Lotus Elan

Oval Exhaust

PostPost by: Famous Frank » Wed Feb 20, 2019 3:01 am

intermediate-exhaust-5.jpg and
elliptical intermediate exhaust pipe middle shape
As a manufacturer of Exact Reproduction Seat Covers, Door Panels, Consoles, etc, I've been receiving more and more calls for exact reproductions parts. Lotus Owners across the globe are converting race cars back to street cars, wrecks back to street beauties! Typically I don't make a part that is available someplace else.

Lately, I've received requests for exact reproduction exhaust system parts. Nice stainless S1, S2, and S3 mufflers have been available from a number of suppliers both here in the states and across the pond. But no one to my knowledge has manufactured the elliptical (oval) ( what's the difference between elliptical and oval?) intermediate exhaust pipe. To answer these requests, I've spent the last few months working on an exact reproduction elliptical intermediate exhaust pipe. It's now finished. The only move away from the original is it's manufactured in 304 stainless. It looks great!

My question is, does anyone have an idea of when Lotus stopped installing the elliptical exhaust pipe? I know they were installed on the S1's from the factory. They were also installed on S2's in standard form. I owned one and it was fitted on my first S2. And I'm guessing they were also installed on S3's, again in standard form. By standard from I mean the non SE with the standard 105 HP motor and still using the transverse muffler.

Can anyone enlighten me or provide more info?

Many thanks,
Frank
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intermediate-exhaust-16.jpg and
intermediate-exhaust-10.jpg and
intermediate exhaust pipe
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PostPost by: gherlt » Wed Feb 20, 2019 6:41 am

An ellipse is a special oval. Oval (from ovum, latin for egg) is not necessary simmetrical, it's omething that looks like an egg.
The ellipse is mathemativally defined, an oval does not need to be.
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PostPost by: gherlt » Wed Feb 20, 2019 6:44 am

This is the first time I read about oval exhaust pipe. I can image that there is a slight gain in ground clearance, but also a slight loss of flow rate as cross section would be less.
If Lotus searched for more power and/or making cheaper parts, I suppose one easy way to go would be using ordinary pipes ...
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PostPost by: Gray » Wed Feb 20, 2019 8:28 am

I had a low mileage 1967 S3 (not SE) in 1974, which had the cast iron manifold and may have had the original exhaust. I'm fairly sure it had a round centre pipe.
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PostPost by: ericbushby » Wed Feb 20, 2019 9:34 am

An oval is two equal semicircles joined by two straight lines.
A ellipse is a figure where all points on it are equal to the sum of the distances from two points inside it.
Stick two pins in a board with a loose loop of cord round them.
If you now put a pencil inside the loop and draw round in a curve controlled by the cord it will describe an ellipse. Noticeably, it has curved sides.
The Ford `Oval` badge is an ellipse, as an example.
Well, what else have I to do this morning, it`s raining.
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PostPost by: Certified Lotus » Wed Feb 20, 2019 10:38 am

Frank, I?ve never seen one on an S1 or S2. Not that they didn?t come that way, just have never actually seen one. The exhaust bracket that mounts on the transmission with the associated clamp would hold the exhaust pipe at a specific distance to the chassis. I?m assuming the oval part is after the clamp? That might give you an extra 1/2 inch of additional clearance.
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PostPost by: rgh0 » Wed Feb 20, 2019 11:46 am

An ellipse versus an oval is a precise mathematical definition. When you press a circular tube to get a clearance improvement it depends on the press tools used as to whether you have something like an ellipse or an oval .

I have no ideal as what tools Lotus used on early Elans but they will have started with a round tube and pressed it into a specific shape. Interesting as both my 1999 Landcruiser and my sons Mk4 Golf R32 both have an oval / ellipse section in their exhaust to clear the rear suspension. My Elan and Plus 2 or Esprit just have plain round pipe

cheers
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PostPost by: Mazzini » Wed Feb 20, 2019 12:20 pm

I've been around Elan's for the best part of thirty-six years, I've owned quite a few, but I've never come across anything other than the standard round pipe. I'm not saying it didn't happen, just that I've never seen it.

I wonder if a US dealer didn't do it to improve ground clearance?
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PostPost by: theelanman » Wed Feb 20, 2019 12:52 pm

as the overall cross sectional area has not been changed I cant see that the flow rate would be altered........
you could put fairings on the inside to start the gasses spinning in order to create a vortex allowing the gasses to escape faster.........but then stutter as you get to a box...........lol
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PostPost by: elj221c » Wed Feb 20, 2019 2:12 pm

Mazzini wrote: I'm not saying it didn't happen, just that I've never seen it.

I wonder if a US dealer didn't do it to improve ground clearance?


A long time ago I worked on an ex IWR rally Elan. That had an oval pipe, I would guess for the extra clearance.

Also, my edition of the workshop manual, 36T327, Section D page 2 has a cross section of the rear suspension clearly showing an oval pipe.

Not shown in the exhaust section, though......
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PostPost by: Famous Frank » Wed Feb 20, 2019 3:16 pm

Oh my! I'm older than I thought.

The oval / elliptical intermediate exhaust pipe was INSTALLED AT THE FACTORY ON ALL EARLY ELANS! I'm just not exactly sure when they stopped installing them. It was for additional ground clearance.

To my knowledge they have not been available for decades. Mine are built to factory specs with the only deviation being they are made with 304 stainless versus mild steel. Which is why no one has seen one in years. Mild steel exhaust components many times did not last much more that a year. It's what kept companies like Midas in business. I've included a pic from an original Elan Parts Manual. It depicts the oval / elliptical exhaust pipe used on the S1 Elan, the non SE S2 Elan, and the non SE early Elan Coupe. I'm assuming the oval / elliptical pipe went out of production in the 1966 / 1967 time frame.

Oh wait, I just talked to a young gentleman in Starbucks this morning. He never heard of Midas.

Thank you all for the elliptical / oval education.

Frank
Attachments
shop-manual-exhaust.jpg and
S1, S2, Coupe Shop Manual oval exhaust pic
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PostPost by: Certified Lotus » Wed Feb 20, 2019 3:23 pm

Frank, are you also welding the mounting bracket on the pipe for the transmission mount?
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PostPost by: gjz30075 » Wed Feb 20, 2019 3:36 pm

Rotated picture
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shop-manual-exhaust.jpg
shop-manual-exhaust.jpg (53.21 KiB) Viewed 541 times
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PostPost by: Famous Frank » Wed Feb 20, 2019 4:09 pm

Thank you Greg! That is much better.

Glen, no, I'm not welding in the tab. I considered it but if installing the pipe behind the original down pipe with the expansion tank, versus the dual down pipes, versus the tubular headers, etc may change the location of the tab.

The biggest item that affected my decision to not led the tab on is the fact the tab was only welded on S1 pipes. On S2 SE and Coupe models the tab was part of of the exhaust pipe clamp part number 26 S088.
As the pipe is the same on all models S1. S2, SE and Coupe models, and the only difference is the location of the tab, I'll let the customer install the tab.

Glen, if you need one with the tab installed such as on an S1, I'll try to do that for you.

Good discussion!

BTW - I'm also currently working on the down pipe from the exhaust manifold with the expansion tank.

Not a big market but it's great seeing customers that want their vehicles to look like they did when they left the factory!

Frank
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PostPost by: 1owner69Elan » Wed Feb 20, 2019 4:37 pm

And then there is this "extreme oval" center pipe as fabricated for Leno's 26R to clear the 6-speed sequential Quaife transmission.

oval-lotus-pipe.jpg and


I wonder about the possible restriction on his 2 liter twincam.
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