BBC output overview - chapter 2

General engine tech -- Drag Racing to Circle Track

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Erland Cox
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Re: BBC output overview - chapter 2

Post by Erland Cox » Mon Nov 26, 2018 2:01 pm

Why do you cut the quench area so much on the exhaust side?

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Re: BBC output overview - chapter 2

Post by Old School » Mon Nov 26, 2018 2:56 pm

What are your intake seat angles?

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Re: BBC output overview - chapter 2

Post by David Vizard » Mon Nov 26, 2018 4:13 pm

rebelrouser wrote:
Mon Nov 26, 2018 11:54 am
Just a dumb question, but since we are talking about different ways to port heads with right or left turns. Does the coriolis effect, have any affect on the flow, and is it different for the guys porting down under where it would make it spin the other way?
No - it is far to small an effect to even measure in something he size of a cylinder bore.
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Re: BBC output overview - chapter 2

Post by David Vizard » Mon Nov 26, 2018 4:17 pm

Erland Cox wrote:
Mon Nov 26, 2018 2:01 pm
Why do you cut the quench area so much on the exhaust side?

Erland
Because that design makes more power than when it is not cut away. On a 540 with a 10.5/1 CR it's worth about 18 hp on a nominally 750 HP build.
It also makes the chamber less prone to detonation when using pump gas.
DV
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Re: BBC output overview - chapter 2

Post by Ron E » Mon Nov 26, 2018 4:35 pm

David Vizard wrote:
Mon Nov 26, 2018 4:17 pm
Erland Cox wrote:
Mon Nov 26, 2018 2:01 pm
Why do you cut the quench area so much on the exhaust side?

Erland
Because that design makes more power than when it is not cut away. On a 540 with a 10.5/1 CR it's worth about 18 hp on a nominally 750 HP build.
It also makes the chamber less prone to detonation when using pump gas.
DV
It shows up on the flowbench too.

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Re: BBC output overview - chapter 2

Post by Erland Cox » Mon Nov 26, 2018 4:52 pm

Taking away quench area should loose power.
Is it a low octane pump gas thing to slow down combustion velocity with less quench?
Trying to get slower pressure rise to control detonation?
I have only seen smog head BBC oval port heads look like that and never an N/A race head.

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Re: BBC output overview - chapter 2

Post by Erland Cox » Mon Nov 26, 2018 6:04 pm

David Vizard wrote:
Mon Nov 26, 2018 4:17 pm
Erland Cox wrote:
Mon Nov 26, 2018 2:01 pm
Why do you cut the quench area so much on the exhaust side?

Erland
Because that design makes more power than when it is not cut away. On a 540 with a 10.5/1 CR it's worth about 18 hp on a nominally 750 HP build.
It also makes the chamber less prone to detonation when using pump gas.
DV
Just out of curiosity, have you tested this type of head on a 540 with and without that chamber mod and no other modifications?
No flack just a scientific question which I hope I will get a scientific answer for.

Erland

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Re: BBC output overview - chapter 2

Post by swampbuggy » Mon Nov 26, 2018 6:22 pm

Erland.....David has already answered your question just barely above your question, :-k Mark H.

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Re: BBC output overview - chapter 2

Post by hoffman900 » Mon Nov 26, 2018 6:26 pm

Erland Cox wrote:
Mon Nov 26, 2018 2:01 pm
Why do you cut the quench area so much on the exhaust side?

Erland
That is on the Swiftune BMC A-Series heads as well.
Image

David, did you have a hand in developing those too?

I've seen it a few times - always thought it was what happened when you design a chamber for the flowbench and not combustion, but if someone has the data and shares it...

On vintage heads I've seen welded up or started with raw castings, they typically look like this SB2.2 chamber
Image
-Bob

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Re: BBC output overview - chapter 2

Post by Erland Cox » Mon Nov 26, 2018 6:31 pm

swampbuggy wrote:
Mon Nov 26, 2018 6:22 pm
Erland.....David has already answered your question just barely above your question, :-k Mark H.

No, he only said that the mod gave 18 hp so I wanted to hear more about the 540 test,
The head he is porting looks like it has never been run before the porting started.


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Re: BBC output overview - chapter 2

Post by Ron E » Mon Nov 26, 2018 8:52 pm

Now that mini head is weird. And only BBC head we've ever cut back a substantial amount was Brodix solid conventional type on a blown alcohol motor. So, can't answer to Erland's concerns about N/A. But, the modifications I'm talking about are more like the SB2 above. Nothing radical. Just moved back about .200" at the deck. The exhaust valves are so deep in a hole in those things, I think it just helped the flow from that area to hug the chamber and continue toward the valve seat instead of skating across the face of the valve. In the blown application, the engine liked it.

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Re: BBC output overview - chapter 2

Post by Ron E » Mon Nov 26, 2018 9:04 pm

Just looked at the pics again. Ours wasn't as radical as DV's. DV has some 'splainin to do!
But, on ours it was good for 25 CFM at peak lift and the motor thought highly of it.

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Re: BBC output overview - chapter 2

Post by GARY C » Tue Nov 27, 2018 5:42 am

He showed me a similar SBC ex quench pad a cpl of years ago.
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Re: BBC output overview - chapter 2

Post by David Vizard » Tue Nov 27, 2018 4:34 pm

Erland Cox wrote:
Mon Nov 26, 2018 6:04 pm
David Vizard wrote:
Mon Nov 26, 2018 4:17 pm
Erland Cox wrote:
Mon Nov 26, 2018 2:01 pm
Why do you cut the quench area so much on the exhaust side?

Erland
Because that design makes more power than when it is not cut away. On a 540 with a 10.5/1 CR it's worth about 18 hp on a nominally 750 HP build.
It also makes the chamber less prone to detonation when using pump gas.
DV
Just out of curiosity, have you tested this type of head on a 540 with and without that chamber mod and no other modifications?
No flack just a scientific question which I hope I will get a scientific answer for.

Erland
I did some extensive testing on a 572 that GM's involvement meant the expenses were covered.

DV
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Re: BBC output overview - chapter 2

Post by digger » Tue Nov 27, 2018 4:45 pm

What was the mechanism that gave more power ?

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