951_VAB

Thanks everyone for some very good info. Controversy makes the world go round!

Jon Milledge Engineering... http://www.jmengines.com/index.htm.
A couple other highly qualified engine builders: Bill @ www.autotechplus.com and Jon @ Circle Performance.

AutotechPlus is currently preparing me a 3 ltr turbo engine with the tweaked 2.7 NA head.

Dan Hix

Tomas L

After reading this I feel that the truth may be somewhere in between all thats been expressed here. I'm by no means a air flow engineer but here are my views.

I do belive that it's possible to obtain around 120% VE in a limited rpm range. However before quoting such figures as truth one should do a dyno test measuring air flow into the engine. By the way, why does no one measure air and fuel flow at the dyno these days? Is it just Superflows that have the capability? That information should be very helpful in tuning the engine.

Regarding wet flow testing I see a problem in that water is a fluid that can't be compressed opposed to air which can. That should make make wet testing different from dry. However I don't think that necessarily means that wet testing is useless. I've seen pictures of F1 cars draged at the bottom of water tanks just because it was easier to test than in a wind tunnel.
The future (for the big $ guys anyway) must be in CFD. Yesterday on discovery channel I saw an interview with a technician at Ricardo, during the interview his computer were showing the results of a CFD calculation of the flow through the intake port into the cylinder.

Regarding turbulent or laminar flow, if I remeber correctly then turbulent flow can only exist above a certain airspeed (Re number) but it doesn't necessarily forms immediately this speed is exceeded. Isn't it possible that we have laminar flow for a while after the intake port opens and while the speed increases? And is turbulence desired? I thought that flow resistance increased when the flow becomes turbulent?

As an example of the need to engineer the engine as a system we can study camshaft vs port size. If you have small port with high velocity (and maybe long runners) then you should have a camshaft that closes the valve late to get maximum advantage of the speed ramming effect. On the other hand if your port is larger then you have to close the valve earlier to avoid back flow.

The engine is a very complex system and no one knows all the facts. The people that knows most is not likely to work on 951:s or even be willing to share their information at all. Therefore I hope that we can educate each other (without useless bashing) and hopefully we then learn something new each day...

Tomas

Russ Murphy

Hear, hear.

TonyG

All I an say is one thing:

SFR 420 package which consists of a modified JME head (with additional porting over what JME provodes) with stock valves, a JME cam, race valve springs/retainers, SFR 4 into 1 header/cross over, SFR 3" exhaust, ported stock intake manifold/throttle body, stock intercooler, 60-1HiFi - full garrett turbo, MAF, Tial 46, 72lbs injectors...

375RWHP at 1 bar boost
401RWHP at 17 psi boost
415RWHP at 18psi boost

The head was was most definitely ported on both the intake and exhaust.

TonyG

Russ Murphy

The questions are: What would the outcome have been with the stock port size? What would the outcome have been with a necked-down port a la Skunk Workz.

I realize it's a little bit moot to suggest the head swap at the dyno after the fact (waayyy after the fact ), but that's the only way we'll know ultimately.

Skunk Workz

That's just what I intend to do...dyno it,mod just the head,and dyno it again,to settle the score once and for all.

Thing is...one thing about Rennlist confuses me. You all say that you go for big torque and w-i-d-e range...yet when you've modded the thing,all I seem to see is "I had THIS much peak RW-HP!!"...Seems like a little contradiction to me.

The smaller port area doesn't give you an instant quadrillion hp at 6290 rpm and 3 psi boost. It's more about the goal you all claim here,to get as much hp/tq within your rpm range...and for that range,the stock port is "slightly" too big.

And,of course a heavily "conventionally" ported head CAN work down low in the range...(more flow is in most cases better,that is,up to a point...more port area is NOT)...but if the "head" does give more hp down low,then I'm leaning to belive that the head does almost nothing of it...
altered ignition/compression/fuel-curve (to suit your mod's,of course ) low in the rpm range is the reason for most of that hp you acclaim to the head. Now I am repeating myself. Better go take a ****.

TonyG

This is not "peak" Hp.

Here it is at 17psi boost with a non bb turbo and a turbine that's too small:



TonyG

Skunk Workz

I wasn't thinking specifically about your dynorun,Tony...I was thinking in general. (but if I am picky...seems like it has peak hp at 6200 or so.. ..then again it should. )

Nice torque curve,though. How was it with the properly sized turbine? And what backpressure did you have,to claim it was too small? The torque doesn't seem to fall that much at the end...

Bengt Sweden

It's more like, "laminar flow can only exist below a certain RE or corresponding speed".
Above that, the air is ripped to pieces and the individual molecules do not adhere to each other. This leads to that the air in the center of a pipe is not slowed down by the wall friction so it is good.
But then you can have negative effect as well. You would want to utilise the full port size and especially have flow all around the valve circumference, but since the port is making a turn downwards you need to have the air to follow the short radius in order to use that part of the valve. If the short radius is too small then the air can not turn that fast and will continue to the other side leaving the close side of the valve in the "shadow". If you can maintain laminar flow along the floor of the port then it will be easier for the air to make the turn. The short radius is the most important part of the port and normally what is destroyed by too ambitious porting. Too widen the floor like on the shown heads is a good idea.

No I am not an air flow engineer, this is knowledge gained through a mix of education and listening to tell tales and some practical experience.

special tool

Tony - that's 17 psi, right?

TonyG

special tool

Yes (2.5L)

TonyG

TonyG

Skunk Workz

Didn't measure the back pressure... but I previously ran it with a .70 a/r bb turbo and it had the same lag, the TQ was in the same spot (same TQ as well), but the HP peak came in about 400 rpms later. The larger turbine was good for another 15RWHP at the same boost up top

TonyG

inactiveuser92616

Bengt... just to add some **** to the fire... I have read that laminar flow is very prone to seperation when it must "hug" to the surface rather than "push" against the surface. because of this, aerodynamic bodies actually encourage turbulent flow in some areas as it is not as prone to seperation.

Bengt Sweden

What do you mean by separation? If you mean that the laminar flow becomes transitional or turbulent you are correct.

What is an aerodynamic body? Bodies can be designed for different aerodynamic purposes like minimum drag or maximum up/down force. For minimum drag you would like to have turbulence behind the body or otherwise you would need an extremely long body. For maximum up/down force from a wing you want the flow to follow the wing and you want to use the combined forces of all the air molecules. Therefore you need the media to be able to transfer the forces i.e laminar flow.
In some cases you can design so that you get turbulence at a set speed and therefore limit downforce and drag but this is tricky since you are dependant on air density wind conditions etc.

Wing shapes or drop shapes like a 911 body have high lifting forces and high drag. Box shapes with slant nose and cut off rear have low drag, contrary to popular belief.

Bengt

ehall

"What is an aerodynamic body?"

This thread definitely took a turn for the better. I'm both learning a lot, and am also completely lost about some of it. But, one question, How do aerodynamic bodies related to ports? Other than the obvious, that air flows over/around/near both, aren't they very different concepts? Aerodynamic bodies are only affected, in our context, by air flow when in motion themselves. Yet, in our application we are talking about air being pushed/pulled in the application of a head port. Shouldn't some of the key aerodynamic concepts of each application be very different from one another? Also, there's the concept of temperature, that must have a very significant effect on the density of the air. It takes a pretty fantastic wing to fly at 100,000 ft, because of the lack of molecular density of the air. So doesn't the density have a huge effect on the different propertis of the aero bodies described, and the aerodynamic effects within a head. After all, the air in a head works a lot more like a tornado, the it does like an airplane. Anyway, those were some thoughts/ slash questions that I was having. TIA for more info. E