Topic: The CB550 downdraft port project

[speedracer741]

So now that I have just finished getting all of the tooling necessary to make some real headway on this project I decided to start a thread showing the progress of this experiment. So if it's a disaster, you will all get to see it right here! The idea behind this project is to develop the 500/550 head to a point that will support much higher flow rates than can be achieved with the stock casting. The 500 and 550 head are the same and when big bore kits are installed in the 550, the head really becomes the bottleneck in the potential of the displacement. Great gains are to be had from conventional upgrades such as porting and cam timing, however there is quite a bit more to be tapped from one of these things and this project is my little attempt to see just what those gains are. The stock intake manifolds result in a rather long runner length, not ideal for a small high revving engine but my guess is that it was Hondas attempt to retain some useable torque for the smaller bikes. For high perfromance purposes this isn't as much of a concern so the idea here is to shorten up the runner length to be more optimized for the Megacycle 126-21 cam that will be used in this build. The other design goal is to straighten the intake runner resulting in greater flow and velocity, greatly improving cylinder filling after bottom dead center which will also help optimize the cam timing. This intake design is nothing new, all modern sportbikes use this technology and it has been around just about as long as internal combustion.

To begin I have taken a CB550 head and cut it open with a ban saw to get a cross sectional view of the ports so I can see what I can get away with. 30 degrees is as steep as this head will go. Modern bikes have steeper ports however they have far less angle between the valves which allows this but 30 degrees is a huge jump nonetheless. The new ports will also have to be moved over so that they are in line with bore centerline. This will require plugging the stock ports with aluminum slugs. Some welding will also have to be done to the inboard side walls of the ports as there will be a void there when the new straight ports are machined. Then aluminum blocks will be bolted to the old manifold surface and milled at the new 30 degree angle. Spigots will then be pressed into these to mount the carburetors. The carbs for the prototype are Keihin VE series in 32mm. 1.5mm oversize intake valves and 2mm oversize exhaust valves are currently under construction, pictures soon!   

[speedracer741]

Making quick work of tearing apart the first head with the pneumatic valve spring compressor. I will most likely be doing several heads at once as I'm sure to make a few mistakes along the way!

[speedracer741]

Machining the blocks that will cover the old manifold surface. The holes are counterbored for the allen head bolts as deep as possible as most of the material will be gone once they have been milled at the 30 degree angle and I don't want to end up chopping the tops of the bolts off. Once the head is near completion, material will be machined from the blocks between the ports allowing air flow through the cylinder head. The first head has been machined for the port plugs but will not be welded into place until some welding has been done to the inboard sidewalls of the ports. I also want to get at least one more head to this point before continuing. Everything after this point requires setting up angle mounts in a mill and set up time will rather high so having more than one head ready would be a good idea

[jonbuoy]

Thats impressive work, its great to see people do this stuff. Will be watching your progress.

Cheers & good luck

John

[Jonesy]

WOW! I'll be following this thread with great interest. Compared to what you're doing, I did some rather mild porting work to my 550 over the winter:

http://www.sohc4.us/forums/index.php?topic=17374.msg179632#msg179632

That cutaway view of the head would have been very helpful then, but it looks like I removed metal in the right places.

So far I have everything stock on the bike, but I did notice the engine being more lively beyond 5,500 RPM. (Still need to write a follow-up post on the performance...)

Neat stuff. Keep us updated!

[puppytrax]

That is some cool stuff!!! 

Will you be sectioning each cylinder in your display head to insure that they are all identical?? [hint, hint]   

[puppytrax]

OK, this is a bit off-topic, but...

I'm getting old, and my memory is failing, but I seem to recall that either Cycle World or Cycle News reporting back in '71 that Honda had to deliberately cripple the production 500 Four by port/cam changes due to the fact that the prototypes were quicker/faster than the 750...and they didn't want sales of the "big four" to suffer because of that...   

Just an observation...It would be helpful to know if any other old farts remember any Yoshimura head mods back at that time, that restored the lost HP from the altered port/cam mods...It might help your project...   

[Ricisan]

Reinventing the wheel? Trying to reinvent the CB 500 head will I think be a disappointment. I read an article by "Jewell Hendricks" where he said the "biggest cyl head gains" came from a very simple
change in head. I don't remember exactly what that was, and I do not want to misinform. Check it out. This article might be in one of the many  "Gentleman's Express" tech articles.
KISS works for me.

Ricisan

[speedracer741]

Reinventing the wheel? Trying to reinvent the CB 500 head will I think be a disappointment. I read an article by "Jewell Hendricks" where he said the "biggest cyl head gains" came from a very simple
change in head. I don't remember exactly what that was, and I do not want to misinform. Check it out. This article might be in one of the many  "Gentleman's Express" tech articles.
KISS works for me.

Ricisan

I'm not really trying to reinvent anything. I'm just a guy having some fun with his hobbies. Some of the most significant advancements in engine technology were the result of some guy breaking from the norm and doing something unorthodox. Though there is nothing new to engines that I am doing here, it sure is fun to see what is possible from one of these cylinder heads. If the thing rolls down the road under its own power I still won't be disappointed, but phenomenal performance would be nice though

[puppytrax]

I'm not really trying to reinvent anything. I'm just a guy having some fun with his hobbies.

Same here. I just like to make stuff!   

If it works, great! But if it only looks good, that's OK too! 

[Ricisan]

Sorry if I sounded negative. At some point, you will want to gain extra flow. I wish I could remember exact phrase. I didn't tell you what to do???

Ricisan

[speedracer741]

Sorry if I sounded negative. At some point, you will want to gain extra flow. I wish I could remember exact phrase. I didn't tell you what to do???

Ricisan

Oh no offence taken. I appreciate all input on this project. I have done a lot of research on this head to see what has been done in the past. It seems that it has not gotten nearly as much attention as the larger displacement machines so there just might be some uncharted territory here? Only time will tell I guess.

[turboguzzi]

hei speedy

good to see you here! once sent you an email through ebay about the porting mods I am doing to my 500 racer. keeping my fingers crossed for you!
I am going quite a lot more conservative here. managed to get a nice 12 degrees of downdraft without going into welding, so a bit envious of your planned 30 degrees. my mikunis spacing lets me get fully strait ports (looking from above) so that's pretty nice already.
wanted to ask you if you could send me a high rez photo of that sectioned head. a side view from an even lower angle would be even better as it could help me a lot with my porting work.
going to weld this week my custom made manifold and will be posting pics too.

must say that as much as I like the 30 degrees downdraught idea, I have a big question mark about 32 mm carbs for a 125 cc cylinder
even 500 gp mv agustas fours had 29-30 mm carbs and these were four valve dohc very shortstroke designs.....
dont remember the carb size on the honda 500-4 racers of the 60's but I doubt if even those 15,000 rpm beasts had 32's
cheers from milan
TG

[speedracer741]

hei speedy

good to see you here! once sent you an email through ebay about the porting mods I am doing to my 500 racer. keeping my fingers crossed for you!
I am going quite a lot more conservative here. managed to get a nice 12 degrees of downdraft without going into welding, so a bit envious of your planned 30 degrees. my mikunis spacing lets me get fully strait ports (looking from above) so that's pretty nice already.
wanted to ask you if you could send me a high rez photo of that sectioned head. a side view from an even lower angle would be even better as it could help me a lot with my porting work.
going to weld this week my custom made manifold and will be posting pics too.

must say that as much as I like the 30 degrees downdraught idea, I have a big question mark about 32 mm carbs for a 125 cc cylinder
even 500 gp mv agustas fours had 29-30 mm carbs and these were four valve dohc very shortstroke designs.....
dont remember the carb size on the honda 500-4 racers of the 60's but I doubt if even those 15,000 rpm beasts had 32's
cheers from milan
TG

Hey there! Yes I remember your email. I typed up a huge response but when I tried to send it discovered that I had gone over the character limit. I shrunk it down until it would go but I'm not sure if you got it. I will get some better pics and send them to you by next weekend. Might post some better ones on here as well. I also have a cross section of a CB750 piston that I will put on here as I will be using those for my big bore kit. 32mm seems big indeed but this engine will be 600cc. Even with the added displacement 32mm would still present problems at lower rpm however the VE series are vacuum slide carbs so they don't really become 32mm until the engine is ready for it. This engine will be used mainly on the street so I think the use of CV carbs will have some benefit. I would like to build a 29mm version of this head for use in competition 500cc engines that will use smoothbore carbs so we will see how this one goes. I would like to see some pics of your project. Before I decided to do this one I was working on a similar build to yours that used custom bolt on manifolds but they had no downdraft, just straightened the carbs to the ports. Think I still have them somewhere.

[masonryman]

You know, sometimes I do stuff just because I can, But I don't have access to toys nearly that cool.

Good luck
Mark

[speedracer741]

You know, sometimes I do stuff just because I can, But I don't have access to toys nearly that cool.

Good luck
Mark

That's what it's all about. I have been following your exhaust build. I would love to hear that thing run!

[masonryman]

I will start it soon and post somewhere, last weekend I got distracted rebuilding the carbs on my daily rider

[speedracer741]

Here are some better cross section pictures. The piston is a CB750K. I don't have any spare F pistons but I really need to get my hands on some! If anyone has some used F slugs laying around I would be very interested in obtaining them. I cut this one to get the thickness as I will be using modified 750 pistins for this engine. It is a tried and true mod however the larger valve size requires adequate valve pockets to be machined and I wanted to make sure there was plenty of meat and there certainly is!

[rhinoracer]

I'm impressed at the amount of work you're putting into the project to end up with a single ported head.

Based on your nickname I'm guessing you're looking for an advantage over other racers, so good luck there. Let us know how it all ends up.

[speedracer741]

I'm impressed at the amount of work you're putting into the project to end up with a single ported head.

Based on your nickname I'm guessing you're looking for an advantage over other racers, so good luck there. Let us know how it all ends up.

I'm actually planning on building several of these. The first one will certainly be the most work but I am taking notes along the way and once all of the jigs are built other heads will be much easier. I have some local friends that will be running these once the prototype is finished.

[Soos]

Looks like you know what you are doing, I'm interested too see how this works in the end!

Keep up the god work, and don't scrap too many heads!

l8r

[maksuttt]

2speedracer741: I have spare set of F0 (1975) pistons in bad condition and can share one if you need.

[FunJimmy]

Anything new?

[dusterdude]

yea,this is good stuff

[speedracer741]

Well, I have been pretty busy this summer as may be noticed by my absence from the board recently. The brake rotor jobs have had me completely buried and are starting to slow down now. Plus the shop I work for has been giving me way too much port work to do, which I do flat rate on my own time at home. Bike heads, import cars and American iron, you name it I have been grinding every night for the last 3 months! The aluminum welder has left our shop and gone on to greater things and since I don't excell in that art the prototype 550 head has been at a standstill. I am however working on the prototype set of oversize valves and hope to have them completed within the next couple of weeks. I am now myspace and youtube literate so I can post video clips of various machine operations, mistakes and all....HA HA! My myspace page is: http://www.myspace.com/mpwrpdx  And no, the profile picture is not of me! It's a joke for some of my friends. Most of the pics I have uploaded are of BMW car stuff I did this summer but I will be putting up lots of bike engine work pictures over the next few months. The keeper groove grinder is up and running in its finished state now and has produced a few sets of valves, ran it today actually. I just installed a new chuck in the lathe as well. Since the 550 valves will be ready long before the head I need to find a donor engine to try them out in. Any volunteers?

[754]

Speedracer, Keep up the good work.. Guys like you move things ahead..

 Myself I have a small shop and have had my hand in a lot of projects.. really wild stuff being built around here, like

 8 sec 1/4 snowmobiles..

 125 mph single v-8 boat...

 wild 4x4's tilt levelling cabs, rear steer, huge clearance, etc

 Wild bike engines..85 hp 250 80 + hp H-D singles, Sportster with Downdraft Carbs in the middle of the tank.. stuff like that.

 Go for it its a lot of work but it will pay off..

 754..

[paulages]

Any volunteers?

chris-- if i can ever wrap up my 714cc project i'll have no need, but i have a couple of spare 550 engines laying around i was considering doing something with one in the meantime, because my current one is leaking oil like a mother#$%*er. also, i have enough frames and spare parts laying around to build up something around another motor easy, so i'll always be a donor recipient if you get the downdraft or anything else going!

gimme a call sometime--you should come see where my project is at.

[FunJimmy]

Chris

How are things progressing? Have you had time to come up for air yet?

Just checking in

Cheers
FJ

[Bill/BentON Racing]

Speedracer Go for it!,Damn I'm jealous,If I pull my Pops Head anytime soon I will post,opened up might be a decent way to describe them,I call them a work of art,they are big time noticeable esp next to stock head.Your project is awesome your head,TG's cylinder,who knows?Bill

[turboguzzi]

Hei Bellcow

would sure be interesting to know how is Spedracer's project going, the posts here are from more than one year ago

my downdraft project thread is another one:

http://forums.sohc4.net/index.php?topic=19554.0

[Bill/BentON Racing]

TG,just checked your downdraft post,how cool,I bet you did sleep well when you finished this up.I love 750's but give me a track and I want CB500/550.You said your class was 500cc's.Do you use a 500 or 550 bottom end,I switched to 550 for clutch arrangement and cases.Good Luck,Bill,Did anyone do anythig with CB650 heads? 

[turboguzzi]

I will sleep even better once I finish adapting the 29's to that head 

I am using a 500 bottom end for no better reason than that's what I have..... 500/550 parts are not that easy to come by here in italy. 550 should be indeed better.

There are quite few threads in the forum regarding tuning around 650 parts, check paulages posts and threads, he OWNS that niche.

If you are planning to race the thing in vintage, make sure to check the regulations to see what allowed and what not before deciding to use a 650 head.

TG

[Bill/BentON Racing]

TG,you deserve a 550 bottom end,we have not discussed tranny mods,what have you done? I will look for you a 550 bottom end,I think I have a 500 or 550 thats stuck from sitting.I think shifting would be improved,I used a 9 plate Action Fours kit,ran total loss,no rotor,bump start,could remove starter clutch and kickstart shaft etc.Tell me more.Bill

[turboguzzi]

Hei bill

Done all that, removed everyhting + undercut the dogs. It made a huge difference to shifting, really good now, so at the moment I am not in a hurry for a 550 bottom, though I would really love to calmly build myself a second motor with all my learnings.

I will add today a big post on gears, let's see what you have to say on the subject...

TG

[Bill/BentON Racing]

Cool,did you undercut the gears yourself ? What RPM's do you turn? I installed 86 electronic tach off GSXR750 in 86.Went thru a few stockers,they didn't like 13,000RPM+.Bill