Header Design !

[stevenx40]

Who has built there own,what are the advantages and disadvantages of 180 degree design.How do you figure out the sequence? Steve

[Brian]

Plus one other little tidbit, the theory of which I can't prove, but the headers are assembled in such a manner that the cylinder gasses entering each collector fire in the following manner: top left, top right, lower right, lower left and round and round in a clockwise manner creating a vortex. I would not know the physics around it helping to extract the gasses. However the full crossover system sounds great!....

[Robert Logan]

Brian,
It is pulsed this way to "rifle" the gases out through the mufler / megaphone. The gases are spun in a clockwise direction.
The sience is called scavenging and is usually concentrated in the removal of the exhaust charge from the combustion chamber. Computers are now used extensively in producing mathmatical models to simulate this. It is much more important that realised as the only way to get a FULL charge into a cylinder is to remove ALL of the exhaust gases. A combination of good piston design, good cylinder head / combustion shape / exhaust port design and finally header / exhaust system design are all critical.
These are what extracts the very last HP from your cars and are very important at the sharp edge of racing.
Best wishes, Robert

I don't know if there is any real advantage of than the awsome sound. To cross them over into 180 degree headers you send the two middle cylinders to the opposite collector. Because the firing is now evened out with each collector getting a pulse every 180 degrees you can use a smaller collector which you can see in pictures.

[Frank Catt]

Steve, having got to the point of needing headers for Robin Batts car (see"a few GTD pictures" on forum), and because I had radically lowered the engine to copy original car layout, the only thing was to sit down and make our own. We looked at all of the books, selected the original car pattern that we thought looked right (sorry, cant remember which car)and made wire profiles for each pipe and went for it. It seems to me that mainly two parameters apply, to get the pipe lengths as close as possible the same, and to get as much air space round each pipe. we were pleased with the results, even though we are amatuers. I am doing a second set now for another car, but they can only be built to the individual car, so I cannot do them mail order!

[Sebring GT]

Steve - Given the Ford firing order 1-5-4-2-6-3-7-8, with cylinders numbered 1-4 on the right bank and 5-8 on the left bank (facing forward), and both banks of cylinders having individual headers, it would follow that two cylinders firing sequentially on the same bank will create a bottleneck when the gasses reach the collector. This is exactly what happens when cylinders 4 and 2 as well as cylinders 7 and 8 fire. The theorim which supports the crossover header concept is that evenly spaced pulses in the exhaust collector will create less back pressure. It follows that if there will be two collectors, they must be fed by cylinders from opposite banks to create even pulsation. In order to do so, the two inner cylinders of each bank are fed to the opposite side collector. Thus 1 and 4 go to the right side, 5 and 8 to the left. This leaves the two inner cylinders of each bank to be crossed over to the opposite side. i.e. right bank cylinders 2 and 3 cross to the left side, while left bank cylinders 6 and 7 to the right side. This makes the pulses in each collector evenly spaced. i.e. right side has 1-4-6-7 (every other cylinder in the firing order sequence) while left side has 5-2-3-8.
The only disadvantages I know of are that it is more difficult to fabricate and may require slightly more room, but this is not really major obstacle in a GT40 since the collectors are placed so close together anyway. If you look at some of the pics of cars with crossover headers you can see how tidily it can be done.

[ January 19, 2002: Message edited by: BlueOvalBlood ]

[ January 19, 2002: Message edited by: BlueOvalBlood ]

[ January 29, 2002: Message edited by: BlueOvalBlood ]

The HP advantage of the crossover system
is low compared to the extra/trouble/cost
involved.

But in my humble opinion, if it doesn't have
a crossover exhaust..it ain't a true GT40!
(and yes I know some GT40s came without).

The looks and sound of that system are
50% of the charisma of the car.

MikeD

[gheacock]

180 degree headers scavange the exhaust gasses from the cylinders providing much better cumbustion mixture efficiency. Each car is different and will require its own header tube layout. Buy mandrel bent "U" tubing, and a length of straight tube and go to it. A "sawzall" with metal cutting blades or a abrasive cutoff saw will insure close fitting joints. Tack things in place untill you like your routing. Break the tack and do it over if you don't. When everything fits, final weld all the joints. It just takes time.... and you have lots of that. Be sure you check the timing of your cam(engine). The old engine timing was 15426378. New engines are 13726548. I have pictures of my car's system, and good pictures from some real cars if that would help. Let me know.
Greg

[Sebring GT]

Question for anyone with an engineering background: In order to optimize the header design should the "rifling" action referred to above be made counterclockwise in the Southern Hemisphere ie: the way water swirls when you pull the plug in the sink (you know, don't fight Mother Nature)? [img]images/icons/grin.gif[/img]

[Chris Melia]

The snake pit

[Chris Melia]

Once again the snake pit

[Chris Melia]

nest of viper's

[Chris Melia]

Is there a plumber in the house

[Chris Melia]

A GTD at Gtd AGM November 2001
Middle two pipes cross over.

[Chris Melia]

GTD at last years UK Kit car show

[Chris Melia]

For 302 cu/in engines use 1.5/8" dia pipes
For 351 cu/in engines use 1.3/4" dia pipes

[jimbo]

Chris:
Does the pipe diameter spec change depending on whether you are running open exhausts for track-only use, or running silencers (mufflers here) and driving the car on the street? It would seem that if the system has silencers, the afterload (back pressure) is higher and you'd want larger pipes. Or, isn't it enough to make a difference?