Bundle of snakes question

Daryl Adams · 01-06-06, 01:07 PM

Maybe someone can help me better understand our exhaust setups. A friend asked me to explain why GT40's use the "bundle of snakes" exhaust arrangement. I explained to him how in a traditional exhaust system the V8 firing order sends pulses to the collectors in a uneven pattern. Twice per cycle it fires two in a row into the same side. I told him the the "bundle of snakes" arranges and separates the pulses to alternate evenly, side to side, between the right and left collectors. (a 180 degree arrangement) Now, here's my problem. I was also under the impression that, in order to maximize the "scavanging effect" from each individual pipe, the various pipes were arranged so that, in each collector, the pipes fired in a "rotational order". When I checked this out on a couple photos of systems, though, I found that there was rotational order in one collector and diagonal order in the other. Am I seeing it incorrectly or am I mistaken on this whole issue?

Brian Magee · 01-06-06, 01:43 PM

I checked this out some years ago when I was having my exhaust system built and I found the same. I cannot remember where the problem was but I believe it would have just needed two pipes changing over which could have been done quite simply. As I was having mine made 'piggy back' with someone elses and we both prefered to go for originality, then we did not persue it. However I am sure you are correct.

Brian.

TimB · 01-06-06, 05:08 PM

I don't know if this could be related or not. Remember that small block Fords have used two diferent firing orders

351(1-3-7-2-6-5-4-8) compared to the 289/302 (1-5-4-2-6-3-7-8).

Is it possible that people have blindly replicated an as origional exhaust system that is no longer optimal due to a change in firing order?

Jim c · 01-06-06, 05:58 PM

I might be wrong but I think if your collectors are made correctly it would not make any difference if it was diagonal or rotational on a bunch of 4 pipes.

The collector should waist down after the collector to about the primary pipe size or slightly larger then expand out to the system size.
This helps increase the the negitive wave ,the fact they are next to or diagonal I wouldnt think would have to much effect unless you had a bunch of open pipes maybe.?

Jim

Jac Mac · 01-06-06, 07:21 PM

Hi Fella,s. I will try to clear this up. Daryl you were seeing correctly.If the rotational sequence in the rh collector is changed to 1467 then both collectors have rotational orders[Left bank anti clockwise, right bank clockwise]on a 15426378 firing order. With 13726548 f/o the rotation changes in each collector. Does it make a difference? With the early type collector fabricated from 4 tubes maybe, on later types where the primarys dump into a tapered cone type probably not. If you create a " prism" in the centre of the collector it will complement the rotational order. Regards Jack.

Mike · 01-06-06, 10:38 PM

Here's two cents worth. To clarify, the firing order of SBF's goes with the cam, i.e. if you use a 351 cam (regardless of 289/302/331/347), you get the 13726548 order. If you go with a 302 cam, you get the 15426378. I started with a 302 cam, and recently changed to a 351 cam, along with the new firing order...after first trying to figure out why it was spluttering

. Would you believe the guy I custom ordered it from 'forgot' to mention it was a 351 cam?

Mark Worthington · 01-06-06, 11:57 PM

[ QUOTE ]
If you create a " prism" in the centre of the collector it will complement the rotational order. Regards Jack.

[/ QUOTE ]

Would you mind explaining this a bit? I'm having trouble visualizing a prism inside a 4-into-1 collector. A cone, yes, but not a prism.

Jac Mac · 01-07-06, 02:00 AM

Hi Mark,Yes I stuffed up. A better description would be a 4 sided pyramid with concave sides,the radius at the base of each side matching each primary pipe as they enter the collector.In the U.S. it is called a "goilet",and works by streamlining the flow into the collector and reducing the pressure drop. Rgards Jack.

Bill Musarra · 01-07-06, 03:11 PM

The description at first threw me a little as well. Imagine the four pipes without the collector. Your looking at it on end. There is a gap between the four pipes in the center. Jack is descriping how they come together to a point in that center

Bill

Jac Mac · 01-08-06, 03:51 AM

Fran Hall has posted a photo of this part in a collector under "All GT40- tubular sex". Who would expect to find it there! Jack.