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5 GT Turbo Headwork

Hi there people

Im the one that will be doing the head work, The next step is get the other half on a borrowed flow bench ( i will be getting my own soon ) Once i find the weak spots in flow then it will be ported. As soon as i find some over size valves then i will port the head to match.

I'm also looking into porting the inlets and exhaust manifolds
More power without the risk of loosing torque making it a more efficient head
Meaning that he can run less boost and still get the same power or just gain more power with the same boost
I like the sound of that. I'll be following this with interest. I'll be especially keep to see the gains on either larger inlet or exhaust valves. And would I be right in saying that bigger exhausts would be the 1st thing to mod before the exhaust?
That's not taking into consideration the gas flowing.
I'd say, first, relieve or point the tips of the guides and get rid of the step behind the head of the valve.
You will also find that before the valve seats fell out (possibly on the powered saw bench?) that there is a step in and around the port where they fit.
If you want a contact for valves, I have the details for the only valve manufacturer left in the UK. They are very good and will do low volume bespoke work.
I had a set of exhaust valves made from Nimonic 80A (80A is used for gas-turbine components (blades, rings, discs) in jet engines, bolts, tube supports in nuclear generators etc) for my car. Great properties for an exhaust valve. Not very cheap, but you get what you pay for. IIRC they were £84 each, plus VAT. Thats per valve, not per set.
I like the sound of that. I'll be following this with interest. I'll be especially keep to see the gains on either larger inlet or exhaust valves. And would I be right in saying that bigger exhausts would be the 1st thing to mod before the exhaust?
That's not taking into consideration the gas flowing.

It's so massively more complex than bigger = better.

The biggest gains you can get come from just below the valve seat to just above it. The whole region from the valve throat through to the chamber walls should be treated as a single piece where mistakes in one place will have downstream effects. One of the most important factors in cylinder filling is gas speed in the valve throat just as the inlet valve is closing. The piston is rising rapidly up the bore and trying to force the last of the incoming gas to turn round and go back down the port. If the inlet valve closes too late this will happen and the engine will run poorly until the rpm is high enough to let the cam duration work properly.
If we can maintain a high gas speed around the valve seat the incoming gas will resist this piston pressure and fill the cylinder better. Logically this leads us to conclude that the valve throat must not be too big or the gas speed will drop.

It might seem obvious that exhaust ports flow in the other direction to inlets but that key fact is often forgotten. Mainly what contributes to the flow efficiency of the inlet is how well the port guides the charge to fully use the entire circumference of the valve seat. In nearly all cases this cannot be achieved because air travelling at high speed can't get round the short side bend in the port and just skips across the back of the valve head and tries to exit through the long side of the valve seat. Only on the most steeply downdraft and straight ports is there such a minimal bend on the short side of the port that the air can come close to using the full circumference of the valve seat at high valve lifts. Take, for example, this representation of an older F1 head....I think this is from a BAR....stunning....


At a guess the average stock inlet port only flows at about 50% of "ideal". Well modified road heads maybe 60% but to get any more requires custom design. The exhaust port does not suffer in the same way. The air already uses the full circumference of the valve seat by virtue of the fact it's going into the seat from all round the combustion chamber anyway. Provided the port itself is big enough then almost any design of exhaust port will flow at 65% efficiency or more because the valve seat is being used effectively. Even the shape of the short side bend is not that critical because it's not having to guide the air into the seat - all it's doing is guiding the air into the straight section of the port.

Read this thread, it's a cylinder head masterclass from Formula one.

*some of this post plagiarised from Dave Baker of Puma Racing
Also, another point I like to mention as it's a common misconception.

The port gas speed does not change when the engine has [forced induction]. If the manifold pressure doubles then so does the gas density and therefore the mass flow and power. The speed stays the same.

Think about that very carefully.

Also: How far can I open my valve before I cannot flow enough to make it worth opening any further? [Probably only 0.3 x Valve Diameter].
No mate, that head got destroyed when we dropped a valve years ago.
was a good head that :)
Last Clio Sport head I saw that dropped a valve managed to re-insert the valve head back in the throat, the wrong way up (With the stem sticking down). It took a hammer and chisel to get it out. Scrapped the head! What a mess :D
I guy on rtoc mfaulks a , an engine builder , started the same topic ,but it never developed on ,hope this does ,it's another c1j grey area
Problem with the C1J is that the inlet ports are different, which creates a considerable imbalance from the get-go. Getting a flow match through 1-2-3-4 is incredibly difficult, let alone an improved, matched flow.
Interesting thread.
I thought the coolant going through the inlet was there to help speed up the car get to full running temp? Also the carb is heated to stop it freezing in winter?

it's not there to improve power/performance?

If you've got water passing through the inlet at 90* it's just going to heat up the charge temps which your trying desperately to cool to 30* with the intercooler.

Dont most people remove these hoses?

Or am I getting mixed up with something else?
You have to remember that theses cars were designed in France, where you have the heat of the south (perc fan needed) to the cold of the alps (manifold/carb icing).
I ran my car in the uk without perc fan, manifold/carb heater for the 10 years I drove/raced it without any trouble.
MartinF did a lot of investigative work on the C1J and probably has a lot of good advice to offer if you would like .He is very time poor tho and we are tryting to get another couple of PRV6 done atm but he may have some bits he can pass on .
Developing all the flow work isn't a problem as I have access to a flow bench and will have my own soon. As for the cooling of the inlet it was the first time I've really looked at it so it was just a idea as it could be used as a gain rather than just warm up devise
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