ive been reading and ive came across a few ppl sayin that the s4 TII's were only good to about 400hp before they start to crack around the dowel in and are unreliable, is this true? and what about the s5's? are the the same, cuz i heard they were more reinforced?

 

go s5, and dont look back

 

s5 is stronger. but if the tuning is right, the s4 can support 500ish hp

 

That is absolutely untrue. The strength issue is a bogus one. The problem is the lateral deflection of the rotor housings carrying the dowel pins, stressing the dowel lands on the front and rear irons. Mazda in about 90 or so began casting the irons w/ thicker dowel lands to help keep them from breaking. True, sheer power won't break a land; severe knock may do it.



B

 

would having an rtek ecu 1.7/1.8 help prevent this?

 

yes but you should not go for 400hp with just the Rtek.

and the power WILL break the land in situations such a drag launches or when the clutch is dumped quickly, especially with the stock flywheel.

 

This is a S4 that broke when a customers wastegate hose popped off and he over boosted. Motor didnt blow apart, and no signs of detonation probably due to the alcohol injection, was perfect inside other than this. He was putting down over 400WHP.



The casting of a S5 is close to double the thickness in this area.

 

tom, since when did you start posting on NP?

 

I agree, I think the torsion of the housing stack contributes to cracking the land and broken seals in some cases. (In the FC and similar setups) I dont think the trans is mounted rigid enough, and torsional stress is sent right to that rear iron and rtr housing.

 

http://www.tjwakeman.net/TR/Net_transCracks.htm