crossover exhaust question

[Clayton]

Thanks Brooke
Not knowing what angles I needed at the start, I ordered a selection of 30, 45, 60, 90 and 180 degs in 1 ¾”. But with a problem in the quality of the bends I ended up buying more from 3 different places $$$.
The finished system has 38 bends at various angles. For a start I would get 4 x 180’s and maybe 25 x 90’s if I was going to do the same system again.
As for the straight pipe, 3 odd metres.
The length of the pipes were in the 35-36” range. The longest being 2 and 6 and the shortest, 4 and 8.

Jim’s collectors can be found in the “How to Do” section under “Engine and Transaxle”
Hope this helps.

Thanks Denny Dera
It helps when you were brought up by a fitter and turner as an old man.
Big shoes to fill though.

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[Brooke]

Clayton thanks for the inspiriation to build my own 180s.
They are for my Pantera.

 

[Clayton]

My pleasure Brooke, you’ve done a great job on the pipes. :thumbsup:
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[Lee]

I know it's an old thread but I am really struggling to find a decent set of pictures of a crossover exhaust system which DOES rotate round on BOTH sets of 4 headers.
Looking from the back of the car towards the front, most sets I have seen follow the below pattern which as far as I can see rotates on the left hand bank but not the right hand bank.

- 8 3 - 7 4 -
- 5 2 - 6 1 -

With 13726548 firing the left bank rotates clockwise and the right bank does a criss-cross
With 15426378 firing the left bank rotates anti-clockwise and the right bank does a criss-cross.

Has anyone got photos of a set of pipes which rotate BOTH sets of 4. Is the below drawing showing the original design? It has 4 and 7 together therefore NOT rotating. Heaven forbid, is this drawing WRONG?

The Gelscoe cars copy this design. You can see very easily on the 2 attached photos that 4 and 7 are next to each other on the top of the right hand set and therefore this bank is not rotating.

Here is another set where clearly you can see 7 and 4 next to each other.

This is where I got the 3 above images and the drawing from.

RS fabrications search results: gt40
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[Clayton]

Hi Lee
Hopefully you can that 4 & 7 are not side by side in the set that I made.
Will add a few pics of them been coated as well.

Clayton

 

[Lee]

Hi Clayton.
Very nice set of pipes, but I am still a little unclear.

It appears you swapped both sets of internal crossover pipes to keep symmetry. 6 and 7 have been swapped to fix the right hand bank. So your right hand bank appears to use 1467 which rotates. Fixed from the standard 1476 which does not rotate.

But to keep the symmetry it looks like you also swapped 2 and 3 on the left bank which has changed the left hand bank from the standard 2583 which would have rotated, to 2358 which does not.

Please can you clarify?

 

[Lee]

I also see in the thread http://www.gt40s.com/forum/gt40-tech-engines-induction-exhaust/35127-2-headers.html another very nice set of pipes which have not followed the old drawing. Again it appears that the order on the right hand bank has been 'corrected' so that they rotate, and the left hand bank has also been changed so now the left bank does not rotate.
That set appears to have been made as follows

- 8 2 - 1 4 -
- 5 3 - 7 6 -

The search continues, or am I missing something?

 

[Jac Mac]

This Help...? bear in mind that thru the entire GT40 competition lifespan around 1969 the only firing order was the early 15426378 & all the 'race' camshafts in use were for that order, even the 351w engine in all the Muscle Parts catalogs had the camshafts with 15426378 order as options with repeated advice notes about changing the firing order to suit.... Thankfully the 351c was never an option as its cam was dimensionally different. We have also learnt a bit more in the last 40+ years so the rotation thing has become more fashionable... any advantage probably wasted on 90% of these cars though & would probably get you kicked out from FIA passports etc as non-standard..

 

[Clayton]

Well there you go, after all that I still managed to get it wrong :stunned:
At least one bank is original :laugh:

Clayton

 

[Lee]

What material to use?

Hey Clayton. Don't worry. As far as I can tell 99% of all GT40s and replicas have got it "wrong", so wrong is actually right, as Jac Mac says, if you got it "right" it would probably upset the FIA. I am starting to work out what to do for another attempt at sorting out my exhaust - I am hoping this will be the final version, so I may as well make sure it is made exactly as I want it. I haven't got an original so not following the original thinking at every point is not much of a problem for me.

I am also trying to work out what is the best material for the headers. Plenty of stainless steel out there and also ceramic coated mild steel. Trying to compare the pros and cons of each.

Advantage of stainless = pretty and long-lasting. My current headers are stainless, but they don't fit well hence they need making again or modifying which is why I am asking the questions.

What are the disadvantages of stainless? More heat transfer with Stainless, therefore higher engine bay temperature and more back pressure? Or have I got that the wrong way round as well.

 

[Paul Thompson 'Hooligan']

Re: What material to use?

Advantage of stainless = pretty and long-lasting. My current headers are stainless, but they don't fit well hence they need making again or modifying which is why I am asking the questions.

What are the disadvantages of stainless? More heat transfer with Stainless, therefore higher engine bay temperature and more back pressure? Or have I got that the wrong way round as well.

I seem to remember Janspeed in the UK saying that stainless systems are generally reckoned to be 2-3db louder than similar items made from mild steel. So if anticipated noise is going to be an issue, then mild steel is often preferred. I'm sure someone will be along with first hand exp to explain all...

 

[Russ Noble]

I know it's an old thread but I am really struggling to find a decent set of pictures of a crossover exhaust system which DOES rotate round on BOTH sets of 4 headers.-

Posts 92 and 93 here :-

http://www.gt40s.com/forum/gt40-build-logs/16138-kiwi-scratchbuilt-4.html

Photos dont show it very clearly but firing orders

3-2... 4-1
8-5... 6-7

Has the benefit that you can remove the heads without removing the exhausts.

 

[David]

Re: What material to use?

I seem to remember Janspeed in the UK saying that stainless systems are generally reckoned to be 2-3db louder than similar items made from mild steel. So if anticipated noise is going to be an issue, then mild steel is often preferred. I'm sure someone will be along with first hand exp to explain all...

While it doesn't mention sound I found this ( MYO exhaust system. ) which is relevant and may be of interest:

... Mild steel exhaust tube conducts roughly 220% more heat per foot than stainless steel exhaust tube, and as exhaust gases travel through a mild steel system they cool down, thereby losing velocity. By keeping the exhaust hot, the velocity will be higher, resulting in a better scavenging effect. Reverse flow will be reduced at lower rpm too. A good way of keeping the heat in a mild steel exhaust system, is to coat the system inside and out, with a thermal coating such as Jet Hot.

More heat stays inside stainless header tubes which can be beneficial; by not allowing the contraction of the cooling gases as they flow down the tubes, more exhaust velocity is retained which promotes better scavenging. This retention of velocity increases the overall header efficiency.