'65 289 block
bored .040 over
TRW flat top pistons
stock rods
.010/.010 under crank

'65 289 iron heads
stock valves, springs and rockers
3 angle valve job
slight mill on them to true up

Edelbrock F4B high rise and 500-600 cfm (to be decided)

Long tube headers.


Is the 2.5" going to be too big or should I drop back to 2.25"?

I already have a 2.5" X-pipe made up. Would it work to run 2.5 to the mufflers then 2.25" after to regain some back pressure?

 

2.5 will be OK. Dont go any larger.
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California dispensaries

 

2.5" will be better for future upgrades. But to answer your question you could run the 2.5" X and then 2.25 the rest of the way.