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Little update, mainly for the information gathered today 
So, as you know, this new engine procured for the project is a bit of a mental one. Toyota went bonkers and ripped up the old design of the gen 3 and changed lots compared to the gen 4. This engine has bigger valve buckets with the shim underneath, a tighter valve angle for steeper ports and a more compact combustion chamber, giant cams (11mm lift!!) and bigger titanium valves....
Yep, Toyota fitted titanium valves to this as a stock feature! This is where is got a bit sticky for me, as I want to turbocharge the engine, and titanium valves are not great with heat. This issue is two fold, first of all the material is prone to oxidation at high temperatures, resulting in surface imperfections. This then knocks on to another problem, titanium is prone to fracture with any surface imperfection.
Secondly, creep is an issue. This is where under load the material can deform even when the stress is below the yield point. This is exacerbated by high temperatures which cause a significant loss of strength in the material.
So, what the hell were Toyota thinking? Well, on the inlet they have used 6al4v, this is a strong material with excellent properties and reduced creep, great.
The white elephant are the exhaust valves, continuous operation over 750 degrees centigrade whilst being thumped open and closed by a bumpy stick, not great. Being an unusual application I thought 'There must be some literature on the subject', sure enough after some hunting I came across two small but significant references. First is this one -
So.....it turns out that Toyota did lose the plot and used spaceship material for the exhaust valves. This has exceptional high temperature properties to resist creep and an oxide coating that gives it much better notch failure resistance.
The second bit, and most interesting for me is this -
From here (a great resource for engine information) -
High Performance Media - Valve Materials
I was still worried about the elevated temperatures seen with turbocharging, turns out that the only material better within the scope I am looking at is Nimonic 80A, a nickel superalloy! The kind of material you would use when building a turbocharged racing engine (think WRC + antilag). I would have been happy with standard stainless exhaust valves, looks like the Ti834 valves should be much better
So, I decided to have a look and see how the engine looked under the cam cover, I have not delved into this engine at all, it has stood outside for two years at the previous owners house as a spare for his car. I was quite frankly worried.
Ready....
Well flip me, its immaculate! This engine has been looked after, many oil changes and not ragged from cold, never got too hot either
Valve clearances all check out bang on too, if anything towards the top of the range, something I am happy about given titanium's tendency to creep!
So, there you go, spaceships!
So, as you know, this new engine procured for the project is a bit of a mental one. Toyota went bonkers and ripped up the old design of the gen 3 and changed lots compared to the gen 4. This engine has bigger valve buckets with the shim underneath, a tighter valve angle for steeper ports and a more compact combustion chamber, giant cams (11mm lift!!) and bigger titanium valves....
Yep, Toyota fitted titanium valves to this as a stock feature! This is where is got a bit sticky for me, as I want to turbocharge the engine, and titanium valves are not great with heat. This issue is two fold, first of all the material is prone to oxidation at high temperatures, resulting in surface imperfections. This then knocks on to another problem, titanium is prone to fracture with any surface imperfection.
Secondly, creep is an issue. This is where under load the material can deform even when the stress is below the yield point. This is exacerbated by high temperatures which cause a significant loss of strength in the material.
So, what the hell were Toyota thinking? Well, on the inlet they have used 6al4v, this is a strong material with excellent properties and reduced creep, great.
The white elephant are the exhaust valves, continuous operation over 750 degrees centigrade whilst being thumped open and closed by a bumpy stick, not great. Being an unusual application I thought 'There must be some literature on the subject', sure enough after some hunting I came across two small but significant references. First is this one -
So.....it turns out that Toyota did lose the plot and used spaceship material for the exhaust valves. This has exceptional high temperature properties to resist creep and an oxide coating that gives it much better notch failure resistance.
The second bit, and most interesting for me is this -
From here (a great resource for engine information) -
High Performance Media - Valve Materials
I was still worried about the elevated temperatures seen with turbocharging, turns out that the only material better within the scope I am looking at is Nimonic 80A, a nickel superalloy! The kind of material you would use when building a turbocharged racing engine (think WRC + antilag). I would have been happy with standard stainless exhaust valves, looks like the Ti834 valves should be much better
So, I decided to have a look and see how the engine looked under the cam cover, I have not delved into this engine at all, it has stood outside for two years at the previous owners house as a spare for his car. I was quite frankly worried.
Ready....
Well flip me, its immaculate! This engine has been looked after, many oil changes and not ragged from cold, never got too hot either
Valve clearances all check out bang on too, if anything towards the top of the range, something I am happy about given titanium's tendency to creep!
So, there you go, spaceships!
The panels will be painted first, while the shell is on the spit, having the underside prepped for paint. I cannot tell you just how excited I am 
