I have both 10.5 hot side one is a dual flapper from a 2005 evo 8 and the other is from a evo 9, any diference which one is better? Any one that has used this dual flapper 10.5 hot side? Here is a picture of what I am talking about:

 

I already did some porting to the hotside as you can see. i did not take a lot just polished.

 

I think the dual flapper was known for breaking a few years back.

 

That is not good, it seems that the dual flapper would be a better choice.

 

The dual-flapper 10.5 was the original design. The TME's were fitted with it....I think?

The single-flapper 10.5 is the factory upgraded design which superseded the double-flapper. The single flapper is preferable. It has a less restrictive turbine inlet chamber design as well as better bypass port lead in radii. Hence, keep the single-flapper and jetison the dual-flapper.

 

It looks like I have more porting to do with the single flapper hot side, thanks for the information.

 

10.5 hotside, single flapper:

 

IInitially yes the turbine exit area is more shrouded on the 10.5 single-flap. Lay down a factory gasket and scribe the circumference on the machined flat area surrounding the turbine exit area.

Luckily you are working with a used housing that has exhaust coloring. Once you lay the factory gasket down onto the exit chamber, positioning it via the O2 hsg. Studs, you'll notice that most of the area where you'll be doing heavy grinding is between 1 o'clock and five o'clock. Radially most of the removal will be bordering the divider wall between the turbine exit chamber and the WG bypass exit chamber.

Basically you'll want to grind all the exhaust blackened area between your concentric scribe circle and the circumferencial edge the turbine exit chamber. The 180* area furthest from the divider wall requires little to no grinding.

In fact, you can really sag down and grind a lot of the thickness from this dividing wall. You want the exiting exhaust gases to have a straight large bore shot leaving the exducer. Always attempt to achieve an exit contour akin to the inside of the bellmouth on a trumpet.

Unshrouding the exducer area will greatly reduce backpressure. You will achieve a reduction in boost taper.

 

Thanks sparky for your inputs, basically that is what I tried to do with the dual flapper hotside housing. But after much thinking and looking at both 10.5 hotside, I decided to use the dual flapper, why, mainly because I already had it ported, also the sigle flapper had a small crack inside where it is divided, also to me it looks like the dual flapper would do a better job at controlling boost. Here are a few pics.
Small crack on single 10.5 hotside:


For comparasion purpose:

 

Here is another picture of the dual flapper 10.5 hotside showing the flappers open:

 

Think I remember reading that the dual flapper hotsides would tend to crack more between the openings.

That was a few years ago though so I'm not completely sure without searching.

 

good info didn't know this ^