How to remove Coupe/Gtransport exhaust headers

vqsassa · Dec 11, 2014

Please tell about the task flow how to remove and exchange the exhaust headers from Coupe/Gransport.

Does it need to take out the engine with headers and disassemble?

I'm planning a project to replace my US headers with EURO headers and hatve the primary pipes modified to fit EURO headers.

I would like to ask some exhaust shop to make estimate on above work but they don't have the experience to do that, so I would like to understand the concept of the work and tell them it and have them estimate their work fee.

Thanks.

lcdave · Dec 11, 2014

IIRC the book says to loosen/remove the mounts but you don't actually pull the engine. When I removed my headers I had quite a number of other things out. Radiator, condenser, etc. It was difficult to get them out, harder to get them in, and almost impossible to torque them. And I have lots of tools. If I were to do it again, I would definitely lift the engine.

vqsassa · Dec 11, 2014

Was it so hard?
So it can't be accessed and removed by lifting the car up like changing front pipes.

I was expecting to do by removing front pipe and then the header from the bottom side.

lcdave · Dec 11, 2014

There isn't enough room for the part that bolts to the head to come out the bottom with everything in place and the curve prevents top side removal. So, yes it sucked.

JoshH · Dec 11, 2014

You do have to loosen the engine mounts and lift the engine. I think we pulled the a/c compressor to gain access to some bolts as well. As Dave said, having a good tool collection makes a big difference.

lcdave · Dec 11, 2014

I had the A/C compressor off, the radiator/condenser assy, the water pump hoses, and some other stuff off too.

vqsassa · Dec 11, 2014

Guys,
Thank you very much for your infromation.

It may cost a lot to me but I already have the headers to replace so no choice .....

lcdave · Dec 11, 2014

In a couple of months you'll have long forgotten the money but you'll still smile every time you stamp on the fun pedal. :autofahrer:

vqsassa · Dec 12, 2014

Is there so much differece from the US headers to EURO headers?

lcdave · Dec 12, 2014

Yes. You are removing a very dense catalytic converter, increasing the header pipe length, and eliminating a squish section. All of those things add up to much better flow.

JoshH · Dec 12, 2014

We gained about 40whp simply by removing all of the catalysts, on our track car.

Craig · Dec 12, 2014

ECSofVirginia said:
We gained about 40whp simply by removing all of the catalysts, on our track car.

Did you leave the squished down pipes on the car? I've always wondered about this. I know we talk about a car needing back pressure which I understand is a misnomer really. We are really wanting flow velocity/exhaust scavenging. We say backpressure because that's what some understand it by. Technically speaking we want a good flow velocity, that creates exhaust pulse scavenging.....the faster it moves the better it can clean out all the spent gases during valve overlap.
My question centers around this .....my assumption has always been if we removed both cats that would decrease the exhaust flow velocity such that the scavenging would be terrible and we would have a loss of power. But by having many bends or twist and turns in an exhaust this would also create a certain amount of flow velocity, and thus that low pressure area behind it known as scavenging. With our cars we have that unique pancaked downpipe design. I have to admit that I haven't always liked it but I have always wondered if a secondary effect of this would be to create enough flow velocity/scavenging that our car would not lose power if we removed both cats. Since you have done so I figured I would aim the question at you to see what you think.

I already gutted my primaries to begin with and I was going to add Cats with a lot less cell count in place of my secondaries for the reasons spoken about above. But since you're here and you've mentioned it. :cheers:

vqsassa · Dec 12, 2014

My primary aim to replace headers from US to EURO is to get better sound in over 4000 rpm rev zone where the sound, tone and volume can't clime-up fantastically.

The more power comes the second but happy to have them.

I think the design of the US type makes the flow worse than EURO type because of the primary cat in the manifold.
US type has ceramic cat 400 cell inside manifold and 600 in the secondary on the front pipe.

My GS has custom front pipe which has 200 cell secondary metallic cat on it.
So I'm planning to add primary cat on the front pipe which anyway needs to be midified to fit to EURO headers in the angle of the joint frange face and frange bolt holes from two to four.

Then how is the size of the metallic cat to add as a primary cat should be, 400 ?
(I would like to keep the exhaust outlet clean to pass the test)

lcdave · Dec 12, 2014

The cell count is cells per inch. The purpose is to provide surface area for exhaust gas conversion. So, you can't just add numbers to try to figure out what you need. If you need the increased surface area to pass emissions, then get cats with enough area or run two cats per side. I pass emissions here in Colorado with 100 cell per inch cats because my cats are 5" diameter and have sufficient length (8 or 9" of core IIRC) to convert the gasses. They are the only cats because I fabricated a new collector to replace the cats in the headers. I also eliminated the squished part at the bottom under the cats. Together with the SS decat, I have a very free flowing exhaust.

For what you need, it depends on how restrictive the test is and how much surface area you can get in the location you are mounting the cats. Mine live where the resonator was which has plenty of room. The Euro headers ran cats under the engine where there is no room.

vqsassa · Dec 13, 2014

Thank you, Dave.

I'm thinking of having add another cat on the front pipe which already has one closer to the center pipe, so my front pipe will have two cat per side and a new cat will be closer to the header like genuine front pipe for EURO header.

According to what you told me, I can't do caluculate how much cell per inch will be enough so I'll leave it to mechanics who will do the replacement and adjustment/modification to my front pipe.

lcdave · Dec 13, 2014

They should be familiar with the emissions regulations and what it will take to achieve the required results. From that it can be determined about how much surface will be required. With that and the location, the density can be determined based on the size of cat that will fit.

JoshH · Dec 13, 2014

The back pressure created by the catalyst core does nothing but choke exhaust flow and cost power, plain and simple. It's a blockage in the exhaust pipe and accomplishes nothing towards improving exhaust gas velocity. Our race car is fitted with the standard Larini secondary cat delete pipes.

kodpkd · Dec 13, 2014

More flow = more air from the engine. More air means a leaner fuel. How does the fuel injection compensate for more air flow? If you increase HP by 40 HP just by changing the exhaust, something else must be changing.

lcdave · Dec 13, 2014

The mass airflow sensor measures the amount of air flowing into the engine. It uses relative temperature to detect the actual mass of the air flowing past the sensor. The ECU sees this and when several other factors are computed (RPM, throttle position, etc) it modulates the time the injectors are open allowing fuel int the combustion chamber. It's only when you reach the max flow of the injectors running full duration that you will be limited. That's when you need higher flow injectors.

kodpkd · Dec 13, 2014

Is there a way to tell when you reach max flow? If you go over this amount, you could burn up your engine.

How to remove Coupe/Gtransport exhaust headers

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