Im well aware of lt1 tb Ive owned 3 of them. What im saying is that you could unbolt the iac and see what the max airflow is. Im betting you need to drill the iac port bigger in the housing. Being an engineer i see why you want to figure this out but in real life it really doesnt matter.
The greatest benefit to tuning idle on a cammed lt1 is having the iac port from the throttle body connected to the intake idle air passage which most of the aftermarket castings fail to do and just dump behind the blades instead
http://www.noid.org/~lj/PCM%20Tutorial/SplitBLMinfo.htm
Last edited by flame; 02-04-2015 at 09:21 PM. Reason: add link
Gotcha, I just usually have to point it out since there aren't many 24X LT1's.
Actually it does matter since the PCM calculates how many IAC steps to use and will command more steps than the LT1 IAC can deliver. So if I can get the PCM know that it only has ~ 200 steps, not 310, AND have it know how much area is added with each step, it will be able to better match the desired airflow its trying to deliver. Right now it isn't really that close. Does the car run? Yeah, but it could run better and I'm planning and even bigger cam in the near future, so getting the idle air tuning dialed in before hand would be nice.
I know what you're saying about the max airflow that the BBK TB that I have will deliver.
Yeah, I know LJ and Nick (noid). Started tuning this LT1 with LT1 edit many years ago. Fixed my TB with some JB weld to seal up those dump in passages and route the air to the hole in the TB. Got the split BLMS mostly fixed in the LT1 edit tune. But I am having some issues adapting that tune to the 0411 PCM.
Thanks for the thoughts. They are all appreciated.
Jason
Man I used to fight with that crap all the time...every LT1 I tuned (TONS OF THEM) had an aftermarket TB, and messed up fuel trims (BLM's) when it got to me to tune...drove me mental.Originally Posted by flame
I've taken more LT1 intake manifolds off to remove the plugs from the bottom and clean the IAC passages out than I care to remember...so many of them were full of filth.
I also used to find that tweaking the TB stop screw just a little one way or the other would help calm the split down, usually letting a little more of the idle air just go into the plenum actually seemed to work. Opposite of what LJ did, but it worked.
Last edited by MikeOD; 02-06-2015 at 07:08 AM.
2010 Camaro SS M6. Stock Bottom End, Heads/Cam/Intake/Headers/Exhaust.
2005 Silverado RCSB. Forged 370 LQ9/Borg-Forced Inductions T6 S484/Jake's Stage 4 4L80E with D3 Brake/4WD.
2023 Durango Hellcat
Jsons5555 please let me know when u square this up. id like to finally get my iac counts and idle correct in my 24x conversion
All you need to do is drill the bypass hole or make it larger if using a stock TB until your warm, unloaded IAC counts are in the 20's range and you will be fine and not have to crack your blades open creating the split. The key is getting as much air to bypass the IAC as possible, but still entering the manifold idle passages. Really no different a concept than on LS motors, you just don't have the passages to think about.
Actually there are a few differences in the aftermarket TB IAC holes and there certainly is a difference in the number of steps the IAC stepper motor can execute. So similar concept, but certainly come key differences.
Jason
I understand the differences. I've been doing LT cars since 2002 and still do 1 or 2 a month. Nothing has changed, I assure you.
Yeah I tuned quite a few with LT1 edit.... This is my first stab at tuning one with a 411 pcm...
So how are you getting the air to go into the idle air passages without going through the IAC?
Thanks,
Jason
You have to drill a hole from the front through the idle passage to the rear passage creating a bypass hole. If you look at the stock throttle bodies, they have a hole already there. Most aftermarket TBs don't because when used on stock engines it's not really an issue. Even on a ported TPIs 52mm they plug the hole. On a big cam car I usually start at 1/8-3/16 and work up until the warm IAC counts are 20s. This will allow you to keep the blades closed as much as possible and help prevent the large fuel trim split.
Last edited by ElecTech; 02-19-2015 at 08:11 PM.
Ah, I now understand where you're drilling the hole. I'll have a look at doing the same. Thanks.
Jason
I submitted two files to support with different max IAC step counts and the max IAC step count is up in the new build. Just got an email from support. The level of support and response time is great! This is for a 2001 F-body 0411 pcm. Not sure how many different OS's have the new feature.
Jason
This is na old thread, but I cant fint the MAX IAC STEP COUNTS parameter to tune my 24x conversion.
I assume it is not the IAC reset position parameter, or is it?
Using VCM Editor version 3.6.
Somebody point me in the right direction, please.
RG
Ricardo
1996 A4 FBody with LS7 swap
any updates on this?
Been waiting on this one myself.
I don't know how this popped up in my search, but it's been in the back of my mind since seeing it a few weeks ago.
I swear I saw another post that says they added access to that scalar. I'm betting it was in a different OS though.
I'm trying to find it as well......
Max steps is in software 4.0 or greater
At least for the 0411 OS I have
1997 30th SS. Torqhead 24x, TFS heads, 223/235 cam, 4l80e, S60 D1SC 14psi
Have you and do you do this to every LT1 tune you have done. In other words I guess is this a must do in your experience? I have been fighting with trying to get my 94 LT1 24X conversion to run for over three years now with no success. I wish I never would have put this in my hot rod. I am looking for answers any where I can find them. To try and save this big expensive change over. Maybe you could email me a contact email or phone number so I could ask more questions. I am not very sharp on this HP tuner stuff. Thank you.
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