Radical boost spike 41psi!!!
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Teching In
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Radical boost spike 41psi!!! Can anyone explain this? I have a 355 LT1, GT42 76mm, with a 14lb spring in the wastegate. On 2 seperate ocassions the car has spiked to more than 30psi. The lastest time I caught it on a data log registered at 288kpa. I have a walbro 255 fuel pump and 75# holley injectors, other than that the fuel system is stock. A/F never went above 10.81 and I didn't register any knock. This is all on 93 octane. Usually the car will stay below 16psi and pull hard. These odd times the boost has spkied the car doesn't feel like its boosted at all, very sluggish. I have not duplicated this since because I am afraid of doing damage. I don't really think these readings are what the combustion chamber is seeing because there would be pieces of my motor on the freeway. The car is not pushing water and everything under the hood looks fine. Any ideas?
Staging Lane
Joined: Aug 2006
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From: clemson / charleston SC
Maybe sticking wastegate, but I would think that the car would act differently if there was a spike that big... different A/F ratio, lots of knock, or an explosion. that sounds pretty scary.
good luck,
-John
good luck,
-John
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Teching In
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The wastegate will be tested to make sure its opening. Its not just the gauge that sees that pressure its also the MAP sensor with FAST. The Autometer gauge stops at 30 and its sees the "oo" of the word "boost" the the bottom. One mech. and one electric, same reading.
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Atmosphere is around 100 kpa alone so you need to subtract that if you are logging map. Do you have any kind of controller? If it was my car I would run a new line from the boost source of your choice directly to the side port(reference) on the wastegate and eliminate the line as well as any possible controller problem.
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Verdad Gallardo Thread Starter
Teching In
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hey anthony, raz was telling me the same thing at work today but I didn't think about the automatic atmosphere subtraction. I have run a new, larger line directly from the compressor housing to the wastgate but have not driven it since. I want to find out what all might be causeing this before it happens again.
If it is only 25-26psi then I won't worry as much about it as I would if it were 40+. But why would my 30psi autometer gauge still peg out way past 30 if its only 25?
You guys are being a huge help. I will get the car out tomorrow night and see what happens when I data log with PSI.
If it is only 25-26psi then I won't worry as much about it as I would if it were 40+. But why would my 30psi autometer gauge still peg out way past 30 if its only 25?
You guys are being a huge help. I will get the car out tomorrow night and see what happens when I data log with PSI.
If you have enough time drive by the shop we will get it sorted out. Autometer guages are not the most accurate thing on the planet....but I would add some fuel to it after the target boost incase it does spike it will just be too rich to hurt anything.
