It is currently Sun Aug 20, 2017 12:04 am

All times are UTC - 5 hours [ DST ]


Forum rules


Please click here to view the forum rules



Post new topic Reply to topic  [ 35 posts ]  Go to page Previous  1, 2, 3
Author Message
PostPosted: Sun Aug 23, 2015 12:28 pm 
356 Fan
User avatar

Joined: Thu Mar 27, 2008 4:16 pm
Posts: 486
Location: San Antonio environs, TX
Tag: '63 S/R project, '80 911SC, '11 Cayenne
Hi Edwin,

What you see is what I've got. Those are mufflers from the Honda 900cc twin engines. Figured that since two of our cylinders rate at about 800cc each (read I'm staying with the original cylinder filling Porsche used back in the day), a slightly larger muffler volume would be better than less. Weight wise these SS mufflers from Honda are about the same as the larger original steel muffler Porsche supplied when our tubs were new. I'll always agree that Porsche knows what they are doing, but, I'm looking to up the anti by inserting later exhaust technology to the mix of my projects solution.

I've followed that principle with all the modifications to my project. The twin plugs in the heads, the dry sump upgrades from the 911 approach to oil flow and cooling, even the direct oil pressure and flow to the rocker spindles that are hollow and a perfect place to introduce better oiling and cooling to the engines top end. Better cooling to the heads has been one of my project goals. And yes, the fan shroud is a 911 style with a modified 12V Bosch 911 alternator producing more amps at 6V than the original generator ever considered possible. If Porsche were developing this engine today, what would they do differently to improve on their earlier technology. Nothing stands still, and I like all that has come forth since the time our tubs were state of the art.


Attachments:
IMGP8990.JPG
IMGP8990.JPG [ 4.11 MiB | Viewed 1459 times ]
Top
 Profile  
Reply with quote  
PostPosted: Mon Aug 24, 2015 8:24 am 
356 Fan
User avatar

Joined: Sun Apr 13, 2008 7:48 pm
Posts: 173
Location: Hillsborough, NC
Glen:
Your exhaust tubing and muffler solution is an elegant solution if it all fits, as I hope it will for you. Please share your exhaust tip when you get it mounted.

No doubt the folks on the 912 Registry would be interested in this thread, as some enthusiasts there are experimenting as well and showing their results. What length of tubing have you employed? I was wondering what part of the power band you were focused on (extraction from resonant exhaust pulses, etc.).

Best,
=rdsieber

_________________


Top
 Profile  
Reply with quote  
PostPosted: Mon Aug 24, 2015 1:20 pm 
356 Fan
User avatar

Joined: Thu Mar 27, 2008 4:16 pm
Posts: 486
Location: San Antonio environs, TX
Tag: '63 S/R project, '80 911SC, '11 Cayenne
Hi Ron,

There are several tubing lengths involved that appear critical for proper extraction resonance and what advantages can be gained from what is called the reflected wave resulting from the initial reflection of a given pulse from the first instant an exhaust pulse engages a muffler's baffle. I do not pretend to have a handle on the engineering dynamics as each system seems to present its own complexities, thus, the trial and error approach, with some attention to the details of tubing diameter sizing's and lengths between connections with other resonance sources. I was initially surprised by the recommended diameter of the primary tubing leaving the engines exhaust port. Matching this port with a smooth transition envelope was given considerable attention to detail.

The 4 into 2 into 1 tubing assembly approach was chosen as it seemed to be most advantageous for accommodating good torque readings from the lowest through the mid ranges of the engine's RPM surge. In order to not take the tubing beneath the engine (reducing under body road clearance) to obtain the optimum primary lengths, I chose to maintain the original alignments used by Porsche whereas they gave benefit to the overall collection of the two primary lengths (as well as retention of the original heater ducting system) that would be joined to improve primary wave extraction from the natural sequencing of the firing order. This decision led to the tubing's crossing behind the engine, and far enough back to allow the auxiliary pump that's piggy backed onto the original pressure pump's drive gear. I incorporated a modified Ford Cleveland (a design developed by Leo Droughton) oil pump as the sump'a extraction pump. This required that the primary tubing lengths become a bit longer than what Burns Stainless recommended in their analysis of our engines cylinder volume and timing order. Just the same, the lengths of combined primaries have been kept equal length to their collectors.

The next objective was to insure that there is a crossover assembly that allows the pulses to naturally boost scavenging when beneficial to either secondary tubing's exhaust flow. That is, if a pulse is on its way out and it senses a vacuum ahead of its wave, an opportunity is provided for the pulse to take the direction of least resistance. This was accommodated by a series of gill slits in the tubing's curvature where the flow of the exhaust gases are not inhibited by the formation of the gill effect. I tested this feature by passing compressed air down the tubing with the gills to determine if the flow of air continued as anticipated in the preferred direction of flow, or was disturbed by the gill slits in the tubing's curvature. My casual observation was that the air passed through the gilled curvature zone of the tubing unrestricted.

That patch where the two secondaries meet is where the gills lie, beneath the patch. All that was left to accomplish was the passing of the secondaries through the mufflers with equal tubing lengths that remained within the rear body skirt sheet metal. I am told these secondary lengths are also critical, and I have kept them as short as was possible using the bend sizes available to create what we have as a first trial solution.

The Honda 900 cc mufflers are unique in that their design allowed easy attachment with a normal triangular flange at their inlets, and direct welding or clamping to their outlet port.

If there is any magic in what has been fabricated, only the dyno will provide some interesting insights. I do anticipate a quiet exhaust note and excellent muffler volume. The optimization of torque, well that's yet to be determined.

Pushing on the technology is part of the challenge. If the assembly is even close to what I am hoping to gain, there are still modifications that can be incorporated to make further adjustments. There is seldom progress without the risk of failure. However, based on my investigation into this theory and the said to be improvements, the proof will be in the testing.

I'm still years out from having an operational project. Its the continuous adventure to bring about such improvements by establishing goals that are self generated to give the designer some level of satisfaction when all is said and done.


Top
 Profile  
Reply with quote  
PostPosted: Fri Nov 06, 2015 1:34 pm 
356 Fan
User avatar

Joined: Thu Mar 27, 2008 6:23 pm
Posts: 44
Here are some pictures.


Attachments:
DSC02905.JPG
DSC02905.JPG [ 2.94 MiB | Viewed 1316 times ]
DSC02904.JPG
DSC02904.JPG [ 2.86 MiB | Viewed 1316 times ]

_________________
Bob Kelly
62 Hardtop
66 912
Top
 Profile  
Reply with quote  
PostPosted: Fri Jan 20, 2017 9:00 pm 
356 Fan

Joined: Sat Apr 26, 2008 1:22 pm
Posts: 74
Bob after seeing yours I built one similar using two mufflers with 2 1/2" id. I turned mine up before teeing so the pipes would exit the existing cutouts. It was a little loud so I added baffles to quiet it down at cruising speeds. Mike


Attachments:
image.jpeg
image.jpeg [ 467.7 KiB | Viewed 314 times ]
image.jpeg
image.jpeg [ 290.16 KiB | Viewed 314 times ]

_________________
Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 35 posts ]  Go to page Previous  1, 2, 3

All times are UTC - 5 hours [ DST ]


Who is online

Users browsing this forum: No registered users


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
Powered by phpBB® Forum Software © phpBB Group