Guide boss shaping

[travis]

I’ve been looking through a lot of old posts at pictures of people’s intake porting work, and one thing I’ve noticed is a complete lack of consistency of how guide bosses are shaped. Some are completely rounded, some have a leading edge point pointed towards the center of the port, some have the pointed leading edge pointed towards the center of the chamber, some have a pointed trailing edge pointed towards either the center of the chamber or in line with the port, and some have the leading edge pointed towards the center of the port and the trailing edge pointed towards the center of the chamber. Is there any significant difference between these styles? How do you determine the best method on a head you don’t have experience with?

The heads I am piddling with right now all have a small bowl, so there really isn’t room to put a pointed trailing edge on them without fear of hitting water.

[Carnut1]

[attachment=0]main-qimg-f5827a37b147219497a6f08f0bbb3352-c.jpeg[/attachment


If I have room I will make it as teardrop as I can.

[Carnut1]

Resized_20190402_114140_1094.jpeg

[travis]

Resized_20190402_114140_1094.jpeg

Is that a pressure relief hole there in the port?

Thanks for the info. Looks like the shape can make a pretty significant difference.

I’m curious too...how do you get the finish like that? Sanding roll after a double cut burr?

[PRH]

For me, how much time I spend messing with the guide boss if proportional to the level of effort of the whole porting job.

I recently freshened up some heads on a motor where the guide bosses had a lot more time spent on them than what I would have for the level of effort that went into the rest of the porting(basically bowl ported heads).
For what else had been done to the intake ports, I would have just gotten rid of the edges around the area where the boss is spotfaced in the bowl, and very mildly blended the ridge left by the spotfacing at the backside of the bowl.

I flowed the heads with the extra guide profiling........ I didn’t see any gains as a result of it. For what else had been done to the ports..... the extra material around the boss wasn’t holding the flow back.

For a basic bowl blend type job, this is all I do to the guide:

3D05D832-0730-4367-9D84-A849F35AE32E.jpeg

0E1AD9D0-EFE2-4236-9B90-253795136540.jpeg

[travis]

For me, how much time I spend messing with the guide boss if proportional to the level of effort of the whole porting job.

I recently freshened up some heads on a motor where the guide bosses had a lot more time spent on them than what I would have for the level of effort that went into the rest of the porting(basically bowl ported heads).
For what else had been done to the intake ports, I would have just gotten rid of the edges around the area where the boss is spotfaced in the bowl, and very mildly blended the ridge left by the spotfacing at the backside of the bowl.

I flowed the heads with the extra guide profiling........ I didn’t see any gains as a result of it. For what else had been done to the ports..... the extra material around the boss wasn’t holding the flow back.

For a basic bowl blend type job, this is all I do to the guide:3D05D832-0730-4367-9D84-A849F35AE32E.jpeg0E1AD9D0-EFE2-4236-9B90-253795136540.jpeg

Is that a mopar head?

It looks like you took more off the cylinder wall side of the guide. I guess that is called bias (I really need to learn the terminology better)? Does that help on a too small port, or was that just kind of the basic shape to begin with?

[PRH]

It is a Mopar Head....... they have that bias cast into them already.

[PRH]

It is a Mopar Head....... they have that bias cast into them already.

Technically....... I took more off the curved wall side of that guide boss, but the port is wider between the boss and the straight wall(cylinder wall) side.

[Carnut1]

Resized_20190402_114140_1094.jpeg

Is that a pressure relief hole there in the port?

Thanks for the info. Looks like the shape can make a pretty significant difference.

I’m curious too...how do you get the finish like that? Sanding roll after a double cut burr?

Funny, but no. Rocker stud boss. Old double cut burr, beat to death and modulated speed.

[RevTheory]

I think people often put their own artistic twist on them.

[MadBill]

I contoured a tall (almost an inch protrusion) cylindrical guide for an Alfa Romeo into a more or less airfoil and compared flow numbers to a stock one. Absolutely no difference. It should have worked! My best explanation is that the air is flowing diagonally across the guide, so the path followed is already an ellipse and thus a much lower Cd than a cylinder.

Some engines have pushrod tubes running vertically through the port and these definitely should respond to air-foiling.

[Carnut1]

I contoured a tall (almost an inch protrusion) cylindrical guide for an Alfa Romeo into a more or less airfoil and compared flow numbers to a stock one. Absolutely no difference. It should have worked! My best explanation is that the air is flowing diagonally across the guide, so the path followed is already an ellipse and thus a much lower Cd than a cylinder.

Some engines have pushrod tubes running vertically through the port and these definitely should respond to air-foiling.

I have a friend doing ram air 5 Poncho heads, he designed foil shaped pushrod tubes and got a sizable gaing in flow.

[MadBill]

Darn, there's another wheel re-invented!

[swampbuggy]

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.

[travis]

You guys’ stuff makes mine look like it was hacked on by a 5 year old

I’m probably going to wear Gary out by the time I’m done