Xtreme Cylinder Heads for Porsche

[304065]

OK, the cat has been out of the bag on these for a few months now, considering that there is a public domain website advertising them I see no reason not to bring this to the attention of the Pelican community.

These guys have broken the code, namely, how do you get 120BHP per liter out of a 911-based engine. The pictures speak for themselves.



More information here. . .http://www.xtremecylinderheads.com/index.html

Everybody's first question is "how much does it cost" but I would recommend you contact the manufacturer directly via the information in the link above." Bill, as you will see below, is a very nice guy and has answered many of our questions about these heads.

[911 tweaks]

so what is the real skinny on these 304065? Do you know anyone whom has used them and are their claims any where realistic?
Are these only for race and a short life span or can these be used for the average joe looking for a bump in performance i.e. the while you are in there kind of deal...
Thanks, Bob

[Lukesportsman]

You've got my attention. I've been waiting on more info ever since I've tried to put away any temptations of CMW's......the rough tooling just scares me of what I can't see.

[Jeff Alton]

They list some interesting clients... does anyone have first hand back to back dyno info on these??

Cheers

[kenikh]

They are legit. I know someone who has been using them far longer than the public domain has been aware. Their port configuration is pretty awesome.

[gestalt1]

am i missing something here? i went to the web site and all they have is the photo that is posted and price sheets for valves etc., not the heads. there is no info on anything about the heads. what makes them so special? how much?

[ErVikingo]

They are legit, the pieces are beatifully made also. I have the seen the raw casting and the finished product and they are awesome. I don't use them as I still have good S heads available but know people using them.

The guys are top notch and very nice to boot. Not sure of pricing but I can find out for you guys.

[304065]

For you math whizzes:

In geometry, a slice out of a sphere (which is the basic geometry of the Porsche 911 combustion chamber) is called a spherical cap.

The volume of a spherical cap is calculated as follows:

V = 1/6*PI*h*(3*a²+h²)

If you backsolve the combustion chamber volume using this formula, and make a few assumptions, here's what you end up with:



Now of course this is a gross oversimplification, because there are two spark plugs that INCREASE the volume, which means that the actual height is really less than my formula, and there are two huge flat valves, which act like chords across the surface of the sphere, further decreasing the volume-- another way to think about it is that you can pour more water into a bowl than a plate of the same diameter.

So where am I going with all this? I think these heads are an improvement on the factory-- we know that in 1970 with the 2,2 liter engine they made the combustion chamber smaller and the valve angle shallower in order to accomodate the larger valves. (My guess is 1 degree less, see below)

In the original 901 head design the valves were set with an included angle of 59 degrees. The inlets were inclined at 27 degrees from the vertical and the exhaust valves at 32 degrees. The next data point I have is the included angle for the 3,0 RSR, inlet was inclined at 25.5 degrees and exhaust at 30.25 degrees (so less by 2.25 degrees than the previous heads). This suggests that the included angle of the 2,2-2.7 heads was 58 degrees.

Anyway, by making the combustion chamber shallower it's possible to use a piston with less of a bump on it to get high compression. This is the limitation of the very early heads-- even with twin plug, the bump on the piston to deliver 10,3:1 (Porsche's racing spec) or the higher compressions common today is pretty big, making good flame propogation difficult to achieve, the fire not wanting to burn around corners. So by using a smaller combustion chamber the dome volume can be lower for the same compression and flow is improved.



Not a mystery to cylinder head designers, it just took someone to expend the enginering time and testing and signifcant tooling cost to break out of the Porsche head mold to achieve this. And, I imagine, many, many hours of testing.

Maybe we can get one of the designers to comment on this thread, or others who use these.

[xtremech]

304065, thank you very much for the positive input on the new product. We have worked very hard on this for a number of years. Recently joined Pelican, we appreciate any questions or feedback.

[euro911sc]

I had my SC heads done over there (it's 15 mins down the road). Bill is a great guy and did a fantastic job. He showed me those new heads in progress and they were amazing. He was still playing with some of the shapes, but the numbers he mentioned were good... very good. He's not cheap, but like all of the high quality vendors we all deal with you get what you pay for.

+1 for Extreme

Best regards,

Michael

Michael

[304065]

Originally Posted by xtremech

304065, thank you very much for the positive input on the new product. We have worked very hard on this for a number of years. Recently joined Pelican, we appreciate any questions or feedback.

Bill,

Thanks and WELCOME to the forum. We have tried hard to make the Pelican Engine Rebuilding Forum the #1 place to gain useful information about the rebuilding and modification of Porsche 911 engines. In addition to knowledgable amateurs here, we have a number of professional engine rebuilders who frequent the forum. We try to keep the discussion as commercial-free as possible while focusing in on the technical aspects of what makes the flat six tick.

So in terms of feedback I can only offer congratulations for taking the time to engineer a great product -- the dyno numbers I have seen speak for themselves.

In the question department, I will open it up with several of my own.

1) What challenges did the factory 911 heads present when you started the design process? Were there structural limitations of the Factory's design that made it impossible to get better flow? How does your design address those limitations?

2) What changes were made to the geometry of the head to accomodate the huge valves? And how were those changes made to work with the Factory cam carrier and rockers? It seems to me that if the included valve angles are changed, this would put the tip of the valve stem in a different place, requiring a different length stem. Is this correct?

3) Am I correct in assuming that the combustion chamber was made shallower in order to increase compression ratio without increasing piston dome volume?

4) Can you describe the development process a little? e.g. what motivated you to undertake this project, how did you make the prototypes, how were they tested?

That's enough to get started, thank you in advance for any reply. I have deliberately avoided asking you to disclose obvious trade secrets e.g. which alloy etc., let me know privately if you think anything is over the line.

Once again, WELCOME.

[MBruns]

As an engine builder and engine shop that does alot of 911 machine work along with an engine dyno that has had alot of very good 911 race engines over the last 6 years that I have been at JB Racing I must tell you that Bill's cyl heads are VERY good ! I have seen some of the same engines go across the dyno over the years from teams that support alot of customers with several engines per car and when the heads were changed to the Xtreme program they all improved alot. and thats from 2.0 up. We just built a 3.0 for an HSR customer that got the full house engine and only difference was Bill's heads and it made 25 hp more than the best OEM based cyl head to date. I am looking forward to testing them on our 3.8 engine when they are ready.
Keep up the good work Bill

Regards, Mike Bruns JBRacing.com

[xtremech]

John,

(1) The challenges that an OEM casting presents on a "performance level" are countless. Very thin cross sections in the ports combined with a significant amount of core shift makes it very difficult to CNC these heads for a desired port configuration. The design we have developed not only allows for such ports, but also incorporates stability after porting by having material in the correct areas. Another obvious concern was the age of these heads and the overall casting process which originated 40+ years ago.

(2) No changes were made in the geometry of the "standard" heads we offer. We do have the option to alter valve angles (for example an RSR 2.8ltr) and have done so in the past as a custom order, but for the "off the shelf" product, I feel simplicity is the key, and have had great success thus far. An engine builder should not have to change years of fine tuning an engine program to use our head package. Standard cam towers, manifolds, headers..etc.

(3) Combustion chambers are factory configurations. Spark plug location and "eyebrow" volume play the major role here as well as "flat faced" valves when a titanium valve is used. Again, the option is there for a custom combustion chamber.
(4) As far as the delopment process.......long,expensive, painfull education LOL. No regrets, we have a great product now and are glad to bring it to the Porsche industry. It is long overdue. The prototype testing was done on the dyno as well as on the track by some of my clients that were extremely interested in this project.

I hope have touched on the areas in question. Regards, Bill DiCondina

[Jeff Alton]

Bill,

First off, welcome to the forum.

Are these heads available for all configurations? 3.2 based motors running more displacement etc? 3.6 based motors?

What sort of gains can one expect on a hot 3.4 motor that currently uses twin plugged, but otherwise stock configured, 3.2 heads? The 25hp Mike mentions on the 3.0?

A couple of general questions regarding head design.

When one uses a performance head such as these, is the power gains spread out across the RPM band or is it down low or up high?

Is there any sacrifice to the power band in certain rpm ranges?


Sorry if the last two questions are basic, but to be honest I have never messed with the 3.2 port design for fear of buggering up a set of heads

Cheers

[xtremech]

Jeff, the castings can be machined for any 911 application. From a 2.0ltr with a 36mm intake port, all the way up to a 3.8ltr with a 44.5mm intake port and anything inbetween.
As far as gains are concerned, 20 -25 HP has been the gains on a full race prep. I do not know what the gains will be on a "stock" configuration. I will say that we have done heads for "hot" street applications with success, just no definitive numbers. The choice of port sizes is the key. A 3.2 Carrera port intake in my opinion has adequate size, just no shape to speak of.
The power gains are in fact spread out across the RPM range. The broad torque band that the 3ltr series carries has been a very hot topic.
Thanks for the questions, they are always welcome.
regards, Bill DiCondina

[xtremech]

Mike, appreciate the compliment. It is always a privilage and a pleasure to work with a top quality team such as JB Racing. Big thanks to you and Jim for all the help along the way.
Bill D

[RSstop]

Bill,
Wow! I need to get up and see your new creations.
Obviously easier than welding up ports and machining?
I am about ready to try some of your 3.6 head ideas.

BTW, Bill has been building all my 911 heads forever (15 years?)
His heads always make more power, even in stock form.
Lyn

[RSstop]

This is a set of 2.7 heads Bill did for me a few years ago. 8mm stem valves, 38mm CNC intake ports, a work of art!
Lyn

[911 tweaks]

that looks sweeeeeeeeeeeeeet !!!!!!!!!!!! and how expensive??

Was that for a stk 2.7 or a tricked out engine?

What were the differences in air flow of that head vs.a stk head?

Did it provide any useable hp on only at WOT ??

Thanks for sharing!
Bob

[911 tweaks]

typo... OR only at WOT?