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Tune necessary after LT headers?

This is a discussion on Tune necessary after LT headers? within the Computer & Tuning forums, part of the LSx Technical Help Section category; I have Lt's and ORY (along with 160 therm and NGK plugs) on the way. Currently have 85 MAF (de-screened), ...

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    Tune necessary after LT headers?

    I have Lt's and ORY (along with 160 therm and NGK plugs) on the way. Currently have 85 MAF (de-screened), catback w/ QTP cutout, Lid, Z06 clutch, and 4.10's.

    I hear the Lt's will lean out seriously lean out car - will I need a dyno tune? The nearest dyno tuner is 4 hours away.

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    Token V6 Guy
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    most of the bolt on cars with headers I've seen were rich before a tune but yeah a tune would definitly be able to grab a good amount of power with your mods.

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    I have the same things on my car and i think i have experienced the richness too. I asked the local performance shop (speed inc) what they thought and they said they charge like $400 for a dyno tune so they didnt recommend spending the money and then i decided against it untill i get something that really needs a tune like a cam. But if your shop will tune your car for a reasonable amount or you have the money to do it then go ahead it cant hurt right?
    Last edited by RED02HAWK; 02-28-2006 at 03:42 PM.

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    More specifically - will my car run alright without the tune subsequent a LT header install?

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    SUPREME member-oderator oneBADDz's Avatar
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    It will run good, but it will run rich. I had to take a long highway trip (200 miles) before the computer got close to leaning it out enough not to run TOO rich, by the end of the trip there it was running lean enough again that I got back up to 26 mpg on the return trip. You'll be safe since it should run rich rather than lean, but a tune would still be a good idea when you can get to it. I heard that a MAF leans it out? If that's true your maf alone should help you out with running rich anyways, but I don't know if that's true or not -but I'd like to know if someone could pipe in with an answer

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    I've been running my lt's for about 1 and a half yerars and havent had a problem yet. Although my car runs hell a rich. But cant go bad when you can hit 12's right? Anyway don't worry about tunning headers or small bolt ons like that, as stated above wait till you have something worth while like heads and cam or even just the cam alone.

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    Token V6 Guy
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    the maf & o2's will keep your a/f from going rich at idle...just because it smells like gas doesnt mean your rich...it just means you probably dont have cats

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    Yea, cats and 02 sensors will play a huge roll in running rich. I have no cats and 02 sims in place of the rear 02 sensors so im still a bit rich because the computer thinks everything is fine from the sims so i wont be getting 26mpg like Zdriver with out a tune. And also true about the MAF i got an 85mm one and put it in before the Lts came and my CEL light came on and i had it checked out and it was running lean so i took it off until the LTs came.

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    Tech Junkie hammertime's Avatar
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    At part throttle, just driving around town, the computer should be in closed loop. Therefore, no matter what mods you have done, the PCM will always attempt to keep the A/F ratio around 14.7:1 for both mileage and emmisions.

    As I understand it, its when you go WOT and you revert back to the VE table that the car is running richer from the header install. I'm sure someone will come along to correct me if that is wrong.

    Also, O2 simms don't change a thing for the A/F ratio or drivability. Their sole purpose is to monitor the catalyst efficiency for emmisions reasons. With the converters doing their jobs, the output to the rear O2 sensors will always be the same, which is essentially what an O2 simm does - sends a dummy signal back to the PCM.
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    Quote Originally Posted by hammertime
    At part throttle, just driving around town, the computer should be in closed loop. Therefore, no matter what mods you have done, the PCM will always attempt to keep the A/F ratio around 14.7:1 for both mileage and emmisions.

    As I understand it, its when you go WOT and you revert back to the VE table that the car is running richer from the header install. I'm sure someone will come along to correct me if that is wrong.

    Also, O2 simms don't change a thing for the A/F ratio or drivability. Their sole purpose is to monitor the catalyst efficiency for emmisions reasons. With the converters doing their jobs, the output to the rear O2 sensors will always be the same, which is essentially what an O2 simm does - sends a dummy signal back to the PCM.
    for the most part your absolutly correct...the only part thats off is about wot...over 4000 rpms the computer relys on the maf to determine what #'s to pull from their respective tables...with cot active not to mention the factory setting of ~11.75:1 a/f ratio you will go rich in most cases at wot. Part throttle is a different story as mentioned...as long as you have working front o2's they will do a pretty good job to keep you at 14.6-14.8:1 at all times...most of the time when people say they are running rich its because they removed their cats and are just smelling the exhaust biproduct that cats alleviate...its not that their car is rich its just that they've never smelled what stoich smells like with no cats.

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    Quote Originally Posted by foff667
    for the most part your absolutly correct...the only part thats off is about wot...over 4000 rpms the computer relys on the maf to determine what #'s to pull from their respective tables...with cot active not to mention the factory setting of ~11.75:1 a/f ratio you will go rich in most cases at wot. Part throttle is a different story as mentioned...as long as you have working front o2's they will do a pretty good job to keep you at 14.6-14.8:1 at all times...most of the time when people say they are running rich its because they removed their cats and are just smelling the exhaust biproduct that cats alleviate...its not that their car is rich its just that they've never smelled what stoich smells like with no cats.
    Now I understand the the whole concept of the o2's ect. but I say that my car is running rich because since the header install my gas mileage has dropped signifficantly from 22mph city to 16mph city, no joke, now this happened gradually. Now my question to you is if a car is running rich it is safe to say that it is using more fuel correct? Now would the richness of the a/f mixture in any way hinder top end power where I believe a/f ratios are critical? Please correct me if I am wrong.

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    Did you get coated headers? If so, you've probably fouled the O2's and they aren't reading correctly.
    Second: a tune is always helpful after any mod. With LT's, it's good because you can not only make more power, but you can also turn off SES codes and whatnot. Compared to stock exhaust, an average gain from LT's will probably be 5-10 more hp and 5-10 more lb-ft of torque with a tune that without one.

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    Tech Junkie hammertime's Avatar
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    Quote Originally Posted by 98-NBM-Z28
    Now I understand the the whole concept of the o2's ect. but I say that my car is running rich because since the header install my gas mileage has dropped signifficantly from 22mph city to 16mph city, no joke, now this happened gradually. Now my question to you is if a car is running rich it is safe to say that it is using more fuel correct? Now would the richness of the a/f mixture in any way hinder top end power where I believe a/f ratios are critical? Please correct me if I am wrong.
    If you are logging data, that would tell you what A/F ratio you are running at, or at least if the O2's are reading properly. I should say, if you are logging data from a wideband, that would tell you what your A/F ratio is.

    I'm with jimbo98z. I've heard several people say that they've had to replace the O2's after installing coated headers.

    Thanks foff667 for keeping me in check - I'm still learning this stuff too.

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    I have the hooker LTs coated and havent had a problem with them fouling out. I do have the 85mm MAF though so i think that helps. I just figured more air out allows for more air in.

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    Quote Originally Posted by jimbo98z
    Did you get coated headers? If so, you've probably fouled the O2's and they aren't reading correctly.
    Second: a tune is always helpful after any mod. With LT's, it's good because you can not only make more power, but you can also turn off SES codes and whatnot. Compared to stock exhaust, an average gain from LT's will probably be 5-10 more hp and 5-10 more lb-ft of torque with a tune that without one.
    how would coated headers affect your o2's as compared to uncoated...explain please.

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    95+% of people that run longtubes use ceramic coating. This will not hurt your O2's. There are several reason's that people end up with O2 problems after installing longtubes, and the ceramic coating isn't one of them.

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    Quote Originally Posted by SLOW346
    95+% of people that run longtubes use ceramic coating. This will not hurt your O2's. There are several reason's that people end up with O2 problems after installing longtubes, and the ceramic coating isn't one of them.
    i know i just wanted jimbo to explain his reasoning...I like to

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    I am new to the board, I have a 02 WS6 with a 6 speed. With the LT's I am having a problem with the SES light. I had the code read and it's shooting 3 o2 codes. I replaced the o2's and reset the light but it came back on in three days. Any suggestions as to how to fix this problem?

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    Tuning

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    Would a hand held tuner be able to make the adjustments I need? ie air fuel ratio
    Thanks for the help

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