head porting

i like flex shaft grinders but ive never seen a setup quite like this before it seems to mount to a bench grinder somehow,much better for motorcycle head work than a big ol makita

I used one of these to do my head and it worked great. www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=40457
These things have a tremendous amount of torque. and they are dirt cheap. I bought two because I thought I would burn one up, but I did three heads so far with the first and it is showing no sign of slowing down. You can get fantastic 1/8" mandrels and sanding cones with different grit at McMaster-Carr for next to nothing also.

they will work fine if you just doing a general clean-up but if you have to remove a bunch of material they just don't cut the mustard my favorite tool is my 1/4" drive foredom cable driven set-up it can take out a lot of material fast and works well doing precision work as well if you get the optional foot pedal assembly you don't have to look at any dials or anything it's just like driving a car. in a pince i have used dremal type tools too i also use those for blending in the bowl area underneath the valve head i always use the cable drive attachment for those as well and i also hook those up to the foot feed as well. my cutters that i got from snap-on have lasted me years and just now i have noticed that they are finally starting to clog up when they get hot. where as the cheap chinese cutters that i buy from time to time hoping i might get a good never last so i've pretty much quit buying junk. i try to buy as good as i can afford at the time they take less time are easier to work with and usally they will cut your time in half. so it can save you in the long run.

Believe me- that was a lot of material. you can see from the second picture because there is a comparison.

Second picture. It cut like butter.

kzz1p wrote:

Becker wrote:

I don't have a whole lot of experience porting heads but I'd really like to get into it. I have a few spare 650 heads I'd like to try some stuff out on. I've read alot about the theory and have a pretty good grasp on it. My question is what kind of stone or burr do you guys use for your porting?? Does APE make any shorty valve guides for 650 heads?? I'm starting to gather parts for an 810 motor and I'm wondering if GPz 750, KZ750, or KZ650 heads will make the best starting point?? Any answer would be awesome.

I'll take a shot at the head question. It all depends on what size carbs you plan to run. The 650 head can use 24mm,26mm,28mm,29mm,31mm and the GPZ head can use 34mm & up.
It's all what you think, will be your best all-around choice. Myself, I would not even think of the 34mm carbs, buts thats just me..........

Thanks that actually makes a big difference in my choice. I want the motor to be streetable so probably 28mm carbs.

This sounds like its gonna be alot of money. I'm gonna have to start saving. Good to know there is alot of experienced people on here I'll definitely be saving this stuff to my KZ file for when I do this come fall.

Oh and APE Jay, I'll be sending in my order as soon as I get my next pay check thanks!!

Personally, I like air power for porting. I have 5 favorite, long bits that I use most often on pretty much every type of head I port.

The spin rate and the agressiveness of the cutter is what you have to develope a feel for. Spin a cutter at different speeds and get different finishes.

Sometimes, I don't even touch the port with any polishing tools. The finish from the cutter leaves exactly what I like. Just depends on what I'm after.

Also, moving the cutter left to right vs right to left will give you a different finish with some cutters.

You can buy lube or use ATF cut with WD40 for those situations where you need to rip out some meat and get on with it...

A slotted mandrel and rolls of 60 & 80G paper will give you a nice finish.

Kay Rolls & cartridge rolls are best used for putting final touches on shapes [JMO].

I don't heat heads to do guides anymore. They go in nice & straight as long as you have a properly prepped guide bore and guide.

All the bronze guides get put in the valve machine and polished with some 1000G paper. Guide bores get polished too.

Lube everything up good and DO NOT try to drive the guide home in one or two hits. Just tonk on it lightly and it will go in pretty straight as long as you've prepped things properly first.

jordan wrote:

Stock for stock, the gpz head is better, but i bet with a little porting, the 750 head could easily surpass the gpz head.

That's an interesting observation. Let's define "better".

Better how?

More flow?

Better valve efficiency?

More appropriate CSA for the intended size of the engine and it's intended use?


"Better" has many possible outcomes

Here's an example of what I'm talking about.

83 GPz11 head flows 82CFM @10" of water and uses stock 38mm Intake Valve.

KZ head flows 68CFM @10" of water and uses stock 36mm Intake Valve.

Port volume on GPz is greater than KZ.

Push 82CFM through the KZ ports and compare valve coefficient of discharge and CFM Per Sq.In to that of the GPz11 head flowing the same peak volume with 2mm larger valve.....

Even better and very realistic, push 86-88 through the KZ ports and then do the comparison.

But the story isn't just in the valve. A comparison of Avgerage Port CSA, Mean Port Air speed & Throat CSA / Coefficient of discharge gives more important data to consider.

Then you have to consider how the head is going to be applied. What size carbs? What is the intended purpose of the application of the motor?

Will your be putting the had on a 1200cc drag motor?

Will you be intending to use 36mm carbs?

Much easier to use those carbs on the GPz head & with the same porting effort also raise CFM per Sq.In, valve and throat coefficients of discharge to obtain an even more appropriate cylinderhead for the drag bike application.

So its not just a numbers game. The entire concept of what you're trying to end up with has to be considered and taken into account....

Yes, you are absolutely correct. A stock Z head can be improved upon considerably to bring it up to stock GPz11 flow standards. But when you look at it from the perspective of..."I have two castings available and I want to do this particular thing with this much money", it becomes easier to decide which way to go...

This link may get wiped out because I'm not a paying sponsor on KZR and this is on my website. But here are numbers to look at www.flowbenchtech.com/porting/CRH/kz-data.htm

Larry C

class is in session! :laugh:

Here's some data on a Z head

kpier998 wrote:

Last one:

I think this is a GS850 head. I don't know if the intake was originally round or not. If so, what do you think was the reason for the new shape - kind of D shaped near the bottom but only slightly so.

I can't comment on whether this is a good design, or if it just looks good...

What do you guys think that have done some porting?