I have a Z170 FTW motherboard. I just watched (seems I cannot post links) "Let's build a Skylake 6700K Gaming PC" by JakesTwoCents. A build video of what is basically my own exact build and it kinda confused me. In the video @ 8:24 he explains some issue he had with SLI config of the 2 EVGA 970s, but it is kinda muddy what the problem is. I need some advice! I just ordered a second EVGA 970 GTX SSC for SLI setup. Is it not possible to use PCI lane 1 and 3 so that you get proper spacing for airflow, or do you have to use lanes 1 and 2 cramming the cards together?
 
A secondary question is what type of EVGA SLI bridge should I go for? Pro Bridge V2 (2-way Long)? Or is there another SLI bridge that looks better with my cards?
Paul

Thank you for posting the video Zuhl, I guess I need some more post under my belt to be able to :)

palandresen
I have a Z170 FTW motherboard. I just watched (seems I cannot post links) "Let's build a Skylake 6700K Gaming PC" by JakesTwoCents. A build video of what is basically my own exact build and it kinda confused me. In the video @ 8:24 he explains some issue he had with SLI config of the 2 EVGA 970s, but it is kinda muddy what the problem is. I need some advice! I just ordered a second EVGA 970 GTX SSC for SLI setup. Is it not possible to use PCI lane 1 and 3 so that you get proper spacing for airflow, or do you have to use lanes 1 and 2 cramming the cards together?
 
A secondary question is what type of EVGA SLI bridge should I go for? Pro Bridge V2 (2-way Long)? Or is there another SLI bridge that looks better with my cards?
Paul

Hello and welcome to the forums.  In this case I can see part of or at least a potential problem in the video at the 5:20 mark, the second slot Jay put the card in is NOT a x8 slot and as such it cannot be used for SLI.
 
If you are NOT new to this feel free to skip over the explanation, otherwise this may shed some light on things, but there are x16 physical or mechanical slots, which is only an indicator of its physical size, and x8 electrical (not an overly accurate term frankly) but this indicates how many PCIE lanes are actually allotted to the slot.  This CPU only has 16 PCIE lanes which is what runs the cards and slots 1 and 2.  So it will run at x16 for top card, or x8 and x8 for a SLI.  Below that all of thew lanes come from the PCH (Platform Controller Hub) which is basically what replaced Southbridge on modern chipsets.  It has it's own PCIE Gen3 lanes as well, and the slot he tried to add the bottom card into does not have enough lanes to run the card, as it is x4 lanes max.  Jay did reference a PLX, which is a PCIE lane replicator, it takes 8 PCIE lanes from the CPU and duplicates them through a hardware replication process, the entire point of a PLX chip (or an NF200 chip if you used some of the high end X58's or P55's back in the day, NF200 is for Gen2 lanes and a PLX is for Gen3 lanes) the FTW does not have one, the Classified does.  PLX gives Z series chipsets the ability of going 3 or 4 way SLI, or having additional slot options (more than 2) for 2 Way SLI. 
Because the lanes are routed to the slots by traces, it is not possible do adjust lane allocation between slots, such as a BIOS option as I have been asked in the past, to set the other x8 slot to be the 3rd.  Now the statement about the M.2 is not accurate, you can run the M.2 and 2 cards in slots 1 and 2, the M.2 uses lanes from the PCH not the CPU, which is a major factor for Z170, with the PCH now being Gen3 you can run Gen3 devices at Gen3 speeds without having to borrow lanes from the CPU.
The Lane breakdown is also found on page 11 of the manual here http://www.evga.com/support/manuals/files/140-SS-E177.pdf
 
I hope this clears things up, but the TL;DR part is the 3rd slot is traced to the PCH not the CPU, so SLI can only run at slots 1 and 2.  CPU is 16 lanes so it is not as configurable in that respect as say an X99 which has 28 or 40 lanes, and does not have a PLX to make up for the lane difference.
 
If this didn't clear things up, please let me know any follow up questions.
 
For the other question, go with the regular 2 way bridge, not the long, that would be is you have say an X99 Classified and wanted to have a single slot spacing between the cards and run them at Slots 1 and 3.

Thanks a lot Dave! I really appreciate you taking the time to explain properly, I’m new to this :) 

 
Using slots 1 and 2 I’ve been concerned about the airflow to the fans of the uppermost GPU. I also have backplates for both cards so it will be a tight fit (maybe not use the backplate for the lower card to increase clearance?). Are my concerns groundless?

gitdat
Why can 2x SLI no longer be ran at x16? This x8/x8 is killing me! I used to run 2x SLI @ x16 on my old EVGA Z77 FTW motherboard Is this a limitation of Skylake/Z170 platform?

The x87 Classified moved the PLX to carry the fake 2x16. The chips that were usable on the z77 series were still only 16 lanes total, so you weren't getting actual 16 lanes, you were getting 16 lanes total from the cpu and they were split on a plx.

The z77 ftw was the top end board at the time and now the classified had those features, so you would need to buy the classified to get the same feature. Reading through the product specifications explains that portion and the ability of 2x16 right on the product page.

It is still only 16 lanes, as the enthusiast grade cpu's (x79 x99 type cpu/board) are the only cpu with higher than 16 lanes available. To get true 16 lanes you would need to get one of those, as your cpu and the one you reference on the z77 only have 16 native lanes.