Would the head not be a better place to remove material to increase squish?
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| head milling choices https://slantsix.org/forum/viewtopic.php?t=8599 |
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| Author: | sandy in BC [ Wed Mar 03, 2004 8:50 pm ] |
| Post subject: | head milling choices |
I got my 69 head back from the machine shop. For the price of a standard valve grind and guides I got my SBC valve seat work done ,new guides , spring seats machined for SBC springs. He also enlarged the throats below the valve seats. $300 US I need to blend in the bowls and do a little port matching. My questions revolve around deck heights and where to mill. Dart 270 angle milled the head to achieve compression resulting in a more closed chamber with more quench. Long rod engines use the raised piston to achieve compression rather than milling. This creates a more open chamber and less quench. On a torque oriented engine at a target ratio of 9.0 to 1 is the closed chamber with more quench going to be more efficient? Is angle milling for quench worth the trouble? 3000 lb 65 Valiant 225 super six 5 speed 3.23 gears 4500 rpm max TBI to follow http://www.arrowtipi.com/My%20Webs/index%20Valiant.htm |
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| Author: | Doctor Dodge [ Wed Mar 03, 2004 11:18 pm ] |
| Post subject: | |
The truth is that you will not be able to get quench with a 9 to 1 SL6 unless you get a set of custom made pistons. Quench chamber Slants run around 12 to 1 compression minimum. For your application you should take some measurments and mill the block and head the amount needed to get your target 9 to 1 compression ratio. DD |
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| Author: | sandy in BC [ Thu Mar 04, 2004 8:35 am ] |
| Post subject: | head milling choices |
My buddy has a machine shop where I have full priviledges. We plan to mill both the block and head to get 9-1. By the time I clean out the chambers and relieve a little around the valves my chamber volume will be greater than stock. I can take meat off both the head and the block. Is there an advantage to milling one more than the other? Is there a "target" chamber volume? Do bigger Valves and ports mandate a larger chamber volume? Am I being overly fussy about where to remove for compression? |
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| Author: | mpgFanatic [ Fri Mar 12, 2004 7:16 pm ] |
| Post subject: | Re: head milling choices |
Quote: is the closed chamber with more quench going to be more efficient?
Yes. And that does seem to be the direction that cylinder head design has been going, in the past few decades.I'm guessing what you're looking for in efficiency is the "squish" action. This rather sudden turbulence at the end of the stroke does a great job of spreading the flame front quickly. (Increased turbulence is also the underlying reason for so-called swirl induction created by appropriately placed intake valves.) I was told years ago that milling the block was better than milling the head because it increased the squish action and therefore the efficiency. That would seem to make sense, as long as we're considering the closed chamber head design. Quote: The truth is that you will not be able to get quench with a 9 to 1 SL6 unless you get a set of custom made pistons. Quench chamber Slants run around 12 to 1 compression minimum.
That is very believable, given the -.140 deck height of a 225. What about the zero deck height of the 170? Wouldn't "squish" be much easier to obtain?- Erik |
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| Author: | sandy in BC [ Fri Mar 12, 2004 8:19 pm ] |
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Would the head not be a better place to remove material to increase squish? |
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| Author: | Dart270 [ Sat Mar 13, 2004 6:29 am ] |
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That would be my thought, Sandy. You will decrease the chamber area presented to the bore by milling the head. Basically, all Slant heads are open chamber unless you mill them at least 0.100", and more like 0.150". Lou |
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| Author: | sandy in BC [ Sat Mar 13, 2004 7:43 am ] |
| Post subject: | |
I am thinking of "bore notching" or relieving the block a little for better flow around my larger valves as well as sweeping the chamber. Both those operations increase volume. If I mill everything from the head to get my 9:1 ratio I might approach .100. Time to have a closer look at the Docs "smiley chambers" |
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| Author: | Dart270 [ Sat Mar 13, 2004 8:11 am ] |
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0.100" is no problem at all for a Slant head. I've done a 0.080"/0.180" angle mill (0.120" net for flat mill) head and a 0.100"/0.200" mill (0.140" net) head and no worries after 40k+ on each. The latter is 30-33ccs if I remember right. Don't ask if the angle milling makes a difference. I just did it on a recommendation from Meril Bruner and they have worked well for me, but I have no direct comparisons to flat milled heads. The chamber may get a little smaller area with the angle mill, esp on a pre-68 head. Lou |
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