Landracing Forum
Bonneville Salt Flats Discussion => Build Diaries => Topic started by: Gimpy Joe on March 24, 2011, 04:21:51 PM
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I'm new to land speed racing, but I've been welding and fabricating for a long time and I'm obsessed with anything on two wheels. So far I have built three bikes with varying degrees of success. My goal is to get out on the salt in the next year or so. I'm glad this forum exists, since there will obviously be a steep learning curve and I'm going to need all the help I can get.
Anyway, the plan is to start with a 90's 750 Nighthawk. I want this bike to stay street legal since I can't justify spending a lot of time and money on a bike I can only ride a couple times a year. I know I won't be setting any records that way, but that's fine with me. I just want to go fast :lol:
I will be modifying the frame, adding the required safety equipment, and fabricating my own bodywork. I will also make some relatively minor tweaks to the engine and exhaust and hopefully gain a few horsepower.
Supposedly the Nighthawk will do about 130mph stock. What kind of speed could I realistically expect to achieve by streamlining the bike and changing the final drive ratio?
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Is it really fast(or fast enough) if you don't set a record?
Maybe this question needs a new thread.
Honey do list fell to zero, Joanie went to Nashville this morning. A recent text message has her sitting in a bar with live music, pizza and beer while waiting for her sister's flight.
DW
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That was her sister?
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Is it really fast(or fast enough) if you don't set a record?
DW
I don't care if it is fast, so long as it feels fast. If I don't feel like Wylie Coyote strapping himself to a rocket, then this project has failed.
(http://www.rinna.it/rinna/eroi/rr/rocket.jpg)
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I seem to recall the coyote hitting a rock and continuing in his trajectory, sans rocket.
Welcome aboard Joe. Yep, we pick on newbies.
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I thought that the ACME bodywork was outlawed?? :mrgreen:
Mike
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Joe, don't pay any attention to these characters. It is the off season and they have too much time on their hands. What is an honest rear wheel horsepower for that bike and how big are you? I can look on my handy chart.
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Welcome to the addiction Joe! :cheers:
Do you plan on running at Bonneville or one of the paved venues?
What do you have in mind for the bodywork, lots of enclosure like a Charlie Toy or a full cafe style fairing? With limited hp, your biggest gains will come from improved aerodynamics.
They made @75hp at the crank with very mild cams and only 9.3:1 compression. You could certainly wake it up with cams, head work, higher compression pistons, bigger carbs etc.. but then you would sacrifice some streetability and you mention that it will still serve as your street bike.
LSR is all about the experience itself...record or not. Your Nighthawk is a good bike to start with, you will learn lots and make some great friends along the way.
Cheers,
Scott
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Is it really fast(or fast enough) if you don't set a record?
DW
I don't care if it is fast, so long as it feels fast. If I don't feel like Wylie Coyote strapping himself to a rocket, then this project has failed.
(http://www.rinna.it/rinna/eroi/rr/rocket.jpg)
:-D :-D :-D :-D
:cheers:
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Joe, don't pay any attention to these characters. It is the off season and they have too much time on their hands. What is an honest rear wheel horsepower for that bike and how big are you? I can look on my handy chart.
(http://i1222.photobucket.com/albums/dd487/GimpyJoe29/Motorcycle027.jpg) Me a couple of years ago on my first bike, a '76 CB360 that started as a pile of old roadrace parts. These days I'm 5'10", 220 lbs built like a linebacker. I hope that won't hurt top speed too much :oops:
Welcome to the addiction Joe! :cheers:
Do you plan on running at Bonneville or one of the paved venues?
What do you have in mind for the bodywork, lots of enclosure like a Charlie Toy or a full cafe style fairing? With limited hp, your biggest gains will come from improved aerodynamics.
They made @75hp at the crank with very mild cams and only 9.3:1 compression. You could certainly wake it up with cams, head work, higher compression pistons, bigger carbs etc.. but then you would sacrifice some streetability and you mention that it will still serve as your street bike.
LSR is all about the experience itself...record or not. Your Nighthawk is a good bike to start with, you will learn lots and make some great friends along the way.
Cheers,
Scott
I want to go to Bonneville and also go to some of the paved events because they are closer (I'm in Atlanta).
I will use Airtech's John Cronshaw fairing if it'll fit.
(http://www.airtech-streamlining.com/images/jcf.jpg)
Other than that I'm going to fabricate the seat, tank, rearsets, etc. myself since that's what I really enjoy. I'm not much of a mechanic, but my brother is. I'll let him fiddle with the engine a bit, but I will probably still end up with under 100hp.
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Welcome to the salt! I am just building my 1st bike and hoping to go slower than you but maybe fast for my class...250cc pushrod. From what I see by looking at the bikes, reading this board (its great) and relying on experienced advice, I would get your bike running as fast as possible before installing the fairing. They tell me you will lose about 10% of top speed on pavement to salt. One thing to consider is removing your front brake system as you won't need it on the salt and it catches a lot of air. Weight is important but most of the fast bikes have added weight to their swingarms to keep traction. Running on the salt requires the motor to be running at top performance for up to a full minute when you count the run-up to speed before shifting to top gear. I don't know your bike but my estimate of top speed on the salt with your head on the tank would be 120 in perfect tune and condition. My goal is 80 mph and I need to lose 20 lbs. Good Luck
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Welcome aboard Gimpy,
I too am pretty new to this game. I ran RWB last year on a '79 cb750L last year. It had sort of the standard street mods, pod aircleaners, Mac 4 into 1 exhaust, jet kit, Dyna ign. The engine internals were untouched. Slightly taller final drive. Small wind screen.
It dynoed at ~60 rear wheel HP. I ran through the mile at an average of 120 and maxed at 123.
I'm going back in an AMA class this year, hope to see you there!
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Its about the journey not the destination
if you have zero drag you dont need horsepower and vice versa.
welcome to the site dude always happy to see another honda!!!
Caution its addictive
Oz
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I'm going to look at a couple of Nighthawks I found on Craigslist. Wish me luck!
I will also be working on my other project today. It's a 1970 CB100 that I'm turning into a monoshock cafe racer sort of thing.
(http://i1222.photobucket.com/albums/dd487/GimpyJoe29/cb100progress002.jpg)
Back to the garage :-)
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Joe, this is part of a reply to your first question "How fast will I go with streamlining?"
There is a formal method that involves estimates of frontal area, drag coefficients, friction losses, the effects of altitude on drag and power, the racing surface, etc. It is good to know and most of us use it. There are frontal areas and drag coefficients listed on links to this website for many different vehicles. There are spreadsheets, too, to help with the calcs. A person can figure out potential top speed with careful work.
The author, John Bradley in his book "The Racing Motorcycle" (ISBN 0 9512929 2 7 for Volume 1 or ISBN 0 9512929 1 9 for both volumes) discusses this formal method. He also made a simple graph. It is a plot of rear wheel horsepower versus top speed from published data on modern road bikes. Road testers are hired guns that can tuck down very well, the "standard" bikes they ride are typically the pick of the litter, and tests are almost always done near sea level on a paved surface. The data resembles bikes at Maxton, Loring, etc. more than at B'ville.
The upper line on his graph represents road bikes with more than average resistance to motion. Resistance is friction and air drag. The lower line represents bikes with less than typical resistance to motion. A typical beginner guy or lass out will be at or near the upper line. A road legal street based bike well tuned with a good rider is somewhere between the lines. A well streamlined production road bike with a skilled rider is at or near the lower line. The goal is to be below the lower line. We can do this with our home built streamlining.
At B'ville the air is thinner and we naturally aspirated bikes lose power. I use a typical power loss factor for the salt flats. We race on a natural surface which creates more drag and we push against thinner air which produces less drag. My assumption is both cancel each other out for a street bike. I do not use factors for them with Bradley's graphs. The first post is an example of a little Honda.
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This is the second of two posts. Honda 100's are on the bottom of Bradley's graph. The Nighthawk will be closer to the top. Bradley's upper and lower curves are shown. Disregard the dots. They are for Triumph and I add a couple each year.
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Wow! Thanks for the information Wobbly. I didn't know it was possible to calculate top speed precisely. I figured someone would just say "maybe around a zillion miles an hour, give or take."
I'm assuming the full formula is in the section of this site that lists various LSR-related math. My math is a bit rusty but I will give it a try.
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It is not possible to be precise with any method except running the bike and looking at the time slip. The graph gives a rough estimate. Probably plus or minus 10 mph. It is a start.
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That makes sense. Precise is a relative term haha.
What other books besides Bradley's should I buy? I want to learn as much as I can before I start building. I'm still waiting to get my hands on a bike. I've got the money. I just haven't found the right motorcycle yet.
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Joe...........if you still looking for the bike, take a look at www.sohc4.net for a lot of good info on the older Honda 4-cylinder models. When or if you move up to more modern bikes, you will find the competition gets very interesting. If you notice..........the number of competitors is somewhat split between modern power and very custom older models. There also appears to be a growing interest in having the fastest bike of a particular model without regard to an AMA or FIM record. Hope to see you on the short track........
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Yes sohc4 is a great site. I currently ride a CB750A Hondamatic and love it. I would use it as the basis for my lsr bike but unfortunately it isn't that reliable. If I can't find another motorcycle I may tear down the Hondamatic and race it after all. We shall see... :evil:
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Allowing for what you plan to do and what Lady Bonneville will take away 130 should be a realistic target. If you keep your expectations realistic you won't be disappointed. Its also highly addictive. And thankfully there is no known antidote.
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Joe, on the subject of books. Most of my library are old books that are hard to get and and articles clipped out of 40 years of magazines. Some useful newer books are Rick Voegelin "The Step-by-Step Guide to Engine Blueprinting" ISBN 978-1-884089-26-8, David Vizard "How to Build Horsepower" ISBN 978-1-93470-17-7, and Harold Bettes and Bill Hancock "Dyno Testing and Tuning" ISBN 978-1-932494-49-5
A thought on the bike choice. Eventually a person is going to need some strong racing rods and pistons, bigger or better valves, stronger and better quality springs, hotter cams, etc. Honda was, and is, constantly changing their designs. It is hard for an aftermarket company to justify the tooling, research, and development for racing parts when the design is limited to a few model years of life. Some of the other makers such as Harley, Triumph, and Kawasaki keep their designs for longer periods. There are many more racing parts available for these. Take the modern Triumph Bonneville I ride as an example. The heavy ill handling beast is the slowest bike Triumph makes. It has been in production for a long time and a large volume were sold. There are far more aftermarket parts available for it than any other modern Triumph.
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you are spot on there Wobbly,Every single bit of the engine work on the CBR has been a complete nightmare, everything has had to be made one off and usually on your side of the water (USA)
If I had thought about it before I had started I would have researched availability of parts but unfortunatley I am too far into the project to change now.
So Joe before you go too far you may want to think about it very carefully old hondas are not the easiest of bikes to source go faster bits for but on the plus side, Strong and over engineered and forged cranks as standard.
Oz
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Maybe I should turn my '76 CB750 into the racer instead of buying the Nighthawk. There are millions of parts for CB750's. Any thoughts?
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Millions of parts definatley but performance parts I dont really know, I would imagine that there were plenty in there day but are they still available? it would pay you to make some inquirys I guess.
As long as you are enjoying what you are doing and aint too bothered about colossal horse power figures either would be ok I would probably opt for the CB rather than the nighthawk but that would just be a personal preference.
I would certainly make some enquirys before you commit though it will save money and headaches later.
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Gimpy Joe,
If you decide to run the CB, check out this forum;
http://forums.sohc4.net/index.php (http://forums.sohc4.net/index.php)
There is still aftermarket support for the CB, and the members of that forum
can steer you in the right direction.
Cheers,
Dave
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I just had a quick look at that site I would go for the CB750!!! lots of good gear available by the looks of it.
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Now you guys are finding the good stuff.................take a look on the high-performance page for all of the different motor builds.....and look how reliable the CB750A drag bike is at 10,000 rpms............Also search the site for the most recent builders looking for improved torque. Then take a look at www.cyclex.com or something like that..............and we have not yet discussed the proven turbo power options..........There are roughly a half-million CB750 sohc/4 motors in the US...........Oh, and if you want a stroker, just drop a crank from a CB900 into the stock cases........along with the hyvo-chain and a Goldwing clutch basket......about as bullit proof as you can get.........just ask the builders that still perfer these motors in the midget dirt-track racing.
I think you can tell what my next build project will be for Bonneville.........just have to prove myself with my Triumph Tiger Cub so I will know my way around on the big white place on the earth with no speed limit signs.
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I'd definitely go for a CB750. A ton of speed parts are still available.
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The problem is that by the time I've spent all the time and money to make the CB750 fast, I could have just bought a faster bike. I could put over $2,500 into the CB750 motor and still have under 100 horsepower. I love my CB for riding around town pretending to be a cafe racer, but as a LSR bike I don't think it adds up. Any thoughts?
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Leave the Nighthawk engine alone and concentrate on streamlining. You'll be surprised how much free horsepower there is in reduced drag. Plus if this is your first trip to Bonneville you don't want to bring some engine that is on the ragged edge and spend a week trying to get it sorted.
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Joe, you are a young guy at 21. The future is in water cooling, electronic fuel injection, computerized engine management, etc. My advice is to start out with as modern a bike as you can afford. Do not dump a lot of money into it. Simply learn how all of the systems work, data collection, EFI and ignition chip programming, modern chassis setup, intake and exhaust tuning, how to ride, traction control, streamlining, etc. All of these skills need to be mastered to be competitive during your career. The sooner you get started the better you will be.
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So today was an interesting day. We split the cases on my old '76 CB750A Hondamatic, hoping against hope we wouldn't find bits of metal in there. Turns out it is absolutely pristine inside! We're going to replace the seals and bearings and button it up. We completely rebuilt the top end last month so we know that it's good.
Because the 'matic is much better inside than I thought it would be, I think I will ditch the Nighthawk idea.
NEW PLAN: I will use my 1976 CB750A for my LSR project. It may not be the fastest, prettiest, most modern bike out there, but
1. I already own it
2. I am in love with it
3. It is begging to be turbocharged. The stock cam and lower compression ratio are perfect.
Now I just have to figure out how to change the topic title :|
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Just suggestions.............up the front sprocket to 19 (from Cycle-X); smaller rear sprockets; extra chain and master-links; larger carbs from a standard CB750 K1-K6; Jets from 105 to 120; Free-flowing air-intake but in a box; 4-1 header; Prep the bike for the Salt and you should do 120 or better. Another low-buck motor wake-up is switch the cam to a CB750 F2 (Black Motor). You can return the bike to near stock and continue to ride it on the street when you get home.