I found a fascinating article from 1933 on just this subject. They were testing v-12 aircraft engines, but many of the same priciples as well as conclusions are applicable here.

Its perhaps more interesting as a historical reference than for anything practical to this disscussion.

http://naca.larc.nasa.gov/reports/19...i?page0001.gif

 

i know on my 98 LS1 i get a water like sludge on the oil fill cap between oil changes. I was using Mobil 1, then went to Valvoline Synpower, then to regular Valvoline....I run a 170 T-stat and my guess is that its too cold and the oil does not get up the proper operating temps.

oil looks fine when I drain it, its just on the top end it is kinda sludgy water mixed oil. concerns me but the car runs fine still

 

First time to post in this room, but here goes...

In a pure physics world, you would want to have the heads and cylinder walls at their hottest. Combusion process is a change of state of the gas/air mixture. Some of that change of state is in the form of heat, the other, in the form of the mechanical energy. If less of the total energy goes to heat, more will go towards the mechanical. A lower head and wall temperature will absorb more heat and thus have less energy for the mechanical force.

That is why aluminum heads will make less power than cast iron. Whoa you said, that is not what all the experts say. Well, the reason aluminum heads make more power is because they can run higher compression and more ignition(because they run cooler and less detonation).

So in the real world, a cooler running engine will be able to run higher compression, and more ignition advance with lower octane gas. But... run the same engine at higher temp and with higher octane gas and it SHOULD make more power. But then you have the problem with intake air density getting lower due to the higher temp. It all a balancing act.

So the solution is to run hot as hell head and block, cool as ice intake, 110 octane gas, and as much ignition advance as the engine will take. I have always thought of casting an intake with cooling lines running around and use the A/C compressor to run the intake at supercool temps.

But to answer your question... I dont know the ideal temp. Surely someone has done some dyno work with these ideas put into practice.

My 2 cents... Ken

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FOR SALE
96 Z28 6spd
Usual mods (thermo, SLP cold air, pulleys, airfoil, borla cat back, hypertech, SLP LW Flywheel, clutch, pressureplate)

13.4@104MPH

 

Pretty interesting.I know the busch north car that I used to work on would like to run best about 200-210 but they could be tough to keep their on a short track in traffic in the middle of the summer.But I recently saw a show with Warren Johnson,He likes his huge compression prostock Moters in the 140 range.I missed most of the show.I was flipping through the channels and that got my attention but I missed the theory behind it.

Best educated guess,Busch car low compression,needs the Higher temp for a complete burn compared to High compression of a prostock moter that makes plenty of combustion chamber heat.

As far as premature wear of cylinder wall sealing in an lt1 with a 160 stat.I dont know?Good theory but We have been puting hyper pistons in standerd small blocks for a while with the same stats and alot less compression (8.5-9 street moter).

I figure the factory engieneers set the lt1's up with emmissions in mind Thefore the defenetilly wanted decent combustion chamber temps.The aluminum heads soke up the heat and the reverse flow also keeps them cooler.

Theory is great but actuall dyno time comparison is wear it is at.
Does it come down to increased longevity vs. More power?

I have used 160 and 180 stats in my lt1's.I beleive alot of it comes down to fan control.Try running a 160 stat with stock fan settings,not much diference in overall average temp. especially when in traffic.

Regardless of oil or water temp you still want the intake charge cool as posible.Does keeping the water/eng temp down help control that? In my opinion yes and no.Lets say you are at the drag strip in the middle of the summer The car starts out cold.You go through the staging lanes shuting it on and off.You get to the line .temp is about 170.You run 13.8 or so at 100.Now you hot lap the car temps at the line are in the 200-215 range best guess you run 13.85 to 13.95 at 99 or so.Is it heat soak of the intake or overall temp that efected your et?I say heat soak.On the next pass Ice the inake for 15 minetes or so.You still are at the same operating temp once you stage the car.Do you find that lost .05-.1.I bet you do.

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95 Formula Solid Roller 9 Inch 4.10 H.D. Locker,6 speed

94 Hardtop Heads up Drag car


94 Formula A4 Stock
120,000 miles 13.82

 

I know this one's been dead for a long time, but I really would like to hear Chuck's comments on this.

I feel neglected

 

It would be nice to hear Chuck's comments on a lot of things but I havent heard from him for months...

 

Somewhere along the line, common sense and logic need to rear their ugly heads.



OK, how hot is ideal? Through tests, the ideal WATER temp to keep engine component wear to a minimun, without sacrificing efficiency is 175-180* Ironically, more cooling of critical areas of the engine is done with the oil, not the water. I didn't answer the oil temp directly, did I?

I did say water temp above, NOT thermostat. If you need to install a 160* thermo, you have a weak link(s) elsewhere.

I believe you are a hair low to pretty close.


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I'll be back



[This message has been edited by arnie (edited July 07, 2002).]

 

ttt

 

Man, talk about ressurecting the dead.
My sincerist of apologies to everyone who waited for an answer from me on this. Feel like I've let some of you guys down....

This must have been right before my ISP nightmare... but anyways. I WILL type out something coherent on this subject tomorrow although I covered quite a bit of the thermal efficiency issues in the "How much compression" thread here the other day. May want to check that out in the meantime.
My day starts early.

Take care,
Chuck Riddeck
Progressive Race Engine Development

 

Sorry not my intention to make you feel bad. But I would really like to hear your view on this and apreciate the time you take to talk to everyone .

 

The theory of a 160 thermo being bad doesnt seem to hold up well at all. In an otherwise completely stock 97 I run a 160, and its been in for 20,000 of the 50K total miles on the car. the needle never comes more than halfway past the very first mark unless idleing when its hot, and it runs better than the usuall stock LT1.

The car has ran a best of 13.51 @ 104.3 on a 2.1 60 ft, on a dead stock car 9 i dont considder the thermo really a mod since you can do the same thing by lettign a car with a 180 thermo sit and cool off) When i race I let the car sit for a hour between runs, start it and let it idle until the needle gets to right off the first tick (about 160-170 prolly) Usually runs 1-2 mph slower when at full temp

 

From an engineering standpoint, it's simply a matter of thermal efficiency vs. volumetric efficiency.
Generally speaking in non technical terms, the hotter an engine's coolant temperature is, the lower it's volumetric efficiency.

This is an example of what I'm talking about: It is output from a test engine, all oil temps were the same for each test (thermostatically controlled). The intake was also cast aluminum for this engine which displays a better comparison for the LTx guys than a test with some composite or thermoplastic design.

With 95ēC coolant temperature:

85.3% VE at 3000 rpm
104.5% VE at 6000 rpm
98.8% VE at 7200 rpm

A minimum BSFC of 263 g/KWH at 3000 rpm

273.48 lb ft at 3000 rpm
313.39 lb ft at 6000 rpm
389.83 Bhp at 7200 rpm

With 105ēC coolant temperature:

83.8% VE at 3000 rpm
103.6% VE at 6000 rpm
95.7% VE at 7200 rpm

A minimum BSFC of 261 g/KWH again at 3000 rpm

270.24 lb ft at 3000 rpm
304.4 lb ft at 6000 rpm
388.89 Bhp at 7200 rpm

In each test, the spark was adjusted for MBT.

This is just a snippet from the whole test but it makes the point. I can post more of this type of testing for those interested. Take from it what you will... leave the rest. Considering the fact that it took me about an hour to dig this out of my files, I feel like posting more but I think that little bit gives a good understanding of what's going on.

Chuck Riddeck
Progressive Race Engine Development

 

Go to bed Chuck Its 4am here and you're making me think waaay to hard...

But since you're here anyways...

How signifigant is the change in BSFC from 263 to 261? I mean it doesnt sound like much, less than 1%. It almost seems like the potential gains in fuel economy would neglegable in comparison to the loss in VE (almost 3% @6K).

 

Chuck, while I do not have a disagreement with you regarding what you stated, I respectfully disagree in the direction and emphasis given to the answer of what is an ideal water temp.

While pro drag racers know that a cooler engine is a quicker engine, way down their list of priorities is engine wear in this case. For those of us that actually put street miles on their cars, lower water temps and the resultant increase in engine wear, is a concern that should be a priority. Chuck, much like knowing that narrow valve seat/valve contact widths generate better flow. But for those of us that don't plan on valve touchup at 500 mile intervals, that little extra torque gain is more than negated by the sacrifice in longevity/durability of the valve job.

 

Arnie, where have you seen A motor fail due to the addition of a 160 degree thermostat? There is probably 100,000 LT1 and LS1 cars runnign around everyday with them, and no one has voiced a serious concern about them. The only guys who Ive seen hurt motors with a 160 in them were ones that sucked bolts into the intake, nitrous motors, turbo motors that went lean in a cylinder. I just dont see any basis to saying a 160 degree thermostat can hurt a motor.

Im runnign one, adn this motor is arguably the strongest runnign stock LT1 Ive seen.