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Head Bolt Tension

Dale FZ1

By Dale FZ1,
in Engines & Forced Induction

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Dale FZ1 Veteran

Dale FZ1

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Looking at available specs, and the instructions on my ACL Race Series MLS gasket I have come across something that's worth asking you engine builders about.

Stock RB25 specs require a tightening sequence, with final tension of 93-103Nm

Stock RB30 specs require similar sequence, with final tension of 88Nm

ACL spec sheet still follows the same sequence, and final tension as per the stock RB30. Difference is that the gasket is listed for fitment with 30ET 2 valve head.

I'm leaning towards a final tension of 95-100Nm on the basis that the needs of the 4 valve head are different and requires the extra. Will call the ACL tech help line, but meantime what are the settings commonly used by those of you who've built your own 30DET?

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Dale FZ1 Veteran

Dale FZ1

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I wasn't aware of the difference in length, but would nearly think that a longer bolt would require more tension due to extra flex/torsion in the shank.

Either way, the higher torque value for the 4 valve head application looks to be the go for me.

Any opposing views or experiences?

r33_racer Grand Master

r33_racer

Posted
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Im assuming your using used rb25 bolts. I would go the higher value with a 10% extra on top (say around 113-115nm). I think the extra should allow for the stretch and flex in the used bolts and since its not a bearing, having abit more wont really hurt. I went the extra in my road rb25 when i rebuilt it, not a rb30 block, but same head and bolts and a threaded hole is a threaded hole. The only thing you might think about is that you are probably running a higher static comp to what the std sohc rb30s ran...so naturally you now will have more force trying to lift the head and that will only grow depending on how much boost your going to run from whichever turbo your system utilises.

Dale FZ1 Veteran

Dale FZ1

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New head bolts - Nissan genuine.

Static comp running cast pistons ~ 8.35:1, so lower than the 9.0:1 advertised for 30E with the 2 valve head. But running in boosted configuration, I felt the higher tension than 30ET would be better. Perhaps a touch higher still at 105-110Nm is not a bad idea for a reliable seal.

I'll find out what the ACL tech advice is today.

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