Twin cam carburettor cross over pipes plus other noob questions.

[berni29]

Hi There Guys

Apologies for the noob question, but did all Fedral Twincams originally have those crossover pipes that run from the exhaust to the Stromberg manifold? I presume this is to combat carb icing? I have only ever seen one photo of a car with them, namely Fourloti's car 3826R, which is what got me thinking about them.

Why do people remove them? Do originality nuts put them back when missing? Whats the story?

Other noob questions, on a TCS, what is the standard cam cover colour, and all TCS's apart from the JPS were available with black or oatmeal interiors right?

Many thanks in advance

Berni

[Kendo]

The crossover pipes were an emissions solution, I think to warm air entering the engine so gas wouldn't condense. They make a long air passage, reducing engine responsiveness. If you wanted to fake originality, you could retain them, but block off the ends with a thin patch of aluminum. There are also a second set of butterflies that would have to be removed.

My 1974 TCS cam cover is black.

I don't remember when the oatmeal interiors came in. But mine had that color.

[4129R]

I have never seen any other colour on a "Big Valve" Twin Cam engine other than black, with the BIG VALVE lettering on that cover.

I have only seen red on small valve twin cam engines.

[berni29]

Hi Guys,

Thank you for the answers.

With regards to the "Big Valve" legend, I have seen it misquoted as "Big Value" and "Bio Valve". It does quite often look like "Bio Valve" I must say.

All the best

Berni

[BDA]

The crossover pipes are commonly deleted. When I bought my car at the distributor, they were deleted for me without asking me (which was fine with me). Also, headers are a common mod that shouldn’t affect the originality since headers were a Lotus option. Although I have seen a picture of headers that support the crossover pipes, most don’t, notably the original Lotus headers (which are probably very difficult to find - newer headers are quite common).

[berni29]

Hi BDA

Very interesting, so if the car was optioned with headers, and fitted at the dealership I would think, then the crossover pipes would have been binned at that point.

Thank you

Berni

[Pfreen]

BDA.
 Are you saying the dealer removed the crossover pipes?  If so, they are lucky they were not caught since that is very illegal.
I have never heard before that headers were a factory option.  That's interesting.  I wonder what they looked like.

[jbcollier]

Yes, all Federal TCs had the funky pipes fitted.

Nothing to do with carb icing.  It's complicated system with an extra throttle plate to divert some of the mixture to the manifold hot spot.  The amount of mix diverted depends on the throttle position.  Most at idle, none wide open.  Reduces the amount of unburned hydrocarbons at idle and low speeds.

They are removed as they reduce performance and drivability.

Originality nuts do refit them.  Some people fit the pipes but alter things internally so they are disabled.

[BDA]

I bought my car from the Lotus distributor in New Orleans and they did indeed delete the crossover pipes for me. I guess it was technically illegal but I don’t think there were any checks for emission equipment there then. My memory is a bit foggy but I think they commonly did that for the Europas they sold.

Check out this page of the Europa TC parts manual for the Lotus headers: http://lotus-europa.com/manuals/tcparts/s/tcsa.pdf

Ironically, I don’t remember seeing any Europas with headers or any mention of them at the Lotus distributor when I used to hang around there. They did have a few Vegantune motors lying around presumably for sale.

[Bryan Boyle]

***deletia***

Check out this page of the Europa TC parts manual for the Lotus headers: http://lotus-europa.com/manuals/tcparts/s/tcsa.pdf

Ironically, I don’t remember seeing any Europas with headers or any mention of them at the Lotus distributor when I used to hang around there. They did have a few Vegantune motors lying around presumably for sale.

I think that the native and ROW cars used the 2-piece header assembly that is in the parts manual, it was only because of our emissions regs that they went with the cast header to allow the cross-over piping to be installed.  In theory, they probably could have gotten it to work...but most of the cars that I've seen with the crossovers have them just for 'show' and the functionality has been deleted.  I can't use them (unless just as decoration); I modified the secondary body by removing the butterflies and plugging the preheat circuits, butterfly shaft openings and leaving the balance tube in place.  Which reminds me...I should put a heatproof gasket in under the plate to seal the out-and-back just as a precaution...  It could be a source of air leaks...

[BDA]

That makes sense. I guess providing non-state-approved parts was a bridge too far while just taking off bits that were supposed to be there was not.

[SilverBeast]

My UK 74 TCS has a cast header. I believe the tubular header was an option over here too.

[berni29]

Hello again

I have been doing some research on standard cam cover colours, and going back to that particular question, do any Fedral TCS owners have a red (big valve) cam cover that they know is original?

I read that Big Valve TC's for overseas markets had red and domestic black covers, but that is clearly not true.

Thanks again

Berni

[BDA]

I don’t think I’ve ever seen a Federal Europa TC cam cover that was not ribbed and black. But then I found I this accounting of TC can cover ribs and colors (https://lotuselan.net/forums/viewtopic.php?t=20706&start=).

I make no guarantees as to the accuracy of that post or my memory.

[Arizona]

The early federal TC's were red. The TC Special's were black.