Std Gti6 Pistons

[p1234 22 2 Cars]

What's the most I can get pocketed out of a set of standard gti6 pistons? Also wondering if it's just the inlet side of the piston that needs pocketing.

[pip470 61]

I took 70 thou extra on the inlet and exhaust pockets. That was with cams with 11.7 mm lift.

[petert 554]

To find the exact amount you'd have to cut a piston open. However, I'd suggest that the cams that could be used with the CR of the standard pistons will restrict the amount needed anyway. Keep in mind that it's also a viscous circle. Deepening pockets reduces CR. Taking 0.070" out of each probably gives a low 10's CR. The exhaust will need considerably less than the exhaust. You should work out the cam(s) lift @ TDC, measure what you have now, then calculate from there.

[welshpug 1,626]

Martin (crf450). Took 1mm from my inlets, allanallen commented that they wouldnt take any more as they are not thick enough.

 

Good enough for a mild cam upgrade, but you certainly need proper pistons if you want more.

[petert 554]

The exhaust will need considerably less than the exhaust.

 

whoops. I meant, the exhaust will need considerably less than the inlet. As per above, I'd suggest 1mm on the inlet and 0.5mm on the exhaust would be ample to cope with possible cam combinations.

Edited October 31, 2012 by petert

[p1234 22 2 Cars]

Would I be right in thinking that after market pistons have more 'body' on the rest of the surface to make up for the large pockets they have, or am I thinking complete rubbish altogether.

 

Im going to be using a diesel crank which I believe has a longer stroke and the cam you re profiled for me Peter. Will 1mm inlet and .5mm exhaust be enough otherwise its aftermarket pistons needed. I haven't a clue how to measure the lift at top dead center

[welshpug 1,626]

you need aftermarket pistons, using a diesel 88mm crank will smash the gti6 piston into the valves, if not the head.

 

you measure lift @ TDC with a dial gauge on the tappet.

[pip470 61]

my last build was with s16 rods and pistons. Sorry not the gti 6. I also had the mi16 88mm crank to increase the capacity. This countered the 70 thou pockets and I ended up with aroung 11 to 1 compression. It worked really well and made 230hp.

[p1234 22 2 Cars]

Ah, the plot thickens!

 

I know the S16 rods are a different length but are the gti6 pistons the same as S16?

Edited November 1, 2012 by p1234

[dcc 855]

No.

[allanallen 528 2 Cars]

Just to echo what's been said, from our past experience I'd not want to deepen gti6 pistons by any more than 1mm. The crowns are very thin!

S16 pistons on the other hand are a lot more substantial and as pip says -2mm is easily achievable on the pockets. S16 pistons also have more 'room' to start with anyway.

[p1234 22 2 Cars]

Thanks for all the info,

 

Give me a saw and hammer i'll build you a house, when it comes to building cars i'm only a tea boy!