exhaust manifold question

[BAD942B]

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]

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.

[BAD942B]

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.

I think so aswell but just wondering how much of Dave Vizards book re the Dee shaped exhaust port is still relevant in today's world, its not an A series so only flow & Dyno testing would really tell but I only have one head as it came off a Renault traffic, its much better than the poor inlet ports of the original Lotus head.

[andy1071]

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...

[BAD942B]

this is what I've had made so far, it just got put in to the laser cutters with other work projects. its easy to change now they have the basic drawing

[BAD942B]

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...

not much room at the bottom of the exhaust flange as a stud gets in the way

[andy1071]

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.

[BAD942B]

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.

I havern't built an engine in years where I lined up the port exactly, I always have the manifold slightly smaller than the port, 1mm diametrically, the flanges on this engine allow for 2 x 1.5mm pipe & porting the head.

The cam will almost certainly be a Cosworth grind or a modernised version of a Cosworth grind

[Exminiman]

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 ?

[BAD942B]

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 ?

No its a 60s design that was used in the Renault 16 & modernised in the late70s for the Renault Trafic from square inlet ports to round inlet ports.
There is unlikely to be anyone with experience of this engine still left alive, Salve Sacco is an expert in the Crossflow version & I have a lot of parts & experience for that engine, I wanted to recreate the Hermes conversion on this non crossflow engine using the parts I have in stock, Hermes got 138bhp from 1470cc in the 70s.
I have been trying to reduce exhaust backpressure in my modified engines for the past 45 years, not keep a level of it

[Exminiman]

Ah, sorry, missed the Europa bit, just picked up on the S2

[Alex]

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.

[BAD942B]

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.

Is that the one in Lyon

[Alex]

No, it's the warehouse museum out in the middle of nowhere - it was a stop on a navigational rallye, so I'm trying to find the notes.