I am almost finished polishing my plenum. I started with 80 grit then went to 120 then to 400 then to 600 and finished with 1150. But there is still a lot of fine scatches. How should I remove these?

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87TA,
Im in the process of porting and polishing my plenum, runners and intake as well. I started with 400, 600, 1000 and 1500 followed by #00 steel wool. Have you tried 1500 or 2000? How deep are the scratches?

 

The scratches are not very deep at all but they dont seem to want to come out. I have tried the steel wool #00 but it still didnt work.

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Have you tried a wheel buffer that attaches to a drill and used a emery compound on it? Then you polish the plenum with it. You can get this stuff at a hardware store like Home Depot and it works great!

Good Luck!

 

I just did mine. Looks mirror, no fine scratches.

Went to 80 (make sure you get rid of the cast), then 120, 220, 320, 400. 400 is the most critical stage. When you sand, take your time and do it evenly and slowly. After 400 buff it out with 3M Marine Aluminum polish or Tripoli compound I think it's called . This is your test buff. If there are still fine scratches stay with 400 until the finish is smooth. There should be a dull shine.

Go to 600, 800, 1500. Now buff out again. After this go to 1500 WETSANDING this time.
Now buff one more time. Apply MOTHERS aluminum polish. Theres your mirror finish.

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91 Formula
305 TPI 5speed
1LE/G92/WS6
Custom K&N cold air intake, SLP airfoil, ported & hi-polished plenum, TB coolant bypass,Crane AFPR (47psi),94 octane,Crane Extruded Alum. 1.6 full roller rockers, Timing set from 4*BTDC to 10*BTDC,MSD coil,MSD6AL, Holley 9mm Annihilator Laser shot 50 wires, Ac Delco cap,rotor and plugs, Bosch O2sensor, SLP 1 5/8 headers,SLP catback,3:73s,JET 195* fan switch, Macewen white face gauges, Autometer gauges, Zoom hi-performance clutch.
Street legal with stock throttle body, runners,intake manifold,cam, and heads.

 

Thanks a lot guys. The plenum is looking good.