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  #101  
Old 26-04-2016, 10:38 AM
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Daz your attention to detail in the postmortem analysis is simply exceptional.

Wish you all the best with the next stage of build.
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Last edited by GTB Liberty; 30-04-2016 at 07:43 AM.
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  #102  
Old 26-04-2016, 08:04 PM
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Looking a little deeper into this and my pictures I took during the build, all of the pistons have slight witness marks on them from the inlet valves. So this piston to valve contact was happening before I even owned the car.

At the time I dismissed it as I just thought the car had a mild over rev at some point. It was running single valve springs and stock valves that I was going to replace anyway so I didn't think any more of it. Another assumption that's cost me.

So bottom line I should have measured when I built it but there was just far far too much advance done on the original tune long before I bought the car.

Here's the pics, you can make out the marks from the valves on the pistons, just below the cut outs.
















Pretty damn conclusive I'd say.
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Last edited by dazdavies; 26-04-2016 at 08:06 PM.
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  #103  
Old 26-04-2016, 08:11 PM
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Daz, could it have been from connecting rods being too long?
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  #104  
Old 26-04-2016, 08:26 PM
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No, the pistons would stick out of the top of the cylinder if they were longer.

Cosworth only sell a stock length rod too.
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  #105  
Old 26-04-2016, 08:27 PM
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Wow that's amazing! Well done! Good analysis for sure
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  #106  
Old 27-04-2016, 08:51 PM
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I don't know much about the built in clearances of stock valves but wouldn't the stock valve train be designed to deal with the full amount of advance or retard available within the avcs system? Otherwise why not have hard limits set within software?

My reasoning for this is that often the tuner is not the same person who built an engine. I also recall reading a letter from Cosworth that suggested their big valve heads could accommodate the full avcs advance.

If not, then it would be easy for a tuner to clip valves on Pistons when tuning to the max.

Would love to hear from those that know.
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  #107  
Old 27-04-2016, 09:20 PM
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Higher lift, longer duration cams push the valves further open for longer.

If you don't get the cam timing right then you'll have problems like i have.

This makes interesting reading.

AVCS: Max advance on a built motor research results - NASIOC
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  #108  
Old 29-04-2016, 02:56 PM
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Hey Daz,

I'm curious to know what internals you will use again for your heads? Will
you go with SuperTech again?


Cheers
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  #109  
Old 29-04-2016, 05:56 PM
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Quote:
Originally Posted by Darken View Post
Hey Daz,

I'm curious to know what internals you will use again for your heads? Will
you go with SuperTech again?


Cheers
Daz is going ferra 6000 i believe

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  #110  
Old 29-04-2016, 10:37 PM
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Now that I know the cause wasn't a valve failure I'm going with Supertech again. There's a few reasons for this.
The Ferrea valves have propierty locks which makes swapping not straight forward and adds cost.
I also want Inconel Exhaust Valves which ferrea don't do.

I want to swap my titanium retainers for steel ones and Supertech make them to go with my double springs.

Lastly I've been in contact with Supertech who are doing prices that no one else can get close to. $8 each for intake valves and $12 each for inconel exhaust valves. Plus $4 each for the retainers.

I.know many people that use Supertech and everyone speaks highly of them. So I'm willing to give them another go especially at those prices.
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