Low boost on CX-7 turbo in Mazdaspeed3

[originalmarshmello]

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?

 

[Easter Bunny]

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

 

[originalmarshmello]

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.

 

[originalmarshmello]

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

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?

 

[SyntheticAtmosphere]

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.

 

[Raider]

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

 

[Raider]

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

 

[originalmarshmello]

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

 

[originalmarshmello]

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

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!

 

[Easter Bunny]

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

 

[jsilva]

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.

https://www.ebay.com/itm/2526524805...XPpyVP3R1G&var=&widget_ver=artemis&media=COPY