The exhaust is another huge hurdle to overcome. Making mods like 2 barrel or four barrel carburetors will do very little without modifying the exhaust in "some" fashion. This includes at least porting the stock manifold and opening up the outlet, or going straight to headers. So many people fail to do that and then wonder why all of their mods didn't add much. The stock manifold only has a 1 7/8 outlet. That's no good for any kind of performance. The slant 6 responds better to a complete approach, rather than piece mealing it.