Head work for a 750 job

Jack · Full Member Joined: Mar 15, 2005 Posts: 411

John............Regardless of how fast you go or what you intensions are,increasing the volumemetric efficiency is one of best bang for the dollar and if done correctly not only does output increase ,so will fuel economy by means of increased port velocity creating more swirl action of the fuel mixture as it enters the combustion chamber and by increased homgenization of fuel particles to further enhance the effectiveness of combusion process there by reducing the fuel requirements for the same amount of hp at any giving RPM range.

The casting flaws in the 80 heads are terriable,particularly in the corners,there are several ways you could port this head though...............Jack

xsjohn · Posted: November 14, 2007, 10:01 pm Post subject: Re: Head work for a 750 job

Dang....tell me more please.....now that you know my intentions....if it is a bit of a trade secret I can understand...sounds like plugs would be cleaner....less throttle......saving a bit on gas shouldn't bother anyone....

Could porting reduce any vibes........since it seems it would not be struggling as much.....noticed that richer mixtures on mine reduced vibes noticeably and carb balance too ........

John

lester · New Member Joined: Mar 17, 2009 Posts: 4

I just put 750 kit from mikesxs,engine runs great.how many miles or hours before I need to re-torque head?

xsjohn · Posted: June 12, 2009, 3:57 pm Post subject: Re: Head work for a 750 job

Until your torque readings don't change...........xsjohn

lester · New Member Joined: Mar 17, 2009 Posts: 4

thanks johnxs ,I live NC

xsjohn · Posted: June 12, 2009, 4:16 pm Post subject: Re: Head work for a 750 job

Where......I'm in mocksville.........xsjohn

lester · New Member Joined: Mar 17, 2009 Posts: 4

Asheboro Lester

royfisk · Posted: June 12, 2009, 5:50 pm Post subject: Re: Head work for a 750 job

Jack how are you? been off the site for awhile. I took you up on trying to do my own port work. I havent started the engine yet. Waiting for my forks to arive. John Just go in and clean up whats crude looking. And flow to the diameter of YOUR headpipe. i HAVE A PRACTICE HEAD FOR YOU IF THATS WHATS SCARING YOU. I cant wait to try mine and if I dont like it Ill pull it off and try again.

xsjohn · Posted: June 12, 2009, 6:11 pm Post subject: Re: Head work for a 750 job

Roy .........not scared........just always have something else on my mind when I have the head off........almost 70K on the ole thing now.......dang that would amout to about 3 trips around the earth....... Very Happy

xsjohn

Jack · Full Member Joined: Mar 15, 2005 Posts: 411

Roy,how ya doing? Me I've been laid off drawing unemployment for the past year and a half and it's not very promising around here. What did you do on you ports? At present I'm working a new profile on the exhaust port roof that biases the flow both towards longside and outside turn of the roof that distributes the flow evenly for increased velocity,looks very promising but requires a great deal of welding to turn the flow to prevent impeding it,so far I've seen a gain of 16 cfm and more but if the ports have sufficient material,no welding would be necessary and a 90 CFM flowing exhaust port is well within reach with a stock valve,I've already done once by accident.

Roy if I may ask how old are you? I'm not getting any younger,if you know what I mean. I'll be testing this head as soon as some money comes in and if flows what I think it will,I'd like to pass this information on to someone like yourself who's share's a deep passion for the XS. These port profiles come from my own flow testing and they don't infringe on Bob Bertauts,3Ms,Craig Weeks,etc years working the XS head.

If,you're not satisfied with the performance of your head porting,box it up and ship it to me while i still have some free time...........Jack

royfisk · Posted: June 13, 2009, 8:19 am Post subject: Re: Head work for a 750 job

Just turned a ripe age of 48 last sunday jack. As for my porting I basically did as I told john and cleaned up the nasty rough areas, and feathered back to my 1.5 diameter of my exhaust header. This is my first attempt at porting and useing what I have for tooling. Which is a dremel with carbide burs of various shapes and sizes, I bought off ebay for $9.00. I was surprised as to how fast the burrs actually worked. The big shelf located in the exhaust port went quickly. I may have the whole thing wrong and if I do thats fine cause I have at least 5 more heads to play with and I will chaulk it up to a learning experiance. I plan on doing a 750 kit this winter and want to have a 75 head done for that project jack and I want it done by you. That head and engine I want to perform peak performance. I want it to run with all the tork and power in the lower to mid range. Which means I dont need bigger valves. I know bigger valves build more power in the top end and smaller valves with longer intakes will build power in the lower to mid range. Right where I want the power. Im not sure if the 75 head is the right one for that or the 78 head but I have both years plus a couple 80 up heads. got to go to work, will talk later.

weekendrider · Posted: June 13, 2009, 9:35 am Post subject: Re: Head work for a 750 job

Jack, glad to see you posting again. I've always enjoyed your input. Even if it is above my skill level Embarassed

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650skull · Support Staff Joined: Jul 19, 2007 Posts: 1186

Hey Roy what is the difference between the heads from different years

royfisk · Posted: June 13, 2009, 10:11 pm Post subject: Re: Head work for a 750 job

I am not sure but I know that there are some casting differances that you can visually see. Weather that is from differant castings or differant year specs I am not sure. Ive seen posted before that the 75-78 heads are the better performance orianted head. IF YOU CAN BELIEVE WHAT IS POSTED. Most of which is gossip or second hand information or made up just to sound knowledgable. This question would be better answered by Jack where as he has been in a lot of these heads from various years.

Jack · Full Member Joined: Mar 15, 2005 Posts: 411

Roy.........doesn't matter what head just as long as the short turn in the intakes don't have the cap exposed,I can work around the exhaust port.
As to which XS head performs best with minimal effort would be the XS1 (256), at 300 lift the #s some what drop off cuz the way the corners leading to the ST are cut but more than make up for after 350 lift,you'll never notice the difference. With the right valve,working the guide boss area and valve job this head will flow up to 110 CFM at peak lift.

Pm your email with address Roy, some time this week I'll re-do an exhaust port for you to copy that flowed 80CFM at 400 lift and 88CFM at peak lift. It doubled it's flow at 400 up till peak. The floor wasn't touched on this particular head. I reprofiled the floor on the outside turn leading up from the ST to see if I could improve flow,didn't happen,so I filled it back in,just copy it. When I get the time I'll be sending you a few heads one head will flow 70CFMs and the last one will be with the modified roof and I'll try to explain how you can use a shop vac using exhaust pressure to compare the flow pressure differences on each head. If you can get the flow up at peak lift,then the flow at lower lifts will fall into place.
If you still want me to,I'll port your head but at least give it a shot first,I'll guide you the best I can....Later Jack

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