When gauging GM iron heads for big flow gains the two main conciderations I go by are 1) the fact that on average I have .180" of port wall thickness to work with if rust and core shift are within reason, 2) how much overall short turn height I have to work with. Heads in there third valve job can right off the Bat cut back on the Intake flow of a max porting job by 15 CFM if I can not go up to a oversized valve! In regards to. Buicks I have only worked on nail heads and 455 heads and never ground them out to the point of punching thru a port wall.
Once again, sound advice. I'm hoping the other forum readers differentiate between 'grinding through a port wall' and intentionally removing or replacing a major feature for the purpose of extreme output. The old days of Pro stock stacked and milled heads aren't that far behind us. I've not yet done that to a sbb head. Looks like a piece of cake if someone wanted a max effort engine and insisted on iron cores.
I have a quistion for you Steve and F85, I have flowed a head or two in the past and was getting noisy turbulence at around .510 or so lift. So I used my small flow ball and found that on the floor in front of the ssr it picked up some cfm and quoted down. So I took back the ssr a little at a time and it started to bring in cfm a little at a time. Also got a smooth sound and not noisy . Picked up about 15 cfm at .500 and .600 came in real nice. My quistion is by smoothing down the ssr as needed does that kill TQ? I couldn't tell the difference on the car but have read defferant opions. I am getting ready to do a set of sbb heads, great thread
Specifics would be needed to quantify the supposed torque loss...err, numbers would make this make sense. Are you talking about losing some torque well below the existing torque peak due to the head's CSA already being 'big', or is this following theory that peak torque might be shifted up 1-200 rpm based on the fact that it does when there's a slight slow to the airspeed and that peak torque rpm is calculated based on how it factors to the size of the cylinder? I see many times the torque go up due to higher VE and lower pumping losses. Lower rpm torque shouldn't drop, except at the extreme end of the powerband... far below where you should be running it.
I have seen a few articles where they say you mess with the ssr and you kill TQ. I haven't seen that yet but was wanting a couple opions. I do realize there is more to it than just grinding down a ssr. Guess it really is head specific. I do recall having around 395 to 410 FPS at at the floor on the ssr and tubulance. Started takin king it back a little and I just kinda widened it a little and it settled down the noise and went to aroun 340 to 360 FPS and cfm went up. I didn't notice any TQ loss. I am gonna start a sbb set later this winter and find this thread very informative:gp:
I edited my above post for clarity and it seems like your flowbench steered you to the right direction. Now that you can use your tool to quantify and verify a change, you can begin to disregard generic hot rodding articles as the 'too vague to be useful' trivia they are.
To answer the question about the potential of the 350 heads here is some info. Bill Mah and Scott S. From this shop here: http://www.shafiroff.com Built this engine here for fun on the weekends and I have talked with bill extensively about the head porting and they did raise the roof on the heads and modified a stock iron intake for the effort... They had 290 flow on the intake and it made 550 HP at 8:1 compression NA and used a roller cam, 355 cubes, eagle billet crank, billet rods and good pistons. No block girdle. Then they added the boost... Edelbrock replesentatives were at the dyno testing where it made 1021 hp and they even made a prototype Buick 350 head but it needed more revisions than Edelbrock was interested in so it was dropped.... Bill did caution about cracking head issues due to the overporting... The engine was put in a car and ran 8s according to bill. Tomorrow I will post flow sheets and pics of level 3 gessler 350 heads. http://www.v8buick.com/showthread.p...uick-350-ran-8s-in-the-quarter&highlight=1021
A word of caution about reporting any power figures with nothing but raw CFM numbers, as in order for it to be believable one must know where every molecule of air and fuel is at any given point in nanospace within the runners, their ratio to each other, factor in atmospheric impurities introduced when the earth was forming, and measure the gravitational influences given by the event horizon threshold for the nearest black hole down to an atomic level, in order to calculate the accuracy down to thousandths of inch pounds. Or we could just use rounded numbers using whole integers and call it close enough based on other realistic atmospheric conditions that will always be there to influence an engine's output on a day to day basis.
Good stuff, I remember the thread! I guess my question was more along the lines of 'has anyone taken the head beyond the limitations of the casting? What were some results?' as more of an interesting read. Any engine is exactly what you design it to do. The limitations aren't difficult to see. Other than the love for a particular engine...not too many builders aren't going to spend time working with a platform unless there's someone paying for their time. My contention is that the valve job, valve, and chosen geometry will ultimately dictate what the head can do. Any limitation in a casting can be overcome, to the level of commitment any skilled builder might give to it. (no splitting hairs here, lol)
A guy I showed my sbb heads to, that works at Livernois Motorsports, wanted to weld up, fill, & straighten runners out to get the very best flow. Big $$$ Let's hope the new TA aluminums will have some of this incorporated in the design. I still may seek his porting expertise on a spare iron set if needed. I could see his wheels turning as he examined my port work. I liked his thinking.
Well I know Bill hit water a few times and a few sets of heads were ruined in the pursuit of greatness... I know he learned a lot though trial and error. I know that Greg Gessler did some epoxy on the floors and raising the roof on some 350 heads I posted the pics on here at some point. Have you read this thread? http://www.v8buick.com/showthread.php?120529-350-head-project&highlight=heads And regarding the comments about the CFM air flow and how it is not the end all be all of head performance it is a benchmark for comparisons... Of course the professionals such as Chris Skaling who is porting my alum 350 heads know far more than CFM is needed to give good Dyno and track performance... But they still talk CFM because there is no other well recognized and repeatable metric to compare head flow.
Exactly. Cross sectional area and velocity formulas are readily available....but those are the #'s not often shared. Nor do they always equate from bench to bench.
One of the best things I've purchased was a sonic tester. Get a small probe so you can get it down ports, but... For aggressive head porting, simply drilling some 11/32" holes for small pipe plugs can get your eyes almost anywhere.
What your describing is the inability of the air flow to follow around the the most high speed part of the short turn which in a paired port head is on the common wall side. This tumble action as others and myself call it is the air getting pulled off the crown of the short turn and trying to merge back in with the air coming down the back of the bowl/ long side,which of course it can not do and hence the flow drop off you have seen! There is good in this as it means you have a lot of air avalible at the port area that resides at the crown of the short turn that you just need to get control of again. This tumble action is a sign that you need a taller short turn and a wider one. The width of the short turn needs to be the width of the valve bowl throat for as far back up the runner as you can go without blowing thru the port wall, and as much of this width as possible needs to be once again on the very active side of the port which is the common wall side. Height wise in terms of the short turn in iron heads we can not easily add material to make it taller so We need to fool the air flow on coming across the floor into responding like the short turn is taller. To do this we lay it back to a softer arc, but this new arc must compliment the throat size we are using. I will post a picture of a template I make up to do such , and it is just a 90 degree arc of the throat size I happen to be using. One thing to keep in mind is that it's the total amount of air trying to make it over the short turn that adds up to tumble issue, so one other possible cure is to reduce the amount of low lift flow the port has to reduce the total air mass that the short turn has to deal with. Another thing to keep in mind is this,if you view the short turn as being a upper and a lower half height wise as you look at it from the bowl end is this. The upper section ( mid point to short turn crown ) controls the high lift velocity and hence high lift air flow numbers. The lower section controls the low lift air flow, so we are basically taking about the valve job angles. On some heads I port I have so much velocity to control that around most of the short turn width I can only have a 2 angle valve job going on , and many times most of the second angle/ bottom cut I have ground away, yet the port still flows very well at low lift, to the tune of 220 cfm @.300" lift! also keep in mind that on most heads up to about .300" lift the Intake air flow that it's passing will take the path of least resistance, which means that tge air mass is using as much as possible the center line of the port. As air flow levels go up with increasing valve opening then the air mass more and more will start to use the contours / shape of the port! In light of this you can also see how the air arriving out of the flange of the Intake Manifold can have a big effect on air flow numbers and not just due to the port area that it may have. 45 degree seats or steeper will trick air flow into thinking that we have a taller short turn and inturn produce greater high lift flow , but at the expence of low lift flow, so this may not be the way to go! For most motor builds that are not all out full time race it's better to have the fattest flow numbers you can around the 1/2 lift point of whatever Cam you are running. remember high VE numbers are made at the overlap period where tuned header system is pulling new Intake charge in much better than the motor can on its own on the Intake side. Also the ram action produced by this keeps packing the new Intake charge in well after the piston has started up the Bore on its compression stroke. I gotta go now, more latter!
You guys really know your stuff. This is all very fascinating and educational, and I want to thank everyone for participating and sharing. This old dog can still learn a new trick or two. The head work I've done was mainly working with the existing engineering and keeping it mild, and so the porting/smoothing is easy for this, and respectable gains can be had even at this basic level. What you guys are talking about is out of my experience level, but it's great to read and learn more! Thanks again to all.
I still think using raw CFM figures can give a decent idea of what one might be able to expect, even if it's off a bit from what you'd see on a real dyno (which can vary as much if not more than software from dyno to dyno!), saying nothing about the correction factors that practically make no two dyno runs the same, even on the same machine. There are soooo many things that contribute to how the numbers turn out, and in real world usage, would vary greatly on a day to day basis. So what we end up with is simply using ballpark figures, and so I think software dyno simulation can be a useful tool, rather than just simply a plaything or toy that one would do for amusement... I can understand and respect why people would want to keep some things 'secret', even though head porting has been around for a long time and there's really not much left to figure out (although there's still plenty for others to learn who haven't gone this far before). As I've said before, telling someone how it's done and being able to do it are two different things. Head porting is metal contouring, and requires experienced, artistic and scientific hands.
had to dig for some other info to chew on. it is 7yrs old but useful Quote from Kallita in National Dragster -> Top Fuel Dragster - Doug Kalitta - { High Wing DownForce model } April 2003 Houston, Texas 10 Feet Elevation { NHRA specs } 30.04 Sea-Level Corr.Barometer, 66 deg.F, 45 % Rh, 91 F Track surface 60 Ft= .847 330 Ft= 2.150 660 Ft= 3.058 - 279.04 MPH 1000 Ft= 3.822 1320 Ft= 4.486 - 333.91 MPH 2250 Lbs. 496 CID 4.187 Bore x 4.500 Stroke Peak HP= 7933 @ 6715 RPM Peak TQ=6205 { 8550 RPM limit } 6.8:1 Compression Ratio , 2.400 Intake 1.940 Exhaust valves 39.3 % overdrive on Blower 62 deg BTDC at Starting Line & 58 BTDC at Finish Line 1.940 / 2.400 = .80833 E/I Valve Ratio 2.020 SBC Chevy Intake Valve = 1.632 exh Valve at that same Top Fuel Supercharger application the Power is on the Intake side !
Porting heads properly is mainly Geometric and scientific, art work comes from the time involved and the shine of a polish job! Unfortunately steady state flow numbers as seen on a flow bench do not at times directly relate to the HP that can be made , the ratio of 4 Intake cfm @28" H2O per HP may not pan out,as in a real running motor the Intake flow is constantly stopping and starting as the valve opens and closes. Everytime the air flow stops it needs to put back into motion again and this takes energy ( remember nothing is fee in life !) and although high port velocity is good, above a certain level it just restrains air flow at a certain point as all the energy has been used up! As it turns out if your going for max all out racing power above 6000 rpm you do not want to have Intake port velocities anywhere in the choisen Manifold or head port to top / exceed 350 FPS, on lesser motors you can work with 450 FPS if that's what's seen at the motors rpm of peak torque, but once 600FPS rears its head all addition power output is done, its Fork time!
