Cop Car

iTrader: (14)

yes, going down the highway the fans are being pushed faster than the electric motors and they will go out.

the only reason why these cars run at close to 200* is for emissions. heat has a negative effect on performance. you should do a t stat for several reasons IMO, 1. your 70k+ mileage car should have it replaced anyways, and 2. running it cooler will make everything last longer. personaly i love it that after 2 minutes of sitting there running i have heat.

Sunset'01Z

iTrader: (10)

small lesson in thermodynamics: the fuel burns cleaner at higher temps, resulting in lower emmissions and more power due to a leaner mixture in the combustion chamber. lower temps mask problems such as detonation and other problems caused by lean a/f ratios that plauged carbureted engines. running the car hotter will help it to run leaner and more effeciently. if you tune your ls1 to run at 160* then you will suffer mileage loss and you run a good chance of shortening the life of your cats and 02 sensors if you still have them. a low temp thermostat is good on a drag car because it helps prevent your engine from becoming "heat soaked" which will stress out a built race engine. it will also keep your 4l60e from going into lockup mode on the highway untill it's up to proper operating temp.

bottom line, the car is designed to run at 200* so unless it's heavily modded and you know what you're doing, dont **** with it

02wS6firechicken

What he said. These cars have a hotter running temperature to burn the excess hydrocarbons left after combustion. If you run a lower temp you'll in a sense "flood" your cats and O2 sensors with left orver emissions. That can result in plugged cats which will reduce power very fast. Or coat your O2 sensors causing a false or modified reading. Also alot of things on the car watch the ECT to perfrom properly. Ex. Skip shift should not work if the car runs at 160 F. (not that anyone uses it ) IMO its not worth it.

Cop Car

iTrader: (14)

this is why whenever you mess with the car it needs to be tuned. if you dont have it tuned the fans will run all the time. and also for the performance reasons

Muerte_X

iTrader: (1)

I'm not in expert in thermodynamics, so forgive me for asking you to explain further, because this doesn't make sense to me. True, you want combustion temp to be higher, this is why higher octanes and higher compressions ratios make more power. They go hand in hand to create a more powerful/hotter explosions. What I'm not sure about is that you mention a/f ratios. I understand a/f measurement to be a measure of how much fuel was burnt off in the combution process, and that you can never have all the fuel burnt off completely, at least it seems that way, or you'd tune an oxygen sensor to read 0 volts. Are you saying then even though I've adjusted the a/f ratio on my car to the optimal point (most hp) that even though the oxygen sensor says there is not much unburnt fuel and everything is good, that i'm still "flooding" it? Or that it will take less fuel being put into the engine, everything else the same, to produce the same optimal a/f and power with a hotter engine? Or that you will achieve more hp with the same a/f and same amount of fuel input with a hotter engine?

What I don't also understand is how the coolant temp directly effects the combustion temp. I don't know the temperature of an explosion going on, but I would assume it's close to exhaust gas temperatures, probably higher. So somewhere near 1000-1500 degrees(please correct me if I'm wrong). Does 30º difference from 160º vs 190º coolant effect the cylinder walls temp enough to produce a significant difference on the combustion without affecting the air density before the explosion negatively?

Or am I looking at this all wrong? Like I said I'm not an expert on thermodynamics.


Also, does anyone else have any evidence to support either idea? I personally have noticed quicker 1/4 mile times and no decrese in mpg. But has anyone else noticed worse gas mileage or killed their cats/o2 sensor that knows it was caused by a cooler thermostat? Or measured EGT's and seen that a cooler thermostat causes higher EGT's given the same a/f and makes less power?

burnzilla

iTrader: (3)

^^ I agree somewhat.
Not to question you Sunset, but here's what I have learned.

A Cooler running engine means more power. Just putting a 160* Stat in w/o a tune is not going to have a drastic effect, but it will help the motor run cooler longer before the fans come on, due to more coolant flow at an earlier temp, or 160*.

Its a fact that the hotter the parts get, the faster they wear.
Internals, transmission parts, headers, etc...

Also, a colder operating temp would help get more HP, a better mix duel to more combustible cold air and temps, and I dont see how "anything" is going to get clogged up. With the RPMS some of these guys run and race gas, or 93 Pump gas too, I dont see any issues with build up or deposit build up with your car running a lower temp.

And FWIW, us LT1 boys have a bigger issue with heatsoak and hot temps with our Aluminum intake.

lsx24

iTrader: (45)

That's an interesting point. How much could 20º coolant temp really have much of an impact on combustion temperature.

300bhp/ton

stick to the stock stat and adjust the cooling fans to kick in earlier.

Ls1 ones work better with heat than when cold. There's a massive article and technical discussion over at one of the corvette forums all about it.

Muerte_X

iTrader: (1)

Link? Or at least which forum? I'd like to read it, but not sure if I want to try searching all the different vette forums.

300bhp/ton

Bear with me....

300bhp/ton

Think this is one of them: http://forums.corvetteforum.com/showthread.php?t=906208

Muerte_X

iTrader: (1)

Thanks a lot, was mostly a good discussion, unfortunately it didn't answer my questions, and I'm still not convinced. I hear the same "hotter is better" or "because GM did, it's automatically the best". I'm sure they had a reason in mind, was it necessarily performance? or even longevity of the motor? I would say for emissions purposes would be a good bet. I mean, if they weren't so concerned with emissions, you wouldn't have the EGR system and the AIR system on the car, or even oxygen sensors to maintain the a/f at ~14.7:1. It's at least reasonable to consider that making the most power was the most important thing on thier list, considering the alternatives that must be done first. (reliability, emissions, etc)

I wonder if the higher thermostat temp is just better for the cats and emissions, but not necessarily more power. I think of it like this, you want the cats to be hot to work the most efficiently. In order to heat them up, you use exhaust gases, right? Well, unless I'm thinking of this wrong, hotter exhaust is less efficiency, because the exhaust is the energy not used/waster in moving the piston down/crank, etc. The unused energy is released as heat. If more of it was used (more efficient) there'd by less waste, right? So, less heat. But if you want the cats to do their job right, you want them nice and hot. That's the whole point of EGR, is to reduce combustion temp by introducing the exhaust, which interferes in the combustion, absorbing some of the heat and reducing your combustion temp,creating more exhaust/waste heat. Also, cats have an optimum a/f that they like, and that's the same a/f your Oxygen sensors try to keep your car at during cruise. The stoichiometric ratio, which by definition means the most complete burn, all the fuel present is being used up by all the air present.

If a warmer thermostat is better, I think we'd see a couple things, hotter thermostats would allow for a/f's closer to the stoichiometric point, which mean a more complete burn (meaning, the hotter your engine was, the leaner you can run it), and the car would make more power. If it is more efficient, you'd see exhaust gas temperatures decrese with a hotter thermostat, as more energy is used in the movement of the piston/crank and is not wasted as heat.

So does burning all the fuel in the combustion chamber mean more power? More volumetric efficiency, no. It's been seen that 12.5 a/f generally (note I said generally) makes the most power (my car in fact, demonstrates this nicely, where compared to a a/f in the 14's, an a/f of 12.4 made almost 20 more whp), if a leaner burn made more power, people would tune for much leaner a/f's. Which you don't, it means better efficiency in the sense that more fuel is better compared to air burned, but that doesn't lend itself to making more power. If you did, you'd see the most powerful racing engines passing emissions no problem.

Efficiency of a burn (as in having a stoiciometric a/f) is not the same as having the best a/f for making power, and I think that's what confuses people. If indeed a higher temp thermostat is there for the sole purpose of producing a more complete burn, then you surely won't get the best power from it. They don't seem to coincide, having the best emissions does not mean you'll make more power, it's almost the opposite. Because a more complete burn means better emissions, not more power. And if you're making more power at an a/f other than 14.7:1, then your making more emissions.

So it seems like the whole point of having a hotter thermostat is to produce better emissions. Considering the other benefits people have seen with a cooler thermostat, it seems that it might not be the best choice for making power to stay with a hotter thermostat. This obviously needs to be researched more though, so there can be some concrete evidence.

Sunset'01Z

iTrader: (10)

im going to assume we're comparing carbureted engines to todays efi engines here. back before efi, people ran colder tstats to gain power, and it worked because engines couldnt be tuned as accurately as we can today. the a/f ratio is never going to be perfect when you have to adjust a few screws on a carburetor. with a cooler running engine, you can lean out the mixture more and advance timing a few degrees and not have to worry about spark knock, resulting in a few more ponies. yes, you will see more power at 12.5:1 over 14.5:1 but when i say leaning it out more, i'm talking leaning it out from 11:1 back to 12.5:1 because that's where your car is going to be when you lower the temp. that's why people see bad mileage after a tstat and temp tune, and not a spark or a/f tune. but, hotter cylinder walls help the combustion process as long as your fuel will not pre-ignite. you're right though, there is a fine line between a powerful burn and a clean burn.

Changing your tstat isnt just messing with the a/f ratio and effeciency, there are lots of sensors that dont even work untill your car goes into closed loop, especially for auto guys. yes i agree most of gms reasoning behind making hotter running engines is to help with emissions, but what i'm saying is the ~5 rwhp you might, and i emphasize might, gain by lowering your ect 30* will not outweigh the negative effects, mainly a significant increase in fuel consumption.

Black Plague

iTrader: (13)

I had a 160 with the stock rad but now with the fluidyne I went to a 170 and it's perfect all around to cold with the 160.