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BAD942B wrote: ↑Sat Jan 27, 2024 5:45 pm I am fabricating my inlet & exhaust manifolds for my Lotus Europa S2 1565cc bored to give 1605cc, its along the lines of the Hermes conversion in the 70s fabricated by Mike the pipe,, this conversion entails going from a dual barrel Solex to twin 45 Dellorto's, this brings its own easily sorted problems.

But the exhaust manifold brings another, the head has rectangular ports similar to an A series but bigger, in fact the port itself is very similar but with a an angled valve like a Longman head but more angled.
I have made the holes in flanges about 4mm bigger all round than the port so using 1.5mm pipe pressed into the shape from a round pipe it leaves 2.5mm all round for antI reversion mismatch or do i just get the exhaust flange remade with round holes with a larger mismatch in the flat part of the port & very close to the pipe dia at the corners.
Then modify the exhaust ports to a D at outside flat like Vizard suggested years ago ?

Ronnie wrote: ↑Sat Jan 27, 2024 5:59 pm

BAD942B wrote: ↑Sat Jan 27, 2024 5:45 pm I am fabricating my inlet & exhaust manifolds for my Lotus Europa S2 1565cc bored to give 1605cc, its along the lines of the Hermes conversion in the 70s fabricated by Mike the pipe,, this conversion entails going from a dual barrel Solex to twin 45 Dellorto's, this brings its own easily sorted problems.

But the exhaust manifold brings another, the head has rectangular ports similar to an A series but bigger, in fact the port itself is very similar but with a an angled valve like a Longman head but more angled.
I have made the holes in flanges about 4mm bigger all round than the port so using 1.5mm pipe pressed into the shape from a round pipe it leaves 2.5mm all round for antI reversion mismatch or do i just get the exhaust flange remade with round holes with a larger mismatch in the flat part of the port & very close to the pipe dia at the corners.
Then modify the exhaust ports to a D at outside flat like Vizard suggested years ago ?

Engineering projects should be well engineered, you sound as if you are doing a good job, form the pipe rectangular.

andy1071 wrote: ↑Mon Jan 29, 2024 11:36 am The 'normal' thinking is to have the upper part of the port and manifold flush, as this tends to be the area of highest gas speed, and the mis-match at the bottom where the gas speed is slowest.
-You'll see this arrangement on many/most motorcycles...

Are you thinking of having a 4 into 1, or a 4-2-1...?

-If you e-mail me the engine bore + stroke and the valve timing I can do a calculation of the required pipe diameters and lengths...

andy1071 wrote: ↑Tue Jan 30, 2024 10:42 am No, not much room....

The same principle applies to the inlet/intake, but the other way around... you want the manifold to have a 'step out' to the head port.

Exminiman wrote: ↑Fri Feb 09, 2024 6:38 am My suggestion ( if you havn’t already) is to have a word with someone who has experience of that engine, presumably its the Rover K series ?

You could quite easily lose power making things bigger in the wrong places, especially if its a 16V as it will need to maintain a certain port velocity ( speed) of the gases ……in the ports….

As you have probably relalised, Square ports or manifolds flow better, because for a given space envelope a square section is bigger than a round section…..

These people seem to have an idea of what to do https://www.hangar111.com/lotus/rover-k ... ne-tuning/ they also quote “Exhaust Manifolds – specific to the level of tuning to maintain backpressure” so it may be something to watch ?

Alex wrote: ↑Sat Feb 10, 2024 1:18 pm The chap who runs the Berliet museum in France probably knows about the engine - he was a Renault engine development engineer.
Fascinating chap, we listened to him for hours.