How a combustion chamber takes shape at HeadGames
May 3, 2010, 09:55 AM
#32
As much as people like to rely on flowbench numbers, I've seen some very interesting posts on a board where numerous Pro Stock engine builders post.
When somebody that has been winning in Pro Stock says they can change the valve job (throat to valve face ratio and valve head design included here) and it will DROP 30+ CFM but the car goes faster, it gets my attention and makes me doubt a lot of flow bench numbers.
When somebody that has been winning in Pro Stock says they can change the valve job (throat to valve face ratio and valve head design included here) and it will DROP 30+ CFM but the car goes faster, it gets my attention and makes me doubt a lot of flow bench numbers.
May 3, 2010, 10:22 AM
#33
As much as people like to rely on flowbench numbers, I've seen some very interesting posts on a board where numerous Pro Stock engine builders post.
When somebody that has been winning in Pro Stock says they can change the valve job (throat to valve face ratio and valve head design included here) and it will DROP 30+ CFM but the car goes faster, it gets my attention and makes me doubt a lot of flow bench numbers.
When somebody that has been winning in Pro Stock says they can change the valve job (throat to valve face ratio and valve head design included here) and it will DROP 30+ CFM but the car goes faster, it gets my attention and makes me doubt a lot of flow bench numbers.
May 3, 2010, 10:27 AM
#35
As much as people like to rely on flowbench numbers, I've seen some very interesting posts on a board where numerous Pro Stock engine builders post.
When somebody that has been winning in Pro Stock says they can change the valve job (throat to valve face ratio and valve head design included here) and it will DROP 30+ CFM but the car goes faster, it gets my attention and makes me doubt a lot of flow bench numbers.
When somebody that has been winning in Pro Stock says they can change the valve job (throat to valve face ratio and valve head design included here) and it will DROP 30+ CFM but the car goes faster, it gets my attention and makes me doubt a lot of flow bench numbers.
These huge port heads with crazy high flow #s and large valves don't always work with ones combination and there is a good reason for that. But im not the one to be explaining why so if someone else wants to take the time then they can explain it much better then i could im sure. 
May 3, 2010, 10:45 AM
#36
Simple pysics as a previous poster stated. Air moving into a chamber is going to slow down to fill and take up said volume. When you're talking about the flow# it can be huge, but if you're not supplying enough air via the turbo in your car, it's going to react the opposite of a venturi. The bottom line is more air = more horsepower, but you have to be able to deliver it to the combustion chamber. The air we speak of is the air going thru the filter/MAF/turbo/intercooler/associated piping/throttlebody, intake manifold, cam duration and lift to valve size/seat volume. All of which is drag or restriction for the air pathway.
May 3, 2010, 10:48 AM
#37
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we have seen flow numbers mean less when making big hp per cubic inch as well. During our 2JZ race program, we tried a big flow number head thinking it was the best thing and the car slowed 2 tenths. It was only 15cfm better then our best. The smaller port made more power. And that is on a 1800hp engine.
May 3, 2010, 10:57 AM
#38
The thing that surprised me the most about the post I was talking about was that it wasn't even a change to the port. It was a change in the valve face angles, the throat diameter, and the style of valve used. Same size valve and the port was only affected to the extent that the throat diameter change had.
It would seem like gains in that area would translate to HP gains as those areas I would think would have a minimal impact on air velocity. My thought was completely wrong in comparison to what a world renown head porter had to say though.
The suggested throat to valve face ratio was up in the 0.91-0.92 area, quite a bit higher then the 0.82-0.85 ratio I have often heard about. Maybe that high of ratio is only applicable to certain conditions that see a lot of rebuilds due to the small seat contact area?
It would seem like gains in that area would translate to HP gains as those areas I would think would have a minimal impact on air velocity. My thought was completely wrong in comparison to what a world renown head porter had to say though.
The suggested throat to valve face ratio was up in the 0.91-0.92 area, quite a bit higher then the 0.82-0.85 ratio I have often heard about. Maybe that high of ratio is only applicable to certain conditions that see a lot of rebuilds due to the small seat contact area?
May 3, 2010, 11:09 AM
#41
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Exactly. I've seen drifto's car and have spoken with Tedb enough to know that neither of them just go and throw unproven junk at their setups. If it's good enough for those guys, It'd be good enough for anyone else on here.
May 3, 2010, 12:58 PM
#44
That could very well be the case if the 1800hp 2JZ in question can't generate enough VE in its present form to utilize the larger port. We have to remember that the 1800hp is coming vastly as a result of increases in air density, while the port characteristics affect air volume. The presence of a turbo is a fudge factor that tends to obscure mechanical efficiency.
Changes in the shape of the backside of the valve, seat angles, etc., all affect the final picture, and we haven't even mentioned swirl and tumble.
We can talk about static flow data, but it's a bit like talking about camshaft lift and advertised duration while omitting things like LSA and LC. It paints things with a broad brush, but the devil lies in the details.
We can talk about static flow data, but it's a bit like talking about camshaft lift and advertised duration while omitting things like LSA and LC. It paints things with a broad brush, but the devil lies in the details.
May 3, 2010, 01:38 PM
#45
Agreed, my personal perspective is that I'll either limit my self to very minimal port clean up and bowl blending on the 4G63 with just a simple 3 angle valve job and the stock valves, or I'll rely on track results to select a professional to do the work. I've just seen too many flowbench numbers as a companies claim to fame when it's not that hard to make the flow bench say it should make 20% more power since it's flowing 20% more air...