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Thinking about swapping heads

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Old 06-03-2018, 07:35 AM
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Default Thinking about swapping heads
I’ve been toying with this idea for sometime.

The current heads are TMS CNC 317s at 69cc. I believe the intake is 235cc.

I procured a set of 243s. I want to have them gone through and milled down to 59-60cc, which bumps my compression up quite a bit.

Here’s the hard question, is it going to run better or worse?

Anyone have any thoughts?
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Old 06-05-2018, 05:35 PM
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So, I'm moving forward with this.

I am going to mill the 243s .025, run a .051 gasket.

I should be around 11.5-11.8cr.

Thoughts?
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Old 06-05-2018, 07:33 PM
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Doubt it will hurt it. Just don't expect huge gains.
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Old 06-05-2018, 08:28 PM
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With no port work? Don't be surprised if you lose some power on the top end.
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Old 06-06-2018, 04:44 AM
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Originally Posted by 1FastBrick
With no port work? Don't be surprised if you lose some power on the top end.
That's what I'm afraid of.

On top, it pulls like a damn freight train. 3rd gear, from 80'ish to redline (6500) it holds a rock steady 12.5-12.7 afr.

Would it be better to to swap head gaskets?

Even with a calculator, going from a .051 HG to .027 (Cometic) only bumps up the compression to around 11.5.

I also understand that this will tighten the quench up and my DCR goes from approx 9.1 to 9.7.
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Old 06-06-2018, 12:20 PM
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With the higher compression it should feel way better at low rpms and still perform at high rpms.
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Old 06-06-2018, 12:33 PM
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Your quench will probably be too tight with a gasket that small.
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