Well anyhow, I can't seem to get the WOT curve right, and I don't understand why I can't run less than even what seems to be the norm. Most people run what, 32 - 34 degrees WOT? I've got it at 30 degrees by 3200 rpm and still get knocks above 3200rpm. Also down low, say I'm coasting along at 20 mph and punch it while in second, I get a couple knock counts at 2200, 2400, 2800 rpms, along the wot curve. It's not lean, I made sure of that, even on from AE.

Here's my curve, tell me what you think. Should I be able to run more than this? Yes, static timing set with bin, etc, etc, don't think it slipped, idle SA seems to be accurate for the combo, at 23 degrees at 800 (gives lowest averaged kPa). No PE knock retard since no PE advance.

Don't know if I continue pulling timing in these areas or look for a vibration or something from exhaust or anything else hitting under acceleration. Should I basically zero out knock retard for an area of rpm that I'm gettin knock and try it?

Thanks for any help or suggestions.

Ben

 

Fast burn heads require way less timing than a typical 23* head. Even 30* IMO is to much. One of my friends have vortec heads on his car and we started with 27* for his set up, but each car is different. Remember Vortec heads are fast burn, which means the combustion is faster than 23* heads = less timing needed. Leave all knock settings stock. Never mess with those settings because they are in place to save your motor.

 

Never mind what YOU think should work.
What does the ENGINE think should work ?

I'd be backing it off until performance drops, then sneak back up REAL slow.
When performance doesn't increase, back off a degree or two. You're REAL close.

 

What I started with was an LT1 graph, which started in the negatives, well it was 0 degrees at about 800rpm I think, then maxed at 20 degrees at something like 3200, then dropped to 19 degrees by 4 or 5k.

I did a lot of reading of what people with fastburns are using, to get me close, and what I got came up with most often was 30 - 34 degrees max, in by 3200. That's why I'm wondering.

Another question, while datalogging, I take it the SA relative to TDC number does not reflect actual (minus knock retard), is that right?

 

Is your PE Spark Advance vs RPM zeroed out?

 

I started with a LT1 table too. This is what I'm running now (still in development). Since my caprice is 4500 lbs I can only run 25 deg. Also the slight mods I did to the 193 SP heads makes it burn faster. If you notice the 90 map has some lower numbers that's because I'm up in the hills and can hit 90 map without going into PE.
Just because it does not ping, does not mean it needs more timing.
If it pings take it out!

 

Yes

I'm just trying to get rid of the knocks. Timing is ending up being way less than I would have thought, but I guess that's just the reality of it.

 

Well, your problem, or apparent problem, could easily be caused by a miscalculation.
Don't know which ECM, whether SA is available to you in the ALDL stream or not, but if you've set the static right, got the bias right, and all that, the actual crankshaft timing light indication should agree exactly with that reported in the ALDL stream minus the static.
More than once I've had to resort to Rbob's old write-up on ECM spark timing, and walk through it. You know, start with the main table, manually add in choke spark, hiway spark, subtract bias, etc. etc. and gone "Why doesn't this agree with the light ? Oh, yeah, add back in the static !" or similar.
At least twice, I've taken a long 3/4 extension and a 2 oz tap hammer, and rapped on head bolts with the thing running to see that what the ECM says is knock retard agrees exactly with the timing light.
Maybe you think you have a 10 degree bias when it's really 20 in the bin ?
It's happened to me !
If you're doing it right, YES the SA relative to TDC DOES reflect actual, including knock retard.

 

It's a '727 with 8D code, SA is out to ALDL.

I'm having my brother bring my timing light back today since he's visiting, so I'm going to double check static (else I would have already).

In response to the rest,
I'll check that out, thanks for the tip.

 

I'd verify TDC while you're at it.

 

There are a lot of factors that can affect the amount of TOTAL timing your engine can handle that always must be considered:

1) The type of head & combustion chamber. GM is going for "swirl & tumble" in a small combustion chamber. This typically needs less timing. Big cc heads with conventional design typically require more timing.

2) Camshaft. Short duration camshafts with wide LSA typicall want less timing. Long duratio camshafts with narrow LSA want more timing.

3) Elevation. The higher you are, the more timing. The closer you are to sea level, the less timing you need.

4) Gas Octane. Today, even with the octane stated, with the high price of oil, don't be surprised that even "national brand" gas may be a little less octane than actually stated.

This was REAL common in the 70s (when gas was high too). I recall a TV station taking samples of a gasoline on a number of gas stations and less than 10% actually had the octane rating they were suppose to AND in almost 50% of the cases you were often buying regular when you were paying for premium.

Also, as the gas "ages", it loses octane and becomes unstable. Premium gas is one of the "slow movers" for gas stations, so your gas may be old and thus losing octane.

5) Your spark curve when working in conjunction with the Knock Sensor. A smooth spark curve can often let you run slightly more spark advance than a "bouncing spark curve". This is why you want to limit how much spark advance you allow the Knock Sensor to pull out. In fact, once I get the spark curve where it should be, I will often minimize the KS to pull the mimimum amount out In WOT (just so I can see it) to run the smoothest spark curve possible. This is how I have found the I can run a tad more spark (once the KS is no longer interfering).

 

Hi 5.7RamJet,

At your initial post your mention one possibility that I have encounter for two years long.
My car (Cobra) has a narrow engine bay and the headers just fit very close to the foot boxes. (No side-pipes)

It has cost me two years to nail down the problem. I was using at that time the 165 with the code $6B and did have knock at every 2 to 3 and 3 to 4 shift.

Visual it was enough room between the headers and the aluminum box but we always where focused at the drivers side, till one day we just lift the engine and we found at the foot box of the passengers side some nasty marks from the headers.

A pry-bar did solve the problem and man the engine did love the new SA table.

Conclusion, don't overlook this area it can be a pain.

Regards,
Cobra289

 

Hey, Ram.....
Curious. What did you find ?

 

Well...my brother came up, but without my timing light. So I bought a cheapo advance light with the dial from harbor freight, not sure how accurate it is. I had to set timing with EST connected, made sure idle and SA was steady (removed error correction to keep from jumping around) and used the dial to set at what my idle SA was, 22*). It seems to run different than before (oh ya, forgot to mention, pulled intake and dist. to seal up a leak at back of intake, so who knows where its at compared to before). BLMs are way off in areas, whereas before they were good. So anyhow, it seems to run a bit different, and idles at a slightly higher MAP value. It does'nt seem to give me a correct value for initial (dial at 0* with EST disconnected does not give me the initial value set in the bin). Anyhow, I might take another look today and see what I get, and report back.

So either it was set wrong before, and my VE is tuned to the wrong SA map, producing different BLMs now with timing set right, orr....... my new timing light is wrong and that's why the BLMs are different.

 

Ok here's the deal. I broke down and bought an actron advance light, to be sure my cheapo light wasn't bad. I set the initial timing DEAD ON at 6* advanced. I made sure, and triple checked everything (this shouldn't be that difficult but we're going to cross our t's and dot the i's here). Plug in EST connector, make sure bin reflects 6* for initial, zero out rpm error tables for SA correction to get a steady SA number. Idle SA table set to 24* for 0 through 1200 rpm, idles at 700 rpm. ALDL reports SA to be 24*. Go check by light and I'm getting 15* advanced. Unlimited (correction) SA is reading 18* on ALDL.

So, just to see how it would react, I change initial timing to 2* in the bin, upload, restart. ALDL still reports 24*, and correction SA reads 22*. But actual measured is about 17*.

Idle is rougher, idles a good 6kPA higher than what I can get by fudgine the timing numbers, which is around 38kPA, and that's the best I can pull.

Getting no knock counts, although I don't believe it will pull timing at idle not moving anyhow.

Also, low octane retard has been disabled (S_AUJP binary).

Any ideas? Other than swap the ignition module, I don't know what's going on. Please advise.

 

Another Update: Swapped modules, still getting 15* advance at idle.

 

I'm getting ( I'm sure you are, too ) a little confused by some of this.
All that "unlimited ( correction) " stuff is something unfamiliar to me.

You set the BIN and the idle "test mode" SA at 6 BTDC.
SA map calls for 24 at idle. Light shows 24. ALDL shows 18.
Am I following so far ?
If so, that would be correct. The extra 6 degrees, the difference between crank and ALDL is added back in mechanicly by the distributor offset. That static setting number is used in the calcs, but is not reflected in the reported hacked ALDL stream, so far as I understand, and is true in the 7747 and derived ECM's anyway. ( 8746, other numbers for the same basic hardware )
Seems to me that you have enough now, anyway, to determin whether your original premis is even close. If your actual spark is all THAT far off of the stuff you were initially comparing with, subject to all the stuff Grim posted.
Unless, of course, I'm not understanding ??
----------
It's sparking, and advancing on comand, methinks the module is fine.

 

I don't think I'm confused.
You misunderstood me. Sorry for that.

By unlimited, I mean the SA reported that is to be corrected, or added to initial, as I believe that to be. The 'Unlimited SA' is how it is labeled in the .ads file.

Set initial in bin at 6*. Mechanically, initial is set at 6* also, with EST disconnected.

At idle, it calls for 24. Verified to be in idle mode by ALDL. Also, ALDL reading for SA at TDC reads 24. It wants 24*.

Now, with these settings, when I go check mechanical SA (at the crank, with a dialback light) I am only getting 15 degrees SA. It SHOULD be 24, with the ecm commanding an extra 18 degrees additional to the 6 degrees initial which was mechanically set.

I'm about to pull my hair out.

Arg.

 

Lucky you that still have hair.

Without jokes, I would try a new bin just a plain standard AUJP perhaps the VATS removed and see what happens.

Sometimes clean it up helps to have a good base reference.

Good luck!
Regards,
Cobra289

 

That was my next step. I copied VE and SA tables, and the basic constants over to new AUJP last night, I'll be trying it today.

 

Well, tried NEW AUJP bin, with my VE and SA, I'm getting the same thing.

For the heck of it, I tried increasing my idle SA from 24 to 30. As expected, it ran smoother. Measured at the crank, and it increased from 15 to 21 degrees. So it is linear, and consistent. I don't understand.

 

Think I figured it out, I'll post what I found later. I just didn't want anyone to write up a big long post when I've already found the problem (I think).

 

don't forget to post back

 

When warming up, $8D uses the 100kPa spark advance value at idle for catalyst warming. Is that what you're seeing?

 

No, I made sure I added timing to my table at idle rpm/100kPA for that (runs horrible with 0*, as per the generic vortec timing table thats out there). I always made sure it was fully warmed and in closed loop when doing my adjustments and readings.

I read the write-up on spark timing, although not for $8D, it made me realize about the bias for the correction table. I knew about both, however, what I didn't know was that the bias was in SA degrees . It was labeled Deg C in the xdf, so I never paid much attention to it, like the few other things also in that xdf that I don't need to mess with. (I generally use two xdf's, because one has O2 constants and a few other things, but I've been too lazy to add them to the xdf I normally use).

Anyhow, I changed the bias to 10*, and the table I also corrected accordingly, so that (Main SA - bias + correction table + etc = Total SA). It seems that the ALDL 'Total SA at TDC' is without the bias, so I offset by bias amount in the .ads file. Seems to correspond exactly with my readings at the crank now.

BTW, I believe the bias is also commented as Deg C in the AUJP hac.

 

I believe I have the fastest burning heads around in this family of engines I am still working with the timing curve but some things I have discovered.

1. Knock will happen when tc locks or unlocks if you are pushing it

2. A engine that has the power enrichment disabled and running at stoch will be less likely to detonate then with a rich mixture. I would like to say a lean mixture is less likely to detonate then a rich but I do not have time to defend that. (pull out the pe and see what happens,, alot of pepole have overly rich in the head) There is power in rich to about 10% more then stoch after that you are promoting detonation

3. A quick look compared to my old tpi motor with flat tops and stock iron heads running 94 octane and to the edge of detonaton you have to much timing by + 5 degrees in the 2400 to 3000 rpm area

37.97 46.05 46.05 46.05 37.97 35.16 32.34 31.64 33.05 33.40 33.75 33.75
37.97 46.05 46.05 43.95 39.02 34.45 31.64 29.88 31.64 31.64 31.64 31.99
37.97 46.05 46.05 42.19 36.91 32.70 29.88 28.48 29.53 28.48 28.13 28.13
37.97 46.05 46.05 42.19 36.91 32.34 29.53 28.13 28.48 28.13 27.07 27.77
37.97 46.05 46.05 40.08 35.16 32.70 30.23 26.02 25.66 24.96 24.61 24.96
37.97 46.05 46.05 46.05 40.08 35.16 31.29 25.66 24.61 24.61 24.61 24.96
37.97 46.05 46.05 46.05 40.08 37.62 33.40 26.37 23.55 22.85 22.85 22.85
37.97 47.11 47.11 46.05 41.84 39.02 35.51 26.72 22.85 21.45 20.74 20.74
37.97 48.16 47.11 46.05 41.13 39.73 35.51 24.96 22.85 21.09 20.39 20.04
37.97 46.05 46.05 46.05 41.84 39.38 34.10 24.96 22.50 21.09 20.39 20.04
37.97 43.95 43.95 43.95 41.84 38.67 34.10 26.02 23.55 21.09 20.04 20.04
37.97 41.84 41.84 41.84 39.02 36.91 32.70 26.02 22.85 21.09 20.39 20.39
29.88 34.10 40.08 40.08 37.97 35.16 31.29 25.31 21.80 20.39 19.69 19.69
20.04 24.96 37.97 37.97 35.16 32.70 29.18 23.55 21.09 19.34 18.63 18.63
20.04 20.04 29.88 29.88 28.13 25.31 22.50 20.04 18.98 18.28 17.93 17.93
20.04 20.04 20.04 20.04 20.04 21.45 20.39 18.63 18.28 17.93 17.93 17.93
20.04 20.04 20.04 20.04 20.04 20.39 19.69 18.28 17.93 17.93 17.93 17.93

As far as suggested timing at wot I can not say because my table for my 13:1 engine is water alchol injected . But the engine will take 34plus with out knock on the secound table.

Cruise timing under 50 map no water alchol injection it likes a table that is between stock aujp and vet for gas milage.

 

Seems everytime I pick up knock it is super rich. I've never heard that said before, though, about a rich condition causing knock. Can anyone else verify that?

In the meantime, I'll see what I can do about reducing the AE. I made it pretty fat, in order to rid a brief lean condition on tip-in, usually only 1 or 2 samples of data, which isn't saying much. That could easily be a few power strokes.

 

Nope. In fact, I can deny it !
Detonation is cause by heat and pressure, not mix.
Some mix can be more prone, because it is a burning of sorts. As such, stoich should be by far the most susceptible. Rich tends to *not* burn, so is LESS prone to detonate.
That rich doesn't burn well, it needs more advance. THAT can promote detonation, but it's excessive advance causing premature pressure that causes detonation, not simply being rich, or lean.

 

That's what I knew, but I wondered if there was something I wasn't aware of. Never know.

 

I'm still working on this problem. I verified beyond a doubt that the SA in the datalog is real at the crank. I had the timing down to 20* at WOT, 3600rpm before I could get no knock counts. I have a seriously hard time believing that this is right. Again, no PE or any other adders. The thing is still a dog...no seriously, its rediculously underpowered. I think my stock GTP would spank it right now.

If you haven't noticed, I'm AGGRAVATED! ARG.

 

I too found this occasionally with $8D (AUJP), but I have never discussed this because this is completely contrary to all logic. I believe there are other factors at work that I never had time to figure out.

I have also encounterd some "knock" when dropping out of Highway Mode (with a lean AF ratio) to the regular tables (and going back to 14.7:1)/

But you are not nuts - I too have had this happen occasionally using $8D at certain times.

 

I'm on to looking for something mechanical. I looked for rubbing AGAIN on the headers/collectors. I did see one spot underneath where the y-pipe bends towards the back, under the k-member, and it is awefully close, probably 3-4mm. Looks like it rubbed at one time, very slightly, but has surface rusted over the small scratch. I had it knock today on a test run, I don't think it woulda rusted that fast. But I'm going to try and give it some room anyhow.

I came across another post earlier today when searching, about a guy whose SDPC vortec heads' spring dampers broke, and was causing knock. I might pull the covers and check that out, I'm getting desperate. Thanks all for staying tuned, I'm still taking any and all suggestions here.

 

Try this, seriously.
A garden hose.
Yup ! A garden hose ! Preferably a short one, about 15 feet or so.

Chop off the ends.
Take one end, and slip it over something on the engine where it fits pretty tight.
A bolt, a bracket, something, preferably on the block, or manifold.
Stick the other end in your ear. No, I'm not being cute !
Now, you are doing the same thing the knock sensor is doing. Listening to the engine.
There's a difference, though.
The KS only cares about sending a signal to a particular sound that could be knock, regardless of what else it hears.
You, on the other hand, have a brain, and can immediately distinguish a rattle from a real knock.
Basicly, you've constructed a "voice tube" as used to be quite common on ships for communicating all the way across the thing easily.
You'll be surprised at what you can hear.

 

Been there, done that! But I used fuel hose with a copper tube (that's what I had on hand, so used it) touching the engine, and some wire to keep the open end pointed basically at a spark plug (without rattling). Also, I put a set of stethoscope ear things on the other end. Can hear some interesting stuff. The tool is also good for finding the source of a tick or rattle when you point it at things. The rubber hose does reduce the amplitude of the noise a little (attenuates it, I believe is the proper speakage. me fail english? that's unpossible - Ralph 'The Simpsons'), but does seem to isolate the input noise from the surroundings.

 

If you really want to have some fun, try a set of head phones connected to the knock sensor.

RBob.

 

FWIW, recheck your ADS definition is correct.
Unlimited SA TDC (item 39, Factor 0.351600, Offset = 0)
This will read correctly and include the initial (static) setting.

The output of item 41 is different and I can't confirm if the calculation being the same is correct or not.