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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: 1980K20 on September 11, 2022, 07:48:39 pm

Title: Optimal operating temp for SBC
Post by: 1980K20 on September 11, 2022, 07:48:39 pm: I was thinking about my fan shroud that doesn’t come close to covering the manual fan and how well the cooling runs, 180F thermostat, rarely see it much higher than that. I also read that these SBC run better and have better gas mileage running warmer. This thing sucks gas like crazy.

Looked at Derale PWM based fans. You can set the operating temperature. I like this type of feedback controls.

My engine is 91 350 with a mild roller cam and vortec heads.

What is optimal temperature? Will I get some gas mileage back?

Thanks!

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Title: Re: Optimal operating temp for SBC
Post by: Shifty on September 12, 2022, 09:07:03 am: Doubtful of the mpg improvement, at least not that you'll notice. Say what you will, but mine have always run best about 190 max.

Now, emissions testing, different story....they pass better at around 215-220. Being in AZ, I hate that short window between running for emissions and overheating.
Title: Optimal operating temp for SBC
Post by: 1980K20 on September 12, 2022, 09:54:05 am: Thanks… I won’t make any changes based on MPG, if I do it will be for other reasons.

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Title: Re: Optimal operating temp for SBC
Post by: VileZambonie on September 12, 2022, 05:54:23 pm: When you think about thermal efficiency, you want to be as close to the threshold as possible without risking mechanical failure. The stock thermostat is best for regulating the cooling system performance. If you lose heat energy to the cooling system, it is considered wasted energy unless you are heating the cabin with it. If that energy is used to do work then you are getting more of your BTU's to perform work. Now once you start advancing timing, changing, cams, exhaust, intakes, carburetors, etc, etc, then you have to deviate from that mindset as you've chosen the performance matters most route. You have to decide where your priorities lie, fuel economy, or performance.
Title: Re: Optimal operating temp for SBC
Post by: TexasRed on September 12, 2022, 08:19:31 pm: What kind of mileage are you seeing and how does she run?
Title: Optimal operating temp for SBC
Post by: 1980K20 on September 12, 2022, 10:46:36 pm: I’ve only got 600 miles on it. It ran great, but I kept getting comments on smelling rich. It had a broken exhaust collector gasket, likely running rich due to it, now runs awful but new o2 sensor on its way. Cross your fingers.

I was getting around 9 mpg. We’ll see what it is once its fixed.

Could’ve would’ve should’ve, I kept the stock th350/np205 combo, it appears to be original and simpler than swapping for 700r4, it won’t be that many miles to cover the costs for even a few mpg. Lesson for other builders.

Curious about the timing and setup. I’ve got a mild cam, vortec heads, sniper efi. Timing was around 18 at idle, I changed it to 14.4. The builder put it on the dyno, 359 hp, 400 ft-lbs torque, a lot more than original.

Thanks,
Mark

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Title: Re: Optimal operating temp for SBC
Post by: 1980K20 on September 21, 2022, 07:08:18 pm: The guy who set up the EFI said he thought a 195F thermostat might get 0.2-0.3 MPG. He thought 180F is perfect for these engines.

Initial timing is now 16 at idle, no vacuum advance anymore to work better with the EFI

Mark

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Title: Re: Optimal operating temp for SBC
Post by: VileZambonie on September 22, 2022, 06:16:19 pm: Don't focus on initial timing unless all you do is idle most of the time. Set your total timing to 36° BTDC and go from there.
Title: Re: Optimal operating temp for SBC
Post by: 1980K20 on October 08, 2022, 01:24:59 pm: Checked the timing, 34 max currently. Do you think the two degrees will much difference?

Thanks,
Mark

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Title: Re: Optimal operating temp for SBC
Post by: JohnnyPopper on October 08, 2022, 07:25:26 pm: I think I recall VZ say that 36 degrees at 3500 rpm is the pin.
Title: Re: Optimal operating temp for SBC
Post by: TexasRed on October 10, 2022, 06:41:15 pm: With vortec heads, a little less timing is probably better.
Title: Re: Optimal operating temp for SBC
Post by: 1980K20 on October 12, 2022, 08:42:43 am: Sounds like 34 is a good place.

Gassed it up after mostly Highway driving, 65-70, rpms 2500-3000, 10.5 MPG. Found on internet claim original was 12 city / 17 highway. Same transmission, but 100 more horsepower than original, probably figures. Another site says to expect 9-11, fwiw.

Now, what I’d I had changed the drive train out to newer with overdrive? Let’s say I got 3mpg more. Consider 1500 miles max per year, it’s about 32 fewer gallons per year, $160 per year. Extra cost of $2000 for the conversion, 12.5 years, lol. If I drive it that much. Would help with range anxiety though.

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Title: Re: Optimal operating temp for SBC
Post by: Shifty on October 12, 2022, 09:14:40 am: Honestly, I'd make it run where it's happiest, and enjoy the smiles per gallon, rather than sweat the difference. We're only here for a short time, and it could be worse, you could be in a hybrid. :o
Title: Re: Optimal operating temp for SBC
Post by: 1980K20 on November 04, 2022, 11:33:49 pm: Got another tank run through, mostly 35-45 mph. 12.7 mpg. Keeping the rpm’s down and not having the wind resistance made a huge difference!

I can feel confident about 175-200 miles to a tank. Yeah!

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Title: Re: Optimal operating temp for SBC
Post by: VileZambonie on November 06, 2022, 05:40:13 pm: Quote from: Shifty on October 12, 2022, 09:14:40 am
Honestly, I'd make it run where it's happiest, and enjoy the smiles per gallon, rather than sweat the difference. We're only here for a short time, and it could be worse, you could be in a hybrid. :o

Definitely. Run it where it's happiest and you will be happiest.