For ETC tb's; Interesting observations regarding ETC throttle area conversion

[ArKay99]

I have been looking at this a bit recently since I now have a good tune in the car, I naturally have to find ways to tweak it, because I can.
I recently read a thread started by Redline Motorsports Redline MotorSports threadand one of the contributors, DrX, had very good insight and helped with some calcs to narrow this down. I took a look at my stock settings for my operating system (12221588 - 2002 Z06) and what I ended up with. I also looked at a stock 99 C5 values and they were the same. They both were .0255. I looked at the units as per DrX's illustration and they didn't match. When I found the root of the calculation of .0255 I came up with ~70.65mm for the throttle area. I had a stock -ported 78mm throttle body in the basement and got the caliper out and started measureing. I found that the overall outside measurement was ~101mm. The inside overall at the lip was 94.5mm. The opening at the back of the throttlebody was 78mm and the operating area of the throttle blade was 75.1mm. The throttle blade itself is 75mm. These measurements are subject to the accuracy of my caliper and my ability to get it at the correct spot. The inside of the throttlebody right in front of the blade, where the rise is is ~73mm. So where is the last 2.35mm? I looked at the blade sitting at rest and it is open ~10% giving an elliptical cross-section to the incoming air. If I eyeball measure this cross section with my caliper I get slightly larger than 70mm.
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The difference in cross sections from closed to open is ~6%. When my car is idleing nicely my throttle position reads close to 6%. I don't know if this correlates but maybe worth noteing.
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I haven't done anything with my 90mm throttle body, because I have to take it off to make these measurements. I'm thinking of trying some value between 6% and 0% for this throttle body and figureing the ETC parameter from there. When I get a chance later, I will report what I've found.

[Redline Motorsports]

I just made a spreadsheet to figure the area vs. different throttle openings. I am not sure how GM came up with those values so if you look at that value as a root number and change it by the perecentage of difference, I think we are OK.

The difference between a 90mm from a 78mm is 24.89%. I think by changing that value by that amount should be it. If we understand that table properly it is telling the PCM the current throttle area.

I have a 01 ZO6 that we are going to be tuning with a 90/90 setup so I am going to try this again..

[redhardsupra]

care to post that spreadsheet?

[DrX]

I have seen the .0255 B4349 value in some calibrations. I actually removed a reference to it from my response in the other thread for the sake of simplicity. As you have stated, and according to the formula presented, this would represent a throttle diameter of 70mm. The formula only applies to throttle bodies in which the radius is constant throughout the circumference. Some throttle bores may be elliptical or have mutiple radii, such as the SSR TB which has different radii for each of the top and bottom halves. I would like to see the .02077 and .0255 TBs side by side. There must be some differences.

[Redline Motorsports]

How come some years the value is zero?

[DrX]

What year/vehicle? This only applies to ETC vehicles. Otherwise the IAC parameters will apply. Unless you aren't showing enough decimal points.

[Redline Motorsports]

What year/vehicle? This only applies to ETC vehicles. Otherwise the IAC parameters will apply. Unless you aren't showing enough decimal points.

Yeah I agree......but I was looking at a 99 file earlier today and the value was 0.0 which means you are correct and there might not of been enough decimals!

[Redline Motorsports]

Another sucessful 90mm ETC tune last night!

2001 ZO6, big head cam setup with a 90mm TB on a modified LS6 intake. Started with stock idle parameters accept the effective throttle area which I changed to .0157.

Hit the hit and it idled like a champ with no other changes. I logged the warmup up to operating temps to check the DAF rate. Warm startup the car fluttered a bit so I raised the DAF at from 133 F up by .500 and it starts up perfect.

The B4349 table seems to be really resolving my 90mm TB tuning issues. I would like to hear more guys trying this table with the 90 setup.

Very happy!

Howard