Howard Coleman

iTrader: (6)

my friend w the 20b fd recently sent his 550/1600 injectors to RC. he would like to locate the largest flowing injectors at the leanest rotor.

generally the rear rotor is leanest on a 2 rotor. i remember reading something about one of the rotors on the 3 rotor being lean but don't remember which...

i would appreciate any help.

thanks,

howard coleman

IronMdnX

iTrader: (1)

I believe it is the 2nd rotor.
Correct me if i'm wrong.

GT1-20b

Rotor "Order" , has nothing to do with "MIXTURE STRENTH".
This has ALL to do with injector sizing & Flow rates at a given temperature & presure, specifically : how "uniform or equally" the injectors are flowing.
The only other factor in this equation is: Manifold Designe. Wether a particular cylinder or rotor is favored or NOT, by the designe of the Intake's "Air Flow" characteristics.
What makes a PARTICULAR Rotor be prone to damage more than another, is THERMAL LOAD. In other words, "Working Temperature"
In the case of the 3rd. gen Rx7, The primary reason for the Rear Rotor's familiar failure, is due to a "Fuel Cut" at any boost avobe 12.5 psi. addressed to the REAR ROTOR ONLY.

Now, for the question of wether a Rotor runs leaner on not ?

On a 2 Rotor engine, the #2 rotor runs HOTTER. Only because the cooling medium (water) has already been super heated by the 1st rotor's ignition cycle, & the heat that's been released by it's combustion process along the firts 70+ degrees of expansion. This "Heated" water, must ATTEMPT to cool the 2nd Rotor, plus PASS BY THE EXHAUST SIDE OF BOTH ROTORS, AND PICK UP MORE HEAT along the way before exciting the engine through the water pump.

On a 3 Rotor engine, It is kind of the same thing, with 2 big distinctions.
A) The 3 Rotor generates 50% more BTU's (Heat), for ANY given power level.
B) The 2nd Rotor, gets exposed to heat from BOTH SIDES.

It gets it in both directions. And by designe, specialy under boost, when using the OEM Intake Manifold, the "Air Flow" FAVORS the center rotor, giving it a theoretical DENCER CHARGE.
All theese combined, the #2 Rotor on a 20b experiences the highest Thermal Load and therefore the most likelly to fail when at to the edge.

On countless Dyno setions, the second Rotor ALLWAYS has shown higher EGT's & O2 readings, even with individual Throtle Bodyes.

GT1-20b

CCarlisi

. . .Middle Rotor.

Supporting info:
1. posts/ramblings of other forum members
2. most of the blown core motors I looked at had damaged center rotors.

now

iTrader: (1)

yep Middle Rotor seems to be the one to go first

Howard Coleman

iTrader: (6)

thanks

howard coleman

Jeff20B

iTrader: (13)

My middle rotor had the least carbon buildup. That makes sense since it's the hottest.

fdracer

middle, due to the tb placement. when the tb opens, air shoots straight into the middle rotor, leaning it out. this discrepancy is even greater than the 2 rotor condition w/ the rear rotor running lean. a great solution would be to cut up the stock im (or fab a new one) and run twin tb's, similar to the bullish solaras.