The bowls are cut on the valve inclination angle due to the cutter being piloted on the guide. Unless a Head I am working on is being ported for all out racing then I try to not go with more then a 89% valve to Throat ratio. This will leave the needed meat to allow for a future valve job without having to install seats to gain back the same multi angle valve job I may have put into the Head. For most iron factor heads that where not designed with top performance in mind I have found that the minimum port area should be equal to no more then 94% of the Throat area , this is in sq in. In doing things this way even if I am lacking in short turn height / radius I will still have control of the air mass as it passes over the short turn . This gives me rising air flow numbers without regression at lifts above .500" as is seen in some ports. If I intensionally grind too tight radius into the short turn on some heads I can end up with what's called flow seperation / tumble at as low as .450" and get regression in my flow numbers. In short if you do not really know what you are doing porting wise I would not shot for more than a 86 % valve to Throat ratio if you are currently under 85% and just do a gentle bowl blend to meld everything back together. The factory did a good job on the stage II heads as they top 260 Intake cfm and 190 on the Exh side! If your able to get a look at those casting you can get a good idea of what needs to be done. One thing to note on with any brand Heads is that the smaller the stock height of the short turn you have compared to what you should have as calculated by the Throat size the easier it will be even when just bowl porting to get yourself less flow then what you had stock!
Ok. So you have bowl work and runner work and they are both typically done? Is bowl only the cylinder side of things or also behind the valve. Stevem, in your very first photo, you show a wire gage is that for the short turn? Only one side of the runner is the problem, right? The heads I am thinking of doing are 71 or 72's while my engine is a 70. Ill do those after I get some experience. Also how can I plug the heat risers as we don't have cold weather. I also didn't under stand the last line of Stevem's post wrt less flow as that would be a problem.
Mike this may help you see things a little better in terms of changing things on a geometric basis--- photo 1. Notice how in photo 1 that the Throat is 1.60" which is only 75.8 % of the 2.11" Intake valve used, this 1.60" Throat makes the minimum radius that the floor should be . 800". This 75.8% is a far cry from the minimum of 85% needed to make good use of that 2.11 valve! That first shot from lay last post is a lenght of solder raped around the center. ( left to right ) of the short turn from the crown of the short turn to the chamber floor. You also need to understand that in all Heads there is a 2 stage process to the flow passing the valve and entering the chamber. At low lift and low flow rates ( maybe up to .350" lift on some heads ) the air mass passing thru the port will take the path of least resistance and run on the center line of the port if its more or less a straight run the the Intake flange to the start of turn leading into valve bowl--- photo 2. The overall height of the short turn can be broken down as in my photo to a top section and a bottom section. The top section from the mid point to the crown or high point will control the velocity and hence air flow level attained at high lifts above .300" lift---photo 2. The lower or bottom section controls the velocity and hence the low lift amount of flow below .300" lift, and this includes the valve seat angles which have a large effect---photo 2. The valve seats are where between the shape of the valve and it's back angles you can with a lot of air flow testing form a Venturi which like in a Carb can achieve greater flow then 100% of the actual area you have. At higher lifts and flow rateds the air mass will more and more with increasing lifts follow the area and contours of the port--- photo 3. I hope this helps some , but this is all I have time for today!
wares GMC Gunther this seems like a topic that he could refer us to his go to guy , that one guy damm. Gunther s avatar has to rank high up there with the al bundy guy.
Hugger here's the info I have. I went back and dug out my flow sheet from back in 98 when I tested this head. It's casting number X 1235714 and I was told that it was as cast factory stock, and from what I recall it looked stock! Here are the dimensions I recorded. Intake Intake valve 2.13" with a 3/8" stem necked down to 11/32". 45 degree seat, no back cut on valve. Valve inclination angle 14 degree. Height of Intake flange 2.325" Port width at flange 1.412" Port width at the minimum area location 1.552. Port height at same location 1.910. The all important valve bowl Throat area a wapping 1.905" Intake flow numbers @28" .100"----.200"----.300"----.400"----.450"-----.500"-----.550"----.600"-----.650" -62.9-----119.5----165.5-----219.2----237-------246-------258------264.5-----267.4 This makes for a 89.4% Throat to valve size. This makes the Throat area =2.85 sq in. The minimum port area works out to be about 2.90 sq in. With port areas like this on hand there is no way that the Intake port would not flow what I tested out of it. Exhaust side. Valve 1.750" Stem 3/8" necked down to 11/32". Throat diameter 1.550" Minimum port runner height 1.865" Minimum port runner width 1.568" No back cut, Face cut on valve. Port shape and size at flange , round, 1.990"!!!! Exh flow @28" .100"----.200"----.300"----.400"-----.450"-----.500"----.550"----.600" -55.3-----99.6-----136.9----169-------180.7-----196.6----204.7----213 A retest done at .600" lift with a 2.1/4" OD tube produced 232 cfm. I will guaranty that these Exh flow numbers are correct, as they jive with others I have seen. Hugger ,By my testing the Head produced a excellent 80% Exh to Intake ratio without tube efficiency factored in, if as you are stating they maybe flow only 230 cfm then the ratio would be a a crazy high percentage for a factory head 90% which I just can't see!
No worries at all. Please hijack away. It very informative for me as I am very interested in all this.
I bought david vizards "how to port and flow test cylinder heads". So far the first 50 pages have been a disappointment as he talks about what a genius he is for building a flow bench at a very young age and how he was ahead of his time. Thought there would be more practical and techniques info. I did find one illustration to be useful to explain the importance of bowl work.
Briz, contact Bob at finish line motor sports in michigan, they just cnced my te2 heads. Minus the spread of the valves I think the ports are about the same. He does not do them in house, not sure where has partnered with to do the work but it's amazing. My heads actually flowed better than the advertised number by a few cfm almost all the way through. Ended up with 383/267 at .720 lift. I believe the number would continue to go up if I could had measured at .800, .720 was retainer to guide contact.
So what valve seat angles and back cut angles do these buick 455s like? Valve to throat ratio makes sense. But what does "the minimum port area should be equal to no more then 94% of the Throat area , this is in sq in." I'm not sure I understand the minimum port area. Thanks much!
In a nut shell all that Davids book tells you is that High velocity air wants to travel on a straight path, to make a given High velocity air mass turn around anything greater then a 15 degree bend it needs to be slowed down, and to make it slow down it needs to expand into a larger port area! On 95% of all heads to go under surgery dealing with the difference between the slower moving air making its way thru the valve on the long side ( the roof path) and the much faster flowing short side is where the game is won or lost in the quest for greater flow number! The minimum port area is also termed the port choke. On a non super charged NA. motor ( nomally aspirated ) it is this port area that determines at what rpm the runner will stop passing any additional air flow even if flow bench test show otherwise due to the port velocity being too high. There are many different places where the port choke should be placed and in reworking stock castings all too many times we do not have much of a choice as to where to place it. For the aboslute most HP the choke should be the Throat of the valve bowl and the Throat should be no more than 91% of the valve size. For non full on race use with conciderations for driving needs then the port choke should be one stroke length back up the runner from the center rear of the valve or example .
Thank you, so for most cases the port area (choke) is typically the throat. Just trying get a handle on this before I hack away at some heads. So when you say "the minimum port area should be equal to no more then 94% of the Throat area , this is in sq in." , I think I'm getting hung up on this and have some kind of mental road block.
With heads like you are dealing with we can get the Throat up to a size / area of some 89% with can pass a good amount of air , but we need to control that air coming into the bowl. By porting the Head so that the minimum port area at the crown of the short turn before the bowl is only 94% of the Throat size we have chosen to use then we have a good expansion rate as I posted up before to slow the air mass down and get to accually make that turn thru the bowl and out into the chamber.
