[glow=red,2,300]Porting For XStreme Power On The XS 650[/glow] The gentleman on the left is my friend Bobby or other wise known as "The PowerMaker",of course you know the Head in the middle as Mr. XS and I'm on the right. This summer I had the opportunity to do some port work on the XS head and flow test it to see if any gains were achieved. The results far exceeded my expectations from what little effort I spent massaging the ports. And it just goes to show,that with some time, alittle patience,ect,that its possible for anyone of the members on this board to achieve the same results with guidance of which areas need attention to increase air volume.
Some of you are probably wondering,why the hell are you spending so much time on this subject. Well, porting is a area that's for most of you, been shrouted in dark mystery and for some,might find it intimating to tackle a project such as this. There's no black magic or witch craft involed,but porting does take a sculptor's touch and a basic theory of how air behaves,based on the physics of fluid dynamics and the results are usually through experimentation and flow testing. My goal is to unshroud this dark side,so that you can stuff some extra cash in your pockets,instead of paying someone else and so that you could gain some knowledge along the way but most important,having the satisfaction of producing this extra HP yourselfs.
Basic cylinder head porting will improve the performance of production cylinder head by removing the casting flaws that come through mass production and believe me,the XS heads really 'Suck' by the crude methods the Japs used through the machining process of the bowl port areas and casting of the heads. In production intake and exhaust ports,air starts flowing smoothly,but once the air encounters casting flaws of the ports,the once smooth flowing air breaks into a tumbling and turbulence motion,which causes restriction to the overall air flow in the port. So by removing these casting flaws you,improve throttle response,you improve volume efficiency of the intake port thus allowing more air/fuel mixture in the combustion chamber,which equals in most cases,more XS power.
The XS head is by no means a High Performance Head compared to todays stanards, but it does have potential and I'll take you through the steps which will allow it to be more efficient. The areas I'll cover are the ,tools I used, the bowl blend,shortside area, guide boss feathering and polishing.
The topic of D-shape of the intake port has been brought up on several occasions on this board wether or not the ports of the XS heads would benefit from such extreme modifications,so i called Bob Bertaut,who we all know has a strong reputation with the XS and he said,there's a dramatic improvement in performance,being the port velocity was increased through the whole RPM range,will produce much more torque and horse power will occur at a much lower RPM,which in return makes it more potent for street use and highway roll-on response.Now some are prabably asking,why is port velocity important to making power 1) The higher the airflow speed,the better the air/fuel mixture is atomized as it passes through the carburator. This improves the combustion process . 2) The higher port velocity improves the combustion 'swirl effect'. The 'swirl' distributes the air/fuel mixture in the combustion chamber,thus improving the combustion process. 3) The higher the velocity,the greater the inertia of air flow.This helps in filling the cylinders to their maxium,improving volumetric efficientcy.High velocity ports designs can achieve volumetric efficiencies of almost 100% in certain RPM ranges. Meaning,you just put 6 lbs of mixture in 5 1/2 lb area as a example. So I've got a mig welder, a spare head and I have a big itch to explore this topic down the road. Jack
[glow=red,2,300]Stock Head vs Modified On The Flow Bench[/glow]
To those who are unfamiliar with a flow bench,it's basically one big vacuum pump that flows in both directions and is used to see where gains have been made in certain lift ranges,relative to the port areas that where modified and to analyse this data as to wether or not material needs to be added or removed for what your tring to achieve. And one more element that plays an important roll in flow testing,is the quality of air at the time of testing,being it has a direct effect of the amount of cfm reading and if air quality is down,so are the cfms.
The two heads used in the testing,the stock recieved your basic V/J and nothing else. The modied recieved a tricked out V/J angles and the intake port had the guide boss area feathered,the port opening enlarged slightly and the pocket area semi finished. The exhaust port recieved the royal treatment and the data speaks for itself but you could say the exhaust cfms are to good,being there's a standard rule that head porters use and you want the exhaust to flow about 70 to 75 percent of the intake flow in order to prevent over scanvenging on the overlap cycle. But we're talking small displacement engines here and they need cylinder pressure to develope HP and torque,so the overlap isn't quite as severe as a V8 motor.
When you look at these flow numbers,you must keep in mind,that the XS head was pulled on a 4 inch bore not a three inch and these are exceptional flow #s being the XS head has small ports and valves. There are V8 small block heads out there,that don't even come close to these #s in this lift range in their stock form. So who says the XS head does'nt have POTENTIAL. One of the greatest assets the XS head has is it's Hemi combustion chamber shape in that ,the valves are inclined(most importantly the intake) and as the valve breaks from it's seat,it moves away from the cylinder wall thus minimizing the negative effects of shrouding,allowing a higher flow efficiency and the fuel mixture is dumped in the center of the cylinder not to the side.
The valve job is the most important area that needs attention cause if it isn't seal,you loose. So find a machinest who has a respectable reputation in valve work cause there's cfm #s in those valve angles and a machinest who knows his craft, have tricks up their sleeves to jack those #s around like you won't believe. And some of the areas you gain flow are 1) Valve head margin thickness,which gives more area for the flow to increase and this sortta acts simular to a shortside effect. But you'll need to check valve to piston clearance with this mod( depends on camlift) and it'll increase the compression in the process 2) Seat widths play a major roll in airflow but for street use stick to the stanard widths for longevity 3) Radius the seat widths but this is generally racing stuff 4) the contact point of the valve seat to the valve face contributes to airflow(intake only) 5) back cutting the intake valve on top 6) radius bottom of exhaust valve but there needs to be a thick valve margin for this process 7) polishing the intake top section might help
Here's a formula used to calculate the HP potential of any given cylinder head by it's flow capacity- Hp equals cfm X .2575 x the number of cylinders. So in the numbers above just subtract 25 to 30% being it was pulled on a 4 inch bore.
If you want your XS to achieve it's fullest potential in producing torque and HP,then go MegaCycle because their camshaft profiles complement the XS head in every aspect of the flow chart..... Jack
[glow=red,2,300]Pictures of the Flow Testing[/glow]
This is Bobby doing what he does best "Porting Cylinder Heads". This is my head and it was just lightly ported in areas to gain a general view of the amount of CFMs that could be abstracted from a XS head with a light touch.
In this picture Bobby is setting up the Dial Indicator to the intake valve tip to simulate cam lift to record the CFM readings from .100 lift to max .480 lift, at which the bottom of the valve retainer butted the top of the valve guide. So when using lift ranges between 440 to 500 lift,you need to check the clearances of the valve retainer and valve guide or damage will occur.
In this picture bobby is adjusting the flow bench(the tube with the red liquid will rise or fall ) indicating the point at which max CFMs where obtained at certain lifts and this figure is recorded, then there's a formula used to break this data into a CFM rating.
This concludes the flow pictures and I would like to add, that the exhaust port on the XS head in my opinion is the most restrictive in preventing our little XS motor from unleashing it's true potential and though my R&D porting of the exhaust port maynot be the caliber as Bob Bertaunt or Mike Morse and having no real basic knowledge of the XS head. I feel the numbers speak for themselfs in regards to what can be achieved with some backyard low tech technics, that'll produce outstanding results where they can be felt in conjuction with the engine parts chosen. Jack
These pictures of the ports below are from the head used in the flow comparison testing. And in the next few days I'll be posting port pictures of various heads to show the inconsistent casting flaws from the foundry that Yamaha used. The intake ports flaws are generally the pocket areas,the floor and shortside but the real inconsistent shocker are of the exhaust ports. So when dealing with XS head,you must work with what you have or if your a perfectionist,you'll need to either weld or apply an epoxy in the areas that require modifications to gain a perfect port. Jack
I had to darken this picture to bring out the flaw imagines but i'll continue to work with this picture.The pictures in my files are of sharper depth and when transfered from Photobucket they appear blurred. The crude machining process and casting of the exhaust bowl area restricts flow tremendously
This set of pictures are of the right & left exhaust port exits and if you'll look at outside wall(by the stud),this is the area that has the most casting deficientcies and is the area you work with what you have. The thicker it is in this area will help assist in making the flow turn but what's the real kicker is the opposite site and that hugh valve guide and boss that really restricts flow. The area with the thickest material, is what's referred as the "TURN" and I'll address this when we get to that stage. Jack
[glow=red,2,300]Picture of the tools I used[/glow]
From left to right: blue point die grinder,guide knocker,a long 8 inch cartridge roll mandrel to avoid nicking the valve seats,inside deviders used to record dimensions in conjunction with the sliding dial calipers,emery cloth and a 3/8 drill. On top you'll need the Red and Gray Scott Brite for the exhaust. Three types ot cartridge rolls,they should be atleast 36 grit,or 40 for the intake ports surface and for the exhaust start with 36 grit to remove mass materials and work up a smoother grit for a smooth finish.
[glow=red,2,300]Exhaust Port Modfications That I Used[/glow] I think when push comes to shove,the exhaust port on the XS head,is the area to address first,cause if this motor can't exhale the gases,your not going to the"Moon" on your XS but with some guidance our little XS well feel like it's carring :"Rocket Boosters" in those ports and the differance will be felt! Now my methods maynot be appoved by some but you can't ignore the facts, that i got results with little know how and just used basic common sence to achive some extra performance,without taken out a second morgage. Hopefully in the end,we can all share technics,ect that some of us used,that might cut the cost down or just past some vailuable imformation through the ranks of our XS club.
Here is a shot of the port used during the testing
On the exhaust of the XS heads,you want the flow on the roof not the floor. Use the floor to keep the gases near the roof and that port will pull like a freight train from idle to redline.I'll will take you through my steps and hopefully you'll find these tips usefull on your next project. Jack
[glow=red,2,300]Pocket Power[/glow] There are several means in which one could begin to increase an engines " Volumetric Efficiency". So lets look at them first
2) camshaft replacement
3) exhaust system upgrade
4) and finally head port modifications
Now out of these four items,which would come first? If were my motor,the port modifications would come first on the list being that there's no sense in tring to increase an engines volume efficiency if it can't properly inhale or exhale any increasements,so any improvent on either end,will be a benefactor on the power output,a exhaust system upgrade is a major plus in seeing drastics results along with port modifications, carburation rejetting will be needed most likely and finally,install a HP camshaft to keep those valves off them seats longer and your off to the "Moon"
A great deal of power typically hides under the valves, around valve guides and in the port bowl(or pocket),just begging to be unleshed by you and your grinder and this is generally referred as to " Pocket Porting". The idea is to remove the rough casting flaws from the factory to a smooth finish were there's no resistence to flow along the bowl area,alongside the port to the guide boss area and even profile the guide boss to a degree. Remember when pocket porting, you need to stay within 90% of the valve to avoid fuel seperation from the seat but we're safe here>
Now for some,you'll find it much easier to remove the valve guides to gain better access to those tight spots and it does make a world of difference. Just make sure you mark weither its for the right or left exhaust port and make a indication point as to line the guide back in it's original location in the spring seat area. [glow=red,2,300]One word of caution in regards to bronze guide replacement. Stay the hell away from them,they distort to a point where they need a guide within a guide to straighten them out!!!!!!!![/glow] If your guides need replacement,have the stock guides honed out and install a .060 solid bronze Kz liner not the cheap grap,these are solid bronze liners!!!!!
The one thing that jumped at me ,even after the porting,is the port volumes are still over the limit for it's given exhaust valve size,which should be in the vicinity of 85 to 90% of the valve to maintain higher speeds of velocity to expell the gases and pull harder weither on the street or track,"Velocity is a MUST" IT's my opinion that a choke down would be in order for this type of correction to speed velocity and have I got a port in the works,you bet ya. There'll be no close up shots of this port untill I've tested it's effectiveness as a producer. Jack
Here's a angle shot of the D shape that's epoxy filled for testing purposes only, The floor and the rightside turn,should in my opinion should take the low lift #s to the moon. This picture does this port no justice at all !
So before we get starting in massaging our XS heads,you must take safety seriously,use a full mask shield or safety glasses will do, gloves if your skin as a womans feel ;D but remember turn your speeds down to around 300 to 350 just enough to spin the cartridge roll and apply light pressure to avoid digging in and keep the roll moving and keep the first aid kid stocked with a good german"WiseBeer" a case
When you look at the picture below,what do you see? I see a bulging valve guide that does nothing as a performance advantage,so you either drive that guide out or you can use the trusty old drill to eliminate the guide. First if you drive it out,look down the exhaust guide and you'll notice that there's a section in the guide that serves no purpose to support the valve. Grind the guide down to that point( dip in water to cool off) and radious the outside of the guide tip to a 45 degree angle. Or leave the guide in and grap a drill bit,that's larger than the outside diameter of the guide and drill down to that inside lip,I referred to. Now the tip will look like a vulcano top,so take a small tip carbide cutter and flatten the top down but go slow and easy. The overall lenght should be atleast 2.020 to 2.033 or 2 and 1/16 inches.
When this task is completed,your ready to move on to massaging the exhaust port and again,this is the methods I used and are nothing but suggestings to ease this task of porting
In the picture below,this well be our starting point. Do you see the top arrow, well the aluminum in this is as smooth as can be and flush,where the cap meets the rough casting flaws(bottom arrow). When removing these flaws,you want a smooth transition from the top arrow,down to roof of the bowl where the guide is. I mean lets face it, there well be gouge marks but take it slow,real slow. To remove these flaws I used a Matco carbide cutter #ZC1L, lenght is 6 1/2 and comes with lifetime warranty no matter what destroys the tip or use a 36 grit cardridge roll cause either one will be sufficient for what were doing
Remove the casting flaws all around the port and use your finger as a guide to judge your workmanship. If you have no die grinder,get that 3/8 drill out because you'll be using low RPMs and it's the perfect tool,just have your buddy support the head for you and don't forget to use some source of light at the other end when porting,a low light.
When removing casting flaws,try and remove an equal amount around the port and follow the contour of the port for reference.
In this picture,if you've removed the guide to obtain better access to those tight spots or you've cut the guide down. Do see the bottom arrow?Well in this port,it as a smooth transition from the cap area to the bottom arrow,so from the bottom arrow to the top,all away around the port,remove this material to the edge where the top arrow meets the guide boss material.
Slimbob: Did you try Mike's XS or 650 Central? They usually have them.
Dec 6, 2013 14:29:26 GMT -5
joshelrich: Hey guys. new guy here. Where is the map and where does one introduce himself to the group? I've got a pretty cool project in the works. Trying to relive my youth. Ha ha. 80 frame, 71 engine case with 650 central long rod, big pin 750 kit. Shell 1 cam.
Dec 19, 2013 21:02:48 GMT -5
mwb122: Another newbie here. I appreciate the page and being accepted. Just brought home a 78 xs650 special. She is running good after a little TLC. So far I have cleaned the carbs, battery, fixed leaking clutch push rod oil seal. Now what to do with her.
Jan 3, 2014 8:50:55 GMT -5
mwb122: Bought a 79 special in 79. Was a great bike then and it is great to see they have such a large following!!!
Jan 3, 2014 10:30:04 GMT -5
oldcodgerhenry: Gooday ,all .new Pamco basic ign replacement arrived yesterday ,But the coil wires are different color ,to the trigger wires ,don't want to fry new one.
Jan 29, 2014 15:41:34 GMT -5
floris: at this moment, my XS is with Jerry v.d. Heiden, a well known XS tuner in the Netherlands.
Feb 4, 2014 16:28:08 GMT -5
floris: The engine become's a rephased 270 crank.
Feb 4, 2014 16:28:37 GMT -5
floris: Also a bigbore cilinder set of 890 cc.
Feb 4, 2014 16:29:10 GMT -5
floris: Also a long stroke is gona be applied, what makes the total about approx. 1000cc.
Feb 4, 2014 16:30:12 GMT -5
floris: 965 cc to be exact.
Feb 4, 2014 16:30:35 GMT -5
mahanlee: need help identifying a gas tank i bought on Ebay for my 79 xs. it has a tall neck and the new mikesxs cap i ordered will not work on it. any suggestions?
Apr 10, 2014 13:43:49 GMT -5
mahanlee: Need help identifying this part. It came in a box from the previous owner. I have searched Google and Ebay and haven't found something similar. It has a short bolt with a flat side. The only place I figure it goes is underneath the battery box.
Apr 23, 2014 8:14:07 GMT -5
djonesxs650: Batteryless setup for '78 XS650 with points ignition....I need a wiring schematic, simple as possible...does anyone know of any posts that can help?
Jun 28, 2014 16:02:09 GMT -5
gwc1147: I snapped the outer push rod for the clutch while removing front sprocket. I want to change to the longer rod. 77 650d I would also like to replace the seal and front bushing. How do I remove the broken rod? Any help please.
Aug 10, 2014 20:29:00 GMT -5
boxertwin1: I have a 76' XS and need petcocks for the tank. I don't want to rebuild, I want new ones. Weird, but you can only seem to buy right-sided ones. Any source for both sides?
Aug 21, 2014 14:56:18 GMT -5