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#504261 - 17/03/18 09:41 PM Sigma 4/4 throttle body improvement for free
Heinz Offline

Talk Morgan Addict

Registered: 07/09/09
Posts: 3668
Loc: Cologne, Germany
This is a tip for a small but fine improvement. As a result, the machine may run silkier and more evenly over all rev ranges.

Of course, you can leave everything as it is, but if you enjoy doing some handicrafts and love your car also for that reason, you've come to the right place. The nice thing is that it costs nothing.

The point is to improve the match between the throttle body and the connecting pipe. This avoids soluble turbulence, which can severely disturb the air flow. The picture shows the original throttle body. This bulge, which forms a semicircle at the edge of the TB, is clearly visible.

Image TB

Here is the connection as it runs in the Ford Focus or Fiesta directly from the TB to the air filter box. You can see the groove at pic 2 into which the protruding edge of the TB fits perfectly. This makes sense and ensures that the fit is perfect even in mass production. The hose is perfectly controlled.

2 Pictures accordion tube.

In our 4/4 Sigma we also have the iron tube between the TB and the accordion tube. The accordion tube is only used at the exit of the iron pipe and makes the connection to the air box after that.

We use a rubber hose to fix the TB to the iron pipe. And now this protruding edge on the TB comes into play. It causes the rubber hose to be decentered. The iron pipe is also decentered as a result and the strong tightening of the clamp does not change this.

Picture TB with rubber hose.

Now we file or sand down the edge. And look, the rubber hose and the iron pipe are centered. Attention, please never sand anything inside the TB! I made it worse once than I thought I could make the surface smoother. The car drove very horribly after that and I bought another TB from the scrap yard so that everything is fine again. Cleaning the TB is of course always good. And make sure that the TB is absolutely free of iron chips before assembly.

Picture TB after treatment

A word about the iron pipe. My Iron pipe was very clearly oval at the opening to the TB and not round, as it must be. This is probably the result of welding together the individual sections of the iron pipe. It's under tension. It must not be the case with yours but it may be. If it is as strongly oval as mine then you only have four contact points on the TB. And also here is a cause for very bad air flow and turbulence. I clamped the end of the tube in a vice and carefully pressed it back to a circle. You have to do this several times because the tube springs back into the oval shape at the beginning.

Here is the tube with the round end after treatment. Picture.

Another important point. Since everything is dismantled, take the chance and hold the iron pipe without the rubber hose and really fit exactly to the now re-installed TB. (don’t overtighten the scews of the TB they go into plastic). Then you can see if the welded bracket, which is screwed to the Intake manifold, is in the right position.
I had to bend mine a little bit and I also had to enlarge the hole for the screw a little so that everything fits exactly. Otherwise the whole work on the TB is a dog's breakfast.

At the end mount everything together, first fix the rubber hose to the TB, then push in the iron pipe and feel the correct fit in all directions. Then tighten the second clamp and finally tighten the iron pipe with the screw without any tension in the system.

Also the accordion tube should be repositioned evenly between air box and the front of the iron tube because at this point you also have an influence on a smooth engine run.

All together are about 2 to 3 hours for the TB and the filing, and again some time, if the attachment of the iron pipe would have to be adapted.
Try it out, it will be fun if the car runs a little smoother and reacts better to fine gas shocks.

#504267 - 18/03/18 03:48 AM Re: Sigma 4/4 throttle body improvement for free [Re: Heinz]
deano Offline

Charter Member

Registered: 12/02/12
Posts: 5307
Loc: Taunton
Top tips Heinz. Beauty is in the detail and the principal can be applied to any induction system where similar flaws exist.

Edited by deano (18/03/18 03:51 AM)
Martin (Deano)

#504268 - 18/03/18 04:23 AM Re: Sigma 4/4 throttle body improvement for free [Re: Heinz]
OZ 4/4 Offline

Talk Morgan Expert

Registered: 25/11/11
Posts: 2530
Loc: Australia - NSW Mid North Coas...
Nice work Heinz. Thank you for posting.
A Morgan Identified Fastidious Owner...
2011 4/4 Bespoke, 1981 Delorean DMC 12

#504338 - 18/03/18 03:21 PM Re: Sigma 4/4 throttle body improvement for free [Re: Heinz]
+8Rich Online   content

Member of the Inner Circle

Registered: 15/12/09
Posts: 19262
Loc: Devonshire

Great advice Heinz, too many people seem to love spending money on software upgrades when gains can be found by going back to basics and clean the flow up a bit.
1999 Indigo +8

#504361 - 18/03/18 05:04 PM Re: Sigma 4/4 throttle body improvement for free [Re: Heinz]
Rog Offline

Talk Morgan Regular

Registered: 31/05/12
Posts: 856
Loc: Sumerset
Well spotted Heinz. Improvement tips are always interesting.

You are fortunate with the Sigma, it looks like you have a nice solid cast ali TB. The Duratec has a horrible plastic Mickey Mouse TB. You have to be so careful tightening the air filter hose clip. You can easily distorts the plastic body allowing extra air to creep past the butterfly raising the idle speed. If anybody suffers from slow dropping revs or rev hang on a Duratec check the hose clip is not over tight.
2006 4/4 Duratec


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