Topic: 750 Homebrew port job

[Brantley]

10 hours of proper work will yield huge results. A production machine would never get that time.

if you rewrite that as "10 hours of proper work{by someone experienced in port modification} will yield huge results {in the upper RPM ranges}"  I would be happy to agree with you.

However if you write it "10 hours of work{by an inexperienced shade tree mechanic} will yield huge results{ in all RPM ranges.}"  I will disagree.  I have seen way too many heads ruined by someone with a die grinder and a set carbide burrs.

Well, hows about sharing some of that knowledge your keen eye has experienced? There are five photos showing my work and all I'm reading from you is that mildly porting/ matching the ports is beyond the scope of the average "shadetree". I didn't start the post to ask whether I should do it... it's done. No turning back. I posted photos to ask folks that have done it to say, "although our medium is three dimensional and photos are two dimensional: I see nothing wrong/ I see this, this and this wrong, do this/ you have completely boned this head, go find another". It seems "someone experienced in port modification" that joins a forum might want to share a 'lil knowledge rather than serve to further mystify it. Let ya know how it runs in a few weeks.

[Brantley]

Ron and R R- What do y'all see? I can take more pix?

[Retro Rocket]

Ron and R R- What do y'all see? I can take more pix?

The job we did on my car was not done with ccing the ports , we made up a template for the port openings to keep them all the same size externally, then shaped the first port trying to straighten the inlet tract as much as possible, we then used that as a guide for the rest of the ports, i have no doubt that it could have been done more accurately or even using fluid {alcohol was suggested} to measure each port volume accurately but in the end it worked unbelievably well and made a huge difference to the cars performance.
I think its great that you made an attempt at it by yourself mate, the way i see it , there was no porting manual originally until someone tried it for themselves, worst that can happen is that you need another head....Yours looks fairly mild but should make some improvement. Don't be afraid to polish the hell out of the exhaust ports, gets the gases out faster which also helps...

[MCRider]

Ron and R R- What do y'all see? I can take more pix?

I am not qualified to comment on someone else's work. I just know that many have done it successfully at a rather amateur level. Mine have all been done professionally.

[cgswss]

I did try to help.  I was the one that told you that we found best results with a slightly rough in take port – no finer then 80 grit.  BTW, that is only true for the Intake port, the exhaust should be as shiny as you want to make it.

I also tried to tell you not to take too much out and slow down your intake speed.  Despite what some will say, if you make the intakes ports bigger, the engine will have to spin faster to get the intake velocities back up to most effective speeds.  I am NOT a fan of removing part of the valve guide, and would never have that done on a street bike.  This is the place where the “art” of porting takes place.  The perfect port would have the exact cross section area of your carb all the way to the valve head.  Well you sure can’t take that valve out of the middle, so the trick is to remove stock around that valve guide area to still get the same cross section area as the round part.  Where I have seen too many home grown port jobs go wrong is removing a lot of metal BEFORE  the valve guide.

So my suggestion to a porter would be to remove very little other then casting marks and keep the intake port a little “rough” (80 grit)  work mostly on the area where the valve guide obstructs the port.  On the exhaust side polish the hell out of it and remove material only from the port where the valve guide is.  Both side do everything you can to match the port to the manifold.

And again, I would recommend putting your time and money into a 3 angle valve job.  This requires special reamers and machine work on the valves.  The goal is to get a narrow seat that unmasks the port as quickly as possible.

…………

In answer to your question about my porting experience… I have never ported a 4stroke head.  I’m not qualified to do so and back then I was working mostly on customer bikes and would not take the chance of ruining one.  HOWEVER I have build up a lot of  engines with ported heads, test drove a bunch of them and been part of the dyno testing on a lot of them.  You have to remember I was working on these things when they were NEW.  I originally raced Nortons and set a lot of B mod records with them.  Our source for most of our porting was a guy we called Sammy G.  He did a lot of work on small blocks and raced a few chevy powered gassers.  Every time we went over to do a Dyno run on an engine with a ported head, he would be their- weather he did the port work or not.

When the CB750 came out our big trick was putting Kawasaki 3 cylinder motors in Norton frames to make screaming fast but stable Drag bikes.  (most of which ended up in the hands of street racers).  If you ever rode one of those triples in a stock frame you would understand why switching frames was so “trick”.  So in ’72 it was natural for or biggest efforts to go toward making Kawasaki 4s go faster.  And we build and raced Kawasakis until about ’78 when we switched over to Suzuki.

Even thought our race bike were Kawasaki powered, we had a lot of people bring us Hondas.  And we had a lot of people come in asking us to use them for port work (If you wanted a head done by Sammy, you better hand us a $500 bill about 4 months in advance.)  Our standard reply was we has access to a dyno, if they would build an engine with their port job (with stock cam and valves) we would dyno it and depending on the results we might use them.  My brother in law bought the very first Honda 750 and upgraded every time they came out with a new model.  And each one he bought we converted to the ultimate “cheater” bike.  Perfectly “stock” looking but with all the best go-fasters inside- then fine tuned on the dyno.

Any way I can remember 6 different times we had test engines this way.  And each time we would do a run on Jim’s engine as a “control”  We were NOT expecting their test engines to come any where near Jim’s- his had a good 30hp on these stock camed engines.  But his engine was consistent so if his engine was 5hp down from the last time we ran, we knew to “fudge” the numbers for the test engine.

Anyway, while the test engines varied, not one of the 6 produced as much HP under 3500-4000 rpm as a box stock 750 (Jims engine before mods)  Some of them pulled very strong 5000-9000 area before they “ran out of cam”.  At least 2 of them didn’t even get to the performance of the  box stock engine under 7000.  The best one we tested was done by a guy that made his living doing Hemi heads.  It pulled thru the mid range like a big bore bike and at 9000 produced 7hp more then stock.  Sorry if this disappoints some of you but that was a total of 72 hp on basically a “new” motor.

We did throw some work this guys way, but he was far from a home brew porter.  BTW he was $200 cheaper then Sammy.  He even offered his engine to go in my drag frame (I was between engines at the time)  With his full on engine (porting, multi angle valve job, big cam, springs and the prettiest set of rocker arms I have ever seen)  I got that engine down into the high 9s.  I only took it out for 3 weeks (5 races) because it wasn’t legal for modified class and it wasn’t completive in drag bike class.  So I ran it in “run what you broung”  races and always got paired up against some guy on a Harley with and extended frame that I had no chance against.  (I got my revenge a month later when my Z1 race engine was done<G>)

[Brantley]

I did try to help.  I was the one that told you that we found best results with a slightly rough in take port – no finer then 80 grit.

Granted. Take into consideration I am also a shadetree photographer working with a LED flashlight and a phone camera. It's not as shiny in real life. And a lot less artsy...

I also tried to tell you not to take too much out and slow down your intake speed.  Despite what some will say, if you make the intakes ports bigger, the engine will have to spin faster to get the intake velocities back up to most effective speeds.  I am NOT a fan of removing part of the valve guide, and would never have that done on a street bike.

Again, I probably mistitled this thread. Perhaps "Homebrew port matching job" would be better. And perhaps photos of another port for reference. The only parts of the intake ports I've made larger by removing aluminum are the parts that were already that size (feel?) in another port- such as #3's valve guide still has less material surrounding it from the factory than what I removed in #1. Trust me, I ain't standing ankle deep in a pile of aluminum shavings nor is my sandpaper actually bleeding; I'm trying to err on the side of caution. Thanks for the input.

[RRRToolSolutions]

Hi Brantley, I was reading through this thread and said I'd just keep my comments to myself until I realized you don't live far from me. We have an outstanding builder and porting specialist within an hour of both of us. He works for Clements Racing and has been their head porting tech for years. They have won Builder of the Year several times and his engines have been featured in every venue of racing. He builds cars, boats, Harley's and Hondas.

Back in 2006, I bought a K4 for $112 on eBay with 9,000 original miles, but still very rough. After some time to think, I decided to build a period hotrod - something that looked stock, but with Kerker, K&N's and since the plugs had been removed years before it sat in the rain (mold covered the bike), I had to go with a forged 836 Wiseco overbore kit to get rid of the rust inside the cylinders. I had never ran a ported head, but gave the head to Bobby and told him that I wanted a great "street bike" and would be adding a cam and heavy springs. After talking with Buzz at Dynoman, I bought his titanium retainers and Kibble White valves, keepers, guides, and valve springs which Bobby installed after doing his porting magic using a flowbench and a Serdi valve job. After I assembled the engine and restored the frame and components, it ran so strong, the brand-new factory clutch would not hold at 8,000 - just when the front end would be coming off the ground with stock gearing and the stock carbs. I actually bought and installed a Dyna 2000 with a rev limiter to keep the engine from going over 8,500 rpm in fear of the stock rods failing (they will fail).

After several nights of pondering and 600 miles, I pull the engine down and have the crankshaft balanced (checked) special-order a new set of Carrillo connecting rods ($1,000) a new set of CR29's road-race smoothbores, and install a new engine/primary chain, and install all new APE heavy-duty upper and lower studs. I've never looked back. Bobby's porting made all of this possible/necessary. The Jerry Branch article mentioned above states clearly that the stock head will NOT flow over about 8,000 rpm. Flow and velocity have to be substantially improved in order for the engine to breathe and reach volumetric efficiency at higher rpm, else horsepower is not going to result. My stock looking CB750 will pull the wheel off the ground under acceleration only in 1st and 2nd and stock gearing. I have a KZ900 Kawasaki that I restored 5 years ago and even with mild port clean-up, new rings, ceramic coated pistons, and all new stainless valvetrain - is no match for the little Honda. I've owned several H2 750's triples and the Honda will out perform them stock and with chambers and pods.

I mention this only in-case you just want to spend more money. Getting your head ported by a professional will mean you'll have a lot of other areas you can work on.  Just remember that if you do get that fire breathing started, you're going to need some performance rods and a great profile camshaft, some valves and springs, then a good pipe to scavange the spent gases. It's all about how much you want and are willing to spend.

Regards, Gordon

[Brantley]

Gordon,
 Interesting. Most of my build is a K4 I got from a buddy for $100 and it sat in a leaky, rust holed, corrugated metal shed without the dipstick in the oil tank and oil pressure switch. The rust on the con rods and valve stems made the decision to use the K5 mill that'd been sitting in the "engine room" of my house for 10 years. At least I knew it "ran when parked"...
 I'm sort of taking the same direction, but on a stricter budget (for now). The plan is to use stuff I already have. The cyl. is already bored to 836. Bead blasting the stock springs and rods, APE guides and cylinder studs, replacing cam and primary chain, K0 cam. And, of course, a valve job.
 Thanks for the heads up- please PM me Bobby's info or Clement's location. Not promising I'll use 'em this time, but that info is handy for a new kid in town. Where are you? Shoot me a further PM if you head into AVL; I'd love to see the bike.
Eric

[RRRToolSolutions]

Eric, I'm south near Seneca, SC. I'll send you the phone number on PM. Here are some photos of the build -













Regards, Gordon

[MCRider]

Wow!       

[Scott S]

 Brantley and Ilbikes, I'm not too far from either of you guys....over in Rock Hill, just south of Charlotte.
 Here are some pics of our homebrew P&P job on a 550 head. I only have ~115 miles on the bike so far, but it certainly doesn't seem to be lacking anything down low. No driveability problems either. I'm still waiting on the rings to seat, but there's definitely a surge at 5-6K rpm. (CB650 cam, 1.00mm overbore).
 port matched manifolds


intake

exhaust

various



We also polished the valves and lapped them in. Knowing what I know now, I would've sprung for a 3-angle valve job, too.

[Scott S]

 And I have to add....this is a mild P&P job. We could have taken more out of the "football" and sharpened it up more, but this is a street bike and we didn't want to go too far.
 We looked at pics of professionally ported heads and used them as a guide, as well as talked to some local head porters and got some pointers from them. They said it looked good. The bike feels great, so far.

[RRRToolSolutions]

I'll never forget an article I read some years ago about flow. Bigger is not by anymeans always better. Without experience, it is possible that you create eddys which actually reduce flow and cause puddling. A port has to do two things - first maximize the volume of flow and maintain the velocity of the flow so that the cylinder can still be filling even when the valve is being closed - That velocity and size being matched to the other components is key. Unless I'd had the years of experience to test/feel what works and what doesn't or have access to a flowbench where improvements can be precisely measured and compared - I'm going to leave my porting to a Mick Rieck or Bobby at Clements Racing.

I love the 500's and have had 2 of the 1972 CB500 Fours. As I understand them, the heads on those flow mush better that the CB750's did stock.

Best Regards, Gordon

[lucky]

I DID NOT SAY.... "And Lucky, there's no way a 3 million dollar DYNO was used on every machine that left a few different factories."

Go back and read again.
Get you facts straight before you attack me.

[Brantley]

Gordon- The "before" similarities keep piling up. But I had a hog rim on the back. Bet yr jealous. I saw some of yr older posts during the build and admire the attention to detail. Got yr pm and will holler at ya soon.

Scott- Saw previous posts on yr build, too. Thanks for the photos; I feel a bit more confident in what I've done. A three angle valve job is definitely required on mine. Every head is either chipped, dented, mushroomed or is super pitted after removing the layer of carbon in an attempt to polish...

Anyone know how the quality of Vesrah valves is these days? Kibblewhites are a bit overbudget... (drag)

Lucky- Uh, attack? Mild sarcasm, maybe. I didn't see the pertinence of the post in response to Les's. I'll be over in time out pondering my decision to have a little fun on a motorcycle forum if anyone needs me.

[Retro Rocket]

Do Manley still make valves for these bikes.? I have Manley valves in one of my engines....

There's a stock sized set of Manley valves at Cyclex, scroll down a bit...

http://www.cyclexchange.net/Used%20HighPer%20Parts%20Page.htm

[Brantley]

Funny you mention that. I was thinking 'bout those when I figured out mine were shot. What's your experience with Manleys? I mean- the name almost sells them itself... Then I started thinking of the fact the last time I ordered from CycleX was summer of '09 and they were in the used parts section for a good two years prior. Lack of popularity, reputation, Ken forget they sold X number of years ago? (oops, there I go having fun again...)

[Retro Rocket]

I can't comment on the ones i have except they were in a very fast drag bike and i am going to use them in a 970cc engine build..  Manley has a pretty good reputation.

[754]

 Man I cant wait to see what a ported head will do to my next built motor. I ran stock with a good 3 angle valve job with a RC 315 and 836 kit, and it was niot done pulling at 9500.. If I get any increase at under 5K it will be breaking the tire loose throttle only.. it did with the unported head.

 BTW I believe MReick recommends grinding some off the stem of Manleys, and using lash caps.. they are soft..