LT4 Best LT4 Mods

[Stallion]

As far as the tune goes, how exactly does that work? What's to say that the factory didn't get the best parameters for a fuel ratio combine both the best performance and economy? Is there something these hand-held computers know that the GM factory doesn't?

I'm just curious, because I would like to do a tune as well, but this question seems to plague me.

 

[JEFNLSA]

As far as the tune goes, how exactly does that work? What's to say that the factory didn't get the best parameters for a fuel ratio combine both the best performance and economy? Is there something these hand-held computers know that the GM factory doesn't?

I'm just curious, because I would like to do a tune as well, but this question seems to plague me.

Really, the "tune" becomes more applicable/necessary once you start changing things ie. heads/cam/headers etc...

Some mail order tuners (ie. pcmforless) are very familiar w/ the LTx stock tune and know the things that can be adjusted in order to obtain optimum performance. In addition, they will adjust fan on/off temp settings, rev limiter etc...

You can get more out of a stock motor w/ a good tune but the whole tuning thing really comes into play once you start modding.

 

[Kevin Doyle]

Hi I was wondering how much for gears and install on your lt4? Also tell me about your clutch noisey or about the same? Love my 96 lt4! Thanks Kevin.

 

[JEFNLSA]

Hi I was wondering how much for gears and install on your lt4? Also tell me about your clutch noisey or about the same? Love my 96 lt4! Thanks Kevin.

Hi,

I think I wound up paying around $750 total for the gear swap...love 'em! As far as my clutch goes, it's noise free and a far cry from the way the original clutch felt. This clutch is excellent!

Cya,
Jeff

 

[Louis Bartay]

As far as the tune goes, how exactly does that work? What's to say that the factory didn't get the best parameters for a fuel ratio combine both the best performance and economy? Is there something these hand-held computers know that the GM factory doesn't?

I'm just curious, because I would like to do a tune as well, but this question seems to plague me.

Find a Performance shop that has tuned a C4 with the OBDII. The best way is a Dyno that has a Air/Fuel Meter. They will do a base line run and see what your HP and Torque and Air/Fuel Ratio is at the rear wheels. Then they will hook up a PC with the correct software and adjust your Air/Fuel Ratio for what ever Mod's you have done. And make another run on the dyno to see the results. Ft Worth where I live is 700 Feet above sea level so the same auto would make more HP at Sea Level. So the shop will adjust the PCM for my Borla exhaust and all the air intake Mod's I have done to add more air into the engine and adjust for the altitude that I drive at.. Sometimes they add more spark and I have a adjustable fuel pressure regulator so they can adjust it for max HP and also have my Air/Fuel Ratio set so it is the same at all RPM's. By doing this I will Gain HP and Torque over the stock GM mapping. Fans and rev limiter can also be changed while they are tuning it. Some of the shops can get close by sending then your computer and telling them what mod's you have done and where you live. PCMforless and others can get you close. But by tuning on a rear wheel dyno at your city is best and more expensive.

 

[sanjirelli]

I agree with you Louis. I just looked back at the dyno sheet (I was able to plot out the past run with the LT header runs... the first runs were plotted vs MPH instead of RPM) and in stock form I was rich then too. Right around 12.5 AFR, with a little dip to 13 between 5200-5500, right where my suspected opti break-up is, not to mention peak HP. With the headers I was richer, right along the same curve, the dip gets to around 12.2 but the break-up is still there, for the most part I was around 11.5 AFR my peak HP was almost exactally 10 less being so rich.

I didn't use an AFPR just to see if the computer could adjust for the increased exhaust flow. Well actually I changed out the airbox also, went with the SLP claw. Either way I proved, at least to me, that the computer needs a little help. The hardest thing I've found is finding a data logger that will record the data I need. This being the first year of OBD2 its a little different, my current scanner does good ... except ... no knock retard. Kinda important if you ask me. I found that my STFT's were way rich (not a good thing when transitioning to WOT) I've got them back closer to zero now, still working on a few areas, but I'll have it worked out before the next trip to the dyno. Im gonna do another dyno session before I do my cam swap just to see where the tune is. Of course after the cam swap I'll have to do it all over again. That's the fun of it though right.

Hrtbeat1,

What software package are you using for your PCM tune?

Thanks, Sanjirelli.

 

[Hrtbeat1]

I'm using CATS OBD2Tuner. You can't get it anymore, they sold the rights to Jet, its now called Jet Dynamic Spectrum Tuner, IIRC.