Pray

iTrader: (7)

I just lightly ported a set of 799's that cam on my truck. Now I didn't have them flowed before I started because I wasn't planning on doing anything to them. But looking at them when I got them off I decided they needed a clean up. On the intake side I took the rocker boss hump out but didn't increase runner cross section, and polished the bowl under the valve guide. No work was done to the guide it's self. I took a sanding roll to knock off the casting bumps in the runner and that is it. No material other than that rocker hump was removed and there was no short side work. On the exhaust side I blended the bowl into the valve seat and polished the runner. I also blended and polished the chamber. I took about 2cc out of the chamber and had them milled .015". The exhaust valves were jacked so I had a three angle valve job done and a 30* back cut put on the valves. Here are the average numbers from other stock 243's vs. my 799's on the same flow bench.

Stock 243's Ported 799's
int
.100 70.8 70.8 +0
.200 138.6 151.9 +13.3
.300 191.7 215.3 +23.6
.400 236.0 253.7 +17.7
.500 265.5 277.3 +11.8
.550 265.5 280.1 +14.6
.600 265.5 262.5 -3

exh.
.100 60.4 62.6 +2.2
.200 107.4 110.6 +3.2
.300 139.0 159.5 +20.5
.400 164.3 183.2 +18.9
.500 176.9 197.5 +20.6
.600 180.1 203.8 +23.7

So now the questions.

1. Why does the stock head even out at .500 lift?
2. Why does my head crash so hard at .550?
3. Is this a good gain for such minimal work?
4. What would I have to do to increas the flow after .500?
5. Is the stock valve the limiting factor?
6. My cam has .604 int lift, is the flow backing up going to hurt my power?
7. Heads were flowed before the milling. Does milling help or hurt flow?
8. Is porting around the valve guide worth it?
9. Should I have polished the short side radius?
10. I know intake runner volume is critical. Does exhaust runner volume mean as much?

I am thinking of starting on a another set of 799's and see what I can get out of them. Any suggestions would be great.

Vortec350ss

iTrader: (20)

I wish I knew more about this stuff, but the mid lift gains look pretty impressive to me. I don't think there is any way that your .600 lift flow being down that tiny bit could hurt power, the flow curve is so much more beefy that you're gonna get much more air in there.

I can see why you would be concerned though. The intake runners are bigger now and the flow is less (although it was never tested on your heads) which can't be good for your air velocity. I think the flow increase down low will help velocity over all though.

Gadgetized

iTrader: (9)

I think you did I very good job. I would assume it has to do with the runner volume.

An angle mill can increase flow #'s.

Do you do any work in the com Harkin chamber? When I do a head (i don't do them often, and I am no pro), I open up around the exhaust valve near the cylinder wall. I have never touched 799 heads though, I bought mine done, and cleaned them up.

Pray

iTrader: (7)

I didn't open the chamber at all due to the 3.78 cylinder. It is already too big as is. It measures exactly 3.90. I really don't think larger valves would help either. I don' think I lost any port velocity because I didn't change the overall port cross section. I only knocked out the hump around the rocker boss. Maybe 3-5cc's at most. I wish I would have flowed and measured everything first but in the end this thing cost me $300 more than I originally planned on spending. I really didn't wnat to increas the intake volume due to it being a 5.3. I will have dyno numbers soon and post them up.