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Quote:
Originally Posted by copbait73 View Post
A couple of statements I must take on:

“Equal length headers yield better off-boost performance but IMO it's hardly worth the effort since a turbo engine spends so little time off-boost.”

Really, you must be something to see in traffic or is this statement based on driving strictly on the racetrack? If you reflect on normal driving you will notice you are on boost maybe 10% and full throttle much less. What does your engine like best off boost, equal length or something other?
Seems like everyone thinks "on boost" means full boost.
When I push the accelerator just a little more than in granny mode, I'm getting 3-5 psi of boost. Acceleration is brisk but not warp speed. That's what I'm referring to.
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Old 01-09-2010, 06:04 PM
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Quote:
Originally Posted by 911st View Post
Are you sure?

I used to have up to .2 bar if I measured before the throttle plate with my K27-7200.
Just asking.
Is this off to:
I know you understand turbos well.
Yes, positive regarding idle.

Regarding pressure differentials:

Actual Porsche 1978 published data; @ 6000 ERPM, intake .8bar (11.6#), exhaust manifold roughly 1.2bar (17.4#).
Intake is roughly .8 bar at 3000 RPM (W/G regulated). Pressure differential goes exhaust positive at 4300ERPM.

Porsche has always been a high performance installation, with that slower boost response, but lower exhaust backpressure before and downstream of the turbine.
When you have installs typical of DET cars they have much higher exhaust system backpressure (downstream of turbine) therefore higher negative differentials to compensate.
Old 01-09-2010, 06:24 PM
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Sorry to jump in late guys, I would like to hear some opinions (nice and mean) on these headers I had made. Im not going to cry as I did not spend a whole hell of a lot on them.
I have since moved the passenger side wastegate mirror image to the driver side..

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Old 01-09-2010, 06:25 PM
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Are those for a CIS car???? 'got some big pipes there...

How do you like their performance?
Old 01-09-2010, 06:43 PM
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Quote:
Originally Posted by 911nut View Post
Seems like everyone thinks "on boost" means full boost.
When I push the accelerator just a little more than in granny mode, I'm getting 3-5 psi of boost. Acceleration is brisk but not warp speed. That's what I'm referring to.
Paul-

I apologize for making a point at your expense. Yes, I know no sane person does this. But you are still taking about acceleration which at any rate, 100% or something less, is still a small % of the total driving cycle. Most Porsches do not have pressure/vac instrumentation, that's unfortunate as these show how the car responds N.A. then boosted.
Old 01-09-2010, 06:45 PM
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I've owned my equal length pipes for quite a while now and for street use, they're a waste of extra money I spent. I also find it odd that nearly all header builders consider "equal length" being just back to each collector, not to the turbine. If they aren't perfectly equal to the turbine, who cares - a bit of a challenge with most of our turbos being off-set.
Old 01-09-2010, 06:54 PM
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Will have some exhaust spoolperformance info later this year. Have changed from stock euro to a short length 321 system. No other changes made except all oil-lines from thermostat and rearwards.

With euro exhaust and K27-7200 + HKS "doubleacting" boostcontrol

0.5 bar at around 2900rpm
1.0 bar at around 3100rpm

Hope to see some improvement.. Collectors are far from optimal but I got the system from a friend fairly cheap..
Will let you know the numbers for the stainless later on (lots of snow)

Old 01-09-2010, 07:25 PM
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Everyone is getting very close to the correct understanding. Let me make a few brief comments to help guide things along:

1.(gskrken) Your thought experiment is in many ways exactly right regarding the effect of addtional header volume. You just have the conditions wrong. When we go from low boost to full boost we do not just have to fill up additional volume, we have to pressurize it. Until we meet the pressure demand of the turbine, the volume continues to need "more filling". Thus, even a relatively small volume can require many liters of exhaust gas compressed into it before the turbine energy requirement is met. When you consider that a .2 second improvement in time to full boost is noticable in the seat of your pants, I think you can see how this can make a difference

2. (lucittm) Your basic grasp of gas dynamics is very good. The individual pipes must be arranged so that, in our case, the pulses are spaced 120 degrees apart. This naturally occurs when each bank is grouped together. An open end reflects back a negative pulse (low pressure). If this negative pulse arrives at the exhaust port just as the exhaust valve is opening, it increases flow out of the cylinder, just as you more or less stated. For all cylinders to be doing the same thing at the same time, the lengths of the tubes have to be the same, as you pointed out.

The condition that we have (and that you recognized) is that we have no open end to reflect a pulse back. It is neither open nor closed. Any pressure pulses are expanded through the turbine and used to compress air. This is the fundamental fact that, unique to turbo engines, we have to recognize. We do not reflect back ANY negative pulses. Without any reflected pulses the length of the tubes becomes non-critical, except from the standpoint of volume that needs to be filled, and surface area for heat loss.

There is only one way to use the pulse energy in a turbo engine, and I mentioned it in my original post. If the individual cylinders of one bank are connected to one side of a divided turbine housing, and the other bank likewise, the pressure of each pulse can be expanded in turn through the turbine, measurably improving its efficiency. This picture is about right (there should be a wastegate on each side, and the divider wall is melted away. It should go all the way to the turbine flange):



One last word, about temperature. Temperature lost is energy lost. How critical it is depends on how much is thrown away.
Old 01-09-2010, 08:00 PM
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Quote:
Originally Posted by DonE View Post
Are those for a CIS car???? 'got some big pipes there...

How do you like their performance?
They are for an efi car- they work pretty well, still never drove the car with a proper tune with them installed, but I can say that the car dropped 300 rpm of spool time, so I guess they are an improvment over the last set (B&B's modified for a T-4 flange and single V-44 wastegate).
I am doing a diffrent injection system next week which I will post a thread on and at which point I will see how it does on the dyno.
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Old 01-09-2010, 09:52 PM
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Well if I may chime in here, on my 3.8tt the headers on her are custom equal length setups - they wouldn't be on the car if they weren't vital to the amount of sheer torque that the motor produces as well as top end breathing...but that being said it makes for an EXCELLENT street motor.

Look at the 935s, the setup i'm moving to now to be exact to place the turbos at the rear of the car...they're designed for high rev and single purpose use, track suited so to speak.

So the header debate is great but keep in mind, its about the use of the car and motor and what is needed from it that will designate the header design.

Just my $.02
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Old 01-09-2010, 11:18 PM
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Kris,

For what it is worth.

For a sortie I love you headers.

You kept the WG volume at a minimum, great collectors, modest turns where possible...

Do not know about tube size. Looks like a T4 style turbo which has interest to me.



Quote:
Originally Posted by 930gt-40r View Post
Sorry to jump in late guys, I would like to hear some opinions ...
Old 01-10-2010, 07:52 AM
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Here is a peak at a Protomotove Equal length.

Short as possible primary's but still equal length, equal secondaries, short WG pipe. Probably very expensive.

This guy is one of the best at getting the most 'efficiency' possible out of a turbo motor.

Old 01-10-2010, 08:02 AM
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There is probably small differances as to pre boost TQ, boost response, and efficiency, back pressure... between well designed and sized shorties and equal length system as it relates to a 930.

What maybe 100 or so rpm difference as to lag and a couple of poneys here and there. Again, on a well done for the application system.

If off idle a motor can only make 40 hp there is not much we can do with just the headers.

Other factors like turbo selection, intercooler volume, AFR, timing, compression probably make make and much or more of an impact.
Old 01-10-2010, 08:09 AM
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Quote:
I also find it odd that nearly all header builders consider "equal length" being just back to each collector, not to the turbine. If they aren't perfectly equal to the turbine, who cares - a bit of a challenge with most of our turbos being off-set.
Which is why I built mine equal length to the turbo.

The unequal shorty headers should take their "design" one step further and eleminate the collectors. Just use a step-up log design and reduce the exhaust volume to absolute minimum.
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Old 01-10-2010, 08:24 AM
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thanks man- the turbo is a Pt-67 ball bearing which is basicaly the a gt37r- I only used twin 44 wastegates because I already had a single 44 and bought a second cheap. It will perform well when I get a better injection system and have a better tune. This is what I did with the wastegates instead of having them asymetrical... It is also divided up to the turbo for future plans of a 40r with a divided housing.
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Old 01-10-2010, 11:13 AM
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Yes, an equal length system is best to have equal secondaries.

Or-- keep each side a split system including the turbine.


Kris, love your car but your tail pipe looks a little small!


Suspect that the state of tune, turbo choice, and what happens after the turbo is probably more important than short v long, assuming a solid header design for both.


My votes for what it is worth:

Best equal lengths, Brian's system.

Best shorties w heat, M&K converted 993NA's.


A solid contender is the stock late 930 HE system for quality and originality.
Old 01-10-2010, 12:05 PM
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Quote:
Originally Posted by Reaper930 View Post
Well if I may chime in here, on my 3.8tt the headers on her are custom equal length setups - they wouldn't be on the car if they weren't vital to the amount of sheer torque that the motor produces as well as top end breathing...but that being said it makes for an EXCELLENT street motor.

[snip]
OK - different animal (twin turbo). On the tt projects I've been part of, I would submit you couldn't tell the difference between short vs equal on a street car (day to day driver). Equal pipes really come into their own at high rpm but give up some down low. I witnessed this directly when I replaced my B&B pipes with a set of Marco Manzie equal pipes and found I traded performance from one end of the power band to the other. It wasn't a bad trade, but I do most of my driving under 5000 rpm.

Brian - have you made a genuine equal length header yet? If so, do you have a picture? I would really like to see how you handled the turbo placement. Might be in the mood for a new header
Old 01-10-2010, 02:48 PM
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I like zeb930's setup. It is basically the 934 arrangement with no divided turbine housing, heat exchangers, and a single wastegate. Hope he defrosts early over there so we can see what it does.

930GT40's is interesting because of the dual wastegate locations. I would jet-hot coat that sucker to keep the heat in and call it good. Do you think the slip joint will keep loose over the life of the system? I think those things get stuck after awhile, which can lead to cracking.

I know that the equal lengths are a waste on an undivided housing, so I wouldn't roll with RarlyL8's setup myself.
Old 01-10-2010, 05:40 PM
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Quote:
Originally Posted by Speedy Squirrel View Post
I know that the equal lengths are a waste on an undivided housing, so I wouldn't roll with RarlyL8's setup myself.
But what about RarlyL8's equal length primary and secondary headers with a divided flange Gt40?
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Old 01-10-2010, 07:26 PM
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Yes Don my headers are true equal length from the port to the turbo. The turbo rests in the stock position. I would not have gone to all the trouble for nothing. Take a look at any high end header system vs the Chinese stuff and you will see a distinct trend toward equal length. You will also see superior metals being used.

Latest Project - Headers

It should also be noted that split volute systems are being built as well as twin turbo systems using my headers. A component design allows for options to suit the application.
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Old 01-11-2010, 05:20 AM
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