Porting and polishing - $1500

I built this machine based on research I found in university aeronautical lab websites, as well as information I found reading the NASA website and Efunda. The main intake tube after the intake elbow is over 6 pipe diameters long because that was what has been shown as a minumum to stabilise airflow and negate turbulence before the air strikes the orifice plate. The downstream tube is over 4 diameters before any disturbance to prevent upstream turbulence. I put a sheet metal vane type air flow straightener/difuser just inside the intake tube at the elbow flange to further stabilise air flow downstream. The differential pressure ports are 1 diameter ahead, and half a diameter behind the orifice plate flange, because thats where its been found that the air is the least disturbed. I built an air flow control valve (actually the entire machine) out of 4 inch PVC plumbing parts. The valve is a PVC "T", and I made a plug that just slips inside the throat of the T, connected to a long threaded rod. I can screw the plug in or out through the top of the bench top to regulate air flow, and its located far downstream so to have no effect back upstream at the orifice plate. If I ever want to reverse flow to blow through the exhaust, I would only need to swap the main tubes around end for end and blow air through. I would have had them equal length, but I just didnt want to take up the entire wall so a compromise was made. I suppose its not real user friendly, but its about as "scientifically correct" as anything I could find. I also made the machine so it comes apart in sections should I want to take it apart for storage, or modify any paticular section later on. I already dont like the flow control valve and want to make a new one, so having it in sections helps that idea as well. It all connects together with bolted toilet flanges with gaskets between. The only possible addition I know of that would make it more accurate at this time would be a pitot static tube upstream of the orifice plate for velocity readings, but I believe this should give me numbers about as accurate as possible as long as I get the math correct. Ive calculated my orifice plates at .65 flow Cf by calculating the Reynolds numbers, I'm calculating true air density with an aircraft altimeter checked against the local AWOS station, dry and wet bulb temp readings to find dewpoint to further narrow air density figures, etc., etc., and I seem to be getting repeatable numbers of air flow after corrections, which from all I have studied so far, repeatable numbers at different air densities would tend to indicate its fairly accurate.

All I ever wanted was a Ferrari that ran under its own power. Thanks to people like Russ, Will, Dave, Mark, Kermit, and others, I dont even really work on the car anymore, lol. And if it wernt for the myriad of online calculators that can figure out all this math stuff for you, I would still be lost. All I have to do now is answer some easy questions and it figures it for me.

 

Ive ran three tests this evening, with and without the manifold again to test my previous numbers, and with and without the carb. Without the carb I still consistantly get 79 CFM, but with the carb attached it climbs back up to 84.8 CFM. Tomorrow I'll try playing with clay.

 

I told you so

The air tumbles if you have a sharp corner at the entrance so the number will be low and any port work you try to do will probably be wrong in the full assembly that doesn’t have the sharp entrance.

About a 1” radius works very well, bigger doesn’t work much better but smaller hurts. It doesn’t need to be a full 90* radius either, as long as it flares at least ¼” or so per side it will work pretty well.

Before you break out the grinder, measure the port cross-sectional area in a few easy to repeat spots. I think you’ll find the smallest area is right at the flange for the manifold which is not where you want it. Ideally it will be at the seat….so you’ll have some grinding to do and you’ll pick up 8-10 cfm. Then of course you’ll nee to open up the manifold….but there really isn’t enough metal to open it up top optimal…..then the carb will be too small. It’s a viscous circle.

 

Don't tell anyone, but I cheat on my math/calibration work. I don't measure air temperature, presure or anything else when I'm flow benching. I have a plate with 3 orifaces in it and I know what they should flow a STP (Standard Temp and Pres) from the math. I measure the plate at the beginning and end of the session and use those results to correct the data for the day's conditions. No anything that can go out of calibration ever and all the results are normalized so they can be compared with no questions. Also, I put the oriface on top of whatever cylinder I'm using to adapt the head so any different in the way the cylinder to bench interface flows is also removed.

 

Your correct, thats exactly where it is on all 17 ports. I dont plan to do any grinding until I have a better understanding how the air is flowing through or how best to improve it.

 

That is the beauty of a practice head, no worries about over grinding

Once you finish all your base line stuff, what I do is add a thin film of clay any place I think needs grinding and work it out nice and smooth. It the flow goes down it's safe to grind, but if it stays the same it isn't safe to grind. It takes a long time to develop a port a little at a time..clay then grind, clay then grind. If you grind and nothing happens then don't touch it again, it's right in the edge.

I think you will find that if you open the the flange area to be larger than the seat area and make the port taper the whole way you will see significant flow and velocity improvements (the critical velocity is at the seat where the air enters the cylinder the fact that you've lowered the velocity up stream will have no effect on cylinder fill or low end performance).

Good luck!

 

Call these guys- http://www.performancecylinderheads.com/mainpage.htm

 

That is certainly somewhere to go if your not interested to know or learn anything deeper, just send in your heads and pay the man his money. But thats not what this is about. A few people in the past have suggested (some have done it) simply port (gasket) matching the engine while they were doing a major service or had the carbs off for rebuilding, etc., would increase power, and I myself was interested in doing something simularly as well. And Russ insistence that a flow bench should be used to actually measure any changes is how this all came about. So the work I am doing is simply to prove or disprove if its possible for the average Joe with a 308 to gain some engine performance by simply and cheaply port matching the manifold to the head. If your not interested, thats great, but im not doing all of this work just to hear myself breathe.

To those who are still interested, I currently have been working on a port that had a choke point at the gasket to manifold interface very simular to a 308. Opening it up in that area and blending the entire port into a constant taper should have increased air flow, but has so far only worked to decrease the original flow rate by almost 18%! So as far as I understand at the moment, I would advise that going in and willy nilly port matching a 308 intake port without a flow bench could cost you HP. But I will continue to work with this and if I find something that shows promise I will pass it along.

One thing to consider about that 18% decrease in flow, however, is that so far I am only working with a test pressure of 10 inches of water. Because head porting is so secretive, its difficult to learn much of the secrets from the people doing it. But we should understand that as air flow/velocity increases, air behaves much differently. Im still working to learn what kinds of speeds and pressures are being seen within the port and combustion chamber, but it should be of interest to know that some are testing cylinder head air flow at 60 inches, to as high as 190 inches or more of water. So while I am currently showing a decrease of flow on this particular test port, at higher test pressures it may actually have worked the opposite way, as the air would have been acting as more of an incompressible fluid, simular to water. In actual engine operation, the air is bouncing like a pogo stick inside the port against the opening and closing valve, and continuously changing in pressure. There is fuel mixed with it too, which further complicates its physical behavior, many many factors come into play that are far outside of simply watching flow rates on a flow bench. What im trying to say is that even though I lost measurable airflow, it may in reality still show up as an increase in HP because of other factors.

 

Paul,


fun isn't it

Dropping flow is dropping flow at any test pressure. I have seen literally 100s of heads ported at 10” including a bunch of race and dyno shoot out winners. The problem is not your test pressure, there is something wrong with what you're doing, but it does clearly illustrate why you never ever ever grind on a head without a flow bench.

The first thing is how did you open up the choke? Normally you want to take all the material on the top of the port whenever possible.

The second question is how are you blending it in? The flow past the guide very very sensitive and no one answer works on all heads but I’ve had the best luck going tall and narrow instead of wide. The second place that is even more sensitive is the tight radius on the bottom of the port at the seat….never ever ever remove material that will make that radius tighter.

I would say you want to start filling things back in the clay and try to figure out where you’ve over ported. With a drop of WD-40 on your finger you can get the clay perfectly smooth.

 

I bought a Ferrari, thats what I did wrong, LOL.

I guess if your not afraid to show the mess your making in your basement I can come clean too. I port matched one of the heads on my first 308 over two years ago. Had I known then what I knew even a year and a half ago I wouldnt have touched it without a bench. And with what I know right now today, I am positive I can make them work better. Had Russ not been so insistent that I flow the heads to see what the changes did, id have assumed I improved it. Now I have a lot of work to do.

All I have done is take out the shelfs on either side of the ports where the manifolds didnt match and blended into either side a short ways to smooth the surfaces back to roughly match the original finish. Im nowhere near the guide or anywhere down inside the head, its all at the gasket area, I simply smoothed the pathway.

At the port openings in the heads its more or less a round hole but there is no rhyme or reason to thier shapes, they appear more randomly ovoid. The tops of the intake manifold carb openings range from 41 to 43 mm, and again a goofy randomness, some dont even appear perfectly round. The valve seat inner bore diameter is 37 mm, and is the only place there is any real consistency. The choke point is at the manifold gasket area, with choke points all varying in size from slightly smaller than 31 to just under 35 mm, the average around 33 mm. On the head I "corrected" the choke point is 34 mm. Some manifold ports match really close, some are offset over 1/8 inch, some offset high, some low, some to either side.....nothing consistent in any way. And incidently, the gasket is angled to the flow, so any shelf could also cause rotational swirl one way or other depending on which way theyre offset. I havnt checked enough ports yet to find an honest answer, but I surmise the cylinders are all over the place flow wise. I think they just eyeball burnished the intake ports and manifolds seperately and tossed it all in boxes, then put motors together out of whatever parts they pulled out of the box that day. They never "flowed" or port matched these things at the factory in any way shape or form, if they had you would see their work. I really hate to say anything discouraging because I really love these cars, but it looks like someone was pretty inebriated when they put these together.

Mark, I think the port needs to gradually and consistently taper down from the carb base toward the pocket area. But the only way I know how to test that theory is to make some type of model. Would you agree?

 

very punny

Yes, a taper to the seat is what you want. It's really the cross-sectional area that you want to taper, not actual dimensions. The air doesn't really care what shape the port inlet is or if the smallest dimension is 30 or 40mm, but it does care about the cross-sectional area.

 

Paul
Keep up the hard work .You are definately teaching me something .I was going to do exactly what you did "port match the maniolds at there interface ". Now I'm not touching them until I learn more from this project . Thanks

 

I popped one of the heads from the other motor onto the machine and flow tested all four ports. #1). 86.1 CFM, #2). 83.1, #3). 84.6, #4). 85.8. Thats an almost 5% difference from low to high.

 

Paul a while back Robert from Louthancomp posted some really great pictures of the inlet port that he does .I think for someone who is looking to port there heads and does not wanting to learn something in the process Robert is your man . For the guy's who want to pay school fees and learn the hard way them selves .I think there's quite a bit we can learn from his picture's .I'm not sure I am alowd to repost the pic's so I won't at this stage . You can see quite clearly from his picture that he works the long side radius at the valve seat and his ports are quite off set as they come towards the carb flange .I'm sure you have studied those pictures just want to make sure .

 

I think talking to Carobu would be a better bet. They have a lot of experience porting ferrari heads and have flow charts and DYNO numbers for all the work they've done.....Louthancorp doesn't.

IMO the stock intake valve is already too big for the flow numbers the heads make, putting in bigger valves to try and avoid buying a proper cam seems like a mistake and that is really what the Louthancorp job did.

 

2 valve 308 heads need weld on the bottom of the port, and need to be D shaped when done. You won't get that done for 1500. Not even close. Better spend the money on a cam, and live with the weird powerband.

Art

 

There are epoxies that seem to hold up well on intake ports, but I think you could get at least 10% to maybe 15% improvement with re-shaping before needing to add material. It's still a $3k+ job before you start in with epoxies or weld though....unless you build a flow bench and do it yourself