manifolds question

[Francois Duval]

Hi, I had my 911 T manifolds machined yesterday to the S specs of 36mm to match my engine`s output.

now the finish inside the manifold is kind of rough,,,,,,,,, not as smooth as it was before the machining.... do this have an impact on performance
will this create turbulence on the air being sucked into the engine ?

any experts out there ? thanks

Francois

[andrew15]

My understanding is that you want a rough finish on the intake side to keep the fuel air mixture in a bit of turbulence and prevent the fuel from creating droplets.

AM

[Alan.uk]

Hi,

In case it helps, when we machine throttle stacks or manifolds the finish is as original. For example here are some mag MFI stacks finished machining today. These were enlarged to 50mm top to 42mm bottom tapered bore, not an easy task.





HTH

Alan

[docrodg]

The rough finish is perfect. It "shreds" the air, creating turbulence that keeps the fuel atomized well. Smooth finish is good for the combustion chamber and exhaust port.

That is some nice machining on those tapers! that must have been a PITA job!

[RS-GT]

Salut Francois,

I also heard that rough finish is fine on the intake to get good air/fuel mixture, but the combustion chamber and exhaust should be polished.

Who machined them for you in Quebec ? Does he do porting on heads ?

Thanks

Jean-David (Candiac)

[Francois Duval]

Thanks for all your input guys, its really appreciated. I take it that
I will keep the rough finish and it should be fine.

The company who did the machining is called DC Usinage here in Joliette.
Its a small business that does many different tasks I heard.
They kept the shop open for me late at night to do my job, it took them about 1.5 hour to do it. real nice job.

FRancois