Balancing question!

j9fd3s · 07-20-2011, 11:43 AM

basically T_g is correct.

the rotary doesn't reciprocate like a piston, and also the rotors are iron and comparatively heavy (piston is 500 grams, rotor is 5000 grams, give or take).

what mazda did with the engines prior to the Rx8 engine, is to cast a batch of rotors, and then grade them PER BATCH, lightest to heaviest. then they will match up pairs of rotors that are close, and balance them to the counterweights. mazda's production tolerance is something like +/- 50grams, a piston engine would explode but the rotary is fine up to 8000-8500*

when mazda does a high performance engine, like they list in the competition book, they will balance the rotors closer than the normal production, and then its good to 9k*

so what does this mean? this means if you have a factory pair of rotors and counterweights, that you are in good shape. since they grade rotors per batch, this also means your rotor from 1987 and your rotor from 2007 are different weights (2004+ rotors are lighter, and they added the side clearance cut too).

it also means that counter weights are slightly matched to the engine.

it means that if you want to build a high rpm engine, you wanna either use a matched assembly, or balance it in some fashion.

i had my P port balanced, and it is very smooth

*depends on the year/model/apex seal choice

***TitaniumTT*** · 07-22-2011, 04:53 AM

Quote:

Originally Posted by j9fd3s

mazda's production tolerance is something like +/- 50grams, a piston engine would explode but the rotary is fine up to 8000-8500*

Excellent post!

My theory for this is that they're still matched within about 1%, and the rotor is rotating at 1/3 eccentric shaft speed. So while you may be spinning the engine to 8500 rpm's the rotors are only spinning @ 2833rpms.

j9fd3s · 07-22-2011, 01:07 PM

Quote:

Originally Posted by TitaniumTT

Excellent post!

My theory for this is that they're still matched within about 1%, and the rotor is rotating at 1/3 eccentric shaft speed. So while you may be spinning the engine to 8500 rpm's the rotors are only spinning @ 2833rpms.

lol, i didn't even think about that, but you're totally right.

that's the mazdaspeed motor sports page. the 20B is the 13G based engine, NOT the cosmo engine, they are TOTALLY different.

i'm also not sure which 13B and 12A rotors they are using either....

07-20-2011, 11:43 AM	#1
j9fd3s Rotary Fanatic Join Date: Mar 2008 Posts: 123 Rep Power: 18	basically T_g is correct. the rotary doesn't reciprocate like a piston, and also the rotors are iron and comparatively heavy (piston is 500 grams, rotor is 5000 grams, give or take). what mazda did with the engines prior to the Rx8 engine, is to cast a batch of rotors, and then grade them PER BATCH, lightest to heaviest. then they will match up pairs of rotors that are close, and balance them to the counterweights. mazda's production tolerance is something like +/- 50grams, a piston engine would explode but the rotary is fine up to 8000-8500* when mazda does a high performance engine, like they list in the competition book, they will balance the rotors closer than the normal production, and then its good to 9k* so what does this mean? this means if you have a factory pair of rotors and counterweights, that you are in good shape. since they grade rotors per batch, this also means your rotor from 1987 and your rotor from 2007 are different weights (2004+ rotors are lighter, and they added the side clearance cut too). it also means that counter weights are slightly matched to the engine. it means that if you want to build a high rpm engine, you wanna either use a matched assembly, or balance it in some fashion. i had my P port balanced, and it is very smooth *depends on the year/model/apex seal choice