Thread: big block head flow?

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Of all you guys that have experience big block chevy heads(mainly oval port). Stock 781's oval ports usually flow 250-260 peak cfm intake and 175 peak cfm exhaust. I wanna know on average how much they flow when you do port matching, bowl work, and three angle seats and a back cut of the intake valves?

I have a good friend who runs 049 oval ports on his 454..they're the same casting as the 781's. He did a minor bowl blend, intake gasket match, and smoothed out the exhaust port. He then took them to Creative Flow Management for testing. They flowed 308 cfm at .600 intake, and 215 cfm at .700 on exhaust. This was his first time at porting, if you're thinking of doing it yourself. Mike from Creative Flow Management told him they would easily support 600 HP. It's easy to get good numbers out of stock castings. Well, porting is never easy! But you get my drift. John

wow! that very good! your right sometimes porting ain't easy it sure takes skill!

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Originally Posted by steelsixpack101

Of all you guys that have experience big block chevy heads(mainly oval port). Stock 781's oval ports usually flow 250-260 peak cfm intake and 175 peak cfm exhaust. I wanna know on average how much they flow when you do port matching, bowl work, and three angle seats and a back cut of the intake valves?

Is that with you porting them or a pro. cylinder head guy porting them?It might be eaiser if you give us some engine specs. and we can tell you if the are even worth using.

Originally Posted by erik erikson

Is that with you porting them or a pro. cylinder head guy porting them?It might be eaiser if you give us some engine specs. and we can tell you if the are even worth using.

My specs are 408 cubes, 4.155 bore, 3.76 stroke, 300in 310exh duration Mechanical cam with .556in 568exh lift. edelbrock rpm intake, 12.5:1 compression. hooker headers 2in or 1-7/8 diameter. L88 crank, stock truck rods with ARP bolts.

Originally Posted by steelsixpack101

My specs are 408 cubes, 4.155 bore, 3.76 stroke, 300in 310exh duration Mechanical cam with .556in 568exh lift. edelbrock rpm intake, 12.5:1 compression. hooker headers 2in or 1-7/8 diameter. L88 crank, stock truck rods with ARP bolts.

The 781's will work fine.
I would install a set of 2.19/1.88 do a good valve job,bowl blend, gasket match.Is this a street car or a drag car?If it is a drag car then I would look into a victor jr. intake.If it is a street car then your intake would work better because it will make torque at a lower rpm.

It's weekend drag racer, but i will drive on the city streets, so i'm going with dual plane intake, how much more CFM can you get out of 2.19/1.88 versus 2.06/1.88's? do think it will make a noticeable gain in power?

If you mean seat of the pants noticeable, no it wont...but it will give you slightly better times at the races. The bigger intake valve will likely help at higher rpms, but the heads flow surprisingly well at low and mid rpms, as in street driving, with the stock valves. But with the combo you're proposing, I would install the larger valves. The problem with the larger intake and the smaller bore is going to be shrouding around the intake valve. That's one argument for sticking with the smaller valve.

since i got smaller bores i'll stick with the 2.06/1.72. probably use stainless steel valves though.

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Why does it appear Pat's posts have been deleted/removed/edited?

Question on thses 781 heads some of you have been talking of. With regards to gasket match porting for a street strip engine....where exactly is material being removed? From my limited instruction and understanding, gasket matching goes into the port only about 1-1.5" in depth wise....matieral is removed from the sides, the roof and floor of the ports except on the exhaust sides. I've always been interested in port work, and read many articles,,,but have never actually watched someone port a set of heads. So how much of what I know is true? Any port people out there know the answers to this?

Originally Posted by 30-A Rider

Why does it appear Pat's posts have been deleted/removed/edited?

Question on thses 781 heads some of you have been talking of. With regards to gasket match porting for a street strip engine....where exactly is material being removed? From my limited instruction and understanding, gasket matching goes into the port only about 1-1.5" in depth wise....matieral is removed from the sides, the roof and floor of the ports except on the exhaust sides. I've always been interested in port work, and read many articles,,,but have never actually watched someone port a set of heads. So how much of what I know is true? Any port people out there know the answers to this?

well it all been said. so i pull it . port matching is a waste of time for the street you want the intake ports smaller then the intake ports of the heads by .030 all the way around if you do not know where the intake will sit then you can make good stuff in to junk i have did a lot of port work but it all at the chamber front of the valve and in the back of the valve bowl work were you see power. and in the valve job i do all this so if you can not do the valve job then you should not cut and move things if you do not know how it works have seen many screwed up heads and intakes that were junk by some one thinking they were making them better and if you hit the seats with a die grinder . you will ruin a good set of heads