TOPIC:

Nebr_Rex wrote: Another restriction is that the airbox is formed to fit around the down tubes that sit in front of the no. 1 & 4 carbs.
All motor vehicles are full of compromises. I'll let you folks swoon over the old days of beating up on the Honda
sohc 750. I'm more interested in applying more modern tech and engineering to improve upon some great machines.
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Down tubes in front of the no. 1 & 4 carbs? Seems like an odd configuration. My KZ650 has the cylinder head in front of all 4 carbs.

Honda sohc 750? I don't know about swooning, but you might find it interesting that the 750cc records that the KZ650's set were retained for 8 years after which the GSX-R finally set new 750cc records (but of course the KZ650 set the records using the smaller 652cc engine). I would suggest that between 1976 and 1984 there were plenty more 750 class bikes other than the Honda sohc 750. So what took the others so long to catch up to the KZ650? It wasn't a lack of money since Suzuki, Honda, Yamaha, etc. were pouring buckets of money into racing; and they certainly had riders willing to run on the track. Maybe they just didn't want to be embarrassed by not being able to beat the KZ650 records.

I understand your point about applying modern tech to increase performance, and if the engines have been modified with bigger valves, larger displacement, bigger carbs, etc. velocity stacks etc. might provide better top end performance. However, on a stock engine I am convinced that the stock airbox passes all the air the engine can use. Others may hold different opinions - that's ok too. Ed

For those who may have missed it .............

FWIW, I got my carbs dialed in yesterday and rode to work. Let's just say it I didn't take long. Glad I have the UK spec speedo so I could keep it reasonably under a ton. I don't know if I'm even going to worry about doing anything else to it.

I'd like to mention for those not familiar with my bike that I put 132.5 jets in when I was having issues after swapping on a ZR7 header. This seems to be the thing that was needed to make it all come together. I might see what happens if I lift the needles a notch.

Nebr_Rex wrote:

JaFlo wrote:

Irish-Kawi wrote:

650ed wrote: +1 The airboxes were not just slapped together without considering performance and noise. Here's some info that some may not have seen; a link to a Cycle World comprehensive pod test back in the day and an article quoting a Mikuni engineer who helped design airboxes. Both are related to stock street engines and airboxes vs. pods. Ed

kzrider.com/forum/3-carburetor/585949-po...-a-free-lunch#585949

Brilliant read and article Ed, and exactly what I was stumbling and bubbling through while trying to get across haha. Air is not looked at or seen as a gas in terms of engineering these bikes and how to tune and get performance out of them, it is treated as a liquid because in these conditions it behaves as a liquid. That means that there are man many many variables to consider as was touched on in that article. Unless someone has a fluid dynamics degree and engineering experience we just aren't going to outsmart these guys

Brett

Again, the engineer that designed this air box had to compromise. If the goal was only maximum air flow, the box would look much different. Since intake noise has to be kept to a minimum on a stock bike, restrictions are put in place to do so.

Our goal as "enthusiasts" is to reduce the restrictions at the cost of increased intake noise. The trick is figuring out how to reduce restriction and not disturb the engineered resonance tuning or air velocity.

I recommended placing the vents near the factory air filter to attempt to keep the intake resonance length close to stock. Cutting the pipe off of the cap is fine as long as the radius end of the cap is left in place. The pipe is simply there for noise reduction. The air filter creates air turbulence no matter what, so no worries about screwing that up. The air box boots are velocity stacks as I mentioned earlier. These will "smooth" air flow into the carb and maintain velocity. Don't mess with them.

Another restriction is that the airbox is formed to fit around the down tubes that sit in front of the no. 1 & 4 carbs.
All motor vehicles are full of compromises. I'll let you folks swoon over the old days of beating up on the Honda
sohc 750. I'm more interested in applying more modern tech and engineering to improve upon some great machines.


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Not sure if it is just how I am reading it or taking it, but I can't figure out why you are trying to pick a fight.

As I said many many many times in this thread, we are each entitled to our own opinions and your opinion is no more right or wrong or factual than mis own, easy to just let it be I also don't recall anyone "living in the past" or talk of that in this thread but rather discussion on how modifications to the stock airbox may not be the benefit that many believe. In one of the examples a few posts back the author was talking about how changes to a VW airbox netted 5hp on the top end and further changes netted 10hp. I think that i a tremendous gain and hugely beneficial.... for power on the TOP END. What was not mentioned was what HP changes (loss or gain, but likely loss) was netted in the low and mid range due to those changes. As stated, any change is a compromise and f you gain HP in one place, chances are good that you lost HP in another to get that gain.

There was a gentleman named Tak Shiarmizu in Denver, CO that owned and ran Tak's Mile High Machine Shop... when I met him at 16 yrs old he was already 93 years old and had lived through the Japanese Internment Camps in California during WW2. He was one of the smartest machinists I have ever known and lived with him for 2 weeks while he taught me his trade and we machined, blueprinted and balanced my entire engine for my Camaro. But the very first time I met him he asked what I wanted my car to do... I started saying stuff like pull 1 G on the skid pad, do a 13 second quarter mile, get 25 mph etc etc. The more I spoke the bigger and bigger his eyes got until they bugged out and looked at me like I was a complete simpleton (and truth is he was right ) for wanting my cake and eating it too. Before he replied he went back into his shop on his hands and knees digging around before he pulled out a 1 foot length of 2x4 wood. He walked up and shook it in my face and said very heatedly... "If you want it to do a 13 second quarter mile, we will cut some of the 2x4 off of this end and put it on the other end, then it do 13 second quarter mile. If you want it to do 1 G on the skidpad, then we will cut some off the other end and put it on the opposite end. If you want it to do 25 MPG then we cut some from the middle and add it to the sides. But there aint no more F'ing 2X4, you can't add 2X4 to both ends and the middle, there is only so much 2X4 to go around and you will have to take it from some place to add it to another!!!!"

The whole point of him saying that is that there is always a trade off... in the VW example to get more top end ponies you cut off one end of the 2X4 and added it to the other end. The compromise was to take power from somewhere else in the curve to add it to another area, but this still holds true... THERE AINT MORE 2X4!!!!

Brett

Steve

Well I guess I cut some off the farting end then cut some off the breathing end. I'm sure I'll have to shove more into the drinking end in the middle.

It's all good.

........THERE AINT MORE 2X4!!!!

That's priceless!!!! Ed

650ed wrote: ........THERE AINT MORE 2X4!!!!

That's priceless!!!! Ed

Ever since I hear that from Tak I have never forgotten it and used it many many times since lol, sure as sh!t gets the point across though don't it?!

Brett

I'm finding this discussion very interesting. Unless you are an expert in tuning carbs and have a lot of time and gas to kill, for the best overall results, I would say stick with a properly maintained K&N filter in the stock air box and properly install and tune a Dyno-Jet kit. Most of my own stock CV's have Dyno-Jet kits in them now. It is relatively easy and works well enough. I don't drill out the stock slides unless I get an extra set first, just in case I ever want to return the carbs back to original. BTW, of all the CV carbs - I hate the BS34 Mikuni's the most - absolutely hate them!

I believe there is lots of things you can do with the intake side of the carbs (any carbs) that you can mess with to get more of whatever it is you want. One factory OEM example was the differences in the V65 Honda Sabre and Magna. The engines were nearly identical, yet the Sabre, with larger volumes in the exhaust and air box, made 4-5 hp and 2-3 Ft-lb. more torque than the Magna (cams were slightly different, too). So changing the air box can have some effect on performance if you try it. It might not be worth the effort, and you might end up not happy with what you get, though.

Other than maybe sort of looking like a racing engine should, and maybe making tuning access easier, I don't think pod filters are worth doing...(particularly on CV carbs) but are still better than open stacks or bells...that is crazy.

Kray-Z wrote: I'm finding this discussion very interesting. Unless you are an expert in tuning carbs and have a lot of time and gas to kill, for the best overall results, I would say stick with a properly maintained K&N filter in the stock air box and properly install and tune a Dyno-Jet kit. Most of my own stock CV's have Dyno-Jet kits in them now. It is relatively easy and works well enough. I don't drill out the stock slides unless I get an extra set first, just in case I ever want to return the carbs back to original. BTW, of all the CV carbs - I hate the BS34 Mikuni's the most - absolutely hate them!

I believe there is lots of things you can do with the intake side of the carbs (any carbs) that you can mess with to get more of whatever it is you want. One factory OEM example was the differences in the V65 Honda Sabre and Magna. The engines were nearly identical, yet the Sabre, with larger volumes in the exhaust and air box, made 4-5 hp and 2-3 Ft-lb. more torque than the Magna (cams were slightly different, too). So changing the air box can have some effect on performance if you try it. It might not be worth the effort, and you might end up not happy with what you get, though.

Other than maybe sort of looking like a racing engine should, and maybe making tuning access easier, I don't think pod filters are worth doing...(particularly on CV carbs) but are still better than open stacks or bells...that is crazy.

Hey Kray, curious why you have such a disdain for the BS34's? I am new to carbs for bikes and just starting to get my feet wet, but I have had very little issues if any with my BS34's, just wondering why the hate?

Brett

One more - thoughts on what the old Japanese machinist said about the 2x4...funny, but way to serious! I guess that's what happens when you make performance into your job, not your hobby.

Everyone interested in modifying our old bikes and cars and trying to get more (fill in the blank here) out of them should fess up to one great truth:

All our attempts at squeezing out performance from old junk are usually futile and completely senseless. Dad used to be an ace at pointing this out to me all the time. Out on the public roads, new cars and bikes can still run onion rings around us and get better fuel mileage while doing it. And they don't blow up nearly as often, either. I've often thought, after dumping thousands of $$$$ into boring out a 1000 cc engine to something like, say, a 1260 cc engine, that if I really wanted to go big displacement / power at the strip, I could have used a 2.4 L DOHC 16V car engine from a junkyard for about 1/3 the price and twice the power / torque, and reliability. Maybe next time...

So why do I keep coming back for more abuse - because it is a challenge, and it is fun!

Admit it - practical and sensible has absolutely nothing to do with it.

Kray-Z wrote:
Admit it - practical and sensible has absolutely nothing to do with it.

Of course it does! Otherwise, this would be a Harley forum.