Im thinking about getting a blox intake manifold soon and i am going to port match it to my 68mm tb. but before putting it on, i was wondering if i would see any gains if took a dremel to the insides of the runners to smooth and polish it out a bit. Should i do it, or would it just be a waste of time?

 

If youre referring to where the runners meet the cylinder head, what you really want there is to get the gasket youre going to use on the head, and match the manifold to that, then match the head to that. Youre trying to eliminate any 'lips' from the flow path.

Opening up the entry where the TB bolts up to the TB size is a good idea, even better idea is to go just a tad bit bigger than the TB size. By a tad, im talking a mm or so, nothing drastic.

More power can be had by cutting open the plenum and reshaping the entrance into the runners from the plenum, as well as cleaning up any casting slag. So , to sum it up


Gasket matching runners = 2/10
Matching TB entrance = 4/10
Plenum/Runner work=7/10

 

so should i polish up some of the inside of the runners, whatever i can reach with my dremel or would i just be wasting time?

 

bump, anyone?

 

you could clean it up as CC mentions. Its not a good idea to have a completely polished finish on the intake runners. A slightly satin finish will allow the fuel to atomise more freely and same when it comes to the ports on the head. As CC says gasket matching is good, but one thing that should be done for accuracy of allignment is doweling. This means that refitting manifold and gasket to head ports maintains percise allignment. Commonly this is disregarded and so all hard work port matching is lost through poor reallignment.

 

Injectors are at the end of the intake manifold,not in the plenum...