Return of a Tuning Tale. Chasing classic knock

[XfireZ51]

So as some of u know, I ended up discovering a few issues with my motor including oil seepage into cylinders and defective injectors. With the better weather, I have been able to get back out there to now datalog th car w the changes and fixes I did including new FIC injectors, so its back to tuning. However, I am still recording knock altho its not exactly like previous. Before I would seem to get knock almost on a random basis and at a steady cruise
and with little to no change in operating parameters. I now believe that was due to oil seepage causing the detonation. Contributing to that was one particular injector whose aerator had deteriorated and was basically
streaming fuel into the cylinder. That kind of knock seems to have been eliminated.
I have attached some snippets of my logs where the knock continues to occur but inspecting the plugs doesn't show sign of any detonation (I have attached some pics of two plugs, one from each bank). Once I started to log, it was clear that the previous tune had been very rich contributing to why the right bank plugs were black. Oil also contributed to this. I believe what had been occurring is that the left side was signaling LEAN and so it was forcing the right side to make up for it by richening the overall mixture. With the injectors now replaced I could go ahead and re-balance the VE table. I took out quite a bit of fuel. Of course since all other fueling is dependent or based on the VE, I suspect that now the AE needs to be tweaked and that may be the cause of the knock. I can induce knock by simply punching the throttle and I have a couple of examples of that. Also show a screenshot form TPRT w a before and after comparison w current bin v starting point and the amount of fuel removed. In fact, as I look at it, the area I am recording knock appears to be the same region of the VE where the most fuel was removed.
An added piece of information. lLatter C4 Corvettes w ZF6 trans came w dual mass FW due to the square cut of the trans gears and heavy duty nature of the trans, especially Black label ZFs. A popular mod is to replace w a SM Fidanza. At idle the trans rattles depending on state of tune.

[XfireZ51]

Putting this extra image due to lack of space up above, but this shows that the most fuel reduced from the initial bin appears to be in the same region of the VE table as where the knock occurs. That leads me to suspect AE even more.
I am sort of talking out of both sides of my mouth. In one instance, at least a part of the evidence suggests I am dealing w false knock. On the other hand I am discussing adding AE fuel because of real knock. Question is which is it?

[Hib Halverson]

I have zero experience calibrating a 1G LT5, however, I have done cal with many different 96-up GM cars. While the method one uses to calibrate a pre-96 ECM differs, the same principles apply.

Some comments and questions.

1) Are you using a wideband O2S to gain information as to lambda or AFR?
2) In a 1G LT5 cal, is there a burst knock table?

Oil ingestion can indeed cause detonation.

It's interesting that most of your KR issues are coming at part throttle.

If you've backed off the AE, that could cause knock at tip-in.

It's very difficult to see detonation on plugs even with WOT "plug runs". I would think to see evidence of part throttle detonation on the plugs would be virtually impossible.

All C4s with the ZF S6-40 had dual mass wheels. Also, the gears in a ZF were never "square cut". All ZFs had helical gears but the early transmissions had a lower helix angle.

[XfireZ51]

Hib,

Thanks for ur input and perspective. Much appreciated. My exoerience has been w OBD1 and principally w Speed Density, not so much MAF.

First to answer ur questions,

1. I do have a WB O2 permanently installed in the RH header collector. Its a
Zeitronix ZT-2. Been using it since I had my 84. However, since I tune part
throttle in Closed Loop, I use the data from the NB O2s and the BLMs.
Tapping into the ALDL data, I use ALDLDroid app for datalogging and
TunerPro RT in combination w a Moates Ostrich 2 for calibration updating
and prom emulation.

2. No there is not any “burst knock” table in the LT-5 calibration as I understand
there is in the LS cals.

I currently believe that what I may have here is a combination of too much spark in that area of the SA table and also not enough AE pumpshot for tip-in.
In comparing my current calibration w a stock 92 cal, it seems as I may be a bit too aggressive w SA. In addition, as I stated previously, the most recent tuning sessions have had me take out significant amounts of fuel in the corresponding area of the VE table, consequently affecting the amount of AE for that RPM/MAP
region.
So my next cal will have a marked reduction in SA approaching more what had been used in the stock calibrations. If the knock decreases or goes away, then I’ll know I have real knock. If not, then I may begin to suspect trans and/or FW noise instead with corroboration from the spark plugs.
As we know, these motors do use oil, but the oil ingestion I had previously has been mitigated by redoing the IH gaskets and better sealing of the cylinder head crankcase vents. The detonation is not random as it seemed to be previously.

I have seen evidence of detonation in reading plugs when tiny particles of metal appear to have embedded themselves in the insulator tip of the plug.

BTW, yes the ZF were not “square cut”, I was using that description to characterize the how more aggressively the ZF black label gears were cut compared to the latter blue label gears. As u said, the black label used a lower helix angle.

[Hib Halverson]

Ok, so much for my wondering if LT5 cal have a burst knock table.

With later model stuff, I can' tell you how many times I've seen people, not knowing about how burst knock works, assuming they have trouble with knock.

My guess is you are not seeing evidence of detonation on the plugs because you're dealing with knock at light load. Detonation under heavy load, may pepper the plug end with those little flecks of aluminum because that's the piston starting to "burn" which may start happening under heavy detonation. Unless your part throttle detonation is massive and beyond the ability of EST to stop with knock retard, I doubt you will see aluminum flecks.

As you suggest, detonation at light load can be caused by by oil ingestion. I've seen that myself on an engine which had very high oil consumption. Obviously, it happens because oil is very low octane, thus, only a small amount of oil vapor present will put the engine in detonation.

I think your idea of making the spark table less aggressive and, maybe, bumping up the acceleration enrichment is a good place to start.

As for the ZF, somewhere around here I have the helix angles for both styles of transmissions, but I can't find the info.

When I had Barney, I had a standard flywheel installed. I never had trouble with any KR due to the lack of a dual-massl.

[XfireZ51]

Thanks for the comments Hib. I did a compare between the stock cal and the current SA tables. The knock has been occurring pretty much in the area of where SA appears to be significantly higher than stock. So I have made the mods to the SA table, and hope to take her out today or tomorrow to do some datalogging. I’ll post up what I find.
When u say “standard FW” was it steel or Aluminum?

[XfireZ51]

I did a recent datalog showing the effects of scaling back the timing in the area of the SA tables that was experiencing knock retard. Dropping the timing made a pretty significant difference in the KR recorded which would confirm that knock was, in fact, present. The knock that would occur at steady cruise is gone which also would suggest that the oil infiltration into the cylinders is also gone. You will see that the are a total of 3 Slow knock counts. Some of that occurred w Port Throttle Closed and I have made some additional reduction in SA for that table. The remaining knock, for the most part, was "induced" by blipping the throttle at cruise speeds. My next step is to bump up some Acceleration Enrichment(AE) and see if that addresses the remaining incidents of knock.

Unfortunately, I can't upload the datalog due to file size constraints. Other sites allow at least 1MB uploads of .txt and .csv files.

[XfireZ51]

Did some additional logging yesterday. Any knock I am getting is almost exclusively coming at strictly 1900-2000rpm and in the 55-70kPa range. I have basically reverted back to stock timing at this point in that area.
Getting burst knock at that rpm but at 90-100kPa or basically WOT, however, the timing there is again stock, so I am increasing AE as a test for that.
The burst knock is occurring when I am jabbing the throttle at highway cruise speeds. Really wondering if this is not a function of the on/off transition in the drivetrain.

[XfireZ51]

So took car out again today w cal that bumped AE by 10% along w small changes to SA in affected areas. Pretty much eliminated steady cruise KC. And frankly, I think the motor likes the additional pumpshot. Throttle response appears better by SOTP. I will probably bump AE again particularly where I could still induce some burst knock altho it was more difficult to do so than before.
Would love to get this thing on the dyno finally for some WOT tuning.

[XfireZ51]

Another datalog today. Primarily, I’m looking for KR at either steady highway cruise or with sudden accelerator movements. I bumped AE again mainly in area of 40-60% increase in MAP kPa. That seems to have worked. No KC at steady cruise, and 1-2 KC when jabbing the accelerator. The added AE seems to also have benefits in takeoff from standing start and responsiveness to accelerator inputs even very slight ones. It feels as if u have a 1:1 correlation between movement of ur right foot and and how the motor responds and moves forward.
Getting close. Feels good. Need to check oil usage.

[XfireZ51]

It may be hard to believe, but I actually think I have arrived at a final tune. Really running well. Very few changes needed for VE tables and of the changes needed we're looking at BLMs off by +- 1 from target for the most part.
Any KC came from me either lugging the motor in 3rd gear from a light, or jabbing the throttle to 100% TPS several times. Otherwise nada.
As always, there will be something that pops up to conquer. Maybe I can take a break. Yeah sure!!!!

[XfireZ51]

I continued to do additional logging and VE/SA table tweaking. But I have finally solved the Knock Retard puzzle. The engine would exhibit “knock” in a pretty specific range of rpm and MAP. Had lunch w Marc and he said it he could only think it would be something mechanical and not knock at all. The spark plugs did not exhibit any sign of pre-ignition.
Well, it was a loose rear muffler hanger on the driver’s side. Made one and now no knock. Time to put timing back into the tables.:dancing:dancing

[jss06c6]

There ya go! Glad you found it...

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[XfireZ51]

An update on this. I had a newly rebuilt short block installed by Dr. Greekenstein.
Turns out the old block had front and rear crank bearings worn in opposite sides plus the crank thrust bearing. The assessment is that detonation had caused the wear and even after removing the original cause of the detonation, ie faulty injectors, the damage had been done to bearings enough for a false knock to be present at very specific load and rpm.
Bloc and crank are fine with no damage altho the pistons and cylinder barrels are suspect which is why I am selling them as “momentos”. 😁

[Neat]

I know it's late, but cutting off the threaded portion of the spark plug would help you read them. You can chuck the porcelain in a drill, turn the drill on, and lay a hacksaw at the base of the threads.

Trying to read the plugs after some drive / idle time is pretty tough; but a new plug, pulled as quickly as possible after the knock event, will give you the best chance of seeing what's really going on.

On my LS powered Mustang, I have a switch on the dash that shuts off the coil and the fuel injector on the #7 cylinder. That way I can install a new spark plug in #7, make a pass at the drag strip, flip the switch, drive the car back to the pits on 7 cylinders, and have the best chance of getting a good read on the #7 spark plug. I don't know how involved a single cylinder kill switch would be on an LT5, but something like that might help give you the best chance at the most accurate plug reading possible. You'd do a new plug in whichever cylinder, drive the car to the knock event, flip the switch and shut down that cylinder, and then drive it home to read the plug.

The second photo shows some slight detonation / preignition in my opinion, but with the post knock run time on the plug I can't be certain. Mayne someone with some more plug reading experience could make that call with certainty, I'm not sure. Regardless, a new plug with as little run time as possible after the knock event, is the easiest to get an accurate reading from.

Glad you found the false knock issue, good luck with everything!

[XfireZ51]

Neat,

Thx for the advice. However, I have an epilogue to this story. I began tuning the ?new? motor and everything appeared fine, but then I started recording knock again. Sort of ready to tear whatever hair I have left. Put new plugs in and #2 appeared to NOT be firing or running extremely lean. The datalogs showed a lean condition just a 1-2 frames before Knock Retard was activated by the ECM. Sometimes, quite a lot of it. So I started w the more easily replaced items.
1. I did fuel pumps which apparently were originally in the car when I bought it 10 years ago. No change.

2. Replaced right side O2, which was showing very lean readings, sometimes for quite a few frames while the left side appeared normally swinging. No change.

3. Poured in a can of injector cleaner. No real change altho it can?t hurt.

4. Finally, I decided to do the plenum pull which I was trying to avoid, to check on
the #2 injectors.

In the course of doing the plenum pull, I decided to check primary and secondary coil windings on the bench, especially since I had gotten a higher ohm reading for the #2/3 coil when testing from plug end to plug end. However, it was still within spec <20k ohms. The other coils tested at ~14k, while 2/3 tested @~ 17k.

Close inspection of the coils revealed cracks in the casings of 3 of the 4 coils, including #2/3. Carbon tracks were visible on the body of the coil.

New coils are in and ready to pop plenum on today. 🤞

Just a side note to the Registry. It really doesn?t make sense that altho I am not a registry member, I can?t even expand the pics to the content that I myself provide. Just sayin!

[WARP TEN]

....Just a side note to the Registry. It really doesn?t make sense that altho I am not a registry member, I can?t even expand the pics to the content that I myself provide. Just sayin?.

Hey Dom--you should be a member and support the Registry, then no problems. Just sayin...--Bob

[XfireZ51]

Hey Dom--you should be a member and support the Registry, then no problems. Just sayin...--Bob

Bob,

I consider the content I provide as support. Apparently, you?ve read it.

[Neat]

Hey Dom--you should be a member and support the Registry, then no problems. Just sayin...--Bob

I'll cover him for a year, who do I PayPal?

[Jagdpanzer]

Dom,
MSD 8224 DIS coils?
How old?

[Neat]

The lean condition you are seeing may be cylinder misfire. I'm not sure about the narrowband O2 sensors, but I have seen the wideband on my car show lean when a cylinder drops out.

It was explained to me that the O2 sensor is just that, an oxygen sensor. It is not an air/fuel meter, even the widebands that are sold as air/fuel ratio meters use an oxygen sensor - which, not surprisingly, only senses oxygen. When the spark drops out for some reason, there is no burn to consume the oxygen or the fuel. The unburned oxygen and unburned fuel make their way into the exhaust, but the oxygen sensor only senses the oxygen and reports a lean condition; even though raw fuel may be coming out the tail pipes.

The momentary lean condition you describe sounds like it might be just that. There may be an intermittent loss of spark (which jives with your carbon traced coil) which causes a non-fire on one or more cylinders, the O2 reports lean because of the excess oxygen in the exhaust. I don't know how fast the ECM reacts, or if it even does closed loop correction during your knock / misfire event, but my LS powered car with a Holley stand alone will make a closed loop correction for the false lean condition in about 1/25th of a second. The sudden addition of fuel (again, on my LS car, not sure on LT5 stuff) causes a dopey rich effect, and one or two combustion cycles later I'll get multiple flame fronts from the excessively rich mixture hiding out in the ring pack / ring land area. The ECM then reports knock. The problem is exacerbated if the dodgey coil comes back online after only one or two misfires and then drops out again.

The scenario above only happens at light throttle. At WOT the extra fuel from the closed loop correction of the false lean is consumed enough to prevent extra fuel from hiding from the combustion event.

That's all real world stuff I've experienced with my LS car and the Holley EFI. I don't know how much, if any, of that is applicable or helpful to the LT5 / stock ECM; but maybe something in there will be helpful. Please keep us posted!

[XfireZ51]

Dom,
MSD 8224 DIS coils?
How old?

Phil,

I got the MSDs when I first ported the top end on my motor which was back around 2007-2008.
Got the motor put back together today, started logging again, and saw the same lean condition again, and yep knock retard.
I?ll also check the spark plugs later today after cool down and then probably taking plenum off again and run injector check.
Sometimes this gets pretty GD frustrating.
I?m also going to run Marc?s knock sensor check just for the hell of it altho that would not explain the right bank O2 sensor reading lean. Knock retard comes on when motor gets to about 3k rpm. Happens under no load as well.

[XfireZ51]

Just a quick update. I did swap out the coils for new AC Delcos. I also swapped
back in my MSD 8.5 wires in place of Magnacores based on some comments from Hib on the subject.
I had also run a test on the injectors and found that two secondaries (2&4) tested at 48ohms when hot while the rest were in the 16.9-17 ohm range after a 30 minute heat soak. Thank you FIC for warrantying the injectors and shipping replacements quickly plus they sent prepaid package for returning defective injectors. They want to take a look at them.

I use the ALDLdroid app to datalog these days. Along w a .csv file the app also produces an .xdl file which can be read into TPRT and then used to produce a History Table. You can build a table of your own which I did to "map" where the KNOCK RETARD was occurring rather than hunting thru a spreadsheet. I've attached a sample of the output from that. Its really helpful altho I don't see a way of breaking it down by Port Throttle status (Open/Closed). It seems to only handle 2D tables.

[XfireZ51]

A followup on this. I have been corresponding w Marc and mapped out a plan to help narrow things down, mainly to help determine whether this is true knock or something mechanical. So the plan was to:

1. Make sure my prom had the correct KS filter circuit. Marc provided part# of the acceptable filters that would be found onboard the prom. Mine has part#
2061252 stamped on it which came specifically w the 92 proms.

2. Filled tank w 93 octane and poured a bottle of Lucas octane boost. see attached TPRT KR mapping from datalog 12.09.2020. As you look at this, the SA table being used is at or below SA Marc uses on his performance setup for modded motors. Most of the "knock" recorded here is occurring in steady state cruise with little to no change in parameters like TPS%, MAP, or vehicle speed. Marc tells me
LT-5s will exhibit tip-in knock.

3. Ordered KS from Jerry just to make sure it is the correct sensor. Inexpensive enough (thx Jerry for quick shipment). Qjacks make it a pretty easy swap. In the process of doing this, I did check resistance values of BOTH KS. They were both at 3.9k ohms. In the process of installing the Jerry's KS, I found that the in place sensor was hardly torqued. It appeared that only 1-2 threads were engaged w the block. I installed the new KS(an AC Delco) and torqued it down paying attention not to over torque it. Using the same calibration and existing fuel you can see the resulting knock "map" w the new KS and properly installed. See attached from 12.10.2020. Altho still showing some "knock", the pattern is significantly minimized and less random. But I believe it still points to having some kind of mechanical noise setting off the KS rather than detonation occurring. This is also confirmed by inspecting the plugs. They show no indication of detonation occurring. No metal flecks embedded in the ceramic portion of the plug tip. Going WOT produces no knock.
Motor sounds and runs great with no apparent pinging noted.

N.B These knock maps are derived from logs which comprised about a 1hr drive of 40-50mi incorporating stop and go, hills and highway driving at
70-80+mph. In both logs, I had a total of 7-8 KCs during the logging session, most of which were .35-.7* KR. In some cases the ECM will increment the KC without any actual KR being invoked which did occur during these logs.

[wfot]

Have the Knock tables been altered on the chip? I from what I understand, the factory knock tables are fairly aggressive and can been tamed down some, but there needs to be some safety margin in them or if you eliminate all knock ability from the ECU, the engine will knock... If you have a stock bin file, you can compare the tune you have and see any differences.

is it possible that the air temp sensor could be bad/wonky? if the ecu thinks it is getting a one temp "x" and it is really getting temp "y" that could cause a problem. again I recommend GM parts for sensors, the aftermarket stuff can have much wider limits than OEM I have found

TPS adjusted to .53 volts?

and I think you did say you modified your accelerator map - maybe compare it to a stock bin and see if there is an unusual difference in the lower KPA settings ??

first time reading this thread and it does sound frustrating

there is also a table to adjust the fuel flow rate of the injectors, I think FICs are really close to stock flow and usually that value does not need to be adjusted if you are running their stock replacements but if they have a different flow rate then stock that could be a place to check as well...

my 4 cents

John

[XfireZ51]

Jon,

Thx for ur input. I?ve been doing my own tuning for the last 20 years and the LT-5 in particular for the last 13. I am aware of the areas u point out. The motor is fairly well modded w porting, cams and exhaust. The driveline is modified w SM flywheel, sprung hub disc and 4.10 Dana 44 gears.
My latest effort has been to confirm what I am seeing, or not seeing, on the spark plugs, which is a lack of evidence that would indicate detonation. In conjunction w Marc?s suggestion I mixed Lucas Octane Boost w my 93 octane and am running a less aggressive SA table than Marc does for his upgrades. Also installed an AC Delco KS from Jerry?s Gaskets just to make sure. As u can see, even after that, some knock still is registered in low load, steady cruise conditions. That strongly suggests that the KS is picking up a false knock from some mechanical source. There may be some kind of harmonic developing which the KS is sensitive to. At this point I just may ignore it because it doesn?t appear to impede performance and does not have any consistency other than occurring at 77-80+ mph range when it does occur. Other than that car runs and idles great.
One thing I did find before this last datalog, is that the previously installed KS was hardly torqued into the block. It was hanging by just a couple of threads. This may have contributed to the knock pattern u see in the first scan and why its so different from the second scan.

[XfireZ51]

Hoping that the saga here ends. The corollary in tuning is that you first make certain all the mechanical bits are operating on nominal levels, ie they're working the way they're supposed to work. Otherwise you'll be chasing your tail tuning around the deficiency. As part of a recent rehab of my motor, which included a freshly rebuilt short block, it was necessary to replace my Accel injectors. After 10 years, they'd pretty much given up the ghost with the #7 secondary having a deteriorated aerator which caused fuel to simply stream into the cylinders creating a lean condition. That in turn brought about knock ultimately cracking the top compression ring in 4 places. So enter a new set of injectors which are advertised as flow matched to within 1% of each other.
In the course of tuning, the plugs did not show an even burn among the cylinders however, so I had my suspicions. I waited for an reason to pull the plenum and a blown alternator gave me the opportunity. I had the injectors flow tested and I have attached pics of the actual flow for both left an right banks. IOW, each primary was flowed along w corresponding secondary. The diagnostic report w the values for each injector is also attached.
As you can see, these injectors were NOT within 1% of each other, essentially confirming what I was seeing on the plugs. Steve Schroeder recently went thru this same process w his injectors, altho I believe they are Bosch.
With the information of the flow test I was able to match up pairs of the injectors so that I was able to tighten the range of fuel flow(on a cylinder to cylinder basis) from 10ml down to a difference of only 2ml. when operating on all injectors. To me this also strengthens the argument for running all injectors during engine operation.
For idling operation, I was able to lower overall fuel and reduce the disparity between banks by 50%, albeit 1 ml.
As Steve will also likely attest, the SOTP is readily discernable. Engine smoothness and responsiveness, is pretty obvious. It feels like it has more power altho I don't have any measurements yet. Along w a change in calibration and spark plugs (NGK BKR6E @ .035"), knock is pretty much eliminated. The LT5 is a noisy motor, and when modified becomes even noisier so my objective was to eliminate any knock that was consequential, which appears to have been achieved.
I would make injector flow testing a basic part overall "tuneup" regimen. The $112 the flow test cost me, it was more than well worth it and would recommend it to anyone.

N. B. My injectors have 5k+ miles on them, so I am not being accusatory of any vendor's claims. Just saying that "trust but verify".

[jss06c6]

Good for you Dominic! Very happy for you and admire your persistence! I have made this part of my rebuild process on all ZR-1's as well as LT-1's. I too find the LT-5 to be much smoother. Our engines present a unique challenge by using 16 injectors intermittently (8 then 16 under load)..

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[XfireZ51]

Another update on this. The re-balancing of the injectors has had clear impact on how the motor is running. Much smoother and quieter. However, I have found that in doing the necessary re-mapping of the VE tables, I have taken out about the 3-5% fuel, resulting in better mpg(>1.5mpg) and cleaner exhaust as evidenced by my exhaust tips. But since all fueling is dependent on the VE tables, I am also needing to re-visit my Acceleration Enrichment. Removing fuel from the VE tables is requiring me to put it back in for AE. I have been getting audible knock in certain circumstances resulting from an insufficient ?pumpshot? due to reduced fuel. So AE now needs to be not only increased, but also lengthened in terms of duration.
This also would affect the PE parameters for WOT, but I?d rather do that on a dyno.

[Erik]

Great info. Thanks!

I don't think it can be overstated the importance of properly operating injectors to keep an LT5 singing happily. Injectors are usually not something I worried about much in other cars, but the sure seem to matter a lot here.

[XfireZ51]

Thx Erik. Glad u find this informative. As we all know, an ICE needs air/fuel/spark. Just as we expect each spark plug to provide the same level of combustion ignition, we can?t overlook how the injector is providing the necessary proscribed fuel. Uneven fueling leads to compromises in the tune. In our case, the 16 injectors actually makes it a bit easier to even things out when both primaries and secondaries are in operation. That?s why I think this exercise has highlighted an additional benefit to deletion of running in Valet mode or on primaries only. Of course, its not necessary to yank everything out. Simply have the secondaries begin operating just off idle.

[XfireZ51]

As a number of you know, I?ve been ?struggling? w eliminating a particular area of the SA table free from knock. It happens to take place right where the motor runs during highway cruise. And it seemed that the slightest change to MAP could bring on knock retard. Sometimes minimal, other times 1-2*. Basically, it made me hesitant to even take long trips in the car.
Recently, I have been focusing on AE delivery as an primary area for modification. Altho I was doing this primarily to eliminate knock, I have found that the process has also produced a real improvement in how the motor responds to accelerator input. Its just that much smoother accelerating and more responsive. I should say that re-configuring and balancing the injectors has resulted in much tighter control of fueling and results in much less ?compromising? of the disparity (split BLM) between left and right cylinder banks. And finally, along w a slight reduction in SA in that ?cruise? area, I was able to either completely eliminate knock or reduce it to a couple of knock counts invoking minimal ECM intervention. That was not the case in earlier attempts of reducing SA. It was a matter of getting the AE correct which then allowed me to get the SA right also. Its allowed me to get BLMs throughout VE table to 128 +/- 3. As a result, the car is sooooo much more fun to drive. Motor and exhaust are also noticeably quieter and smoother sounding. Additionally, MPG has improved by 1.5-2mpg. Just as a note, my LT5 has significant mods from the stock configuration, and so the calibration that ?works? represents a substantial modification from the stock calibration.

[jss06c6]

Great news Dominic!

I've been having fun tuning a 1996 supercharged LT-4 that I've almost finished.. Just a "blast" working on a system with a '95 ECM. Alcohol injection, ARP 195 heads, Tick Performance MAGA 2 blower cam... Etc. Etc, etc.. Speed Density, no MAF. 2 bar MAP.

Very close now. Will finish WOT on Mustang Dyno hopefully this week.

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[XfireZ51]

Steve,

Sometimes I just can?t keep things alone. Pulled a couple of plugs which are the
BKR6Es gapped at . 035. I looked at a previous set of BKR5E-11 gapped at .044? and thought they looked pretty good. So I tried them again, and even better results re:knock.
All of this makes the ZR so much more fun to drive. Acceleration is very responsive and very smooth. All u hear is the exhaust note which is monotone, as it should be.
Now I?m considering going to the dyno for some WOT tuning.

[jss06c6]

That will certainly be a benefit! Each engine has it's own fingerprint. Mine wanted AFR to be at 13.1 at WOT..

I'll be doing same with the LT-4 this week, if I can get on the dyno schedule. Target is 11.5 AFR at WOT. Alcohol injection comes in at boost and cools IAT from 115F to 84F!

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[XfireZ51]

Steve,

Yes my previous WOT tuning also pointed to an optimum AFR of ~ 13:1.

[Paul Workman]

Fascinating thread! Anyone would be pressed to find a better example of the proper application of the "scientific method" - i.e., discovery resulting from cause & effect analysis! . Very thorough, Dom.

[XfireZ51]

Thx Paul. I?m glad u have found the thread informative. Like the rest if us on here, I look to share information about our great cars, and how to maintain and have them run better especially when modified. We keep pushing the edges of the envelope on a ~ 32y/o platform, which demonstrates the forward thinking that went into it.

[XfireZ51]

An additional update. This weekend I had the opportunity to take the ZR for a 600+ mi round trip to Michigan. Car ran flawlessly. And when I checked gas mileage I was pretty amazed. 25.5mpg at least 75-80mph average, which include the the typical I80/I94 traffic jam thru Gary, IN. Not bad for a modified LT5 w 4.10s and cams.