boost spike?
Jun 26, 2012, 09:33 PM
#1
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boost spike?
so a while back my car was over boosting and the knock sensor was coming on, lowered the boost never seen the light again until once tonight. flashed a couple of times did a pull to make sure i wasent running lean and i wasent. was it maybe a boost spike that caused it bc im tuned to 23 pounds and if i spike over that can it cause the sensor to go off? im pretty sure i have a sh*tty boost controller also, plus it was a little cooler outside last night compared to the weather we have been seeing here
Last edited by deadstockkpomp; Jun 27, 2012 at 05:28 AM.
Jun 27, 2012, 02:34 PM
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Will you explain how exactly you are determining knock? Do you have a dedicated knock gauge, or are you logging knock counts? What's the sensing device?
Last edited by sparky; Jun 27, 2012 at 04:16 PM.
Jun 27, 2012, 04:09 PM
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When the nights are cold and the days are relatively warm you can have boost control issues to a certain extent. Let's suppose that there is a 20-30* F. variance between the ambient temperature high and the ambient temperature low and that your car was tuned for and the boost set while the warmer temperature was prevailing. Then at night it would be reasonable to expect boost to increase anywhere between 2-4 PSI.
This is always going to happen if you are using any MBC. In contrast, with ECU controlled boost or an EBC this air temp induced boost variance shouldl not be an issue.
This is always going to happen if you are using any MBC. In contrast, with ECU controlled boost or an EBC this air temp induced boost variance shouldl not be an issue.
Last edited by sparky; Jun 27, 2012 at 04:12 PM.
Jun 27, 2012, 06:25 PM
#6
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I bought the car it was tuned for 23 pounds,cel started flashing, so i turned the boost down and though it was fixed, then last night it came back i turned the boost down to like 18 pounds now its not knocking anymore, my gauge is off by about 2 pounds maybe when it was tuned someone did not notice it sits slightly below zero, i belive the flashing lights a tephra mod, but i lowered my boost today and did a bunch of pulls and dont see it anymore, hope it stays like that. I did some good pulls so its set fine now i believe..
Jun 27, 2012, 09:00 PM
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I bought the car it was tuned for 23 pounds,cel started flashing, so i turned the boost down and though it was fixed, then last night it came back i turned the boost down to like 18 pounds now its not knocking anymore, my gauge is off by about 2 pounds maybe when it was tuned someone did not notice it sits slightly below zero, i belive the flashing lights a tephra mod, but i lowered my boost today and did a bunch of pulls and dont see it anymore, hope it stays like that. I did some good pulls so its set fine now i believe..
You really need to know exactly what your peak boost setting is. Consequently, I would throw your present gauge in the trash if it is 2# off. BTW, 2# off at 18# is 10% error margin. But your gauge is 2# off at atmospheric, so it may be even further out of whack at 18#.
What gear are you doing your WOT boost testing in anyhow? From my experience it is best to do it in fifth or the highest gear possible given your local road safety conditions. I realize that it is kinda dangerous to go WOT in 5th on public roads. So, try it in 4th on a slight uphill grade on the turnpike instead.
Oh and get someone really good to tune your car. I think that a road tune is best if possible. Set your boost at night under the coldest seasonal ambient temps. In Northern California during the spring and summer it can get pretty hot during the day and cool off down into the mid to low fifties at night. So, when I used to live there I would set the boost on my GN at night. I figured that this was the safest thing to do. That way during the day the boost would automatically be a couple PSI lower than at night but I was tuned for the higher nightime boost scenario.
I don't much like third for testing boost as there is not enough load on the engine and the motor tends to pull through the turbo. That is the motor revs quicker than the turbo spools. So, you hit engine redline too quick before turbo shaft speeds fully overcome rotational inertia. Turbo shaft speeds and engine revs are not directly proportional as would be the case on a supercharged motor.
Last edited by sparky; Jun 27, 2012 at 09:21 PM.
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Jun 27, 2012, 10:21 PM
#8
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Get a new boost gauge. Digital such as zeitronics are the most precise. Get one that has a peak boost hold or playback feature. I think that the zeitronics has an adjustable high boost alarm output function.
You really need to know exactly what your peak boost setting is. Consequently, I would throw your present gauge in the trash if it is 2# off. BTW, 2# off at 18# is 10% error margin. But your gauge is 2# off at atmospheric, so it may be even further out of whack at 18#.
What gear are you doing your WOT boost testing in anyhow? From my experience it is best to do it in fifth or the highest gear possible given your local road safety conditions. I realize that it is kinda dangerous to go WOT in 5th on public roads. So, try it in 4th on a slight uphill grade on the turnpike instead.
Oh and get someone really good to tune your car. I think that a road tune is best if possible. Set your boost at night under the coldest seasonal ambient temps. In Northern California during the spring and summer it can get pretty hot during the day and cool off down into the mid to low fifties at night. So, when I used to live there I would set the boost on my GN at night. I figured that this was the safest thing to do. That way during the day the boost would automatically be a couple PSI lower than at night but I was tuned for the higher nightime boost scenario.
I don't much like third for testing boost as there is not enough load on the engine and the motor tends to pull through the turbo. That is the motor revs quicker than the turbo spools. So, you hit engine redline too quick before turbo shaft speeds fully overcome rotational inertia. Turbo shaft speeds and engine revs are not directly proportional as would be the case on a supercharged motor.
You really need to know exactly what your peak boost setting is. Consequently, I would throw your present gauge in the trash if it is 2# off. BTW, 2# off at 18# is 10% error margin. But your gauge is 2# off at atmospheric, so it may be even further out of whack at 18#.
What gear are you doing your WOT boost testing in anyhow? From my experience it is best to do it in fifth or the highest gear possible given your local road safety conditions. I realize that it is kinda dangerous to go WOT in 5th on public roads. So, try it in 4th on a slight uphill grade on the turnpike instead.
Oh and get someone really good to tune your car. I think that a road tune is best if possible. Set your boost at night under the coldest seasonal ambient temps. In Northern California during the spring and summer it can get pretty hot during the day and cool off down into the mid to low fifties at night. So, when I used to live there I would set the boost on my GN at night. I figured that this was the safest thing to do. That way during the day the boost would automatically be a couple PSI lower than at night but I was tuned for the higher nightime boost scenario.
I don't much like third for testing boost as there is not enough load on the engine and the motor tends to pull through the turbo. That is the motor revs quicker than the turbo spools. So, you hit engine redline too quick before turbo shaft speeds fully overcome rotational inertia. Turbo shaft speeds and engine revs are not directly proportional as would be the case on a supercharged motor.
I did most of my pulls in 2nd and 3rd gear strong pulls no knock so im pretty happy, just went for a ride and its pretty cold no issues.
Jun 28, 2012, 07:53 PM
#9
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Get a new boost gauge. Digital such as zeitronics are the most precise. Get one that has a peak boost hold or playback feature. I think that the zeitronics has an adjustable high boost alarm output function.
You really need to know exactly what your peak boost setting is. Consequently, I would throw your present gauge in the trash if it is 2# off. BTW, 2# off at 18# is 10% error margin. But your gauge is 2# off at atmospheric, so it may be even further out of whack at 18#.
What gear are you doing your WOT boost testing in anyhow? From my experience it is best to do it in fifth or the highest gear possible given your local road safety conditions. I realize that it is kinda dangerous to go WOT in 5th on public roads. So, try it in 4th on a slight uphill grade on the turnpike instead.
Oh and get someone really good to tune your car. I think that a road tune is best if possible. Set your boost at night under the coldest seasonal ambient temps. In Northern California during the spring and summer it can get pretty hot during the day and cool off down into the mid to low fifties at night. So, when I used to live there I would set the boost on my GN at night. I figured that this was the safest thing to do. That way during the day the boost would automatically be a couple PSI lower than at night but I was tuned for the higher nightime boost scenario.
I don't much like third for testing boost as there is not enough load on the engine and the motor tends to pull through the turbo. That is the motor revs quicker than the turbo spools. So, you hit engine redline too quick before turbo shaft speeds fully overcome rotational inertia. Turbo shaft speeds and engine revs are not directly proportional as would be the case on a supercharged motor.
You really need to know exactly what your peak boost setting is. Consequently, I would throw your present gauge in the trash if it is 2# off. BTW, 2# off at 18# is 10% error margin. But your gauge is 2# off at atmospheric, so it may be even further out of whack at 18#.
What gear are you doing your WOT boost testing in anyhow? From my experience it is best to do it in fifth or the highest gear possible given your local road safety conditions. I realize that it is kinda dangerous to go WOT in 5th on public roads. So, try it in 4th on a slight uphill grade on the turnpike instead.
Oh and get someone really good to tune your car. I think that a road tune is best if possible. Set your boost at night under the coldest seasonal ambient temps. In Northern California during the spring and summer it can get pretty hot during the day and cool off down into the mid to low fifties at night. So, when I used to live there I would set the boost on my GN at night. I figured that this was the safest thing to do. That way during the day the boost would automatically be a couple PSI lower than at night but I was tuned for the higher nightime boost scenario.
I don't much like third for testing boost as there is not enough load on the engine and the motor tends to pull through the turbo. That is the motor revs quicker than the turbo spools. So, you hit engine redline too quick before turbo shaft speeds fully overcome rotational inertia. Turbo shaft speeds and engine revs are not directly proportional as would be the case on a supercharged motor.
Jun 29, 2012, 06:06 AM
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Good to see everything is back under control! Did you have to make any adjustments to your boost? So, if it is controlling boost at night in 4th then you should be safe for the remainder of the summer months. When the weather cools in the Fall you may have to lower the boost a couple PSI again. So, just keep that in mind. Nice looking gauge setup, BTW.
Jun 29, 2012, 06:37 AM
#11
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Good to see everything is back under control! Did you have to make any adjustments to your boost? So, if it is controlling boost at night in 4th then you should be safe for the remainder of the summer months. When the weather cools in the Fall you may have to lower the boost a couple PSI again. So, just keep that in mind. Nice looking gauge setup, BTW.
Jun 29, 2012, 06:33 PM
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I imagine that your Evo being an '03 VIII with the stock turbo might still have the 9.8cm turbine housing. Or are you aware whether the previous owner had done the popular upgrade to the 10.5cm housing?
You might want to check the housing to see if it is the original 9.8 piece. If so, then you might consider upgrading to the 10.5 single puck housing. It will free up about 10-15 WHP. But, more importantly it has a less restrictive inlet area and less tangential bypass port radius. In other words it has better bypass flow which helps minimize creep relative to the more restrictive 9.8 dual port design.
You might want to check the housing to see if it is the original 9.8 piece. If so, then you might consider upgrading to the 10.5 single puck housing. It will free up about 10-15 WHP. But, more importantly it has a less restrictive inlet area and less tangential bypass port radius. In other words it has better bypass flow which helps minimize creep relative to the more restrictive 9.8 dual port design.
Last edited by sparky; Jun 29, 2012 at 06:36 PM.
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