Best OEM pistons for pikey small block 16v turbo

Discussion in 'Turbocharged, Supercharged or Nitrous !' started by theboymike, Apr 30, 2011.

  1. theboymike Forum Junkie

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    I'd like to build a 1.3 small block turbo running a later 1.4/1.6 16v head. On account of the extra volume of the head compared to the flat 1.3 8v heads, G40 pistons are a no-go, and since this will be a budget build (if it ever gets going) I'm looking for cheap alternatives.

    The three possible pikey solutions I've come up with so far that give reasonably suitable compression ratios are:

    Machined down 1.05 pistons:

    [​IMG]

    Reckon I'd have to lose about 6.5mm from the top of the piston, with associated loss of top ring land depth and crown thickness. Probably the worst idea.


    HH/GT pistons:

    [​IMG]

    These are from engines that had a partial combustion chamber in the head, meaning the pistons have a flat crown and lowish compression height. Probably a reasonable bet if they won't melt, however a bit of a sod to source.


    Machined 1W Diesel pistons:

    [​IMG]

    Either with the original 1.3 crank with a bit machined off, or perhaps even as part of a complete diesel bottom end, however I'm not overly keen on the under-square design. I realise I'd have to machine off the features on top of the crown, however I like these on account of their enormous top ring land, which I think should be good at not melting. However, I am concerned about the enormous gudgeon pins (22mm dia) and mass in an engine that's required to rev 1.5 times faster than the pistons were intended for. Obviously the diesel pistons are designed to take much higher cylnider pressures, however I also understand that petrol engines tend to run hotter so this might compromise any additional strength.

    Anyone got any thoughts? Do we think that all of the suggestions will end in certain death? :lol:
     
    Last edited: Apr 30, 2011
  2. theboymike Forum Junkie

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    Thanks for the excellent link; I've actually been using that for much of the information in my smallblock uber-spreadsheet :thumbup:

    I'm after a 75.0mm bore, as used in the earlier 1.05 / 1.3 small block lumps since I think the rods, pistons and gudgeon pins are stronger than the later alloy blocked 76.5mm bore 8 and 16v engines.. I've also chanced a look at 75mm pistons from other manufacturers (courtesy of the rather useful Mahle catalogue search engine) but haven't found much really..
     
    Last edited: Apr 30, 2011
  3. amstrange1 Forum Member

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    GK engined Polo was 11:1 CR with an hydraulic head (i.e. the flat design), possibly some scope there?
     
  4. theboymike Forum Junkie

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    Thanks for the suggestion; unfortunately due to the flat head the GK pistons have a farking great bowl in them; meaning the CR turns out too low with the 16v head.

    Currently wondering about 2.4 Petrol LT pistons; biggest issue with all of them (aside from whether they actually fit) is how much boost they'll take before they melt..

    Also looking at offerings from other manufacturers, however it appears that 75 and 76.5mm bore isn't that common outside of VW circles..
     
  5. amstrange1 Forum Member

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    What's the CR work out at using the GK pistons with a later 16v head? They look very like 3F (Polo GT) pistons, but the dish in the centre is a smaller diameter.

    There's also the MN diesel motor - that was 1272cc (same bore/stroke as the petrol 1.3) and 22:1 CR...
     
  6. theboymike Forum Junkie

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    Based on the following assumptions the GK bottom end with 16v head gives a CR of around 6.3:1:

    Volume of 16v chamber in head = 31cc (calculated from 1.4 16v compression ratio and displacement)
    Volume of GK piston bowl = 28cc (calculated from GK compression ratio and displacement)

    There is obviously some margin for error in the calcs, plus the influence of different head gasket thicknesses.. I don't think it'd be enough to bring the compression up to the 8.5-9:1 that I'm after though.


    The MN engine interests me; and given the flat topped pistons would certainly allow the correct compression ratio to be achieved with some machining. What puts me off is the following:

    - Availability - this engine was only available in mainland Europe, making getting bits potentially difficult. A whole bottom end would be nice though (if impractical to get hold of) since the MN crankshaft is the same as the G40 item.

    - Mass - the pistons are intended to be used in an engine that probably tops out at 4000rpm; so not sure how suitable they'd be in something revving to 6K+. Also the gudgeon pins are 22mm dia in the diesel rather than the (already large) 20mm used in the petrol engines.


    I'm quite interested in the concept of using modified diesel pistons though; they'll obviously be made to take greater load (since the CR and BMEP of the diesel engines are so much more) and hence have a much higher top ring land thickness which has to be good for heat dissipation. That said I'm a bit concerned about the mass, and also the fact that despite being manufactured to take more mechanical load, they might struggle with the elevated temperatures of the petrol combustion process.


    Another possible route I was considering was the construction of an engine from the following bits:

    1.4 AEE tall block (6N Polo, Mk3 Golf, 76.5mm bore, crank centre to deck is around 208mm I think)
    1.3 ADX crank (6N Polo, 76.5mm bore, 70.5mm stroke, 47.8mm pins. The only engine that uses this stroke I think)
    1.8 PG rods (Golf Mk2 / Corrado, 136mm length, 47.8mm ID big ends, 22mm ID small ends)
    2.4 DL Pistons (From LT van 76.5mm bore, 22mm gudgeon pin, nice flat crown).

    [​IMG]

    With a bit skimmed off the pistons this should give an acceptable CR. I like this configuration as it gives a nice oversquare engine of 76.5mm bore, 70.5mm stroke, a nice long rod ratio (136/70.5=1.93) so should like to rev. Also the AEE blocks are common and cheap as chips.

    That said, I have reservations about the strength of the pistons given their initial application, and obviously they might be a bit of a swine to source. Also, the availability of the ADX crank is going to be limited...
     
  7. prof Forum Addict

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    could you ceramic coat the pistons? and use oilsquirters
     
  8. theboymike Forum Junkie

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    Thanks - I had briefly thought about ceramic coating, although I suspect the cost would be moving towards forged territory. Will look into it a bit more though :thumbup:

    I was planning on using oil squirters but I think they're only present on the 16v and diesel blocks. I think I've seen some retro fitted, that said I don't relish the thought of access to spot face, drill and tap the block inside the crankcase. I think tonight's task will be some oil squirter research on ETKA :p
     
  9. Yoof Forum Member

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    As soon as you consider ceramic, DLC or any other piston coating you're beyond the realms of a budget build...

    I just bought a rebuilt G40 bottom end for 150- ready for lots of boost, with oil drain and knock sensor provision, I'd be surprised if you could build something as reliable for the money.
     
  10. LeftcoastTigger Paid Member Paid Member

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    Standard VW bore diameters

    Cerips,

    If you have similar information for 82.5 to 85.0mm bores, would you please post them on another thread under that heading? Mass, ring widths etc also much appreciated - - :thumbup:
     
  11. theboymike Forum Junkie

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    Cheers.. I think you may well be right about the coatings etc.. however I will look into pricing. G40 bottom end sounds like a bargain; although as I'm sure you're well aware the G40 pistons have too much volume in their bowls to be any use with a 16v head..

    I've seen your motor cropping up here and there on my travels; do you have any links to a build thread?

    Thanks - not heard of some of those; will have to chase them on ETKA :thumbup:

    You may find this helpful for piston dims; although it doesn't give component mass unfortunately..
     
  12. LeftcoastTigger Paid Member Paid Member

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    Thanks, TBM:thumbup:
     
  13. theboymike Forum Junkie

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    No problem - best say goodbye to countless hours of your life :lol:
     
  14. LeftcoastTigger Paid Member Paid Member

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    Thanks, just looked, been outtatown, will research next week - - also very interested in what the Audi 4.2 pistons are like including full dimensions, ring pack, and mass:p
     
  15. Yoof Forum Member

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    G40 pistons can work with 16v heads, just got to pick the right crank...:thumbup:

    Build threads are on Club G40, Club Polo etc if you're interested :)
     
  16. theboymike Forum Junkie

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    Cheers - do you know of anyone who's actually used G40 pistons in a 16v conversion? They have a lot of bowl volume so I think the only way to get a decent CR would be to use a longer stroke crank and remove a lot of the piston crown..

    Found your thread on club Polo - very impressive [8D]
     
  17. LregG

    LregG Paid Member Paid Member

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    just out of query, why do you want to go to the trouble of using a 16v head if it's a budget build?? the 8v head on the 1.3 engines flow really well from factory....190bhp has been acheived on a few cars at 1.5bar boost on G40 engines with the standard rods being well up to the job, standard G40 pistons can survive if the engine is mapped correctly as well.

    what car is the engine going to go in?
     
  18. amstrange1 Forum Member

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    Mine's running a standard head too, but 16v is better.
     
  19. LregG

    LregG Paid Member Paid Member

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    this is my point though, if you are making 207bhp, 215lb/ft on a 8v head then mike is best off staying 8v if he is looking for a budget build and using the money that would have gone going 16v to uprate the transmission etc
     
  20. theboymike Forum Junkie

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    I'd like a 16v head as it gives more valve area than the 8v alternatives (roughly a factor of 1.3 on the inlet and 1.8ish on the exhaust). The aim of the project is to create something that will give good low load / part throttle / cruising economy (thanks to it's small displacement and hopefully high gearing in 5th) but will go like a stabbed rat if poked.

    I'm hoping the 16v head should help with this since it should flow better at high engine speeds (port design notwithstanding, although it looks good); allowing the engine to rev higher and reduce the amount of boost required for a decent amount of power. Also, I think the flow characteristics of the 16v head should improve torque spread across the rev range too.

    I'd like the engine to be fitted to a MK2 Golf, so low end tractability is is of a bit more concern than in would be in a Polo on account of the extra weight.

    :thumbup:

    The project is not all about peak power; I'm also looking for high efficiency and good low-end response. In my head the project is like a more extreme version of the MK5 TSI engine, but with twin sequential turbo instead of the supercharger / turbo setup which I'm hoping should make things more simple and even more efficient.

    When I first had the idea I was hoping that I could get away with stuffing a late 16v head onto an earlier bottom end to give a cheap low comp engine a'la KR head and 2E bottom end in the big block world; thus gaining the efficiency of the later tech while retaining the strength and cheapness of the earlier block.

    Unfortunately I've run into problems with piston choice (since most earlier 8v engines have their combustion chambers in the pistons and hence give too low a CR when the additional volume of the 16v head is factored in).

    There also appear to be problems with the 8v block / 16v head combination as the head bolts are different sizes and the oil / water channels don't quite line up.

    I was hoping to use the more common AHW style head (timing belt drives inlet cam only) since the bottom ends on these engines are sh*t and I envisage a flood of such vehicles down the scrappy soon enough.

    These heads have the advantage of being cheap and plentyful (reckon I could get a complete head for 100) as well as being compact and allowing a lot of space at the front of the engine for the twin turbo setup. They're cheaper, less sought after, more compact and far more common than the AFH head that the Polo boys all love, however I think the AFH head should directly fit the 8v block.. looking at the head bolts and the oil / waterways.

    I've more recently been looking at de-stroking a complete 1.6 16v engine with an ADX crank to give a nice oversquare 1.3 with huuuuge rod ratio.. but then of course things start getting expensive again and I'm back to using the weaker, newer parts again..

    How much boost do you think a 1.05 8v engine would take if the piston crowns were machined to drop the CR to say 8.5-9:1?
     

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