Louie928

About a month ago there was a thread claiming xx% gain with a certain brand of headers on a 928. I made a post relating information I thought was correct. That information was that I had put headers on a '90GT that had an X pipe and 2.5" rear exhaust and the headers showed no improvement. I was wrong with that information. We had some difficulty getting a good Sharktune the first time and didn't get any more power with the headers. Recenty, I spent a couple of days doing the tuning over and found success this time. After Sharktuning, the headers gave 11 hp and 27 lb ft more than the X pipe. The real Sharktuning gains came with ignition timing changes. After Sharktuning, the X pipe had 327hp and 322 lb ft tq. That's about exactly what my '90GT made with the same setup so probably close +/-. The header system, but with a different X pipe to connect to the header collector, made 338hp and 349 lb ft tq. Those are SAE corrected numbers.

I thought I should set the record straight. The headers were Devek level 2 and they help significantly. Worth it if you want the max, but the X pipe still the best increase for the money.

Here is a screen print of the dyno chart showing a Sharktuned X pipe and the Sharktuned Headers. Both systems used the same 2.5" rear exhaust. The other picture is of the X pipe connection to the Devek L2 header collectors.

BTW, The odometer turned over 150,000 miles during tuning. It is very fast and runs smooth. It is for sale $14,000. The suspension is Eibach springs/Bilstein shocks. Exhaust is stainless. Good Toyo tires & I think 993 wheels. Near new clutch with stronger pressure plate. Need a big left leg for traffic driving. Sport seats. GP white/tan.


https://rennlist.com/forums/attachme...1&d=1223263567
https://rennlist.com/forums/attachme...1&d=1223263567

SeanR

Ok, now where can I get some headers?

Damnit.............all these mods.

andy-gts

Louie,
ARe those Tom Cloutier's headers Looks great~!
andy

slate blue

Thanks Louie for posting this info, it a lot of work to do testing that actually proves changes as you need a good baseline and then need to swap thing about, I think a lot of people don't realise this.

Also if I might add I just read Excellence, I know I'm a bit slow on that front but I was busy till I got banged up and put into hospital. Allowed me to do a lot of reading and i have to say what a massive body of work! All of those jobs are massively time consuming.

I really like the throttle bodies and your housing of them, a real professional job and just so perfectly designed arrangement at the front for the air cleaner, this is in fact what I intend to do but the idea you gave me was the extra sheet metal at the front. Much like the Ferrari 599. I wonder if that adds to some stiffness too? BTW Did you manage to get the carbon housing right first go? I want to have a go in the near future and it doesn't look that easy.

I know we have discussed this before but what was the length used for the intake tract? For my engine I am using the 2V engine I am able to comfortably able to get 10" runner to the back of the valve without canting the intake runner I can get more by angling it but I would like to keep it straight for max flow.

Also are your trumpets elipse in design as I recently read a Race Engine Technology article where all the various trumpets were tested and the elipse is the best, the best also for spitback. A short fat elipse was the clear winner.

I also like where you placed the oil coolers, that is where I am going to place the dry sump tank as I think we need to get as much weight to the rear due to traction problems. I also must say I really like the Devek style headers, for us RHD guys these are the best to modify, too bad they are now no longer available, I am in the process btw of making a set of Tri-Y headers from Inconel, it is a very tough material if you have ever used it, have you got any idea of what the Devek Headers and X pipe weigh? My first set of headers weighed in at 10 kgs exactly. Which I think was just lighter than the cast iron manifolds.

Anyway good reading on the X-pipe and headers and you may be interested to know that some Nascar teams are using an X pipe on their restrictor plate engines.

Cheers Greg

Louie928

The headers are Devek level 2. NLA, except for the set I have in a box on the shelf.

They seem to really help below 5000 rpm.

Louie928

Thanks for the nice words, Greg. It is a lot of work. I strongly felt that the earlier results I had with trying to tune with the headers and seeing no real gain shouldn't be right. Sometimes, things don't work as you think they should either. I had to try again just to see. This car came with the X pipe installed and no baseline dyno so it is hard to say how much total gain there was. GTs can have anywhere from around 290 to a bit over 300 rwhp stock.

The sheet metal in front would stiffen a little, but probably not enough to notice. The way I did it with air coming from the front filter with the tilted back radiator is a huge amount of work and I think I would do it differently again. My goal was to not alter the hood and that was costly in time and effort. A better way would be to accept a raised center hood section and have a horizontal air filter where the top of my air box is. Then duct air to the top of the filter through a scoop in the raised center part of the hood. The air opening could be front, or rear, facing. The mold for the air box and air filter housing was the first real attempt. I did have wood and foam mockups first. When all seemed right, I did the real thing. Still, there were a few surprises.

The total length of intake tract is about 12". The port length from valve head is 4", and the length of the TB and air horn is about 8". Canting the intakes inward on the 32v head makes for a straighter shot to the valve head.

The intakes are round, not elipse in cross section.

The oil cooler location is working out ok. The area of the inlet scoop in the rear fender isn't big enough. Pulling a long, fast, climb in the mountains will elevate the oil temp to around 235F on a hot day. I don't like it higher than that so I back off power. The fan helped, but not enough as I'd like. Oil temp stays below that on the track. I don't know what the Devek headers weigh. They are made from 16ga mild steel. More than 10 kg for sure. It was my goal too to move weight to the rear where possible. One downside is that the longer piping and probably more difficult mounting increases overall weight so it's a tradeoff.

drnick

louis,

my friend recently fitted the 928 international headers to his 90 GT and there is a noticeable difference over the X pipe he had fitted. on my car i fitted new camshafts at the same time as headers and gained 30 bhp over just the X pipe, but i still need to shark-tune.

do you know if you can still get to the clutch with the devek headers in place? these are the headers on my car at the moment, i also have a spare set which i was thinking of using as a basis for some RHD sets.

slate blue

By Louie

No worries you deserve it, until people take on this type of work they will never realise what commitment it takes to get a good to great result. Also it isn't until you start digging that you find out that Porsche only did part of the job on the development front, not wanting to sound too unfair as by and large it is a fantastic car if it wasn't we wouldn't have one, or make that two in my case.

As to the intake tracts, on the 2 Valver if I cant them outwards, i.e towards the fenders/guards they will be straighter, just a little difference between the two and four valve engines. I will try to get another inch or 2, as my engine will have another 1000 rpm 11 inches may be O.K but I want to make sure that there is enough clearance in front of the trumpet. Don't want to create a scenario like Porsche did with the S4 manifolds.

As to the weight of the headers I am building, They are 18 and 20 gauge and will weigh including the X-pipe and the first set of mufflers a total of 12 kgs that is a total of 48 inches back from the front of the engine, so I am taking getting the weight from the front of the car seriously. I see the weight bias as a very important issue.

I totally agree with the trade off, my car can easily light the tyres now so I don't want to even go there when another 50% more power is added. So it ends up heavier! Everything I can send to the back I will. The other thing I want to do, is add a flat floor with diffuser, I plan on putting NACA ducts into it and use various aero techniques used in F1 to pull the air through the coolers. In reality it is not that hard to implement but may be hard to get it to work correctly. I will get to find out in time I suppose.

Going back to the throttles for a second, are you happy with your idle? What does your car idle at? You will have more power than me, that is for sure but I want to be able to idle mine at a 1000 rpm or less, I do have a pretty big cam I was wondering if you are happy in this regard?

Cheers Greg

Peter F

Hi Tom,

I second Greg's comments and always consider your posts highly interesting and very detailed.
I have been redaing this through and maybe missed it but what is the difference between the GT with x-pipe and the same but after shark tuning the EZK and ECU?
I'm curious since I have the x-pipe and wonder how much more there is to possibly gain from sharktuning on top of this?
There is a person in the Swedish 928 club that have a Sharktuner but no dyno unfortunately, how far will the autotune option enabled on open road driving possibly help?

Maybe impossible questions to answer but curious if you have an idea.

/Peter

Rick Carter

Thanks for posting Louie. I have a set of MSDS 1 5/8" headers from Abby that I will be installing with a single 3 1/2" exhaust and a larger crank pulley for a couple pounds more boost. I will dyno before and after the exhaust change but probably not before and after the pulley change only as I don't want to spend the money. I don't understand why the collectors are 3" instead of 2 1/2". I will be using a Burns Stainless Y dual 3" into single 3 1/2". If I had the time and money it would be nice to try and fit a long transition from the 3" to 2.5".

RKD in OKC

Oh man, so NOW I gotta get, an X-pipe, GT Cams, Sharktuner, AND headers for my GTS, Thanks a LOT.

Cheburator

The difference is like night and day. I have to say the X-pipe was extensively modified in order to accomodate the longer 928 Intl headers. It feels like I have shifted the powerband up by around 500rpm and there is just more of it. The car has not been on a dyno, but I did some runs from 30 to 90mph in a straight line - between two signs on the motorway - vs. my Z4M Coupe, and I got on average 10mph faster speed at the end of stretch. The car will happily hit the limiter in 5th on the Autobahn. The Z4M is 343Bhp and 1465kg, the 928 is currently at 1470kg ready for the road...

jodypress

I too have X-pipes and would love to know what can be gained by a shark tune?

morganabowen

In other words, just slapping the headers on the car will not yield much of an improvement, correct? In order to benefit from the addition of the headers, you need to sharktune the car?? I already have the X-pipe, but did not consider the headers due to the post suggesting that there was no power gain or advantage. I am mechanically challenged, and would depend on my local 928 mechanic.

Louie928

Yes, the clutch cover can come off with the Devek headers in place. You have to slide it over and drop one side first to get it out. I think slide to the left, then drop down the right side and it'll come right off.