Low boost on CX-7 turbo in Mazdaspeed3

Hello,

My speed3 is running low on boost (13.57 psi is the most I can get from it if I’m pushing it hard, and this is in 5th) but seemingly not leaking boost when I tested leaks from the turbo back. I can only make 8psi in a 3rd gear wot test.

I’m running the Mazda CX-7 turbo (K0422-582) that came on my JDM engine which I swapped. They looked nearly identical and the CX7 turbo had less shaft play. For reference, the turbo that comes in the speed3 is a k0422-881.

Is the turbo likely the culprit of low boost?

 

That turbo doesn't move as much air as the speed one

 

Would that be enough to limit my boost in lower gears like I’m experiencing? I can barely make 8psi in third gear.

 

Also, is it harmful to run the CX-7 turbo in a Mazdaspeed3? Will I be doing damage, or just not making as much power?

 

It wont do damage, but the CX-7 turbo compressor housing has an outlet that is necked down compared to the MS3 ko-4. The CX-7 turbo is good for about 15psi (I think) where as the MS6/MS3 can run closer to 18 reliably and some have even pushed 21-22.

 

Yeah less power in those. Won't have as much fun. Get a speed turbo.

 

Yeah less power in those. Won't have as much fun. Get a speed turbo.

 

Thanks guys! I will get a speed turbo in the near future and check back in to see if that was the only issue

 

I have an old speed3 turbo, but it has a little bit of shaft play and has about 151K miles on it. Would you recommend rebuilding it or just getting a new one? If I need to get a new one, do I get brand new OEM or are used ones ok?

I'm new to this all so I apologize if these questions come across as dumb or something I should know. I appreciate all your help!

 

I would run the one you have. If you needa used one you can usually get one pretty cheap

 

For what it’s worth…I’ve mentioned this before elsewhere but in case marshmello is interested.

I’ve been running this $300 turbo for around 15 months. It appears to be a stock turbo housing (has the 881 number on it) with a new CHRA. My plan was to use it temporarily while I rebuilt my stock turbo but it’s been fine so I’ll keep using it. I don’t know how it will end up comparing in longevity, but I can say that with my latest tune I see boost as high as 20psi.

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