JBrady

Fireballs, the exhaust is exiting at tremendous velocities and temperatures. The entire spent exhaust gases have only a few milliseconds to get out of the cylinder. The sharper the turn that must be made the less efficient the manifold becomes. The WORST possible shape is a 90 degree turn. Componding the problem is the construction design that is shown in the below picture... the sharp edges protruding into the gas flow are horrible. Go to the link to read more about this phenomena.

https://www.clublexus.com/forums/sho...highlight=flow

Here is a picture of the stock manifold looking down from the port into the "log". Notice the overhanging sharp edged metal. This goes completely around the port even though just one edge is clearly seen here:

jmecbr900

So if I'm following this....the design you're working on will improve on the severity of the bend in order to help with velocity of the exiting gases AND also have a bigger diameter to improve volume?

Is this why the design has to be careful not to be too radical otherwise we run out of install room?

Just trying to make sure I'm following.

JBrady

Yes. The things to focus on are preserving the energy/velocity while increasing the maximum capacity.

The pipe diameter will be slightly larger than stock but without the horrific bends and sharp edges at intersections and merges.

Look at the above picture and note the sharp edges inside the manifold that protrude into the gas flow. The turbulence caused by this type of aerodynamic interference functionally makes the passage smaller. It also converts flow energy to heat energy. You can see this by looking at the factory dyno picture below and noting the hot spots at each intersection. This loss creates a flow restriction AND has less energy to scavenge. By improving these points we can achieve a significant improvement in flow capacity without lowering velocity or converting flow energy to heat and backpressure.

jmecbr900

Who was it that was questioning your expertise?????


Expert in my book. I understand and SEE what you are refering to. Excellent write-up.

I'm still sold and in on this.

fireballs gs400

i'am in too, i am very excited about this, the headers can open up sooo much hp. this ranks up there to the new gs.

SCWells72

Scanned the thread to see if my question was answered, and this is the closest I could find, so I'm going to ask my question. Is the expected ~20hp/20lb-ft rw gain already in conjunction with a full cat back and/or intake, or is that before any other modifications?

I ask because I already have the L-Tuned exhaust which, while more free flowing, is certainly no cat back. Can I expect my current exhaust to work well with these headers, or if/when I sign up for the headers am I implicitly also signing up for a new exhaust and high flow air intake to realize the gains?

Sorry if this is a dumb or previously answered question...

Wide LS

I think your question will remain unanswered until the headers are complete and a dyno is done.

Guru

I'm in. I can provide dyno results as well for you. I'm installing these with test pipes and full exhaust. I have a bone stock GS400 with an S-AFC II in it. I have dyno'd many times stock at around 240-244 whp.

JBrady

Thanks, it is nice to be appreciated

JBrady

As Wide LS responded we will have to wait until they are built and tested before we can know the actual improvement and what effects other mods in conjuntion with the headers will have. However, a cat back system is highly recommened. On your car it is less necessary than on mine because your center resonator is 60mm (2.36") vs mine at 50mm (1.96") and your single to dual splitting Y section is much better than the LS or SC parts. Your L-Tuned mufflers will be fine with or without changing the rest of the system. A new intake is not necessary either. Remember, an engine is a SYSTEM and all the components effect each others results. The most critical area is the headers on our engine so starting there is a great choice.

jcramair1

You can count me in for a pair. I think that the headers will make the engine breath with the S/C the way that it needs to.

AppleGS4

i'm in

koreanpers

make sure to send a pm as instructed on the first page

dewey

I'm in and will pm as requested.

CJGS4

Got word of this on the is300.net forums.. Definately in on it for my GS400..

-Chris