Topic: how to port 500/550 four cylinder head?

[kranta]

so, i was thinking to do mild porting to my cb 500 four and i havent done it before so, how i get muchest power from porting? and should i take every irregularities out and which kinda spots i should take? and how i know that in every intake holes have same kinda porting? and what tools i should use? should i use sand paper or tremel ?
sorry about bad english!

[Powderman]

Porting is not something that can be accomplished by the average DIYer. You can seriously destroy your head if not done correctly. There's an art and a science to porting for gains.

[SOHC4 Cafe Racer Fan]

Porting is not something that can be accomplished by the average DIYer. You can seriously destroy your head if not done correctly. There's an art and a science to porting for gains.

Yep.

[jeffg]

I have done porting, sure it is true you can damage things, but you can also do a good job yourself.

their are basically 3 stages:
1 Polish
2 case match, casting flaws.
3 reliving areas that are unneeded to create more flow.

case match:
 is, in my opinion easy. All your going to do is cut, grind casting flaws, and case mis match. With a careful eye it is, this is easy to spot.

polish is pretty easy as well, you can buy a bit kit from summit racing for polish.
I had a 1/8 pneumatic grinder from harbor freight worked great. I had carbide bits for the die grinder from northern tools.

It is a very noticeable power difference to complete case match, casting flaws, & polish.
I always did it on my dirt bikes, and once on a v8 408 stocker motor I built.

If I do a cb750 - 836, someday which I expect I will I will definitely do a stage 3 port polish.

Cutting can go bad because if you go to far you will go through a jacket!
keep In mind when going to 1 extreme, usually requires additional tasks, lumpy cam, pods,...

[Powderman]

I have done porting, sure it is true you can damage things, but you can also do a good job yourself.

their are basically 3 stages:
1 Polish
2 case match, casting flaws.
3 reliving areas that are unneeded to create more flow.

case match:
 is, in my opinion easy. All your going to do is cut, grind casting flaws, and case mis match. With a careful eye it is, this is easy to spot.

polish is pretty easy as well, you can buy a bit kit from summit racing for polish.
I had a 1/8 pneumatic grinder from harbor freight worked great. I had carbide bits for the die grinder from northern tools.

It is a very noticeable power difference to complete case match, casting flaws, & polish.
I always did it on my dirt bikes, and once on a v8 408 stocker motor I built.

If I do a cb750 - 836, someday which I expect I will I will definitely do a stage 3 port polish.

Cutting can go bad because if you go to far you will go through a jacket!
keep In mind when going to 1 extreme, usually requires additional tasks, lumpy cam, pods,...

The art of porting is knowing what "areas are unneeded to create more flow." Most of us have no clue what those areas are or how much to take away. Take away too much and you create less flow, slower flow, etc. none of which will improve performance.

[SOHC4 Cafe Racer Fan]

It's not just about maximizing flow, but as much about getting the right flow pattern according to what Mike has told me. Some things are probably better left to pros.

[seanbarney41]

I really have not inspected 500/550's ports, so I don't know what they really need, but if they are anything like a K1 or later CB750, all you have to do is take a peek down the ports, think about airflow, and you will see why these ports are garbage from the factory.  CB750 ports are often so bad, that as long as you are careful, don't expect huge power gains, even a clumsy child with a piece of 80 grit(that would be me) can't eff 'em up any worse.  Get Hondaman's book, go slow, just clean up the major problems(there are plenty), and don't surface finish the intakes too smooth.  Obviously, pros like Mike R. are gonna get better results, but he is also gonna make you pay for his experience, as well he should...

An easy thing to do to help visualize basic airflow/fluid dynamics...get a clear hose for your shop vac and a big pile of sawdust...

[RAFster122s]

HondaMan has some guidance on the forums about it and there is one thread where a fellow did HondaMan's recommended mods.  I don't have the links handy. Search might yield results.

HondaMan also takes on work rebuilding motors and mild/moderate head work.
MRiech does it for a living and knows how to yield excellent results.

If you give it to someone,  then they need to have experience with the Honda CB heads.

[camelman]

I ported the head on my 350f and it made an unbelievable difference. I went from downshifting going up a particular hill at 60MPH just to maintain speed with only me on the bike to staying in top gear and accelerating up that same hill with a passenger. I had never ported a head before, but spent a few weeks reading all of the articles I could find online. I ended up using a Dremel tool with sanding drums as well as some flapper wheels. Take your time, think it through, and CLEAN it up when you are done.

[seanbarney41]

Cal, or anyone else for that matter, do you have any pics of an unmodified 500/550 port?...because if they are as bad as a 750 port, the pictures from the linked thread are probably better than stock.

[seanbarney41]

the ports on that linked thread are destroyed by a knucklehead with a dremel. They are not even close to equal in shape or volume, off center to the intakes, and way over-worked! That head is now worthy only as a piece of alloy scrap. A new head has been substituted and a professional will do some tuning and polishing on the ports.

Are stock ports on these motors poor and very restrictive? Sure. But that doesn't mean anyone with a Dremel and an outlet should take to them. Polish them up, sounds fine. But grind on them and reshape them? I wouldn't go near it. And seat of the pants dyno results are anecdotal horse hockey in my book.

well alright then! so this must prove that the only way to improve performance is to spend thousands of dollars and don't bother trying to learn anything because someone else collecting those dollars already knows far more than you...and I agree the butt dyno definitely does not work, especially when your butt is not seated on the seat, going down the road

[seanbarney41]

Yeah , your right.  I promise to give up learning new skills and will just throw money at all of life's challenges from now on.

[Retro Rocket]

Sean, what Cal is trying to say is that without the knowledge, the trial and error method is born to fail many times, thats why experst do the investigative work using flow benches, unless you are just cleaning up the ports, poor castings and the like, not many people I know have an "accurate eye " or know how to measure accurately a port and combustion chamber, Jeffg said "polish" the ports, thats completely wrong for the inlet side of the head, you should only ever polish the exhaust ports, the inlet ports need a rougher surface to correctly atomize the fuel. correct porting is quite a complexed thing to do and a very easy thing to completely screw up, cleaning up the ports isn't porting as such,  and is far easier to do....

[SOHC4 Cafe Racer Fan]

Sean, what Cal is trying to say is that without the knowledge, the trial and error method is born to fail many times, thats why experst do the investigative work using flow benches, unless you are just cleaning up the ports, poor castings and the like, not many people I know have an "accurate eye " or know how to measure accurately a port and combustion chamber, Jeffg said "polish" the ports, thats completely wrong for the inlet side of the head, you should only ever polish the exhaust ports, the inlet ports need a rougher surface to correctly atomize the fuel. correct porting is quite a complexed thing to do and a very easy thing to completely screw up, cleaning up the ports isn't porting as such,  and is far easier to do....

There are some skills I'd like to develop. This is one that I'm out of my depth on tools-wise and knowledge-wise.

[seanbarney41]

cleaning up the ports isn't porting as such,  and is far easier to do....

this is all I am really saying....with the added caveats that cb750 ports got a LOT of stuff that obviously needs cleaning up(still hoping someone would post some pictures of stock 550 ports.  perhaps they are not as bad as the middle year cb750 ports and thus easier to "ruin"), and I am positive that M. Rieck was not born with a die grinder in hand turning out 90 hp sohc4 mills.

I never said anything about polishing the intake ports and agree it is generally a bad idea

I also never said anything about diving in head first with a die grinder and the biggest carbide burr that fits to create a huge pile of aluminum swarf without doing any research...and if someone would actually look into a cb750 port and note the factory port match "swipe" that was done, at the factory, along with fairly massive amounts of casting flash, and think about it for  a few seconds, they might realize that, with a few specialized tools and quite a bit of care and time, this should be able to be improved substantially

and if a stage 3 port job from Mike R. is really only $300...well...that is just crazy

[Retro Rocket]

Sean, what Cal is trying to say is that without the knowledge, the trial and error method is born to fail many times, thats why experst do the investigative work using flow benches, unless you are just cleaning up the ports, poor castings and the like, not many people I know have an "accurate eye " or know how to measure accurately a port and combustion chamber, Jeffg said "polish" the ports, thats completely wrong for the inlet side of the head, you should only ever polish the exhaust ports, the inlet ports need a rougher surface to correctly atomize the fuel. correct porting is quite a complexed thing to do and a very easy thing to completely screw up, cleaning up the ports isn't porting as such,  and is far easier to do....

There are some skills I'd like to develop. This is one that I'm out of my depth on tools-wise and knowledge-wise.

I have a friend that ports performance car engine heads, he spends a lot of time making templates {changing external port shape on inlet and exhaust}  and fluid measuring, I watched him port my Old SLR holden V8 heads, he took about a cup of metal out of each head, they were a work of art and made a huge difference to the cars performance, {ask the gearbox}  ...

[Retro Rocket]

cleaning up the ports isn't porting as such,  and is far easier to do....

this is all I am really saying....with the added caveats that cb750 ports got a LOT of stuff that obviously needs cleaning up(still hoping someone would post some pictures of stock 550 ports.  perhaps they are not as bad as the middle year cb750 ports and thus easier to "ruin"), and I am positive that M. Rieck was not born with a die grinder in hand turning out 90 hp sohc4 mills.

I never said anything about polishing the intake ports and agree it is generally a bad idea

I also never said anything about diving in head first with a die grinder and the biggest carbide burr that fits to create a huge pile of aluminum swarf without doing any research...and if someone would actually look into a cb750 port and note the factory port match "swipe" that was done, at the factory, along with fairly massive amounts of casting flash, and think about it for  a few seconds, they might realize that, with a few specialized tools and quite a bit of care and time, this should be able to be improved substantially

and if a stage 3 port job from Mike R. is really only $300...well...that is just crazy

Cool, and I agree with what you are saying about cleaning up the casting rubbish, still, someone will screw it up, its inevitable... , I threw the polished bit in as there is still a lot of misinformation and opinion on what works best.  I think the $300 is just for port work, nothing else, No valves, seals, guides etc....

[scottly]

I ported the head on my 350f and it made an unbelievable difference. I went from downshifting going up a particular hill at 60MPH just to maintain speed with only me on the bike to staying in top gear and accelerating up that same hill with a passenger. I had never ported a head before, but spent a few weeks reading all of the articles I could find online. I ended up using a Dremel tool with sanding drums as well as some flapper wheels. Take your time, think it through, and CLEAN it up when you are done.

Hey C-man, didn't you put together a make-shift flow bench so you could compare relative flow before and after? I also seem to recall a major core-shift issue with one port?

[flatlander]

(still hoping someone would post some pictures of stock 550 ports.  perhaps they are not as bad as the middle year cb750 ports and thus easier to "ruin")

i have pics here but they are not great. they don't show enough to really understand what's going on but may be better than nothing.











and after mike had a go at them:

[BomberMann650]

those look nice.

not that you'll ever see that work at work on the road.
covered by manifolds and all

[flatlander]

transparent head and manifolds and exhaust headers would be a good idea to show off the work. until then these things stay the internal secret of the engine

[seanbarney41]

3 hp gain on a otherwise stock 550?  That's close to a 10% hp improvement...yeah, you are going to notice that in the seat of your pants.  Cal, I know you want more and I will not argue that there are free performance lunches being handed out anywhere, but if all I can afford is a bruised apple, I ain't gonna skip that meal.

[camelman]

Scottly, you're right and good memory! I did make a flow bench to test my head and it was very helpful for tuning it. I shifted an exhaust port by a bit, but tuned out the shift using my makeshift flow bench. I had Reick build a head for me a year later with new valves and a stage one port job. He did a great job and that head was a vast improvement over stock, but my port job made much broader and higher power. Not a knock against Reick at all because we were workibg towards different goals, and I definitely recommend his services.

BTW, I thought my porting thread was posted as a sticky, but I can't find it.

[camelman]

Cal, the only other things I changed with the two ported heads I worked with were the top end gaskets. I might have a leg up over others on these types of things since my first engineering job was in flows and heat transfer at GE Energy on gas turbine engines (100,000+ HP engines) where flow characteristics were highly critical. However, the work needed to correctly port a cylinder head isn't rocket science and a simple flow bench can help balance out the ports as they are cleaned up.  I cut a lot of material out creating domes above the valves and cleaning up the intake and exhaust tracts, but even simple cleaning of the ports is going to yield a smoother idle and better power. Combine cleaner ports with matching intake boots to the intake ports, and you're going to notice a difference.

The flow characteristics I was working towards were: decreased turbulence; decreased pumping losses; more laminar flow expansion for increased pressure recovery; and flow acceleration directed more accurately at the valve face.  Again, spending a couple weeks reading about this online will give you plenty of empirical knowledge to work with, so engineering experience in fluid dynamics isn't necessary.

[camelman]

Meh, I was being lazy earlier when I couldn't find my old thread. Here's my original post on how I ported my head: http://forums.sohc4.net/index.php/topic,67722.msg747109.html#msg747109

Turboguzzi made a great point towards the end of the thread about molding the ports to see what they really look like. I never figured out the spark plug length issue.