911 head flows

[snowman]

Originally posted by BK911
The bellmouth (clay) does makes an improvement to the airflow of the head. It significantly reduces the turbulence of the entering air. In some cases I was getting ~10% more airflow using a bellmouth.

I've flowed 2.2S and 2.4TK heads without a bellmouth at 28" Hg. My numbers for the S heads are very close to yours. But for the TK head, they are not even close.

By the way, I use a superflow too.

BK

The heads I flowed seemed to have very smooth ports, ie no bumps on the short side radius. I don't know if they were ported or the factory just did a good job on these specific heads. Check the performance without the clay at half inch opening for comparason.

[snowman]

Originally posted by 69911e
Jack: I sent you an email about sending you 2 'E' heads to flow (2.0, 2.4), and have not heard back. Are you still interested in flowing more heads?

Please use the message service of this bullitin board to send me messages. I get over 1500 e mails per day and its hard to sort it all out.

[snowman]

Originally posted by BK911
The bellmouth (clay) does makes an improvement to the airflow of the head. It significantly reduces the turbulence of the entering air. In some cases I was getting ~10% more airflow using a bellmouth.

....

BK

This is not correct. With the intake connected there is no turbulance at the head interface. The clay allows one to approxamate this condition without the intake connected. Measuring head flows without any smoothing or an intake connected is very very inaccurate.

[snowman]

PS

I have flowed my 912 race car heads, intakes, exhaust, carbs, all connected on a cylinder. I was able to maintain the max flow, 195 cfm at 28 in water with everything connected. I also filled the intake (with the valve closed) with water to the top of the intake stacks. I got 110% the cylinder displacement. The length of the intake stack is exactly correct for peaking at 7800 rpm, as well as the cam. Compression is 12.0:1,I have stepped headers, which hurts peak power a bit, but spreads it out somewhat. The car dynos 140 hp ON THE GROUND at 7800 rpm. Not bad for a 1725cc 4 banger with 80 year old technology.

For the technologh, ref :Glen Curtis, of Curtis aircraft, also motor cycles, and so forth. He built an air cooled engine around 1920 that looks just like the VW, Porsche one. He also invented, designed and built an air cooled V8, FROM SCRATCH, put it on a bike and set the world speed record with it, him self, thats right he drove it. If you ever get a chance there is a museum on the south end of Keuka Lake, Hammondsport, NY, the Glen Curtis Museum. Take a very very close look at the air cooled 4 banger he invented and built for an airplane. Makes you wonder who really invented the Vw, Porsche engine. He also received a pilots license, number 1.

[garibaldi]

Here is something that we have been working on in regards to valve seat technology. How do you think this will effect the flow?
It is a continous parabolic radius from the valve bowl into the combusiton chamber, this along with a valve seat that is convex to the seat yield a smooth transistion leading past the valve seat, eliminating the multiple angles often used in valve seats, which in turn can create eddies that disrupt the flow. This method we are working on will eliminate these occurrences and cause the flow into the chamber to pass through a true varying venturi whos effect changes in relation to the valve lift. THis is a prototype piece in the picture, so diregard the step at the edge of the seat. Would you be interested in flowing this, if so we can arrange to send a spare head for you to collect some data on.

[jluetjen]

garibaldi;
Very interesting. I have always heard various things about the incremental improvement to valve flow by using radius instead of the standard 3 angle valve job. The improvement is as you describe. The negatives which I've heard are that while a 5 angle flows better then a 3 angle and a radius flows better then a 5 angle, that it is a case of diminishing returns as well as a significantly shorter life. So if you are building an all-out 3 hour race motor (like a Runoff's motor), get the radiused valve job. If you want your engine to remain strong for a couple of seasons, it's most likely better to go with a good 3 angle or 5 angle valve job.

With your professional engine building background have you built many engines with this feature? Do you have any sense as to the life of this feature -- especially with high-pressure valve springs?

This may be worth a separate thread rather then making this one thread conveluted then it already is.

[garibaldi]

To begin, the seat to valve contact is quite small due to the radius and where the two meet, but as the progression of the valve wears in , we find that the contact margin will reach an acceptable level of about .030 to .040, due to the increased unit load in that concentrated area. Once the contact reaches this state, its further progression seems to greatly diminish as the load is spread out over a larger surface area, and it in turn behaves as any standard valve seat would in terms of load spread. We have also tried moving that process along by a light initial lapping of the vave to the seat and it works fine. This is easily checked and verified without even having to disassemble the motor by either measurin valve lash change, or by more accurately measurin stem depth in the head

[ChrisBennet]

This isn't quite the same thing but it is interesting....

"Or you can try valve seating surfaces-maybe someday you can tell me why sharp edges are better here than rounded ones. The worst valve I ever tested was one I made the mistaken belief my eye could judge how air would behave between the valve and seat. I ground a valve head with a radius instead of a flat where it seated, along with a similar-shaped grinding stone for the seat. Testing this idea required tons of work, yet my streamlined valve and seat combination was worse at all lifts than the typical series of abrupt, sharp-edged flats."

Motorcyclist June 1996: Cylinder Head Tech

[garibaldi]

Read the last paragraph of that article. It basically says that there are no real answers, and they are trying to make a science from the artform, and it jsut isnt adding up- or in brief, it isnt neceesarily so, or maybe it is.

Good article- sure sounds good, and is good brain candy, but what conclusions does it draw- NONE except that no one has figured it out yet.

SO , in repsonse to the quote you posted, there are so many variables that could effect his particular findings that as far as I am concerned, they writer could be full of ####.

[jluetjen]

Hopefully Snowman will be able to run one for comparison. Christian; do you have this feature on a 911 head?

[ChrisBennet]

Christian,
What I got out of those two article that I posted was that
(A) The flow bench doesn't measure the most important stuff
(B) What intuitively "looks good" doesn't mean squat
I posted the link first article because it bolsters your "flow benches don't win races" view and it was the nicest way I could think of disagreeing with my buddy John.
I posted the link to the "full of ####" article because the part I excerpted looked like it might have some relevance to your smooth radius case.
-Chris

[garibaldi]

Thank you, I wasnt offended by your posts at all.

I am by no means an expert on any of this stuff, and do not have all of the answers, all I can go by is my experience. Like I said, we are experimenting with this type of seat, we are trying various angles and combinations to try and yield the best results. SOme can be more detrimental than others, and that is what we are trying to decifer. The funny thing is that no matter how much "science" so many people try to put on these types of things, there is always a circumstance that comes along at the last minute and seems to defy its logic. All of the technology in mostly every aspect of society- but for this argument dealing with automotive is based on an artform. Way back when before there were computers, dynos and flow benches, guys were making hp based on a seat of the pants and experience approach. I still beleive that when all is said and done- thats what matters, since like I said, you see the technology get defied everyday without any concrete explanation as to why. At some point I think its smart to scrap the computers and data sheets etc, and try your idea, put the motor in the car and run and see what it does. Spending all of that time and energy in a lab is great, but your losing precious driving time. Youve heard the argument that a bumblebee cannot fly right?

[jluetjen]

Chris;
Your're lucky that I agree that "Flow benches don't win races", otherwise you'd have to start buying your own lunches . Flow benches DO help a person to understand one facit of how an engine works and potentially (if used correctly) help a person to optomise that facit. But it is just One Facit of the total package. Then there are the other phases of an engine's operation such as was described. Then we get into chassis layout and technology, tires, race craft, driver psychology, gaming theory, financial management, marketing, etc. etc.

The trick is to come up with the best combination of all of those things when the green flag drops. To dismiss any of them is to immediately hand a potential advantage to your competitor since you are opting to not compete at that level.

Besides, (apologies to Christian, Steve W and any other professional engine builders who are reading this), but I see a lot BS and Urban Myths in the Porsche competition industry hidden behind the "dark magic" mystique. Now, I may not fully understand fluid dynamics and combustion theory, but I DO recognise "Salesmanship" and "Creative Marketing". You know what they say -- it takes one to know one!

Now can we get back to talking about flow numbers for 911 heads which is what I think this thread is about.

[snowman]

I can flow more heads but with a tight time restriction. If i receive the head between April 17th April 23rd I will be able to flow test them. Otherwise next September thru Dec.

To flow a head I need the following:
1. the head
2. a cylinder (can be bad but in one piece)
3. intake valve, can be very used
4. exhaust valve, can be very used
5. valve keepers,
6 valve retainers.

IF you want say an intake runner and carb and exhaust header or whatever included I can also do that, but please arrange for return postage if you send any more thant the basic head (items 1 thru 6). Allow two weeks to return items.

Jack

[snowman]

Originally posted by garibaldi
Here is something that we have been working on in regards to valve seat technology. How do you think this will effect the flow?
It is a continous parabolic radius .....

The ONLY way to tell if this helps is to do a flow test. "To flow is to know".

Small changes like this can make significant changes in head flow. These small changes generally make more HP for more flow and less HP for less flow. The changes are usually less than 10% for something like this so they do not tend to affect any of the other engine chacteristics, except for AF ratio. More gas has to be added to compensate for the additional air. Carbs are self compensating. Again nothing else must be the fundamental limit for the flow, otherwise there will be no affect.

One last comment. There are several old sayings, one of which is "The power is all in the heads". There is a lot of truth to this statement. Heads seem to be the fundamental limitation on power, everything else can be adjusted accordiingly, but are limited by the heads flow performance. Thats why all the attention to multiple valve heads. For example, Variable cam timing is a great thing, but the limit of POWER is still the head. All the cam timing does is widen the useful power band, it dosen't change the peak power obtainable.

Personally I suspect that a lot more useful power could be obtained if some way to place ribblets in the intake runners could be found.. Another promising method of stuffing more air into the cylinder is to convert the airflow into a circular one, eg a tornado like flow. Notice how much faster water goes down the drain when the swirl becomes fully developed? Same thing works for air. Newer chevy heads have a built in swirl for example. Also a device called the "Tornado" has proven to work on a lot of differn't engines.

[jluetjen]

Oh no! He's said the "T.." word. There goes this thread down the drain like so much water...

[ChrisBennet]

Originally posted by jluetjen
Oh no! He's said the "T.." word. There goes this thread down the drain like so much water...

spinning water, it has to be spinning water down the drain John.

-Chris

[garibaldi]

yeah, I have been up at 4 in the morning not being able to sleep and seeing that infomercial too.

[350HP930]

A fluid will not go through a pipe any faster if it is spinning. In fact, enough spin could contribute towards the restriction of the flow.

Usually the only time anyone is concerned with swirling air around it is for the purpose of mixing stuff, like air and fuel.

[garibaldi]

or a cocktail