Machining S16 Pistons

[Rob Turbo 3]

I'm getting a set of s16 pistons for my 16v turbo build to save me having to press the pins out of my turbo pistons for machining, I was planning on taking 2mm off the crown to take them to roughly what the flat top 8v turbo pistons are, but would this weaken the piston too much? or would it make them the same thickness as the 8v turbo ones?

 

Also, if I don't machine the pistons and keep the standard C/R (with a gti6 head), how much abuse could it take in a turbo setup? What would my power limit be?

 

Thanks,

Rob

[wracing 19]

depends on the squish ratio and time at tdc, how much boost are you planing on running i know from testing my s16 engine it can take 5psi+ on std compression, tbh i would say 2mm skim is a bit heavy! i would go for a 1mm tops enlarging the chambers and thick headgasket.

 

depending on boost levels you may find radiusing the valve pocket edges a benifit.

[Rob Turbo 3]

I was planning on starting at 6-7psi (lowest I can set it to) then working my way up, I know the turbo is good for lots of boost, I was running 18psi on the 8v turbo before the head gasket gave up, I'll be using the same turbo but with a different exhaust housing (standard t25 housing instead of the peugeot special jobbie)

 

Low boost levels are no good to me, if machining the s16 pistons isn't an option I'll carry on looking for some flat top 8v turbo ones and find a home elsewhere for the s16 ones.

[wracing 19]

s16 pistons are great they seem strong just i think 2mm is excessive and will lower the compression ratio to much, if you run programmable there is no need to drop the comp ratio so much! why is 6-7 psi the lowest? i would say the t28 is better matched than tb25 is far to restricive at the higher rpm need something with a larger A/R for a 16V

[Rob Turbo 3]

The turbo isn't standard, it's a standard turbine/housing, but has a 60 trim compressor wheel and A/R 80 compressor housing, the actuator is only a 6 or 7 psi one, I was using a dawes device type boost controller to set the boost to whatever I wanted.

 

I'll be running it on megasquirt with a wideband lambda. I know my way around it fairly well now!

 

So if I take 1mm off the pistons I won't be weakening them too much?

[wracing 19]

well im not going to say no cos then when you put a hole in one youll come and kill me

 

ive taken 30 (0.76mm) thou off mine and the xrays show loads of material left. under the crown its fairly flat and the valve cuts a fairly deep. if your running megasquirt, use the boost control much better that a "posh" bleed valve you will need the extra code though.

 

how are you planning to remove the material i used a lathe with nylon jaws and a rag wrapped round the pistons

 

the a/r of the comp housing doesnt really matter that much its the turbine housing that matters, turbo info

[Rob Turbo 3]

The ms I have on the v6 has the extra code, I'm planning running msII extra on this one, I never got round to trying the boost control with the ms when it was running the 8v turbo.

 

I have access to a lathe, I was planning on making a jig to hold the pistons for machining.

 

The reason I'm sticking with the t25 is I already have it and can't really afford another turbo on top of everything else, although if I fancy I can always upgrade to a t28 later.

[brumster 135 1 Cars]

They're packed up and ready to go, Rob

[wracing 19]

fair play i dont blame you, saving money the best way!

 

i was going to do mine in a single pass on the milling machine, but dad said lathe with a super low feed rate Tungsten carbide cutter about 1500rpm i modded the feed they took about hour per piston as i didnt want to crack them chamfered the edges by about 3 thou and linished to tops at 4500rpm by hand with 1500 + 6000 grit sandpaper (the stuff they use for polishing plane canopies) almost mirror finish

 

boost control is good don’t use boost targets use the duty cycle table the PID loop is temperamental and leads to creep.

[Rob Turbo 3]

Spot on

[wracing 19]

i have a manifold you may be interested in!

 

 

 

im doing the flow analysis now not equal length but phased pulse delivery

[Rob Turbo 3]

I'm not going for anything too technical with regards to the manifold, I already have the bits I need to build my intended design, which is basically a gti6 flange, 4 runners, into a collector, then a t2/25/28 flange!

[wracing 19]

give me a shour if you get stuck ill be selling these in a weld your own kit for about 65ish

[whizzer71 0]

How much for a "ready to bolt on item" I'd deffo be up for one and I could easily shift another,maybe two even !