All Things Mk5 > Members Rides
Black magic Mk5 GTI track car
xht20:
I have 9.5:1
s3dubbin:
I run 9.5:1 JE. Stevie.
the bruce:
--- Quote from: fuscobal on April 06, 2012, 08:05:32 am ---In the unhappy case of finding marks on the pistons, I will have to change them. As the OEM ones cost about the same as Je pistons, I'm thinking of upgrading them. My OEM compression is 10.5 (highest of all, being my AXX was the first TFSI engine code). Je has CR of 8.5:1, 9.5:1 and 10.25:1 with bore 82.5(OEM), 83 and 83.5. I will not go with 8.5 but wouldn't know what to choose between 9.5 and 10.25 (they also make custom so I'd go a little bit lower but not too low). Also, in terms of bore, should I go 83 just to be sure ? (even if the actual diameter is still closer to 82.5). How does lowering the compression affect everything on this engine ? (updated REVO software ?, engine temps....)
--- End quote ---
Simply go for 9.5:1 !!
Reducing CR will compromise torque at lower revs and overall efficiency,
but you'll get increased safety and engine life and you can also run higher
boost pressueres.
Going for the larger 83 mm bore will require maching to your crank case.
If maching is already necessary I'd go for 83.5 , if not stay with 82.5 mm.
fuscobal:
Ok guy, 9.5:1 will be if it's the case (hopefully not). However, I have yet to see if I need extra bore on the cylinders. I'll let you know once the engine is opened up !
fuscobal:
2 option arise at this point :
1) Use TEFF's OEM pistons wich have low mileage but a CR of 9.8:1 wich will probably require new software (I will have to talk to Revo about this). Also, I've measured the cylinders and they seem closer to 82 than 82.5 !?!? Why is that ? However, I will have to sand off the whiteish vertical marks on them left by the pistons wich expanded. Now, those marks cannot be felt while passing with the thinger but at the upper side of the cylinders, the last 5mm or so have marks that can be felt. Theoretically those doesn't matter as the piston rings don't reach that area (they are lower, only the top of the piston reaches that area but is not in contact with it). Tis is why I don't know if to stay with 82.5 or go to 83. I will not go to 83.5 because I want to keep room for another bore in the future if another disaster like this one occurs again !
2) JE Pistons with 10.5:1 & 83mm (as advised by Revo & IE) + new IE rods (The IE rods I have now work with OEM pistons only !) + new Calico bearings. This option is much more expensive but is safer and doesn't require modifying the software. Keep in mind I don't need the extra strength of forged pistons since I will even lower the software to 340-350HP and 450NM for the next track days. I will lower the boost and fuel (richer mixture to cool things down) to achieve that. The setting used until now was 9-7-9 wich may seem high for most but it's what worked for me with close to no CF (timing retard). The f9 setting is the leanest and hottest of all so I may try 7-7-7 or even 7-7-5 (can't say for sure until I make some logs) !
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