i7-8700K OC dilemma

[Thomasso 224]

Hello everyone,

I recently made a major upgrade to my PC. My current rig is as follows:

• GPU: Gigabyte GTX 1080 Ti OC
• CPU: i7-8700K
• RAM: G.Skill 2x8 GB 3200 MHz
• MOBO: AsRock Z370 Extreme4
• COOLER: Corsair H115i AIO
• PSU: Seasonic Focus 750W
• STORAGE: 240 GB SSD for Windows and essential programs, 1 TB SSD for P3D, 1 TB HDD for simple things
• CASE: Corsair Obsidian Series 750D

Obviously I want to OC the system so I can take full advantage of its power. I did many some test, these are the results:

 

It is quite disappointing in my opinion. I finally settled for the green row settings - 4,8 GHz, 1,18 V and HT on. However, the P3D keeps crashing (BSOD) approximately 40 minutes into flight. (FSLABS A320 and other demanding add-ons).

When I turn HT OFF, the OC is much better. I'm stable at 5,1 GHz and I can even finish some tests at 5,2 GHz (reasonable temps around 80 °C). But I keep hearing that i7-8700K with HT OFF is essentially a more expensive i5-8600K.

So I'm not sure what to do... My options:

• Increase voltage to 1,20 @ 4,8 GHz & HT ON (temps in the sheet are lower there, but the test was made on a different day and I have no idea why)
• HT OFF and OC to 5,1 GHz (is it really like i5-8600K with HT OFF?)
• Send the CPU for delid

What do you guys think? Do you get similar results with the i7-8700K?

Any advice will be appreciated 🙂 Thanks.

Tomas

[patrice_bambou 85]

Hi,

What I think:

1. Forget HT with P3D, this is totally useless in this context and brings higher temps, so many problems and more stress for the CPU.

2. I delidded myself my CPU (i7 8700k) and it surely helps containing temperature.

3. Going to 5.1, 5.2 Ghz gives a ridiculous performance improvement (2%?) at the cost of more stress, voltage and heat to the CPU, giving finally a reduced timelife for the chip.

Patrice.

 

[Thomasso 224]

7 minutes ago, patrice_bambou said:

Hi,

What I think:

1. Forget HT with P3D, this is totally useless in this context and brings higher temps, so many problems and more stress for the CPU.

2. I delidded myself my CPU (i7 8700k) and it surely helps containing temperature.

3. Going to 5.1, 5.2 Ghz gives a ridiculous performance improvement (2%?) at the cost of more stress, voltage and heat to the CPU, giving finally a reduced timelife for the chip.

Patrice.

 

Hi, thanks for the reply. So basically you are saying that I should delid and do 5,0 with HT OFF?

[J0nx 48]

Not nearly enough voltage for that clock. I would say start at more like 1.24v and run prime95 for 30 minutes. If it’s not stable then increase to 1.25v and try again until it is. If your cooling can’t keep temps under 70c at that voltage then you need to buy something else or investigate the thermal compound and contact to the processor and cooler. My 8700k needs 1.285v for 4.9 and 1.365 for 5 ghz. Huge jump for only 100mhz more.  It won’t run at any speed above 5 ghz with HT on. I tried all the way to 1.42v until my cooler couldn’t keep temps below 95. If you are getting BSODs then you aren’t stable and you need more voltage. 

[Bob Scott 7,710]

I'd go with 5.1GHz HT OFF.  In my experience with P3Dv4 on a hexacore CPU, HT off is smoother than with it on, and as you observed, with HT off you can get a >6% clock speed boost over your best HT-enabled overclock.

I don't think delidding is necessary unless you get a real heat monster of a chip.  The extra 100 MHz you might gain, or the 5-10 deg temp drop aren't, IMHO, worth voiding the warranty.  Also, consider running a non-AVX stress test instead, something like Prime95 with the AVX instructions disabled.  AVX presents an unrealistic FP load on the CPU that's not at all typical of P3D, or for that matter most other software. 

The i7-8700K brings 33% more L2 cache (12MB) to the table than the i5-8600K (9MB), so even with HT off, it's something more than just an expensive i5.

Regards

[Bob Scott 7,710]

One more thought w/r/t your temps--make sure you have a good fan curve set up on that H115i.  One of my secondary boxes has a 7700K on an H110i, and the default fan curve is dismal--it does not even begin to keep up with the CPU when it gets loaded up.

I programmed the curve (using the Corsair Link software) to keep the fans at 500 rpm until 25 deg coolant temp, then ramp up to full speed at 30 deg C.  This avoids lots of speed shifting on the fans as the CPU temps fluctuate, and it responds fairly aggressively to actual heat in the system as it is loaded up.  If you're just using the default fan curve, it is not surprising that your temps spike high.

Regards

[troyboy66 66]

2 hours ago, Thomasso said:

• Increase voltage to 1,20 @ 4,8 GHz & HT ON (temps in the sheet are lower there, but the test was made on a different day and I have no idea why)
• HT OFF and OC to 5,1 GHz (is it really like i5-8600K with HT OFF?)

Try increasing your temp to 1.350. I did an offset of 0.280 v. and I'm stable at 5.1 Ghz on all cores and never exceeds 70C. 

[martin-w 3,234]

Quote

or the 5-10 deg temp drop aren't, IMHO, worth voiding the warranty. 

 

I'm nor agreeing or disagreeing regarding voiding ones warranty... just pointing out that with liquid metal the drop in temp is more like 10 to 20 degrees. 5 - 10 degrees would be delidding with conventional TIM. Nobody should delidd unless they can afford to replace their CPU. Having said that, the practice is a lot safer now with the available delidding tools and reasonable care.

 

 

Edited December 4, 2018 by martin-w

[martin-w 3,234]

8 hours ago, J0nx said:

Not nearly enough voltage for that clock. I would say start at more like 1.24v and run prime95 for 30 minutes. 

 

Theoretical max voltage for the 8700K is 1.5 volts. I'm not recommending that anyone use that voltage, as high temp is the obvious peril, just to give some perspective on why the OP's voltage is relatively low. 

My 8700K does 5 GHz on all cores at something like 1.34 volts I recall. It's delidded. Max it will do is 5.2 GHz at over 1.4 volts. 

[Thomasso 224]

Thanks for all the replies! I'm currently at work, I will write back when I get home. 🙂 

[Thomasso 224]

18 hours ago, J0nx said:

Not nearly enough voltage for that clock. I would say start at more like 1.24v and run prime95 for 30 minutes. If it’s not stable then increase to 1.25v and try again until it is. If your cooling can’t keep temps under 70c at that voltage then you need to buy something else or investigate the thermal compound and contact to the processor and cooler. My 8700k needs 1.285v for 4.9 and 1.365 for 5 ghz. Huge jump for only 100mhz more.  It won’t run at any speed above 5 ghz with HT on. I tried all the way to 1.42v until my cooler couldn’t keep temps below 95. If you are getting BSODs then you aren’t stable and you need more voltage. 

I figured 🙂 The problem is that my CPU starts to overheat above 1.20 V with HT ON. There is just no way around it. I even pumped the H115i on 100 %, both fans and pump. Still massive overheating.

 

18 hours ago, w6kd said:

I'd go with 5.1GHz HT OFF.  In my experience with P3Dv4 on a hexacore CPU, HT off is smoother than with it on, and as you observed, with HT off you can get a >6% clock speed boost over your best HT-enabled overclock.

I don't think delidding is necessary unless you get a real heat monster of a chip.  The extra 100 MHz you might gain, or the 5-10 deg temp drop aren't, IMHO, worth voiding the warranty.  Also, consider running a non-AVX stress test instead, something like Prime95 with the AVX instructions disabled.  AVX presents an unrealistic FP load on the CPU that's not at all typical of P3D, or for that matter most other software. 

The i7-8700K brings 33% more L2 cache (12MB) to the table than the i5-8600K (9MB), so even with HT off, it's something more than just an expensive i5.

Regards

That's actually what I'm trying now. Well, I am at 5.0 GHz @ 1.35 V, HT OFF. Just took off EDDT in the FSLabs A320, everything pretty much maxed out, and so far I got average 53 FPS. That's awesome imho 🙂 One of the cores spiked to 85C once, but normally all of them are below 80. Fan is at 1900 rpm, pump 2900 rpm.

 

18 hours ago, w6kd said:

One more thought w/r/t your temps--make sure you have a good fan curve set up on that H115i.  One of my secondary boxes has a 7700K on an H110i, and the default fan curve is dismal--it does not even begin to keep up with the CPU when it gets loaded up.

I programmed the curve (using the Corsair Link software) to keep the fans at 500 rpm until 25 deg coolant temp, then ramp up to full speed at 30 deg C.  This avoids lots of speed shifting on the fans as the CPU temps fluctuate, and it responds fairly aggressively to actual heat in the system as it is loaded up.  If you're just using the default fan curve, it is not surprising that your temps spike high.

Regards

I even tried 100 % fixed mode, sir. No help.

 

17 hours ago, troyboy66 said:

Try increasing your temp to 1.350. I did an offset of 0.280 v. and I'm stable at 5.1 Ghz on all cores and never exceeds 70C. 

You mean voltage? Like said before, that is impossible with HT ON.

 

9 hours ago, martin-w said:

 

Theoretical max voltage for the 8700K is 1.5 volts. I'm not recommending that anyone use that voltage, as high temp is the obvious peril, just to give some perspective on why the OP's voltage is relatively low. 

My 8700K does 5 GHz on all cores at something like 1.34 volts I recall. It's delidded. Max it will do is 5.2 GHz at over 1.4 volts. 

That value is truly theoretical, I would not recommend this to anyone, as you massively reduce that life span of your chip at 1.5 V. Do you have HT ON or OFF?

[ZLA Steve 370]

Rock solid 5.0 at 1.31v for my chip. (Avg temps at load are 68-71. Max I've recorded is 79ºC)

If you can keep temps under 85º increase your voltage.
 

 

[J0nx 48]

If your cpu is overheating above 1.20v then there is something wrong with your cooler. It's either not installed correctly or the TIM you are using is bad or your AIO pump is broken. You aren't going to get much going with 1.2v. You are lucky it's working at all at that voltage. Delidding will do nothing for you until you figure out what's going on with your cooler. Even the lamest of air coolers could do better than this at 1.2v. That cooler should easily be good enough for 1.35v or even more maybe. I know because my other machine uses an H80i single rad cooler and keeps my 6700k perfectly cool at 1.285v under prime load. It would probably do above 1.3v and it is a single rad cooler. Something is wrong with your cooler install.

Edited December 4, 2018 by J0nx

[Thomasso 224]

15 minutes ago, J0nx said:

If your cpu is overheating above 1.20v then there is something wrong with your cooler. It's either not installed correctly or the TIM you are using is bad or your AIO pump is broken. You aren't going to get much going with 1.2v. You are lucky it's working at all at that voltage. Delidding will do nothing for you until you figure out what's going on with your cooler. Even the lamest of air coolers could do better than this at 1.2v. That cooler should easily be good enough for 1.35v or even more maybe. I know because my other machine uses an H80i single rad cooler and keeps my 6700k perfectly cool at 1.285v under prime load. It would probably do above 1.3v and it is a single rad cooler. Something is wrong with your cooler install.

The weird thing is that when I turn HT OFF, I can set it to 1.35 V easily and the temps are fine...

[Charlatan 68]

I've had my 8700k running at 4.8ghz since I had it.  After reading other reports on here for the last few months, I've turned HT off and am now clocked at 5.0ghz.  As others have said, seems to run soooooo much smoother with it off.