Need some advice on a head design

[Overkill]

I've been reading around the forum about redesigning the combustion chamber of a blaster head. Since I'm a machinist I'd like to attempt it myself. I drafted up a design and was wondering if it would work for my style of riding and still be able to stick with pump fuel? I typically ride wooded trails. My blaster is stock stroke with a 66.75 bore. Would my head design work? It measures about 22.15 CC's. Dimensions are in inches.

 

[joeak47]

I encourage you to re-chamber your blaster head! Its a learning experience. Its fun. You learn something, and you receive fruits for your labor. The stock chamber shape is a very poor design for squeezing power out of the power stroke. Make it a "Hemi", keep it around 23 cc's (+ or -), set the squish at around .030 to .045 (thousandths).
If I'm reading your specs in the photo above correctly, you plan on keeping the general shape of the stock combustion chamber including the "cone" shaped top of the chamber that shrouds the spark plug? If so, DON'T DO THAT.
Make it a true "Hemi" where the top dome of the chamber blends right where the end of the spark plug threads end. There are photos on here for reference.

A head re-chambering will make a big difference in power output that is noticeable in the seat of your pants when you ride. Very noticeable! I would suggest that you also port the cylinder to match the that new "Hemi" head. Get the porting templates here...
http://kenoconnorracing.com/portingtemplates.html
The head re-chambering and porting will net an EASY 30HP when coupled with the stock carb, and quality pipe. It will run very well, and still maintain its longevity. One last thing...let the stock copper head gasket (.035) set the squish distance for you. No need to machine a toe step like in your specs above. Pull up some photos of re-chambered blaster heads and you'll see what I mean. I made a video series on youtube years ago on machining a hemi head. The video quality is crappy, but it may help you.

 

[Overkill]

Thank you Joeak47,

The reason the first design was close to stock was because I was trying to follow a design I found on here. It was missing a couple dimensions so I was shooting in the dark. What's your opinion of my new design? It measures 22.434 cc. As for porting would Ken's DIY Blaster Cylinder Porting work for this design?

Bad news is that my blaster may be up on the bench for awhile. It started to blow a lot of smoke and oil out the exhaust Friday during a ride. I think my crank seal went out on me. Going to do a leak down test tomorrow. Good thing is that I luckily have the seals on hand for this exact situation.


-B

 

[Markblaster]

 

[joeak47]

Thank you Joeak47,

The reason the first design was close to stock was because I was trying to follow a design I found on here. It was missing a couple dimensions so I was shooting in the dark. What's your opinion of my new design? It measures 22.434 cc. As for porting would Ken's DIY Blaster Cylinder Porting work for this design?

Bad news is that my blaster may be up on the bench for awhile. It started to blow a lot of smoke and oil out the exhaust Friday during a ride. I think my crank seal went out on me. Going to do a leak down test tomorrow. Good thing is that I luckily have the seals on hand for this exact situation.
-B

The attached file on the left is the one your looking for. Or there about. Don't get hung up on numbers when calculating head chamber cc's. In my personal experience, and I've done about 40-50 head designs and re-chamberings, if you keep the cc's in the 21cc to 26cc range (preferably around 23-24 cc's), you'll be fine with pump fuel of 91 octane. Don't drive yourself nuts splitting hairs with number like 22.434 cc's vs 21.892 cc's, vs 23.369 cc's, blah, blah, blah. You won't see the difference when you put all the variables like jetting, air temperature, choice of pipe, and so on and so forth. The "SHAPE" of the chamber, and the squish distance that you set is THE most important part!
As for the porting templates that Ken sells...will they work well with a head
re-chambering? Its more like the other way around. will the head re-chambering work well with the porting? I answer that with an astounding ABSOLUTELY!!! I wouldn't do it any other way. I have a few blasters that I ported with the templates, and a few that I ported with my own templates. Proper porting and a head re-chambering go together with a quality pipe and proper jetting like it was meant to be!!! These 200 CC Yamaha engines have lots of areas that are de-tuned at the factory, and the cylinder and
cylinder head are two of the major ones. Wait till you see how much meat was left in the head and cylinder from the factory when you start cutting.
I look at it this way... Your half way there. the engine is going on the bench! Now is the time to treat yourself. I'm not trying to sell you porting templates, but I will say that you will be VERY disappointed in yourself if you go as far as putting it on the bench, pulling the head for re-chambering, installing new crank seals, leak testing (Awk sells nice testers), and NOT porting the cylinder while you were at it. Its easy to do. Its fun to do. You'll leran a lot, and It flat out works! The longevity is still there like a stock engine,while at the same time, it feels like it grew a second cylinder. Highly recommended! Stock HP is around 17HP expect around 30HP when you are done.
What pipe are you running now?
As a side note, I'm the guy that still runs the stock oil injection with all those modifications. It also works flawlessly.
Once again, my advice to you, is to not get hung up on numbers, or else your brain will explode. The chamber shape and squish distance is the most important things! If you do decide to purchase the templates, you can always sell them when your finished using them. Please keep us up to date with your progress.
Later, Joe

 

[Overkill]

This is my current setup,

2000 blaster: 66.75 Wiseco, fmf fatty with stock silencer, k&n intake, boyesen reeds, open air box.

I when I acquired it had a blown piston, all the parts I'm running now (except the piston), and some "custom welding" done to it. It also had a main jet of 360 and a hotter plug. The plan was buy it and sell it but after the first ride it wasn't going to be leaving soon.

 

[joeak47]

Did you disassemble the engine and bore the cylinder when you replaced the piston? Or, just install a piston in a used bore?

 

[Overkill]

I had it bored by a local shop.

 

[Overkill]

Sorry it's been awhile, but I finally got to run my head. I'm currently having a local race shop port my engine. I told them what kind of riding I do and they knew exactly what I was wanting. The price was right and I was able to get a good deal on parts for when I reassemble my top end.

By chance would anyone know a ballpark range to start with on jetting for a ported engine with a head mod plus all my other mods?

My elevation is about 900' and current temperature is averaging <50°f in the winter. For summer jetting temps should be about 80-100°f.

 

[joeak47]

That head looks dialed in tight! What was the final chamber volume?
Give us a list of all your modifications, so we can help with jetting. Just for fun, you could start with a bone stock head, ride a bit, then try the re-chambered head to see the difference. A head swap won't change your jetting. However porting will. Or do it the other way around. Build it like intended, set up your proper jetting, ride for a bit, then swap to the stock head to see the difference. Just a thought.

 

[Overkill]

I may try swapping heads. I'm curious to know what work did what.

The chamber volume is 23cc.

Starting with the intake I have an open air box, k&n filter, stock carb, premix 32:1, boyesen reeds, wiesco 66.75 piston, rechambered head, ported for lower end power, fmf fatty, stock silencer.


Thank you again Joe for all of your help.

-B

 

[Overkill]

Well I reassembled my top end and was able to break it in and jet it and Wow it has a lot more spunk. Problem is that the next day we got snow and it went from 40°f to -1° so I haven't been out much. Hopefully once it warms up I'll be able to get out.

I'd also like to thank all that has helped me with this project. Special thanks to joeak47, Markblaster, and Cycle Tech in Fremont, Iowa (for the porting and parts)

Thank you all,
-B

 

[best]

Joe's advice is bang-on. Look back on his old posts. Joe did me up a same cc hemi and torroidal head for comparisons. The torroidal makes better mid-range torque and self-limits over-revs. The hemi makes better peak power and rpm. Again Joe is right about compression. High compression will kill rod bearings and pistons in these motors without much return in max HP. I found shallow chamber was better than too deep. Less squish area build high rpm power, more squish area build low and mid-range torque. Like Joe says, there is no perfect shape, build for where you want the power. Don't get hung up on numbers other than keep it around (+-0.007") 0.035" squish. Good luck!