will NEVER ever get into this range of the injector flow rate table except in this specific scenario, there isn't any other time injector delta would go down to 37psi.

Now 0.9 was not only a starter it was also nothing but a guess, you can see how injector duty cycle now goes UP during the dip, I think you should now try to multiple that range by 0.95 but again you need to smothen to make sure the changes are not abrupt. Keep doing small steps until the it doesn't get lean enough, a little lean during the shift is fine, I confirmed that my car does it as well yesterday but I cant use this trick to fix my lean spike unfortunately lol.

Also I did notice the timing thing, lower the timing in that portion of the table by a few degrees and I think your problem is gone for good even if you don't restrict the blower bypass valve. Now put the MAF sensor back on!

It does seem to be a little ironic that I can fix my lean spike due to an inadequate fueling system . I guess this means no fuel system upgrade for me! Moving back to MAF tune and setting it all up now...hope to test drive tonight.

(my damn car is so obnoxiously loud...I hate driving through the neighborhood after 10pm...)

[PMJ]

Well, I did a little testing on the tune after rolling back to the MAF tune and then updating all the new settings. Unfortunatley I didn't get in as many test runs as I would have liked...police decided they didn't like my going 140 down their road. (I swear its a safe feeder road for tuning, and luckily he agreed and let me off w/a verbal warning .) Normally I don't get quite that fast, but the mile is coming up, and last year I had a hell of a time shifting 4-5th at 6K... I think the new clutch is going to help out greatly!

Decided to call it a night.

I reduced the low pressure injector size a little more and smoothed after I got home...I think I'm ready to try it out at the track!

[ayousef]

Originally Posted by PMJ

Well, I did a little testing on the tune after rolling back to the MAF tune and then updating all the new settings. Unfortunatley I didn't get in as many test runs as I would have liked...police decided they didn't like my going 140 down their road. (I swear its a safe feeder road for tuning, and luckily he agreed and let me off w/a verbal warning .) Normally I don't get quite that fast, but the mile is coming up, and last year I had a hell of a time shifting 4-5th at 6K... I think the new clutch is going to help out greatly!

Decided to call it a night.

I reduced the low pressure injector size a little more and smoothed after I got home...I think I'm ready to try it out at the track!

Did that two days ago so I know how it feels, for some reason it freaked me out much more than before, maybe im getting old I dunno.

But yes, it definitely is ironic, cause if you didn't have the fuel pressure dip there was no way you could have solved the issue lol. Again though I don't think your fuel system is inadequate, its just that it cannot respond to a sudden increase in demand from the ECM that quick, with that said try to keep your fuel level as high as possible to avoid any possible issue

Please report back on what you end up at with the new changes.

[PMJ]

Will report back when I get back to the track. Hopefully with a 10.5 number!

[Blue70SS]

Originally Posted by JANNETTYRACING

A simple fix is to restrict the vacuum source to slow the closing of the bypass.

You can use a motorcycle carb jet in the bypass tube I would start around .030

Ted.

About how much longer is the bypass held open doing this? And does it have the opposite effect on opening the bypass - takes slightly longer initially?

Sounds like a great idea, in that it seems to take about 1/2 second to ramp the boost back up for me.

[JANNETTYRACING]

Originally Posted by Blue70SS

About how much longer is the bypass held open doing this? And does it have the opposite effect on opening the bypass - takes slightly longer initially?

Sounds like a great idea, in that it seems to take about 1/2 second to ramp the boost back up for me.

It really depends on the size of the orifice.

If boost is slow to ramp up either the throttle is slow or the bypass is slow and a jet would just slow the bypass more.

Ted.

[Blue70SS]

Originally Posted by JANNETTYRACING

A simple fix is to restrict the vacuum source to slow the closing of the bypass.

You can use a motorcycle carb jet in the bypass tube I would start around .030

Ted.

Originally Posted by JANNETTYRACING

It really depends on the size of the orifice.

If boost is slow to ramp up either the throttle is slow or the bypass is slow and a jet would just slow the bypass more.

Ted.

Thanks Ted...sounds like a balancing act, but if I can hold boost during shifts, I suppose getting into boost off the line will be the easy part. I just ordered a .30 and a .35 to experiment with for the 1/4 mile. It looked like the smallest was .30 for Mikuni.