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.

mark21742

I would take a little off the short side, but not much, then blend it around really good. Also I always grind the hell out of the guide and knife edge it till you have about a 1/16" of the guide showing and work the back edge of the guide too. In my opinion around the guide is where you can see a lot of gain since the valve it self is the largest disturbence of flow.

chrisfrost

iTrader: (8)

Stock heads from what I've read on here crash at those rpm's because the designers figured they did'nt need to make power past red-line . 1 thing You can do is to remove either part or all of the ramp in the intakes next to the guides . Yes those are pretty good #'s considering the little that You did .

Pray

iTrader: (7)

Thanks guys. I was going to attack that huge ramp behind the valve guide but my machinist (who builds winning stock cars) said that area is what can make or break a head. He said I shouldn't do it unless I was cutting and checking on the flow bench.