romandian

my 99 c5 runs 27° timing stock. optimum timing is 29° and i would think they know what they put in there. i believe a holden runs around 17° and i dont know about them being degraded powerwise. when supercharged i havent noticed any noticable gain going from 12° to 17° (no dyno). i also find the engine doesnt respond to leaning out beyond 11.6 (supercharged). pe on the stock tune is 11.8 btw.

so my conclusion is the engine doesnt respond much to changes in timing and mixture. how come people often claim gains of over 10% in torque and hp from a tune? usually theres a dyno sheet included.

thoughts?

Chevy Guy

Here is my opinion and I expect to be attacked for it.

Tuning a stock car (n/a) or a car with minimal mods like headers or a CAI, doesn't get you anything except increased fuel consumption. The tune can also take things into consideration like skip shift and Torque management that can result in benefits, but having been through all permutations of tune from street, dyno, etc etc - I would never get another car tuned unless there is a major change like a cam.

jglassmaker

If you data log most stock cars, or even just very nearly stock w/ CAI or something small, you will notice fuel trims very often taking 2-4% fuel out. This is because GM and many others err on the side of caution and run a bit rich, you also see PE often commands 12.1 or even 11.8 NA.

So most of the time if you tune a stock (or near stock) engine you often have to lean things out a bit (just to get fuel trims a bit closer to 0% or -2%) but this won't make the car feel different since it was already adjusting to stoich. Leaning out the PE should get you something like 15-30 whp and a bit less toque on a 400 whp motor - thats 5+%.

Now as you add mods and increase airflow you are leaning the car out yourself a bit (the fuel trims try to adjust but are not that precise). So where a stock car would gain 5+%, a car with say CAI & LTs might only gain 1-2%. It isn't until you get further with mods like a cam or heads do you start to go the other way and the stock tune is too lean or the fuel curve is completely off.

But either way you cut it the human senses (at least mine) are not able to distinguish small changes like this - even if the engine is truly making more power.

PS 10% gains sounds irrational - thats 40hp out of say a stock LS6... nope.. not going to happen.

tblu92

There is a huge difference between "commanded timing or asked for timing" VS actual timing
It doesn't matter what the commanded timing is as all tuners alter the commanded "timing deducts" differently due to coolant temps and more importantly IAT temps---
The only way to see EXACTLY what the actual final timing is is to do some data logging
Yes even boosted your tune may show 27* commanded timing but that is NOT your actual timing otherwise it would detonate like crazy---
Best actual final timing with LS6 stock heads is usually around 24* with LS1 heads that have lower compression you can get about 26-28*
Boosted timing normally runs from 15* to about 18* max at WOT depending on the boost levels-----

romandian

irrational, yes, i agree, but there are just so many threads stating 10% or more, on here and elsewhere. i saw somebody reporting a 60 hp gain, i believe, going from a low octane to a high octane tune. so is all the stuff made up (by the tuners and dyno operators) or im i missing some secrets? i mean, you can only adjust timing and fuel, right?

jglassmaker

More than likely these are exaggerated numbers in some way or another. There are far more than just simply timing and fuel, but those are where you see the power differences usually. Absolute dyno numbers are not something many depend to be accurate anyways - look into the corrections the must be done in order to get adjusted final numbers.

Our C5 cars have 100s of tables & settings in the stock computer you can adjust and once you start putting in much larger cams & heads and other big items, you're going to need to touchup many of these tables to go beyond just WOT power.

In the end an engine is simply an air pump, the more air an engine can cycle through it - the more power it can produce. All you can do is put the correct amount of fuel for the amount of air that is coming in, once you put in the correct amount of fuel you cannot gain anymore power with fuel. Next you can use timing - generally speaking more timing = more power until the motor starts to knock and pre-detonate. This is an over simplification, but in the end its all about giving the motor exactly what it needs for the amount of air it inhales - you can only add so much fuel, spark, or whatever else to perfectly use that air.

Blue-Z

I tune for a living and use a dyno almost daily. Tuning a 100% stock car will get you minimal gains, 5-10hp typically on a C5. The factory tunes are a tad rich and of course very conservative, seat of the pants feeling would be minimal, if anything at all.

Bolting on a cold air kit or headers, a tune is necessary. Literally yesterday, I put a set of headers on my car and put it on the dyno. My car had a tune in it by me previously as it has a Vararam cold air kit. The headers picked up only 8hp on the first pull comparing to the last pull with cold air kit and tune only (don't remember torque difference. After dialing in the fuel and spark, the car picked up 29HP and 40Ft/lbs of torque, with gains all across the RPM band.

When the airflow of the motor changes, the tune needs to be modified to compensate, period.

Podium

Are you serious? You should be attacked because youre talking about something you know nothing about. A stock car (ls) will gain power and increase fuel economy from only a tune unless the tuner is a moron. You should definitely tune a car with headers.

romandian

here we go. thats a good axample. so in round numbers, originally 300 rwhp picking up 10% due to headers. makes sence. now, you probably had leaned out the mixture previously. where to, 12.6? thats the "text book value" for most power, but i see people going over 13.0, so there is probably not much difference in this range. (as the original pe is to 11.8 the question is how safe you are.) 10% more airflow takes you to 13.9. so you put in 10% more fuel and got 7% more power. still makes sence. did you decrease timing because cylinder pressure is higher now?

but, a stock engine running on 11.8 pe would go to 13.0 with the headders. while that might not be safe it seems to be the ideal mixture for max. power. so where do tuning gains come from in this case?

also, what makes these engines insensitive to timing? i have a turbo car where every 2° can be felt. i couldnt stop tinkering and it cost me two head gaskets to find the spot, where it doesn blow up anymore.

Chevy Guy

LOL, yeah. Sure.

Roddy13

thanks, food for thought!!

tblu92

Tuning ALWAYS helps any car from the stock tune --period----And it's not always a matter of timing and fuel----Cars like Camaro's and Corvettes are already well tuned bone stock--Altering the timing by adding 2-3 * at WOT and leaning the pig rich WOT fueling from the high 11's to an even safe 12.5 alone may add 10-15 RWHP
However the greatest advantage is by deleting the TQ management and TQ limits in your tune to allow your engine to make "all the power it can make--all the time"
The worst culprit is the drive by wire limits of the throttle opening-----Even if you floir the throttle from a dead stop the stock tune does NOT allow WOT until you hit approx 3600 RPM Making it a turd and lazy off the line---This simple one entry tuning mod nay not add any top end HP but it will allow your engine to act more like a cable throttle and really wake up the bottom end---Letting the eng not to ever limited by TQ or throttle position

romandian

well, the ls1 sees full ambient pressure in the manifold untill about 4000 rpm. regardless of the blade being fully open or not. you also get "wot" condition at 40%-60% throttle in the lower rpms.

Gordy M

What TBLU92 was saying in a stock engine, a good tune will be most beneficial in the lower RPM range. Most of you serious autocross/HPDE/road race/drag cars have had tuning done to maximize those areas. While you might not make a ton of HP over stock, your intermediate rpm ramp up can be improved. For those that have had the delay in the TB tuned, especially autocross or HPDE, will swear by the results. An example, I autocross a BS C5, 2000. I was having difficulty running 2nd gear at lower speeds compared to the 2001+--they have more low end torque--recalibrating DBW delay among other areas brought me parity and also first place.

Sub8

A boosted engine is more sensitive to timing because you are knock limited at the higher cylinder pressures they run. On an NA engine usually anything over peak torque RPM is not knock limited. i.e you can actually start to reduce torque as you add timing.

The timing Vs torque curve looks like a hillside /\ - as you add timing you add torque until you reach the optimum (the peak, known as Minimum Best Torque, MBT) and then adding timing takes you down the other side.

On boosted engines and high compression NA engines you reach the knock limit timing before you reach MBT. Therefore if you add octane, reduce back pressure, improve scavenging etc you move the knock limit further `up` the slope. If you then add timing you gain torque.

How `steep` the hillside is also changes with engine speed. The hillside is much steeper at peak torque than at peak power and much steeper on a boosted application than NA.

For example on the LS6, when you add headers you greatly improve the cylinder breathing (more air-in, better VE) and scavenging (more heat out), this moves the knock limit `up` the hill. You then add timing and you get a chunk of torque.

Bear in mind that leaning the fueling increases exhaust gas temperature and that adding timing decreases it.

Also note that with HEGO sensors fuel trim is only applicable when in closed loop operation i.e quite low load.

romandian

facts:

1. changing to another timing strategy yielded around 10° timing in the mid range. no power increase to be felt. stock boosted 99 c5.

2. ls1 engines run anything between 18° and 28° stock (go and check out the tunes for australian commodores). im not aware of different power ratings, of course there might be some small differences in reality.

tblu92

THKS Glad to hear some real time experience with what I was trying to communicate----Again these Corvettes are well tuned bone stock--so tunng a bone stock engine won't create any miracles--maybe 10-15 RWHP--However the throttle response in the lower RPM ranges really wakes up the car from low speed launches---Without adding any HP or mods or timing or messing with the fuel you can make your car "quicker" just form tuning out the throttle delays
Now when it comes to heads and cams and LT headers again tuning only allows you to achieve all the benefits from those mods---Almost always if someone adds heads.cams/LT's without tuning they will report almost NO HP gains or maybe less than stock That is because in order to obtain the full benefits of any mod the car must be data logged again and retuned to achieve all the HP on the table from those mods--This even includes some CAI systems that radically improve airflow

Ed@TheVetteDoctors

Certainly the gains expected from a stock setup tune vs even a simple upgraded setup with Headers and an Air-box would be a lot less but none the less could be beneficial and noticeable for many of the reasons already discussed above.

The real bang for your buck actually comes with automatic equipped vehicles and a transmission tune to firm up and speed up shifts for that seat of the pants dyno ....Engine wise we would perfrom improvement like lean out the otherwise rich wide-open settings of Power Enrichment, lessen (with safe areas) the Intake Air spark retard and reduce torque management settings to get you back those burn outs you so miss :-)

The real question is should you spend $600 dollars on a dyno tune or $150-$300 on a remote/email tune using HP Tuners or EFI Live. If you have access to the cable(s) then you can take advantage of a service like ours where we mentor (if you are interested in learning) you through a street tune or provide the completed tune and walk you through the logging sessions to fine tune. All the benefits of a tune at half the price.

Ed M

romandian

where do you recalibrate the dbw delay?

911Tr8er

tbBlu and Gordy M are IMO spot on. UP to one week ago I had 2LT C7. The worst part of the car is that drive by wireless feel. The hesitation at launch is so obviious that as someone who knows little about tuning and my experience with tuned chips in my 911 Porsches being so negative I was truly dissappointed in my C7, Until I had my first DE day. A more experinced Stingray driver told me to put it in TRACk mode and then do a couple of other button presses and bang it was a new car. WOT from stop and it leaped. I had been thinking that my C7 needed the flywheel lightened. The adjustments by turning the **** must be similar to a tuned chip.