opcorn: what an interesting looking question!!!! , wish i had an answer opcorn:

 

funny you mention this. I just posted about this in the fuelish thinking thread where my 2nd gear pulls on the street have no KR, but my 3rd and 4th gear pulls on the street have enough KR to cause performance loss. I figure if I have KR on a 3rd gear pull on the street, i suspect i would see KR as well on a dyno, maybe not as much, but enough to give lower Torque/HP than expected.

 

i know, i posted in Fuelish in regards to your situation..
it got my brain turning, and then i saw a thread blow up where a guy said he was tuned in 3rd gear on another forum, and some jackass basically told him hes in for knock and detonation under "normal driving" in other gears based on what hed seen.

i know theres a lot of guys who have experience with this, and i want to make a thread dedicated to it,

as far as i know.. tuning outside of 4th gear (on the dyno where its feasible) is taboo.

 

well i dunno about tuning, but to get the closest scent of what you got brewin at the back wheels, the closest 1:1 gear is the only gear to get you that, which happens to be 4th, usually on most 6 speeds its forth but on most 5 speeds its third, but our 5s is 4th

now i get about 1-4 degrees of ST kr in 3rd and 4th only, this is because that 3-5th are the gears that put the most load on the motor(this is also key when tuning to get a good accurate tune, must put a load on motor)

what kinda kr are you seeing ST or LT, usually with st you can add fuel via pred and tune it out.

 

im not getting ST or LT (rander is, talk to him)

im asking why people are tuning in 3rd gear still,
and whether or not(how much of an effect) it has when the car is not in that particular gear.

basically i want to know if and why its safe to tune in 3rd, like some people are doing, even tho ive heard the exact opposite.

i dont care about power to the rear wheels and if its inflated in 3rd, thats BS on a dyno anyway

 

Heck.. *I* should know this... I'll let the tuners speak for themselves tho.

 

lafrad tuned me in 2nd gear... is that the defacto?

 

When i first started with the LX platform i made the runs in 4th.
I tired 3rd at a later note just to see what the number offsets would be and there where none power wise.
I mainly tried it so i did not have to pull the vehicle to 160mph every single run.
The load ranges between 3rd and 4th did not seem too different so i stuck with doing it in 3rd.
Simple as that.
As long as i did not see a power difference and load difference was negligible so I was ok with it.

 

So is tuning WOT in 2nd worth anything? Did you run any tests in 2nd?

 

Tuning in 2nd does not put enough load on the motor.

 

There is nothing wrong with tuning in a lower gear. You will show lower horsepower but if you are tuning and the load is similar you should be fine.

From a tuning standpoint you would want the greatest range for mapping and if the times for 3rd and 4th are close it is a wash. If 4th is a longer run then I would use it.

One thing about dyno's as Diablotoona can attest to, they don't let the car hit full load on a run. If you set timing for max power on the street you will hit KR. The modeled rotational mass on a dynojet is around 2500 lbs for a 248 and less on a 224.

Do most tuners only tune in one gear or is this how open loop fuel and timing are set?

Sean

 

I am trying to comprehend why there is some mysterious tune needed for differing gear ratios. I have even seen this question raised when a 3.06 axle ratio is substituted for a 2.82. The car is thought to have to "learn" the new axle ratio. This might have some merit as far as the TCM, but the engine tune?

3rd gear is the most useful gear asfar as practicality just as it is the most useful gear for acceleration @ the top end of the 1/4 mile.

True, if the gear reduction factor where not entered correctly, the HP/TQ #s would be skewed, butbthat's about it.

Tuning our cars in 4th would be like tuning a Ram P/U in 5th gear.

The engine does not "know" whether the transmission is in "direct drive" (1:1 ratio) nor does the dyno for that matter.

All that matters is the FDR as far as HP/TQ #s & our 3rd gear gives the dyno operator/tuner the most useful FDR.

IF you were tuning a car for extensive road course use where it might be doing 160 + MPH for extended periods, then 4th gear pulls, or 5th gear for that matter, might be useful to gauge spark knock/detonetion tendencies @ high coolant tempoeratures under extreme load.

 

The engine does not "know" whether the transmission is in "direct drive" (1:1 ratio) nor does the dyno for that matter.

the concern is not whether the dyno knows or the tranny knows what gear it is in.
the conern is NOT what the horsepower and torque says.

the concern is
how perfect is a tune that is written based on 3rd gear pulling compared to fourth gear pulling.

as has been stated, there is a difference, but that 3rd is close enough,
im just not sure i would want "close enough" done on my car regardless.

 

so if the load on the motor is close enough between 3rd and 4th, why am have i seen tunes that detonate and knock to hell in 4th gear WOT that were tuned in 3rd? but run fine in 3rd?

isnt 1.41:1 still 41% less load than 1:1?
not as drastic and 2nd (which is like...2.18?)... 118% as much load?

maybe my math is bad, but still... i see how 1.41 is close to 1, but 2.18 is not close.

but i would think that on some pretty serious builds, .41 less load (or however it factors) could make a difference, right?

 

"The engine does not "know" whether the transmission is in "direct drive" (1:1 ratio) nor does the dyno for that matter."

Actually it does. That is what load is. When you tune open loop you are looking at throttle angle against RPM. If you change the load on the motor then you change the characteristic of the engine map. You may have more fuel where it is not needed or too much timing for a given load now that it hits sooner or later on the map.

"True, if the gear reduction factor where not entered correctly, the HP/TQ #s would be skewed, butbthat's about it."

At least on inertia chassis dyno's there is no need to input gear ratio. It is calculated using the rpm of the vehicle and the speed of the drum.

"All that matters is the FDR as far as HP/TQ #s & our 3rd gear gives the dyno operator/tuner the most useful FDR."

Depends what you are tuning for and what range of cells you are looking at to adjust. As you said in you post, some people drive 160 for say 90 minutes in a race. Not only would this be a different tune, but things like ignition dwell time and throttle rate come in as well.

Ask the tuner why they are doing what they are doing. If they tell you, it may shed some light as to what you are trying to acheive.

If they say "You wouldn't understand..." run!anic:

Sean

 

"The engine does not "know" whether the transmission is in "direct drive" (1:1 ratio) nor does the dyno for that matter."

Actually it does. That is what load is. When you tune open loop you are looking at throttle angle against RPM. If you change the load on the motor then you change the characteristic of the engine map. You may have more fuel where it is not needed or too much timing for a given load now that it hits sooner or later on the map.

Maybe I should have stated that the engine does not sense a magic 1:1 transmission ratio. It only senses a given FDR AKA "load".

So my statement that you quoted above still rings true.

 

We use a load bearing Superflow 840 so all the runs have vehicle weight and drag coefficient factored in.
The 3rd gear runs are only used for open loop tuning.
When i set a vehicle up i usually dial in crank, then idle, then part throttle and last wot(open loop).
During our "canned" tunes development, after i am done on the dyno i take the vehicle out on the street for a few hours and datalog to ensure everything looks ok.

 

My Innovate on my car shows very different AFR's in each gear. I was having problems in third after 5000 RPM's going down the track. Car would start to hit the mid 10's at the end of the 1/4. I finally got it tuned and on dyno in 3rd gear car showed the same at the top of 3rd (very rich). We leaned her out to show a nice mid 12 afr. and i thought life was good. Weekend after that i got tuned in 4th gear and it showed pretty much the same afr UNTIL i hit around 5K where it was so lean i coulda blown her up 14+ on the afr. After being tuned in 4th gear i will NEVER get tuned again in 3rd no matter what 1:1 for me or bust!!

Ofcourse these are my experiences and others might vary. Some dyno owners i guess don't want their dyno to see that high a mph maybe or the owner of the car might not either. After what i have seen with my own eyes its 4th for me.

 

Where you tuned on an inertia dyno?

 

The only factor the 1:1 transmission ratio brings up is a slight difference in drivetrain loss.

When a transmission is driving direct 1:1 there is basicly a direct coupling of power through the transmission therefore there is slightly less drivetrain lose through gears driving gears.

I think that this is perhaps more applicable to a manual transmission than an automatic.

 

The only factor the 1:1 transmission ratio brings up is a slight difference in drivetrain loss.

When a transmission is driving direct 1:1 there is basicly a direct coupling of power through the transmission therefore there is slightly less drivetrain lose through gears driving gears.

I think that this is perhaps more applicable to a manual transmission than an automatic.

I think there are some confusing issues at hand. Probably by me.:sad:

When you tune a car you would want to tune to the tables. An eddy current dyno or one with some type of brake and ability to hold a steady speed is essential.

If you tune in 3rd gear under load there are places on the table you won't hit. If you never plan on going above that you are fine.

If you tune in 4th under load you will hit more of the cells. But the reality is that you should tune in all the gears to make sure you hit every spot as 351freak pointed out.

If you are using inertia and acceleration runs to fine tune a car you would want the gear that has the least drive line losses. After all, you are looking to make the most torque (or horsepower or whatever...).

That is the 1 to 1 transmission gear. If you use a higher or lower gear then mechanical inefficiencies work against you. Even on an automatic. Direct drive is usually the most efficient. You also want to have as much time during acceleration as possible (within reason) to deal with transitions between cells. The ECU will interpolate values between cells. If you have large steps between, under acceleration you may have issues. This is cured by modifying the around the area by modifying cells above, below or around the spot. Trying to tune this at a lower gear will be more difficult as you will go through the map much quicker.

If you dyno a car in 2nd, 3rd, 4th and 5th you will see the highest power in 4th. Try it.

I would not tune on an inertia dyno in 5th for a street car because you will never see that kind of load/speed there. But if it was integral to the operation of a race vehicle I would get as close as I could and tune the rest on the track using datalogs.

Dynoing for comparison and fine tuning a tune on an inertia is common. Mapping from scratch on an inertia dyno can be done but you better have a lot of time for road testing as well. Fine tuning an Open Loop map on an inertia dyno will work as long as you realize that you will not hit all the spots and additional road work with datalogging will be necessary.

Full tune = load style dyno
Fine tune = either style although inertia is more practical

Hope that helps,
Sean

 

i see what youre saying PW,
thanks for adding another variable for me to try to wrap my head around hahaha

 

You raised some valid points about the 4th gear vs 3rd gear tune.

Me, I think I would spend my money (time) on the 3rd gear pulls merely because they would be a bit more practical, but given facts presented in this thread I would want some pulls in 4th along the way to check A/F ratios.

If there seemed to be A/F ratio problems in 4th, then I would reverse the process. Do the tuning in 4th W/checks in 3rd gear for A/F ratio.

Most of my hard driving will be in 1st, 2nd & 3rd gear.

 

The answer is "Load"...nothing more...nothing less...

"Load" to the ECU means a point on the MAP scale vs rpm.

Different gears (gear ratios) put a different load on the motor...if its just a "plain ole dynojet" dyno...

The wheels on the dyno do NOT accurately simulate the load of the car on a dry road at full weight...simple as that.

If it's a "Mustang" type dyno (read: eddy current) then the story is different...those types of dynos can be "programmed" to increase the load that the motor sees...SIGNIFICANTLY...

And very subtle changes to the "map" scale can definitely cause some problems to creep up...especially if you are on the edge...which most people always try and do...

It's understandable...by god...it's YOUR money...you want every last little ounce of torque you can get...

The price is a tune that can sometimes be a degree or two off...couple that with a tank of gas that had 10% methanol...or a slightly "off" batch of 93 octane (it is still the "winter" blend of gas in march) and viola...you get some knock...

Simple fix until it can be tuned on an eddy current dyno is to go to the handheld and pull a couple degrees from the WOT tables...or back the tune down to a lower octane rating...

Tuning isn't easy ... or cheap...to get it dead on everywhere on the map...

For example...a 16x16 grid of cells has 256 map points...at 30 seconds each...thats over 2 hours of solid dyno time before you even begin to make adjustments...


.02

-Freak

 

good stuff guys. Mike is looking my tune over tonight... hopefull he gets it even closer to perfect. Dude is a beast!

 

you got lt or st kr rander?

 

thanks for all of the great input on this thread, ive learned a lot! i love to learn

 

X2 I'm getting ready to get mine dyno tuned so this is very interesting. Thanks for all the good info.