D type ports

[RJM3]

How does this design of ports make the head so much more efficient? thanks for any information...regards jer

[JohnC]

1) I believe the "D" shaped port is usually found on the exhaust side of the head.
2) The "D" shape mintains a higher gas velocity in the port.

The gas velocity on the "floor" of the exhaust port is typically stagnant or very slow. Most of the flow occurs at the top of the port. By lifting the "floor" the gas velocity is increased due to a reduction of the turbulent air caused by the slow gas speed at the bottom of the port (floor). I suppose the effect on the gas is similar to a larger radius turn......or somethin' like that.......

[RJM3]

Thanks John I get it....hmm...wonder if they're worth the cost???regards Jer

[ChrisBennet]

How long to patents last? It patent for the D port was granted in 1981. I tried posting a link to it but that didn't work. Cut and past the link at the end of this post.
-Chris

http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=/netahtml/srchnum.htm&r=1&f=G&l=50&s1=4,302,935.WKU.&OS=PN/4,302,935&RS=PN/4,302,935

[Rich911E]

A patent granted in 1981 expired 17 years from the date of issuance (they are not affected by the General Agreement of Tariffs and Trade (GATT) which has changed the patent term). Consequently the patent expired in 1998.

Once a patent has expired, you are free to practice the patent. It is not proper to mark items as patented (e.g. "US Patent No. 1,234,567") once the patent has expired. People still think it is patented and shy away from copying it that they are otherwise free to do.

Rich Murphy

[Early_S_Man]

Some of you out there are consuming too much caffeine before typing!

The only reason ports are EVER D-shaped, or rectangular, is when a desire to increase the port area is constrained by some object ... whether an injector boss, stud, dowel pin, water jacket, etc.

The simple fact is that the US patent office is staffed by clerks and lawyers, not engineers or scientists ... so you will find plenty of 'mumbo-jumbo' in patent applications! It is purely intentional, and designed to confuse, intimidate, and appear 'original' in thinking!

How about some nice rectangular ports on your 911 heads?

[Rich911E]

Early S Man:

Sorry to disagree, but the substantive review of all patent applications is conducted by the "examiners" at the USPTO, almost all of which ARE scientists and engineers. Almost everybody I deal with at the USPTO examining corp in Art Group 1600 is a Ph.D. Very few of the USPTO staff are lawyers.

Regarding the "mumbo-jumbo" in the patent application, the statute (35 USC 112) requires that the "written description" of the invention be sufficient to enable one of skill in the art to practice the full scope of the issued claims. Consequently, the text of the patent application is drafted to encompass alternatives sufficient to enable alternative embodiments of the invention. A narrow description of the invention leads you to only very narrow claims which can easily be "designed around" and makes your patent worthless. Nothing in the specification is designed to intimidate or confuse.

If you disagree with the "originality" of an application, perhaps you can spend some time reviewing the patent applications which are now published 18 months from their priority date and submit relevant prior art to the examiner to avoid these "unoriginal" applications from maturing into issued patents.

Secondly, JohnC's description of the port flow is correct.

Rich

[jluetjen]

I'd venture that JohnC and Warren are both correct. Ideally, both the intake and exhaust ports would be a straight shot right to the valve. One of few breathing compromises which I've seen in 911 heads when compared to other heads is that the ports have to make something resembling a ~75 degree turn. There is where I could imagine the D shape port providing a benefit (operative word is imagine!).

Lots of engine have sharper angles that that, not to mention (as Warren has) push-rods, water jackets, etc. In classes where it is allowed, it is not uncommon for people to weld material to heads and then recut ports with a considerably reduced bend. If you can get the angle down to 45 degrees or so I guess there is a significant improvement.

So I propose that you're both right!

- John

[Early_S_Man]

Rich,

You are entitled to your opinion, though you obviously haven't examined many approved patents from 20 - 50 years ago ... confusing language abounds ...

Funny, though ... you won't find any D-shaped ports in any pure racing engines designed over the past 80 years or so ... but, then racing engine designers aren't too concerned with patents ...

[Rich911E]

S Man:

I would hazard a guess that I have read a few more patents than you have and I do not find them to be misleading. They can be quite exhaustive (my personal record is 171 typed pages) and it can appear confusing and wordy but there is a reason for it.

Racing engines do sometimes have D-shaped ports. It depends a lot on the RPM range in which the engine is to operate and the degree of curve necessary to the exhaust port. If you are free to design the engine with short exhaust ports and nearly straight shots from the valve face to the exhaust system you can deal with the radius problem in the exhaust pipe and make the curvature nice and long. However, if you have to make a 90 degree turn in 2 inches of exhaust port, the difference in velocity between the top and bottom of the port is substantial. As JohnC pointed out, it is to maintain a high exhaust gas velocity -- it you are running flat out all the time maintaining velocity at low and midrange piston speeds is not so much of an issue. However, if you are trying to maintain high velocity to scavenge the cylinder effectively, the D-port will provide an advantage. There is also a slight anti-reversion advantage to a D-shaped port exit into the round exhaust system when operating at low RPM because the exposed wall of the D port inhibits return into the port.

Rich

[TimT]

I guess the debate is on regarding CMW cylinder heads. D shaped ports provide better scavenging. have been used on indy cars, and tested and possibly used on 962's