781 porting - Chevelle Tech
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post #1 of 14 (permalink) Old Feb 2nd, 16, 8:26 PM Thread Starter
 
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781 porting

Any key areas to get back into?
I'm going to have them cut for 2.25/1.88.
I have toyed with the idea of just jumping to 2.19 and leave the hot side stock with good valves and seat job.
A little input would be good. I've been reading up on these for a while. Intake and exhaust have been cleared of any casting flashes or boss bumps ( i got into the threads for the rocker stud on two ports per head)
Sorry if this is jumbled... I've been drinking
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post #2 of 14 (permalink) Old Feb 2nd, 16, 8:50 PM
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Re: 781 porting

Wow!! ...a little liquid courage for your first post???..welcome to the forum show!!!!
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post #3 of 14 (permalink) Old Feb 3rd, 16, 7:20 AM Thread Starter
 
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Just a little, and thanks. I have been lurking in Chevelles.com for a long time.
I'm wanting to take them in to get cut soon but would like to only have to bowl blend when they come back. I'm wondering if some folks are going to chime in with any area that will gain flow that needs to be addressed.
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post #4 of 14 (permalink) Old Feb 3rd, 16, 7:24 AM Thread Starter
 
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Only other picture I have on my phone
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post #5 of 14 (permalink) Old Feb 3rd, 16, 7:55 AM
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Re: 781 porting

Not bad for a first post.

From what I have observed,
we don't need to have the razor thin
ridge on the exhaust. Look around and
read you'll find that most recent heads
are rounded off in this area.

Other folks here could confirm this.

Cheers,

USMC_Spike
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post #6 of 14 (permalink) Old Feb 3rd, 16, 9:26 AM
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Re: 781 porting

What size bore is it going on? I would be worried about a 2.25 and chamber shrouding. A 2.19 may actually flow just as well by having more space around it. A 1.88 exhaust valve is pretty big for any engine really. A 2.19/1.72 may not be a bad combo. I was looking at doing that setup on a 408 being used in a drag car. I figured since my 540 uses a 2.35/1.88 setup, a smaller engine shouldn't need such a big exhaust.

Ray


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post #7 of 14 (permalink) Old Feb 3rd, 16, 9:34 AM
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Re: 781 porting

We did 2.19/1.88 on my 049 heads used on the 427. No work in the combustion chamber but complete work in the ports per recommendation of the guy who did the porting (who is also a Pro Comp drag racer). They work VERY well.








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post #8 of 14 (permalink) Old Feb 3rd, 16, 12:48 PM
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Re: 781 porting

No need for 2.25 valve. I would stick with 2.19 as others have mentioned. I have seen 700+ HP 496 pump gas motors with 2.19 valves w/GM heads.


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post #9 of 14 (permalink) Old Feb 3rd, 16, 1:24 PM
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Re: 781 porting

Quote:
Originally Posted by mr 4 speed View Post
No need for 2.25 valve. I would stick with 2.19 as others have mentioned. I have seen 700+ HP 496 pump gas motors with 2.19 valves w/GM heads.
X2 on that. This link has some good pointers.

Do-It-Yourself Small-Block Cylinder Head Porting - Tech Article - Chevy High Performance Magazine

67 SS BBC
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post #10 of 14 (permalink) Old Feb 3rd, 16, 1:48 PM
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Re: 781 porting

Quote:
Originally Posted by Rich-L79 View Post
We did 2.19/1.88 on my 049 heads used on the 427. No work in the combustion chamber but complete work in the ports per recommendation of the guy who did the porting (who is also a Pro Comp drag racer). They work VERY well.







Couple of questions:

Did the guy have any feedback on the typical practice of cleaning up the chamber surface with a spiral roll? I see it's as-cast here.

Did he take material out of the walls/roof/floor, or just transition/blend?
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post #11 of 14 (permalink) Old Feb 3rd, 16, 3:26 PM
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Re: 781 porting

We were trying to maintain the combustion chambers as small as possible to keep compression and dynamic compression ratios up. He said he didn't see any advantage to smoothing out the combustion chamber surfaces for what I was trying to accomplish.

He took out material to open up the throats, smooth the transitions and increase the flow. He has a flow bench and he has worked heads like this many, many times. He removes what helps flow not to simply increase the size of the ports. I honestly don't know the particulars of what he does or doesn't manipulate. According to his flow bench they all flow quite well for what they are.

For example, the intake ports were measured to flow about 307 cfm at .600 lift. .

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post #12 of 14 (permalink) Old Feb 3rd, 16, 4:15 PM
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Re: 781 porting

On this platform, the OEM CI "oval's", I would use some 2.125" or 2.150" x 5.250" SBC intake valves and some 1.810" x 5.370" Mopar exhaust's. We use this setup all the time on the 100% stock-appearing builds.

If you use theses sizes AND do a decent port job the heads WILL deliver.

Have 3 sets being done this week, most get Ferrea's valves. Fairly straight-forward operation. Occasionally we'll use Manley's intakes also.

(Add) With respect to porting on the exhaust's, I would stay away from the bottoms of those guides, this is a "high-stressed" area where the guides are pressed in and very close to water!! Just a tip.

Thanks, Gary in N.Y.

P.S. The lengths work well and all have SBC .343" stem diameters.

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Last edited by GOSFAST; Feb 3rd, 16 at 4:20 PM. Reason: Add info
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post #13 of 14 (permalink) Old Feb 3rd, 16, 9:54 PM
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Re: 781 porting

Quote:
Originally Posted by GOSFAST View Post
On this platform, the OEM CI "oval's", I would use some 2.125" or 2.150" x 5.250" SBC intake valves and some 1.810" x 5.370" Mopar exhaust's. We use this setup all the time on the 100% stock-appearing builds.

If you use theses sizes AND do a decent port job the heads WILL deliver.

Have 3 sets being done this week, most get Ferrea's valves. Fairly straight-forward operation. Occasionally we'll use Manley's intakes also.

(Add) With respect to porting on the exhaust's, I would stay away from the bottoms of those guides, this is a "high-stressed" area where the guides are pressed in and very close to water!! Just a tip.

Thanks, Gary in N.Y.

P.S. The lengths work well and all have SBC .343" stem diameters.
Great advice!

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post #14 of 14 (permalink) Old Feb 4th, 16, 11:38 AM
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Re: 781 porting

Quote:
Originally Posted by GOSFAST View Post
On this platform, the OEM CI "oval's", I would use some 2.125" or 2.150" x 5.250" SBC intake valves and some 1.810" x 5.370" Mopar exhaust's. We use this setup all the time on the 100% stock-appearing builds.

If you use theses sizes AND do a decent port job the heads WILL deliver.

Have 3 sets being done this week, most get Ferrea's valves. Fairly straight-forward operation. Occasionally we'll use Manley's intakes also.

(Add) With respect to porting on the exhaust's, I would stay away from the bottoms of those guides, this is a "high-stressed" area where the guides are pressed in and very close to water!! Just a tip.

Thanks, Gary in N.Y.

P.S. The lengths work well and all have SBC .343" stem diameters.
Quote:
Originally Posted by VORTECPRO View Post
Great advice!
So why not just use off the shelf 2.19/1.88 BBC valves with 11/32" stems? Seems like they'd be easier to find (and maybe less expensive?) and provide roughly the same valve size.

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