valve modifications
Discussion
Hi study a degree in motorsport engineering, and im building a peugeot 205 turbo.
I have modified the stock valves, but im not sure if i have gone a little OTT and may have made them too weak.
I have undercut the inlet valve stem by 1mm (which is fine) and decreased the underhead radius of the valve
The exhaust valves are the main concern, I have also undercut the stem by 1mm, and the underhead radius (but there is much more material than the inlets)
[IMG]http://img.photobucket.com/albums/v459/jacobs53/DSCF17.jpg[/IMG]
Need some advice, I should of read up first before jumping into it.
cheers lee
I have modified the stock valves, but im not sure if i have gone a little OTT and may have made them too weak.
I have undercut the inlet valve stem by 1mm (which is fine) and decreased the underhead radius of the valve
The exhaust valves are the main concern, I have also undercut the stem by 1mm, and the underhead radius (but there is much more material than the inlets)
[IMG]http://img.photobucket.com/albums/v459/jacobs53/DSCF17.jpg[/IMG]
Need some advice, I should of read up first before jumping into it.
cheers lee
Hell, you tell me, Lee - you're the one with the motorsport degree; I spent my time at University chasing girls and drawing houses.
...but for what it's worth, my gut feeling is that reducing the valve stems on a high performance turbo engine is a bad idea.
Somebody correct me if I'm wrong, but an important part of the job of the valve stem is to transfer heat from the head of the valve up to somewhere that the oil can cool things down a bit. Sodium valves are fitted for this very reason - the liquid sodium sloshing up and down inside the valve stem helps transfer the heat away from the combustion chamber end.
I'd have thought that reducing the amount of metal available to perform this task in a turbo engine (which naturally tends to generate a lot of heat in the exhaust ports and tracts)is asking for a dropped valve.
...on the other hand, maybe I should stick to what I understand!
...but for what it's worth, my gut feeling is that reducing the valve stems on a high performance turbo engine is a bad idea.
Somebody correct me if I'm wrong, but an important part of the job of the valve stem is to transfer heat from the head of the valve up to somewhere that the oil can cool things down a bit. Sodium valves are fitted for this very reason - the liquid sodium sloshing up and down inside the valve stem helps transfer the heat away from the combustion chamber end.
I'd have thought that reducing the amount of metal available to perform this task in a turbo engine (which naturally tends to generate a lot of heat in the exhaust ports and tracts)is asking for a dropped valve.
...on the other hand, maybe I should stick to what I understand!
Hmmm....
Well, like the last poster, I'm not an expert, Marquis Rex might be good for advice on this one. Looks a bit iffy to me.
Surface finish looks "just turned", I'd have thought a ground finish might be more appropriate for the application.
Also, given the way circles work, I'd have thought that there'd be more to gain by increasing the OD of the valve, than reducing the OD of the stem.
By this rationale, I'd say that you've removed most of the conductivity and strength in the stem.
I reckon, you would get more horsepower from improving the efficiency of the oil/water pump myself.
>> Edited by dilbert on Friday 3rd June 22:20
>> Edited by dilbert on Friday 3rd June 22:22
Well, like the last poster, I'm not an expert, Marquis Rex might be good for advice on this one. Looks a bit iffy to me.
Surface finish looks "just turned", I'd have thought a ground finish might be more appropriate for the application.
Also, given the way circles work, I'd have thought that there'd be more to gain by increasing the OD of the valve, than reducing the OD of the stem.
By this rationale, I'd say that you've removed most of the conductivity and strength in the stem.
I reckon, you would get more horsepower from improving the efficiency of the oil/water pump myself.
>> Edited by dilbert on Friday 3rd June 22:20
>> Edited by dilbert on Friday 3rd June 22:22
TBH I would fit standard valves.
You are adding massive amounts of thermal stress, and even though your cam has to be mild to avoid blowing all the inlet charge straight out the exhaust, the thermal loads will be super high.
Thinking about the way we would do it for a production engine, we'd model it thermodynamically, then run the stress model on the valves and optimise the profile of the cam to keep the loads at a tolerable level, but maintain power.
You'd do a few iterations and then you'd have an answer.
But it is only in recent years that we have been able to do this with any sophistication.
The method of 15 years ago was to design the parts to a known datum that was proven, then optimise everything on a flow bench. Base engine development would do fuelling and MBT work and optimise the CR. They would know how far was too far when they had holes in the piston or another mechanical failure.
You don't have a budget to do this, so I would be conservative - low CR as it is a 2 valve / cyl head, conservative cam and valves on the exhaust, crank up the boost and put money into an aluminium flywheel.
Alternatively buy kit from somebody who has done the development work for you and enjoy the results.
You are adding massive amounts of thermal stress, and even though your cam has to be mild to avoid blowing all the inlet charge straight out the exhaust, the thermal loads will be super high.
Thinking about the way we would do it for a production engine, we'd model it thermodynamically, then run the stress model on the valves and optimise the profile of the cam to keep the loads at a tolerable level, but maintain power.
You'd do a few iterations and then you'd have an answer.
But it is only in recent years that we have been able to do this with any sophistication.
The method of 15 years ago was to design the parts to a known datum that was proven, then optimise everything on a flow bench. Base engine development would do fuelling and MBT work and optimise the CR. They would know how far was too far when they had holes in the piston or another mechanical failure.
You don't have a budget to do this, so I would be conservative - low CR as it is a 2 valve / cyl head, conservative cam and valves on the exhaust, crank up the boost and put money into an aluminium flywheel.
Alternatively buy kit from somebody who has done the development work for you and enjoy the results.
They look all right to me. Did you check to see if they are 2 piece valves though, if not you could have a problem with the exhaust as it looks a bit weakened?
If this were me, I'd have concentrated on a thin seat contact area for the inlet and waisted the stem as you have done. As for the exhaust, I'd have left the stem stock, left the seat contact area stock to dissipate heat and used a bigger valve head diameter if the seat allowed it.
Boosted.
>> Edited by Boosted LS1 on Saturday 4th June 00:25
If this were me, I'd have concentrated on a thin seat contact area for the inlet and waisted the stem as you have done. As for the exhaust, I'd have left the stem stock, left the seat contact area stock to dissipate heat and used a bigger valve head diameter if the seat allowed it.
Boosted.
>> Edited by Boosted LS1 on Saturday 4th June 00:25
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