ISO: 7 bolt build advice

[Barber613]

Might be a lil long on the explanation, but want to give context.

Bought a 95 TSI with a built 7 bolt. “Just needed buttoning up”. Build receipts accompanied the car. Finished plumbing and electrical, car fired right up. After breaking in the engine, did my first WOT and blew the felpro headgasket that was on it. (Yes it has head studs). Machined the head, new cometic MLS and back together, went and tried another WOT and blew compression into my coolant. Head studs were torqued correctly and checked after heat cycles.

Long story short, pulled the engine all the way down this time. I noticed that it has wiseco 6656M855 pistons. I notice that on my block, they come slightly above deck height (I can catch them with my fingernail).

Checking wiseco’s site, it says these pistons are not compatible with the 4g63t, only the NA version. I know and have seen this be used on boosted builds, so just trying to understand the limits and figure out the recipe the previous owner was trying to do.

Pistons, rods, head look fine, no signs of contact. Car still Ran and drove with no weird sounds, just pulled it all the way down to inspect if I had a low spot on the block, or crack in the block. Was this block machined too low for these pistons? Is this normal for this use of piston? What do I do or check next? Any advice appreciated.

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[dwb]

I'm definitely no expert here but those have relatively high compression at 10.5:1. Are you running e85?

 

[Barber613]

I’m no expert either, quite a novice that’s why I turned to this forum as the gurus lurk in the shadows.

Tune was set for flex with e85 being the end goal. During break in and the few pulls I did it was on pump gas, AFRs and plugs looked great. I was also informed the CR was 9.7:1. Is that possible with these pistons? Other than lifting the head, car ran smoothly. Not signs of any component running hot. With the thick headgasket I ran, my compression in each cylinder was 185psi

 

[dwb]

I googled the pn you posted and got 10.5:1. I didn't really dig into it so I could be off. My understanding is if you're boosting with that much CR, you are likely to detonate on pump gas. E85 helps knock or you need less agressive timing, depending on how much boost you're running. It's like how 1g timing maps are more aggressive than 2g maps. 2g pistons are 8.5:1 and 1g are 7.8:1. Not a huge difference but enough that it needs to compensate for knock somehow.

At least you're just popping the head gasket and not melting pistons (yet). I'd be careful doing wot pulls until you get things figured out.

 

[DSMPT]

Could be just an installation error, most likely lack of flatness of surface or so.
Those pistons are the older gen CR10.5 1400HD, the ones that were advertised incorrectly as 10.5 compression ratio at the beginning. The compression ratio would be around 9.6~9.8 in our early 4g63. It would be 10.5 only if it's used with the late EVO 43cc head.

Checking wiseco’s site, it says these pistons are not compatible with the 4g63t, only the NA version. I know and have seen this be used on boosted builds, so just trying to understand the limits and figure out the recipe the previous owner was trying to do.

You probably misread or misunderstood something. Piston itself has no difference between turbo piston and non turbo pistons, no such a thing beside the compression ratio and some reinforced options.

As for the piston deck height, you have to check with a proper tool. If you press one side of piton top at TDC, the other side of piston would raise is normal. Yes maybe some material has been removed from block surface previously but the pic doesn't look abnormal. Even if the pistons are above deck a tiny bit, nothing would happen in most of case in our engine besides you just get a slight higher compression ratio.