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lt1 tune with afr?

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Old 05-15-2018, 08:26 PM
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barchetta1
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Default lt1 tune with afr?

anyone know if changing the two afr values shown here on the lt1 motor will cause the system to strive to run at the entered value? For example if I change these to 12.9:1 which I believe is ideal for 93 pump fuel will the system lean all the fuel tables out while in closed loop?
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Old 05-15-2018, 08:47 PM
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No it will not lean the fuel tables, if anything it will richen up the mixture but what those settings are used for calculations on warm up and WOT settings. The richer the number the more fuel is added at warm up at throttle transitions. Keep it at 14.7 for gas.
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Old 05-15-2018, 08:50 PM
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Originally Posted by bjankuski View Post
No it will not lean the fuel tables, if anything it will richen up the mixture but what those settings are used for calculations on warm up and WOT settings. The richer the number the more fuel is added at warm up at throttle transitions. Keep it at 14.7 for gas.
I wasnt expecting it to lean it, I was expecting it to richen it.

So is there an across the board setting when warm? Id like to adjust for 93 octane only. Anyone publish an LT1 tuning guide? for example; where did you get your information?
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Old 05-15-2018, 08:52 PM
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Sorry I see why you said it wouldnt lean it.. I meant to say richen in my original post.. ugh..
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Old 05-15-2018, 08:53 PM
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I also have e85 readily available.. so just checking my options. I assume gm was walking the fine line between meeting EPA and power. Id like to go with power not economy. Would also presume running richer would cool the motor.

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Old 05-15-2018, 09:05 PM
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pm me your email and I will send you the complete tables from an LT4 to look at. I have not gone through and checked all the differences, there are some, but I didn't look to see what they were yet.

DO NOT PUT THE LT4 tables into your LT1 PCM or bad things will happen, especially regarding the transmission. but you will be able to look at it, and offload it as a text file and go through comparing them both. it might give you some clues (if there are tuning differences) that GM did for the LT4 having more HP.

I am going to do the same when I get time.
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Old 05-15-2018, 09:36 PM
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Originally Posted by drcook View Post
pm me your email and I will send you the complete tables from an LT4 to look at. I have not gone through and checked all the differences, there are some, but I didn't look to see what they were yet.

DO NOT PUT THE LT4 tables into your LT1 PCM or bad things will happen, especially regarding the transmission. but you will be able to look at it, and offload it as a text file and go through comparing them both. it might give you some clues (if there are tuning differences) that GM did for the LT4 having more HP.

I am going to do the same when I get time.
Will do so.. but I found this info which is really really good:

http://www.lt1pcmtuning.com/tips/

Would seem to me that the lt4 would be drastically different because the cam and cyl heads are different.. not to mention valve size and other factors.

My thought is though like I said that there is some power to be had and at a minumum lower operating temps at the cost of fuel economy. Id prefer to preserve my motor over fuel economy. I can tell that the lt1 was tuned to run very very hot. Hell, the fan values alone show you that gm really wanted it hot to burn every last molecule and keep the cats lit up.

thanks.. will pm you..
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Old 05-15-2018, 11:12 PM
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Originally Posted by barchetta1 View Post
anyone know if changing the two afr values shown here on the lt1 motor will cause the system to strive to run at the entered value? For example if I change these to 12.9:1 which I believe is ideal for 93 pump fuel will the system lean all the fuel tables out while in closed loop?
Even if those values did what you want them to do, they couldn't accomplish your goal because your narrowband O2 sensors can't measure 12.9:1
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Old 05-16-2018, 12:44 PM
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Originally Posted by Vis Croceus View Post
Even if those values did what you want them to do, they couldn't accomplish your goal because your narrowband O2 sensors can't measure 12.9:1
Agreed.. after researching this I have to find the area where I can fool the PCM into thinking a different voltage means leaner to make it go richer

still working on that.
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Old 05-16-2018, 01:22 PM
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Originally Posted by barchetta1 View Post
Agreed.. after researching this I have to find the area where I can fool the PCM into thinking a different voltage means leaner to make it go richer

still working on that.
Narrow band only report conditions to indicate too rich or too lean. If you are really serious about this, and have the budget, you could get a set of widebands, have the bosses welded to the pipes, use a gauge (or datalogger) and tune the car that way.
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Old 05-16-2018, 02:12 PM
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Originally Posted by barchetta1 View Post
Agreed.. after researching this I have to find the area where I can fool the PCM into thinking a different voltage means leaner to make it go richer

still working on that.
What are you trying to do? You can change the commanded WOT AFR in the tune, no need to fool anything. If you want the engine to run cooler change the fan on/off setting. As far as cruising AFR leave it at stoich, no reason to make it leaner or richer, won't make a difference on how hot the engine runs.

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Old 05-16-2018, 03:19 PM
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Originally Posted by bjankuski View Post
What are you trying to do? You can change the commanded WOT AFR in the tune, no need to fool anything. If you want the engine to run cooler change the fan on/off setting. As far as cruising AFR leave it at stoich, no reason to make it leaner or richer, won't make a difference on how hot the engine runs.
Ok thanks. Im just going to leave it stock then if there is nothing to gain by tuning for 93 octane and richening up slightly to keep the engine cool. I raced for years with SCCA and this is what we did with stock class cars but sounds like it doesnt apply to the LT1.

thanks for all the replied.
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Old 05-16-2018, 04:13 PM
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Originally Posted by barchetta1 View Post
Ok thanks. Im just going to leave it stock then if there is nothing to gain by tuning for 93 octane and richening up slightly to keep the engine cool. I raced for years with SCCA and this is what we did with stock class cars but sounds like it doesnt apply to the LT1.

thanks for all the replied.
Let me answer what I think you are after. Usually the factory has conservative timing and a richer then required AFR at WOT. If you are looking to pick up some power with a more aggressive tune, lower your fan setting to 200 on and 195 off, increase your WOT timing from 3000 RPM and up to 36 degrees, and reduce your WOT AFR to 12.7 to 1. These setting are in the ball park but you really need a dyno to see what your car really likes. You should also use a WB AFR meter to determine where your current AFR is.

This is the AFR and timing on a 1995 LT1 that I tuned on the dyno.



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Old 05-16-2018, 06:15 PM
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Originally Posted by bjankuski View Post
Let me answer what I think you are after. Usually the factory has conservative timing and a richer then required AFR at WOT. If you are looking to pick up some power with a more aggressive tune, lower your fan setting to 200 on and 195 off, increase your WOT timing from 3000 RPM and up to 36 degrees, and reduce your WOT AFR to 12.7 to 1. These setting are in the ball park but you really need a dyno to see what your car really likes. You should also use a WB AFR meter to determine where your current AFR is.

This is the AFR and timing on a 1995 LT1 that I tuned on the dyno.



Yes, that is what I was after and thank you. Was a bit like pulling teeth but we got there. The only other item that would be on my wish list would be how to richen the lt1 when its in closed loop to cool it. I realize Ive been corrected in that Ive been told I cant cool an engine by richening the mixture but that statement is very false and I dont want to argue about it. So I just bailed and I will take care of it myself somehow.. So thanks.. this is very helpful.

Was this tune for a modified motor?
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Old 05-16-2018, 06:25 PM
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By the way.. these are the settings I pulled from my pcm.. look awfully close to yours in some areas.. some not.. think someone has been in it?
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