what you have is the even more rare series 4 turbo thick cast rear iron(no difference in front iron).

if you aren't building the car for something serious you can sell the rear iron for upwards of $400(if step wear is minimal) and buy the standard cast rear iron for about $125.

the rear iron becomes a weak point on the engine beyond 350-400whp.

the series 4 thick irons do exist but very hard to find, just finished putting an engine together with one. the series 5 Jspec thick irons are much more common and still just as easy to use with a clip of the coolant temp sender pigtail and replacement with a spade connector if going into a series 4 car, or vice versa into a series 5 car with a series 4 rear iron.

 

So are the dowel landings the same thickness as the s5 irons. Also what did you mean by theres no difference in the front iron?

So is it more commen for the rears to break before the front iron does?

I was looking to buy s5 front and rear irons to prevent the irons front breaking.

 

just as i worded it, the front irons have almost no discernable difference between them. both have thinner dowel castings on the FC and there is no upgrade available for the front.

the rear iron is the weak point and i would say about less than 5% of the time the front irons fails before the rear does(i have a pile of dowel cracked FC rear irons but never have broken a front one). the twisting motion of the engine usually starts at the front and works to the back, not the other way around so twisting at the front of the engine is usually nonexistent. the ONLY difference between s4 and s5 turbo front irons is the porting is ever so slightly different at the intake manifold, but it does not cause any problems(same difference is also in the rear iron).