6.2L (L9H) Owners - Get all your questions answered here

[gonzoid]

Lets here more,what did you do exactly and what are your gains?

 

my 014 6.2 looks like 3.5" pipe,at the flapper it might be necked down to 3" right there for a couple inches

Edited November 28, 2014 by Gonzoid

[Roll Bama Roll]

Lets here more,what did you do exactly and what are your gains?

 

my 014 6.2 looks like 3.5" pipe,at the flapper it might be necked down to 3" right there for a couple inches

Gonzoid, the theory for experimenting with my truck modding was formed from these thoughts.

 

1. I think the 3.5" pipe is a little too big for good lower rpm flow. a 3.5" pipe can support 460-470 hp. When driving, the closer I'm pushing to 400 hp, the more efficiently the pipe is flowing exhaust gas. But in normal daily driving, I'm probably varying between 200-375 hp. The further away I am from 400 hp the less efficient the pipe is flowing as the 3.5" diameter allows the slower rpm exhaust gases more room to expand, cool, slow down and impeded flow. The only time I get near 400 hp output on the road is if I manual shift through first and second and peg the tach needle. But that's not how I normally drive. In auto and during spirited take offs the tranny changes gears by 5k rpm. I think a stock 3.25" exhaust would be a better compromise but it's not a standard size. It would support the 403 hp just fine but would be a little better flowing at low and mid rpms.

 

2. My magnaflow, or any straight through muffler, although freer flowing than stock, also allows the exhaust to cool a little sooner. The stock muffler traps heat better, keeping the exhaust gas hotter further down the pipe. Hotter exhaust flows better. The longer then pipe from muffler to exit, the more important it is to keep it hot.

 

3. Narrower pipes will enhance low end torque whereas larger pipes will enhance top end hp. Capacity favors hp, velocity favors torque.

 

4. On motorcycles, people often swap stock pipe/mufflers for straight through pipes, aka drag pipes, because they look and sound better and shed significant weight. Stock motorcycle exhaust are typically 1.75". Drag pipes are usually 2" to 2.25" diameter. Drag pipes are ideal on the drag strip but hurt low end because of #1 and #2 above. These drag pipes, being larger diameter than needed and without a muffler to keep the exhaust hot allow the exhaust to expand more, cool more, slow down more and ultimately impede low rpm power. Drag pipes become most efficient at drag strip rpms, hence their name.

 

So, we've established that bigger pipes with lower exhaust temperatures flow most efficiently at max rpm but increasingly less efficiently the lower the rpm until you hit idle, where they are the least efficient at flowing. But what about daily driving exhaust flow efficiency? What if the pipe on my truck was designed for better exhaust flow efficiency from idle to say 5200 rpm, where I spend all of my time, and not closer to 6000 rpm where I spend very little time? Would it improve my daily driving experience? The answer, for me, is yes.

 

Increasing velocity is how I accomplished improving the efficiency. A 50 year old technique used to improve low end on motorcycle drag pipes is to install an eye bolt about two inches inside the exhaust exit. This little obstruction forces the gas, upon exit, to speed up or increase velocity. When you increase velocity you reduce pressure. So by adding the eye bolt it increases exit velocity to help clear the slower rpm gases sooner, allowing less time to expand, cool and slow down but it also reduces exhaust pressure. Both of these elements, faster and less pressure, decrease low end pumping losses which translates to better lower rpm power and street drivability. From that, motorcycles exhaust manufacturers began playing with narrowing the end of drag pipes to add velocity/reduce pressure. Further, they began tuning them by varying the amount of narrowing and the length of the narrowed sections for individual motorcycle engines and performance goals.

 

When I added my magnaflow muffler I lost some low end. Then I looked at the magnaflow + 3.5" pipe as being like putting drag pipes on a motorcycle in that the pipe was a little too big and, with no reversion muffler, a heat source was eliminated. I tried the eyebolt in the exhaust trick on my 3.5" pipe and noticed some low end improvement, so I knew I was dealing with a velocity issue and not a capacity issue. I chose to incorporate a narrowed section in the back half of the exhaust, like manufacturers do on motorcycle exhaust. I felt the total exhaust might work better for my daily driving by adding velocity, clearing exhaust gases faster and, since velocity and pressure are inversely proportional, that increased velocity would mean lower exhaust pressure.

 

Subjective gains are more torque vs stock/magnaflow on take off, more torque vs stock/magnaflow when I want to increase speed, and smoother, more even power throughout the powerband. Before it seemed like there was a point around 2400-2800 rpm, both stock and just the magnaflow, where I started to feel a stepped increase in power as the 3.5" pipe began flowing exhaust more efficiently. "Getting into the meat of the power band" is how most would characterize it. The narrower section shifted the power band down some so it's much sooner and I spend more time in it rather than working up to it. Objective gains are decrease in downshifting on hills, tires breaking loose occasionally on normal take offs (I'm a laid back driver), faster acceleration and mpg increase from not pressing the pedal down as much.

Edited November 28, 2014 by Roll Bama Roll

[Roll Bama Roll]

For clarification of my previous post- you can't just go narrowing any exhaust. Most stock exhausts produce flow that matches the engine hp well. But you can go narrower on an exhaust that is larger than needed, meaning it has the capacity to handle more hp than the engine can produce.

[VictoryRed6.2]

So would it make sense to cut out the stock 3.5" muffler and replace with a high flow 3" muffler to help with some low end torque? Or would a baffled muffler that is 3.5" be better?

[NemesisC5]

Since many different engine / exhaust configurations exist I'm focusing my comment solely on the GM 6.2L L9H V8, the engine / truck combo this thread is specific to:

 

Smaller primaries on headers increase velocity thereby create a scavenging effect to empty the exhaust gases making more room for cylinder fill of fuel/air mixture. Backpressure (downsized tubing-smaller or more restrictive muffler) downstream inhibits scavenging of exhaust gases and decreases performance.

 

A smaller tail pipe will not increase performance. As rpms increase you may notice the fall-off of performance on top end creating the illusion that bottom end has increased.

[Jlm02a3094]

Hello everyone, just wanted to introduce myself here, I already did in the new members section. I'm going to pick up my 2012 Silverado ccsb ltz 6.2 on Saturday. I'll post some pictures on either Sunday or Monday. I'm very excited for this truck. I had an 08 Silverado 5.3 and finally left it for a 2014 ram 5.7, been unhappy since so I'll be glad to be back with the bow tie

 

Thanks

Josh

[Bassboats]

I recently tested the 2015 Silverado 1500 CC Z71 4x4 with the 6.2L against similar Ford, Ram and Tundra V8 packages. Silverado bested them in every category and felt far more planted when towing 6,500 pounds sans a WD hitch. Quietest cab interior, too. GM 6.2L acceleration is flat-out strong. It also delivered best towing and unloaded highway mpg between the three. (I also tested the Sierra version with Max Tow package…didn't like ride without a trailer in-tow.)

[RyanbabZ71]

The 2014-2015 6.2 is not an L9H

 

 

Ryan

['01LS1]

Hello everyone, just wanted to introduce myself here, I already did in the new members section. I'm going to pick up my 2012 Silverado ccsb ltz 6.2 on Saturday. I'll post some pictures on either Sunday or Monday. I'm very excited for this truck. I had an 08 Silverado 5.3 and finally left it for a 2014 ram 5.7, been unhappy since so I'll be glad to be back with the bow tie

 

Thanks

Josh

 

Congrats & look forward to seeing it.

[Jlm02a3094]

Here she is! Drove over 6 1/2 hours to pick her up

 

Josh

[RyanbabZ71]

Well worth the drive

 

 

Ryan

[Zebrafive]

Here she is! Drove over 6 1/2 hours to pick her up

 

Josh

 

Quite a drive to get her, but they are not easy to find with a 6.2L V8

[Stex]

Here she is! Drove over 6 1/2 hours to pick her up

 

Josh

Congrats! Is there a way to search for a 900 model 6.2 or just a long auto trader, check each truck that comes up method?

[RyanbabZ71]

Cars.com in the search

 

 

Ryan

[Jlm02a3094]

I couldn't figure out a way to filter the engine-size using cargurus. I ended calling 4 different dealers before coming across the one I wanted. Well worth it

 

I've done a few mods already too, but not sure if this is the correct section to discuss them.

 

Josh