How To:Basic Cylinder Head Porting for Beginners

Cant say, my experience is with C1AE's. I also have some email correspondence I printed out from a few years back with a guy who was using some of the later 390 heads. Let me take a look at the flow charts he sent me, and get back to you. IIRC, he also worked the floors...

 

He was doing C8AE's with a stock 2.055 intake valve, he laid back the short-side on a .900 arc, widened the floor of the short-side substantially, dropped and blended the floor to match, and raised the roof approaching the pocket,. He wound up getting mid 260ish@ .600, which is better than the Edelbrock heads as they come out of the box.
Mine were C1AE's, quite a bit more radical, 2.15's, putty in the floor of the entrance, port-matched to a medium riser gasket, .97 floor arc, raised the roof quite a bit, still had to drop the floor approaching the short side to maintain csa, I had already opened the roof of the port quite a bit around the guide boss, and theres water there. I got close to 300 [email protected] but I was really pushing the limit of the casting. I could feel hot spots with my fingertip in the roof and sides of the port as I was porting, which tells you you are getting very close to going through(as it gets thin, it has a harder time dissipating the heat generated by grinding).

 

Thanks George.

 

I actually have a pair of later FE heads(I haven't checked, they are probably C8AE's) I should take a good look at them, and compare the port to a C1/C4 352/390 head, and see how they stack up.

 

One more thing I'll mention, I almost always go to a bigger valve than whatever was original to the casting I am working on. Theres a very good reason behind this, namely you are now cutting a new seat on fresh material. Re-cutting the original seat on a 30+ yr old cylinder head almost always results in a sunk valve, which devastates low-lift flow. Even if the casting is CSA limited relative to the new valve size, given a choice between a CSA dead-on 89/90% of the valve diameter with a sunken seat, or a 85/88% CSA with a nice seat profile, I'll take the latter every time.

If I had to choose between one or the other, I would rather be 10% too big on CSA/valve size than 5% too small. The pressure drop/port velocity on a running engine is a WORLD of difference from what you see on a flow bench @ 28 inches...

 

Thanks again, George.

HE'S A LUMBERJACK AND HE'S OKAY!!!!!!!

 

I sorta skimmed over the thread, and most of the stuff I believe is here. But I'll recap what I've picked up over a few years of working on "hot rods".

About all I'll do anymore is port match, deburr castings, blend machined areas into as cast areas, pocket port (leave a venturi under the seat, helps the mixture change directions when it hits the underside of the valve), unshroud valves in the chambers. I'll flatten the port floors in most Chevys (but not lower them) and raise the roofs of the ports on some.

When it comes to changing the shape of a port or hogging one out, I won't do it unless I have templates like Chevy made for their 292 Turbo heads. Making improvements in flow without a flow bench, lots of clay, and even more time to research what works and what doesn't is about as likely as hitting a baseball blindfolded. And you need a couple of extra heads to cut up and see where your going to drop into a water port or pushrod tunnel.

Anyway, a little work will probably help with a little flow and add a little horsepower. A lot of work could destroy your heads.

Dart Pro 1 Platinums are looking better all the time!

 

I always enjoy porting my own heads with good results, example on a 460 ford with closed chamber heads I did bowl blending and exhaust side only taking out hump common to the ford heads with no intake work at all, my theory being let the exh. catch up to the int. to get closer to a good percentage flow between the two, result being 4 tenths in et reduction in the 1/8 mile which is 40 hp.

 

i typically size up the valves....

 

Great thread and thanks to Falcongeorge for the link to Mcfarlands page.

 

X2!
Nobody can get you thinking like Jim McFarland.


Posted using two Dixie cups and a medium length piece of string.

 

Thanks Falcongeorge for the tip on things getting hot MAY be getting close to water that is a keeper

 

just be careful, its subtle, and requires some experience. I dont want a bunch of guys making holes, and saying "I didnt feel anything".

 

Wait till you get that Harold Bettes book! If you go to the speedtalk website, there are some excellent audio cd's there, Harold Bettes, Darin Morgan, Mike Chapman, Tom Kolimatsis, and Audie Thomas on cam selection with flow numbers are especially good.

 

Lots Of great info in this thread! Thanks to all who have contributed!


Sent from my iPhone using Tapatalk

 

Hey All,
Cruising through the thread, looked interesting. I actually develop ports and chambers at an engine company, and have always enjoyed sharing knowledge with enthusiasts out there.
-Aaron

 

Ok, what this thread needs is some MATH! I was planning to expand on my comments regarding csa’s and valve size, finally found the time to type this out.

The formula for calculating mean port velocity in a running engine is fairly simple, and as follows.
Port Vel.=(mean piston speed/60) x (Bore squared/CSA). Lets use the 327 I am building for my Chevy II as an example, as I already have all the numbers handy, and I am a lazy bastard. 6800ish HP peak, AFR 195’s.

So we have (3883/60) x (16.2409/2.2313), 61.3833 x 7.6499764= 469.58 ft/sec. So we need to convert this to a mach number, so 1087 ft/sec is the speed of sound, correct for a ball-parkish 100 deg. F mean intake runner temp, we get 1162 ft/sec for the corrected speed of sound, divide 469.58/1162= mach .40

Ok, just for shits and giggles, lets try the same calculation with a 10% larger intake runner. Just ballparkish, this is a 215cc head, pretty much any magazine writer would say this is SUBSTANTIALLY too big a runner for a 327 peaking at 6800 rpm. So lets crunch the numbers, and see how much this actually changes the port velocity. Mean piston speed stays the same, so theres no change to the front half of the equation (3883/60) X (16.2409/2.2313), 61. 3833 X 7.2787 = 446.78888 ft/sec divided by temp corrected speed of sound of 1162 = mach .38

So as you can see, a 10 % increase in CSA results in a 2% reduction in port velocity. Anyone starting to question some of the things they have read in magazines regarding the “consequences” of choosing too big a cylinder head? Anyone wondering about the stories they have heard about what a “stone” the Boss 302 is? (more on that subject to follow).

So far, we are looking at mean (average) piston speed. Piston speed varies considerably through the pistons motion, and R/S ratio has a big effect on said variation. “Short” rod combinations move the piston away from tdc quicker (have higher peak piston acceleration numbers) than long rod combos, so considering that the total distance the piston travels, and the mean (average) piston speed are unaffected by rod length, its obvious that the long rod combo is moving the piston faster more towards the middle of its travel (if mean piston speed stays the same, it has to “catch up&#8221. So the short rod combo is going to pull harder on the incoming charge early in its travel, and that “pull” is going to taper off more quickly relative to the long rod combo. This is why “short rod” combos tend to favour narrow LSA’s, the narrower LSA moves the opening point earlier in the pistons motion, which means that the valve will be farther off the seat as the piston is moving away from TDC relative to a wide LSA. This is why short R/S ratio combos also favour a relatively larger CSA than a longer rod combo, they initially pull harder on the incoming charge, generating relatively higher port velocity #’s in the early part of the pistons motion. The flip side of this is that the longer rod combo is going to favour a relatively later intake closing point, as it will be pulling harder on the charge as the piston passes mid travel. Of course there are several other factors influencing LSA selection, and I am making some generalizations, I am sticking with the factors that have a direct influence on head selection/porting.[/SIZE][/FONT]

 

George,
I have a theory with magazines and internet "experts" harping so much on port velocity. Basicly the lower the port velocity ( mean / peak ), the more sensitive it becomes to intake runner design and cam profile. Most shops and even aftermarket OEMS dont have the ability to design intakes and match a cam profile to utilize low induction velocity without poor run quality. So....its safer and easier to run fast ports. An engine with a decent torque curve typically has around 100m/s mean port velocity at rated speed WOT, developing maybe 65-75 hp/litre. Quite honestly small changes in rod ratio don't seem to influence cam selection or runner design, the company I work for has done the studies, and the data just doesn't support it. Rod ratios are selected for the lowest FMEP values and that seems to be the biggest bang for the buck.

 

Well, and in all honesty, while most magazine writers (and HAMBers) would think the ports I commented on are fairly "large" for the engine in question, both of the examples I sited still have what most head porters would consider very "high" port velocities. I know lots of porters far smarter than I are targeting speeds in the 250/270 ft/sec (around Mach .2/.25) range. Larry Meaux recommends a minimum mean PV of 250 ft/sec. The 327 I am building is expected to also perform well at small throttle openings (cruise rpm in OD is around 2200 rpm), if it wasn't, I would probably be looking at a larger CSA.

As far as selecting rod ratios for lowest FMEP, that dovetails fairly well with my way of thinking, but there are a lot of guys that have quite a different take on that, including some pretty well known EMC competitors.

 

FWIW, If you asked them, I dont think the magazine writers harping on port velocity could even put any sort of a number on what constitutes "low" port velocity if you asked them. I dont think they have any sort of theory at all, I think they are just talking out of thier collective asses...
But then, I am not known for mincing words, or being "diplomatic" either...
This isnt to say that its impossible to have too big a CSA, like most myths, there is a grain of truth at the very core of it, but the "too big" port is a hell of a lot bigger than what most guys would think, and if people are sweating over using a 180cc port on thier SBC vs a 200cc port, they are deluding themselves.

 

Funny thing is that in all the professional head designing companies I have worked with, you start the port design with an intake throat sized for a specific velocity, and build the port/valve from there. The object is maintaining uniform velocity, obviously. The aftermarket "hotrod" companies will have 15 different port sizes for the same valve size.....which baffles me. The racing world just adds confusion to the mix, most of them have no idea why one thing works and not another, yet somehow write books on it.

 

It sounds like you have real world, engineering and science that you can bring to this thread, which is great...do you think in general that basic gasket matching will pick up some hp in general, in most street driven cars?

 

This thread here is what the hamb is all about

 

It all depends how bad the mismatch is to begin with. It is counterproductive to "bellmouth" both the intake and head to match a gasket though as this results an a sudden increase in port area at that joint, and a loss of energy. What I will do is make my own template out of thin aluminum by first cutting it to match the head, then fitting it to the manifold, opening up the template in any areas that the manifold is larger than the head was. This gives me a template to match the parts to each other with the least amount of material removal. I have seen on current vortec SBC engines an average of 4-6hp in getting that joint lined up per the above method.

 

I've been pretty much in agreement with you till now, but this last statement is out to lunch. I dont know who you are talking to in the aftermarket, its sounds to me like you are talking to the advertising people, not the port designers.
Firstly, the focus on flow-bench numbers to the exclusion of all else is completely advertising driven, and has little/nothing to do with what is going on with the guys who are actually porting/designing the heads. Not only that, I will predict that in the next couple years, there will be a shift away from this at the advertising level as well.
Heads are being designed exactly the way you describe. Hell, I am a self-avowed amateur back-yard hack, and, if you read between the lines, its pretty clear even I am using the approach you describe, and have been for several years now.
The aftermarket is just that, the aftermarket. That means it makes improved parts for existing designs, not clean-slate, ground up engines.Taking the SBC as an example, even if you go to a 15 degree head, theres a distinct physical limit as to how big a valve (around 2.08) you can fit in a 4.155 bore with a conventional wedge valvetrain layout, thats why if you look at aftermarket heads for a given engine family, they will all end up at more or less the same valve size. That size is set by physical limits of the bore diameter/valvetrain layout of the engine the heads in question are being designed for, NOT by the guy designing the port. By the same token, you can move them around somewhat, but you have to have room for pushrods, and they have to be at least reasonably in line with the lifter bores, or the valvetrain geometry goes completely to hell, and you cant spin the engine high enough to take advantage of those wonderful ports you have just designed.
The aftermarket operates in the real world, they have to manufacture parts that racers are actually going to buy. The parts have to have decent interchangability with existing parts, and for the most part, they have to be parts that will be accepted by the various sanctioning bodies for at least some classes. That means that you have to work within certain parameters, and that gains are much harder to come by than if you are starting with a clean sheet of paper. Working withing these restrictions, aftermarket head porters/designers STILL manage to make big gains on the basic SBC platform every year. To imply that they dont know what they are doing because they cant start from a clean slate, is, well, I'll be polite here, off the mark.

 

George,
I have worked with a good number of these "race" head suppliers, including AFR. I stand by my statement that many times they don't know why something they did worked. Not saying they don't make something better, but I see many times that false assumptions are made that can confuse situations, especially when going from one engine design to another. Hope that clears things up a bit. Don't even get me started on marketing and numbers. We have bought over the years crate engines with advertised HP figures WAAAAAYYYY over what the engines actually put out, and heads that had large high lift flow numbers, but burned so horribly and were so poorly developed they made little over stock power. You are correct though that in the world of 2 valve engines, you really cant put too big of a valve in, but you can put too big of a port in.

 

Unlike post #141, I have no problem agreeing with this. Those glorious "crate engines" cripes, dont get me started. Just out of curiousity, can you clarify what you mean by "small" changes in R/S? I realize its not something thats cut and dried, but can you put a ballparkish number on that?
I was going to type a response to Larry T's earlier post about the role of flow benches in port development earlier, but got tied up in the whole port speed/CSA thing, but you have indirectly opened it up again, so I will relate this little story.
First, let me preface this by saying that this doesnt mean that flow benches dont have a role to play, or that a newby can develop a working port by just going in and hacking away whilly-nilly with a carbide. I have been using a home-built flow bench for over 3 decades, and I have learned a hell of a lot. They are virtually a necessity when you are trying to learn what the air is doing in any given port, and some time spent mapping various different ports with a pitot-tube, flow balls and a flow wand will teach a wanna-be porter a lot. I still use mine to decide where I will remove material in trying to get to the CSA I am targeting, but I don't port anywere NEAR as many heads in a year as a full-time head porter would do. But you must keep in mind that flow benchs definately have thier limitations, and cannot even remotely tell you what is actually going on in the port of a running engine. With that disclaimer out of the way, I'll move on to my anecdote.
Around 12-13 years ago, I was having a conversation with a local head porter that I have a fair bit of respect for. He had been using a flow bench for more or less the same amount of time I had, and over that time frame, had probably done ten times the number of heads that I had. He mentioned that he rarely, if ever used his flowbench anymore. I just about keeled over. HERESY!!
Six months later, I was having a conversation with another local guy I had a ton of respect for, who did a lot of stock, SS and comp elim. heads, and whose engines held numerous class records over the years, and he made virtually the same comment.
Aero's comment about designing a port around a target port velocity, and porting the head with an eye to maintaining that velocity within a relatively constant window is dead on the money, and I first heard reference to that more than a decade ago. Prior to that, I had been working along the lines of trying to get the highest flow bench numbers possible with the smallest hole possible. Since then, I have been progressively moving in the direction Aero is talking about, and my approach now is to start from a target port speed, and work from there. I'm still using a flow bench to shape the port, but the whole approach is different from what I started out doing for the first ten years, and I know for a fact that there are very savvy porters out there who have dispensed with the flow bench as part of the development process entirely. Just a little food for thought...
Aero, are your initials JS by chance?? These forums can be a little like the old game show "Whats My Line"...

 

I just realized everyone on here is going to jump to the conclusion that "JS" stands for Joe Sherman. Thats not who I am thinking of here...

 

One thing I've reciently found...
In reshaping the Studebaker V-8 intake ports, using up three different heads to learn how to gain flow, you can "port" to a given size valve, then go too large, then gain it back by using a larger" valve..!

I shaped and reshaped, keeping track of the numbers vs. the shape...lotsa pictures...etc. Then things slowed to no more gain.
I decided to try something. The flow dropped like a rock with the oversized valve (larger thAn stock) I was using at the time.
Hmmm...didn't know quite what to think. I decided to try an even larger valve than what I was testing with....what happened...the flow numbers picked up greatly.. The only problem...the valve I used required a lot of combustion chamber wall moving, which dropped the compression ratio AND....moved the already "chamber over the deck" to...chamber WAY over the deck. I'd need a 4.00" bore to use that port...but it worked..

I've done work on most American car heads and a few Offshore brands (including a few motorcycle) and haven't found lowering the floor to be benifical in any of them. Reshaping to smooth, build a smooth radius...yes, but not actually lowering the floor to the point of making the short turn radius..smaller..!?
Chryslers (early Hemi's and wedges) are the worst to get to work well.

There is also a trick in shaping the radius that gains "low lift" flow, or that benifits high lift flow. So far, I've not been able to get a good compromise.

Mike

 

As I alluded to earlier, as a general rule, the CSA should be around .89 of the valve. from what I have been told by others better than me, you can sometimes pick up flow with a CSA exceeding 90% of the valve size, but the port becomes VERY sensitive to small changes in the shape of the short-side, and its very easy to have things go all to hell over .89. Thats why I dont go over that number, my feeling is I dont have sufficient skills to make it work, and I am not a full-time professional porter.
As far as the valve cone moving out over the deck, to a degree, you can notch (scallop is probably a better description) the top of the bore. Its relatively common practice on BB chevys and 4.13 bore Ford FE's. I'm not gonna continue to debate the "dont touch the floor" stuff, it is what it is. My experience differs from yours. Thats why I didnt post anything of the original "how to port my FE heads", I wasnt interested in the pissing match that would have surely ensued.