Sam's build thread

[sambb]

you're good at spending other peoples money.......I'm good at over thinking stuff!
I guess I was looking at the older generation engines (they went into production in 96' I think), pre-variable valve timing/lift and all that jazz which varies dynamic compression doesnt it and definitely pre DI engines. Perhaps I was going back too far.
Well if I do go 9+:1 there are plenty of options. After doing a bit of reading it seems that while VAG quoted 9.5:1 for the K03 cars and 9:1 for the K04 cars, the actual compression when cc'd puts them both at closer to 9.25:1, so its possible they are more or less the same comp anyway.
Yeah maybe I will get MIA to have another look at the pistons. He didn't like any of the rings though. I remember him saying it was one of the tiniest little oil control rings he'd seen and that it looked like the 2nd compression ring gets used as a double duty oil control ring too which is why he said ditch them for something that'll last. Interestingly when we compression tested it a while back trying to pin down oil consumption, the comp test and leak down test came back sweet and my mechanic/tuner buddy next door to them did ask if these engines are known for doing oil control rings. But like you said if they can be cheaply modded to accept more stout rings then that may be worth exploring, cos there's no point looking at shiny new pistons if I don't have the dollars left over to complete the build. I think I did read somewhere that the stock pistons are a forged Mahle made out of that more brittle 4032 I think so hopefully they are not too brittle to be machinable. As I said above the other option is to use my spare engines pistons if they are in better condition but that'll need 900 bucks worth of 19mm pin end rods (only one brand from the US does them) - still cheaper than pistons though. So i'll suss out salvaging the S3 pistons first, failing that look at using the Polo pistons next, and failing that I'll have to go with aftermarket pistons.

I'm going to do one more measure session of the MK6 gti turbo mounted on the spare engine and double double check that it wont fit against the steering rack before I turf that idea because it really does have a lovely manifold compared to the K0x ones and really is like lego the way it all integrates with the stock pipework routes, intercooler, intake and exhaust etc. Not bolt n' play like a K03 hybrid but the next easiest option I think.....provided it fits against the firewall.

[Sydneykid]

As used in pistons, 4032 is OK to machine as long as it is really well lubricated, don't machine it dry. There's a lot of non performance friendly stuff being done to engines these days in the quest for ever lower fuel consumption and emissions. Particularly in regards to friction reduction.

Thinking outside the square, basically you are only going to use the standard crankshaft and block deck height. Everything else is variable, so maybe you don't have to use rods and pistons specified for a "Polo". If you can find a conrod that has the same big end bearing dimensions then it will fit the crank and with the same length so it will fit the block. Doesn't have to be exact as you can select pistons with the appropriate pin height so it suites the block or machine the block down if that's necessary. In the RB I run VG pistons as they are a perfect flat top with 1 mm larger bore and 2 mm larger little ends. Just had to machine the block down 15 thou so they were flush with the deck.

If you get stuck with finding pistons these guys will make anything Special Piston Services High performance Forged Pistons it might be cheaper than buying "Polo" conrods and "Polo" pistons. Since you already have rods. I just send them a sample piston and then specify the changes I want made, wider rings, 3 piece oil control etc. Honda B series engines also have 81 mm bores with 21 mm little ends, they are very common and turbo conversion pistons are readily available. https://www.wiseco.com/Catalogs/Spor...cura-Honda.pdf

A MK6 turbo and exhaust manifold would be a pretty good choice, my son has MK6 Gti and it works OK for him. On a 10% smaller capacity engine the airflow versus boost ratio should be even better, so lower inlet air temps.


Cheers
Gary

[metalhead]

I also cleaned up all the sharp valve pocket edges on my pistons, I used scotchbrite pads while keeping it lubricated/washed, worked really well. I can't believe the piston prices you're talking about - my set of 8 US made forged SBC pistons was less than $700 from memory...

Generally I lean towards maintaining higher compression because it's just so much more responsive, but maybe it might make sense in your case. I wonder why they have such issues with knock? Not being familiar with the engine, does it have much flat squish/quench area? What's the piston to head clearance like? I run ~11.2:1 compression in the Vette, which people say is way too much for 98 in such an older design larger engine, but it works perfectly fine. I put a fair bit of effort into smoothing any sharp edges in the chamber though, and have a large flat quench area and very small piston to head clearance to maximize the quench. I've never had any problems with detonation / pinging.

[sambb]

yep pistons are all $1200-1300 landed. In terms of factory gear I could turn the engine into a 2.0L+ as a TFSi crank (92.8mm stroke) is a direct fit except for swapping over the crank signal pickup wheel and the timing gear. TFSI rods would go in too as they are the same dimensions as my 20mm pin end rods. Provided I bored out from 81 to 82.5mm the TFSI pistons would go in too but they are DI pistons. The MK5 gti motor had mid 9's:1 comp but I think it gets too high in the golf 6's. The DI pistons have have swirl profiles in the pistons and deep dishes etc for DI which I don't know if they'd work with a port injected engine or even clear the centre inlet valve - I have three they only have two. I think 82.5mm bore might be pushing it in my older block though as 83mm is the known max. I'd discussed going to 83mm at stock stroke with the engine builder but he said there's no point worrying about all that till he sonically tests the wall thicknesses because if there's a bit of core shift and then it gets taken out that far we might be pushing it too much. There are other options than to go to 82.5mm to fit TFSI pistons though as the aftermarket has stroker pistons from 81.5mm up I think. I don't think I can run stock 81mm bore at that long stroke as the rods hit the skirts and there are issues with having to modify squirters too or so I've read.
Not sure if I want to take an 81 x 86mm 1.8T and turn it into a 81-82.5mm x 92.8mm super undersquare stroker. Might be worth it if I could find a wrecked TFSI. But when you start looking at a decent over bore, line boring, basically having to do the full blueprint etc all the different issues etc I think its a big can of worms. I imagine it wouldn't rip through the revs like a lighter rotating mass , closer to square 1.8 -never driven one so I don't know, but maybe a stroker could be the go by making its power lower which would make breaking something in the valve train less likely!
God now I have to go and do research to see if DI pistons have to be moddded to clear my centre inlet valve or even work at all with port injected combustion. Worth looking into as even if I didn't go stroker I still could run my crank, my forged rods, and at 82.5mm would be up just under 1.9L from 1781ccc and running a closer to square engine.

[h100vw]

I fitted a 2 litre bottom end to a MK1 GTi golf. It had s big valve head. Rev'd like a motorbike as an 1800. Was fully ruined by going to the long stroke 2 litre. Barely rev'd to 6k versus well over 7 as an 1800. Based on that I'd not go 2 litre myself.
I know it is turbo in the polo. But I'm still not a fan of the idea.

[sambb]

Yeah I am umming over the amount of weight it'd add right through the bottom end. Not sure but isn't either the TSI or TFSI cranks forged? No idea if that makes them lighter but might consider it if their cranks were lighter than the 1.8T cast one. I do however prefer doing an 82.5 x 86 bore stroke. You'd be adding reciprocating weight at the piston but being nearly square you'd imagine it'd rev up fast.

Looks like I buggered up before - EA113 TFSI (MK5 gti) and EA888 TSI (Mk6 gti) had 144 x 21mm rods it seems, not 20mm pin end as I thought. Regardless of crank I could go a standard TSI/TFSI rod (whichever is better) and honda pistons (21mm pin) maybe if they're cheaper.

edit: it seems EA113's had 10.5:1 comp so those pistons would be out. EA888 gen 1 had 9.6:1 though

[sambb]

1.8T 20V piston EA113 piston EA888 1.8TSI

note the valve relief for the centre of the 3 inlet valves in the 1.8T 20V. It does run a dish not dissimilar to the EA888TSI though.

[Stuwey]

edit: it seems EA113's had 10.5:1 comp so those pistons would be out. EA888 gen 1 had 9.6:1 though

Remember though that the compression ratio is entirely dependent on the combustion chamber size. That same piston running with a different head will provide a different compression ratio.

Knowing the head CC of these alternate engines would give you a clearer idea of what you'll end up with.

[Sydneykid]

$1200 to $1300 for 4 pistons it's definitely time to look at more common engines with the same major dimensions, bore, pin to deck height and pin diameter. As in the post above Honda B series pistons are 81 mm, cheap as, very common from multiple piston manufacturers with turbo options. I'd start there and stop paying the "VW tax" (applied just because they aren't as common).

Page 3 of the Wiseco catalogue is good place to start, they kindly show all of the relevant dimensions, including combustion chamber cc;
https://www.wiseco.com/Catalogs/Spor...cura-Honda.pdf

Just compare those dimensions with your engine's, you might hit on one that will suite. Armed with a part # and specs then you can compare prices from sources other that Wiseco.

Adding a fly cut for the 3rd inlet valve is no big deal, it shouldn't need to be deep enough to cause issues with the piston crown strength.


Cheers
Gary

[sambb]

Yeah you're right Stuwey. I'd been thinking that the ea113 and 888 heads were the same but they changed a bit after the mk5 didn't they. And yeah different chambers change everything between the motors.
The 1.8ts only have like 8.7mm lift. Maybe selecting the highest crown out of the tsi/tfsi would mean one of those pistons could be machined to be able to run in my engine - someone must have done it.