Problem, is it intake reversion?

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:)

larrycavan wrote:

before you run away

Rest assured. I won't run away.

I have a couple of questions for you it that's OK.

Perfectly OK.

Cam was installed and degreed in as per the supplied cam card, which is not currently on me. I know it was 110 deg separation angle. But not sure of the centers.

Have not experimented with cam timing yet.

pilot jet = 17.5
screw = 1/4 turn
needle pos = 3 (middle): 1 position richer with open ports
main jet = 125

No BSFC numbers

Difficult to say about the port reduction time. I’d never seen anyone make removable D shapes so it took a little while to come up with a method where I felt confident that my engine wouldn’t eat a chunk of epoxy. It’s been about 6000 miles with no issues and they’ve been in and out a few times. Once I figured it out maybe 8 – 12 hrs.

300 Feet Per Second mean velocity as the "ideal"

Note: The mouth of the RS34 (where air enters the carb) is 34mm. The outlet is 32mm.

Is this because 300fps through the carb will generate the proper AFR?

Mikuni claims that the flat slide design provides a much better signal at the jet than traditional round slide carbs and will produce the proper AFR with less velocity. True? Don't know but that's their claim.

With reduced ports and a competition baffle (which made a difference) My AFR was very steady (around 12. throughout the rev range during the dyno pulls. A little fluctuation below 5000 RPM but then spot on.

Exitpupil wrote:

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:)

Flow numbers alone don't mean all that much. They're an indicator of what could be possible. Over the years I've gathered a lot of head flow data and gather more pretty much every week.

I think you guys are doing a hell of a job & getting some positive end results. It's good to have various inputs, results and data to evaluate.

You and Dave have both put a lot of thought and effort into making your bikes perform up to your expectations. No matter what your approach is to the cylinder head, flow and velocity are always players in the end result.

I just try to give you hard earned information that you can use in your efforts to keep improving your setups. Knowing the results I get from project to project is one thing. Seeing what other guys get and share their information is always a bonus.

For any given engine, the piston will demand a certain amount of air to achieve the HP goal for the Peak HP RPM. But, when you're working with cylinder heads, the CFM number falls down the list of important items. Proper cross sectional area and velocity profile should get a higher priority.

Dave made a smart move IMO by using the Wallace calculator. It suited what he was after.

So, you guys now know a stock KZ900 / 1000 head flows 68 - 70 CFM @ 10" in stock configuration. At 28" it's multiplied by 1.67.

I'll choke a port to motoman's 65% setting and give you the flow and local port velocity number dead down the middle of the runner so you have them to work with.

In the mean time, use the stock flow with the following formulas to derive some data.

Average_CSA = Port_Volume_CC / (Port_CenterLine_Length * 16.387)

Port_Volume_CC = Average_CSA * Port_CenterLine_Length * 16.387

Port_CenterLine_Length = Port_Volume_CC / ( Average_CSA *16.387 )

FPS = ( Flow_CFM * 2.4 ) / Average_CSA

Flow_CFM = Average_CSA * FPS * .4166667

To get port centerline, measure the roof and the floor, add together, then divide by 2. Measure from port entrance to your 45 degree seat cut.

IMO, if you're going through the effort to reduction port the head, try not to leave peak HP behind.

For a 1075cc KZ, stock head, stock valves and .360" lift cam. Peak HP at 8000 RPM.

--- Cross-Sectional Areas at various Intake Port Velocities (@ 28 in.) ---
166 FPS at Intake Valve Curtain Area= 1.608 sq.in. at .361 Lift
169 FPS at Intake Valve OD Area and at Convergence Lift = .354
209 FPS 90% PerCent Rule Seat-Throat Velocity CSA= 1.279 sq.in. at 8000 RPM
350 FPS Velocity CSA= 0.764 sq.in. at 8000 RPM Port Sonic-Choke with HP Loss
330 FPS Velocity CSA= 0.811 sq.in. at 8000 RPM Port Sonic-Choke with HP Loss
311 FPS Velocity CSA= 0.861 sq.in. at 8000 RPM Smallest Useable Port CSA
300 FPS Velocity CSA= 0.892 sq.in. at 8000 RPM Recommended Smallest Port CSA
285 FPS Velocity CSA= 0.939 sq.in. at 8000 RPM Recommended Smallest Port CSA
260 FPS Velocity CSA= 1.029 sq.in. at 8000 RPM Recommended Port CSA
250 FPS Velocity CSA= 1.071 sq.in. at 8000 RPM Recommended Port CSA
240 FPS Velocity CSA= 1.115 sq.in. at 8000 RPM Largest Intake Port Entry CSA
220 FPS Velocity CSA= 1.217 sq.in. at 8000 RPM Largest Intake Port Entry CSA
210 FPS Velocity CSA= 1.275 sq.in. at 8000 RPM Torque Loss + Reversion
200 FPS Velocity CSA= 1.338 sq.in. at 8000 RPM Torque Loss + Reversion

Keep up the good work guys. Very nice to have a conversation like this. Very refreshing to see a discussion rather than an argument over right vs wrong type of deal. Closed minds lead to nowhere.

Would love to sit down and have a beer with your guys one day and kick around ideas.

Larry C

Exitpupil wrote:

The problem is I want more power

If you're using the stock baffle try a competition baffle. A potential source of quick, easy and inexpensive power across the entire RPM band. Especially with your combination...might require a little rejetting.

Ok, I'll experiment with the exhaust some. If I am over carbed that would be a good excuse to punch it out to 1200 hehe.