Rotary Car Club - View Single Post - Polishing Rotors

NoDOHC · 09-17-2009, 09:43 PM

Updates and further questions:

I will be removing the engine from the car (hopefully before winter) and installing 9.7:1 rotors, hardened planetary gears and S5 counterweights.

My question that pertains to this thread is:

Should I polish the 9.7:1 rotors? I will already be increasing the side flex clearance by 0.0005"

They are much smoother and more refined than the 8.5:1 rotors were when I started. I also do not want to have the negative effects that I had from the 8.2:1 rotors.

The negative effects (mostly just inability to run lean) could be partly from my terrible compression ratio.

Basically, I am looking to pick up another 30 Hp and 3 mpg (desktop dyno indicates these gains). I get about 26 mpg right now, I got 29 before I put this terrible 0.78:1 overdrive transmission in my car.

I will put the 8.2:1 rotors back in and install the GT37 after I have determined what power gains are to be had from higher compression rotors.

I read one article that indicates that all compression ratios from 8:1 to 11:1 make approximately the same power in a rotary, but that the high compression rotors give better low-end torque.

Everything else I have read says that 9.7:1 is good and 10:1 Renesis rotors are even better.

If Desktop dyno (designed mostly for piston engines) is right, I should have 300 Hp at 7500 rpm with 9.7:1 rotors and about 220 lb-ft of torque at 6100 rpm. (240 WHp - 176 Wlb-ft).

It is also possible that I will lose too much power to the additional flow work required to force the air through a smaller dish (as the rotor passes TDC) and I will make less horsepower and similar torque to what I do now.

This is why I want to make this change (that and I already have the rotors).

Summary:
Perceived Pros:
Better flow at TDC
Allow more timing advance without detonation
Better heat rejection
Carbon buildup resistance

Perceived Cons:
Poor chamber mixing (no bumps to generate turbulence)
More difficult to light charge (no localized hot spots to act as activation points)
Removal of special factory coating (which is actually visible on these rotors)

edit: Oh yeah, I will post pictures of the rotors when I take them out so that we can see if there is carbon buildup or not.

Bearing in mind that this will be an NA only engine (I will put low compression rotors back in before I turbo it), I am looking for input.

What do you guys think?

09-17-2009, 09:43 PM	#33
NoDOHC The quest for more torque Join Date: Sep 2008 Location: Sheboygan, Wisconsin Posts: 855 Rep Power: 17	Updates and further questions: I will be removing the engine from the car (hopefully before winter) and installing 9.7:1 rotors, hardened planetary gears and S5 counterweights. My question that pertains to this thread is: Should I polish the 9.7:1 rotors? I will already be increasing the side flex clearance by 0.0005" They are much smoother and more refined than the 8.5:1 rotors were when I started. I also do not want to have the negative effects that I had from the 8.2:1 rotors. The negative effects (mostly just inability to run lean) could be partly from my terrible compression ratio. Basically, I am looking to pick up another 30 Hp and 3 mpg (desktop dyno indicates these gains). I get about 26 mpg right now, I got 29 before I put this terrible 0.78:1 overdrive transmission in my car. I will put the 8.2:1 rotors back in and install the GT37 after I have determined what power gains are to be had from higher compression rotors. I read one article that indicates that all compression ratios from 8:1 to 11:1 make approximately the same power in a rotary, but that the high compression rotors give better low-end torque. Everything else I have read says that 9.7:1 is good and 10:1 Renesis rotors are even better. If Desktop dyno (designed mostly for piston engines) is right, I should have 300 Hp at 7500 rpm with 9.7:1 rotors and about 220 lb-ft of torque at 6100 rpm. (240 WHp - 176 Wlb-ft). It is also possible that I will lose too much power to the additional flow work required to force the air through a smaller dish (as the rotor passes TDC) and I will make less horsepower and similar torque to what I do now. This is why I want to make this change (that and I already have the rotors). Summary: Perceived Pros: Better flow at TDC Allow more timing advance without detonation Better heat rejection Carbon buildup resistance Perceived Cons: Poor chamber mixing (no bumps to generate turbulence) More difficult to light charge (no localized hot spots to act as activation points) Removal of special factory coating (which is actually visible on these rotors) edit: Oh yeah, I will post pictures of the rotors when I take them out so that we can see if there is carbon buildup or not. Bearing in mind that this will be an NA only engine (I will put low compression rotors back in before I turbo it), I am looking for input. What do you guys think? __________________ 1986 GXL ('87 4-port NA - Haltech E8, LS2 Coils. Defined Autoworks Headers, Dual 2.5" Exhaust (Dual Superflow, dBX mufflers) 1991 Coupe (KYB AGX Shocks, Eibach lowering springs, RB exhaust, Stock and Automatic) Last edited by NoDOHC; 09-17-2009 at 09:53 PM.