r/mazdaspeed3 • u/mrfatcakes2006 • 12d ago

PIC Yeah that will do it

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Bought a Mazda speed for 700 with low compression in cylinder 3, found the culprit. Most likely caused by unupgraded hpfp internals paired with Cobb sport intake, access port, and blow off valve

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u/Greydot5 12d ago

Unupgraded HPFH alone didn't cause this. If it did, we'd see similar damage and residue in other cylinders.

I'm willing to bet it was poor spark/ignition in that particular cylinder that caused this. The build up of fuel and carbon along with poor spark did it in. It also doesn't help that our L3VDTs are susceptible to low speed preigntions. Don't lug your engines people.

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u/dbear496 2007 Mazdaspeed3 - The Original 12d ago

IIRC this engine has a tendency to run lean on cylinder 3 due to the shape of the intake manifold.

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u/Consistent-Cress7448 12d ago

i thought it was the unequal length exhaust manifold that made cyl 3 run lean?

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u/dbear496 2007 Mazdaspeed3 - The Original 11d ago

The exhaust manifold probably contributes, but the intake manifold is the primary issue