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3 restos WIP = psycho
 
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Quote:
Originally Posted by RarlyL8 View Post
Fabricators would not go to the tremendous trouble and expense of creating equal length headers for no reason ...
I meant the length, not the "equalnees" in turbo apps

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Old 06-19-2009, 04:58 AM
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General comment, it’s a common misconception to say a turbo engine intake and exhaust operate in different conditions. This not true. All engines operate under backpressure, atmospheric, 1 bar. Turbos only change internal pressure balance absolutes.

Regarding equal and unequal length, look at all modern endurance racing turbo cars and you will see equal length primaries. They may be medium or long but they will be equal to establish equal operating conditions in all cylinders at all revs. Visualize blueprinting the pressures and flows. This is done to prevent misfiring, HOT cylinders and failure. All this was verified on dynos during the formative days of Indy engine turbocharging in the mid 70s.

Finally, how often are you boosting? Wouldn't you like to have the benefits headers provide for the 95 percent of operation when the turbo is coasting?

Last edited by copbait73; 06-19-2009 at 06:18 AM..
Old 06-19-2009, 06:13 AM
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3 restos WIP = psycho
 
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The reason I ask is that I have a set of beautifully built George Narbel headers, tuned to my motor in naturally aspirated spec. The headers are equal length, but quite long to build proper backpressure for off the line torque in a small bore, high strung motor (the engine is 2.3L).

Now that I am adding a turbo, I expect that this same dynamic will help spoolup, but have also read that longer exhaust tracts increase lag. Just trying to figure out what the net expected effect will be. It seems (from all of the photos here) that everyone building headers for turbos are trying to get gases to the turbine along the shortest possible path.

Perhaps the displacement of 3L and up engines makes this kind of exhaust tuning or torque building an unnecessary consideration. I am thinking that getting exhasut gases to the much larger turbos (mine is a comparatively tiny Mitsu Evo twin scroll), which need as much velocity as possible, as quickly as possible, to mitigate lag.

Thoughts?
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- 1965 911
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Old 06-19-2009, 07:48 AM
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Crotchety Old Bastard
 
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Short path is a relative term. The stock J-pipe configuration has a very long path leading to a single long tube to the turbo. Just about anything in a header will be shorter than that.
Why do most turbo headers have short primaries and unequal length secondaries? Because it is much cheaper to design and build while also remaining superior to the stock configuration.
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RarlyL8 Motorsports / M&K Exhaust - 911/930 Exhaust Systems, Turbos, TiAL, CIS Mods/Rebuilds
'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
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Old 06-19-2009, 08:23 AM
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930TT, nice!


Quote:
Originally Posted by RarlyL8 View Post
Fabricators would not go to the tremendous trouble and expense of creating equal length headers for no reason ...
There are reasons and it often becomes a cost benefit and/or availability decision for most of us.

My understanding is:

Equal length better moves the exhaust events out in a more efficient manner over unequal length headers. This better supports HP and more even temps at the cylinders. Thus given cost and availability is a preferred system for a road race car but a top preforming car can be built with or without them.

Short equal length would be my first choice depending on cost and other factors.

A well designed short unequal length might have a small advantage when it comes to turbo response due to there smaller volume and the higher pressure pulses that result from the non orderly exhaust events. Still many racers are making a lot of HP with this design so it probably should not be discounted as a major limitation given correct choices in tubing size and other design considerations.

Over the years Porsche has used both styles on there turbo cars. The more modern are typically equal length however, it easer to accomplish w a twin turbo set ups.

Two well engineered Turbo motors w unequal length:

580rwhp: http://forums.rennlist.com/rennforums/911-turbo-930-forum/502099-new-dyno-numbers.html

490 rwhp:
AMS 911 3.3 Turbo 490rwhp (Video Inside!!!)
http://www.amsperformance.com/gallery.php?g2_itemId=9571
Old 06-19-2009, 01:04 PM
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Unequal lengths can be theoretically "tuned" to provide a more linear power curve than equal length headers in regards to flat spots. The different lengths each have different resonant frequencies (provided they are not different in length by multiples of wavelengths) for standing low pressure waves at the exhaust valves. Therefore, the rev range where one makes power can be canceled out by others not. The curve will be smoother but a little less powerful at peak than the equal length headers.
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Old 06-19-2009, 01:19 PM
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I suspect comparing a well designed un-equal to a well designed equal length system, most of us are not going to see a big difference in HP and even turbo response.

There may be a difference in cylinder temp variations under intense track duty. For all I know, the radius/bend of the tube coming out of the head may be relevant to cylinder heating.

WG circuit, collectors, primary and secondary tube choices may not be noticed either but might have as much or more effect on VE than equal/un-equal choice.

Turbo choice, muffler, cam choice, compression ratio, ideal AFR and ideal ignition timing may all have more effect or difference than the two different style header systems if both are well designed and built.

I do not drought that a well designed short equal length has the most potential to increase the efficiency of a turbocharged exhaust.

I hope Brian's project comes together as it should be a best of breed system.

I am not an expert on this. This is just what I believe so far.
Old 06-19-2009, 01:25 PM
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Great easy to read article on turbo exhaust design: http://www.tercelreference.com/tercel_info/turbo_exhaust_theory/turbo_exhaust_theory.html

A thread on such: Turbo Exaust Theory


I believe the back pressure created and the type of cams we have to use to run a turbo takes most of the normally aspirated phase tunning advantage out of the equation. Or at least minimizes it substantially.

Especially when we are running quick spool turbos w small restrictive hot sides with larger compressor wheels. Nobody seems to be testing the pressures building up in our exhaust systems with these quick spool turbos.

It used to be tuners would test the pressure differentials going in and out of the intercoolers and the exhaust pressure before and after the turbos when developing a quality motor. Not seeing it anymore with 930's.

Last edited by 911st; 06-21-2009 at 09:29 AM..
Old 06-19-2009, 01:43 PM
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Brian, will your system provide heat? A system combining the efficientcy of headers (with biggers primaries than SSI...) with heat at an affordable price (cheaper than SSI...) would be a hit!

Quote:
Originally Posted by RarlyL8 View Post
Work in progress:

Old 06-19-2009, 03:14 PM
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Quote:
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Brian, will your system provide heat? A system combining the efficientcy of headers (with biggers primaries than SSI...) with heat at an affordable price (cheaper than SSI...) would be a hit!
cheaper then ssi and made in the US that would be hard if we are talking the $1200 N/A ssi as the bench mark
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Old 06-19-2009, 04:14 PM
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The 930 SSI system complete goes for ~$2500. The price point we are shooting for is less than that. Yes heat exchangers will be added once we get the headers going and have plenty of data on hand. We plan to make them "bolt on" to retrofit headers in the field.
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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
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Old 06-19-2009, 08:35 PM
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Quote:
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My old girl is in having some detailing done, back end was looking scabby! I wouldn't class this as a "SICK" exhaust pic, but tell me how many other stock looking 930's you've seen with 993tt engines in

9930!!!! ha, that's a good one.
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Old 06-19-2009, 11:05 PM
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Brian: Will this system require backdated oil lines, or does the design allow you to leave the lines as is?
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Old 06-20-2009, 04:59 AM
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Not sure this is sick...but any reason to post a pic and I'm there

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Old 06-20-2009, 05:01 AM
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Is that spoiler actually functional? IIRC, I believe the previous owner was Bruce Wayne.
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Old 06-20-2009, 05:19 AM
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Crotchety Old Bastard
 
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Gabe I'm pretty sure that qualilifies as sick.

Chuck, no my system will not require new oil lines. I'm trying to make it plug and play. Biggest obstical will be using stock turbo sump tanks. There are 3 different types in 3 different locations ...
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'78 911SC Widebody, 930 engine, 915 Tranny, K27, SC Cams, RL8 Headers & GT3 Muffler. 350whp @ 0.75bar
Brian B. (256)536-9977 Service@MKExhaust Brian@RarlyL8
Old 06-20-2009, 05:24 AM
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Chuck: Actually yes they will be we're adding supports to the bottom of the endplate to facilitate stability. The endplate sizes were calculated at:

Effective Aspect Ratio (AR_effective) = Actual Aspect Ratio (AR_actual) * (1 + 1.9 * (endplate depth/span))

So at 12" front to back and 20" in height, I've effectively enlarged my rear wing significantly without much drag being added.
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Old 06-20-2009, 05:41 AM
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SICK exhaust pics?

well

*this* is "SICK" (clinically - don't ask, I have issues)

and

there is "exhaust" work being done (tacking up my RarlyL8 system):

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Old 06-20-2009, 05:52 AM
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Anyone running Brian's stuff is truly luck that stuff is ART!
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Old 06-20-2009, 05:57 AM
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Brian: The fact you're designing it so that it doesn't require the back dated oil lines saves abot $250 right off the top. You've obviously put a lot of time into thinking and designing this setup. I wish you all the best in terms of marketing success. The price point is becoming such a critical issue these days....but given the fact you and Ben are using the best stainless and those "artful" TIG welds, you have a fine balance to maintain between keeping the prices reasonable and using the best material....while still making it worth your while.

Then there's the fact that the Chinese will be ripping off your "intellectual property" and introducing something similar in no time.....of course there'll always be a US based marketer who will be all too willing to help them market it and aid them in their unethical practices.

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Old 06-20-2009, 06:24 AM
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