2001CamaroGuy

iTrader: (6)

I have been working with my 388 all bore and a wide band for about a week now and thought I would put up what I have learned thus far (the car still isn't "tuned" but it's going in the right direction).


specs:

-388 all bore
-246/253 109 (really inefficient at idle....1000RPM is min idle speed)
-stg 3 heads (2.08/1.60)
-LT headers
-LS6 intake



My first thought was "well this engine will be so inefficient that I will need to lean it WAY out (cut the VE table) at idle." Everyone told me to cut the 400/800/1200/1600 cells of the VE by 55%, 65%, 85%, and 95% respectively. When I put a wide band on the car it was 22:1 air/fuel (LEAN!!!!!!!!!) . So I said "well let me go in and just see what the STOCK VE table would do at idle." perfect 12:1 air/fuel .


So what I learned is:

While the engine is still VERY inefficient at idle (does not like closed loop yet/ever), just by it being 42CI larger it needs as much fuel to run as it will pull as much air as a stock 346 would. The trick with a larger CI engine isn't to lean out at idle, but to richen everywhere else to make up for all the air this big PUMP moves.

NicD

iTrader: (7)

Don't forget you have a very very large cam on a 109 lsa which has a tremendous amount of overlap down low. You are pulling in so much fresh oxygen from the intake right out the exhaust ports at idle you will read very lean when in fact it really isn't. Aiming for a 14.7 A/F with your setup at idle on a wideband won't be very accurate. Your cylinder size adjustment in the PCM takes care of the "scaling" internally. A 408 that I recently tuned with a decent sized cam loves a 55/65/75 scaling on the 400/800/1200 rpm and I am running that one OL at idle. This is to prevent the computer from paying attention to the false readings the stock O2 sensors are giving telling it to richen it up because they read it as a lean condition.

monodax

2001CamaroGuy, I saw very similar results to what you saw when I did a generic scaling using the Heads/Cam formulas that were posted here. I saw around 17-19.0 A/F ratio @ idle and around 1200 RPM's and had alot of sputtering down low. I then just did what I normally do in this situation and loaded the stock VE table and did some data logging using the histrogram tables and increased the VE table as needed and got my LTFT's around -2 and the A/F ratio @ 14.7-15.0 and my WOT A/F Ratio of 12.9-13.1 depening on RPM.

But I am curious as to what Nic00Z28M6 you are saying as with the split duration of my cam 242/248 - .608/.612 - 110 lsa if it is doing what you are saying and pulling air from the exhaust ports which would cause inaccurate readings on the sensors. I have read many post about doing a hybrid setup with open loop at low RPM's and closed loop at higher RPM's when the MAF is more accurate as well but I am not sure how to setup HP Tuner's thresholds to get that scenario or if it would actually do me any good?

HumpinSS

iTrader: (1)

Did you change you clinder volume from .708 to whatever it is for a 383

NicD

iTrader: (7)

How many cubes are you running? With a lot of overlap it can be sloppy at low RPMs and can pull fresh air right from the intake and push it out the exhaust. You could be rich in the combustion process, but the O2 sensors will read it is being leaner than what it really is because of that unburnt oxygen that made it's way out. O2 sensors only do one thing, and that is to read oxygen, not fuel. But all I am saying is that with large cams with a lot of overlap will not read correctly on any O2 sensor.

monodax

I am running the stock displacement 346.