Lancia S3 Thema Turbo 16v unusual valve sizes

[pietch]

Why did Lancia use smaller inlet valves on the S3 Thema Turbo only?

I have never heard of another engine with smaller inlet valves.

I guess it must have something to to with refinement or torque but I am unsure?

I have also heard that it increases port velocity?

[Lowtechguy]

It isn't uncommon, helps the charge mix at lower revs.

[pietch]

Does this hinder top end performance, can anyone expand on this?

[Guy Croft]

Has April 1st arrived early?!

If that is what I think, an OE 16v head with inlets smaller than exhausts (and produced by F/L like that), it's either some tuning thing that I've never heard of (ex valves are always smaller, esp on a turbo unit, I'd never go along with that) or a mistake at the factory or by someone on a subsequent build. I suppose if it wasn't an original head taken straight off an engine someone - ie: not you could have converted the seats and valves to that orientation. I have heard of this being done, though the port layout in that case - running the inlet flow through the low flow ex port - would not be very good (ie: would be really bad)

I just compared with an Integrale head to be sure I wasn't dreaming. I'd like a photo of the ports. Did you lift it off a running engine and are the valve reliefs in the pistons on the right side for the big valves? A production piston would have to be remachined so would have two sets of VRs not just one, the old inlet VR now on the ex side and a new set for the (now) bigger ex valves. You couldn't just rotate the piston, it has a thrust offset on one side. Photos if possible please.

Now if you had two of them - I would be worried.

GC

[NickRP]

Guy,

unfortunatelly, I've almost lost a 100 Euro bet on similar head from F/L! It de facto existed, I've seen it. It seems like it came like that from the factory, because inlet seats were smaller than the exhausts.

A friend of mine has located it at car wreckers, and I came to see it (seeing is believing). Didn't have much time to go deeply into it (ports etc.), but overall - it looked stock.

Regards,
Nikola

[pietch]

More S3 Thema Photos.

[Guy Croft]

So the small valve is on the actual inlet port. I see your head is mounted on an early 131 type block, ie: a conversion , and thus some pictures of the piston tops and background info on where this was bought or came from might shed some light on it.

Sorry, lost without that. Is it OE or has someone changed? That is the million dollar question.


GC

[sumplug]

In all my 30 years around Fiat engines, ive never ever heard of this before!.
Cannot see the reason for it. But proof in the pudding, is to flow bench test it.

Andy.

[Guy Croft]

This has got to be an 'aftermarket' mod.

What you'd most likely find on flowtest is that, compared with the er, 'usual' valve orientation of having the inlet valve located with the inlet port, that the small exhaust valve retricted achievement of high flow on the inlet port and the big inlet valve on the ex port could not acheive its full potential because the ex port was too small.

Even a GC reworked 16v Lancia ex port & seat only flows about 124cfm at 10" compared with about 136cfm from the standard inlet port. And that's with the air flowing the right way. The port shape is hardly right for using the ex as an inlet port. Even a 45/40mm big valve 8v TC can get close enough to that kind of flow to push out 200bhp - why bother going to a 16v for that?

I rarely say things like this but I bet it's not very powerful.

GC

[Lowtechguy]

In all my 30 years around Fiat engines, ive never ever heard of this before!.
Cannot see the reason for it. But proof in the pudding, is to flow bench test it.

Andy.

I cannot speak of engines like the above but in modern Fiat engines such as the fire this is being done, the punto 75 inlet valves are 1mm bigger.

I would post the exact figures but clubfirepowers website is down which has this data in full.

[Guy Croft]

Cristian, hi

I may have missed something but are you sure about what you have written?

Unless I have read this thread completely wrong it is about a 16v head has got bigger ex valves than inlet.

Someone put me straight if need be please.

GC

[sumplug]

The first Pic Guy, shows the Exhaust valves bigger then the inlets!!

Andy.

[Guy Croft]

Totally off topic but re Cristian's post, Punto (Fire) valves from OE manual:

1108/1242 SPI
inlet 30.20-30.50mm
ex 27.20-27.50mm

1242MPI
as above but inlets 31.20-31.50mm

1372 Turbo
inlet 35.85 - 36.15mm
ex 32.85 - 33.34mm

All ex smaller than inlet by ratio of valve head areas 81%-84%.

GC

[Evodelta]

Hello All,

This is no joke, Photoshop or 'one off', the series 3 Themas did have smaller intake valves (7.2mm smaller) and ports than the other 16v heads in the F/L range, matched with a tiny (.36A/R) T3 Turbo it was done to create more low down torque and less lag, they managed 205 Bhp*. The exhaust valves are 1mm larger at 29.5mm. They are said to be very smooth to drive with no power peak, almost like an electric motor.

To further clear up any more differences between integrale and Thema heads (the bottom ends are the same):

Series 2 16v - same size valves as the Integrale, but exhaust valves are not sodium filled.

Series 3 16v - smaller inlet valves, but exhaust valves ARE sodium filled.

Most would not know this, because the Thema S3 wasn't very popular over here in the UK, also as a luxury saloon I suppose it very rarely (apart from Pietros, which must be the only one in the UK sporting a GT28RS) comes in for engine modifications.

* F/L figures

Martin.

[sumplug]

Well I am a little shocked at this!

I wouldn't of thought Lancia would take this course of action to increase low end torque. Seems to me to be poorly thought out engineering. Its supposed to be a performance car. Legend has it , it was the fastest 4 door saloon in the world at one time! I wonder why they went to all the trouble of altering the head like this instead of engineering it, in the conventional way?

Andy.