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I have an 87 turbo with the Lex AFM/550 injector modification, a Cartech intercooler an HKS boost controller and an AEM wideband A/F meter. I want to run 15 psi boost but I find that I can only make full boost in fourth gear. It makes about 11 psi in second and 13 psi in third. Why is the boost depend what gear I am using?
 

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well from what i have read on other threads the stock turbos are only good up to 12 psi after that it is just superheated air and the turbo does not function correctly.
 

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^ It's called overboost. You basically start pumping hot air because the compressor size is too small on the CT26 to get over 12.5 efficiently. Any intercooler won't fix it either.
 

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Check exhaust, make sure its at least 3" all the way, mine had a crappy muffler on it that bottlenecked flow and caused me to lose boost at high RPM, also check your wastegate actuator and look for boost leaks.
 
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