If I put in some big injectors, would the 18cm2 still be laggy for around town driving? I would rather add injectors rather than swap out the whole turbo then wish I had a bigger turbo later down the road. I just don't want EGT's to get any higher. They are high enough already.

 

Yes, that housing is too big for a '40 on a pickup truck. It will be laggy with any injectors, bigger ones will just help you keep it lit under load instead of getting under the turbo when it lugs back a little.