exhaust manifold?

[keohep]

Can any one tell me is it traditionally correct to have the collectors merge directly behind the block on the gt40 ?

Wouldnt it give the motor more power to merge them at the end of the heads and use a better merge collector,and have more room to fit the cats etc.

The reason for my Q is that im at the stage of custom making the extractors and wondering wether to bring them to the centre top of the box and straight out the rear.

 

[Tobias]

it´s usually a crossover exhaust wich means that the center cylinders switch sides in the collector. and the exhaust helps the engine to breathe. It gives the same advantages as a h-pipe or x-pipe on a normal v8-car only more and better.. plus it looks really good to...

make a search and you will find truckloads of exhaust threads...

 

[BruceA]

The idea of an exaust system is not only to pass the dangerous gasses to the outside of the car, but to provide an amount of 'scavenge' effect from the cylinders. This is noticable in 'tuned' headers where a certain length of primary pipe will allow the 'paired (or quaded) pipes, the gas flow from them to suck the gasses from the pipe and cylinder(s) they are paired up with. To be polictally correct, there is always a 'tuned' length where the engine will run at its best with the right amount of scavenging taking place.
If an exaust system is 'too' good, it can scavenge or pull out some of the incoming air/fuel charge from the cylinder and your engine makes less power!
The crossover pipes as used in the GT40 ensure even pulses at the collector for smooth airflow. For what you are talking about, I think, the 'block hugger' type convienence headers have short runners, (about 10 inches or so) and are just that - for convienence of installation and not for outright performance.
A good experiment you may want to try if you havent already is start a motor up with no exaust manifold on it - just the bare head to the world.
It will sound hillarious, but it will hardly want to rev, and you would be lucky to get any decent power from it at all - hence the development put into good exaust science and give you an idea of the importance of how a good exaust is all part of the engine performance.

 

[Chris Duncan]

With a properly set-up crossover exhaust the firing order alternates from side to side in the collectors so that no two cylinders next to each other in the firing order fire on the same side. This means the pulses in the collectors have more time to stay separate thus not conflicting as much with each other in scavenging.

For optimum set-up you also want the firing order to be circular in each collector, so as to create a swirl thus promoting flow.

Finally aesthetics, nothing beats the look or the sound of a "bundle of snakes".

Trying to fit cats though, that's a whole nother problem. Many mid engine manufactures do keep the sides separate in order to fit cats and mufflers.

 

[keohep]

Thanks for the info ....merging them to the middle looks great just wondering whats going to happen after to fit the rest in ...lol