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Built RB25 Head with new hydraulic Lifters - RPM Limit

TurboTapin
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RB25 Hydraulic Lifter RPM Limit  

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TurboTapin Experienced

TurboTapin

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After recently being on a dyno, It seems I'm losing out on a fair bit of power with my RPM soft cut at 7600rpm and a gen2 6466. It's a fully Ferrea built S1 RB25 head with new hydraulic lifters. Can it safely be reved higher? If so, to what? 

I'm thinking I can safety increase it to 7800RPM. 

Edited by TurboTapin
Dose Pipe Sutututu Grand Master

Dose Pipe Sutututu

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I even asked ChatGPT 4 for you :D 

 

 

The RPM limit for an RB25DET head with hydraulic lifters, 80lb valve springs, and new valve guides typically falls around 7,000 to 7,500 RPM. Here are some key points to consider:

1. **Hydraulic Lifters**: Hydraulic lifters are generally more limited in high-RPM performance compared to solid lifters due to potential issues with lifter pump-up, which can cause valve float. This often caps the RPM limit around 7,000 to 7,500 RPM.

2. **Valve Springs**: The 80lb valve springs are an upgrade over stock and provide better control at higher RPMs, but they are still somewhat constrained by the limitations of the hydraulic lifters.

3. **Valve Guides**: New valve guides can improve the stability and longevity of the valve train, allowing it to handle higher RPMs more reliably, but they do not significantly raise the RPM limit imposed by the hydraulic lifters.

In summary, while the 80lb valve springs and new valve guides enhance the performance and reliability of the head, the use of hydraulic lifters is the main limiting factor, keeping the safe RPM ceiling in the 7,000 to 7,500 range. For higher RPM capabilities, converting to solid lifters would be necessary, along with further upgrades to the valve train.

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