Has anyone tried valve pockets in IDI pistons?

[Alcaid]

Hi,

has anyone got experience with machining valve pockets in their IDI pistons to allow more agressive cam timing? Compression gets lower, one f***s up the IDI combustion chamber design, but hey, does it work?

Found online that the valve pockets on PD150 pistons are 0.95mm deep while on the 1Z/AHU they are 1.01mm deep. How deep is the combustion chamber originally on our IDI pistons? Think I have seen a combo on a Toyota IDI piston somewhere. 

[RadoTD]

I thought about it; I was thinking about using an ABA cam (2L 8v, I assume you guys got it too?) for a bigger cam profile as well but never ended up doing it. If I remember right, I would've had to pull ~30thou (about .7mm) out between deeper valve seats, skimmed valve faces and machined pistons

[Alcaid]

I'm going custom cam based on flowdata of the head after porting, but piston to valve clearance would be a limiting factor I guess

[theman53]

Aki had pics of something he did to get to 7,000 plus rpm and cut some into a piston. Here was all I could find.

http://s434.photobucket.com/albums/qq68/Aki-76/moottorin%20osia/?action=view&current=12042009344.jpg

It was in this topic http://www.vwdiesel.net/forum/index.php?topic=19826.msg152601#msg152601

[Alcaid]

Nice find, but no info on an actual running engine with valve pockets?

[Aki-76]

I run that engine 3000-4000km before i crack block.I don't recommend valve pockets, It'll lower compression
and allows air to be in the wrong place.

[Alcaid]

I run that engine 3000-4000km before i crack block.I don't recommend valve pockets, It'll lower compression
and allows air to be in the wrong place.

Thanks for the feedback! Valve pockets down the drain, will get the cam as best as can be without them then.

What cylinder bore where you at when block cracked? And what boost level?

[Aki-76]

bore was 80.5mm and boost 2.8 bar....power was prety good 

[Alcaid]

bore was 80.5mm and boost 2.8 bar....power was prety good 

Crazy man!

[RabbitJockey]

i think a larger valves with proper porting to match might be a bit better (or both how ever both together would drop compression considerably)  but 1.6 head has 34mm in. valves and 31mm, audi idi 2.0td, aaz, and tdi are 36mm intake and 31mm exhaust.

in comparison to the vw gas engines the small valve 8v heads are 38mm intake, and 33mm exhaust, big valve heads(most 1.8l's and all aba) are 40mm intake and 33mm exhaust.

no wonder our engines dont make *** for power from the factory.  they start cutting fueling at 3500 rpms, and plateau on power until around 4500, if you look at a stock gas 1.6 dyno at 3500rpm they make around 50hp as well.

imagine a gasser with much smaller valves that could only make power up to 5500 at the most

valve length is slightly different on tdis but some of the tdi vendors do sell larger valves, 37mm and 33mm with 7mm stems and narrowed stems around the valve head.

just stuff i've been thinking about nothing is necessarily accurate haha.  but it'd be interesting to see how even an na diesel would run with just the "small valve" sizes 38 and 33mm with a giles pump to be providing proper fueling

[Alcaid]

I will have custom valves made up anyway to get a material I'm comfortable with running at high temperatures over time. A dropped valve does not look pretty in a diesel 

1,9 head so further dropping of compression is unwanted

[fatmobile]

bore was 80.5mm and boost 2.8 bar....power was prety good 
Insert Quote
I run that engine 3000-4000km before i crack block.I don't recommend valve pockets, It'll lower compression
and allows air to be in the wrong place.

 1.7 pistons,.. second oversize?
 Cracked block??? cracked a cylinder wall because it was too thin?
 I have a 1.6 bored out to 80mm using 1.7 pistons 1st oversize and am worried about block cracking. Would have liked the extra 1/2mm of cylinder wall standard pistons would have allowed.
 How hard were you working it when the block cracked?