Honda CX 500 Forum banner
1 - 16 of 16 Posts

·
Registered
Joined
·
9 Posts
Discussion Starter · #1 ·
Hello,

My name is Niels aka Nelson, i am major student with a specialication in Internal Combustion Engines and i accidentely bought a bike....

Had the intention to just build it up cheaply to a nice cheacky cafe racer buth the project went his own way...

I bought a 1978 cx500 with 33000 original Km's, had been sitting for a long time and was running poorly when i got it.
Land vehicle Vehicle Motorcycle Car Motor vehicle


tank was rusty that kind of thing, got the thing home to start stripping and rewelding the frame.

Land vehicle Vehicle Motorcycle Automotive tire Car


just a standard modification.
but then when i pulled appart the engine i fount out the left cilinder wasn't happy and probobly had run a bit to lean wich lead to a lot of damage in the cilinderhead from detonation.

Auto part Engine Automotive engine part Carburetor


then i decided to use these heads as an experiment, port them out as much as possible,

with the goal to get about 65-70 hp at the crank.
the porting of the head wont be the only modification to get this number, also running a free almost straight true exhaust 2-2 system.
Upgrading the carbs from the old keihins to 36 mm dellorto's en probobly a ignitech system to advance the timing as much as possible.


yet another project. haha!
 

Attachments

·
Registered
Joined
·
993 Posts
Welcome and fun and ambitious project. Murray is one of the members with experience massaging lots of HP out of the motors but it is best to start with an already strong cx650 motor transplanted into the CX or GL and then build it up and put some Mikuni carbs in the kit Murray has along with his direct coil on plug design and you can see those kinds of numbers... Exhaust would need h box removal and possibly different mufflers to reduce the back pressure and allow the increased flow intake mods to work to develop that power.
 

·
Premium Member
Joined
·
3,265 Posts

·
Registered
Joined
·
24,496 Posts
nelson 65-70 CRANK HORSE POWER is easily done

36s are big for the 500 so you loose bottom end but if you tune them well and have good dual exhaust

only clean up the heads a bit they dont need much unless you are doing the cam

dont advance the timing much more or you will risk detonation you cant hear

you should be very close

ps honda did the crank horse power test with no charging system hooked up and no water pump impeller (dyno supplied cooling)
 

·
Registered
Joined
·
2,385 Posts
Unless you know what you are doing, porting can hurt performance more than help it. The most critical area for porting is the 1/2" area below the valve seat. If you mess up that, or the valve job, you will be subtracting power, not adding it. To get much if any advantage from porting you need to add compression, bigger cam, performance carbs, better ignition, performance clutch, and freer flowing exhaust. All components need a careful balance to realize useful performance improvements.
 

·
Registered
Joined
·
993 Posts
So, if you do a clean up of any flashing on the head, is it going to do any good? The CB550s benefit from some reshaping of the football leading into the valve guide and narrowing the guide as well as putting a pocket above the valve in the head that acts a little like a turbo charger when the cam comes into it power band after 5-6k. The CB550Ks are happy up to 9.5k and with work can handle 10k all day long with no damage. They like having the "tits" revved off them...

What kind of things can you do to the heads to help an otherwise stock motor with the deletion of the Hbox with your mid pipes Murray, keeping the stock carbs and rest of the exhaust?
Is it worth anything or is the heads cleaned up and in very good shape in stock form? -
David
 

·
Registered
Joined
·
24,496 Posts
the heads do well on a 500 if the motor is stock leave them alone

and my first go to mod is to get stainless valves and keepers

the lower shroud at the valve stem to valve head add almost 15 percent of flow rate

with out doing much work
 

·
Registered
Joined
·
24,496 Posts
the heads do well on a 500 if the motor is stock leave them alone

and my first go to mod is to get stainless valves and keepers

the lower shroud at the valve stem to valve head add almost 15 percent of flow rate

btw look into a rae san it replaces the entire ignition system has 4 p reconfigured timing maps built in and you could get them tweaked if needed

with out doing much work
 

·
Registered
Joined
·
2,385 Posts
So, if you do a clean up of any flashing on the head, is it going to do any good? The CB550s benefit from some reshaping of the football leading into the valve guide and narrowing the guide as well as putting a pocket above the valve in the head that acts a little like a turbo charger when the cam comes into it power band after 5-6k. The CB550Ks are happy up to 9.5k and with work can handle 10k all day long with no damage. They like having the "tits" revved off them...

What kind of things can you do to the heads to help an otherwise stock motor with the deletion of the Hbox with your mid pipes Murray, keeping the stock carbs and rest of the exhaust?
Is it worth anything or is the heads cleaned up and in very good shape in stock form? -
David
I doubt you could do much to help in the ports on a stock motor. You will gain more by a perfect valve job done by a pro. The shape at the valve seat is critical and can easily mess up the flow. Cleaning up the flow around the valve guide does help, but do not get carried away trying to widen the port there or open it up, that will slow the flow down exactly where you want good flow. The CX will rev to 9,000+ rpm, but you need to have the springs to go with this, as well as a camshaft that will make power up high.

I would think that for a street bike with the intent of more power that you would look at a good valve job with good springs, carbs like Murray sells, a better flowing exhaust, and better coils, wires & igniters. Anything past that will cost a bunch of money.
 

·
Registered
Joined
·
993 Posts
Thank you for the input. SO, if a pro cleans up the valve shrouding and does a good valve job You can see about 15% more flow.
Murray,
How much are your pipes and exhaust, carb kit?

I was not aware that we had big cams available now. What would a better cam run. Since I am intending the bike to be touring and commuting and some curvy mountain roads... I don't intend or expect to see 9K unless in a place where that can be used. Commuting it would not and highway speeds at 9k would be pretty fast and loud.
I do wear earplugs...for the sound.

i know a guy who is a true artist with heads for the CB SOHC/4s as well as other bikes. He is up in Mass if I recall correctly and his name is Mike Riech. Mike does not have any experience with the CX500 or CX650 or GL500/650 heads.
There is a CB550 SOHC/4 race bike he has worked with the owner to develop the motor from stock 34-36 Rear Wheel HP (RWHP) to 78 RWHP! That bike is raced in the VRRA series in Canada and the north eastern US. Brent and his son have dominated their racing class with the bike and his son is an excellent rider and took over after some injuries from a wreck made Brent decide to let Tyler take over racing the bike.

Thanks for the input guys!
I didn't think asking here on Nelson's thread would be encroaching on it in a negative way as that input would be good for him to know what paths have been paved in exploiting the power from the CX and GL motors.

Thanks!
David
 

·
Registered
Joined
·
9 Posts
Discussion Starter · #11 ·
Quick little update,

have had the heads skimmt, waiting for them to get back at me.

done a little work on the bike itself,
removed the exces wires from the wirering loom.

Land vehicle Vehicle Car Motor vehicle Personal luxury car


with the new straight true exhaust.

removed all the headlight wich arent needed here as the bike is classified as an 'oldtimer' 40 years +

Land vehicle Vehicle Motorcycle Motor vehicle Car
 

·
Registered
Joined
·
9 Posts
Discussion Starter · #12 ·
Also got compete rit of the dash, got 2 simple new clocks (rpm and speed) all mechanical, removed the steering wheel and all the OG switchtes to make everyting custom on the clipon bars.

Hand Floor Finger Metal Wood
Light Hand Auto part Finger Metal


cleaned up some off the valves,

and a little pick of the ported head, Auto part Automotive engine part Carburetor

(was before the scimming)


i hope this week to test the ported head and the stock head on my homemade flowbench to see what is happening.
il keep ya updated!
 

·
Registered
Joined
·
993 Posts
So, you relocated the foot pegs with rear sets but did not change the shifter? No clue if you have done anything for the brake pedal yet.
The lights you removed would be your turn signal lights since it is 40+ years old. Headlight and tail-light must be maintained for safety as you have done... Just trying to be helpful with the type of lights you have deleted.
 

·
Registered
Joined
·
9 Posts
Discussion Starter · #14 · (Edited)
@murray

where can i get the stainless valves and keepers?

i am also getting a regrind on the camshaft to get some more lift and duration in it, i will probobly go well with the ported head.
 

·
Registered
Joined
·
2,385 Posts
1 - 16 of 16 Posts
Top