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Discussion Starter · #1 ·
So I've read the great reviews and thinking of getting the autocal. My truck has 5300 on it now and I just changed exhaust. I put a race bullet with 3 inch dumped over axle. It seems I've lost some low torque. From a stop with the stock muffler, I could punch it and it shift around 2800 rpm. Now it pushes 4000 rpm before shifting. Cruising in traffic at 30 mph and 1200 rpm today, I punched it and it's sluggish/boggy. The acceleration from 1200-2000 rpm seems slower. It didn't do that with stock muffler. Can the autocal take care of these issues?
 

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Yes, but if you are shifting later, you are using more throttle. Shift points are based on vehicle speed and throttle position.
 

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Discussion Starter · #3 ·
So the muffler is actually having negative effect? What's also crazy, the most I gotten on a half tank is 200 miles. Today is first trip after muffler and I got 225 on half tank. It almost seems like power has been moved from down low to high in rpm range.
 

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Rest in Pieces
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Try disconnecting the battery terminals for 30 mins to allow the computer to reset itself. It'll relearn your driving habits. I believe that's how it worked on the nbs/nnbs trucks.

However I would recommend black bear anyways. Their tuning is top notch.
 

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Discussion Starter · #5 ·
Thanks. Yeah I'm planning on it in the next couple weeks. I'm kind of shock a muffler switch changed the characteristics this much. It didn't do squat on my 07.
 

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I did a flowmaster cat back on my 08 sierra 5.3 and noticed low end power loss. Replaced that with a magnaflow and it runs like stock. I also recommend the blackbear tune, I just had mine done and it drives much nicer now.
 

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these trucks will lose some low end torque from free flowing exhaust.
defanitly get ahold of Black Bear.
they tune my truck and its far from stock, it drives like its stock due to the tuning
 

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Just an FYI. I had my tuned by Blackbear and it's leeps and bounds over the stock truck. Feels great!
 

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Discussion Starter · #9 ·
Yeah I'm hoping blackbear can help. I'm am really shocked at mpg since muffler swap and afe dry drop in. 380 miles was most on tank of fuel with stock exhaust/air cleaner cruising at 72 on interstate. With the race bullet/afe I got 410 miles on tank first trip.
 

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Some mufflers can cause a decrease, if it causes a reduction in exhaust velocity. Reduces low end, which in turn reduces MPGs.
 

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Discussion Starter · #11 ·
In my case, it's reduced low end torque and increase mpg. I guess my concern is can a tune get back some low end and still maintain the improved mpg I have now?
 

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In my case, it's reduced low end torque and increase mpg. I guess my concern is can a tune get back some low end and still maintain the improved mpg I have now?
When I got my BB tune I gained power over the entire RPM band and my mpg's increased by 2-4 mpg's. I also used to have the dynomax bullet on my truck and lost a little low end with it, then switched to a flowmaster recently and gained a lot back
 

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Baseball
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Lol you're complaining about getting 225 on a half tank? I would say that's good unless you've got a 30gallon tank
 

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Discussion Starter · #15 ·
I never complained about 225 on half tank. I was simply stating facts that it had increased from the 200 miles on half tank in stock form versus muffler swap. That's a great thing. I'm kinda scared to mess with it. I can live with the low end power loss if mileage stays same (increased).
 

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Mmm Sandwich
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Going off your fuel Guage is not an accurate method of determining milage
 

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Baseball
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oh, didnt show up on my phone that you said it went from 200-225.. but, calculate your mileage... car computers cant always be trusted...
 

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Discussion Starter · #18 ·
So I'm curious, since I bought the truck I've averaged 375 miles a tank on the interstate for the first 5,000 miles of its life. Since the muffler swap. I've averaged 410 miles per tank on the interstate. Truck now has 6400 miles. How is that not a increase in fuel mileage? I make a 400 mile round trip every two weeks and before the swap, could not make it without stopping to fill up. Yes, I watch the fuel gauge and it is in different position throughout the trip than where it was before. Both conditions are driving exact same speed, 72 mph. I haven't looked at car calculation or hand figured. I'm going off how far I can go on a tank.
 

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Mmm Sandwich
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Not saying it's not an indication of something I am just saying it's not accurate. Actual mpg hand calculated will very. Plus the gas Guage is not a very accurate Guage
 

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Discussion Starter · #20 ·
I'm just saying forget the gauge, hand calculations, and computer calculation. I know exactly how far the round trip is. On a full tank cruising 72, I could not make the round trip (400 miles) on stock exhaust. Now, I can with fuel to spare. I understand what your saying and don't trust the truck computer mpg calculations.
 
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