On an LT1, when exactly does closed loop occur?

Also, from doing some searching, one person said that when going full throttle, the computer goes back to open loop using the tables in the computer.

The reason I ask is I have a 160 thermo in, and my car stays around the 170-174 temp range. It is getting cooler, and I have seen it stay in the 168-171 range, which seems way too cool for me. I know I need to change back over the thermo to a 180, but is my car not getting up in temp to be where it needs to be to get the best burn from the air/fuel? My exhuast tips are black from burned fuel, and when I get on it, I get some unburnt fuel, so I know I am running rich.

 

I would be surprised if you are staying in closed loop. This is the number one reason I would not run such a cool stat.

 

Car goes into closed loop when the O2 goes to 600F, which occurs at about 150ish coolant temp. Your car should be staying in closed loop.

If we're talking about best mpg, you'd probably get that staying at the stock temps for the LT1.

 

You're looking right around 140*F to get to closed loop and 90*f to stay there on an LT1 (92-93)

 

Go here for more open/closed loop info.

Jeff

 

It would be impossible for the car to go back into open loop due to the coolant temp.. Unless maybe you lived at the north pole and ran no thermostat at all...

When they go back into open loop is due to the o2's going cold. The computer watches the activity and if they slow down and quit bouncing it will assume they are cold again and kick it back into open loop.

 

your right... I realized my error later, but had already had shut the computer down.

where I wanted to go to was the fact that the engine itself is not warm enough. the various metals have not reached optimal temperatures and as such, wear becomes a serious factor.

I would go back to the stock t-stat... all these "cold" engines are doing is eating themselves up for what? 10hp? If you want more speed in the 1/4, ice down the intake...

 

Optimal temperature for metals? You know steel and alumium are harder and have a higher strength at room temp... not at 200 degrees. They are more ductile (which is a bad thing in a engine) at higher temps but 200 degrees is nothing major to speak about.

The thing that guys are crying about with a 160 degree thermo is that the engines are too tight at that temp and causing extra wear.

That doesn't make sense to me in a materials since because the CTE of aluminum is higher than the CTE of Steels/iron... (this is just from the atomic seperation, steels and Iron have lower ductility/ higher hardness/ higher CTE than alumnium alloys. what does that mean? Well at temperature the aluminum piston expands more than the iron block it sits in.. So if anything at really hot temperatures the pistons are rubbing the cylinder walls more.

If you take a sample of the exact same material.. say a cylinder inside a ring... Heat those things way up and cool them way down the tolerances will not change.. But do a aluminum slug inside a steel ring and heat them up and you'll have tehm sticking together in no time.

THats why when you over heat a engine it doesn't just shut off and continue to turn over freely.. They seize up.



Now, heat in a engine is a good thing in a powerplant/thermo standpoing becuase you waste alot of thermal effecency heating up parts which shed the heat with a heat exchanger (radiator)... But there is a point where the gains in thermal effeciency are nulled out by the waste heat soaking up in the intake parts which heats up in the intake charge and makes the intake charge more volitile/less stable (harder to use)


A big job for material scientist right now is figureing out how to use ceramics in powerplants and engines. You can transfer low amounts of heat, take large amounts of heat before failure, and have really high thermo effiecency (whereas now if you get 33% your kicking major butt) The problem with ceramics is obvious.. they are too brittle.

 

Thanks, finally an engineering argument that supports my time slip results of 160 deg vs 200 (or even 170) deg coolant temps.

Though I know trap speed is higher when coolant temps are lower I'm not sure of the mechanism. I think it is due to a combination of parameters as the ECM is using coolant temp to index into tables for timing and fuel. Even a 10deg F change in coolant temp will show up on the time slip.

 

I think its just waste heat getting into the intake that slows them down.

Makes the car easier on timing and fuel (as far as getting along with the mixture)

 

More fuel for the fire..

I hear all the time too that "the oil won't get hot enought to boil out the water"

Thats BS if I've ever heard it..

You put heat into a fluid and you'll start moving that fluid into a vapor. That is why when you dump water on the hot ground its completely gone after a few minutes. The ground isn't 220 degrees..

 

finally someone else who understands everything going into the problem

but lock the thread anyway

 

Feel free to quote me in the other thread.. I'd rather stay out of it but its suprizing to hear how many experts we have on the subject who make crazy statements like.

1. the car will run in open loop all the time... (wtf?)


2. The car will have acclerated wear... Ok talk to a material scientist.. not me and ask them which is better for working parts.. high temp, high ductility, low hardness (easier to scratch/proprogate a facture) or cool parts (OILED WELL)



3. Why did GM put a 195 in the car.. Um well they where looking it at a powerplant problem.. Lets make the most thermal effecient engine we can with low emmissions and good gasmileage.. not lets see how we can control heat soak.. cram as much air and fuel in as possible and make the quickest pass down the track we can


Now am I reccomending a 160 for everyone.. No, I think a 180 would be a better choice for a street driven L98.. But in my opinion there is nothing to loose with a 160 in a reverse cooled LT1. Its just the "old wives tales" that bug me after a while.. Do people go out and try this stuff on there own? No.. they read what someone wrote on the interenet and preach it left and right like its written in the bible..

Just like the stock car won't pick up anything with tuning.. Boy what a load of.. I did two cars locally in the past week and both wehre at the track last night.. Both picked up a solid 2 tenths and solid 2 mph in the 1/8th with a tune.. One was a LS1 and one was a LT1.