Will the Real ETC Scaler Please Stand Up

[JD White]

2002 C5 Z06. Lots of bolt-ons, personally tuned and running well.

Just installed a TPIS 90mm TB along with their LS2 snout inlet on the stock LS6 manifold.

I have spent hours browsing various guesses as to what the ETC scaler should be and have found no definitive answer as to why people have chosen certain values over others. Little of what I've read has had a data driven conclusion. There is even much conjecture about what the stock TB diameter is.

Ultimately I have found that a simple area calculation minus some shaft area yields the appropriate scaler. I measured the stock TB blade with calipers to verify that it is indeed 75mm, not 78mm (or 80mm) as can be found across the internet.

Since it is difficult to accurately measure the factory shaft area it is also difficult to precisely relate the stock 0.0255 scaler to a 75mm TB minus shaft area. However, since the 0.0255 to 75mm relationship exists, percent change in area independent of the shaft can be used:

75mm (4412mm^2) to 90mm (6362mm^2)
1/ (4412/6362) = 1.44 -> 44% increase in area
4412/6362 = 0.6944
0.6944*0.0255 = 0.0177 = 90mm scaler

Now, 0.0177 is a number that others agree with. I have tested using this value and the "just use 0.0192" and 0.0157 simply derived from using 6362 as a starting point, ignoring shaft area, and using 100/6362. This method would say the stock TB is 70.6mm, but I can believe this based on the subtraction of shaft area.

So, how can I determine which value is the correct scaler?

[oakley6575]

I have a 90mm and use .0192

[redhardsupra]

http://www.marcintology.com/tuning/TBresizing.xls released in 2007, nothing new here.

[blownbluez06]

Just out of sheer boredom and to prove to myself that it could be done, I've put a scalar value of .300 in there and tuned around it.

The consensus has been .0192 for years on the 90mm units.

[SargeZ06]

Just out of sheer boredom and to prove to myself that it could be done, I've put a scalar value of .300 in there and tuned around it.

The consensus has been .0192 for years on the 90mm units.

JD this is exactly what I was saying on CF. It didn't matter if I used .0192 or .0255. It was easily tuned around that number. No difference at all in the drivability or power.

[JD White]

I played around with various values and did some mild work dialing each of them in and wasn't seeing any difference. Only the RAF required large changes to accomodate whatever the scaler was. I threw in 0.0192 and went with it.

[redhardsupra]

yup, you shouldn't see much of a difference, because there's two mechanisms in play here:
the predictive mechanism, where the effective area and throttle angle estimates amount of airflow, the airflow desired by RAF (that's why you need the scalar in question). so you adjust the throttle angle for the two airflows to match. if your scalar doesnt represent reality, you will always over or under estimate the air you think you're getting, causing problematic idle.

then you also have the corrective mechanism, that uses IAC, spark, throttle angle (depending on model/year) to prevent the idle from flaring up or down. if the actual rpm is lower than desired rpm, it will crack open IAC/throttle a bit more. So if the error in the initial estimation isnt too large, and the corrective mechanism can 'fix' it for you, you should not see any differences. but if the error is big (going from 78mm to 102mm is a 71% area increase) then the corrective mechanism might not be able to correct it. so the closer you are on the initial estimation, the less of a job there is for the corrections later. on older cars, IAC can be pegged (on both ends of the spectrum), so you simply would not be able to correct enough.

short version: get the area scalar close, and let the ecu do the rest.

[C5XJEDIX]

input ..more input!johnny five is alive!!love hearing people who have real world know how!

[DGA]

Hi, new HPT user. Trying to input the 0.0192 value into my idle airflow ETC effective area scalar box and it won't accept any values under 0.125. Is there another input somewhere that I have wrong that is limiting this somehow?
Edit, this is an LS1 with LS2 90mm ETC throttle. Stock value is 4,725.0000?

[Ben Charles]

I've put a scalar value of .300 in there and tuned around it.

You see any throttle response gains or anything with such a large change in the scaler? I know the RAF and the remaining tables would probably have to be lowered quite a bit to compensate but just wondering what you have seen?

[caniggia]

I did some modification to excel sheet.
In the file (http://ls1tuningguide.com/files/free...TBresizing.xls) there's no TB size that corresponds to 0.0255 scalar as found in LS1 tune.
LS1 has TB 75mm and scalar 0.0255, based on this lot of people count and it gets 0.192 for 90mm, as above for math 6362mm2 area was taken.
As seen in 90mm stock tune for LS2, it's not 6362 (I belive they put there mm2), but 4725.
Looks they use not full square area for math, but remove shaft area and maybe some more.
So I did some math based on both throtle bodies and I got what attached (ETC scalars for LS1 type and LS2 type tune). From my math for 90mm should be 0.0212 and this settings was working better for me than 0.192 or 0.0177 to tune idle and drivability with some radical cams in 408 engine with AFR heads.

For LS3 TB, there's also 90mm and 5636 scalar (higher than LS2), so don't look at TB diameter, only directly 5636->0.0177 if You need value for LS1 PCM. LS3 is different from LS2, from this we know that there is no direct math from mm2...


Does it makes sense?

GM Throttle body scalar.xlsx

[miami993c297]

I know it's old thread, but did saved it long time ago...
I am ready to install a 102mm TB.
Will the ETC Scalar number to enter be 0.0149?