Head porting question

This winter I plan on rebuilding the engine on my 77 KZ1000. Like most people, money is tight. My goal is to go with a 10.5 to 1 1075 kit and have the head rebuilt. For now I will have to make due with the stock cams and VM26 carbs. Will I notice much gain in horsepower by having the head ported, or will I just be wasting my money?

THanks

it will make a difference more air in the more air out,all these engines are is just an air pump if you had good cam's, carb's pipe and ignition it would make more difference but think of it this it will be ported already when you do get that stuff

I think the big looser in that equation is the vm26s carbs, if you go to vm28s the engine has more air and fuel to work with.

HOGEATER

You probably won't see a huge increase with porting because you can still only flow as much air as the most restrictive part. However, since money is tight now and maybe won't be later I suggest porting it. That way when you do get some money all you have to do is slap on a new set of carbs and it will wake right up and use the full potential of that porting. Of course since you are upping the displacement and compression you will feel a difference in power. Now you just have to decide on what kind of carbs and pipes are going on there so you can port accordingly. Remember, each part has to work in conjuction with the others in order to make the best horsepower.

The progressive, "seat of the pants noticed improvment" order is generally, carbs, porting & cams. With the porting & cams in combination.

I don't really disagree with what anyone else has said so far but this is my perspective on it...

IMO, porting is best when targeted at the components to be used in combination. But I see where you're coming from..."why take it apart twice"?...

Real porting without the rest of the components to make it work correctly is like Superman without the cape..

VM26 carbs will outflow the stock head by a few CFM, believe it or not. However, they will still cork up a head with any real porting done to it.

Been ages since I tested a VM26 but as I recall, with a velocity stack mounted and flowed directly on the bench with a stock manifold and appropriate sized adapter, they were around 74CFM @10". Stock head, 68CFM @10" and it signs off at about .350" lift.

You could take that head to 74 CFM with no real effort. BUT does that constitute a "ported head". Technically yes but IMO, it's not much of a port job. Just a clean up that could be done as part of a valve job. You could take it to 74CFM yourself with some pointers;)

To get noticable power out of that motor, you want at least a drop in cam of .360" lift and at minimum 83CFM @10". That takes more effort and obviously will increase the price of the port work.

There are all kinds of scenarios that could be described but this gives you some idea anyway.

Stock KZ, realistic 64HP at the rear wheel. 1075KZ, 83CFM, drop in cams, 29mm carbs......105HP ballpark at the rear wheel. That's 83GPz11 flow capabilitiy with a 2mm smaller valve to boot....

Take away the cams & carbs....with 74CFM....maybe 70HP.

I can't thank you guys enough for your opinions and advice. I forgot to put it in my original post that the bike already has a V&H four-into-one pipe and Dyna S with green coils. I still have the full factory airbox on it with a K&N filter. I think I will go with air pods after doing the motor work.

I realize the stock cams and carbs will be restrictive on this motor. My goal is to not have to take the motor apart twice. That is why I would like to get the internals built right the first time. Then, as my budget allows, I will change cams and carbs.

As long as I can work it into my budget, I think I will go ahead and have the head ported while it is being rebuilt.

Larry you have some great info on your website!

Thanks again!

do you know what size of cam you want to use because if your going fairly big on the lift you will have to clearance the head and bucket bores before you can put those cams in. so unless you want to take it all down again, when you do the port work and think a head abit and see if you can get a set of cams that you will be using in the future and get all your head work done in one shot then all you will have to do down the road is install the cams.

larrycavan wrote:

The progressive, "seat of the pants noticed improvment" order is generally, carbs, porting & cams. With the porting & cams in combination.

I don't really disagree with what anyone else has said so far but this is my perspective on it...

IMO, porting is best when targeted at the components to be used in combination. But I see where you're coming from..."why take it apart twice"?...

Real porting without the rest of the components to make it work correctly is like Superman without the cape..

VM26 carbs will outflow the stock head by a few CFM, believe it or not. However, they will still cork up a head with any real porting done to it.

Been ages since I tested a VM26 but as I recall, with a velocity stack mounted and flowed directly on the bench with a stock manifold and appropriate sized adapter, they were around 74CFM @10". Stock head, 68CFM @10" and it signs off at about .350" lift.

You could take that head to 74 CFM with no real effort. BUT does that constitute a "ported head". Technically yes but IMO, it's not much of a port job. Just a clean up that could be done as part of a valve job. You could take it to 74CFM yourself with some pointers;)

To get noticable power out of that motor, you want at least a drop in cam of .360" lift and at minimum 83CFM @10". That takes more effort and obviously will increase the price of the port work.

There are all kinds of scenarios that could be described but this gives you some idea anyway.

Stock KZ, realistic 64HP at the rear wheel. 1075KZ, 83CFM, drop in cams, 29mm carbs......105HP ballpark at the rear wheel. That's 83GPz11 flow capabilitiy with a 2mm smaller valve to boot....

Take away the cams & carbs....with 74CFM....maybe 70HP.

I just had a light bulb go on, so what your sayingis with a stock head any thing higher in lift than .350 is just not being used?

School Teacher wrote:

larrycavan wrote:

The progressive, "seat of the pants noticed improvment" order is generally, carbs, porting & cams. With the porting & cams in combination.

I don't really disagree with what anyone else has said so far but this is my perspective on it...

IMO, porting is best when targeted at the components to be used in combination. But I see where you're coming from..."why take it apart twice"?...

Real porting without the rest of the components to make it work correctly is like Superman without the cape..

VM26 carbs will outflow the stock head by a few CFM, believe it or not. However, they will still cork up a head with any real porting done to it.

Been ages since I tested a VM26 but as I recall, with a velocity stack mounted and flowed directly on the bench with a stock manifold and appropriate sized adapter, they were around 74CFM @10". Stock head, 68CFM @10" and it signs off at about .350" lift.

You could take that head to 74 CFM with no real effort. BUT does that constitute a "ported head". Technically yes but IMO, it's not much of a port job. Just a clean up that could be done as part of a valve job. You could take it to 74CFM yourself with some pointers;)

To get noticable power out of that motor, you want at least a drop in cam of .360" lift and at minimum 83CFM @10". That takes more effort and obviously will increase the price of the port work.

There are all kinds of scenarios that could be described but this gives you some idea anyway.

Stock KZ, realistic 64HP at the rear wheel. 1075KZ, 83CFM, drop in cams, 29mm carbs......105HP ballpark at the rear wheel. That's 83GPz11 flow capabilitiy with a 2mm smaller valve to boot....

Take away the cams & carbs....with 74CFM....maybe 70HP.

I just had a light bulb go on, so what your sayingis with a stock head any thing higher in lift than .350 is just not being used?

It's still being used but there's less of it available than there could be with a good port job.

With a good port job, the ported, stock valved KZ head will flow as much at .250" lift as a stock head flows at peak.

There's precious little time for the flow event to take place at high RPM so the more available flow, the better.

aint he dreamy????? :woohoo:

I haven't decided on cams yet, but whatever I end up using will be mild. This bike won't be on the drag strip.


timebomb33 wrote:

do you know what size of cam you want to use because if your going fairly big on the lift you will have to clearance the head and bucket bores before you can put those cams in. so unless you want to take it all down again, when you do the port work and think a head abit and see if you can get a set of cams that you will be using in the future and get all your head work done in one shot then all you will have to do down the road is install the cams.