LS2/7 ETC TB startup

[Bruce Melton]

Assuming a 402 (C5 ETC) moving from 78mm/LS6 to a 90mm LS2TB/L76 setup what should be changed and maybe a starting value going in?

B4349 ETC throttle area conversion>?
B4403 IAC effective area>?
B4307 Desired airflow>?
Other>?

I have seen various attempts to calculate B4349 and they are all over the map from leave it alone @.0255 to .0157 to .0330.
Can someone point me in the right direction on the above?

Did this recently with a LS7 and am not sure my approach was from the proper starting point re. above values.
RAFIG scan values we half ~7 vs~3 in B4307.
IAC steps were maxed.

Desired airflow is really the air required to provide a AFR that works @ idle? Thus if you AutoVE the idle to run @14.7 then the Desired airflow is used to lean beyond the ~14.7 due to cam overlap?
When you enter the B4307 values will it go there absolutely or will other factors contribute to a commanded blend shown in RAFIG?

(engine specs in sig below)

Thanks,
Bruce

[Redline Motorsports]

Bruce,

Not for nothing but I have had a couple C5 ETC cars that we installed 90/90's on in which we changed B4349 from .0255 to .0157 and nothing else and the cars ran and acted like stockers!

This is a great topic which seems to constantly be a debate. My thought is that this parameter is there to tell the PCM the actual area of throttle bore it is working with. We know at .0255 that the car runs fine. If you increase the throttle bore the effective area is increased and if the PCM doesn't know it, it is seeing more air then it is expecting.

I also look at this table kind of like the IFR table. If all you did was install 30lb/hr injectors in a car that had 26lb/hr, the change in the IFR table will keep all other tables in check and the car should be where it was before the change. Now granted we know there are other tables like injector timing etc... that sometimes have to be trimmed but you see my point?

Somewhere I did a whole math runout that got the .0255 to .0157, I'll have to see where it is.

Howard

[Bruce Melton]

Howard,
I have put Fast 90s with LS2 TBs on Vettes with no value changes, but when you change displacement and all it does not sort out as well (even when you change cyl vol).
We need a proper starting point.
The LS2, and probably LS7 stock tunes do not seem to have a TB area (b4349) yet it seems the lower than .0255 values inhibit the ability to "find idle".
I Explored this with Marcin and he does not have personal experience in this area but he was told to increase the effective area value by 48%! Logically it would seem that 90/78= ~15% = ~.0293 (.0255 stock value for 78mm) ? Anyway, larger rather than smaller value.

[redhardsupra]

it's not 90/78, it's area of a circle we're comparing here, and areas of circles have r^2 not r in them, so it's 90^2/78^2

[Redline Motorsports]

Regarding the effective area when going from a stock to 90mm on an ETC car;

I was under the assumption that the effective area is directly related to the area of the throttle blade. Based upon this I have done this math;

Pi*radius (squared)

90mm/75mm

(Pi*45*45)/(Pi*37.5*37.5)
(6361.725)/(4417.864)
1.44 or 44% change to the effective area

I don't have my 'black book" of notes but I think I ended up at a value of .0157 for effective area with the 90mm.

I have experimented with several cars with 90's and with just changing that parameter alone took car of 90% of the idle issues with a 90. The classic high idle touchy throttle goes away and most of the other idle parameters need either none or little adjustment. It would make some sense that as long as the PCM knows the new effective area that it would rescale all other tables so they wouldn't need to be stretched dealing with the larger area. I guess kind of like changing the axle ratio on an automatic and its effects to the entire shift schedule..

From a previous post I had out there.

[Bruce Melton]

it's not 90/78, it's area of a circle we're comparing here, and areas of circles have r^2 not r in them, so it's 90^2/78^2
I knew that just did not apply it :master:

So:
78= 4776
90= 6361
133%(.0255)=~.0334

[redhardsupra]

Redline:
you can drop the PI and /2 from both terms, since they're gonna cancel each other out anyway, then you're just left with d1^2/d2^2

how do you go from the ratio to the 0.0157 number and what units is it?

[Redline Motorsports]

RHS,

I found some old notes from a while back and this is what I had;

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

Units for B4349 are %/sq.mm

100%/4776 sq.mm= .0209 %/sq.mm for a 78mm TB (many factory tunes are at .02077)

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

It is assumed that the engines airflow requirements haven't changed if the TB was the only thing changed. By changing B4349 it should put all the other parameters in perspective. I'm sure theres a bigger formula inside these PCMS which use B4349 to scale the other parameters. This again is just my thoughts and is open for abuse!

Howard

[Bruce Melton]

From the repository it looks like most stock Camaros and Corvettes are .0255 and trucks are .0208.

[Redline Motorsports]

From the repository it looks like most stock Camaros and Corvettes are .0255 and trucks are .0208.

Like I said......kind of a made up theory that seemed to have worked! Still looking for more views on it. We need a GM engineer to chime in!

Howard

[redhardsupra]

made a quick lookup spreadsheet, let me know if it reflects what we've been discussing here, what else you'd want it to do, etc...

http://www.marcintology.com/tuning/TBresizing.xls

[Bruce Melton]

The spread sheet will be more relavant once we figure out how the B4349 value is calculated.
I have a feeling it has a expected airflow factor in it ??
I ran some tests today and by singularly increasing my B4349 from .0255 to .0355 my car goes from a dead stall at 178* (CL transition) with no possible idle to almost perfect idle. I realize that is the opposite of Howard's experience which is ultimately confusing.

As it says at the top of the table:
"Used to convert a desired throttle area from square millimeters to ETC motor position"

[SSpdDmon]

I sent an email to Bruce with the following. Hopefully, he'll try some changes and see some positive results.



IDK much about ETC's or B4349. But after taking a peak, the way I understand it is this: The PCM calculates an "effective area" from the desired idle airflow in B4307. The PCM then needs to convert that effective area into a percentage for the ETC motor. That's where B4349 comes in. It tells the PCM it needs to open the ETC 0.0255% for each additional square milimeter of effective area required to maintain or correct idle. So, in theory, increasing B4349 is going to create bigger steps, which is going in the opposite direction that you would want it to, right?

Example - Say the PCM wants a hair more airflow and it tells the ETC to open up one notch (+.0255% in stock form). If you have a bigger throttle body than before, that 1 notch is going to let in more air than it used to because the ETC is still turning the blade the same amount. Only this time, there's more "open area" than before above and below the bigger TB blade for air to pass through. So, in my theory, B4349 should be reduced slightly for the bigger TB. I assumed a 15% difference (90/78=1.15) and decreased B4349 accordingly to .022172%.

IDK if I'm right, wrong, or indifferent. But, that's what I got out of looking at the tuning software.

[Redline Motorsports]

I sent an email to Bruce with the following. Hopefully, he'll try some changes and see some positive results.



IDK if I'm right, wrong, or indifferent. But, that's what I got out of looking at the tuning software.

SS,

Our numbers are different but the thought process is the same. I agree that the values need to go smaller for going larger in throttle area. The values I posted above have just amazed me on a few C5's. I mean cars I fought with changing all kinds of parameters and couldn't get a decent control of the 90. I returned all the values back to stock and changed B4349 to .0157 and the cars fired right up and ran like stock.

I guess the biggest problem we have is truly understanding the values of these parameters and how GM got them.

Howard

[Redline Motorsports]

made a quick lookup spreadsheet, let me know if it reflects what we've been discussing here, what else you'd want it to do, etc...

http://www.allmod.net/hpt/TBresizing.xls

Nice job putting that together. Do you think this "theory" makes sense? I have had good luck this far.....

Howard

[SSpdDmon]

After thinking about it a little more, I decided to re-crunch the numbers. My geometry skills were a little lacking at 10:30 last night, but then I remembered it's not a straight 15% translation because the area of a circle is Pi*Radius Squared. So, here's what I came up with (similar to what you had...but slightly different):

Area of 78mm: 4778.362

Area of 90mm: 6361.725

Area Difference (90mm/78mm): 1.331361

Stock value divided by difference (0.025497/1.331361): 0.019151

That (0.019151) should be the value of B4349. The other value (0.015) might be the true area calculation. But, I think the GM engineers incorporated the fudge factor here. If you look at the IAC Effective Area table, it's not linear - the lower portion is skewed higher. I think they did the same thing with the ETC conversion. Either way, the true setting for B4349 should fall somewhere between what we have both calculated. If one works better than the other, then pick the better one. That's JMO...

Bruce, can you update the tune I sent with the 0.019151 B4349 value and keep all other changes that I made? Let me know how it does...

Best Regards,
Jeff

[Redline Motorsports]

Looks like it might be making better sense.

I have a couple 90mm installs coming up on cars we have modded and tuned prior. I am going to just change this value only and see how the car reacts to further back this up.

[Bruce Melton]

:Eyecrazy: This is becoming a twisted obsession.

I ran two tunes this AM.

1. Jeff's (SSpD) ran better than my previous as I have detailed in an email to him.

2. On the bazaar side, I ran my previous tune with only a change from .0330
to .0350 and it ran almost perfect. Best yet.

I will try to get VE tuning underway this PM and see what effect that has.

[Bruce Melton]

Finished tunes on my 402 and a LS7, both with ported L92 heads-L76 intake-90mm LS2 TB and biggish cams.

In both cases they would not idle with B4349 <.0335. Both idled pretty well with .0355 with otherwise stock RAF settings and I would say flawlessly with .0335 and SSpdDmon's idle setting tweaks. Solid idle, no dips after rev, no hanging etc. In both cases I went back after good results and entered various<.0255(stock) B4349 values, and the engine would not "catch" idle ie the RAFIG would stay @0 and pedal had to be used to keep engine running.

These are high flowing intakes and heads so maybe they are not typical of all 90mm ETC TB combos but I have to say the higher vs lower B4349 values are the only thing that worked. Just my results-

[SSpdDmon]

Good to hear! :)

[VortechC5]

Just as another data point in this discussion...

I just fired my new 427. I am running a 230/242 115 cam, ported L92 heads, and the L76 intake/tb. I used the .0355 value that Bruce has been using. My car fired right up and idles fine.

Mark

[01Blackerado]

Does this same rule apply if you were to only change displacement, cam, heads, etc...or only when face with an intake/TB swap?

[01Blackerado]

Wow, I think after all this reading i finally understand lol...Do you guys think it has anything to do with displacement too!?!? I mean think about it, a bigger motor needs more air, so the amount of IAC effective area you place will differ from that as well. We know that the IAS motor makes steps to allow a certain amount of airflow for every step the motor takes. Well on a 5.7l motor it doesn't need as much air as a 427 or 402. So since the 90mm TB is more of an over kill compared to the stocker then you have to open the blade less, which is why the lower numbers work for the smaller dicsplacement motors. When you up the cubes and created a giant vaccum, t uses alot more air and therfore requires you to add a percentage to the motor step to allow more air to your larger displacement!! Maybe...thoughts anyone?

[Bruce Melton]

Only with LS2/7 90 mm TB.