Only able to pull 24 degrees at WOT in 04 GTO..

[That_guy]

I recently built this car, it's a 243 headed car with a custom cam of mine. The heads are decked .018 which puts it roughly in the 11.3:1 compression range. Car is running TR6 plugs gapped @ .044.

I've got A/F adjusted in the 12.8-13.01 range on the STREET, and commanded timing of 27 degrees. However she will NOT give me anymore than 24. If I command a higher timing table, it'll knock.

Is this all she's got, or are there other areas I'm missing?

Thanks

<---Rookie tuner

[Mez]

I recently built this car, it's a 243 headed car with a custom cam of mine. The heads are decked .018 which puts it roughly in the 11.3:1 compression range. Car is running TR6 plugs gapped @ .044.

I've got A/F adjusted in the 12.8-13.01 range on the STREET, and commanded timing of 27 degrees. However she will NOT give me anymore than 24. If I command a higher timing table, it'll knock.

Is this all she's got, or are there other areas I'm missing?

Thanks

<---Rookie tuner

I assume you are hitting about .80 g/cyl at WOT. If so, that seems about right. Of course, that is also assuming you have calibrated the VE and MAF tables and IAT is not too high.

Just for fun, take the commanded PE to 12.2 and see if that has any affect.

[That_guy]

Yessir I tuned the VE tables.

Tell me more about these MAF tables. A very experienced tuner got me started on my tuning, and never talked about adjusting MAF tables on heads/cam stuff.

Thanks again

[RWTD]

Why are you concerned with hitting more spark? If 24 degrees makes max power without knock, you do NOT need more spark. Contrary to popular belief the ole saying of "you should run your LSx engine at 28 degrees" and "12.8 to 13.0 AFR" is FAR from reality. That's a newbs tuning guide that posted that years ago (and somehow it stuck, uhhhg). Proper spark is dependent upon ALL sorts of things.

You'd probably make more power at 12.5 to 12.6 AFR, and then you may be able to get 25+ degrees without knock.

[That_guy]

RWTD, I understand and agree with what you're saying. I was more or less inquiring if this is the norm for those cars, or was there something I'm missing. GTO's are heavier cars, which tend to like less timing as it is. I just haven't tuned many of them yet. Built a ton, but not tune.

F-bodies and Vettes like to run between 27-29 degrees all day long from what I see. So 24 seemed a tad low (even though Im commanding 27), but that could be due to the compression of the engine and weight of the car.

[RWTD]

F-bodies and Vettes like to run between 27-29 degrees all day long from what I see. So 24 seemed a tad low (even though Im commanding 27), but that could be due to the compression of the engine and weight of the car.

Again, *that* depends on the VE of the engine. Not all of them like 27 to 29 degrees. In fact, I showed an LS1 customer that his 29 degree file without KR at 13.0 AFR made LESS power than my properly devised spark table with no more than 25 to 26 degrees at 12.6 AFR! But spark should always follow VE, so it can vary greatly from start to finish.

Case in point, here's a stock LS3 spark chart I made below. AFR was a commanded and actual 12.6 (+/- 0.1) across the board. As you can see, spark follows VE. And, yes, that was a degree of KR at approx. 2700 rpms, but I rectified it on the next pull.

I'm also putting up the datalog of a heavily modified LS7 I tuned. It didn't need more than 24-25 at peak torque, 22-23 at peak rwhp (approx. 6.3k), but needed approx. 26 at redline (7k). Again, spark follows VE. This is why you build a spark curve that takes advantage of the actual measured g/cyl. Blocks of spark is newb tuning, and sadly there are still some (tons, actually) so called "pros" who do this day in and out.

[Mez]

Yessir I tuned the VE tables.

Tell me more about these MAF tables. A very experienced tuner got me started on my tuning, and never talked about adjusting MAF tables on heads/cam stuff.

Thanks again

Do a search for the beginners tuning guide. It will take you thru a more detailed step-by-step process. I am not an expert and don't pretend to be.

But the short story is first you need to calibrate your VE table after disabling the MAF sensor. Then calibrate the MAF table followed by the ignition advance, PE table, and so forth. The point is if you don't calibrate the VE and MAF tables, then what the PCM commands for AFR will not be reality and you will end up chasing your tail during the rest of the process.

I started this a few months ago on my 2005 Corvette and I picked up 18 rwhp after it was tuned twice by a pro. I also improved my cruise fuel economy from 22 mpg to 28 mpg in the process. In all fairness, probably most of this additional HP was from the DIY porting of the intake and throttle body. I have a lot more respect for people who do it right for a living.

For reference, my car has Lingenfelter ported 243 castings, DIY ported intake, DIY ported throttle body, TB, Dynatech headers, small Lingenfelter cam, Corsa cat back, K&N CAI.

[GMRACIN]

If you are commanding 27 and only getting 24, something is pulling timing away such as knock retard or IAT. My guess is your IAT table is what is pulling it out as I see that often on GTO's!

[RWTD]

If you are commanding 27 and only getting 24, something is pulling timing away such as knock retard or IAT. My guess is your IAT table is what is pulling it out as I see that often on GTO's!

I'm fairly certain his problem is that if he inputs more than 24 that he gets KR, which is how I read the last sentence in his 2nd paragraph.

[Texsrt4]

Why are you concerned with hitting more spark? If 24 degrees makes max power without knock, you do NOT need more spark. Contrary to popular belief the ole saying of "you should run your LSx engine at 28 degrees" and "12.8 to 13.0 AFR" is FAR from reality. That's a newbs tuning guide that posted that years ago (and somehow it stuck, uhhhg). Proper spark is dependent upon ALL sorts of things.

You'd probably make more power at 12.5 to 12.6 AFR, and then you may be able to get 25+ degrees without knock.

I would KILL to be able to get an LS1 to 28*. Here in Cali, 21-22* seems to be optimal to prevent knock on our horrible gas. On race gas I havent seen many need more than 24* to make maximum power (peak horsepower). any more than that and the power drops off (on race gas so there is no knock). 28* seem excessive to me

[MNR-0]

Lotsa timing and lotsa fuel ...

[KLUG'S SS]

From my experience its all about finding that good combination between AFR and timing whether it's say 12.6 AFR and 26* or 13.0 and 22-23*, etc...

I have always seem to find more power by being a little fatter on the AFR say 12.5-12.7 but every car is different.

I do also agree with RWTD that spark curves need to be built and not just have say 26* at WOT across the entire RPM range. Just speaking from experience and testing.

[LSX378]

From my experience its all about finding that good combination between AFR and timing whether it's say 12.6 AFR and 26* or 13.0 and 22-23*, etc...

I have always seem to find more power by being a little fatter on the AFR say 12.5-12.7 but every car is different.

I do also agree with RWTD that spark curves need to be built and not just have say 26* at WOT across the entire RPM range. Just speaking from experience and testing.

Ditto on that ^^^ . Depends on cam, heads, static compression, exhaust, fuel, coolant temp, ambients. We have pulled 5 - 10 degrees out of some engines from stock tables for a max of around 15 at the top end and seen 60-70 ft lbs of extra torque turn up and air flow increase by 10-15%. Hi static and dynamic CR. No audible knock before or after. Though the knock retard goes away .

[KLUG'S SS]

Yeah what was the old rule of thumb with old school muscle cars, something about turning up advance til you here detonation then back it off 2-3*. That definately is not the case anymore.

[BBA]

F-bodies and Vettes like to run between 27-29 degrees all day long from what I see. So 24 seemed a tad low (even though Im commanding 27), but that could be due to the compression of the engine and weight of the car.

LS2 with high compression and pump gas really doesn't run well with a lot of timing. 24 is about right.

Oh, and the comment about Vettes, I have not seen one yet that liked 27-29º. They may have it in the tables but log it...it will have KR from hell and the timing will be down considerably lower, maybe even lower than the 24º.

[Texsrt4]

Thank you BBA, I was beginning to wonder about my tuning ability. I am glad that I am not the only one who hasnt shown good numbers with more than 24* of timing.

[Gh0st]

Why are you concerned with hitting more spark? If 24 degrees makes max power without knock, you do NOT need more spark. Contrary to popular belief the ole saying of "you should run your LSx engine at 28 degrees" and "12.8 to 13.0 AFR" is FAR from reality. That's a newbs tuning guide that posted that years ago (and somehow it stuck, uhhhg). Proper spark is dependent upon ALL sorts of things.

You'd probably make more power at 12.5 to 12.6 AFR, and then you may be able to get 25+ degrees without knock.

I agree 100% with this statement and I KNOW from experience working on my own 04 GTO with GMPP LS6 heads

People need to get out of the old tuning days where you set your spark to 35 degrees ...it doesnt work like that any more.

[Gh0st]

Just to clarify what RWTD is saying about following VE.

The lower the VE the more spark, the higher the VE the less spark. If you look at his chart he posted, the area where he has less commanded timing is where the engine is operating at peak VE. You will see how the spark slowly starts to raise as the VE begins to fall off.

[BBA]

Just to clarify what RWTD is saying about following VE.

The lower the VE the more spark, the higher the VE the less spark. If you look at his chart he posted, the area where he has less commanded timing is where the engine is operating at peak VE. You will see how the spark slowly starts to raise as the VE begins to fall off.

Good to know...That kind of explains why I usually have to back off timing in cells around 4K to 5K RPM to eliminate KR.

[KLUG'S SS]

Their is some power to be had by having a dip in the timing around peak torque area for sure.

I usually have at least around 3* less around the 4400-5200 rpm range and of course every vehicle is different. Around peak torque is where the cylinder pressure is the highest and the engine benefits from less timing in this area (more efficient burn) I feel that the 98-00 camaro/firebird base HO timing table has a pretty nice curve to it from the factory.

No super expert here just based on my personal tuning experiences.