Generically all engines are known as "heat engines". They convert the thermal energy released during combustion into mechanical work. It's not the cylinder pressure that makes torque it's the temperature rise from the release of the fuel's energy, and the increase in temperature increases pressure. The more heat you remove via the cooling system, the less heat is available to do work.

From a practical standpoint, reciprocating IC engines have to be cooled because of both material limitations - oil and elastomers, such as seals, AND detonation, but ideally, we would not have a cooling system. If fact turbine engines do not have dedicated cooling systems, but the amount of fuel they can consume is limited by thermal considerations. A big deal in turbine engine design is turbine inlet temperature. The higher, the better in terms of both power and efficiency, but materials technology is the limiting factor. Fuel flow has to be limited to a TiT that the engine can sustain, and this is the limiting factor on both power, and fuel efficiency.

As far as why the manifold doesn't get hot in hot lapping versus city traffic, it's because the large volume of air flow keeps it cool. At idle and low speed the small volume of air flow allows it to get warmer. The inlet air is heated up through the inlet system at the track, but not very much. Lots of airflow equals a low temperature rise. Little airflow means a greater increase in temp.

Duke

 

GM's design operating "normal" temperature range is about 195 to 230 for essentially all of their engines. The LOW end is established by the thermostat, and the TOP end is controlled by fan actuation.

Most modern cars will actually run a little cooler in low speed hot weather, because at least one fan is controlled by the air conditioner, so it will be cycling quite a bit when the A/C is blasting to keep the interior cool, and this will keep the engine cooler. Without the A/C on the Corvettes fan(s) don't engage until about 227.

Duke

 

Helpful. I just can't get too excited about this...my car goes like stink, oil pressure is good, no pinging or knocks, no oil consumption, seems to be the way GM planned it? If I do a supercharger at some point, I'll definitely get a low temp thermo and lower the fans "on" point, but for now, won't worry, be happy. Thanks again.

TT :cheers:

 

I just went and re-read the thread. I still get the following out of it:

First, (and Wes, jump in and feel free to correct me if I am wrong!) at the end of the thread, Wes writes, "I have nearly a flat 12.8:1 A/F ratio curve now. No more power going up or down from here."

This means, that he leaned the a/f from factory settings. It doesn't come with a 12.8 at WOT programmed into the PCM, or else we wouldn't bother messing with MAFT's.

Second, I can find nowhere that indicates in his last post, that he had done anything to pull the timing from the 25-26 degrees advance that he mentions earlier in the thread. He even says,

"I did adjust the Spark Retard Attack and Decay tables. This means the PCM isn't as aggressive to pull timing out when it sees knock, and once it does pull some timing out, it adds it back in quicker than the stock programming allows. This really helped make for the smoothest curve possible."

He goes ON to say that he did not add any timing at all, but I'm not clear on whether that was from the 25-26 or factory. As I mentioned above, it appears that he did nothing to pull back that advance that he had talked about earlier in the thread.

Ross, you don' t know what is going on inside the cylinder in relation to the spark advance. You rely on your Autotap more than I rely on my knowledge of engines, theory and web searches combined. I don't say that to start a war, but you seem to have this idea that ALL I KNOW is theory.

If that is your take, fine. But it isn't true and I'll defend it when you make the claim.

Here's the deal though, you can criticize, ridicule and generally disregard all the books as much as you want, but those books are the same books that the powertrain engineers at GM studied before they set out to build the engine.

Without a doubt, they did testing also, but you'll notice there are no news stories saying, "The Engineers at GM have overturned the world of four-stroke engine design by finding that everything EVER taught before was wrong." That's because with the exception of the occasional tweak or nuance, the LS-6 works the same way as the SB 350 or Ford 302.

They can tweak cylinder head design, they can massage cam lobes and play with the computers all they want, but at the end of the day, it's still a four stroke, pushrod, V8 engine.

Sodium filled valves? I had them on a 67 Cougar in 1982 when I was in high school. Expensive - yes, but new tech - no.

Yeah, the PCM's are more advanced, and the heads are better - but they still mass-produce them from castings at a factory. They aren't magic. We've seen tumble flow and swirl combustion chambers and all sorts of quench designs come and go. But the engine still works the same way.

I'm not sure I follow this, but first let me say that I do not believe it will make a SIGNIFICANT change - depending on how you define signficant. But I think there are ~10 rwhp to be found from tuning the car.

What I don't understand, is what is EVERYONE who has a MAFT doing with it? Is there ANYONE who is RICHENING their WOT mix on a relatively stock car?

I'll gladly stand corrected, but isn't everyone adjusting their MAFT to lean it out a little at WOT?

Next, you keep saying you have to use a wideband - which I'm certainly not against - but don't think you need if you know the car's base WOT a/f settings. They make LOTS of Z06's. It should be a KNOWN quantity as to what WOT a/f the cars come set to - at least close. Then, a tuner could easily shoot for a safe number, like 12.6 or so, and leave a little safety room on the rich side, while still leaning it up from the factory setting.

In spite of the fact that Wes does believe in the widebands, he even says that he was VERY CLOSE to peak hp just guessing at his settings in the thread you mentioned above. He didn't get very much else by widebanding it and he was very close estimating.

Again I'm not sure I follow. If the factory setting at WOT is REALLY RICH, then it should be pretty safe to lean it out a bit. If the factory setting is close to ideal, then no one should bother using MAFT's or any other method to bother with leaning it in the first place...

The goal is a known target. Just like stoich at 14.7 - 1, a good ballpark ideal number for WOT is around 12.8 -1 .

Oh come on, what is the point in having the computer if they can't get the Air Fuel ratio fairly close with it? You make it sound worse than jetting a carb. The WHOLE IDEA of the PCM is to self correct.

If for some reason the a/f is off on the car, then the PCM will save this info in the LTFT's and APPLY an adjustment to the WOT tables to make sure that they don't go too lean as well. Kewl pointed this out in another (I think) thread.

There aren't any Z06's coming out of the factory with "dangerously close" specs on the WOT a/f numbers. The PCM's whole purpose is to allow them to CONTROL that sort of thing.


Again, if the car was lean from the factory, the PCM would have noted this and applied correction factors to the WOT tables based on the LTFT's in other cells. The WOT a/f mix from the factory should be a pretty stable number which can be altered by programming - within a safe measure - without irrational fear of melting the pistons.

That is great if you have the resources and ability to tweak the entire curve, but you can STILL get gains even if you don't maximize the entire rpm range. For instance, let's say with the Diablo tune you got ~6hp from 3k-6.5k. But with custom tuning, you pick up an extra 3hp in the 3k-4k part of the curve.

So what? First off, you don't spend much time below 3k in a drag race, and second - you STILL have more hp than you started with, even without the ideal tune.

I know every car is a BIT different, but they are pretty consistently even. The hp spread among the Z06's dyno'd here is amazingly small and probably has as much to do with the different dynos as it does with the engines. The PCM eliminates a lot of the differences right out the door.

Ok, I've been arguing with you on principle up to now. I believe that you can get 5-10 rwhp from a decent power program downloaded to the PCM and I don't think it is as hard, or risky as you do. We disagree with what is possible.

Now, do I think Diablo has done it? I'm not sure yet. I haven't even put the programming in my car because I want to make sure it isn't buggy and I want to make sure they have Z06 specific programming in there, etc...

As you may know, I'm a skeptic! ;)




[Modified by Tom Steele, 3:07 PM 11/1/2002]

 

Wes is currently running the stock 22 degrees. I helped him tune the car, ask him

At this point in time I feel that it would be best if I just stopped with all of our debates. I can't continue debating with you because we are not at the same level of hands-on experience and you just keep doubting my experiences (Dyno, Track, LS1Edit, & Autotap). In addition you do not have any real-world data to back up your doubts. You can read about the theories of I/C engines and intakes all day long, but until you start to take actual readings off the car you are only seeing part of what is really going on.

You are a very intelligent guy and this is not intended to be a personal attack or a flame of any kind. There really is nothing more that I can say. I apologize in advance to Tom & the list if anyone feels that I am being rude, abrupt, or just a plain azz.

 

No offense taken Ross. However, rather than debate, why does it have to turn to that anyway?

Why not just say, "I have found that in my experience and in several others (insert weblinks or whatever here) that advancing the timing doesn't do anything for the LS-6."

THEN, how about telling us what tuning you DO think improves the performance on the engine.

That can all be done without what comes across as "pounding the other guy down."

I rarely, if ever, see you post a response to me that doesn't include something that seems inclined to be an attempt to take away my credibility - along with your disagreements.

Instead of concentrating on our differing viewpoints, why not have a discussion (rather than debate - which means that both of us could acknowledge that the other MIGHT actually be right [and yes, I realize I could do that more, too.]) where we just tell the other person what we think and why, without telling them that they are just plain wrong?

If you wanted to do that, here would be the questions I would pose...

1. When I mentioned what I wanted to get out of the predator in another thread (I think) you commented that "lowering the thermostat temp and resetting the fan on/off's" was my "first good idea." Ok, why? Just to lower the IAT?

2. If you feel that the LS-6 can get no performance gains out of advancing the timing, then what tuning do you think helps?

3. Do you think that leaning the WOT a/f mix from stock generally helps?

Finally, I'd like to point out that while the Predator does - unfortunately - make it's changes across the rpm range (at least for now, their code looks updatable) you can still take a car to a wideband dyno and adjust the a/f yourself. Which is a useful function of the predator.

And, you can take the predator with your car to a dyno and try bumping the timing up to 2 degrees. You won't see KR if you are getting it, but you will see if it is bumping your hp up any. If you are getting KR, then you probably WON'T see any improvement in hp. Of course, the dyno doesn't generally put as much load on the car as WOT on the street, so that could be misleading. However, I can HEAR pinging as a general rule, so if the KR doesn't stop it quick, I would know if I was over advanced.

My 2000 had some pinging in the summer sometimes after I tried one of those MAT relocate/tricker things. I could hear it when it happened.

Either way, no hard feelings, but it is a shame we can't just talk about these things without them turning into battles to prove our positions. And I'll share in the blame with you on that. Maybe we could both work to do better.

Sincerely,

Your pal,


[Modified by Tom Steele, 6:46 PM 11/1/2002]

 

Hmmm... GM never built a factory street rocketship that would go quite this fast before. Not on 346 cubic inches and 93 octane.

Perhaps they might still be learning by doing and there might still be a few things not written in the big book of Go Fast yet.

-Noel

 

Noel,

Anything is possible, and it is possible that 22 degrees is all the advance you can get out of the LS-1, LS-6 engines. But I am willing to bet that one of two scenarios is true:

In really warm summer weather, the PCM is adding KR under certain circumstances that would not be there if you had a cooler thermostat. Keep in mind that on a dyno, you are not getting the full load on the engine that you get on the street and KR is less likely to show up there.

Or, in really cool weather, there may be some more hp to be had by advancing the timing then - because the colder air charge would allow for more advance, and perhaps that is not being taken advantage of if you don't have your timing advance.

There is one option that could make Ross and I both a little "off target" - or at least guilty of not explaining ourselves well.

I looked at VStellas autotaps last night and it appeared to me that his PCM was trying to pull 30 degrees of advance at WOT. I don't know if that is something that Ed Wright has done, or not.

But the KR was pulling him back to 22 almost all the time, best I could tell.

In that case, Ross would be correct on one front, because adding timing won't make any difference if KR comes in and takes it back out. But my point is that if you cool the heads enough, the KR may NOT come in and take your advance back out as soon, and perhaps you can get 24 degrees or so without having it pulled back.

Here's my beef with Ross' "test only" thinking. The facts still remain that in most every case I have ever seen, advancing the timing as far as you can before you get pinging is where you will make the most power.

Is it possible that the LS-engines are different - perhaps, but not likely. The PCM even seems to support this by only pulling timing out if it senses knock. Otherwise it wants plenty of spark.

I think that to find that the dyno seems to show that advancing the timing doesn't improve hp WITHOUT looking at why, may leave you with hp sitting on the table because of something in the PCM programming that you may not be aware of.

Wes got his best results by reducing the AMOUNT of spark the KR could take out, and by having the PCM more aggressively put the spark back in when it was taking it out.

Ross thinks the issue is closed because some folks couldn't get spark advance to make them more hp. That doesn't change the reality of how four stroke internal combustion engines work. The PCM could be hampering their ability to see what is really going on, or hampering their ability to really get more spark to the engine. I feel quite confident that GM would happily trade a few hp to MAKE SURE the engine didn't see any knock. But reality is that engines can handle a little (you'd be surprised actually) pinging without killing them - at least if they are made well.

 

Tom, I not sure if cooler temp would increase performance or not. Probably quite a few competing factors. I am in VA and here is what I have seen so far. (I monitor water, oil temps and oil pressure quite frequently while driving). During summer water temp stays at 190F and oil temp about 210F. Water hits operating temp quickly and oil not too far behind. Only time I saw water Temp rise above 192 was a 100 degree day and traffic. Ran up to 230+ degrees. Came right back down once traffic started moving. Not sure why fans come on at such a high temp with a 192 thermostat. Makes you wonder what the design engineers know.

With the mild winters (35 degree in the morning), water comes up and still runs 190 (as it should). Here is the problem oil temp doesn't get to 190 until I almost get to work at 25 miles and 25 minutes. Most of the driving comes at low oil temp and higher oil pressure.

I am sure there is an optimum oil temp and water temp for reduced friction and wear.

I would also think there is almost no effect of a 20 degree water temp change on air inlet especially at WOT. So it really strikes at friction losses and combustion efficiency for power. I think only design information and testing would help.

The only reason I have even considered a lower thermostat is less heat effect on engine hose, wires, plastic.

My 300ZX really deteriorated from the engine compartment heat. Brittle wires and hose, etc... My 1990 Chevy truck that got a 175 degree thermo by mistake is still on original water and vacuum hoses and such, knock on wood. Never could see a difference in fuel eff or performance.

I am going to wait and do more research before I lower thermo, but I am doing it for overall longevity vice perfromance. And if lower water and oil temps leads to more friction wear I am defeating my purpose. George

 

Yeah,

I wonder if you could run the cooler (say 172) thermostat and 5w-20 oil to counter things out...