Hi all,

Tad here aka ProTools4, TurboSS, and tunedbytad on the various forums.
I have been kickin around tuning LT1s and part of the fourms since early 2000.

I have a crazy idea and wanted to bounce it off you guys before I enter
R&D mode. First a little background then the idea below.

On Boosted Lt1s there are two schools of thought for fueling I know of;

1. MAF tune
Let the MAF max out and use the P.E. table and fuel pressure rise to get
the rest of the fuel needed despite having a flat number in the pulse width
calculation.

On a personal note I have done this to good results with a rising rate regulator custom MAF and big fuel system. Works great, despite how ugly the PE RPM and ECT tables look.

2. Open loop no MAF
Speed Density tune on a 1 or 2 bar MAP. VE table and some time injector constant massaged till you get the proper AFR at all load RPM points.

I have done some Open loop tuning in my time and found it to work good but not as consistent under different conditions as Closed Loop but still very effective effective, and compinsates for over and under boosting once calibrated.

Both tuning styles have pros and cons and both can produce great results if the tune and car are in harmony. I'm not here to debate who and what is better or bad.

**Crazy Idea Break Down**

Situation:
Heavly boosted Forged LT1 with big fuel system looking for over 600RWHP and factoryesque' streetability

Goal:
To have a Closed Loop MAF Reference tune up to a pre determined boost level
then have the tune and EFI operation switch to Open Loop / Speed Density

Why:
Good Drivability and manners in CL, plus the Open ended 2BAR fueling in OL/SD for well past 600+RWHP fueling.

How: (this is the part I have questions about but should work in theory)
MAP / Boost pressure Hobbs switch activating at (say for example) a 4PSI threshold,
This activates a relay that open circuit faults the MAF via the normally closed normally open contacts!
This in theory should immediately send the PCM into Open Loop / Speed Density.
Then when boost slip back under 4PSI the relay closes the MAF circuit and the PCM return to CL.
This would require a full MAF tune and full Speed Density tune then the relay goes in the circuit.

Questions:
-is there a delay or blending when going in and out of OL/CL via fault/no fault?
-or will it take a key cycle to return to CL ?
-What wire or wires is the PCM monitoring to check for MAF fault?
-what else will faulting the MAF effect on an LT1 car? on the LS1 cars timing and line pressure...
-has anyone else done anything like this?
-does anyone else see my need to switch to and from CL? I'm sure there is going to be ppl very pro CL and pro SD stating thier case that I should not get so complicated and stay CL or SD.

if you want to chat about this on the phone call Haddad Motorsports Phone: 310.412.8032

ProTools4@aol.com
tunedbytad@aol.com

 

Well the VE tables that are used for speed density only go to 1 bar so I don't see any benefit of going to speed density when the MAF maxes. If you can put together a 2 bar speed density tune then you would be breaking some new ground and more power to you. Also you are using open loop and speed density interchangeably and they are two totally different things. It is good to see someone with some fresh ideas though.

 

It has been done! Not to big of a deal it just cut the resolution in half.

Easy with that. Kinda nit picky.

I'm trying to do something new and functional for good reason.

 

Another thing we Fbody guys need is for someone to come up with a plug and play way to make an 2000+ LS1 pcm work with our LT1's. This would be awesome because then we would be able to take advantage of all the options and upgrades Moates has done for the LS1.

 

so when you hook a 2 bar map up, your at 50kpa its really at 100 and 100 is 200? or something like that?

 

yes

 

well i might have to try that before i fork out a grand for another system