Guide boss shaping

[steve cowan]

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Travis,
my own testing on my bench has the airspeed around 250-260 ft/sec on the roof and around guide boss area this is @ 28'' depression.this is for a port that has 360-380 ft/sec around the pinch and over the SSR at full lift.

[mag2555]

The only thing craved in stone that I have seen is that steep valve inclination angles like the 23 degree of the SB Chevy and the 26 of the BBC will have good amount of velocity on the roof above .450" lift and in turn make a need for the guide to taper down to valve stem diameter size as soon as possible.

If the port does not have much bias left to it due to the Throat size used you can use a tall wing type guide if cast as such to get some swirl motion back into the exiting flow into the chamber, but it will cost some flow numbers at high lift.

These photos show that shaping the valve guide and its blending into the roof in this Ford 2bbl Cleveland head to match the valve cant angle of the floor was one of the last pivotal tweaks done to getting the port up to 290 cfm from a stock level of 205.

[Carnut1]

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Different designs have more or less material to work with. I prefer a rounded boss on exhaust due to flow shift across boss through the lift range. Thanks, Charlie

[RevTheory]

Here's a BBC "bad" port.

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[Carnut1]

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My version of a tear drop guide profile.

[PRH]

PRH...i brought a set of Brodix 18 Deg. C-Heads that were CNC ported when i got them. We flowed them. The first change to the intake port (in search of) more flow was re-working the valve guide boss. The result was 8 CFM at .700" lift with a 2.200" 5/16" stem 45 deg. seat valve. There is a lot of air moving through that area, near the ceiling of the port. Mark H.

I didn’t say reworking the guide boss couldn’t yield any gains in flow, I said I didn’t bother to do it when doing something along the lines of a “bowl blend”.

As with all of this stuff....... no one approach works on everything.

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[gmrocket]

A lot of the shape would depend on the bowl volume and port height

I work on engines that mostly have undersized bowls even after max porting..so I sometimes remove most of the guide protrusion all together. There is till plenty of support with it cut down .250" to .350"

A high centerline port with generous a bowl volume ,undercut stems and a big distance from valve backside to guide , don't respond as much to guide reshaping...unless it's a big blob of a casting that's supporting the guide.

[ozyfordman]

Mag2555,
Those pics of the 2v Cleveland port sparked my interest. Is that device in the second pic a measuring device/ template? Did these ports @290 cfm back flow at high lifts? I can get those numbers but without stability. Any advice to offer? Also what valve size was used. Thanks in advance.

[ptuomov]

How should I reshape the exhaust valve guide protrusion into the port and the boss in which the guide sits if I want to minimize the exhaust valve temperature and more generally exhaust valve durability in a turbo engine?

[SpeierRacingHeads]

If the front of the guide is important, how important is it behind the guide?

Heads without any type of wing behind the guide, need a wing behind the guide.

[RevTheory]

If the front of the guide is important, how important is it behind the guide?

Heads without any type of wing behind the guide, need a wing behind the guide.

From what little I can find by way of online pics, Profilers for SBC don't appear to have any meat around the bronze guide. Is that the case?

[1972ho]

The 4v cleveland has this cast into the head already so how could this be improved if any.

[SpeierRacingHeads]

If the front of the guide is important, how important is it behind the guide?

Heads without any type of wing behind the guide, need a wing behind the guide.

From what little I can find by way of online pics, Profilers for SBC don't appear to have any meat around the bronze guide. Is that the case?

Only the exhaust.

[RevTheory]

From what little I can find by way of online pics, Profilers for SBC don't appear to have any meat around the bronze guide. Is that the case?

Only the exhaust.
[/quote]

That's bugging the shit out of me, lol.

[SpeierRacingHeads]

From what little I can find by way of online pics, Profilers for SBC don't appear to have any meat around the bronze guide. Is that the case?

Only the exhaust.

That's bugging the shit out of me, lol.
[/quote]

The exhaust doesn't bother me. I've made 860 with a low port casting with that design, it works.