Closed chamber BBC heads

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Mark Williams
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Closed chamber BBC heads

Post by Mark Williams »

How much power can a set of bowl blended oem 206 bbc heads with std size valves support on a 454?
9.5 in comp
Hyd roller 224/230@050 .600 .580 112 ls
Rpm intake
I hope close to 500 hp or am I to optimistic?
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Re: Closed chamber BBC heads

Post by mag2555 »

Those heads with there stock 2.06” intake valve should flow at least 245 cfm to 250 cfm @.600” lift.
This should make you 475 Hp .

If your doing the porting work yourself then be sure to look at some of the better detailed porting videos on YouTube that you can find.

You should have the intake and exh valves back cut with a 30 degree that’s at least.025” wide.

If your budget permits I would step up to the 1.88” exh valve size and blend that in nice to a 3 angle valve job.

If your intake valve bowl work gets you 260 cfm @ .550” lift then 500 hp should be yours!
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Re: Closed chamber BBC heads

Post by Mark Williams »

mag2555 wrote: Sat Jun 18, 2022 7:46 am Those heads with there stock 2.06” intake valve should flow at least 245 cfm to 250 cfm @.600” lift.
This should make you 475 Hp .

If your doing the porting work yourself then be sure to look at some of the better detailed porting videos on YouTube that you can find.

You should have the intake and exh valves back cut with a 30 degree that’s at least.025” wide.

If your budget permits I would step up to the 1.88” exh valve size and blend that in nice to a 3 angle valve job.

If your intake valve bowl work gets you 260 cfm @ .550” lift then 500 hp should be yours!
Heads are already done, local porter did the job.
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Re: Closed chamber BBC heads

Post by 1980RS »

Even with lower Compression an open chamber head with all the same valve sizes will make more power.
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Re: Closed chamber BBC heads

Post by Mark Williams »

1980RS wrote: Sat Jun 18, 2022 10:51 pm Even with lower Compression an open chamber head with all the same valve sizes will make more power.
Might be true but this is what I have, to much money invested to change direction now.
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Re: Closed chamber BBC heads

Post by mag2555 »

No flow test was done even just on one cylinder?

It’s hard to tell from photos how well the needed work was done, but what I can say from reviewing the photos is that at least the work done was not excessive as the guy did not even boat tail the cylinder wall side of the exh valve guide.

In short I don’t think any harm was done to the as cast flow numbers which can many times be the case when work is done unaided by a flow bench!

Even if the bowl porting work picked up on the intake side only picked up 10 cfm by .500” lift, then with the .600” lift that your running your goal of 500 hp should be had.

Also if your running headers they will pick up the exh flow numbers by 3 to 4% especially at peak flow.

Once it’s up and running for a while I would switch to a extended tip plug that’s 1 heat range colder then what your running now depending on where the color change over point is on the plugs you start out with.
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Re: Closed chamber BBC heads

Post by Mark Williams »

mag2555 wrote: Sun Jun 19, 2022 7:07 am No flow test was done even just on one cylinder?

It’s hard to tell from photos how well the needed work was done, but what I can say from reviewing the photos is that at least the work done was not excessive as the guy did not even boat tail the cylinder wall side of the exh valve guide.

In short I don’t think any harm was done to the as cast flow numbers which can many times be the case when work is done unaided by a flow bench!

Even if the bowl porting work picked up on the intake side only picked up 10 cfm by .500” lift, then with the .600” lift that your running your goal of 500 hp should be had.

Also if your running headers they will pick up the exh flow numbers by 3 to 4% especially at peak flow.

Once it’s up and running for a while I would switch to a extended tip plug that’s 1 heat range colder then what your running now depending on where the color change over point is on the plugs you start out with.
No not flowed

He is supposed to be good but no idea? All sharp turns was smoothed and the area under the valve was also smoothed. Before the exhaust almost was 90 deg and lots of edges under the valves so hope it picked up some? Didnt cost me much to have him do them. The seats are multi angle cut and Im using ferrea 5000 valves so hope they flow better than oem.

Will use 1 3/4” headers.

Ngk fr5 is the plugs I will use they are one step colder than oem.
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Re: Closed chamber BBC heads

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1980RS wrote: Sat Jun 18, 2022 10:51 pm Even with lower Compression an open chamber head with all the same valve sizes will make more power.
Although you are correct in a bone stock environment, this in NOT true in an environment where you can utilize changes, those "bathtub" heads can make an incredible amount of power, even with oversize valves and the shrouding that occurs. Too much to type but some simple chamber work including laying that area "underneath" the ex valve will make drastic improvements. Widen the short turn on the ex port, think single pattern or reverse pattern on the camshaft.
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Re: Closed chamber BBC heads

Post by 1980RS »

In-Tech wrote: Sun Jun 19, 2022 3:01 pm
1980RS wrote: Sat Jun 18, 2022 10:51 pm Even with lower Compression an open chamber head with all the same valve sizes will make more power.
Although you are correct in a bone stock environment, this in NOT true in an environment where you can utilize changes, those "bathtub" heads can make an incredible amount of power, even with oversize valves and the shrouding that occurs. Too much to type but some simple chamber work including laying that area "underneath" the ex valve will make drastic improvements. Widen the short turn on the ex port, think single pattern or reverse pattern on the camshaft.
With 2 sets of BBC heads I tested that were both ported, both had 2.19 and 1.88 valves. Set one was a 215 closed chambered heads comp ratio of 8.9:1 and all else being the same my car ran 11.70@112mph. The other set was my ported 360 peanut port heads with the porting treatment with a compression ratio of 7.98:1 ran the best of 11.26@116mph. same intake, carb, cam and headers. Which one makes more power do you think?
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Re: Closed chamber BBC heads

Post by 1980RS »

Mark Williams wrote: Sun Jun 19, 2022 4:04 am
1980RS wrote: Sat Jun 18, 2022 10:51 pm Even with lower Compression an open chamber head with all the same valve sizes will make more power.
Might be true but this is what I have, to much money invested to change direction now.
I certainly understand that, sometimes you have to use what you have, nothing wrong with that.
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Re: Closed chamber BBC heads

Post by af2 »

In-Tech wrote: Sun Jun 19, 2022 3:01 pm
1980RS wrote: Sat Jun 18, 2022 10:51 pm Even with lower Compression an open chamber head with all the same valve sizes will make more power.
Although you are correct in a bone stock environment, this in NOT true in an environment where you can utilize changes, those "bathtub" heads can make an incredible amount of power, even with oversize valves and the shrouding that occurs. Too much to type but some simple chamber work including laying that area "underneath" the ex valve will make drastic improvements. Widen the short turn on the ex port, think single pattern or reverse pattern on the camshaft.
So correct I won't even go there!
Would be awesome to see Mark chime in..
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Re: Closed chamber BBC heads

Post by af2 »

Mark Williams wrote: Sat Jun 18, 2022 10:27 pm
mag2555 wrote: Sat Jun 18, 2022 7:46 am Those heads with there stock 2.06” intake valve should flow at least 245 cfm to 250 cfm @.600” lift.
This should make you 475 Hp .

If your doing the porting work yourself then be sure to look at some of the better detailed porting videos on YouTube that you can find.

You should have the intake and exh valves back cut with a 30 degree that’s at least.025” wide.

If your budget permits I would step up to the 1.88” exh valve size and blend that in nice to a 3 angle valve job.

If your intake valve bowl work gets you 260 cfm @ .550” lift then 500 hp should be yours!
Heads are already done, local porter did the job.
You mean a local grinder. Those are not even close to the ones done in the 60's that flat hauled the mail.
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Re: Closed chamber BBC heads

Post by vortecpro »

Mark Williams wrote: Sat Jun 18, 2022 10:27 pm
mag2555 wrote: Sat Jun 18, 2022 7:46 am Those heads with there stock 2.06” intake valve should flow at least 245 cfm to 250 cfm @.600” lift.
This should make you 475 Hp .

If your doing the porting work yourself then be sure to look at some of the better detailed porting videos on YouTube that you can find.

You should have the intake and exh valves back cut with a 30 degree that’s at least.025” wide.

If your budget permits I would step up to the 1.88” exh valve size and blend that in nice to a 3 angle valve job.

If your intake valve bowl work gets you 260 cfm @ .550” lift then 500 hp should be yours!
Heads are already done, local porter did the job.
Although the 206 casting is the worst closed chamber head in my opinion. The work looks good, and I can that supporting 500 HP, but maybe not with that cam, but possible.
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