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Just wondering the angles and how wide of 45 degree intake and exhasut seats you guys cut for a BBC. The intakes are 2.30" Titanuim and the exhausts are 1.88" SS.

I'm looking at the Goodson cutters and was trying to figure which one to use. Thanks for any help.
 

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.050 to .060 on the intake since it's titanium. .060 on the exhaust. But that's the easy part. It's the angles above and below that make it work. Most good shops have spent a lot of time on thier valve jobs. Be much easier to take the heads to someone and let them cut it. Odds are it will perform better than what you can do. The wrong valve job can kill a head by 20 cfm.
 

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.050 to .060 on the intake since it's titanium. .060 on the exhaust. But that's the easy part. It's the angles above and below that make it work. Most good shops have spent a lot of time on thier valve jobs. Be much easier to take the heads to someone and let them cut it. Odds are it will perform better than what you can do. The wrong valve job can kill a head by 20 cfm.
I've seen flow killed by 30-40 on some heads.....
 

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I'd keep everything in the 15º rule. It works well for a 45º seat. I usually go .050/.050/.050 on most 45º seat. Meaning .050 margin, .050 wide 45º, .050 wide 30º back cut. Now start going steeper on seats, like 50 and 55º, back cut widths and angles will vary. I also run just as many .100 wide back cut valves.

Goodson has some good cutters..

The key is BLENDING the valve job. You get into the 3rd cut on the SSR side and you will kill 10-15 cfm below .500. However, that isn't a bad thing ;)
 

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Discussion Starter · #7 ·
Thanks Chad, that was really the answer I was looking for. I ran a narrow 45 three years ago (250 # seat) and it actual held up really well. I tried a wider 45 last year (285 # seat) and I didn’t like the looks of the seat s when I took it apart. They had zero leakage, just looked weird. I’m going to try the steps, where I used to blend right up to the 45 (sorry old school). We have all the Goodson cutters in the lab and I was trying to pick which 2 to use. I think they have 1.0 mm, 1.1, 1.2, 1.5, up to I think 1.8 mm 45 deg cutters and then the top angles, 30, 32, 35, and 39. Thanks, Jim
 

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74% of the valve heat is transferd through the seat contact with the valve,have seen some engines make more power with wider seats,we like the flow bench numbers but rarely do any seat narrower than .040 intake and .060 exhaust.Bill C.
 

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The key is BLENDING the valve job. You get into the 3rd cut on the SSR side and you will kill 10-15 cfm below .500. However, that isn't a bad thing ;)
Explain to me how killing 15 cfm below .500 isn't a bad thing? Airflow in the valve job is the difference between good and excellent heads. Killing flow below.200 to help control reversion I can see. I can't see killing flow at .500 and below. It would lower the area under the curve and kill the average flow on the port. That makes absolute ZERO sense.
 

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Also, getting into the 3rd angle in the valve job YOU use. The valve job that I was taught and use blends all the way to the bottom of the 60 degree bottom angle for the full 360 of the seat, and that doesn't kill flow below .500.
 

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I've seen flow killed by 30-40 on some heads.....
On fully ported stuff yea. Needless to say I've seen alot, and had to try to fix a lot of junk. Did the flowtesting for an article in a mag a long time ago comparing valves and valve jobs on a 170cc twisted wedge head that I think went like 260 back then. Killed that head 20 cfm by using a 30-45-60 valve job and a Manley valve. I can totally see a port getting killed 40 if it's supposed to be a 320+ cfm piece when it's done right.
 

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Explain to me how killing 15 cfm below .500 isn't a bad thing? Airflow in the valve job is the difference between good and excellent heads. Killing flow below.200 to help control reversion I can see. I can't see killing flow at .500 and below. It would lower the area under the curve and kill the average flow on the port. That makes absolute ZERO sense.

Low lift flow and valve action (ramp, rocker arm ratio) are directly related.

OR, just like David Reher explains it. Think about the valve events in a racing engine: From the point when the valve first moves off its seat until it reaches mid-lift, the piston is either going the wrong way (that is, it is rising in the cylinder) or it’s parked near TDC. The piston doesn’t begin to move away from the combustion chamber with enough velocity to lower the pressure in the cylinder until the valve is nearly halfway open. Consequently it is high-lift flow that really matters in a drag racing engine.

So, you need to rob Peter to pay Paul. High flow means low flow gone.

But, port them up anyway you want, it's up to the head porter on which diresction he wants to go.
 

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I understand the point you use, and it's a valid one in that specific application. It would take .900+ lift and 290+ durations to get you there. Hope you didn't take my initial resonse harshly, but the stuff I piddle with on the side is no where near that level, and that approach wouldn't provide any gains.
 

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I understand the point you use, and it's a valid one in that specific application. It would take .900+ lift and 290+ durations to get you there. Hope you didn't take my initial resonse harshly, but the stuff I piddle with on the side is no where near that level, and that approach wouldn't provide any gains.
I beg to differ.. I've done it over and over. I didn't take it harsh. I'm also talking, 650hp style engines.
 
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