Polishing Rotors - Pros and Cons

[NoDOHC]

I don't know for sure (too many factors). I did polish all the dry areas on the intake manifold to 400 grit and polished the wet (after injectors) surfaces to 150 grit. I also am running lower compression (I think 8.2:1 if I measured the water right). However at 40 degrees BTDC my 9.4:1 6-port sounded like a gnome was beating on my hood at 1000 rpm and this one will advance considerably past that (until the engine generates negative torque). I don't know if it is only due to the polished rotors, but that is what I am blaming it on.

Most detonation is actually the collision of two flame fronts. One is caused by the spark plug, the other is caused by a localized hot spot. By polishing the rotor I not only increased the heat rejection (think shiny handles vs. black handles in the sunlight) but I also minimized the possibility of localized hotspots (due to uniform surface finish, no protruding surfaces to absorb heat).

Actually I am very happy with the results on this engine, I recently discovered that the Borch handbook's advice to advance the timing until it detonates and then back it off 5 degrees is not very good advice on a rotary. I retarded my timing 30 degrees to 8 degrees BTDC at 1000 rpm and the car has surprisingly good low end torque (lugs to 300 rpm, no problem and will actually accelerate from there).

I will be interesting to see this engine with a turbo...

[RETed]

Originally Posted by NoDOHC

By polishing the rotor I not only increased the heat rejection (think shiny handles vs. black handles in the sunlight) but I also minimized the possibility of localized hotspots (due to uniform surface finish, no protruding surfaces to absorb heat).
(lugs to 300 rpm, no problem and will actually accelerate from there).

I doubt this is the case...
I bet the rotor faces are already black with soot and carbon deposits.
You'd be surprised how well deposits after combustion will stick to surfaces.
Since this is a rebuild, the engine would've been burning inefficiently due to inferior compression from the seals settling in.
This is more than enough time to leave a fine layer of soot on the rotor faces.
Too bad we can't tear the motor down just to confirm this...


-Ted

[vex]

Originally Posted by RETed

I doubt this is the case...
I bet the rotor faces are already black with soot and carbon deposits.
You'd be surprised how well deposits after combustion will stick to surfaces.
Since this is a rebuild, the engine would've been burning inefficiently due to inferior compression from the seals settling in.
This is more than enough time to leave a fine layer of soot on the rotor faces.
Too bad we can't tear the motor down just to confirm this...


-Ted

Solution: Teflon coated rotors! It's the next big thing!