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Author Topic: Honda CX500 - EFI and boosted on a budget M-PBF 500  (Read 1881 times)
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Koncretekid
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« Reply #15 on: February 27, 2018, 07:24:11 AM »

11,000 rpm with a 2" (50mm) stroke only results in piston speeds of 3666 fps, which should not be an issue with good rods and pistons and that healthy looking crank.  Compare that to my B50 with 90mm stroke at 7200 rpm which equates to piston speed of 4248 fps with a crankshaft half the size of yours (maybe crank flex contributes to lower stresses on the rod and piston).  Also the B50 is a single while you have a V-twin with better balancing characteristics.
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mtiberio
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« Reply #16 on: February 27, 2018, 07:35:37 AM »

Wobbly, the new 500 is nice, but since it is OHC, it runs with the big boys in G, good try trying to get all of us CX guys out of the pushrod classes.

That is interesting that they took away the shaved V rated tire rule, can anyone shed light on this, was there a problem?  There are a lot of the smaller bikes that run narrow tires and the selections are very limited when you get narrower than a 160.

Having Nate Jones shave your tires, no problem. Letting Billy Bob hack at your tire back in the shed, not so good. With a rule stated like that, ANY shaving would comply with the rules, but only proper shaving actually increases speed rating.

I feel your pain, I have 2.15"x18" rims on my 1000cc Guzzi, and while I haven't busted 150, I could easily with a decent full fairing. I have some shaved V tires from Nate Jones (planned on it when I was going to run A with a +150 record, that was before they added all the low minimum M classes), but would be in a world of hurt if I had to run Z rated radials on those narrow rims. There is no narrow rim solution, no one makes W or Z rated narrow rim tires for bikes. All the radials require fat rims.
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Koncretekid
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« Reply #17 on: February 27, 2018, 07:41:55 AM »

I'm curious about the shaft drive possibilities.  Are there other makes of shaft drive bikes that have a taller drive ratio, and if so, how difficult is it to transplant the entire rear drive assembly to the Honda?
Tom

P.S. In regards to narrow radial tires/wheels, I've gone to 17" cast wheels and have found some 2.5" wide rims on which I can run 110/70 ZR17 w rated tires for the front, and 3.5" rims on which I run 120/70 ZR17 W rated tires on the rear.
« Last Edit: February 27, 2018, 07:45:04 AM by Koncretekid » Logged

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mtiberio
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« Reply #18 on: February 27, 2018, 08:02:50 AM »

I'm curious about the shaft drive possibilities.  Are there other makes of shaft drive bikes that have a taller drive ratio, and if so, how difficult is it to transplant the entire rear drive assembly to the Honda?
Tom

P.S. In regards to narrow radial tires/wheels, I've gone to 17" cast wheels and have found some 2.5" wide rims on which I can run 110/70 ZR17 w rated tires for the front, and 3.5" rims on which I run 120/70 ZR17 W rated tires on the rear.

I race a Guzzi with shaft drive, and I have 3 different rear ends, but there must be 6 or more out there. Most are too short. I have one that is so tall, that I only use 4th gear (out of 5). I also gave myself many more gearing options by bringing 3 rear wheels and 3 tires, a 100, a 110 and a 120 to Nate Jones, and having him shave the 100 to the minimum, skim the 120, and shave the 110 to be exactly in between the other two. He said he had never had anyone stagger their tires this way, but he liked it. They ended up being about 3.2% apart, the same as one tooth on a 33 tooth rear sprocket.  If I was you, if you need to go taller, I'd lace up a 19" rear rim, and runs a Z or (W) rated radial front tire on the back (SCTA, you see what you are driving us to? Does it appear safe?).
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« Reply #19 on: February 27, 2018, 11:45:59 AM »

I have searched for info on using the front tire on the rear in the past and could not find any info about it.  The tire guys go into their dialogue about design, structure, load, etc., but never say it is unsafe to do.  Since none of us in the slow club will ever put huge loads on the tire, it is probably ok.  Now if a turbo Busa shows up with a 120/70-17 ZR front tire on the rear, then we are all in trouble.
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« Reply #20 on: February 27, 2018, 12:07:48 PM »

The CX Hondas have lots of gearing possibilities even sticking with the shaft drive.  With the tallest gearing and that YUGE rear tire, if they spin this bike to 10,000 rpm it will run 190+!  Honda has five different primary gears, two rear drive ratios, and three or more 5th gear options.  Add in the variables with tire choices and Lucas can pretty much dial in the gearing he wants.  Or, with a little more degree of difficulty, just do a build like one of Jim L's and turn it sideways and convert to chain drive.
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wobblywalrus
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« Reply #21 on: February 27, 2018, 08:19:15 PM »

There is a Bridgestone ZR rated Battleaxe 19-inch front tire and a matching 150x17 rear.  Both are radials and they work well together.
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hoffman900
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« Reply #22 on: February 27, 2018, 08:52:17 PM »

That seems counterintutive. The Harley guys have realized on the Spintron that a heavy flywheel helps dampen velocity changes at the camshaft. Some V8 builders are using steel timing sprocket or pulley with a high MOI to help with this as well.
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lucasanderson00
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« Reply #23 on: February 27, 2018, 09:13:21 PM »

Here's the part that makes this even tougher, I just had Nate Jones shave my 23" V rated tire 3 weeks ago before I saw any rule change, so now my tire is shorter and still not allowed over 150mph. There is a Guzzi final drive that exists with a better ratio - 2.91:1, my Honda has a 3.09:1 ratio. That would be great but now I must run a smaller diameter tire with a z rating, so I'm right back where I started.

Unfortunately the Factory CX650 Turbo primary gears that would solve the problem are unobtanium, I will probably have to end up buying a complete CX650T, take what I need, and part out the rest to recoup the 3-4 thousand it costs to buy one, which would be a shame and I would rather not do.

Open to any ideas on gearing, does anyone know of a machine shop that makes one off transmission or primary gears?

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JimL
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« Reply #24 on: February 27, 2018, 11:55:11 PM »

Gearing up ahead of the trans makes the trans act like a wide ratio.  The 4-5 upshift will be tough.  

I ran CX500 primary drive even in my 680cc engine.  I shortened 5th gear by using the 5th gear from a 1978-79 CB 400 twin 5-speed trans.  You don't need both gears just the countershaft one....it mates to the existing 29 tooth input shaft 5th gear.  The part number I used was 23501-413-000 which is a 28 tooth gear (versus the 27 tooth part in a stock CX500 trans).  The result is a .965:1 5th gear which is the best you could ask for.  After my salt flats years were done, I discovered that the countershaft from that 400 twin will fit the CX with very little work, and so the chain drive job would have been much easier!  I was able to buy one of those shafts out of England (the 28T 5th gear that I used came from New Zealand through the good folks at Econo Honda).

The shafts and shift drum geometry (spacing) is the same as the later 6-speed 400 twins.  It should be possible to adapt to the 6-speed, but I think the slightly modified 5-speed will do the job.  That was the 5th gear that finally got me over the hump and saw a 163+ mph time slip from one of my 647cc destroked engines.

I guess that is about all I can suggest.  The final drive problem can only be solved by turning your engine sideways, building the chain drive setup, and then finding a suitable Honda product that has plenty of room in the stock frame so you can stay in M class.

That would be cheaper and simpler than the path you are on.  Daddy always said, "It takes a lazy man to invent a better way."  That was good advice.
« Last Edit: February 28, 2018, 12:00:14 AM by JimL » Logged
mtiberio
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« Reply #25 on: February 28, 2018, 09:03:49 AM »

Here's the part that makes this even tougher, I just had Nate Jones shave my 23" V rated tire 3 weeks ago before I saw any rule change, so now my tire is shorter and still not allowed over 150mph. There is a Guzzi final drive that exists with a better ratio - 2.91:1, my Honda has a 3.09:1 ratio. That would be great but now I must run a smaller diameter tire with a z rating, so I'm right back where I started.

Unfortunately the Factory CX650 Turbo primary gears that would solve the problem are unobtanium, I will probably have to end up buying a complete CX650T, take what I need, and part out the rest to recoup the 3-4 thousand it costs to buy one, which would be a shame and I would rather not do.

Open to any ideas on gearing, does anyone know of a machine shop that makes one off transmission or primary gears?




Just re-read the new rules, and there is an out, although perhaps not in the 23" size. The new rule states:
151-200 MPH Production tires with speed rating of ZR or ZR-w or special tires for racing as designated by the manufacturer.

The 'or' clause is an out for me. I can get "racing" V rated bias-plys from Dunlop, Avon and Conti in 18" sizes. The Dunlops even say, not DOT approved, for racing only. They are also available in 19". I believe I could argue the 'or' clause makes them legal above 149...

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edinlr
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« Reply #26 on: February 28, 2018, 11:16:29 AM »

I tried arguing with an official one time and he quickly pointed out that he wrote the rule, so he knew exactly the intent.  On the salt is not a place for clarification, get it in writing now.  I am guessing an e-mail from an official would be what I would want if I were going to try to use that loophole.  One would think that if you had a receipt that detailed the tire model, manufacturing date, etc., from a trusted shop, that they would accept that.
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« Reply #27 on: February 28, 2018, 11:33:53 AM »

Who shaves the tires can be important.  The first time I went to tech with a shaved tire on the bike the inspector asked "Who shaved your tires?"  I said "Nate Jones" and the insp. responded "Right answer!"

On the other hand, you might get points for a good try if you said back to him "I did, with my kid neighbor's mother's kitchen knife." cheers cheers
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lucasanderson00
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« Reply #28 on: February 28, 2018, 09:52:01 PM »

That's a good point on the jump from 4th to 5th gear, its a tough jump. I couldn't get the bike to pull in 5th gear until this year now that we are finally making hp. Very interesting that the 400 twin has the same transmission shaft spacing, I wonder what other Hondas also have transmission with a similar spacing? A taller 5th gear backed up with a taller 4th gear (maybe even an extended 3rd for the total package) could go a long way for top end mph on our setup.
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