What's your elevation ?

 

took me what.. 2 months to jet my carb? still not completely 100% perfect, but certainly close enough. I've a lot of spare parts if needed.

 

If you look at this crappy photo you can see the lip or step around the valve seat and how the casting forms the chamber. The idea is to smooth that step and more importantly, to enlarge the chamber perimeter where the valves are close to the cylinder wall. The 351 pushes the diameter of the cylinder up about 10mm(can't remember the exact figure) so the biggest problem is going to be at the 4 corners(furthest edge radially from the center of the bore) on the valves. I wish I would have taken some pics of what I did because I fear that I'm not able to explain what I'm talking about.

Just remember, air flows best when it doesn't have to deal with sharp edges or getting pinched between the valve and cylinder wall.

 

You can really see in the new head how a good 1/4 ~ 1/3 of the valve perimeter opens onto basically a wall. The other crappy picture shows the head after the major material removal and before final smoothing.

 

I think we all have waited a long time to get detailed head work instructions.. Thanks guys.

De-shrouding the valves will certainly improve cylinder filling/exhausting and your photos make it easy to know where to begin. Please start a thread on this ( Call something like it "Porting the KLX head"... ) so we can search and find it easily in the future. And how bout more pictures? Who knows, maybe others will add their pics and ideas... I'm wondering about the bowls under the valves where the valve stem penetrates the intake/exhaust ports. That is where power is sometimes found with some porting...?

 

I hesitate to start a thread because I'm far from an authority on this and the potential for destroying very expensive stuff is involved... but I'll provide what hints I can. I've done a bunch of this sort of stuff on old British sports cars - this is first time fooling with a motorcycle. Somebody can cut 'n paste if they want, but I'd hate to be partially responsible for killing someone's bike. Maybe GBAuto can add more details.

Please remember I'm just a shade-tree hobbyist farting around in my garage. No, I don't have dyno numbers. No, I didn't flow bench it. No, I don't know what it did to swirl / tumble / quench / squish blah blah. Yes, I'm sure someone will be along shortly to explain why, exactly, I am full of sh^t. Caveat emptor. lol

* I wouldn't do this to a stock bore, and would be very careful with lower displacements. Removing this material lowers your compression ratio, and the smaller your displacement the more you lose for a given amount of material removal.

* Back of the envelope example - 351 is claimed to be 12.5:1, so combustion chamber volume = 351/12.5 = 28.1cc Let's say I don't want to go below 11:1 compression. 351/11 = 31.9cc. So, I can remove 31.9 - 28.1 = 3.8cc of material. No, I did not actually measure total volume. I assumed the 12.5:1 and 11:1 specs were accurate, and kept my material removal below 3.8cc

* Lay the head on a flat surface and use a syringe to fill the combustion chamber with fluid, measuring carefully. As you work, repeat this every once in a while to see how much material you are removing. It's easy to take off, but really hard to put back! I don't remember my actual numbers and didn't write them down, unfortunately. Didn't really think anyone would be interested.

* Remember that not all of the volume referred to in the numbers above will be in the head - part of it is in the small remaining area above the piston in the bore and head gasket area. So don't expect to fit 28.1 cc in the combustion chamber - it'll be less than that. Important thing is not to remove more than 3.8cc of material.

* Make sure to mark, dye, scribe etc. the location of the head gasket sealing ring, and be certain not to cut past that line! Luckily with the big bore you've got a pretty good area to work with.

* It's pretty obvious where to remove material. Visualize the valve being open and where the air wants to flow. You will see large areas where the air hits a wall. Roll back the walls. Carefully.

* Be extremely careful around those valve seats. If you do this, be ready to spend a few quality hours with the grinder, and be ready to be PATIENT, SLOW, and CAREFUL. One small slip can literally ruin your head. Use a fine burr. Lube it with wax regularly to keep it from loading.

* I did not go into the ports themselves at all. They really don't look that bad, and given the level of shrouding my assumption was that there is so much more to be gained in the chamber that I didn't even bother with the ports. Fooling with the ports is also much more difficult and requires much more control, experience, and finesse.

Anyway, should have taken more pix etc. I guess, but I'm not pulling the head back off now.

She'll pull a 15 tooth with absolute ease. Roll on the throttle at 70mph and she jumps with authority. It's nice. 67 mpg.

KLX351SF, Bill Blue 351, WebCams #101, cylinder head work, UNI filter, lid off, Stock carb, 132 main, 38 pilot, klx300 emulsion tube, dynojet spring, dynojet needle, middle clip, one spacer below clip, Megabomb / Q4

 

I whole heartedly dosagree, the valves definrely need enlargement and port and polish, more so than deshrouding imo. But great info! A DIYer is always hungry for tips!

 

Broussard, you touched very informatively on an often overlooked element as far as the combustion chamber is concerned...material removal and compression ratio. Just a couple of weeks ago on the Power Nation TV series in an Engine Tech program, they covered this issue in fairly good detail on a GM 427 crate motor they were tweaking. They even ended up milling the head surfaces to maintain a desired comp ratio due to material removal and other modifications. Pretty geeky but critical stuff in milking everything out of a performance engine. Still, the KLX probably isn't the greatest candidate for extreme measures to pull lots of power and torque, but many of the things we do with our vehicles aren't always logic based. Some of it is just fun.

 

Broussard, your head work is valuable to those of us that would do it if only we had some kind of guide as to what to do. Every idea will get some negative opinions voiced - even Marcelino had to defend his mod - but that is the nature of beast. Your work is without reproach, except by those that don't get it or are here just to create friction.
I'm tired of reading about someones bike having "head work" and no real info on what "head work" means. Bill BLue told me that there only room for slightly larger valves. But the valves and "head work" can result in 35hp on his 351BB kits.
If you won't start a thread then I'll ask here. Why would you not perform this work on a stock bore? Is there not enough room to spare to smooth the "walls" at the four corners?

 

By all means, go for it if you want, but I would definitely be very conservative. As you say, the worst spots that need the most help are right up at the edge of the bore / head gasket sealing ring on the stock bore, so there isn't much room to work with. If you cut to far and go past that point, you're looking at a big bore whether you want it or not.

Also, you can't remove very much material without dropping your compression ratio pretty quickly.

Maybe someone else can jump in with actual PORT work rather than combustion chamber... but in the absence of hard data, my opinion is that the time is better spent in the chamber on these heads. Far be it from me to gainsay Mr. Blue, but also remember that if you put bigger valves you actually make the shrouding problem worse. I'll bet a dollar that Mr. Blue also spends a good bit of time in the chamber when he fits the oversize valves.

If interested, check out what David Vizard has to say -

David Vizard's How to Build Horsepower - David Vizard - Google Books

I've done a bunch of port work in the past on old MG's and find it tedious at best. It's a lot harder to get up in there properly, especially in the small ports. It's also very easy to ding the valve seats or just generally screw up. More akin to dentistry than wrenching. That being said, you don't have to worry about compression ratio or hitting the bore edge. You just have to worry about cutting into the water jacket.

Anyway, I'm sure there are folks out there who have done excellent work on this and know exactly what they are doing - far more than me... but I also suspect that those guys get well payed for that knowledge.

I've got an old head with a dead cam bearing surface if anybody wants to play with it. It would be interesting to knock together a vacuum cleaner homegrown flow bench and do some testing. I lack the time or interest now that mine is done, but I'll give the head to someone for the price of shipping if they want to fool with it, test, and share the results. Data is always nice.