Tuning a really big cam
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From: Reading, PA
Tuning a really big cam Hey guys, have you had any luck tuning very large cams in the 246/254/108 range on a stock CI LS1? The only way I can get it to work is by tuning the PCM open loop. Closed loop a/f control just does not work. This is the way I tuned my race car but I wanted to actually try to get this cam to run on the street. I know its the LS thats killing me.
Mikey
Mikey
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Originally Posted by mikey
Hey guys, have you had any luck tuning very large cams in the 246/254/108 range on a stock CI LS1? The only way I can get it to work is by tuning the PCM open loop. Closed loop a/f control just does not work. This is the way I tuned my race car but I wanted to actually try to get this cam to run on the street. I know its the LS thats killing me.
Mikey
Mikey
The oxygen that sneaks by, due to overlap, really confuses the sensors - the PCM thinks you're lean and adds fuel.
I'm not sure how the boys Down Under get around the overlap problem but I think they run the O2 sensors MAFLESS.
Oh....My cam 239/251, 106, 0.570. FWIW.
joel
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When the PCM has a tendancy to overcorrect the fueling (adds too much fuel) and sends the LTFTs +xx but the a/f meter shows otherwise. I tune open loop using the injector flow rate to get the steady state fueling right then the PE for WOT. Just disconnect the O2 sensors and deletes the codes. It's actually quite simple to do. The only down side is that you have no part throttle correction so it can adversley affect driveability and fuel economy. But then again, if you use a cam of this size, you better not be concerned about either of therse ... 
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Launching!
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From: Dallas, Tx
Mikey, once you are in open loop...log the map reading, and rpm. Then just adjust the VE table in that area, and bam! 
I have tuned a 251/247 107lsa cam in a stock head 346..and it drives perfect at 15.0:1 at part throttle..13.9 under moderate load, and 12.9 at wot. Just takes alot of playing.
Chris
AMS Racing
I have tuned a 251/247 107lsa cam in a stock head 346..and it drives perfect at 15.0:1 at part throttle..13.9 under moderate load, and 12.9 at wot. Just takes alot of playing.Chris
AMS Racing
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Verdad Gallardo I'm glad this open loop thing is finally catching on. Most people used to cringe or throw up arguments when we were tuning open loop. My personal car has not had O2 sensors on it for over a year and the majority of our BIG cam cars have been running open loop for over a year. Just to provide some legitimacy to the long term effects of running the car without oxygen sensors. Basically, there aren't any long term adverse effects.
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Originally Posted by NoGo
This site has been keeping me pretty busy.......which is good and bad rolled into one.
The tuning has been going nuts lately. The PM box gets full in about 2-3 days now.
The tuning has been going nuts lately. The PM box gets full in about 2-3 days now.
Keeps us out of trouble.joel
LTFT Learn is disabled, not the LTFTs, as I have seen it.
If you know otherwise, please correct me.
Additionally, the type of exhaust that you are running plays a big factor into this. Some exhaust / cam combinations just simply won't report LTerms correctly (with the stock O2 offset).
If you know otherwise, please correct me.
Additionally, the type of exhaust that you are running plays a big factor into this. Some exhaust / cam combinations just simply won't report LTerms correctly (with the stock O2 offset).
Last edited by NoGo; Apr 28, 2004 at 06:37 AM.
Launching!
Joined: Nov 2001
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From: Savannah, TN
Originally Posted by NoGo
That's correct. Once you throw a P0101, the LTerm Learn gets turned off.
