Purist question re: "Bundle of Snakes"

[ragrod]

Bob, Nice!!! I am in total awe, can you show more!!!
Randy

[Howard Jones]

8 into 1. I remember a CanAm car back in the 5.0 spec days known as a frisby(lola chassis I believe). The car was driven by Bobby Rahal and it had a 8 into 1 exaust. 4 into 2 into 1. It did in fact sound quite a bit different that the rest of the field. I asked one of the crew about it and he said it was because it sounded cool. At the time I really didn't buy that but I couldn't understand why nowone else was using something that the front running car was doing if it was a performance advantage.

I haven't seen another exaust like that since and have always wondered about that.

Any further comment? Jac?

[Bill D]

I have heard the term "180 degree exhaust" used to describe the echaust system on a GT40. Every 180 degree of crankshaft rotation there is one exhaust pulse entering the collector. This is ideal timing because, as one pulse exits the collector, the next exhaust valve is opening and the vacuum created in the system pulls the exhaust from the cylinder. In this ideal 180 degree cycling the collector outlet diameter only needs to be 20% larger than the primary tube diameter. (Example: 1 3/4" primary tubes need a 2" collector outlet diameter.) The rule of thumb here is two tube sizes. This keeps the velocity fast to increase scavenging, especially at lower R.P.M.s. Going to a larger outlet diameter will hurt the midrange and low R.P.M.

In the case of a SBF V-8 firing order with a conventional header and collector system, the first two pulses are in one collector, the next two fire in alternate collectors, then the next two fire in the same collector, and the last two in alternate collectors, creating an unbalanced exhaust. If the proper collector outlet diameter is being used (two sizes larger than primaries) the two pulses in succession load up the collector with more air than it can flow. This results in a very strong midrange torque, but causes the engine to "sign off" early, not reaching its potential peek R.P.M. The improper firing order on a V-8 engine results in the need to use large diameter collectors so the engine will perform well at high R.P.M.s. Unfortunately the large diameter collectors cause a tremendous drop in air velocity, resulting in less scavenging through the entire R.P.M. range.

Bill D

[Mark Paris]

Iain,
The silencers in the pics looks pretty unique (at least here in the UK we don't see them like that!). Do you build these, and how do they compare with the standard "original" type silencers?
I'm interested in reducing the overall length of the run from primaries to visible pipe ends.

Mark

[Straight 8 Racing]

Hi Mark,

We built the system here in Australia, we have made the tools/molds to enable us to fabricate replacements, originally to resolve any rear end hits that unfortunatley are a fairly frequent event in our races. They may well be slightly over done but I wanted to be sure we beat the noise meter at the track which is set at 95db.
As they are for the track we do not have any catalytic converters but these could easily be inserted in the 3" pipe over the top of the gear box

Iain

[Jac Mac]

Originally Posted by Howard Jones

8 into 1. I remember a CanAm car back in the 5.0 spec days known as a frisby(lola chassis I believe). The car was driven by Bobby Rahal and it had a 8 into 1 exaust. 4 into 2 into 1. It did in fact sound quite a bit different that the rest of the field. I asked one of the crew about it and he said it was because it sounded cool. At the time I really didn't buy that but I couldn't understand why nowone else was using something that the front running car was doing if it was a performance advantage.

I haven't seen another exaust like that since and have always wondered about that.

Any further comment? Jac?

Thats how I set them up if its possible Howard, made a set for a jet boat once where the primaries were arranged in a circle and in such manner that by rotating the collector 1/4 turn it converted from conventional uneven pulse to even 180° pulse ( two 3" dia tailpipes ), also had a second collector that we could fit which was 8 into 1. The 8/1 sounded absolutely delicious & I reckon we woke up the entire population of Queenstown on one early morning test run to the head of the lake & back.
Now with regard to a system on a GT40 it is a benefit in relation to weight and decibel reading. The TVR that I built a system for, which could be an easy fit to a 40, was checked at 88 db in its final form, similar power cars with conventional exhausts were struggling to meet the 95db limit.
I will be interested to see Ian's results from his system although one aspect that concerns me is the 'heat dam' that may build up under the rear clip with the surface area of the mufflers.

Jac Mac