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Author Topic: Wastegate Porting Guide  (Read 6033 times)

EShepherd

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    • 1991 Capri XR2, 1991 Capri XR2 Rusted out Shell
Wastegate Porting Guide
« on: April 04, 2021, 04:02:46 PM »

Alrighty everybody, here's the how-to guide on porting out the wastegate. If you change the exhaust out on your Xr2 to improve airflow characteristics of your exhaust, you can end up with a boost creep situation. Essentially, you're exhaust flows faster than the stock internal wastegate will be able to keep up with, creating a situation where the turbo creates more boost pressure than it is able to bleed off. This is a bad thing. The only way to properly address the situation is to remove your turbo assembly, pop off the wastegate cover, and increase the size of the bore. Common sense and the factory service manual should be all you need to get the turbo out of the car and on the bench, it's fairly straight forward.


Once you've got the turbo off, this is the part you want to have exposed. The flap disk on the right is covering the hole that the wastegate opens up to allow boost pressure to bleed off, keeping your boost limited to whatever PSI.



Lift up the butterfly valve/flap disk/whatever you want to call it, and this is what you'll see. See where the screwdriver is touching? That discoloration is a decent indication of where you'll want to bring the bore diameter out to. But hold on, there's something you need to pay attention to. Watch the following video, as it is impossible to explain via picture:
https://www.youtube.com/watch?v=4crnBhzHapo


Okay, so you've watched that video and understand what it is you want to do. What now? What I did was take a sharpie and start marking around the hole, checking it regularly by closing the valve and moving it around. As long as you can't see the sharpie, you're good. Continue widening the hole with your markings until you're comfortable with the increase of size, provided it is entirely covered by the flap door no matter where you move it to. You can use machinist's blue, sharpie, chalk. whatever. Just be aware that brake clean will remove your markings, so don't be stupid like I was and do that.



So you've got your template. Grab whatever cutting tool you think is best suited, and go to town. I tried a bunch of different stuff, but what worked best for me was a straight pneumatic die grinder with a coarse bit, tapered stone. You could probably get away with a rotary tool and an 80# cartridge roll or flap disk, but it'll take longer. A carbide burr would make short work of it. Just use what you've got.
For example:





So, get to work. Bore out the hole.




Here's some measurements I took. I don't know how consistent the castings were, so you'd be best to check your own part to see what you've got to work with. Once you know what you are aiming for, you can check your progress and see how much further you've got to go.



That's how mine looked when I was about halfway done. Notice I blasted off my markings with brake clean like a dumbass. Try not to do that.




Here's what mine looked like when I finished up. I didn't take it as far as you can, this was fairly conservative. I don't plan on running anything wider that a 2.25" exhaust, so I didn't feel the need to go crazy with this. If I do end up with boost creep issues down the road, I'll come back and widen it further. This really is a very straightforward process. Two finishing notes here. Make sure you clean the entire part thoroughly when you've finished. You don't want to send little bits of metal through your turbo into your engine. Also, liberally apply antisieze to all of your exhaust fasteners on reassembly. If you've ever got to take it back off and apart, future you will thank present day you.
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Rocketman

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    • 91 BPT AWD Capri & 1991 XR2
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Re: Wastegate Porting Guide
« Reply #1 on: April 04, 2021, 10:17:14 PM »

Excellent write-up, thank you. Sticky'd!
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1.8L Turbo All Wheel Drive Capri... the "GTXR2"


greywolf27030

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    • 1991 XR2, 1992 XR2, 1993 XR2
Re: Wastegate Porting Guide
« Reply #2 on: April 05, 2021, 09:22:55 AM »

Compliments on the write up, really cool.
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Jack Byrd