bolt on boy

A "bolt on boy" is a mechanic in someway. He can bolt things on but doesn't truly know what the parts do and how they work. You can almost relate a bolt on boy to the local oil change technician. There is a difference of a performance shop and a racing shop. Performance shops buy parts from online or magazines and install them and that's it. A race shop will search for parts that suit a build, determine what parts are needed for the type of performance, and understand the fundamentals of performance.

Customer: What cam should I get?

Owed Shop: Well we have stage 1, 2, and 3 cams.

Customer: That doesn't tell me anything. What do those numbers mean?
Perf Shop: The stage 3 is the fastest
Customer: But, why?
Perf Shop: Its our custom grind
Customer: What are the specs?
Perf Shop: I'll have to get you those later.
Customer: Are you just a bolt on boy?
Perf Shop: Well, yes we simply just install parts and have never specd a cam nor know exactly how they work.

Customer: Thanks for being honest!