Topic: Honda Cb 500 Four, Supercharged "BigBang" Chopper

[Keskine]

Hi all, This is my first post to the forum. I started reading the forum about a year ago, when i bought my Cb500 as a project.
First my idea was just to make a really low bike, with long forks. But after i finished the frame, project went on hold for a while.
During that break time i figured that lets make something more special. Since i have yet another long Finnish winter time to build it.
That's where the idea started to take a shape. I have been looking at supercharged bikes for a while so i thought, lets try that.
So i bought an AMR500 supercharger for the bike. I'm planning on running it with a single carb as suck through.
We have had some chat with the guys about a "BigBang" four cylinder bike. So now was the time to try it. I re-phased the camshaft to get 2 cylinders fire at once.
Still a lot to do before it is ready... If it's going to be ready.
Anyways, here's a few pictures of the project so far.

This is how i bought it.

After mock up it was time to cut it.


Still few things to do on the frame but main lines are ready. Looks quite low to me



Here is the process of rephasing the camshaft



And here is some mock up for the supercharger and external alternator

[754]

Welcome aboard..looks like you do well thought out work, looks good.
Can't wait to see more.

[Terry in Australia]

Wow, excellent work mate! I really love quality engineering, and while I'm indifferent to anything else but CB750's, that's going to be a cool bike! I had no idea what an AMR500 supercharger is, so I Ebayed them, and they look ideal for a small engine, I might have to put one on my ride on mower! Cheers, Terry.

[SOHC4 Cafe Racer Fan]

Wow! Re-phased camshaft, supercharger! Looks interesting.

[spotty]

looks cool as fcuk, where did you get the info on rephrasing the cam, I've always thought that would be a great idea for a 750 but no-one I've ever talked to has heard of it being done or even thought it was a good idea (never stopped me before)

[scunny]

for spotty, I think(dangerous idea) the big bang was tried for hill climbers, sure I read it on here ?
I shall be watching this.

[BomberMann650]

What is a rephased cam?

[calj737]

What is a rephased cam?

Don't they have the internet on the farm out there?  Rephasing a crank or cam is cutting it and "clocking" the lobes to alter the firing order. A common practice on the XS650 to remove the vibration and yield a different torque band. It will be interesting to understand what magic potion he has up his sleeve on "why" rephase the cam alone? And what change that will bring about. Much to learn here...

[strynboen]

often done on the old Honda  twin"s..specily the ones vho have half cranks..so you can fase them to parelel firing/or parelel piston run..its a oldscool tricks..back then....but think it are better to grind the lobes dovn..and veld  up and grind nev lobes. but then you need a kopi grinder....but still velding up lobes vill also give some problems.heat .struktur. and strait run..
but looks like there is taken care of all problems there.
..machinists at work

[SOHC4 Cafe Racer Fan]

I would think that requires some careful welding both for structural integrity and balance.

[kmb69]

.....
It will be interesting to understand what magic potion he has up his sleeve on "why" rephase the cam alone? And what change that will bring about. Much to learn here...

Ditto. Same question - why?
Seems counter-productive, especially with a supercharger.

[SOHC4 Cafe Racer Fan]

.....
It will be interesting to understand what magic potion he has up his sleeve on "why" rephase the cam alone? And what change that will bring about. Much to learn here...

Ditto. Same question - why?
Seems counter-productive, especially with a supercharger.

I imagined that the builder has worked out that changing the firing order will compliment the supercharger.  Given the title of the thread, "Big Bang," I assume that the builder is going to big bang pulse firing order.

[BomberMann650]

Glad I asked instead of googling.  Rephasing a small block chevy would be little like an sohc4 honda.

[kmb69]

.....
It will be interesting to understand what magic potion he has up his sleeve on "why" rephase the cam alone? And what change that will bring about. Much to learn here...

Ditto. Same question - why?
Seems counter-productive, especially with a supercharger.

I imagined that the builder has worked out that changing the firing order will compliment the supercharger.  Given the title of the thread, "Big Bang," I assume that the builder is going to big bang pulse firing order.

Completely understand the "Big Bang" or "Twingle" phased firing order.

Don't understand how that enhances supercharging. The AMR500 produces approximately 500cc flow per revolution of the supercharger. So at 1:1 on a 500cc 4 stroke engine, it provides approximately 1 atmosphere of boost no matter how the firing is phased. Pretty sure the pulsed intake doubles the pressure in the plenum at max pressure buildup per revolution.

Just curious why the re-phasing.

[Keskine]

.....
It will be interesting to understand what magic potion he has up his sleeve on "why" rephase the cam alone? And what change that will bring about. Much to learn here...

Ditto. Same question - why?
Seems counter-productive, especially with a supercharger.

I imagined that the builder has worked out that changing the firing order will compliment the supercharger.  Given the title of the thread, "Big Bang," I assume that the builder is going to big bang pulse firing order.

Completely understand the "Big Bang" or "Twingle" phased firing order.

Don't understand how that enhances supercharging. The AMR500 produces approximately 500cc flow per revolution of the supercharger. So at 1:1 on a 500cc 4 stroke engine, it provides approximately 1 atmosphere of boost no matter how the firing is phased. Pretty sure the pulsed intake doubles the pressure in the plenum at max pressure buildup per revolution.

Just curious why the re-phasing.

Yeah there is actually no real reason for re-phasing the camshaft. At least if you are looking for more power. Main idea here is to try how the bike sounds with that modified firing order. Probably it will make more lower end torque compared to stock. But im not really looking to gain any performance with this re-phasing. Just bad sound and #$%*ty idle compared to stock.

[BomberMann650]

Sure it will sound like a chopper!  Couldn’t have that purring zipper sound on a ride like that!

[calj737]

Yeah there is actually no real reason for re-phasing the camshaft. At least if you are looking for more power. Main idea here is to try how the bike sounds with that modified firing order. Probably it will make more lower end torque compared to stock. But im not really looking to gain any performance with this re-phasing. Just bad sound and #$%*ty idle compared to stock.

Pardon my ignorance, I've seen cranks re-phased on twins, but never just a camshaft on an inline 4. How far did you actually re-time 3/4 from their original orientation, and what effect will that have on combustion at that phasing angle?

[kmb69]

Yeah there is actually no real reason for re-phasing the camshaft. At least if you are looking for more power. Main idea here is to try how the bike sounds with that modified firing order. Probably it will make more lower end torque compared to stock. But im not really looking to gain any performance with this re-phasing. Just bad sound and #$%*ty idle compared to stock.

Pardon my ignorance, I've seen cranks re-phased on twins, but never just a camshaft on an inline 4. How far did you actually re-time 3/4 from their original orientation, and what effect will that have on combustion at that phasing angle?

Excuse me for butting in, but pretty sure he re-phased the cam 180 degrees so 1-4 fire at the same time and 2-3 fire at the same time. A "quad-twingle" if you will.
This was done on some SOHC 750 flat trackers back in the day to potentially provide more torque and to give a "traction pulse break" to the rear wheel in theory.

[Keskine]

Yeah there is actually no real reason for re-phasing the camshaft. At least if you are looking for more power. Main idea here is to try how the bike sounds with that modified firing order. Probably it will make more lower end torque compared to stock. But im not really looking to gain any performance with this re-phasing. Just bad sound and #$%*ty idle compared to stock.

Pardon my ignorance, I've seen cranks re-phased on twins, but never just a camshaft on an inline 4. How far did you actually re-time 3/4 from their original orientation, and what effect will that have on combustion at that phasing angle?

Excuse me for butting in, but pretty sure he re-phased the cam 180 degrees so 1-4 fire at the same time and 2-3 fire at the same time. A "quad-twingle" if you will.
This was done on some SOHC 750 flat trackers back in the day to potentially provide more torque and to give a "traction pulse break" to the rear wheel in theory.

Yes you got that right, i found some stories about SOHC 750 hill climbers that have used this kind of re-phasing.

So like you said. I changed 3&4 180 degrees from their original position, to match 1&2. Firing order is 1-2-4-3 and now its 1&4-2&3. Since 1&4 and 2&3 pistons are up at the same time.
 
Those re-phased twin cranks are actually giving some benefits like less vibrations and better revving engine etc. But here i'm kind of going in the opposite direction.

[calj737]

Gotcha. I suspected that was the case, but felt it better to ask because your picture wasn’t clear for my old eyes.

As I said earlier, “Magic potion” stuff... 

[BomberMann650]

Gotcha. I suspected that was the case, but felt it better to ask because your picture wasn’t clear for my old eyes.

As I said earlier, “Magic potion” stuff... 

Us washingtonians have an herbal potion that can help those old eyes. 

[Lostboy Steve]

often done on the old Honda  twin"s..specily the ones vho have half cranks..so you can fase them to parelel firing/or parelel piston run..its a oldscool tricks..back then....but think it are better to grind the lobes dovn..and veld  up and grind nev lobes. but then you need a kopi grinder....but still velding up lobes vill also give some problems.heat .struktur. and strait run..
but looks like there is taken care of all problems there.
..machinists at work

I'll be 100% honest, I can't wait to hear how this sounds.

Sent from my LG-H931 using Tapatalk

[Medyo Bastos]

I ran a Big Bang cam on a CB750 chopper years ago. It added some low end torque. The sound was not at all what I expected, kinda sounded like a big cb350t.


Sent from my iPhone using Tapatalk

[strynboen]

seperate exhost lines vill probely give a nice big banging..if you mix it all in a 4-1 it vill be more boring.

 

[Keskine]

I ran a Big Bang cam on a CB750 chopper years ago. It added some low end torque. The sound was not at all what I expected, kinda sounded like a big cb350t.


Sent from my iPhone using Tapatalk

seperate exhost lines vill probely give a nice big banging..if you mix it all in a 4-1 it vill be more boring.

 

What kind of exhaust did you have on that 750?
Did that big bang cam create much more vibrations compared to stock?

I was planning 4-2 pipes or 4-4. Have to see which one looks better.