78MM ETC to 90MM TB - which scaler???

I had an interesting discussion with someone about Throttlebody Scaler numbers when upgrading from a stock 78MM TB on a C5 Corvette to a GM 90MM TB.

Early on, I remeber that we changed the effective area of the TB from .255 to .320

The I see that there was another school of thought

http://forum.efilive.com/showthread.php?t=2684

B4349 ETC Throttle Area Conversion to .0320 from .0255.

V7.3
Engine Cal-> Idle ->General Parameters -> B4349 ETC Throttle Area Conversion

Area = pi * R ^2

R=1/2D, pi= 3.1416

A= 3.1416 * (1/2D) ^2

For 78 mm A = 3.1416* (1/2 * 78 ) ^2 = 4778.38 mm2 = 47.78 cm2

90 mm A= 3.1416* (1/2 * 90) ^2 = 6361.74 mm2 = 63.61 cm2

63.61 cm2 ( 90 mm) / 47.78 cm2 ( 78mm) = 133.13 % increase in surface area.


Then I see another thread on the subject
http://forum.efilive.com/showthread.php?t=837

Cross sectional area of 78mm= 4776 sq mm
Cross sectional area of 90mm= 6359 sq mm

Units for B4349 are %/sq mm

100%/4776sq mm= .0209 %/sq mm for the 78mm TB
(my factory tune had a value of .02077)

100%/6359sq mm= .0157 %/sq mm for the 90mm TB

So, I'm wondering. Has anyone definitely decided if the scaler needs to be increased or decreased? I've always increased it based on an increase in area. But, the person I discussed this with was decreasing the number in his tunes. I just want to see if anyone had decided which one was correct.

It seems to work backwards. In other words, for a given change in throttle position, the larger throttle body will move more air. Because of this, the throttle doesn't need to be changed as much to achieve a given amount of air movement.

Disclaimer: This has what has worked for me.....

No, I agree with you. An increase in surface area will move more air. I know in the big cam car that I tuned, we changed not only the scalar, but also looked at the IAC steps vs Effective area because for instance you ddn't want the computer fighting to get the car to idle by swinging the electronic throttle open to far (too many steps) based ona bigger throttle blade with more airflow potential.

I'm sure with enought tuning you can get any setting to work. I'm jsut wondering if there was any consensus on which worked better, required less work to implement, and was the best overall setting.

J-Rod, welcome...:cheers:...someone will know.

Thanks. I actually joined in 2004. I've just lurked on the site until now...

133.13% increase?
I think your decimal has wandered the wrong way.
90/78= 1.15385
15.385% increase.

That was copied out of the thread itself. I believe it was posted by bink.

But, that being said I also think you might want to check your math as well since you are looking at diameter rather than area (there is a signficant difference in the two).

What you have to do is simple... Forget about the number... if you have to put there a 1.0 who cares?

1) Put the car into MAF mode 100%
2) make sure LTrims are turned off
3) Ben = 1.0
4) Log g/s
5) Log IACdes_B
6) Input Maf g/s into Desired Airflow table
7) Change b4349 untill your RAFIG = 0 or IACDes_B = MAF g/s

My last 90mm TB I inputted .0190

You are done.

Quote:

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Originally Posted by J-Rod

That was copied out of the thread itself. I believe it was posted by bink.

But, that being said I also think you might want to check your math as well since you are looking at diameter rather than area (there is a signficant difference in the two).

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My math was right (I think) :hihi:
My example was not equivalent because my point was to try
an increase/decrease by XX% of the difference in size of the TB diameter.
This is about half (15%) of what cm² (33%) should have been.
Maybe not the way to go, but if you are going to adjust across the board
by XX% it shouldn't be 133%.