[jmichaelre]

So I've got friends who are running 160' thermostats on their Gen 1 small block chevys and claim they are getting better fuel mileage and power. Is there any truth or theories behind this? Building an engine right now, and comtemplating if this is a good idea for me. All of the engines in question are running mild but better than fuel/air delivery sytems and are carbureted.

[curtis73]

160 stats make more power because of the cooler, denser air. More air means more fuel. I have never encountered any vehicle that got better mileage with a cooler thermostat.

cooler thermostats also mean cooler oil, which means less of the contaminants will evaporate out. The downside is shorter oil life and slightly increased wear. For me, I refuse to chase down 3 hp at the risk of oil health. I would only recommend it for race-only, but that is entirely up to the individual if the trade-off is worth it.

[jmichaelre]

Thanks, for the response, in response to your answer I would ask if you reccomend a 180 or 195 therm? The truck Im putting this engine has never had any cooling issues whatsoever. Also, I live in Nebraska where half of the year the temps are below 60 degrees.

[sqzbox]

Below 60 half the year? That's an understatement. From 100 in the summer to 0 in the winter! If your engine is computer controled you will need 195* for everything to run right. If not, you might get away with 180* year round.

[oldbogie]

Originally Posted by jmichaelre

So I've got friends who are running 160' thermostats on their Gen 1 small block chevys and claim they are getting better fuel mileage and power. Is there any truth or theories behind this? Building an engine right now, and comtemplating if this is a good idea for me. All of the engines in question are running mild but better than fuel/air delivery sytems and are carbureted.

176 degrees is where the computer shuts off cold start enrichment and enters closed loop operation. A 160 degree thermostat keeps the computer feeding the cold start rich mixture. This will enhance power at everything except WOT (which is where the computer again goes to rich) this is an area of the power curve engineer's call "Maximum Rich Torque". This condition will not improve gas mileage since the computer is signaling the addition of more fuel than necessary for a correct mixture. It also decreases engine life as the rich mixtures in low and mid throttle positions wet the upper cylinder walls with fuel which destroys the already tenuous upper cylinder lubrication. It's hell on catalytic converters and will get them so hot the cores will melt out. It's hard on manifolds or headers where an AIR pump is present as unburnt fuel expelled with the exhaust combusts in the manifolds or headers causing them to overheat. And its brutal on emissions if a converter or AIR system is not present, dumping extra tons of HCs and CO out the tailpipe.

Also at 160 degrees the oil never gets hot enough to expel water trapped in it, this forms corrosive acids with other blow by chemicals which in turn attacks the softer metal parts like bearings and pistons in a cast iron engine and the engine structure itself with aluminum blocks and heads.

So you know what you're in for the power gain will come at the cost of longevity and high emissions.

You can trick the computer and retain a high temp thermostat by drilling a hole up stream of the O2 sensor. If you then weld in a piece of 1/4 to 5/16ths inch steel rod that has been modified as I will describe at a 30 to 45 degree angle pointing down stream.

A piece of rod 1/4 to 5/16th in diameter and about 3/4 to 1 inch in length is drilled with a 1/8th bit. The outside of the exhaust pipe end is tapped to accept Holley main metering jets. The now tube is welded into the exhaust at the prescribed angle so the exhaust stream will create a vacuum on the tube. The Holley carb jet is used to size the hole that provides an air leak into the exhaust stream sufficient to trick the computer. When in closed loop, the O2 sensor will read this leak as a lean mixture and signal the computer to supply more fuel, richening the mixture. This with the engine running at a higher operating temperature is somewhat less damaging to the upper end than running the engine cold at 160 degrees. It, however, is still pretty hard on catalytic converters, if present.

Bogie

[jmichaelre]

Sorry,

I guess I should have been more clear, no computer control whatsoever, straight HEI, no sensors, no cats in the exhaust line. Also, they said the cooler therm allows the intake side to say cooler, but the lower half of the engine remains at a good operatinig temperature, because of combustion and the obious movement of the lower end.

[ap72]

If you do a short fill of the block that is pretty true, if you don't then your coolant temp has a big effect on oil temp.

[jmichaelre]

Ok...this is why i ask you guys...bigger pool of opinions...I"ll go with a 180 and give that a try. Also, this motor I'm going to be breaking in soon will be dealing with some low temps at its first startup. Everyone around here says to break in with straight 30, but Im wondering if I should use 10w30 cause of the temp. I dont want parts to be starved of oil cause its to thick at low temps.

[oldbogie]

Originally Posted by jmichaelre

Sorry,

I guess I should have been more clear, no computer control whatsoever, straight HEI, no sensors, no cats in the exhaust line. Also, they said the cooler therm allows the intake side to say cooler, but the lower half of the engine remains at a good operatinig temperature, because of combustion and the obious movement of the lower end.

No that's not what happens, the entire engine temp is proportionally lowered.
Yes the tops of the cylinders and the combustion chamber roofs remain as always hotter than the general coolant, but that's not as hot as they would be with a 180 to 195 thermostat.

Yes the intake stays cooler and at WOT that can be good for power but everywhere else it isn't. Again one needs to understand the physics. What burns is a gaseous fuel. There are two ways of getting there with a carbureted or TBI engine, One is very high velocities with-in the ports, this tears the fuel into small droplets such that it acts when a spark is put to it like it is in a gaseous state and burns quickly and thoroughly in the time allocated to the power stroke. But in an engine driven on the street using cruising type gear ratios the port velocities are not high enough to create this situation, so the result is to throw richer than necessary mixtures at the engine in the hopes of getting enough finely divided fuel particles to support combustion. The larger droplets condense on the chamber walls to wash the oil off and those that don't go out the exhaust unused. The factory knowing that most vehicles aren't driven like race cars, therefore, don't have the port velocities to tear fuel droplets into a fine mist. The OEMs apply heat to force evaporation of the fuel. This puts a fine gaseous mixture into the combustion chamber that burns quickly and completely which protects the upper cylinder walls from fuel condensation and protects your wallet as you get all the energy you paid for. So one finds themselves in a place where cold dense mixtures make better power at WOT but have serious fuel management issues at less than WOT. Heated intakes do a better job of vaporizing fuel at low thru mid RPMs when port velocity is low so they show better power and way better fuel economy in that range than a cold manifold, but they surrender some power at WOT due to the lack of air density. So you need to pick a place that's fit for how you operate this thing or live with the deficiencies of one system against the other.

The factory engineers are not stupid people and have come up with a number of production mitigations for this problem the better of which is port injection and the best is direct into the cylinder. An aside, these work so well without heat or high port velocities being applied because at the high fuel pressures of these systems; the fuel droplets are ripped into a fine mist by the action of the spray nozzle and again the mist emulates a well vaporized gaseous fuel and it doesn't have to travel theu a manifold to get into the chamber. Back to the world of carbs and TBI systems, it is amazing how the seemingly short distance of an intake manifold works to screw the mixture up by the time it leaves a carb or TBI and arrives at the valve, but make no mistake manifolds are a horrible place. The factory guys have carefully crafted air cleaner systems, which most hot rodders discard since they don't appreciate the Rocket Science the factory guys gave them for everyday use and intakes to overcome or at least normalize these induction problems. That is, they use an intake that is exhaust or coolant heated and there is an intake air snorkel that has a flapper valve to pick up heated air flowing over the exhaust manifold before getting into the air cleaner housing when the engine is cold, thus getting the fuel to vaporize before the manifold gets hot, this really adds power, smoothness and life to the engine. Then once the engine gets warmed up the flapper valve shuts off the hot air source and switches to outside air which is a lot cooler. This brings the density up to improve power, yet uses the hot manifold to force vaporization of fuel that has turned to liquid and fallen out of suspension. (You get this everytime the mixture has to turn to change directions, among other causual conditions) The amount of time the air spends inside the intake is pretty short even at cruising speed so the air itself doesn't pick up all that much temperature from the intake. The most important thing is the source temperature.

In a similar vein to the previous description, one can go to an air gap manifold with a factory type air cleaner using the variable source flapper valve (my favorite for a street engine). When the engine is cold and or just cruising (some of these are vacuum operated as well as temperature, where the lack of vacuum (i.e. at WOT) closes the hot air and opens the cold air source. This isn't as good under cruise conditions as a heated manifold, but is better than ice cold air all the time in all conditions. Plus it gives the engine the coldest air possible under atmospheric conditions for maximum power when needed.

Tripping back to oil temp, a cold engine makes for cold oil, cold oil will be thicker than hot oil thus harder to pump which costs power. But the big killer is contamination of combustion products in the oil. People think that water in the oil is atmospheric condensation that gets in, and some does but the greatest source of water is in the blow by. Half, or better, of the exhaust products from combustion is water, next is CO2; so there's no way to keep water out of engine oil. This stuff gets around the piston and into the oil were it forms acids with the other chemistry of the blow by and that of the oil. The oil has reactants like ZDDP that are meant to develop compounds that are harmless, but the chemistry of modern oils has greatly reduced these additives since they are hard on cat converters so the government has mandated their reduction/removal. So modern oils have less oxidation protection, (yes ZDDP is also the boundary lubricant used for flat tappet cams) so you can see it's loss has serious consequences. A too cold engine uses this stuff up even faster, so the protections offered by the additive package will go away much sooner than expected. The other problem is the upper cylinder just can't be kept hot enough to keep any liquid fuel condensing there from wiping out the upper cylinder lubrication resulting in the rings scuffing the cylinder walls, increasing the blow by. See a trend here? Hot rodder's opinions aside, this stuff has been studied to death for a 100 plus years by business, government, and universities and the results of what does what to what is easily available, though not always understandable by people without engineering and science degrees. But you can find Sir Harry Ricardo's and Charles Taylors books on the subject and gleen a lot of knowledge if you want to go fast, or you can listen to your friends and antidotes from various places. One way makes you fast the other lets you keep up to the crowd you run with.

Bogie

[curtis73]

Originally Posted by jmichaelre

Thanks, for the response, in response to your answer I would ask if you reccomend a 180 or 195 therm? The truck Im putting this engine has never had any cooling issues whatsoever. Also, I live in Nebraska where half of the year the temps are below 60 degrees.

I personally do 195. The temp of the stat won't have anything to do with overheating. 195 maximizes my mileage and oil health provided you don't overheat the oil... but with most common american V8s, that is rarely an issue

[sqzbox]

How Long Do You Plan On "breaking In" The Engine ? :d

[sqzbox]

How many of you read ALL of Oldbogie's last post? Raise your hand!

[jmichaelre]

First of all guys thanks for setting me straight on the therm issue. Its hard to know whats right and wrong when you're just learning and hear so many different things, but your explanations make complete sense. As far as the breakin I was going to break in the cam based on the instructions by edelbrock, but they didnt specify anything about engine oil during breakin. As far as the rings go, I have moly faced rings and the college I had machine it for me new that I was using these rings and told me that put a fine plateau finish on the cylinders and said that they should seat during cam breakin or very shortly after. Everyone, I have talked to said to use straight 30 until the rings seat, but Im worried that since its so thick and I need this engine in the truck in the next month that temps will be around 40 degrees and I dont want to starve the cam of oil.

[jmichaelre]

Im going to move my latest question to a new thread thanks for the help

[sqzbox]

30wt is not that "thick". after a few hours I'd want to change the oil and filter anyway. Get's rid of that break-in junk. Then put the 10-30 or 10-40 in
that will get you through the Nebraska winter! When you going to fire this thing up?