Working The Stock Exhaust Guide and Boss Area

[jack]

Please bear with me as I need to text each shot and take a few more pictures

A few members have approached me asking me to go alittle deeper in depth of the exact procedures I use in re-profiling the guide and the boss area surrounding the guide itself. The methods I use to contour the guide is common practice when porting any head as it's free Hp to reduce the resistance of flow and the flow charts I've provided speak for them selfs regarding what's available with little effort and it's quite obvious the XS head is no exception either. It just goes to show that the protruding exhaust guide and boss area in fact does impede exhaust flow and velocity. A good analogy example to describe the influence the bulging guide and boss area have on flow resistance is to place a fan of medium size on high,then cover half of the frontal section of the fan with cardboard and take notice of air movement. Now take that same piece of cardboard and cut it in half and cut a 1/4 off the bottom or more doesn't really matter, then place in front of the fan on high and take notice of the increase in cfm velocity just by slimming up the cardboard...same principle of application

[jack]

First step is to completely clean the head by means of either sand blasting or bead blasting. I prefer to sand blast,then for the final finish,I'll glass bead the head.

Second step is to provide some type of alignment marks to reinstall the guide to it's original position and whether or not this has any significants on proper valve alignment to seat, I don't know but it's a step I use when working with original cast iron guides. The guide in the picture is a bronze guide from Kibble-white that's been machined to accept the Megacycle 440 lift cam and it's been from my experiences that a iron guide is more suitable for street use,as the life expectancy of bronze is short lived by 20 to 30,ooh miles or sooner.

To remove the original guide place the head in an oven set at 350 degrees with the cap facing up for approximately 45 minutes,then tap or press out the guide and let it cool down before you commence to rework it. From A ( bottom of inner spring step) to B,the dimension of length should be between 1.355 to 1.360 and the dimensions for B to C should be about .215 on angle. These cutting steps are done on a simple wheel grinder,nothing fancy here. When you get ready to reinstall the guide,reverse the procedures but do not freeze the guides,just apply grease of a low melting point or Vaseline and apply some to the seal to hold it in place, once the guide starts absorbing heat from the head,the freezing effect is completely lost in a matter of seconds,then just drive the guide home, when the guide fully seats,you'll head a dull thud sound and when the head completely cools down,install a exhaust valve and hold the head up to a light source and pull on the stem to seat the valve and check for exposed light that might exhibit between the valve face and seat. If extreme amounts of light exist,then the guide is out of alignment not being centered with the seat,then proper alignment will require installation of a manganese bronze liner for correct centralization of the valve stem for proper seating of the valve face to seal.

[jack]

In this shot, I've re-installed the modified guide and it's quite obvious that the littlest details to clear the air stream of obstructions should equal a decent gain somewhere in flow curve.

[jack]

When you start to work the exhaust pocket,remove just enough to clean up the casting flaws in the bowl and the corners. You want a smooth transition from the seat down to the valve guide and this is where you'll have to make a judge mental call as to what's needed to clean up port but just follow the info that's outlined in the porting section,along with what I've provided here for ya and your head should perform strongly and remember use your finger for feed back of surface irregularities in the bowl,corners and the very important SHORT TURN.........SMOOTH....SMOOTH....SMOOTH.........if possible

[jack]

This is the cutter that I prefer to use when re-shaping the guide boss area cuz it's small enough to fit in tight quarters and removes smaller amounts of aluminum giving me more control to contour the boss to the desired shape I'm after.




In these two shots,when you start to rework the boss,I always start with the long side and work towards the front. Start at center of the valve stem and work it by removing aluminum at an angle and when you feather the boss,you want the tip of the feather to align with the center of the guide and gradually wrap the feather tip around the guide till it shows a SLIGHT off centered look. JUST LOOK AT THE PICTURES I"VE PROVIDED AT THE END OF THIS POST. It's really quite simple and the second one will be a breeze This is the long side of the port and roof and what you're attempting to do is speed the air up along this section of the port to reduce resistance of flow.

[jack]

I apologize for this shot being out of focus. When working the opposite side of the boss,give it a straight shot approach.

[jack]

Then from the pocket area,take the cutter and work the boss area of what you've feathered by rounding it and to remove any irregularities of the surface.

[jack]

In the first shot it's semi finished but in the second picture I used 80 grit,120 grit and for the final finish I used scott bright using a coat hanger attached to a drill. I don't bother with giving the exhaust port a mirror finished cuz eventually carbon will adhere to the ports,just a waste of time in my opinion.

[jack]

Now for the good stuff. I can't begin to tell ya how many hours I've spent welding and re-shaping the exhaust port on this head during the last few years,hoping to find the perfect port shape to at least pick up the low to mid lift #s cuz the 400 to peak lift #s are about as good as they get using this port shape. What really holds this head back in the low to mid lift #s is the short turn the turn either has sufficient material to work with or it doesn't or you can weld filler in to fill the voided areas but it's not an easy task either. I have quite a few heads laying around and only ONE exhaust port that has a PERFECT short turn from the factory,imagine that ;D and I using that for future reference to alter the turn but only until I can successfully gain better access to rework the turn by means of welding.
Letter" A" is the turn leading up from the Short Turn, again I've played with that turn numerous times and if too much material is taken out or reshaped incorrectly,you'll loose velocity and the #s will drop dramatically to the bottom. When working the ST corner, you want a smooth radius from the seat leading up to the lip step in the port and again,use your finger to feel. If in doubt,it's better to take out less than trying to put the material back in or get assistance.

Letter "B" is the outside turn that I'm still playing with and with this turn,you either have enough material to work with or you don't.
Letter "C" in the middle section of the floor,just smooth it out.

There are several exhaust shapes floating around form various reputable XS enthusiast and each one of them has a place whether it be for street or racing. You've got to remember #s are just that cuz in the end your motor has the final say as to what it likes

[jack]

These shot are of the sleeves I install to reduce back pressure as the exhaust pulses enter the header,you simply want a smooth transition at the section and those are the cutters I use to trim the sleeve. I 've flowed a head using these sleeves and no loses were recorded,so all is good

The demensions of the sleeve are outside- 1.542, inside is made to my bushing driver 1.118 and the width is.475 ,now the width is set to provide a recess incase the lip of the header pipe extends inside the port from gasket compression,you can make it flush if you wish,I just choose this width to avoid problems in the field.

[jack]

Completed port before installing the sleeve

[50gary]

Jack, are those the anti-reversion rings (inserts) in photo #9?
Cheers, 50gary

[slide]

Jack, mine are called Exhaust Inserts for long but Sleeves for short. It's a bit*h going thru the baby book and your spouse chooses a name you can't stand.

[acormier7]

Jack,
They look farmiliar. Looks like they were turned in Canada?
Maybe call them Canadian sleeves.
Thanks for all your hard work and advice. My Tracker will be done before spring.
Art in Peterborough

[jack]

Again like the ports,the step in this head varies in dimensions,so take measurements before machining the sleeves and you want a very tight interference fit or spot weld it in place.