Problem, is it intake reversion?

Sure the cams come into play. Nobody tried advancing both cams to put bottom end in the motor from what I gather.

I'd like to build 2 similar KZ motors. Both the same size and with the same cams. Difference being one epoxied up port job and one of my normal port jobs that flows significantly more air. Put any carb you want on the epoxied up head and I'll put 31mm Keihins on the traditional ported head. Then dyno them and ride them for a comparison test.

That would be a very fun project IMO.

I forgot to comment on the dimples. I don't use them in these heads. However, textures, even ribs, have been used for many years to get the air to grab the surface and help it turn. There are valves out there with dimples applied that can be purchased for some of the car engines. I'll try to find you the link and post it.

Look inside some old V8 cast iron manifolds and you'll see ribs on the floor.

Very shiny ports can cause the fuel to puddle and believe it or not, even flow losses.

larrycavan wrote:

Epoxying up the port floor is nothing new. Motoman certainly didn't invent it. He simply advocates it's use. In some situations, there are benefits, in other situations it just plain doesn't work out.

Thanks for the compliment about the craftmanship and definitely agree about D shaping and mototune. But he isn't the only one that got me thinking about it. Check out www.bertaut.com/gsengine.html He's an old timer that specializes in GS1100/1150s hot street and drag bikes. He was doing epoxy D shaping in the early 80s. I also a have an old motocycle article where Rob Muzzy is extensively interviewed about the mods he made to Eddie Lawson's AMA KZ1000 superbike. He reviels A LOT about what he did to the bike and in the process mentions D shaping the intake ports, maintaining a tight choke point, and spends most of his time discussing combustion chamber and exhaust design! He actually goes out of his way to downplay the importance of camshaft specs...It was also believed that his KZ dominated in the early 80s because of its mid range power and broad, flat torque curve. I will post this article when I have a chance.

Here is an excellent site for calculators to help with engine design and 1/4 mile stats. www.wallaceracing.com/Calculators.html The engine calculators are set up for units in cubic inches but they will work fine for any engine as long as you do the inch-mm conversions. Many of these calculators are derived from a program called Pipe Max written by Larry Meaux - The same guy who wrote the excellent article on reading plugs!

Check out the choke point calculator www.wallaceracing.com/chokepoint-rpm.php This will calculate the optimum choke point area for maximum torque/VE. You must provide bore, stroke and desired RPM for peak torque (Notice how cam shaft specs and carburetor size are not factored in...) 6000RPM is a good place for peak torque on a street bike. According to this calculator optimum choke point area for a 1075cc engine (2.6 inch stroke and 2.8 inch bore) is 0.70 inches squared. That converts to a 24mm diameter. My original choke point was 30mm. According to this calculator, that puts peak torque at 10,000rpm for my bore and stroke. Definitely no good on the street.

I also agree that there are many theorys (and many different calculators). It's all food for thought and experimentation...and none of it is any good without countless hours of testing, tuning and most important riding!

I met a mechanic for a successful Datsun road race team in the late 70's that used D port mods back then. He claimed he got the idea from a famous NASCAR head developer at the time. I probably missed out on some flow from lack of a multi angle valve job. My head only had 4000 original miles on it so I just lapped the valves good. Maybe this winter I'll get the valves done professionally.

cut the cv slide springs a inch shorter.
drill the cv slide equalision hole just a tiny bit larger.

Exitpupil wrote:

I probably missed out on some flow from lack of a multi angle valve job. My head only had 4000 original miles on it so I just lapped the valves good. Maybe this winter I'll get the valves done professionally.

If you have to pull the head off and apart for some other reason then it's worth performing the valve job...but if your bike is running good just enjoy it. That's alot of time, effort and money for a marginal return in my opinion. Do that when you install the 1260 kit 40,000 miles from now.

you can still purchase "turtles" to put inside of intakes on cars, they help the air/fuel mixture flow better into differnt cyls that normally are a bit lean.

back to the bike heads, what have you seen with just cleaning up the rough edges in the ports, is it worth the time and effort on a street motor?
The reason I am asking, I just picked up a 73 z1, and due to time sitting, it will need to be rebuilt, but I dont want to go past a stock motor, just clean up any bad areas

It's a good time to back up a couple of steps here. Great discussion going on. Let's look at some key factors involved. Don't think I'm diminishing your epoxy port efforts or anything of that nature because I'm not. Your results are very interesting and much appreciated.

Let's look at the velocity component. It's the problem you ran into with too large a carburetor.

Take a KZ head and cut the ports the way I've seen them in the posted photos. You're not getting much more air through them than stock which is 68 - 70 CFM @10".

34mm RS Mikunis are just plain too big for the type of throttle response the stock 26/28mm carbs give you on small bore KZ motors anyway. Even with a bone stock head.

Remember velocity is tied to flow volume and cross sectional area. With that said, unless you gain appreciative flow from cross sectional area increases, you simply reduce velocity.

Now, with an already too large carburetor, the velocity loss can further hinder it's ability to deliver the mixture curve the engine requires. Put a set of 34mm RS Mikunis on the flow bench, mounted to a KZ head and probe the bell mouth, the needle jet area and the spigot section of the carburetor. It's not impressive. Back at the bellmouth entrance, it can drop to 200 FPS at 28" of test pressure. Pretty darn low. 300 FPS has long been considered about ideal velocity air speed.


Now, let's look at some numbers from a traditionally ported KZ head I did about 2 months ago and ran complete tests on.

Stock valves, head flowed 86 - 88 CFM @10" after porting. Port runners were near stock CSA to the SSR. The port runners are not what makes the big flow numbers happen on those heads. They need to be sized to Peak HP RPM desired and the proper carb fitted to compliment the intake tract.


Head was fitted with stock intake boots, not resized and tested for velocity. Just inside the port entrance, immediately after the rubber intake boot and all the way to the SSR, Velocity was 320 FPS:ohmy: Too fast IMO.

Why?

Because airflow had increased by 20CFM @10" or 33.4 @28" [1.67 is the multiplier for 10" - 28" flow conversions. My velocity tests are always conducted at 28"]

Next, rubber intake boots were port matched and the head was retsted for Velocity and CFM.

CFM with carbs and K&N Pods mounted to the head, was 79 - 80 and velocity just past the rubber intake boot was down to 305 FPS. Much more suitable. Needle jet went from O-6 to O-4 with needles on the second groove.

The bike has not been dynoed yet. It pulls cleanly from 2500 - 2800 RPM all the way into the red zone without any miss, stumble, farting or chuffing back through the carbs. The power comes in strong at 4000 and pulls hard from 6000. Cams were Andrews 2x .360" lift.

I have always ended up running leaner midrange jetting on a KZ motor with 29mm Mikunis after porting the cylinderhead. But the heads flow significantly more air than stock through the section of the port that controls the velocity required by the carb to deliver a good fuel curve.

It's always the guys that want too big carburetors that end up having stumbles and weak midrange acceleration problems...I've seen this time and time again for over 25 years.

Here's an important factor to understand. When you're going to moderately mod one of these engines and you're going to say with small bores, Start Smart with your parts selection.

Proper carb sizing is among the selection you have to make. Unfortunately [and I completly understand whey a guy would pass on them for new carbs] an old rack of 29mm Smoothbore Mikunis will fetch a totally outrageous price on ebay. 29mm or 31mm Keihin CRS carbs are not cheap either but they are the more appropriate size for engines from 903 to 1075 on a street bike.

Have a Great Day guys....Looking forward to your replies.

Respectfully,

Larry C

larrycavan wrote:

It's always the guys that want too big carburetors that end up having stumbles and weak midrange acceleration problems...I've seen this time and time again for over 25 years.

C

Thanks for the data and it is understood, but first to clarify about carb/part selection:

Mikuni (the manufacture of the RS series carbs) recommends the RS34 for 750CC engines. It is the smallest carb they make that will even fit on a KZ. They actually recommend 36mm carbs for the KZ900-1100. Exitpupil is running BS34 constant velocity carbs on his engine. These carbs came STOCK on all J model KZ1000s. So I don't agree that we've overcarburated.

The main idea behind the high velocity port theory is this: The extremely high air flow velocity at the choke point (which shows up as a restriction on the flow bench) is actually responsible for "charging" the cylinder at the end of the intake stroke when the piston is rising in the cylinder and before the intake valve closes. Without this ram-air effect at the choke point, the piston will push air out of the cylinder and back into the intake port causing loss of volumetric efficiency and positive pressure pulses (reversion) in the port. This is especially true during low and mid-range RPM when port velocity is relatively low.

Larry, you mentioned a side-by-side comparison of engines with different porting methods and carbs, which I think is a great idea...Maybe this is the beginning of an annual KZ street and strip shootout...

davel wrote:

larrycavan wrote:

It's always the guys that want too big carburetors that end up having stumbles and weak midrange acceleration problems...I've seen this time and time again for over 25 years.

C

Thanks for the data and it is understood, but first to clarify about carb/part selection:

Mikuni (the manufacture of the RS series carbs) recommends the RS34 for 750CC engines. It is the smallest carb they make that will even fit on a KZ. They actually recommend 36mm carbs for the KZ900-1100. Exitpupil is running BS34 constant velocity carbs on his engine. These carbs came STOCK on all J model KZ1000s. So I don't agree that we've overcarburated.

The main idea behind the high velocity port theory is this: The extremely high air flow velocity at the choke point (which shows up as a restriction on the flow bench) is actually responsible for "charging" the cylinder at the end of the intake stroke when the piston is rising in the cylinder and before the intake valve closes. Without this ram-air effect at the choke point, the piston will push air out of the cylinder and back into the intake port causing loss of volumetric efficiency and positive pressure pulses (reversion) in the port. This is especially true during low and mid-range RPM when port velocity is relatively low.

Larry, you mentioned a side-by-side comparison of engines with different porting methods and carbs, which I think is a great idea...Maybe this is the beginning of an annual KZ street and strip shootout...

Hi Dave,

Yes, I know the theory behind the high velocity ports. I also know and have seen too high velocity kill HP big time. We pretty much covered that in previous posting. Still, I respect your opinions and I think you're a pretty sharp guy so let's continue with our discussion.

That mikuni chart application is out in left field for anything but racing. If 36mm carbs were appropriate for good, all around carburetion on that engine, then you should have no problem with 34s....

Yep, the piston is a bugger. It works for and against you. There are many crankshaft degrees where the piston is working against you. The more overlap lift the cams have, the more the piston can work against you at lower RPM. That's just the way it is.

Trade offs are always part of the equation in the search for power. Also, there's more than one approach that can yield similar results. However, it is possible to get the midrange performance without the upper RPM HP loss and do it with a smaller carburetor and larger ports.

There's no dispute on my part regarding your improved midrange performance with your epoxy port method. You're missing the point. I'm saying it can be done without taking a hit at the top of the revs.

Let's look at the 34mm CV carbs for a moment.

I've used the stock 34mm CV Mikuni carbs on J engines in the past and they were always tunable to eliminate any stumble. Some were on ported J heads with the 83 GPz11 cams with larger port runners than a stock KZ has. Yes, they will work but they are not big power producers. 31mm Keihins CRS on the same engines will eat the 34CV for lunch any day of the week.

I also have used 29mm Mikuni smoothebores on the same combo. The 29's accelerated better than the 34 CV.

Here's another example for you to think about.

Kawasaki's ZX900 engines. The Ninja & Eliminator.

Save the tranny diffrences for shaft drive, everything else on those engines was the same except for cams and carbs.

There both large port, high flow [95CFM @10"] heads with the same bore and stroke. Port velocity in those heads I measured at 250 FPS, dead down the middle of the port runners. Rather on the low side for velocity.

Kawasaki didn't epoxy up the ports or make them smaller in the Eliminator. They simply chose 2mm smaller carbs and cams with less 1mm less lift and 15 degrees less duration. It worked. In fact that entire engine family from Ninja through Concour was all tuned through cams and carbs. Bores, stroks, head flow were the same. [Actually, same thing for the J engine series up to the 83 GPz11 when Kawasaki finally graced the motor with a head that flowed a little air.]

They were after top end HP with one and bottom & midrange with the other. They achieved their design goal.

Something else we have not discussed is the way HP can fall off dramatically after the peak from having too small a CSA in the port. Not to mention where the CSA is located in the port having a significant effect.

You mentioned the article you read on Rob Muzzy and his superbike development. I read it too, many years ago. I also had a connection at Kawasaki that had one of those cylinderheads in their hands and flow tested it. I know what it flowed and what it looked like;)

Do you remember what Rob said about carbs?

It was something to this affect. Large carburetors are for flowing more air. What you need is the carburetor that delivers the correct fuel curve for the application.

Well, this one is getting long so I'll end it here for now. There are some things I do believe you'll find of interest that are related to the Motoman porting method and flow numbers. I'll pick up there after your reply if you like.

Have a great day,

Larry C

Larry,

That is all understood. Obviously many factors and theorys and I think I'll leave it there.

It is a good discussion and it would be nice to hear from some other members about their experience with porting and carb selection. What was the combination how were the results?...It's a friendly discussion, really.

BSKZ650 wrote:

back to the bike heads, what have you seen with just cleaning up the rough edges in the ports, is it worth the time and effort on a street motor?

IMO probably not worth too much but a professional 3 angle valve job and new valve guide seals are definitely worth your while.

Dave,

You achieved something worthwhile from your efforts. Well done. But, before you run away, I have a couple of questions for you it that's OK.

What lobe centers are your cams on?

Did you experiment with lobe centers at all?

What were your final jetting specs, pilot jet, pilot fuel screw setting, needle position, main jet?

Did you get any BSFC numbers from the dyno tests?

Were they lower on the epoxy ported head or higher?

How many hours did you put into reduction porting your head?

Back in the 80s, there was a Kawasaki High Performance manual available from Kawasaki. I don't know how much of the information came from Joe Minton but I do know he contributed to the effort.

Theres a formula in it for calculating carburetor size. It doesn't apply to CV carbs.

Using that formula and 300 Feet Per Second mean velocity as the "ideal", here are some throttle slide carb size calculations for 72mm bore, 66mm stroke and a torque peak of 6000 RPM.

29mm 266.9 FPS
31mm 233.6 FPS
34mm 194.2 FPS

FWIW.....

Back in 82, an associate of mine buit a GS1000. Traditional ported head with runners opened up as far as they'd go. Stock Zuki early GS1000 runners were very small. It was punched to 1170, Andrews cams, S1 or S2 grind [can't remember right now] and those god awful 33mm mikuni smoothbores....

You COULD NOT give that bike a handful of throttle at 3500 without the front end shooting straight for the sky. I almost flipped the thing over backwards the first time I rode it.:ohmy:

Wow, this is all very interesting. This was my first bike build so it has been a real learning experience. I picked the BS34 carbs because they were used on the factory engines as previously mentioned. I do know a little about carbs and because the slide is vacuum operated I felt sizing was not so much a factor. I feel like I lost no top end power with the high velocity ports. Here is my problem. I believe in using facts and I have no before and after dyno data. My butt is no dyno! I would love to be able to quantify what was done. Larry, I appreciate the data you are sharing with us, seems other pros are tight lipped. There are so many variables in engine induction I can't just go with flow data and assume it translates to an improvement. This is a street bike, not a 1/4 mile machine. All I know is it runs much better for my spirited street riding. The problem is I want more power so the project is never finished:)