Overboost with RBH5 Upgrade
 

I started to notice this last year, but the upgraded compressor has made the over boost much worse. So I took the turbo of the car expecting to just port the waist gate. Imagine my surprise, the flapper valve is not fully opening not even close to fully opening. It's hitting on the Down pipe flange. So my question is how far should the flapper be opening? You can see in picture #3 the extent the flapper is opening, in picture #4 you can see the exhaust stained area that is causing the problem. I can grind out the exhaust flange and probably the actual flapper actuator to get more movement, but how far is it supposed to open?

Thanks

Graham

Wow, that's not even close.

I'll take pics of the angle on mine, but I know it goes past 45*.

sounds like the first batch of cs downpipes for the fwd bp's, they made a notch in them to fix that problem... is that the ebay upgraded wheel and compressor housing? how do you like it, i think its a little bit smaller than my rhb52 vj20/vf8 i made up....

So far so good on the upgrade, it goes into overboost at 14 psi very quickly:)

Graham

Ought to be about 70 degrees.

Corky

Closed

http://lh5.ggpht.com/_p9gPi6Qceak/S6...2005.39.25.jpg

Open

http://lh4.ggpht.com/_p9gPi6Qceak/S6...2005.39.50.jpg


Mine's right at 45*...no overboost, and this thing spools with the quickness.

Get a bellmouth downpipe? Problem solved.

So the answer is greater than 45 degrees and as close to 70 as I can get.
I am sure I am going to grind through the waistage pipe, I am sure I wil end up welding a piece over the hole.

Thanks

Graham

I was actually surprised mine didn't open further....but it looks closer to 60* than 45* now that I really look at the pics.

I believe it used to, but as you can tell I recently had that pipe reconnected to the flange, and the guy at the muffler shop may not have put it spot on.

Mine never gets over my target 12psi though...

I ported the passage on both the turbine housing and the 02 housing (aka downpipe in this case) to the point that the WG flapper would travel to almost 90 degrees. The actuator will control how far it opens, so my philosophy was to open it up as much as possible. Often you can take a sharpie and really thoughly mark the area around the flapper itself when it is closed and then enlarge the opening a bit too. Just e careful on that one not to overstep it. I left a MM or so and had no spooling issues.

In other words, you pretty much cant open it up too much unless you cause a sealing issue or something.

So the answer is 60÷ degrees and as close to 90 as I can get.

Where can you buy new flappers (I am not sure there real name). As I am going to be doing major surgery I might as well do a good job ans increase the flapper size as well.

Thank everyone for your input

Just port out the wastegate hole and add a nice transition on the interior. As far as a new flapper, just tack weld a washer on there.

Because the flange is made of 1/4" steel I managed to grind out enough metal to get to about 60 degrees open, maybe a little more, now looks just like gospeed81's. Anything over 60 degree and I am sure I would have ground through the flange/pipe joint. Not the perfect solution, but it got the car back on the road quickly. A quick test ride showed the max boot at around 12 pounds, which is perfect.

Thanks for every ones help

Graham

http://abefm.smugmug.com/Miata/Modif...49_gcjfY-L.png

Here's closed, open with supplied can and open with another can on a popular turbocharging kit.... Made a huge difference. I ended up doing this and porting and smoothing the turbo and still get overboost.

Adding timing helped a LOT. Nothing I did could fix it when I was massively retarded. After that, I just tuned for survivability at 14 psi and crossed my fingers.

I did drill a new hole in the actuator arm to it opened quicker and farther. I have a set is the Jeff_Ciesielski det cans, so I want to work on the timing.

Thanks for the input.

Graham

Got a pic? I'm curious.

When I re-assembled everything I guess I did not out the E clip on the waist gate arm correctly, so the actuator popped of the arm. Guess what, I could still get 12 pounds boost! Just before the rev limit cut in I could actually get 12 pounds boost with the waist gate fully open! Luckily I am aiming for a 12 pound limit with the over boost set a 14 pounds. The good news is the once the actuator arm was re-connected the car was much better to drive, no more over boost constantly cutting in. I have re-installed my MBC so hopefully I can keep it close to 12 pounds throughout the rev range.

Graham