11/2 or 15/8 primary tube?

[pkj]

i am doing the headers now, but need help on the primary tube size. 68 truck
i have stock 307 that i am planning on keeping for 1 to 2 more years. then i will put 400 with 906 vortec heads in. either way i want to keep the torque up. i have decided on full length ceramic coated hooker comps. exhaust pipes 21/2 non manderal bends, H pipe, exit rear of truck, 3 chamber type mufflers. now i have been wondering about that old/new thread in engines 307 strocker. so i need a compromise keeping in mind i may not go with the 400, but will for sure use a vortec head. any suggestions?

[Alex Hayley]

I am not familiar with the heads you are using, however, I am building a 406 and plan on needing 1.75" headers. Since you may change your mind on the engine, I think it would be a mistake to buy the headers before you decide on the engine. A chicken before the egg kind of thing....

[70c10]

I would go with the larger headers since you are planning some type of bigger engine in the near future.

[pkj]

thanks never sure what i will do in future so i guess i will go with the 1 5/8 primary hooker comps. what about exhaust pipe size? 2 1/2 kink bend over kill?

[crazy longhorn]

1 5/8 " primarys are fine on a mild "street" 383 or 406, & 2 1/2" pipes are about right on for the big inch sb mills......on the 307, I would say 2" pipe tho.....2 1/4 MAX. There is no "free lunch" , if you want to build it once, build it after the 406 is planted..... L