[project] Project 205 Xu13j4

[B1ack_Mi16 67]

What dynamic compression should one aim for by the way?

[petert 586]

8.5-9:1 works for me on 98RON.

 

http://cochise.uia.net/pkelley2/DynamicCR.html

 

[B1ack_Mi16 67]

Using this calculator (http://blackartdynamics.com/Compression/EngineCompression.php) it seem to give 11.61:1 static and 8.92:1 dynamic using 0.1mm lift CAM durations and 106 centreline on the intake and 108 on the exhaust, 0.8mm gasket.

11.38:1 and 8.75:1 with 1.0mm gasket...

Edited October 4, 2019 by B1ack_Mi16

[petert 586]

Sweet, I'd go with the 1.0mm gasket, unless you can improve the valve-piston clearances otherwise.

[DamirGTI 342]

7 hours ago, petert said:

http://cochise.uia.net/pkelley2/DynamicCR.html

 

 

 

Here is an article on High Compression by David Vizard - something went wrong with this one !

 

D

[welshpug 1,657]

thats not right either, nsfw!!

[petert 586]

Whoops.

[B1ack_Mi16 67]

So I started measuring some valve-lift this evening. 

 

Just a simplified calculation this far, as I believe the additional valve clearance when the piston moves 1mm down the bore, will be more than 1mm, due to the valve sitting at an angle. But that I'll have to think more about later as the brain is saying stop now

 

This is what I found, only did the exhaust cam, and measured it the wrong way but numbers should be valid as long as the cam is symmetric.

 

 

Identified the peak angle of the cam and then measured the valve lift in steps relative to that.

Seem like the clearance for the exhaust valve is at it's worst at 9 degrees ATDC, but still in reality more than 2.5mm clearance for the exhaust.

 

[petert 586]

Good work, use the sine rule to work out difference in 1mm

[B1ack_Mi16 67]

Yes should be quite straight forward, what angles do inlets and exhausts sit at respectively? (I could of course measure it but maybe it is common knowledge :))

[SRDT 175]

It should be 49,5° (49°30') for both.

[petert 586]

I make it 64º inlet and 66º exhaust.

[SRDT 175]

My bad, it's 49.5° between inlet and exhaust.

[B1ack_Mi16 67]

Ok, from vertical line I measured like 27 deg for the inlet and 22.5 deg for the exhaust. That match 49.5 deg between the valves at least.

 

Compared to Peters values it converts to 63 deg for inlet and 67.5 deg for exhaust so pretty close.

[SRDT 175]

Looking at some FIA homologation form we have the XU10J4 specs: 25.5° between intake valve and vertical and 24° for exhaust. Bdw 49.5° between valves is just like the 205 turbo 16.

[B1ack_Mi16 67]

Ok, well I think my numbers were quite correct, but I suppose XU9J4 should be the same as XU10J4 anyway,

 

Only bad news regarding the inlet valve clearance. With 1mm gasket and 106 deg timing.. about 0.75mm clearance valve to piston. 
About 1mm clearance with 108 deg timing.

[petert 586]

You really to be at 1.5mm  minimum on the inlet. Thus you need to mill the piston regardless. Did you allow for valve lash in your calculations? Nice graph!

 

 

edit: I guess you must have, if you did it as per the pic, with the head upside down, assembled.

Edited October 8, 2019 by petert

[B1ack_Mi16 67]

I simply just left the valve clearances as they were, but I corrected all the lift values by the difference between specced max lift and measured maximum valve lift, this might possibly be a little bit wrong especially for low lifts maybe?

 

I need to re-measure the inlet clearance I think, I really don't like the idea of fiddling with the pistons at all. Maybe I shall slap some low lift T16 camshafts in it just to be sure it doesn't hit 

[petert 586]

Don't be shy, just find someone with a fly cutter. You only need to cut 1mm from the inlets. Make a jig yourself and it won't cost you much. Set up time is where the money goes. The finished engine will be so much better.

 

In regards to the valve lash, you only need to worry about that if dropping a valve onto a piston, as I do. As yours is all assembled, the lash has been taken up as normal.

[B1ack_Mi16 67]

Really can't be arsed dismantling the bottom end. Maybe I just need to stay with the old 1.3mm gasket after all and put it back as it was. 
I don't have time for more troubles  The main goal is to get it not to leak oil anyway.

[B1ack_Mi16 67]

So.. lots of work later.. 

 

Well, I did go at it with a rotary burr... not something one would do normally, but I though I'd try it.

Pistons might get weak around the first ring land after the change, but that would have happened with proper machining anyway so worst case the pistons are going bust... but that I'll not know before giving it some revs.

 

Cyl 1 in progress 

 

Cyl 1 & 4 done.

 

 

Cyl 2 & 3 in progress

 

 

After this modification the clearance at TDC is in the range 6.3mm +- 0.1mm.

 

Now I need to measure up the new valve pocket volumes.

And I'll probably ask for a 0.9mm head gasket if that is a possibility from the manufacturer.

 

Edited October 16, 2019 by B1ack_Mi16

[B1ack_Mi16 67]

Also picked up the valve spring shims today.

2mm thick so at least the inlet valve springs are now installed height 37mm, I think the exhausts might end up at 38mm if I remember correctly, but that will probably be sufficient as it worked as a charm as it was before without any shims too.

 

 

 

[B1ack_Mi16 67]

Also I have re-measured everything regarding piston pocket volumes this evening.

Piston is also protruding the deck by 0.05mm so adding all these factors together give a final compression ratio of 11.5:1 with a 1mm thick headgasket.

 

That is fairly perfect I think.

 

Updated valve to piston clearance chart shows now just below 2mm clearance as minimum for the inlets when set at 106 degrees.

 

[B1ack_Mi16 67]

Dismantling the head a bit more, all valves out now. Seem like there are some a bit too deep scratches from the dowels just in the area of headgasket sealing so guess I have to have it surfaced too before it can go back on.

 

 

 

[petert 586]

Great work. I wouldn't stress over the scratches. Just smear some 1211 over the area and bolt it down.