Hey everyone. I just have a quick question about the amout of timing at WOT.

I have an 8D calibration.

At 100 kpa I have value ranging from 4 to 6 degrees. With these values it still pings a little on 92 octane gas and a 10 degree initial timing setting on the dizzy. I took it down from 14-16 which was the stock values. It pings less only from 4500-up but it still does.

Does it seem right that I have to pull THAT much timing out ? I know the heads are only 58cc and it's got around 10:5 compression but that seems like too little timing. Could adding fuel help aleviate that ? Any opinions ?

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1991 Z28 5.7 TPI

ZZ4 heads, ZZ4 cam, Harland Sharp roller rockers, Accel base, SLP siamesed runners, 52MM SLP Throttle Body, Hooker Headers, Flowmaster catback, MSD6A ignition, Home made ramair system, aluminum driveshaft, WC 5-speed etc

 

Are you actually at 100 kpa for all of your WOT run? Probably not, so you'll want your spark advance values at 90 (or is it 95?) kpa to be the same as the 100 kpa column.

Adding fuel should help this problem, especially if you're running lean. I have 11.1 compression on my 355 and have to run a lot more PE (Power Enrichment) to even run with 26-28 degrees total at WOT.

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Greg Westphal
'87 IROC 355TPI/A4

 

Greg is correct about the very few cars get 100 kpa @ WOT. The only place I hit 100 kpa @ WOT is at Sea Level.

Where I live, the elevation is 1,100 feet and with the ignition turned off (after the engine is on with Diacom hooked up) the MAP value will rise to 98 kpa. But @ WOT, my MAP reads 95-96 kpa.

Due to a lot of mountains where I live, I have had to adjust my spark table from 85 to 100 kpa. I found that from for each 5 kpa change from 100 kpa, that my spark advance is only .4-.7* different from the next reading. IE. 100 Kpa - 28*, 95 kpa - 28.7, 90 kpa - 29.4, 85 kpa - 30.1 (all total spark advance). With higher elevations, the air is thinner and can support slightly higher spark advance....but not much.

If you only adjust the 100 kpa spark value, it will have no affect on 95 kpa, minimal affect @ 96 kpa (actually an average of 95 and 100 kpa, sort of like 4/5s of the 95 value and 1/5 of the 100), 97 will average with 3/5 of the 95 and 2/5 of the 100; and so forth.

This is why guys that tune their engines at Sea Level and only concetrate on the 100 kpa value often find they might find their spark is less than optimal when they do any travelling at higher elevations. If the 100 kpa SA is dramatically lower than the 95 (and less) values, they might "ping". Conversely, if the 100 kpa is identical to 95 (and lower) values, they might not have as much power.

[This message has been edited by Glenn91L98GTA (edited November 13, 2001).]

 

I thought about what you guys said and I went and changed all the value for the 95 column down to about 3-4 degrees. The values for 100 are ZERO! It STILL pings a lot. Guess I'm going down to 80-85-90 kpa. Damn I wish I still had my laptop to see what the heck is going on in there and see exactly what the MAP sensor is showing. From what I remember it DOES go to 100 kpa though.

Could this have anythig to do with the fact that I have highway fuel & timing mode enabled ? It's set to "come on" at 1600 rpm and over 60 mph. Doesnt the ECM get off the highway mode when it goes in WOT ? I guess I'll tinker with the lower values in the timing table and if that is uncessfull I'll try turning off the highway mode.

p.s. I love the highway mode. I get OVER 330 miles to the tank which I would have never even dreamed of before.

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1991 Z28 5.7 TPI

ZZ4 heads, ZZ4 cam, Harland Sharp roller rockers, Accel base, SLP siamesed runners, 52MM SLP Throttle Body, Hooker Headers, Flowmaster catback, MSD6A ignition, Home made ramair system, aluminum driveshaft, WC 5-speed etc

 

If you're still getting knock, then you have another problem. Check your base timing again. Are you telling the computer that your base timing is at 10 degrees? Make sure your plugs and wires are OK. Make sure the upper MAP limit for highway mode isn't too high (Glenn will have a better idea than me). You're probably running too lean where it's knocking. I had the same problem, and dumping in more fuel cured it, although I had to add it in at a lower rpm since it would be on the edge of detonation before it actually started, sort-of like putting out a fire when it's just smoking but before it bursts into flames.

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Greg Westphal
'87 IROC 355TPI/A4

 

I disengage my Highway Mode at 74 kpa. In fact, I find that in cruising up long hills (we have a lot of them here) that my car is MOST inclined to have knock incidences occur just as it just returns to 14.7:1 after kicking out of HM @ 75 kpa. HM appears to be less sensitive to detonation than 14.7:1, but lowering the SA at 75 kpa fixed that.

Where exactly is your knock occurring and is it actually audible or is it just showing you the knock retard? One thought that comes to my mind is that you installed 58cc ZZ4 heads on your engine (from the TFS 23* heads). Possibly your compression is just a little too high. Also, those heads don't seem to like a lot of Spark Advance.

On my stock iron heads, I cannot run more than 28-29* (and only at 4,000+ rpm). From 2,000 - 4,000 rpm, I have had to slowly increase it from 22* gradually to 28*. This total spark advance including the PE Spark Advance and with the Knock Sensor capped at 1* while in PE, so I have virutal no spark pulled out when in WOT.

I do not recommend capping your KS to 1*, but I was doing some experiments and found that by myself controlling the spark curve, I was able to get a few more degrees of spark advance and let me know the REAL spark advance my car could handle.

PS: I have tried adding fuel (trying over 12-15% at one time). For power, I found 10% was best. Going over 10% just made my car slower and it really did nothing to stop the audible ping if I have more than 28-29* Spark Advance.

I conclude like Bruce, that the new GM heads just don't like a lot of spark advance. These heads just don't like the 36* that you see in the magazines all the time. But I have to point out that these magazines are always running 9:1, a carb and fairly large combustion chambers. I also agree with Bruce's analogy, that these magazine writers are all "English Majors...not mechanics".

 

In a moment of stupidity I traded my TF 23 degrees and bigger cam for less heads and a smaller cam. I've been kicking myself in the *** eversince But.. I wanna work with I have. Eventually will do it right and get some AFR195s and a bigger compcams cam (like a 220/230 .510/.510)

In the mean time, this is a mid 13 second setup and it sucks so far. I havent tried to disable the highway mode or play with anything yet.

My KS has been disabled for about a year and half now. All I hear is very noticeable and audible pings above 4000 rpm. It COULD be because my tach starts boucing around like crazy past 4000. It goes from 5000 to 8000 like nothing. I think it's getting interference from the coil wire or something. I havent been able to figure that out yet. Maybe it's my MSD box...



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1991 Z28 5.7 TPI

ZZ4 heads, ZZ4 cam, Harland Sharp roller rockers, Accel base, SLP siamesed runners, 52MM SLP Throttle Body, Hooker Headers, Flowmaster catback, MSD6A ignition, Home made ramair system, aluminum driveshaft, WC 5-speed etc

 

I found the problem. Sort of...

I decided to redo ALL the wiring in relation to the tach and ignition coil and somehow after I was done.. the car fixed itself! It's HELLA slow now because I have 0 advance from 80 to 100 KPA in the timing tables. Hehe

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1991 Z28 5.7 TPI

ZZ4 heads, ZZ4 cam, Harland Sharp roller rockers, Accel base, SLP siamesed runners, 52MM SLP Throttle Body, Hooker Headers, Flowmaster catback, MSD6A ignition, Home made ramair system, aluminum driveshaft, WC 5-speed etc

 

Nevermind... the next time I started it and drove it... it went back to its old self

I wonder if the ignition module might be bad.

[This message has been edited by crucial (edited November 16, 2001).]

 

Well just an FYI for everyone.. it WAS the ignition module. I replaced with a new GM piece and it works beautifully now with no hint of pining or tach bouncing

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1992 Z28 5.7 TPI

ZZ4 longblock
Harland Sharp roller rockers
Accel base and SLP siamesed runners,
52MM SLP Throttle Body
Hooker Headers & Flowmaster catback
MSD6A ignition
aluminum driveshaft
WorldClass 5-speed

[This message has been edited by crucial (edited November 17, 2001).]