Five Window

Anybody know what I should see on my scanner in terms of timing curve for a stock '86 L98? I've set the initial timing to 8 btdc with EST disconnected. When reconnected, the timing jumps to around 20 btdc at 680 rpm then zooms to 42 by the time the revs approach 1700. This is a really steep curve from my point of view. Is it normal??

The scanner shows some knock counts but no timing correction. The prior owner installed a Hypertech Thermomaster (160 degree therostat) chip. Could this be the cause of the steep curve? Will this chip cancel the timing retard that should be taking place when the knock sensor trips??

Thanks

BBA

They all have a steep curve. This causes pinging at WOT-High RPM. It's more likely your chip has the same curve as the factory, or it wouldn't be emmissions legal to sale.

scorp508

The stock curve is steep, the hypertech is even steeper. That being said my car when stock with that same hypertech chip had its best results around 9.5* BTDC on cool days and closer to 6* on hot days.

0ski_dwn_it

Fellas, fellas, fellas.... :nono:

You can't check for advance that way! Let me explain.....

The timing table is a 3d table. On the x axis you have lv8 w which is the inverse of RPM x MAF (g/sec) x scaler. Not gonna get into how you calculate the scaler or we will be here all year long. Along the y axis you have RPM. In the table itself you have the spark advance.

So if you rev the engine with the car at a standstill, you will achieve a very LOW Lv8 for the given RPM and airflow due to the scaler.

Ahhh man your gonna make me post a pic to get my point across.... :rolleyes: Ok here is the screen shot. I did not have any MAF bins here at work, so you will have to just imagine the MAP is LV8 values. The tables are identical other than that.



Here I added some colors..red would be idle light cruise, blue would be moderate cruise, green would be WOT or heavy acceration right below WOT parameters.

As you can see the left side of the graph is a very quick ramp, for a LOW lv8. Just think of Lv8 as a load on the engine. So basically what your doing is when at idle and revving up your engine you are not seeing the way the cars controls your timing when driving down the road.

This is also why you should not just bump up your base timing. It changes all the area of that map by that factor. It may help WOT, but hurt other areas. The far left of the map is idle or light cruising (say down a hill or flat) middle lv8 is highway cruising maybe moderately into the pedal, and then the far right is WOT...heavy load on the car. If you take out from a dead stop the car will run those values in the last two columns most likey.

Hope this makes sense... :cheers:


[Modified by ski_dwn_it, 11:20 AM 11/26/2002]


[Modified by ski_dwn_it, 11:24 AM 11/26/2002]


[Modified by ski_dwn_it, 11:30 AM 11/26/2002]


[Modified by ski_dwn_it, 11:32 AM 11/26/2002]

dgoodhue

I can't read your chart, but I know the 89 ARAP code goes as high 48.2 degree under part throttle conditions and light loads.

0ski_dwn_it

That is the key! SHould be able to read it now. Until you fully understand the way the timing table works, you will think that just adding timing at the distributer is OK. Its fine for experimenting for a given condition, like WOT, but not to leave it there.


[Modified by ski_dwn_it, 11:27 AM 11/26/2002]

scorp508

I don't really care much about anything except for WOT at the track. :)

0ski_dwn_it

that is kinda foolish to say, especially for someone that drives there car everyday like yourself.

But then again if your like me your foot is throught the floor boards most of the time anyways :D

I still like to get the all around most out of my setup though... ;)

scorp508

What I'm saying is that most people don't have the means or $ to modify the entire spark curve, so their only option is the distributor. If they are in there troying with the distributor in the first place I'm willing to say they won't mind losing some in other areas.:)

0ski_dwn_it

Guess we kinda got off the original subject.

I was just trying to put into easy terms something that took me a while to learn and *understand* how to use. Instead of just saying you can't check the timing that way. This is an area that is still unclear to many people. You would be surprised at the confusion brought about by this table. Just last week I was second guessing everything I once thought was gospel. fortunately, it still is gospel.

At the end of the day, there is a right and wrong way to do things. I believe in the right way. If people aren't willing to spend the $ to do it right, then they should be happy with what GM puts out the door and leave well enough alone.

95% of the people here are more concerned with a street/strip car. That is why I bring up the other areas other than WOT. Also a person that uses the distributer method, is counting on the knock sensor to save his engine. What happens when it quites working?

Ahhh and there you have it, in the end you wind up spending the money anyways. But then it GMs fault for having a crappy sensor right ;)

89vette

Ski is right. I have alot of experience with both the MAF and the SD systems. The timing is a 3D table. Your advance is based on RPM and load. If your in neutral and you increase the throttle to 1700 RPMs like you say, there is no load on the motor. If you have an auto, put it in drive and hold your foot on the brake and start giving it some throttle. See what happens? Most of the table does not need fooling with other than the right side. Its not a good idea to just increase the timing with your distributor. My chip is set up where I can pretty much load it up in 4th gear and it won't ping or pull timing out. Hey, sometimes I'm lazy and I don't feel like down shifting.:D

Are you having any type of problems?

Juliet

Well, if it pings and you know about it and then check the timing, you can back it down. Like I just did. The initial on my 87 was about 11 degrees. :eek: It's now about 7 deg.

I get the load issue and how it affects the curve (which is really a surface in 3D) :D.... but without a scanner, how do you decide where to set the initial advance? Pardon the blonde questions, :) but what other tuning adjustments does one have on a stock L98 other that initial advance via the distributor? Is it all controlled by the computer and only accessible via programming (which I'm not equipped to do). :confused:

With my C3 I can tinker ad infinitum with the carb (idle speed, fuel/air mix, choke, secondaries) / distributor /weights etc... (And I have to every winter when they switch to that damn oxygenated gas to get the thing to run well! :U ) On the C3 I can dial in the secondaries by tweaking the secondaries and stepping on the throttle till it bogs and then back off a bit. ;) What's the equivalent C4 procedure?

scorp508

What happens if your knock sensor quits working no matter what method you've used? :confused: If you've got a knock condition that bad for whatever reason that day, you have other things to worry about.

0ski_dwn_it

Scorp,

When you tune your car via the "chip" there should not be any knock counts. Believe me it takes dozens of chips, adjusting the fuel & spark advance to get best performance.

So even if the knock sensor is removed you will still not have to worry. That is my whole point of doing it the *right* way. I would still run the sensor however, just because you never know when some gas is gonna be bought.

scorp508

Key word is should. That is my point. Even with a chip you can get issues on a day that might be hotter than you tuned for or even with just a bad batch of gas. Unfortunately there is no perfect solution.

I just do not see how anyone can knock adding or even removing base timing at the distributor for track use when it works and works fine. Sure it will throw things off elsewhere. Dozens of us have made back to back runs on the same night and gained multiple MPH just by adding a few degrees here and there. Do we keep it set to that all the time? No. Does it always work? No. Why doesn't it always work? Conditions are never the same twice. How can somebody say "Well even though you gained 2mph that was a horrible thing to do!" Big deal. At the end of the night I'll turn it back and get my 33mpg on the way home.

Why should somebody spend $500 or more for chip tuning on a slightly modified car when they are just looking for a little edge at the track those couple of times a year they might go? It would be ludicrous to do when it is only a single bolt and timing light away. Sure GM has waaaaaay more knowledge than any of us ever will and have tested this things to extremes. It still comes down to they have to build an 'overall' car that will get good gas mileage and also lay the smack down. Kudos to them for putting it all together, but I'm going to have to go with what has been proven over and over.

On a car not even close to stock, sure! But somebody with a couple of boltons it is crazy. I'll go inform my friends that they are all crazy and that their results are fake and that they should empty their pockest...... :)

SloRvette

As long as they realize why they need to put their timing back to base, there's no problem. The one place where you can run into problems at the track is during your burnout.

The biggest thing to remember is that the knock sensor is reactionary. It reacts after the engine starts knocking. There is knock present that can do damage.

0ski_dwn_it

Scorp,

I have to say your missing my point. If you look back on what I wrote I agree with you that for track testing it is perfectly fine. However I also allude to the fact that if someone is going to spend the money on *major* mods they are not gonna be able to fully realize their potential of their car. I have read several time, from yourself, that you are impressed that your car put down 3xx RWHp with no tuning.

Also I stated that this is getting a little off the original post, nice discussion, but nevertheless the original posting of checking the timing ramp was totally wrong. I was just trying to give some advise that took me quite a few nights of scratching my head to figure out. Just trying to minimize the learning curve a little.

With the imformation I was trying to also address the fact of: You know as well as I do 85% of the people who adjust there timing and get a better ET think that is the best setting for it, when in fact they may be hurting performance elsewhere. And as far as a better ET, that doesn't mean your putting out more power. As I explained in posts before, I would be willing to bet when you turn a better ET you are most likely inducing some knock which limits tire spin, ultimately giving you a better ET. And yes I understand that a better ET is what we are all looking for. Take TripleBlack88 stock car with bolts on that I tuned. His car was set at 9*, I believe when he showed up to have it tuned. I left it there for the first log. Before we got out of my driveway he was getting knock counts. The car at the present setting was turning 13.7 or 8s. Not too bad for a stock car. I explained it to him again and showed him what he was doing. We turned the car back to the stock 6* and went for another logging run. Again there was some knock in certain areas with the stock chip. Went back made some changes to get fuel and timing balanced. At the end of the day he could smoke the tires right off the car if he liked. There was no doubt he picked up power. GM has these car very fat in the fuel from the factory to protect there butts

It all boils down to this: Do you want half the package available or the whole thing. If half is the answer then tune your heart out at the distributer. :smash:

ELEVENS

You are warned with the SES "check engine" light.

ELEVENS

Really? I usually see a few knock counts when an engine is first accelerated or revved cold. I've attributed it to mechanical noise, not detonation, becuase it only happens within the first few minutes of a stone-cold motor. You don't get that? Maybe I need to rethink...


[Modified by ELEVENS, 3:58 PM 11/27/2002]

0ski_dwn_it

Elevens your fine....The ecm runs the timing up to induce knock when certain parameters are met. One which is when the engine is first started. It bumps the timing up till the knock sensor activates and pulls timing then it will not do it again until another set of criteria is met. Another being once the car is run over 190*F coolant temp and WOT is encountered. That is the one that bites us who disconnect the sensor. That will set a code if the sensor is not found.

Other than that you really shouldn't see any counts. If you are the car is pulling time. If you are getting some, that you can't get rid of, say false knock...you can also do some pretty neat things with knock pull rates and also recovery rates that the timing is put back in at, so you minimize the performance loss.

My stock setup I got to the point of having No counts anywhere. The car responded much better.

That was a good point you brought up... :cheers: