2.03, 1.56 valves versus 2.09, 1.65 valves

[winr1]

Bench racing and bored ..... cant wrench till I get house and garage finished

Ball park figure plus I know more than a few around here with FEs or going to build one

Most will be mild or a bit more than mild


C8 heads ...  390 ....flat top pistons ... 1 3/4" full length headers ... Ed. Performer ported

Whatever carb would be best

Max HP around 5,500
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Stock valves

CJ valves with throat opened
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Then bowl port both and narrow the valve guides
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What kind of HP and TQ difference would there be ??




Ricky.

[bsprowl]

Wow 5,500 HP.  Tell me about the Supercharger you'll be using.

[Joe-JDC]

First, don't open up the throat as such.  Do the valve job with multi-angles, and let the cutter determine the throat, even if you use stones.  Second, if you do go to larger valve, use 45* for seat and but valves with 45* angle, and cut a 30* back cut on the intake valve, only.  Not the exhaust valve.  Leave the exhaust valve with straight 45* angle.  The flow will be better, with the larger valve, but not as much as you might think.    If you are gong to keep the valve lift less than .500" or so, then a 30* seat might actually be better if you go larger valve.  Only work the throat to the bottom cut of the cutters, and leave the angles as sharp as possible for best results.  Joe-JDC

[chilly460]

Good info.  I have a set of unported but rebuilt C1 heads with stainless 2.03s and was wondering the same thing.  Also good info on the seat angle, took a little digging to find 11/32” 45* 2.09” when I got mine as many are 30* but that may work well with a nailhead valve and small cam

[WerbyFord]

I did that and gained about 25hp and maybe 5 TQ measured on the Gtech on a 400-420hp engine.
I did NOT use narrower valve stems.
I also hit the exhaust roof a little and tried to take out the exhaust Washboard that Ford left in there even though they fixed it on the 427 heads in 63.
Ford really didnt think the exhaust needed to get out, at least after 1957 it seems.
This was with .500 to .520 lift cams. 30 seats on the intakes. B9AE-B heads which look to me just like C1AE-A, C4AE-G, C6AE-R inside.

Pretty much did what Joe said, I used 15-30-45-60-75 degree cutters, just let em do their thing. The seat & throat ended up being bigger, about as much as the valves got bigger. Only exception, IIRC, you can't really get the 75 degree cut to go all the way around or you'd take off too much iron on the water jacket side.

Probably if Joe did it he could gain a lot more than that, but I could feel the difference - "hits" a little, like running a bigger cam - and you can see it on the G's vs time plot.