Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum banner
1 - 20 of 30 Posts

·
Registered
2005 gmc envoy_sle_xl
Joined
·
78 Posts
Discussion Starter · #1 ·
Ok guys....I just got my envoy a few months ago, so I'm not too familiar with the engine, etc. I'v been reading on here that if you go up to a 3" exhuast that you need to get a retune. I'v also been told that the stock exhaust size is 2.75". Is a 1/4" really going to make that much of a difference? What is it with the envoy that requires a tune when you go up to a 3" system? Does it run too lean? If this has already been explained, i'll gladly read the link to it. Thanks....oh and if it does need a retune, is there a program that allows you to do it yourself, and if not, whats the most common place people turn to?
 

·
Registered
2003 chevy trailblazer_ls
Joined
·
1,236 Posts
The bigger question is why the 3" exhaust. It really won't add much to the vehicle performance, and unless your exhaust is just needing replacement, there are probably better places to spend a couple hundred bucks.

It isn't going to sound better, and it probably is going to run worse.

I've covered this before in other exhaust threads, but the deal with exhaust sizing is to attempt to design a scavanging system. Too large a tube is akin to having a big hose on a vacuum cleaner. Yes, you can freely pass large items through that hose, but the speed of that item will be slower and the suction will be less than if the same vacuum draw is done through a smaller diameter hose.

Also, note that many people get the backpressure thing wrong. We don't want backpressure, so many think going big is the way to eliminate it, then when they go too big, they blame their failure on the fact that there isn't enough backpressure. That is really backwards thinking. What is missing is the pulse of one exhaust stroke drawing the next along with it through the exhaust pipe so as to flow more than if just exited to air without any pipe. A properly sized system (in this case, the factory got it just about perfect!) is better than a big x huge system.
 

·
Registered
2005 gmc envoy_sle_xl
Joined
·
78 Posts
Discussion Starter · #4 ·
so then would it even be better to go with a 2.5" exhaust? And i'm not looking to get a huge amount of performance or anything, just some sound and a little performance. Trust me after having my first truck I'v realized that the exhaust doesn't give that much performance (especially when ur pushing 33" tires)
 

·
Registered
2003 chevy trailblazer_ls
Joined
·
1,236 Posts
You probably won't find much in the way of performance gains via the exhaust on a 4.2 Trailblazer platform. It is about perfectly sized, and flows like crazy.

Same deal with sound. If you search around this forum some, you'll find guys doing anything/everything to get "that sound" out of the I-6 engine and it just won't do it. All it does is get buzzy like a ricer. Why? Essentially, it is very similar to a ricer design. We have a double overhead cam straight 6 cylinder with one intake and two exhaust valves using variable cam timing. It just doesn't "rumble." It also doesn't make power low in the rpm band, and it is not a torque monster that can roast the tires at will. Just the nature of the beast.

Now, with a good tune -- and the PCM for Less tune has already been suggested -- a resonator delete, and a CAI (I like True Flow), good synthetic oil (I like Amsoil) and a fresh set of AC Delco Irridium plugs, you are about as hot as you can get without spending mega-bucks (and I mean MEGA). Add a few treansmission goodies like the Vette servo, a .490 boost valve, and synthetic oil. It will get crisper, more drivable, make a bit more noise, get a tad better economy, and make it reasonably fast on the freeway. It will have a bit of a kick in the pants after 3000 rpm.

So, instead of spending about $400 on an exhaust, send in the PCM for about $150, get a CAI for about $200, do the rest for a few bucks here and there, and drive it.
 

·
Registered
2008 chevy trailblazer_lt
Joined
·
619 Posts
You probably won't find much in the way of performance gains via the exhaust on a 4.2 Trailblazer platform. It is about perfectly sized, and flows like crazy.

Same deal with sound. If you search around this forum some, you'll find guys doing anything/everything to get "that sound" out of the I-6 engine and it just won't do it. All it does is get buzzy like a ricer. Why? Essentially, it is very similar to a ricer design. We have a double overhead cam straight 6 cylinder with one intake and two exhaust valves using variable cam timing. It just doesn't "rumble." It also doesn't make power low in the rpm band, and it is not a torque monster that can roast the tires at will. Just the nature of the beast.

Now, with a good tune -- and the PCM for Less tune has already been suggested -- a resonator delete, and a CAI (I like True Flow), good synthetic oil (I like Amsoil) and a fresh set of AC Delco Irridium plugs, you are about as hot as you can get without spending mega-bucks (and I mean MEGA). Add a few treansmission goodies like the Vette servo, a .490 boost valve, and synthetic oil. It will get crisper, more drivable, make a bit more noise, get a tad better economy, and make it reasonably fast on the freeway. It will have a bit of a kick in the pants after 3000 rpm.

So, instead of spending about $400 on an exhaust, send in the PCM for about $150, get a CAI for about $200, do the rest for a few bucks here and there, and drive it.
:iagree: I couldnt of said it any better. :yes:
 

·
Registered
2005 gmc envoy_sle_xl
Joined
·
78 Posts
Discussion Starter · #7 ·
well.....then that it is.....i didn't know it wasn't a good idea to throw an exhaust on it.....but then i wonder why my 4.3L didn't sound like a ricer???? I mean, it's essentially the same engine
 

·
Banned
2003 gmc envoy_slt
Joined
·
7,190 Posts
Nope. Your 4.3l V6 is more like a Chevy 350 OHV with the front two cylinders cut off. OHV without DOD has a much different sound.
 

·
Registered
2005 gmc envoy_sle_xl
Joined
·
78 Posts
Discussion Starter · #9 ·
well definetly good to know. Didn't think that there was that much of a difference to it. At this point....i'm lost as to what to do as far as an exhaust. Do I put one on, don't I? I was going to stick with the 2.75" stock exhaust size, using a magnaflow 59958 or 59928 cat, either the dynomax 17797 2.75" in/out, Cherrybomb 7475 2.75in/2.5out, Jones V415A 2.75in/out, with the tubing to match. Ok so if it makes a difference to have this info, the dynomax is a turbo style internal construction, the cherrybomb is wing plate design, and the Jones is a perforated tube. I figured, since there needs to be a backpressure in these engines to help them run right...if i was going to up the flow from the cat that maybe a 2.5" out would help kind of cancle it out. Call me an idiot if i'm completely wrong, but it was worth a shot! So basically, is that too free flow for this truck and would it totally screw me with less backpressure? And with any of these systems would it still be NECESSARY to get the PCM done???? Or can i see an improvement in sound and a little performance without the tune???
 

·
Registered
2003 chevy trailblazer_ls
Joined
·
1,236 Posts
Again, if you just want to replace the exhaust, go ahead, but don't expect any real improvement in performance or sound.

Also, as I wrote above, the engine does not need "backpressure" and in fact, our exhaust system may be one of the lowest backpressure exhausts I've ever seen come on a factory vehicle. It is HUGE for the size of the engine, and virtually straight through, with gentle bends, etc. This is one place where the factory engineers got it about as right as they could. I believe a well-constructed (tuned, equal length, incremental, 3-2-1) exhaust header could be beneficial, but so far none exists that isn't custom built. We'll see if Stainless Works gets one done for us that is affordable. Otherwise, delete the resonator and leave well enough alone.

Note again the design differences between the I-6 and other Chevy offerings. Ours is closer to an Indy car than to the 350 Chevy. the 4.3 that you had in your other vehicle was a V-6, not a straight inline 6. It had two valves per cylinder instead of 3 (1 intake and 2 exhaust). It was a single cam pushrod engine instead of a double overhead cam direct-drive engine. It had wedge shaped combustion chambers with side-mounted spark plugs instead of hemispherical chambers with a centered spark plugs (that's right, our engines are "hemi" designs). It had a distributor and spark plug wires instead of direct coil/plug ignition. It had an intake manifold instead of an intake log. It had a set valve timing scheme instead of variable valve timing. About the only things close are the fact that both had 6 pistons and that they were similar in overall cubic inches. Otherwise, almost everything is a radically different design that makes a radically different sound, power band, torque and horsepower ratings, etc.

That, and the 4.2 is basically already "hot-rodded" from the factory. We have a 256 cubic inch engine that is rated at 275/275 torque/horsepower out of the box. The old 327 Chevy engine made world headlines when it was able to make 1 hp per cubic inch! We're beating that easily. If this engine were a 350, it would put out about 380 hp! The 6.0 liter Chevy LS2 puts out 400 hp. If the I-6 were the same size, it would put out about the same hp -- 400. Just for kicks, if it were a 502 big-block size, it would do 539 hp. Come on Chevy! Let's get it on!
 

·
Registered
2005 gmc envoy_sle_xl
Joined
·
78 Posts
Discussion Starter · #11 ·
Ok, after reading all of that i'm convinced.....resonator delete it is and leaving well enough alone until the stock exhaust rots itself and needs replacement, then i'll figure it out from there. But until then I have plenty of time to figure it out. Sorry to drag this issue out longer then it needed to be. Thanks a lot for the input......resonator delete here i come!
 

·
Registered
2003 chevy trailblazer_ls
Joined
·
1,236 Posts
No problem... Another education is always a good thing.

Also, it is not that none of us wants to modify the platform -- we sure do -- but more that it is, at best, difficult to improve on the factory in this instance. There is some room for improvement, but the "easy" stuff, like a bigger exhaust, intake manifold, cam, headers, etc., are mostly removed from us unless one wants to REALLY start unloading big $$$.

Cams, for instance, need to be custom ground, and we also need to supply our own cam blanks, as Chevy doesn't provide blanks for the aftermarket. What all that means is that you have to pay a REALLY good machinist to cut a cam blank out of a stick of billet, then send it out for heat treating, then plating, then grinding, and finally, after somewhere in the neighborhood of $2000, you can have a cam that probably adds around 30-50 horsepower at best. Just isn't worth it unless you're running a car on the salt and you want a new world record in that class. And, to make matters worse, let's say you get one made. Then you still have to modify the entire PCM program, including (depending on the year) changing over from MAP to MAF, as mass air flow is about the only way to accurately measure the air flow, and thus the fuel needs for an engine with a radically different VE (volumetric efficiency) versus the tables that are built in to compute the VE based on manifold pressure, atmospheric tempratures, and engine load. Starting to sound complicated? :yes:

Given time, with the cost of owning a TrailVoy coming down, people will start to play around with the platform, and we could see some modifications come down the pike. First the racers get the parts, then they'll trickle down to the street. Biggest issue there is that our engine is not offered in any other vehicle, so no one is racing them... :dielaugh:
 

·
Registered
2005 gmc envoy_sle_xl
Joined
·
78 Posts
Discussion Starter · #13 ·
yea kinda blows that the easy stuff got removed because it's either leave it pretty stock or pay the big money....and i'm not about to drop the big money. I like this place....people don't feed u a line of bull and beat around the bush and tell you "put the biggest exhaust on it, it'll be great" and calling it a day. You actually get to learn something!!! There are actually people on here to take the time to explain to you why you would be wasting your money if you do that!! Amazing....again...thanks guys for saving me the headache and money.....i guess a good 2-3/4" stainless tube and tip and a borrowed sawzall will work to get me the sound and little bit of performance i'm looking for.
 

·
Registered
2003 chevy trailblazer_ls
Joined
·
1,236 Posts
Don't completely give up hope! One thing that will give some bang for the buck has already been mentioned. On a high-tech PCM controlled vehicle like the Trailblazer, you can bump performance by changing the tuning parameters in the computer. There are tons of variables to tune -- shift points and firmness, rpm level, cam timing variables, fuel charge and timing, ignition duration and timing, and a few other things.

A tuner who has spent some time with one of these trucks on a dyno (and who KNOWS something about all the variables and how they related to one another) can bump horsepower, torque, and drivability.

A lot of us here on the board have used PCM for Less. They are a board vendor also -- check their own forum thread.

The process is rather simple -- pull out your PCM (the electronic box hanging on the side of the intake manifold) held in place by 4 small bolts and three wire harneses, ship it off to PCM for Less, send a check (or PayPal) along with the unit, fill out the build sheet -- what you've already (or plan to) done on your truck, gear ratio, shift firmness desired, amount of torque management desired (torque management is the computer controlling how much output power is fed to the drivetrain under a certain rpm to soften shifts, and prevent premature parts failure in the driveline), and a couple of other things, and they send it back tuned.

Most guys see somewhere in the neighborhood of 10-15 hp increase, better drivability, and a MUCH snappier vehicle overall.

Cost is under $150. They can ship you a loaner PCM to use if you need to daily drive your TrailVoy.

DO IT. Bigger bang than an exhaust system. :thumbsup:
 

·
Registered
2005 gmc envoy_sle_xl
Joined
·
78 Posts
Discussion Starter · #15 ·
ok, one last question. I read in another thread that a guy said he used a 2.5" pipe for his tailpipe because it fit right into the muffler and was able to be welded. So then if this is true, does the same go for a 3" pipe being able to slip over the 2.75" of the muffler so it can be bolted together? I'm just currious, and again, will this hinder the exhaust if i were to slip on a 3" pipe and kind of skip the whole welding part?
 

·
Registered
2003 chevy trailblazer_ls
Joined
·
1,236 Posts
The tip really won't hinder much of anything, except if you make it too small, so it restricts the flow. The general theory behind a well-designed exhaust system is that it gets larger as it gets longer. Up until the point where the diameter is so large that the pulses from the exhaust are no longer scavenged from the cylinders, bigger is better. Ours are sized just about perfectly for the air flow of the engine.

So, short answer, stick on the 3" tip and don't worry about it.
 

·
Registered
2005 gmc envoy_sle_xl
Joined
·
78 Posts
Discussion Starter · #17 ·
ok awsome, just wanted to make sure. I'm not exactly sure how far it is from the muffler to the bumper, but i figured it shouldn't make that much of a difference. thanks again for your help
 

·
Registered
2003 chevy trailblazer_ls
Joined
·
1,236 Posts
If you are talking about that big coffee can thing at the rear of the vehicle, it is not the muffler. That is the resonator. The muffler is under the center of the truck.

You can remove the entire resonator if you like. Sound increases some, power gains are insignificant. It will give a little bit of tone that some hear as buzz while others seem to like it. I like it a bit louder myself, it is the sound our engines make. More "ricer" than thumper, as explained above. Wish with all my heart it sounded like the SS with a Magnaflow exhaust, but alas, never to be so we live with it.
 

·
Registered
2003 chevy trailblazer_ls
Joined
·
5 Posts
Again, if you just want to replace the exhaust, go ahead, but don't expect any real improvement in performance or sound.

Also, as I wrote above, the engine does not need "backpressure" and in fact, our exhaust system may be one of the lowest backpressure exhausts I've ever seen come on a factory vehicle. It is HUGE for the size of the engine, and virtually straight through, with gentle bends, etc. This is one place where the factory engineers got it about as right as they could. I believe a well-constructed (tuned, equal length, incremental, 3-2-1) exhaust header could be beneficial, but so far none exists that isn't custom built. We'll see if Stainless Works gets one done for us that is affordable. Otherwise, delete the resonator and leave well enough alone.

Note again the design differences between the I-6 and other Chevy offerings. Ours is closer to an Indy car than to the 350 Chevy. the 4.3 that you had in your other vehicle was a V-6, not a straight inline 6. It had two valves per cylinder instead of 3 (1 intake and 2 exhaust). It was a single cam pushrod engine instead of a double overhead cam direct-drive engine. It had wedge shaped combustion chambers with side-mounted spark plugs instead of hemispherical chambers with a centered spark plugs (that's right, our engines are "hemi" designs). It had a distributor and spark plug wires instead of direct coil/plug ignition. It had an intake manifold instead of an intake log. It had a set valve timing scheme instead of variable valve timing. About the only things close are the fact that both had 6 pistons and that they were similar in overall cubic inches. Otherwise, almost everything is a radically different design that makes a radically different sound, power band, torque and horsepower ratings, etc.

That, and the 4.2 is basically already "hot-rodded" from the factory. We have a 256 cubic inch engine that is rated at 275/275 torque/horsepower out of the box. The old 327 Chevy engine made world headlines when it was able to make 1 hp per cubic inch! We're beating that easily. If this engine were a 350, it would put out about 380 hp! The 6.0 liter Chevy LS2 puts out 400 hp. If the I-6 were the same size, it would put out about the same hp -- 400. Just for kicks, if it were a 502 big-block size, it would do 539 hp. Come on Chevy! Let's get it on!
It's a 4 valve motor not 3. I assume its 2 intake and 2 exhuast.

To the original poster, if it were me and you had 3" pipe readily available to you id go for it but run some kind of muffler. 3" stuff is usually easy to find w/ more options on what to get. You can get as technical as you want about scavenging but in the end it all comes down to real world performance. Not to mention the bigger the pipe the deeper the tone. thats my 2 cents.
 

·
Registered
2005 gmc envoy_sle_xl
Joined
·
78 Posts
Discussion Starter · #20 ·
hmmm..interesting well i do happen to have some 3" pipe laying around for when i do the resonator delete (and yes I know the muffler is under the car and that I cut the "coffee can" off the car).
 
1 - 20 of 30 Posts
Top