Porting - make it as Big as possible or Narrow it??

[fgc]

Hi

I just got a spare head for my nord 1750 and I am curious about the effect of porting. I have both of Jim K's books for the Alfa and I was super tempted to do everything accordingly.

However, this thread is not to call into questioin Jim's work as I think he did a wonderful job, just wondering if there are more than one way to Rome, so to speak, besides enlarging the ports.

Jim's work and the increase in power speaks for themselves. Just wondering about something that I read about (autodelta??) narrowing the port dimension to speed up the charge. Why so? Seems kind of counter intuitive and yet makes sense at the same time. It seems to me that they are trying to rely on the venturi effect to speed up the charge. (I am hardly an engineer so I cannot comment other than to read with a little common sense)

Anyone with experience narrowing ports or following this process? Sorry my memory about whether it was Autodelta that did this or the Competition manual etc I cannot remember.Just that I remembered reading somewhere about narrowing of the ports from the earlier to the later version. Comments will be most appreciated.

Again, I think there are probably more than 1 way to Rome and out of curiosity I would like to learn a little more about alternative ways of doing things apart from what is there since Autodelta apparently tried the same. Just exploring before I make the jump!

The advantage of taking Jim's route is that he has done everything so I only have to follow the text book. whereas anyother way I will have to figure some bits of it out. Anyway that is the fun bit about tinkering

Thanks
fgc

[George Willet]

The ports on the engine were TOO large, and port velocity suffered, so Autodelta made up some sleeves to bring the port size into line with what worked. Later heads had even smaller ports.

Shaping the port is more effective than enlarging the volumn.

[fgc]

Thanks George for your input.

I am wondering if Autodelta, whom I suppose must know their stuff , takes to stuffing the port to narrow it, why does it seem as if this practice is so uncommon in the power mod scene?

The common understanding about porting is quite different from what Autodelta discovered and also what I understand is being practiced by some manufacturer where their later offerings of updated engine in the same capacity showed smaller port. (that could be a red hearing but anyway)

Will appreciate if anyone has any dimension or diagrams on how Autodelta did their mod to narrow the port dimensions.

Thanks!
fgc

[slyalfa]

if you google you will see where this is done a lot on bikes. some of there ports were way way too big.
they fill it with epoxy and reshape it. A big port with a bad shape can be very bad. a small port with a very good shape will be better as long as the air speed is not too fast. I think the speed needed to stay under the speed of sound.

[George Willet]

FGC, I can fax the pages on the autodelta process, or mail copies to you out of the Compitition Advisory Book. Don't think I can put them on the BB. Maybe someone else can scan and paste them for us.

[180OUT]

Quote:

The common understanding about porting is quite different from what Autodelta discovered and also what I understand is being practiced by some manufacturer where their later offerings of updated engine in the same capacity showed smaller port. (that could be a red hearing but anyway)

[Gordon Raymond]

Some of the early work on Alfa ports was done by Horst Kwech and Ron Neal at Ausca. This information was passed on to Autodelta. Ausca's experimental work went further than most realize, with tapered ports and sleeves of different tapers and lengths to essentially move a secondary venturi closer to the port. This was before the days of flow benches and is a lot like Fords tunnel port heads of the era. In the day, Ausca's attempts were by-guess & by-gosh, trial and error. There never was a final solution as cam variables were thrown in the mix. Top end only power did not win races. Some flexibility is required. Autodelta did learn, large ports did not work as well as smaller, tapered ports, and Alfa head castings quickly changed over time. Today, with flow benches, and many other ways of measuring changes in valve pockets, port angles and shapes, combined with the effect of different cams, there are many new and better designs available. While my old copy of CAS does go into detail of how to modify large port GTA heads for as much flexibility as was expected of a race engine of the time, Jim k's more modern approach has the benefit of current technology in measuring gas flow in the Alfa heads. For a much more direct view, I am very interested in Richard Jemisons comments in regards to cam design in conjunction with Alfa valve pocket, valve size, and port runner design. Perhaps Alfar7 will give his opinion of porting possibilities with more current cam designs? fgc, don't hesitate to send him a PM about your post!
Gordon Raymond

[bearbvd]

The real problem with Alfa (nord) ports is the horrifically tight 'short side' radius. Jim K addresses this with his work.

The Ausca/Autodelta sleeves addressed it in a different way--if the port is smaller, PARTICULARLY if you hold the sleeve to the TOP of the port (which Ausca did NOT do), the short side radius gets longer.

What's going on is that the short radius on the short side causes a flow separation--and the turbulent burble downstream of that point makes the EFFECTIVE size of the port and the bowl much smaller than it appears to be.

A bigger port with a gentler short side radius will (generally) work best.

Ideal intake port air speed is around 300 fps, nowhere NEAR Mach 1.

Jim K touches on the REAL solution to Alfa ports--read the part about what happened to the exhaust port flow when some clay was placed in the bottome of the port, so as to give it a D shape---no real reason why this added material can't be aluminium added with a TIG torch, and, YES, it would also work on the intake side.

Greg

[Gordon Raymond]

"The Ausca/Autodelta sleeves addressed it in a different way--if the port is smaller, PARTICULARLY if you hold the sleeve to the TOP of the port (which Ausca did NOT do), the short side radius gets longer.
What's going on is that the short radius on the short side causes a flow separation--and the turbulent burble downstream of that point makes the EFFECTIVE size of the port and the bowl much smaller than it appears to be." >GREGS QUOTE<

Greg,
Having seriously done your homework, you may also know that Ron N. (Ausca) addressed this exact issue by completely reworking an Alfa manifold and head {perhaps 1750 by then} using his "tubes" at a much higher angle through the manifold and head to straighten out the curve before the bowl. The welding, machine work and patching were amazing! By getting the runners way up there, the intake track was not only round, but straighter to the bowl. This worked well on the dyno, but was way to serious an alteration at the time, for the track. Little remained of the stock manifold. Ron's research did appear with the later GTAm's.
Your input is exactly what I have always believed.
Gordon Raymond

[genericwood]

Quote:

Originally Posted by bearbvd no real reason why this added material can't be aluminium added with a TIG torch, and, YES, it would also work on the intake side.Greg

[turbolarespider]

One of the things that you all have to bear in mind is that the head is a complete system- intake, port, valve, seats, cam profile, etc.

For the most part, the most important part is to match the porting job with the cams- as a massive generalization- high port velocities (smaller ports) match well with longer duration cams, and the opposite is generally true, too.

Big ports + big cams generally make an undriveable car....

Anyway, some of the original limitations are cam/ bucket material restrictions- with the materials on the cams and buckets you could get a certain maximum ramp rate- which would then pretty much dictate the lift and overlap all at once. With better cams, you can run more aggressive cam lift rates, and with totally different cams, get almost similar total open area/time.

The moral of the story- it's a system, and always should be considered as such- you pick the parts, and then choose the porting based on those parts.

Eric

[Alex]

Greg, Erik, Gordon, anyone!

Are you able to find and post diagrams, illustrations, photos etc of these ideas? In the past, I've only seen the briefest mention of the issue of tight port radii; and correct me if I'm wrong, but didn't someone once produce D-shaped exhaust manifolds to match a reworked port? I've seen a couple of bad photos of a Nord inlet port which had been reprofiled along one section using some kind of aluminum-rich putty (or JB Weld etc - what would be the best material to use??) but my memory of those is hazy. Instinct tells me that a D-shaped inlet port (as suggested by Greg) might require work to the inlet manifold too. Maybe Erik is right in that development work in this area (in the USA, at least) has been stymied by SCCA rules - but what about work done in Europe and elsewhere?

For anyone wanting to rework a head for the street, this looks like it's going to be a really informative thread.

Alex.

[genericwood]

Quote:

Originally Posted by Alex I've seen a couple of bad photos of a Nord inlet port which had been reprofiled along one section using some kind of aluminum-rich putty (or JB Weld etc - what would be the best material to use??) but my memory of those is hazy. Alex.

[andyb6]

Not to add confusion to the topic,but.... Most engine builders will also tell you that the flow bench results don't always transfer to the dyno sheet. I had read somewhere a number of formula's to calculate an engines performance based on displacement and intake port size etc. The interesting thing was that through the magic or porting it is possible to make a naturally aspirated motor operate at OVER 100% efficiency. The idea being that the velocity of the incoming charge could create a positive pressure charge just before the valve snaps shut. So the magic is to find the harmonics of the intake charge and create the perfect intake speed at a given rpm range.
My race engines are currently operating at only 95% but over a wide range and I am running a relatively small port for a race engine. I know of some other huge port motors that have made more power but are actually less efficient and the efficiency is not flat.

I think the intake efficiency/speed/port size is probably best learned from our NASCAR buddies running restrictor plates. Unfortunately small block, push rod V-8 data does not directly transfer to our motors.

The more I think about it the more sense it makes and the less I understand it!

[Jim K.]

Nice thread you guys got going here! Just a few notes: Most race class rules preclude adding material to the head, but they don't mention the intake manifold! I say this, as if someone wants to create an obviously more effective 'downdraft' port, they can remove all the metal they want until they get too close to the follower well. Then, they can use a specially modified intake manifold with 'tongues' sticking out to fill-in the bottom of the head ports. This trick has been extensively used in F3 where open space allows downdrafting the heads in this way.
Regarding engine VE, its common to have sports/race engines with VE's around 103-107%. My engine simulator program puts my current project V6 engine at over 105% for a considerable part of the rev-range.
As for D-ports: Over the last 2 months, I dealt a bit with making 105 2liter D-shape intake ports through alloy welding and got about 128cfm with 46mm valves. The work was far from perfect, done in double time just to see if the car would perform better and it did. We didn't have the proper electrodes to properly get inside the ports so it looks a bit crappy. No power has been measured yet but we're working on that. One thing we didn't do is optimize valve shape for these ports. Its really strange to see a D ported/welded manifold (2x45DHLA). I should have taken a pic of the gasket we made! Comparable work was done in the exhaust ports with commensurate gains. Keep in mind that we had to make a special exhaust manifold to follow the redirected flow! Having gone through this, I'd say it's not worth the effort, especially since there are high-flow heads out there like the ones available from V.Sharp. Sit back, have a good time and let someone else who's real good at it, do the legwork!
Jim K.