Lancia Integrale 16v valve seat shape

[1NRO]

Hi Guy,

With regard to the exhaust valve seat have you ever tested a radiused seat rather than a cut/ground angle set up?

The reason I ask was after reading about inlet restrictors and their bell mouthed radiused entry. I understand the sharp angles on the inlet are the only way forward but wondered how a radius on an exhaust might perform.

Thanks

Nik

[Guy Croft]

I don't think it matters overmuch whether the ex insert seat angles are radiused or sharp, as the gas is probably turbulent on exit anyway.

GC

[1NRO]

I hadn't thought of it like that, very much like after its passed through a turbo. I thought maybe you would of tested the effect in the past and either approved or discounted the idea.

Thanks for your thoughts.

Nik

[Acki]

In the valves of my brothers head we had made the 30‚° extra angle cut. On the exhaust valves there is a big difference with this :)

[Guy Croft]

well Nik,

in case you think I'm a bit relaxed about that statement I'll just say that to back it up of course I've tested all sorts of configurations on 8v and 16v exhaust and inlet, valves and seats and have determined that ex flow is nowhere as critical as inlet, this is backed up by countless dyno tests.

Provided that the ex port flow is over 65% (full spec Sierra Cosworth) or preferably higher (that engine definitely has a high pumping loss), say 70% or over on bare-port flowtest (no valves) and +75% on turbocharged engines, you're safe. What I am referring to is the relatively modest influence that radiused or sharp angles on the ex side make compared with the inlet side on actual dyno test.

That said, every head type is different and the behaviour of every bit of the whole port from rampipe to valve is interlinked. That's not just me trying to sound 'clever', it's really true, unfortunately I've proved it to myself over and over. So in essence what this means is head/valve X may need different angles to head/valve Y. And if the cam lift is different the way of porting and seat shaping might be different again. Etc etc, ad nauseam.

Now, that said, I am not suggesting that I don't spend a long time reworking the ex seat shape to proven features - I do. And the angles I use top, contact face, throat, throat into port are many and varied.

have a read of 'all the power is in the head' in GC V/W if you have not already. Admittedly it's not finished yet but there is some good background in there. Or so I'm told.

GC

[1NRO]

Guy,

Not for a minute do I think your reply inadequate but thanks for the expansion.

The % values you mention I presume is inlet/exhaust ratios? The engine I have focused in my mind is the Lancia 16v turbo, does the +75%apply here? In your experiance what % would a fully worked head display and does this increase much over a standard head? As you hint at the can of worms that can be opened in this area I understand if it's an impossible question. I realise I can't relate these figures accurately to my head but would just like an % area to base my moments of contemplation.

Thanks

Nik

[Guy Croft]

Nik,

this graph of Coupe 16v - same head as Integrale 16v shows that I have 83% E/I flow ratio on the standard head and 77% after full mods. The ratio of ex to inlet valve area is 68%, a ratio which tells you from the start that the valve sizes are certainly adequate relative to each other - if the ratio was 60% on a particular head I'd be a bit concerned.
It might be possible to get more ex flow on the F/L 16v head but but at 77% I would definitely not be trying to.

There is a finite limit to how much flow you can develop from the head (any head) of course, this limit being set by the wall thickness and valve size. Is it worth porting a turbocharged head? Yes, definitely. You get more power for less boost for a whole batch of reasons. The inlet flow on this particular head, if turbocharged - how much power is it worth? Over 800 bhp with the right cams and boost.

GC

[1NRO]

Thanks Guy, good food for thought. I'm surprised to see a reduction in the ratio, this I presume would be narrowed a little with a standard exhaust port with the guides still fitted but still a reduction in the ratio.

Swimming around in my head is the theory that an increase in I/E ratio requires/allows an exhaust cam with less duration and a decrease in ratio more duration. Am I wrong?

I'm sorry to keep shooting off on tangents on the same thread, it's just I'm trying to knit some of the info in my head into logic.

Nik

[Guy Croft]

Nik, hi

it's E/I ratio not I/E - in other words % ratio: ex/inlet flow.

The flowtest ex flow is always less than the inlet. 77% modified bare port flow (no valves) compared with std port to port - yes it's less because the mods have developed relatively more inlet flow than ex, and that's fine, like I said, there is no need at all to go chasing high ex flow numbers provided that - certainly for a turbocharged unit - the ratio doesn't fall below about 75%..

All I am going to say about cams in this thread about valve seat shape is that the cams should be always chosen to maximise the potential of the new, higher flow ports, that is - where the valvetrain architecture permits.
You have to be careful with lift on the 16v unit, see:

http://guy-croft.com/viewtopic.php?p=2657#2657

I'll just add a footnote here after re-reading your initial post, try and tease the info out of my memory banks...

The behaviour of a fluid stream (ignoring for a moment whether the fluid is air or ex gas) going thru something like a valve seat is interesting. I have read many articles about shape and often seen it rather generally stated that a radius will improve flow. This is not of itself true. If the radius is aerodynamically correct, yes, the fluid stream will adhere to the curve and not break away. If it breaks away it will cause turbulence that will disrupt the flow adjacent to it, sometimes very severely. I have seen this on valves, seats and short side radius, thru splitters, everywhere actually.
The radius of curvature is very critical and - aerodynamically - whether a curvature will help on an inlet seat is very dependent on the physical dimensions of the region. Conversely I have found better results sometimes from sharp edges (8V TC is a prime example) ie: sharp edges on seats and valves working better than radiused ones.

I have back-to-back tested this phenomenon exhaustively on heads that are affected (mainly sidedraft inlet port types), not quite believing my own results because it seems, well, weird, but every time I have got the same effect. Sharp = gain. But even very slightly radiused (just so as to break the sharp edge) = loss.

I think that the reason they are better with many inlets is because although the air breaks away as it goes over, say, the 70 deg angle into the 45 contact face, the disruption is very localised and the air stabilises quite quickly. I have also determined that the relative angles between the contact face (45 deg) and lower section of the throat are very critical. In my own testing I have found every throat angle apart from 70 deg (including parallel bored) on the 8V TC unit to be quite hopeless. The distance between angles is hyper-critical or the turbulence formed at exit of one angle will not recover and be carried into the next angle, producing a rather severe 'compounded turbulence' effect that negates the benefit of 'blueprinting' and modifying completely.

By the same token I have experimented very extensively (I mean weeks of test and dev!) with setups like the so-called 'multi angle seats' popular with top US tuners and found them quite useless with any kind of valve shape. These jazzy things might work on giant V8s with 2.5 +" diameter inlet valves but they categorically don't work on any Japanese or European 4 cylinder 8V or 16V head that I've examined.

[1NRO]

Thanks again Guy, you've done me proud. I'll digest that info and refrain from dragging the thread around anymore.

Nik