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Discussion Starter · #1 ·
Hi!
I have been (very slowly) building a "bitsa" with an Ariel 1950 frame and CB450 engine.
I understand that Honda produced CB400 and 450s for several markets with different power bands. I think those variations were achieved thru different compression ratios and camshafts. Am I right? I need to rebuild the engine and I want to use parts from CB400/450 engines of every possible source to achieve the opposite that every engine tuner wants: I want a LOWER engine output and a flat powerband. I´m trying to emulate a british twin from the late 40s/early 50s so I don't need 43hp and high revs. I want a sedate powerplant and I'm prepared to accept a 10 or even 20% power loss in exchange for a flatter powerband at lower rotations and good torque.
Wich combination of compression ratio, camshafts and/or other parts do you think I need to use?
 

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Looks like a 1952 plunger frame. Welcome to the forum. Of all the 400-450 series, the Hondamatic `A`model has the least HP and most torque.
 

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Welcome aboard. You're definitely going a different direction, one that to my knowledge hasn't been attempted.
All of the 400's have the same bore and stroke, same for the 450's which have a larger bore only. As Dan mentions the A (automatic) has the lowest HP and highest torque, requirements for the use of a torque convertor.
We know that swapping a manual head and necessary parts to a manual transmission engine doesn't work well. Less torque plus driveability problems.
I would be looking for and entire CM450A pistons, head, cam, rockers, carb insulators and carbs. Cylinders are the same for all models. The 400 engine has a different head oiling system so that isn't an easy change over but can be done if needed and may be a way to go if the 450 isn't available or you want to experiment more.
There were only 3 cam shafts made for both engines, the standard, the A model and a reduced HP cam for German plus a few other Euro country new riders.
Heads are identified by a cast HA in the front on the cam chain tunnel plus the smaller valves.
 

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Discussion Starter · #5 ·
Looks like a 1952 plunger frame. Welcome to the forum. Of all the 400-450 series, the Hondamatic `A`model has the least HP and most torque.
It´s a 1950 single cylinder frame modified to accept the 450 engine. The engine in the picture is a hollow 400 used for assembly only. Only frame and gas tank are Ariel. Everything else is from other makers or homemade. Front suspension is 1969 CB450, front wheel is CB350, rear wheel is a Yamaha concoction: XT600 hub, XT500 brake plate and XV250 Virago sprocket plate. Fenders are chinese CJ750 heavily modified and mufflers from modern Triumph. Exhaust headers, fender brackets, engine plates, battery holder and a myriad of other parts are homemade.
 

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Discussion Starter · #6 ·
Welcome aboard. You're definitely going a different direction, one that to my knowledge hasn't been attempted.
All of the 400's have the same bore and stroke, same for the 450's which have a larger bore only. As Dan mentions the A (automatic) has the lowest HP and highest torque, requirements for the use of a torque convertor.
We know that swapping a manual head and necessary parts to a manual transmission engine doesn't work well. Less torque plus driveability problems.
I would be looking for and entire CM450A pistons, head, cam, rockers, carb insulators and carbs. Cylinders are the same for all models. The 400 engine has a different head oiling system so that isn't an easy change over but can be done if needed and may be a way to go if the 450 isn't available or you want to experiment more.
There were only 3 cam shafts made for both engines, the standard, the A model and a reduced HP cam for German plus a few other Euro country new riders.
Heads are identified by a cast HA in the front on the cam chain tunnel plus the smaller valves.
Jim,
Thanks for the information!
I think I will start to hunt parts from CM450A. I found a specs sheet for this bike that says it had 37hp and 30mm carburetors instead of the "normal" 43hp and 34mm carbs but can´t find torque figures.
I think I will have no problems to assemble CM450A engine parts in a brazilian CB450 engine block.
Cheers,
Lúcio
 

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Honda didn't really publish any of the torque/hp graphs, just a gross HP number.
In the US/North American market the A models used 28mm carbs, not sure what was used elsewhere. Brazil/South America seems to be quite different in models than even Europe.
 

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It might be possible to use a CMX450 cam. I've been looking at parts diagrams and I think it'd drop it. The CMX450 cam has less lift than the CB/CM-400/450.
 

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It´s a 1950 single cylinder frame modified to accept the 450 engine. The engine in the picture is a hollow 400 used for assembly only. Only frame and gas tank are Ariel. Everything else is from other makers or homemade. Front suspension is 1969 CB450, front wheel is CB350, rear wheel is a Yamaha concoction: XT600 hub, XT500 brake plate and XV250 Virago sprocket plate. Fenders are chinese CJ750 heavily modified and mufflers from modern Triumph. Exhaust headers, fender brackets, engine plates, battery holder and a myriad of other parts are homemade.
In North America, we only had rigid frame until 1952 when the plunger style was available. I guess Brazil got it first.

firstbike.jpg

This is a pic of my 1951 BSA (same frame as Ariel ). No cushion on the rear made for a hard ride...lol
 
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