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2005 chevy trailblazer_lt_ext
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46 Posts
Discussion Starter · #1 ·
First off im not here to bash anyone so dont take this the wrong way.. But im trying to figure out if i set my expectations too high.. Constructive criticism is always welcome... So here it is..

I have an 2005 TB, 4.2 I6 EXT LS with 47,000 miles. K&N CAI, Helix TBS, Resonator delete, and a PCMforless tune i just installed... Tune is for 87 oct. With CAI, Shift point 2...

First off My top end is AWESOME now that i put the returned PCM in!!!! But i still cant even chirp the tires from a dead stop... I still have NO low end, and very little mids.. Top end is Unbelievable though!!! Am I or was I expecting too much out of the tune? Honestly i expected to pick up a bit more in the low and mids.. But they feel the same... Just top end is VERY noticable!!!

Thanks for you input on this.. No you wont hurt my feeling if im being stupid... But would love some input before i call them and make a fool out of myself for not knowing what im talking about.
THIS IS NOT NEGATIVE TOWARDS THIS COMPANY AT ALL... I HAVE HEARD NOTHING BUT GREAT THINGS ABOUT THEM...
 

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2007 chevy trailblazer_ls
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346 Posts
Sounds like torque management is still playing a good role in it. Have them remove it all next time :D
 

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2005 gmc envoy_sle
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129 Posts
It also depends on what gears you have. If like me you got the 3.42 gears for the highway mileage, then even a short wheelbase truck won't chirp the tires. At least I think it won't, it never has in the full throttle launches I need once in a great while.

ct_mike
 

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2004 chevy trailblazer_lt_ext
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i have an 04 ext I6 w/ 3.42 gears. i dont think ANYTHING i do will make this brick chirp wheels. your fighting alot of different things with this EXT. first is the I6 motor, 2nd the gearing, 3rd the added weight. once im out of warranty im gonna look into a pcm4less. ive been in for warranty work way too many times to risk them not covering something because of it.
 

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Northwest Chapter
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I havent tuned any LWB models but those I have tuned will tell you my 02 with 3.73s is much faster than their 3.42s all around. Yes Im probably blowing a mpg or 2 but it was bought to tow so the 3.42s werent the best option and 4.10s would really kill the mileage (but I didnt know this much back in Dec 01 otherwise I would have pushed hard for 4.10s). I can barely chirp my tires off the line powerbraking and running my 91 tune, it also depends a lot on your tires (Dueler Revos have aggressive tread and are heavy).

For "no low end", is it any better than stock? Or can you not tell a difference? The design of the I6 means you have to rev it a little to make power, sorry but thats the nature of the engine.
 

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2006 chevy
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2,079 Posts
My first trailblazer was a 3.42 and horrible off the line

My Rainier was a 3.73 at it lauched much better

MY TBSS with 4.10 is much more fun... lol
 

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2005 chevy trailblazer_lt_ext
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46 Posts
Discussion Starter · #10 ·
Hey everybody.. Thanks for the quick responce. I honestly have no idea what im geared at.. I was looking at some or the other forums and saw that you can look in the glove box and match the code with the respective Ratio... Funny thing is, mine didnt match any of them on the list.. I am going to go to the dealership and have them match it by VIN. Im thinking that i was expecting WAY too much... As someone asked before, NO i dont feel any difference in my low end at all... Same as the stock feel other than the much firmer shift!!!! What boggles me is that last night i went out and ran my 0-60mph times... No as you start to laugh, I know its not a SS or anything like that but its the easiest way for me to judge my performance gains with the mods that i have been doing.. Well, last night when i ran it, I actually ran an average or 3/4 second SLOWER than what i was running before!!! Same track, Same weight in the vehicle (including full take of gas, just as before), and actually 4 degrees COOLER temp. than before... ????? I would think i would run faster.. This was with 3 runs and not a single time did i even match my time from before the tune... Now i know its only 3/4 of a second.. but as i said, i thought the times would go down.. not up... It does however FEEL much faster, but im thinking that is only due to the stiffer shifting...
Again, PCMforless is an excelent company and i am still VERY pleased with my top end!!! and will definately be keeping the Tune!!! Very fast shipping and turn around time is top notch!! I will definately do business with them again!!
But, any suggestions for better low end torque?
 

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Basic Vendor- Skid Plates
2007 chevy trailblazer_ls
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3,700 Posts
The engine is torque managed in the first 2 gears... If you don't have them take out the torque management, the 0-60 will be about the same, because you're not into third gear at 60mph...

May be slightly slower right now, because the computer has not completely learned the fuel trim yet...

Mike
 

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2003 chevy trailblazer_ls
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1,236 Posts
I agree with the last poster... It will take your PCM some time to re-learn your engine's particular tuning needs. As you drive, this will become more noticable. I recently had to unhook the battery for a day, and lost the additional trims, and it took me somewhere around 500 miles to get the zip back.

About the low end torque thing -- the I-6 is the fault here, not your tune. Our engines just don't make gobs of torque down low. The I-6, with a double overhead cam and 3 valves per cylinder is built more like an Indy car motor than a V-8, they like their RPMs like sailors like their rum... :D

Also, if you left in torque management (as several others have suggested) then nothing will really improve the bottom end launch, as you are only outputting around 30% of available engine power to the rear wheels until after 3000 rpm. That, most likely, why the top end feels amazing.

FWIW, I've done what you have done, including a few transmission mods, plus I'm running 3.73 gears and I can't spin my tires off the line either. Just as well, it would only cost me tires. Put a drop of water on the road, though, and I can blaze them for a city block. Wish I had the 4.10 gears. They would be just right, IMO. I'm running 255 tires (had 265) and the extra height robs the gear ratio. The taller you go, the more gear you need.

If you really want to blaze the tires, replace the torque converter with a high stall unit and drop in some 4.10 gears. That's about the only way.
 

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Discussion Starter · #14 ·
Yep... I have 3.42 Gears. :mad: Oh well.. highway will be good. I asked for them to get rid of all torgue management and was told they wouldnt.. that they will REDUCE it but not get rid or it completely... Oh well... But now i have other issues... I replaced my spark plugs with the new E3's and now have an occasional engine shudder at idle and low speed... Not low RPMs but low speed... When im at low speed at about 2000 RPM's i feel it.. when im cruising at 70mph. with the cruise control set and again at 2000 rpm. I DONT feel it.... man, these TB's will keep you busy the more you get into them!!
 

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2002 chevy
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If you really want to blaze the tires, replace the torque converter with a high stall unit and drop in some 4.10 gears. That's about the only way.
:iagree: you would love the performance upgrade

and 4.10s would really kill the mileage
My mileage stayed the same. its worth changing to 4.10
 

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2003 chevy trailblazer_ls
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1,236 Posts
Yep... I have 3.42 Gears. :mad: Oh well.. highway will be good. I asked for them to get rid of all torgue management and was told they wouldnt.. that they will REDUCE it but not get rid or it completely... Oh well... But now i have other issues... I replaced my spark plugs with the new E3's and now have an occasional engine shudder at idle and low speed... Not low RPMs but low speed... When im at low speed at about 2000 RPM's i feel it.. when im cruising at 70mph. with the cruise control set and again at 2000 rpm. I DONT feel it.... man, these TB's will keep you busy the more you get into them!!
I'd recommend AC Delco Irridium plugs over the E3s. The I-6 engine seems to be VERY picky as to plug type. Yes, the tuning is THAT tight in the PCM.

I'm fond of several other plugs in different engines, and have had great sucess with Bosch Platinum, and +4s, etc., in Hondas and other import engines, but not in the Trailblazer.
 

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2005 chevy trailblazer_ls
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Also, if you left in torque management (as several others have suggested) then nothing will really improve the bottom end launch, as you are only outputting around 30% of available engine power to the rear wheels until after 3000 rpm. That, most likely, why the top end feels amazing.

FWIW, I've done what you have done, including a few transmission mods, plus I'm running 3.73 gears and I can't spin my tires off the line either. Just as well, it would only cost me tires. Put a drop of water on the road, though, and I can blaze them for a city block. Wish I had the 4.10 gears. They would be just right, IMO. I'm running 255 tires (had 265) and the extra height robs the gear ratio. The taller you go, the more gear you need.

If you really want to blaze the tires, replace the torque converter with a high stall unit and drop in some 4.10 gears. That's about the only way.
Figured this thread was pretty much over so I have a couple questions.

When I get the PCMforLESS tune, can I just ask them to lower or remove the torque management for better low-end HP? What will this actually do performance wise?

And how hard is it to swap 3.42s with either 3.73s or 4.10s? I read in another thread it is really costly...but how hard is the actual work?
Also...think anyone on this site would have any interest in swapping gears (does anyone want to go lower, or do people only go higher)?

Thanks
-CUBE-
 

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2006 chevy trailblazer_ls
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From my research, (I'm plagued with the economical 3.42 gears too) I've determined that the easiest way to swap gears is to swap the entire axle in the back and the differential in the front. Much less labor-intensive, and quite possible that you'll be able to make up a lot of the money by selling your existing parts. You'll need to swap both front and back if you're 4wd. You 2wd guys just need to get an EXT rear end with a g80 and call it a day hehe. www.car-part.com
 

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2003 chevy trailblazer_ls
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As was said above, no matter what you do, the 4.2 is probably never going to be a tire burner. It just doesn't make torque down low in the rpm band for that sort of action. I'm not saying it isn't possible, but to do so means a lot more work than JUST a few add-on parts. Oh, and our engines make all the power they're supposed to make -- but do so after 4000 rpm!

Gears, or a stall converter will help the launch -- both require some work and commitment to the cause. With that being said, setting up gears is just another mechanical exercise like rebuilding an engine, transmission, etc. People make it out to be some sort of exotic mystery technique that only a hand full of master mechanics ever learn, but that isn't really true.

Cost of the gears themselves will run somewhere in the $150-$200 per axle. Cost to install those gears will vary depending on the person doing the work and the labor rate. I know a man that sets up gears for a lot of the local shops around my area -- he charges $85 per axle if you carry in the axle to him ready for work. If you bring the vehicle and he has to crawl around under it, costs will run closer to $250 per axle.

You CAN install new gears into your axles at home, but you will have to invest in a couple of tools and you WILL have to master a few skills and have the patience of a saint. That is really all that is involved. Insert gears, measure, if the pattern or pre-load is not good, do it over with a different thickness of shim. Repeat process until it is RIGHT. Sometimes I get it right the first time -- total time involved is under an hour -- sometimes it takes me two days. Just breaks of the game.

Tool wise, you'll need a carrier bearing puller, which will cost you between $175 and $300 depending on which type and where you find it. I've found one source for the $175 and it is a great tool. That's the one I'm using. You'll also need a GOOD inch-pound dial torque wrench to set pre-load. That will run you in the neighborhood of $200 from Snap On -- less other places. Additionally, you'll need a dial indicator with a magnetic stand (to measure gear lash), and a micrometer (to measure shims). The dial indicator can be found at places like Harbor Freight for under $30 (works okay for the money) or Enco for under $50 (works better, and will last longer). Micrometers can be found almost anywhere, from Sears to tool trucks to industrial tool houses like Enco. I like the digital versions -- easier and faster to read.

Here is a decent set of instructions that point you in the right direction:

http://www.differentials.com/install.html

Here is a more detailed manual from Yukon Gears:
http://www.pirate4x4.com/tech/billa...Ring and Pinion installation instructions.pdf
 

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2002 chevy
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tire size can also play a roll on your acceleration. having a small diameter size tires canmakes the truck feel like your running a higher gear compare to a higher diameter size tire which makes the truck run slower off the line.

im changing mine from diameter (22in rims) 35 to 40 due to drivability on the rain and snow. could careless of the protection of the rims since they are already some scratches on them. safety is more important than racing.
 
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