Ported Chevy 081 heads 305 version

[Bob Hollinshead]

It'll be interesting to see what your 781's really flow so I can get an idea of where my test head is at.

[Carnut1]

It'll be interesting to see what your 781's really flow so I can get an idea of where my test head is at.

It won't be off by much since I was flowing them with a 4.11" bore! In fact they may flow better than I posted.

[Carnut1]

Probably part of the reason the gains were hard to find.

[ap72]

I know the industry standard is to use a large bore on the flow bench, 4.125"+ for sbc's.

But if the head is intended for a 350 why not use a 4" bore to test it? Wouldn't testing for the intended application make most sense, even if it does show lower flow numbers?

[Carnut1]

I know the industry standard is to use a large bore on the flow bench, 4.125"+ for sbc's.

But if the head is intended for a 350 why not use a 4" bore to test it? Wouldn't testing for the intended application make most sense, even if it does show lower flow numbers?

049 bbc head going on a 4.3" bore block.

[ap72]

I know the industry standard is to use a large bore on the flow bench, 4.125"+ for sbc's.

But if the head is intended for a 350 why not use a 4" bore to test it? Wouldn't testing for the intended application make most sense, even if it does show lower flow numbers?

049 bbc head going on a 4.3" bore block.

My mistake. I thought you tested the 081 heads in question in that 4.11" bore.

[Carnut1]

I know the industry standard is to use a large bore on the flow bench, 4.125"+ for sbc's.

But if the head is intended for a 350 why not use a 4" bore to test it? Wouldn't testing for the intended application make most sense, even if it does show lower flow numbers?

049 bbc head going on a 4.3" bore block.

My mistake. I thought you tested the 081 heads in question in that 4.11" bore.

Bob's question was from some work I did for him. Thanks Charlie

[BrazilianZ28Camaro]

If you refined the port shape with the hole open could it be that filling the hole "redefines" what the optimum shape should be? In other words; What "should" be an improvement turns out to be a detriment because the port was shaped with the hole open. More fickle things have happened in the pursuit of air.

A perfect canditate for some CFD to reveal how the void changes flow path downstream. Might require a completely new shape in short turn and port roof.

Probably the hole was disturbing the air flow at that area, slowing it down and helping it contour/follow the wall.

When you closed the hole you might have increased the air speed at that area, making the air tumble over the wall for a longer distance, choking the flow a bit due the greater turbulence.

[Carnut1]

If you refined the port shape with the hole open could it be that filling the hole "redefines" what the optimum shape should be? In other words; What "should" be an improvement turns out to be a detriment because the port was shaped with the hole open. More fickle things have happened in the pursuit of air.

A perfect canditate for some CFD to reveal how the void changes flow path downstream. Might require a completely new shape in short turn and port roof.

Probably the hole was disturbing the air flow at that area, slowing it down and helping it contour/follow the wall.

When you closed the hole you might have increased the air speed at that area, making the air tumble over the wall for a longer distance, choking the flow a bit due the greater turbulence.

If I get some time a bit of Pitot tube work with the hole filled and empty may show you are right.

[BrazilianZ28Camaro]

When you closed the hole you might have increased the air speed at that area, making the air tumble over the wall for a longer distance, choking the flow a bit due the greater turbulence.

If I get some time a bit of Pitot tube work with the hole filled and empty may show you are right.

That would be cool, for learning purposes.

You're doing a great work, those numbers are impressive for that head, keep us updated!

[Carnut1]

When you closed the hole you might have increased the air speed at that area, making the air tumble over the wall for a longer distance, choking the flow a bit due the greater turbulence.

If I get some time a bit of Pitot tube work with the hole filled and empty may show you are right.

That would be cool, for learning purposes.

You're doing a great work, those numbers are impressive for that head, keep us updated!

Thanks! Just got a set of 081's with 1.94's to flow 256 at .7" I thought that was pretty good. Try to post up more this weekend.

[Carnut1]

0604161149.jpg

Ported 081 casting with 1.94/1.5 combo. 4.11 bore. 1204 radius. Pitot testing shows a airspeed dip at rocker stud hole due to increased mcsa. Reflow with rocker stud hole filled with clay. Filled hole averages less flow again. Not totally finessed castings.

[F-BIRD'88]

I don't even flow test them at .700" lift. I look at .300, .400, .450" .500 and .550" lift.
The lift of the cams that will be used with the heads. What it flows at .700" does not mean any thing to me.
On my 4416's I gained a little bit of flow by filling in that void under the rocker stud in the port.
1.94 x 1.60

Good testing. Good thread.

[Carnut1]

I don't even flow test them at .700" lift. I look at .300, .400, .450" .500 and .550" lift.
The lift of the cams that will be used with the heads. What it flows at .700" does not mean any thing to me.
On my 4416's I gained a little bit of flow by filling in that void under the rocker stud in the port.
1.94 x 1.60

I know these heads will never see .7" lift but I think what they flow matters. As soon as the flow stops increasing with lift it is backing up. I think that flow backup makes a difference at a lift lower than it appears on the bench. Just my opinion. And Thanks!

Good testing. Good thread.

[Carnut1]

Sorry, I see I posted within the quote.