Tweet
Originally posted by Octagon
The N/A 13B engine is actually pretty weak sauce compared to the older 12A and 13A.
The problem lies in the N/A 13B's six port design as compared to the turbo 13B's (and the 12A/13A's) four port design. The six port engine had far less compression, more of a tendency to burn oil (and apex seals, mind you) and cannot be ported out as big as the four port engines (therefore reducing its power potential).
In reality, most all of the N/A FC RX7's you see in the SCCA use the old SA22C RX7's 12A engine because of its greater power potential and superior reliability. Rarely do I say an engine swap is anything but a last ditch effort for more power, but in the case of the FC it is almost mandatory to hunt down a four port turbo engine.
The N/A 13B engine is actually pretty weak sauce compared to the older 12A and 13A.
The problem lies in the N/A 13B's six port design as compared to the turbo 13B's (and the 12A/13A's) four port design. The six port engine had far less compression, more of a tendency to burn oil (and apex seals, mind you) and cannot be ported out as big as the four port engines (therefore reducing its power potential).
In reality, most all of the N/A FC RX7's you see in the SCCA use the old SA22C RX7's 12A engine because of its greater power potential and superior reliability. Rarely do I say an engine swap is anything but a last ditch effort for more power, but in the case of the FC it is almost mandatory to hunt down a four port turbo engine.
#1) All 12A's came with 9.4:1 compression rotors... Early 4port 13B's came with 9.2:1 compression rotors... 13B's from '84-'88 came with 9.4:1 compression rotors... 13B's from '89-'91 came with 9.7:1 compression rotors... 13BT's from 87-88 came with 8.5:1 compression rotors... 13BT's from 89-91 came with 9.0:1 compression rotors... 13BREW's came with 9.0:1 compression rotors as well
#2) 12A's and early 4port 13B's were able to be ported more (not bigger) because they had much smaller ports from the factory than later 6port 13B's. If you ported them bigger, you would leave less area for the rotor's corner and side seals to run on... This would usually mean quicker death to these earlier engines. Also, porting them really big (disregarding port shape) would make for a much "peakier" motor with a smaller powerband than later 6port 13B's.
#3) 12A's do not have a greater power potential over later 6port 13B's (probably not even over early 4port 13B's). It takes a decent streetported 12A to put out the same horsepower at the flywheel as the '89-'91 6port 13B (...which is 160). An '89-'91 6port 13B with a nice streetport is able to put out around 180rwhp (that is Rear Wheel horsepower, not just flywheel).
#4) I don't know how you have determined that a 12A is more reliable, but since I don't have any factual information regarding this, I can't argue it.
*edit #5) Forgot to mention that the 6port 13B's will have more low-end power if the 5th and 6th port actuators are working. This is because the ports are smaller and help low speed air carry a greater velocity (not sure if that's the correct way to term it). It's pretty much the same principle as a variable length intake manifold.
To sum it all up, you are WRONG about the ability of the 6port 13B's. Please do not mislead people by posting information that is INCORRECT!
Comment