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B20 porting, where to go from here

Throat 87% of valve diameter, bowl 78%, runner 80% would be considered conservative. If you can clean up the bowl and short side radius and get to those numbers easily I'd say that'd be a good place to be at.
 
OVERDRIVE said:
Throat 87% of valve diameter, bowl 78%, runner 80% would be considered conservative. If you can clean up the bowl and short side radius and get to those numbers easily I'd say that'd be a good place to be at.
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Everything I've encountered says to not touch the short side or floor on the exhaust port.
 
Culberro will chime in, but you're correct that you don't want to lower the floor 99% of the time. There might be some transitions in the casting and machining on the short side that could be helped but I don't know for sure on this casting.
 
Are you replacing the guides?

The above numbers are pretty good. It’s hard to get the exhaust to meet those and be smooth flowing without pulling the guides and shaping the hump. One thing to be careful of is going too far. But there’s a bit of flow that can be made from carving around that exhaust guide.
 
cwdodson88 said:
Are you replacing the guides?

The above numbers are pretty good. It’s hard to get the exhaust to meet those and be smooth flowing without pulling the guides and shaping the hump. One thing to be careful of is going too far. But there’s a bit of flow that can be made from carving around that exhaust guide.
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Guides stay. Those are in very good shape. My gut tells me the intake isn't half bad but it is always the exhaust on these. There has been some work on the bad choke point just past the seat.
 
Intake bowl and throat looks small.

I’d 100% reshare the SSR on the exhaust but don’t lower the floor. The exhaust sucks on all 8v heads. I’ll often make the bowl oval vs round to increase the flow area.
 
culberro said:
Intake bowl and throat looks small.

I’d 100% reshare the SSR on the exhaust but don’t lower the floor. The exhaust sucks on all 8v heads. I’ll often make the bowl oval vs round to increase the flow area.
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Oval in what way? Long axis of the oval in line with the port or perpendicular?

I'll smooth out the SSR and work on the intake bowl and throat.

I'm not really going for anything crazy here, just whatever I can easily knock out while waiting on a new camshaft.
 
spock345 said:
Oval in what way? Long axis of the oval in line with the port or perpendicular?

I'll smooth out the SSR and work on the intake bowl and throat.

I'm not really going for anything crazy here, just whatever I can easily knock out while waiting on a new camshaft.
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I saw something like this in one of the heads I was testing on. The bowl/throat on exhaust was ovaled/triangle towards the pushrod side, and up, so no outward near the floor, but lots of outward towards the top. Upside down trapezoid at the outlet.

Haven’t gotten the flow bench done yet for real numbers, but I liked the shop vac yarn on a stick. Looked pretty straight when running around the valve seat.
 
spock345 said:
Oval in what way? Long axis of the oval in line with the port or perpendicular?

I'll smooth out the SSR and work on the intake bowl and throat.

I'm not really going for anything crazy here, just whatever I can easily knock out while waiting on a new camshaft.
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In line with the port. I don't make it too oval on the long side of the turn (if at all), and instead focus all the effort on the SSR side of the seat. This allows for a much better SSR shape vs the sharp angle that's usually there.
 
cwdodson88 said:
I saw something like this in one of the heads I was testing on. The bowl/throat on exhaust was ovaled/triangle towards the pushrod side, and up, so no outward near the floor, but lots of outward towards the top. Upside down trapezoid at the outlet.

Haven’t gotten the flow bench done yet for real numbers, but I liked the shop vac yarn on a stick. Looked pretty straight when running around the valve seat.
Click to expand...

That's where the air wants to be :)
 
culberro said:
In line with the port. I don't make it too oval on the long side of the turn (if at all), and instead focus all the effort on the SSR side of the seat. This allows for a much better SSR shape vs the sharp angle that's usually there.
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So get the smoothest transition possible on the SSR. What does a better bowl shape look like? I'm trying to visualize it.
 
spock345 said:
About 35-ish mm in the intake, 28mm on the exhaust.
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If using a 42mm valve that would be about the smallest you'd want to go (83% of intake valve diameter). Most of the street stuff I aim for 85-86%. With a carb, maybe there would be more fuel shear with the smaller throat ID? A valve job with 4-5 angles would take that out to ~86-88%.

All that being said, if that's the smallest area it will be OK and should work well. Make sure the intake port surface isn't any smoother than a 60grit finish, a burr or 36-40grit finish works well on carbs and most EFI setups.
 
Hold up, does that head have a new valve job?

There's what looks like a section that wasn't cut on the intake side at the top in the pic.
 
culberro said:
If using a 42mm valve that would be about the smallest you'd want to go (83% of intake valve diameter). Most of the street stuff I aim for 85-86%. With a carb, maybe there would be more fuel shear with the smaller throat ID? A valve job with 4-5 angles would take that out to ~86-88%.

All that being said, if that's the smallest area it will be OK and should work well. Make sure the intake port surface isn't any smoother than a 60grit finish, a burr or 36-40grit finish works well on carbs and most EFI setups.
Click to expand...
I found the really sharp edge on the short side of the exhaust, I'll put a good amount of my effort there.
 
So assuming that the guides are in good shape just go in order and work your way out. Start with the valve seats and make sure thats in order and then move up to the throat. Crazy race engines are out in the 89-90% range but less is fine on the street. Moving out clean up the short side but only take out the lumps-try to keep the radius uniform. There are some really good videos on the YT with Charles Servedio,David Vizard etc. I have several well prepared heads if you want to come by the shop and take a look. Kirk
 
Dug these out from the archives...this is the VPD head on mine right now.

oVVWq5r.jpg

RFqJtWM.jpg

M5ejc1X.jpg

qxqGgOx.jpg



Intake:
wQoKjLN.jpg


Exhaust
s0B9wxU.jpg
 
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