Bump for some brake rotor updates. I initially did my conversion using the original OEM 1-piece "co-cast" rotors. Then GM started offering the 2-piece Brembo rotors, so I've acquired a few sets of those over the past few years. Regardless of whether you use the 1-piece or 2-piece V2 rotors, if you intend to use them on V1 hubs, you have to enlarge the center bore (from 67.4 out to 70.7mm), and you have to redrill the bolt pattern to get your 6x115.
Recently, as I was browsing around for brake parts, I discovered something kind of curious. The V2 2-piece rotors are ACDelco 177-1145/1146. I thought that the ATS-V used the same brake setup as the V2, but it turns out the ATS-V has different part numbers for the 2-piece front rotors - 177-1193/1194. According to the specs I can find (clicking the "INFO" button on each part on Rock Auto), they're the same size - 370x34mm - so that made me wonder about the different part numbers. The only thing I can figure is that the hat offset is different; that's one spec that isn't listed for both rotors on Rock Auto (it shows the ATS-V rotor "height" is 2.4", but height isn't listed for the V2 rotors). Someone on LS1tech pointed me to centricparts.com, and sure enough, the specs they list there show the ATS-V rotors have a 10mm different offset (more on that in the pics below).
Similarly, some V7 Vettes (the '15+ C7 Grand Sport package) also run a 370x34mm 2-piece Brembo rotor. It's slotted, but apparently isn't directionally vaned, as I'm only seeing 1 part number - 177-1174. Based on the centricparts.com data, the offset of the GS Vette rotor is the same as the V2 rotor.
I ordered 1 of each of the GS Vette and ATS-V rotors so I can compare them to the V2 rotors I've already got. In the case of the ATS-V rotors it's basically just for the curiosity's sake, as the rotors (at this point) are more expensive than the V2 rotors. The GS rotors are also more expensive, but if someone wants slotted rotors for the V2-calipers-on-a-V1 setup, then the GS rotors might be a way to get there.
I received an ATS-V rotor and a couple of GS Vette rotors and pulled them out of the boxes for a look.
- The ATS-V rotor hat visually has more offset than the V2 and Vette rotor hats. The rotor ring appears identical to the V2 rotor ring, with directional vanes.
- The GS Vette rotor hats appear to be the same offset (to the naked eye) as the V2 rotors, so that's good. The rotor ring is non-directional; it uses pillar vanes that look very similar to the original co-cast V2 rotors (
this style). I have a couple of those co-cast rotors that I picked up last year when Amazon was doing the 20% off ACDelco deal, I'll have to pull one out and compare side-by-side with the GS Vette rotor.
Most importantly (for my purposes, sticking with 6-lug hubs), the GS Vette rotor hats have the same center bore as our V1 hubs (testing with an old hub I've got with all the studs knocked out). That makes modifying the rotors to fit the V1 a much easier/cheaper evolution, as I don't have to pay a machine shop to enlarge the center bore of the rotor from 67.4mm to 70.7mm, and instead just have to redrill the bolt pattern. That's something I'm able to do myself.
As of today the GS Vette rotors (ACDelco 177-1174) are ~$15ea more expensive than the V2 rotors (ACDelco 177-1145/1146) on Amazon, but that cost difference is more than made up for by not having to pay for machining. And as many of us have seen, the price of ACDelco stuff seems to bounce around quite a bit on Amazon, so in a few months the Vette rotors may be cheaper. (Or the V2 rotors may be $75ea cheaper instead of $15, who knows?!)
Some comparison pics.
First, ATS-V vs GS Vette rotor. Centric's catalog said there's a 10mm difference in offset, and you can see that pretty easily with the naked eye:
The GS Vette rotor with one of my modified V2 rotor hats:
Visually they look like the same offset, which jives with what Centric's catalog says:
And a straight edge across the two looks purty good:
Here you can see that the GS Vette rotor has the same type of non-directional, pillar style cooling vanes that the original V2 co-cast rotors have: