turbo lag, short v equal length headers.

[911st]

Zeb,

These make me lust!

Originally Posted by zeb930

935

[DonE]

Finally, some real turbo headers - short, straight and right to the point. Those are worth building a car around....

Thanks for the pic.

[930gt-40r]

And the best part is that they are simple- I could likely fabricate a set of the 935 headers...

[DonE]

Originally Posted by 930gt-40r

And the best part is that they are simple- I could likely fabricate a set of the 935 headers...

That's exactly what I'm thinking. No fancy jigs or fixtures to fool with - just straight pipes right to the back....think dual zork...

I bet I could "stitch" weld using SS wire in my MIG. Only an experienced eye could spot the difference, but since its under the car, who cares.

[930gt-40r]

When I twin my car someday this is the system that I will use.

[JBL930]

Not as short and to the point as 993tt headers though! Bigger bore no doubt, also has exit for external wastegate, but surely if short and simple is the goal then 993tt size/style ones are going to be the best? Also almost equal length

Something like this?

[Reaper930]

These are the same style (copies of actual original 935 headers) that I will be using on my setup in the next week or so. Going to swain coat them white

[930gt-40r]

Gab- Where does one acquire these pieces? Im not in the market yet, but likely next year I will want to switch it up a little bit. White would look nasty on these, kinda like the old ferrari f1 cars...

Originally Posted by Reaper930

[Reaper930]

I'm getting a set from a friend who bought them from a guy who had an original 935 and they are used. Its a network thing and they are incredibly difficult to come by.

[930gt-40r]

Maybe Ill build a set when the time comes... maybe with a set of burns merge collectors...

[RarlyL8]

There is no need to use merge collectors with unequal headers like that, they don't need collectors at all. Step-up log design will work just as well and eliminate collectors altogether. If all you want to do is get the gas to the turbo just use a straight pipe and connect the cylinders to it.

[911st]

I think that is what Porsche did on the newer GT3's.

[911st]

Stole this pic of a log style system from another post.

Originally Posted by Steve W

High exhaust velocity across a perpendicular exhaust pipe does create a venturi vacuum effect onto the perpendicular pipe...

...pic is of the factory exhaust of a 997 GT3 cup car. Not really your traditional header that goes into a pretty much straight through 2in/2 merged out cup muffler.

I am not saying this is a good approach.

[copbait73]

At some stage we need to consider these variations are not necessarily done because they are technically superior, instead they are a compromise for the available space.

A rear engine race car of boxer configuration having very little ground clearance running sustained full throttle at high RPM needs to move a lot of gas in very little available space. Look at the size of those primaries.

Still, I see one key feature modern high performance engine builders do not violate, equal length primary pipes.

[kenikh]

The Japanese marques and tuners take a different approach to welding in a divider. The best approach is to weld spearate tubes to the two inlets on the divided flange. Thus, the divided section won't degrade. This is the approach I am using for my twin scroll turbo. Again, a true equal length header with divided inlet tracts will typically spool to full boost 500 to 600 RPM sooner than a non twin scroll or twin scroll without optimized exhaust system. Well worth the effort.

Originally Posted by Speedy Squirrel

In addition to welding in a divider, you need to keep both sides isolated without a crossover (you need two wastegates). Also, the individual pipes must go all the way to the turbo (no collector). I don"t recommend it for the street. The divider doesn"t last too long.

[911st]

Speaking only of well designed short and equal length system for a 930:


An equal length is 'probably' going to make another 20-30hp in the mid to high range than a shorty.

A shorty is 'probably' going to come on boost about 100 to 300 or so rpm faster than an equal length.

Both will probably come in faster and make more Hp than a stock late 930 HE/header system.

The factory stock late 930 headers are probably less prone to failure and have the best ability to deliver heat.

There are extreme Porsche Turbo builders that are using shorty's and equal length headers to make up into the 700fwhp and higher range.

There are 930 turbo motors running stock late 930 headers making over 500fwhp. (Monster CIS claims over 600hp on stock headers.)

Then there is proper sizing of the primary tubes that can reduce lag or support higher HP or turn a well designed system in to a poor performing if not matched to the motor.


There is no perfect system for all situations and builds.

If we are lucky we have good information to base decisions on and different systems from which to make choices.

[jimmcc]

Joining this thread late with great interest but no knowledge of header design beyond what I have read here.

In the discussion of equal lenght, short/long primaries and the like where do the SSI 930 headers fall in design and what is the general consensus on their performance level?

I have one of the early prototypes which replaced the stock headers. As the car was rapidly becoming track only the muffler was removed at the same time so I never evaluated the contribution to power/drivability from each individually. The torque especially coming out of corners was very noticeable and rear tire wear became a problem until I settled the right foot down.

Interesting thread and thanks.

Jim

1980 930
1995 993

[RarlyL8]

Jim, I'm gessing Billy built your SSI based header system. He did a few of those and can tell you the specific advantages, the main one being low end torque.

[911st]

Originally Posted by jimmcc

...where do the SSI 930 headers fall in design and what is the general consensus on their performance level?

Some thoughts and facts:

The late 930 headers are basically the same as the Carrera 3.2.

Per SW on a Carrera 3.2 w pre muffler and chip at 3500rpm makes about 122hp.
SSI w stock muffler and chip makes about 130hp or about 8 more HP at 3500 rpm.
At all other rpm they were equals.

Per a Bruce Anderson article that had dyno info for different exhaust combo's on a 3.2 Carrera that included comparing a stock header system with a RUF sport muffler against an SSI with 2/2 sport muffler, there was no real difference in hp anywhere except about 3000rpm. At 3k the came in:

98.6 for the stock headers.

102.8 for the SSI's or 4.2 more HP .

Thus on a normally aspirated 3.2 motor there was about a 4- 8hp difference between SSI's at stock headers. However, they were equals at all other points except at about 3000-3500rpm where the SSI's had a about a temporary 5% bump in power (savaging?).

From here we are just guessing!

First, it is debatable if Turbo motors at 3000-3500 would benefit from any savaging. It can benefit from more efficient timing of exhaust pulses.

From these two data points I would deduce or guess:

Boost onset would not change.

The time from boost onset to full boost goal might be shortened with the SSI's.

The HP in the early part of the mid range might be increased some.

What might be more reliant to shortening time to full boost would be the differences in total volume between the two. I would not guess SSI's have an advantage in this area.

What might be more relevant as to which might make the most HP could be tube sizes.

I believe the SSI's are 1.5" and the stock headers about 1 5/8's. However, the secondary tubes might change this. The SSI's may be modest by a big 930 turbo standards and the 930 header has the funky cross over and J tube. Call it a tie for now.

IMO with what I believe so far, the best thing about SSI's is the quality, heat, and maybe some increase in efficiency early and just past reaching one's boost target where the SSI might be a little more efficient.

My guess the SSI with the 1.5" primary tube's might be less than ideal for making HP on a track car but great for a street car.

I could very well be wrong but I would not expect a big difference between the SSI and stock late/euro headers if both use a great low restriction muffler.

[1100sport]

The 3.2 is not the right "environment" to draw conclusion on the advantages of equal length design Vs non equal length design at least if you use SSI for the demonstration. This is because SSI are 35mm inside diameter primaries whereas on the Carrera 3.2l Porsche has enlarged the OEM system to 38mm inside diameter primaries. Still the SSI manage to outperform the OEM system in mid range, but are too restrictive at higher revs. If you take an equal length design with the same diameter as OEM on a 3.2 (B&B for example), you will notice an improvement everywhere, and more than 10hp increase at peak power.

On the 930, the OEM headers are still 35mm inside diameter. You will notice an improvement off boost with a "SSI like" system. But on a turbocharged engine, power comes with boost - and nothing beats short headers when building boost is what matters. Still, for a street application, a SSI like design header is very nice on a 930.