DDK - Die Deutschen Klassiker

Hooligan I was…

Great !! Inspired me to sell my 1303 and get a squareback !!!

Type 3s - very under rated cars

OK, so back to more serious stuff...

One of the things that's always bugged me – and hampered my efforts at Wiscombe Park – is the problem with fuel surge, notably through the Esses and exiting Sawbench and Martini hairpins. I always run with at least a half tank of fuel (usually more) and the stock tank has a built-in swirl pot, so the problem lies squarely with the Weber carburettors. I've carried out the accepted mods, with extended jet stacks and tall vents from the float chambers, but the problem never went away. The carbs are mounted the opposite way to each other, so one carb floods on left hand bends, the other on right hand bends... You can smell petrol to the extent that one of the marshalls reported it on the last outing and the scrutineers checked the car over to make sure there wasn't a fuel leak!

Short of dry-sumping the carbs, as off-road racers do on 48IDA Webers, the only realistic way to cure the problem is to go to EFI, with throttle bodies. That also opens the door for me to go down the root of crank-trigger ignition. However, before we go any further, we (Graham Rawlings and me) both agreed that the regular dual carb manifolds sold for use on Type 4/914 engines are less than ideal in terms of profile – the need to have the carburettor mounted vertically means that the manifolds have to take on a sharp bend as they join the inlet ports on the heads. This results in the back of the valve being shrouded. Wouldn't it be great if you could straighten the manifold to give a straighter shot at the valve? And that's where throttle bodies come into their own, as they don't care what angle they're mounted.

Taking a regular manifold, we've cut it close to the head and moved the throttle body out by a few degrees – so far it's just tack welded so I can check for clearance between the ITB and the side of the engine bay – but looking down the manifold from the top, you can see how much more of the port is exposed. By adding more weld to the outside (top) of the manifold at that point, we can also then smooth out the radius still further, resulting in improved flow and a better shot from the injector. The compound photo shows the comparison between the standard and modified manifold.

It's a small step at this stage, but should help not only cure the stumble but also take us another rung up the power ladder... Boys and their toys, eh?

This shows how much space we have to play with either side of the engine bay...


Roughly cut, rotated and tacked manifold:



Compound view down the manifold, stock on left, modified on right:

Never had such probs with the PMO's on the Lola, or the webers on my 2.2 long ago hillclimbing.
Best to go straight to crank fire etc and all it brings to the party?

The IDFs are very different carbs to the PMOs, Solexes, Weber IDAs, which were designed to run on the 911 engine. Although commonly used, the IDFs weren't... But also the ITBs allow us to sort the fuelling far more accurately across the rev range – crank fire ignition is the icing on the cake, to allow fine tuning of timing at all points. All of this will (should) ultimately help us increase the power/torque.

Hi Keith
I don't believe the 914 inlet manifolds I have are as sharp a bend as yours.
Have a look here https://www.ebay.co.uk/itm/115076470229

On my 914/6 I tried baffling the carbs to prevent fuel flowing up the bowls on hard corners, couldn't get it to work brilliantly so I went to PMO's.

My Crayford used to run on Solex Pii40's with weir returns to tank----another option?

Cheers

Ian


ps I've also got Heidegger Inlet manifolds from a super vee , not for sale at present but might help you with design

By increasing the angle that the air has to turn is there any chance that you decrease the flow?

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neilbardsley wrote:By increasing the angle that the air has to turn is there any chance that you decrease the flow?

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Neil, we're straightening the passage, not increasing the angle... In an ideal world, the inlet manifold would be a dead straight line into the port, but there's not enough width in the engine bay to do that. By moving the throttle body over from vertical, we're doing what we can to improve the flow.

A brief test fit of the mocked up manifold with the ITB fitted shows that we still have adequate space either side to allow for engine movement:



Another possibility is to cut the flanges off the manifold and reverse them so we can fit the ITB the other way round, moving the fuel rail to the inside - that would give us more space and allow us to cant the manifold/throttle body over still further. It's a question of weighing up the extra work involved against the possible performance gains.

Thats the reason you were sooo sooo slow`;)

914-6 wrote:Hi Keith
I don't believe the 914 inlet manifolds I have are as sharp a bend as yours.
Have a look here https://www.ebay.co.uk/itm/115076470229

On my 914/6 I tried baffling the carbs to prevent fuel flowing up the bowls on hard corners, couldn't get it to work brilliantly so I went to PMO's.

My Crayford used to run on Solex Pii40's with weir returns to tank----another option?

Cheers

Ian


ps I've also got Heidegger Inlet manifolds from a super vee , not for sale at present but might help you with design

A little Christmas shopping…

KS wrote:

A little Christmas shopping…

I would be interested to know how much of an improvement that will make.

Which, the ATB diff or the quick rack conversion? Hopefully both will help in my quest…

Have the lsd in my Lola, superb imho.

I’ve got one in my 911. Also a big fan