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Yes, 900-082-030-02 is a grade 8.8 bolt (below is a picture of the OE fastener). "Over-speccing" in what regard? This is the issue here with the ignorance of a well-intended mechanic.
Yes a grade 10.9 bolt is "stronger" in weight carrying strength (our motors weigh a few hundred pounds btw, not tens of thousands). That said, a grade 10.9 bolt is also more "brittle" than a grade 8.8 bolt. This is particularly important when a bolt's application is in "shear" (at least some of the time). If you think about how the motor in our cars is suspended, you have the front of the motor mated to the transmission, which is attached to the car at the front of the trans. You then have the very rear of the motor suspended by these two bolts. Both an 8.8 or a 10.9 bolt can more than adequately hold the motor up while it's just sitting there (again the motor weighs relatively "nothing" as far as either bolt is concerned). The issue is the lateral forces being placed across these bolts attempting to "shear" (or "cut" them) as the motor is tossed around from corner to corner. In this regard, a 10.9 grade bolt is worse than an 8.8 grade bolt where, a 10.9 would be more likely to snap via shear given it is more brittle vs an 8.8 which can withstand a greater amount of deflection.
Will you ever have a problem? Who knows (there are too many variables here given the motor mounts themselves and the calculations are far beyond our reach). But I do know (I'm an engineer) that I would trust the bolt spec that Porsche has determined is appropriate for the application vs what some mechanic decided. I'm not trying to pull punches here, just pointing out that if the mechanic looked at the 8.8 bolts and thought somehow that Prekom was skimping out, I would give that serious reconsideration. They've spec'd exactly what Porsche did (for a reason). Things are not as simple as "higher grade = better".
Last edited by boomboomthump; 04-11-2023 at 10:29 AM.
Don't disagree with what you said there, but it's my 'ignorance'. I did the research, I specced the bolts not Prekom, or FVD.
I agree 10.9 is more brittle than an 8.8, but it's a tiny tiny difference, and you as an engineer know that.
Most 'car' bolts are 10.9 are they not? So (as above) I gave the mechanic the choice as I bought 8.8s and 10.9s, and I'm happy with his experience level.
Hi Bill,
can you describe the added supercharger noise? In more detail? Is it the latest version of the SC? I haven’t found anyone with a SCed 993 nearby to check out, but I’m thinking of getting one and trying to do as much research as possible.
04-11-2023, 09:47 AM
