Question Mounting a 240 push pull AIO in the front of a corsair 750d

NadeMagnet69

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Jul 20, 2020
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The 750 has 2 stock 140mm in the front. I'm yanking those and putting a 240 push pull AIO in its place in the front. I want to slide it up as much as possible because I'm also adding 2 120mm intakes in the bottom, one of which will be slightly roughly half under the push pull. So by sliding it up, the 2 bottoms can get an extra 3 inches of air clearance under the radiator from the front so they'll share the front's intake. Plus the AIO looks better with just a gap on the bottom instead of a gap on both the top and bottom. Of coarse nothing is that simple. I can't get all 8 holes clear by sliding it up that high instead of where it's suppose to go. The 4 middle inner screw holes are blocked now.
Will 4 screws mounted on all 4 outside corners be enough to secure it? I mean hell I only got one screw in so far in 1 corner and it's fairly snug. Each fan I'm mounting to the case will have 2 screws so they won't be able to rotate around plus they are sandwiched between themselves, the case, and the radiator. I think it'll be fine but I wanted to hear from some people who know what they're doing. This is my first PC build.
Thanks
 

Darkbreeze

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What screws are you talking about? For the radiator fans, for the radiator, or what?

Pictures are always helpful.

 

NadeMagnet69

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Here's a pic of what I mean. This is mounted with 4 right now. Notice I can't screw in the inner middles? I can also add 2 more in the middle if I go get longer screws. But 2 are totally blockled unless I drill holes.
Edit: Those 4 screws are going through the fans to the radiator.
 

Darkbreeze

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Drill holes. Get longer screws, or bolts with nuts and washers if necessary. Also, I would advise putting rubber or plastic washers between the fans and the metal of the case to absorb some of the vibration.

If you don't fasten those fans in all four corners, you WILL have vibration and funky harmonics problems. It will probably also shorten the life of the fan motor. Vibration tends to play havoc on small motors.
 

Darkbreeze

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So long as YOU are happy with it, that's all that matters. If each fan has three screws in, and there are no noises, then who am I to argue with it? If however you start hearing anything unusual or any unusual harmonics, you'll know where to look to right away.
 

NadeMagnet69

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lol 1 fan has 2 screws. 1 is now properly mounted. For there to be 3 screws in each fan I'd have to drill holes and this would all be moot anyways because there would be the proper 8 screw setup. Maybe, just maybe, if I drop the whole case from like standing height, the second fan might shift. But if that happens I suspect this mounting will be the least of my problems. :ROFLMAO:
These are Noctua fans anyways. They're well built and they don't vibrate much. I really love these fans. Super quiet too even at max RPM.

Since I'm already here to respond back do you want to hear something funny? Apparently I can't count to 5... :rolleyes:I have so many orders going at once through amazon I forgot that one of the fan orders had 2 140mm. I just counted pics, saw 3 and knew I needed 4. I hadn't ordered them all at once becuase orginally I was going to mount the AIO at the top as an exaust but it wouldn't fit there as a push pull. So now I got another 140mm coming on sat. Bahahaha I think I'm going to mount it in the front in that bottom gap so now my AIO will be a 1 quarter push push pull intake. Or maybe I might return it I don't know yet. But it just seems funny to mount it. I'll show you a pic with one of the stock 140mm I yanked. Or I can go for super overkill and also throw 1 of the stock 140mm on with the new 1 coming. That's where the stock 140s were before. lol Push push pull just seems funny to me. I'm easily amused. :D
 

Darkbreeze

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Each of my three systems are equipped with all Noctua NF-A14, A15 and F12 fans. I am very familiar with the quality of Noctua fans. They are still all mounted correctly using four screws, or actually, I'm using the rubber mounting screws which are not actually screws at all, and when even one is not installed correctly I can HEAR the difference in the harmonics even though the fan itself feels very solidly mounted.

Personally, I think you're wasting your time and going about this wrong. From what I see in that picture, that is NOT a push-pull configuration. You have one set of fans blowing onto another set of fans that are blowing into the radiator, and you are gaining nothing from that. For a push pull configuration you would need one set of fans on the front of the radiator and one set of fans on the back of the radiator AND you would need them to either be the exact same set of fans or you would want the rear (pull) fans to be higher CFM than the front fans so they don't create a restriction and actually reduce the effectiveness of the front fans, and you would want the front fans to have a very high static pressure rating.

Plus, that fan in the very front is facing the absolute wrong direction. None of what you are doing appears to be right unless you are only putting the fans there for mock up and don't plan to mount them that way. I think you need to pull it all out and rethink what you are doing.
 

NadeMagnet69

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I didn;t bother to see which direction the fan is. Do you see any screws in it? I just placed it there to take the pic. I was just trying to brighten your evening. Yes this is a true push pull. And reduced effectiveness is still more effective than just a push or just a pull. The difference in airflow and static pressure between the stock and noctua is negligible. It's only 14CFM and .63 static pressure. I already asked here on Tom's and everyone said it wasn't worth the 27 bucks to buy 2 more noctua to replace the stock arctic fans.
Look, push pull.

I also question why you think I'd gain nothing. It's an extra 140mm intake with most or at least half of the airflow going under the AIO. And why wouldn't an extra 140 help push even more air through the radiator?
 

Darkbreeze

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Yes, like that^^^^you gain something, IF the fans are all facing the correct direction. Like it was in the previous picture, especially if you added another fan like that, you'd not only not gain anything, you'd likely lose almost everything.
 

Karadjgne

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With today's fan designs and the lower fpi count of aio rads and low flow output from aio pumps, there's actually very little gain from push/pull on an aio. Generally you'll see a stress gain of less than 5°C, gaming temps closer to 2-3°C on the larger aios. The only real gains in push/pull are to noise, and often without matched fans/source/speeds you'll get some seriously funky harmonics as air from the front fans hits the rear fan blades out of phase.
 

Phaaze88

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So what you guys are saying is I should throw 2 140mm in front of the push pull.
Been there, done that - just for craps n' giggles, but the turbulence from that isn't audibly pleasant.
Did it with the H500P Mesh's 200mm fans with 3x NF-A14s right behind it: it looked silly, it sounded silly, didn't do anything for thermals, but I got a little laugh out it anyway.
 
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Karadjgne

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No. What I'm saying is More fans does NOT equal better performance, enough to warrant the headaches. Often just adding a fan in the wrong place can Decrease performance.

First. Figure out what range you expect the fans to run. 0-1200, 1200-1500, 1500+ rpm
Pull works better at the low range because the whole rad is used, there's no dead spot where the fan motor sits in front of the rad. In the middle range, they work the same, either push or pull. At high speeds push works better because the higher cfm can overcome the deficiency of the deadspot.

Push/pull simply has the benefits of both at any range, so with low speed fans you get the bonus to pull, with high speed fans you get the bonus of push. Which is generally less than 5°C overall, more commonly only a 2-3°C difference.

Adding more fans will not make it more effective or efficient, just messes with airflow and can definitely make things not only worse, but considerably louder.

You know those fans on stands that wave back and forth? Or even a little desktop fan? Blow into one. You'll most definitely hear the 'chap-chap' sound of airflow out of phase and hitting the blades at a perpendicular angle. That's why it's advisable to have matching fans from a single source if using push/pull.
 

NadeMagnet69

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Jul 20, 2020
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Well if it ends up as a problem I just take the 2 other Noctua off the bottom intakes and switch them around with the stock AIO fans, so it will be 4 identical ones on the Arctic. I don't want to just automatically switch them because the arctic runs the fan wires down the tubing sleeve and the fans are connected to each other. The stock AIO fans and pump is all run through 1 4pin connector. It would be a hassle to switch them out.
 

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