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RB30/25DET Nissan build wastegate size

General Engine Building Discussion

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Hi all,

i'm almost done sourcing all needed parts for my RB30/25DET build

setup so far :

Nissan RB30 block and cranck

Nissan RB25 gen1 head

Genuine Greddy plenum with nissan Q45 throttle body

aftermarket rods and pistons

Garret gen 1 GT3582 0,82AR on a modified Greddy Trust exhaust manifold

wastegate ???

so question is what size gate should i run on this setup ? Engine will be in my 200sx street car so wont always run high boost.

I've tuned several engines with similar specifications. The answer is possibly more complex than it seems as the required wastegate sizing also is dependent on the way the wastegate is plumbed - For example if the exhaust flow into the wastegate is smooth then you can often get away with a smaller wastegate than if the wastegate is plumbed in a way that the exhaust gas needs to perform a 180 deg turn to get out the wastegate.

In reality you always want to attach the wastegate in a way that flow into it is optimised anyway for the best control of boost pressure. On that combination I'd recommend a 45 mm wastegate.

manifold is this greddy , so not the best flowing gate i guess

Attached Files

Yea that's not entirely ideal. How good the control of boost will be will depend on the wastegate size and how restrictive the exhaust housing is too.