Exhaust system

[JamesG]

I need to renew my current exhaust system and have a couple of questions (bearing in mind that as a special bodied car the engine is mounted differently to normal and a standard exhaust will not, and cannot be made to, fit).
The current exhaust has pipework from no 2 cylinder across and joining pipework from no 1, and similarly no 4 is joined to no 3, before 2/1 merges with 4/3 to a single pipe. This makes quite complicated pipework, but I believe it is done so that the exhaust pulses are 180 degrees apart. My question: is this actually necessary on a Jupiter engine? It would be much simpler to join 1&3, and 2&4, and then merge them.
Secondly, does anyone know of a reliable and economic custom exhaust manufacturer in the South West (I am in Sidmouth)? I am following Google leads, but am not too confident in those I have found so far.

[JUP]

Give Luke (Blacktop Restorations) on 01531 650888 a call - He has just made me one in stainless steal for my special bodied Jupiter and it is
fantastic
There is an article on him in the latest ''By Jupiter'' and has a lot of experience with working with Jupiters
I know he is not local, but it is worth considering if you need anything else doing at the same time (like the adaptation of the chassis where the
gearbox shaft goes over, which allows you to take the gearbox out without removing the engine)
I also found him very quick indeed

[JamesG]

Thanks Graham. A fair way from here but not impossible. Will bear it in mind.
James

[RichardMc]

Hi James,
The standard Jupiter is 1&3 and 2&4 with the crossover pipe and works well enough, could you do this but turn the 2&4 manifold round to face backwards, this gives you two rearward facing pipes that can be joined in a single Y piece. The only problem is the standard cylinder head exhaust flows forward when fitted to 2&4 so the manifold needs adapting. If you currently have a 4-2-1 fitted the cylinder head may have been modified in the past to flow backwards. They do sound good with a 4-2-1, you still get that nice Jowett 'warble' but a bit louder.

[JamesG]

Thanks Rich. Not sure what the standard manifolds look like, but I have basically four separate mild steel plates with the exhaust tubing welded on, all facing backwards. See pictures (not great!) Apart from sound, are there any performance benefits by going 1/2 and 4/3 rather than 1/3 and 2/4.

[RichardMc]

Wow! Nest of snakes?
The simple answer is 1&3 / 2&4 isn't as good as 1&2 / 3&4 when it comes to using the previous exhaust stroke to extract more gas out of the next cylinder because it doesn't match the firing order. BUT, unless you are chasing the last few HP out of the engine it doesn't matter that much. Looking at the pictures it is all a bit tight / space limited so even a 4-2-1 is probably compromised by the length of the primary tubes.
If it was me I would go down the path of least resistance and make up an exhaust system that is the easiest to manufacture, the standard system is a compromise and plenty of people are happy with the result.


I did a quick guide to the exhaust a while ago, this pdf might work on the forum.

Performance Jowett Exhaust.pdf

(313.89 KiB) Downloaded 46 times

[Chris Spencer]

Well I don't know about anyone else but that's the first exhaust system that I've seen constructed by someone blindfolded - I wouldn't even fit it to my rusty wheelbarrow - I would suggest that its fit for the scrapheap and as you have already planned start again - The Jowett race teams normally have 4 into 1 systems built with a custom flange to the head and separate pipes to a flute reduction from 4 - 1 - It would probably to pay for you to look at other vehicle manufactures systems that fitted their cars with a flat 4 such as Alfa with a view to what could be adopted or copied

[RichardMc]

Alfa 33 race exhaust.

[JamesG]

Thanks Chris and Rich. Certainly food for thought. I think I might have to sacrifice some ground clearance and have a simpler system than current, with 4 into 1.

[David Morris]

Hi All,

That Alfa 33 exhaust system deserves to be on the wall of an Art Gallery! Absolutely superb workmanship!

All the best,

David

[Forumadmin]

download/file.php?id=5947&mode=view

[JamesG]

Thanks. Looks much more straightforward that way.