Exhaust System for a Gas Flowed Head

[Mazzini]

I was having a chat with a friend about the ideal exhaust system for an Elan with a gas flowed Q420 head.

The TTR fast road system would be the obvious choice, but I've had one before and I didn't like the manifold, it seemed to put heat into places that I didn't want it, even with a Zircotek coating it still managed to melt my headlamp vacuum pipes. I should have bound the manifold in heat wrap. I ended up selling it as I wanted something that looked a bit more standard.

PMS sells a stainless wide bore (internal diameter) manifold, 34mm as opposed to the standard Lotus 28mm. However by the time the manifold gets to the Y piece, it's back to the standard Lotus pipe size of 38mm.

The tailpipe on the S1-3 is about 35mm (off the top of my head)...

I'm starting to think the best solution would be a PMS manifold with a TTR centre pipe with a TTR transverse silencer. The silencer has a larger tailpipe than standard.

I did find the TTR silencer a bit tiring on a long (200+ mile) run.

Perhaps somebody, whom is better informed, could explain the science behind exhaust systems? Is the pea shooter exhaust functionally as bad as it looks? I look forward to hearing your thoughts.

[661]

Kelvedon have a nice looking stainless big bore race manifold.
I believe a lot of the race teams use Lance Pritchard at OJZ. That will be bespoke not off the shelf and therefore $$$
I've gone with the full TTR race set up with zircotec downpipes. I think if I had my time again I'd maybe try the Kelsport one on the dyno instead of the TTR one just for comparison. The other thing I'd want is to be able to take the pipes off individually rather than in the fixed pairs.

[Mazzini]

I suspect that the Kelvedon manifold and the PMS are one and the same.

Agreed the TTR manifold was a pain to remove and refit, at least with the body on.

[promotor]

If you want to spend good money on a custom designed system for a specific engine it might be worth speaking to Tony Law (Exhausts), he's got plenty of experience with TC's, mostly of the mk1/mk2 escort / cortina type but I'd guess he'll have experience of Elans too.

Definitely worth asking what can be done and how flexible the design is in terms of changing engine spec later on down the line. Expensive but custom always is.

[jono]

PD Gough, Nottingham, made custom headers for my old Plus 2 and the system worked very, very well.

They have patterns for most cars including Elans and +2's - worth speaking with based on my own experience

[Andy8421]

Perhaps somebody, whom is better informed, could explain the science behind exhaust systems? Is the pea shooter exhaust functionally as bad as it looks? I look forward to hearing your thoughts.

I am not sure I am better informed, but I do have some understanding of the science behind exhaust design. Putting the issues of noise and physical constraints to one side, the assumption that no exhaust would be the best solution for power turns out to be incorrect. When the exhaust valve opens, it sends a high pressure pulse down the pipe which is reflected by a change in diameter - the point at which the pipe joins the other pipes. This pulse then travels back up the pipe, and is reflected back by the valve. A complex series of high and low pressure waves move up and down the pipe, interfere with each other and with pulses from other cylinders and create static areas of high and low pressure. The position of these is engine speed and pipe length dependent, and the aim is to create an area of low pressure at the valve throat around the time the valve is in the process of closing in order to scavenge the cylinder.

With the appropriate computer model, I am sure that length and diameter of the exhaust can be calculated to generate the best scavenge for a particular rev range. That's way beyond me.

I am not sure whether the current crop of exhausts available are scientifically based, or were arrived at by trial and error. My guess is the latter.

Rgds,

[Mazzini]

Thanks for that

[rgh0]

Burns stainless provide a design service for sizing an exhaust as well as all the components needed for custom fabrication if you want to go down that route. Also general information on exhaust design in their catalogue

https://burnsstainless.com

A friend built his exhaust for a S4 twincam 7 using their design program and its work well. About 10 hp better top end power than a similar spec engine in my Elan with TTR race headers. But the 4 to 1 design he used you can fit in a 7 but not an Elan and is certainly part of the improvement.

cheers
Rohan

[Mazzini]

Rohan,

Thanks for your thoughts on and off the forum.

Rob

[pharriso]

PMS sells a stainless wide bore (internal diameter) manifold, 34mm as opposed to the standard Lotus 28mm. However by the time the manifold gets to the Y piece, it's back to the standard Lotus pipe size of 38mm.

The tailpipe on the S1-3 is about 35mm (off the top of my head)...

I'm starting to think the best solution would be a PMS manifold with a TTR centre pipe with a TTR transverse silencer. The silencer has a larger tailpipe than standard.

I bought one of the PMS SS exhaust manifolds (headers in the US) last year & am just about to fit it, it is an amazing work of art:

According to Paul Matty they are manufactured by the same company that make BMW's motorbike exhaust manifolds.

The ID of the Y piece (exit) is actually 42.5mm with an OD of 45.7mm, the pipe(s) that go into the Y piece have an OD of 38.2mm & ID of 35.1mm.

[Foxie]

<Snip>

Agreed the TTR manifold was a pain to remove and refit, at least with the body on.

I agree it's a more difficult job than the standard manifold.

What I did on the Plus 2 was to shorten the 4 front studs to minimum and use 10mm hex-5/16" UNF nuts, and use 5/16" UNC cap screws at the rear.

I also cut away the fibreglass joint flanges at the fuse box edge, and reinforced the same joint on the inside from the footwell. The fuse box heat shield is temporarily removed for better access.

[Foxie]

I bought one of the PMS SS exhaust manifolds (headers in the US) last year & am just about to fit it, it is an amazing work of art:

Looks great ! Do you have a pic of the complete assembly ? Is it one- or two-piece ?

[pharriso]

I bought one of the PMS SS exhaust manifolds (headers in the US) last year & am just about to fit it, it is an amazing work of art:

Looks great ! Do you have a pic of the complete assembly ? Is it one- or two-piece ?

Here you go:

Unassembled...

& Assembled

It's 2 piece...3 with the Y piece

[alan.barker]

I hope you don't need to modify the Chassis Flange too much so the Manifold doesn't touch.
I think i bought the stainless Manifold for my Sprint from SJS.
I didn't see the Manifold would touch the Chassis Flange untill i had fitted the Engine.
Went to lift Manifold into place to fit the Exhaust Studs and oh dear the Manifold touches the Chassis Flange I think i need to sit down and take a nice cold Beer, fiddle sticks or words to that effect.
The problem is once the Engine is in place the access is difficult to redesign the Chassis Flange.
Unless you feel super Zen and simply remove the Engine a second time.
Alan

[pharriso]

The problem is once the Engine is in place the access is difficult to redesign the Chassis Flange.
Unless you feel super Zen and simply remove the Engine a second time.
Alan

How about using a Dremel tool with a coarse grinding stone? I think there's enough space with the headers gone...