info on VE for big CI LS1s
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From: Phoenix, AZ USA
info on VE for big CI LS1s 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.
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.
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.
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From: Atlanta, GA
Originally Posted by Nic00Z28M6
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.
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?
Originally Posted by monodax
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?
Last edited by Nic00Z28M6; Aug 15, 2004 at 06:53 PM.
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From: Atlanta, GA
Originally Posted by Nic00Z28M6
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.
I am running the stock displacement 346.
