There are numerous pics in Leo Santucci's Chevy 6 Performance Handbook. But extensive brazing to the intake ports and very large intake valves are required to reach those flow numbers....I'll see if I can find some pics to share on here...
U-flow horsepower limitations
- Thread starter Walken100
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I'm curious. Was this an NA application and do you know the HP? I'm wondering how the engine treats the Siamese ports from an area stand point
Outstanding cross post. Thank you! That's a metric crap ton of RPM.... and horsepower.
Yes, it was naturally aspirated and the last time I saw it dynoed in the late 80's it made 612 HP. By that time the engine was no longer in our Chevy II and was put into a Comp Eliminator rear engine dragster owned by Brian Browell until around 1988, when Brian wanted to take over the driving chores. After switching from the inline power, he switched to the Chevy V6 PowerPlant and had Grumpy Jenkins do his engines until his passing some years back. Brian still races in Comp Eliminator and is the owner of Browell Titanium Bellhousings currently....
The dynamic port flow for the three Siamese intake ports is different.
If you look at the 1 5 3 6 2 4 firing order, the intake timing for cylinders 3 and 4 have a 360 degree interval and there is no overlap between valve openings in the center intake port.
However, cylinders 1 and 2 have a 240 degree and a 480 degree interval as does cylinders 5 and 6.
When you have a drag racing camshaft lobe profile with well over 240 degrees there will be valve overlap during the 240 degree interval in those ports.
Valve timing can be altered slightly between those cam lobes to decrease the overlap period.
CNC-Dude can shed more light on the subject.
Otherwise, you are looking at a large volume intake port that is relying on the port lump to increase air velocity and tapered rectangular intake manifold runners for velocity and ram.
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That would explain the high rpm capability...
Here are a couple of pics that Wallen asked for. First, not trying to hijack the thread, but to reinforce what Paul was describing in an outside the box manner of thinking to Wallen and to show with creative thinking what can be accomplished. The top Pic shows the stock intake port with the obnoxious bolt bosses impeding air flow. The middle Pic shows after the bosses removed and the port floor filled by furnace brazing to create a short side radius, or lump as Paul mentioned. The last Pic is the 21st century solution which is a bolt-in lump that is simple to install by most any DIY-er with simple basic tools and at a much cheaper cost. However, they only mimic the street version brazed lump head that the late Kay Sissell offered, but still produces between 260-270 CFM, compared to the factory 160-ish port....
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No need to apologize. My goal is to continue my informal education on cylinder heads and flow. This is a great case study. Thank you.
Here's what the latest technology is in Super Stock cylinder head porting. It retains the factory port volume per the NHRA rules, but flow is increased tremendously over the OEM port location and shape. You could do the same to the Ford 6 ports...
I have, sorta. I've raised the center of the entry CSA .4". So far the best I can do with out finding water. Note the bottom of the port will be raised by offsetting the intake runner~.3". This got me to 250 CFM. In the hands of a pro I believe this technique would get you close to 260. And yes I have to make an intake manifold.
Link to my progress...
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