No retune needed with DP being replaced, with an aftermarket one.

You will lose torque off idle, & at low RPM cruzing speeds.

Try 'coring' the 2nd cat, you'll be pleasantly surprised.

 

I did the second cat mod, it works well....

 

Got to the track yesterday, for the 1st time this year.
It was the Night-of-Fire event, with jet cars, funny cars, ect.

Weather was really bad, really hot & sticky.
At 6pm, I made a pass, with the temp at 86', dew point at 69', DA 3,200'
& a strong 'head-wind', with rain coming a few hours away.

I only ran a 12.77 @ 105.51, with my 'street' 'tune'.
I didn't want to load my 'race' "tune', because of the nasty weather,
& a threat of rain, which did come 2 hours later, resulting in a rain-out, today.

My son made a video with his new phone.
No zoom on his phone, & it shows me beating an open header, small block,
80's Chevelle I think.
Hhr race - YouTube

 

Man, that thing is sick... "ONLY" a 12.77 on your street tune? I'll be lucky to break into the 13's by the time i'm done with mine...

 

I'm not doubting your numbers...but I find it odd that there are several others (HHR's and Cobalts) running more bolt-ons...similar tunes...and they are in the mid-low 13s all day long. Could the lighter brakes and lighter wheels really make a difference? Besides the intake and down pipe do you have any other go fast bolt-ons? I've got a Ecotec buddy that has a Cobalt running a full intake, meth injection, e47 tune, catless downpipe, full Hahn exhaust...he's estimating 350 hp mid-13s although he's never ran it in a quarter mile.

 

Make sure we're comparing similar cars. Autos are quicker and the balts are 5spds. Also anyone of those cars you know of running slicks? Totally believable times imo. Look at his street/slick times in his sig. If I had slicks I'd run mid/high 12s. If I were auto I'd be 12 flat. Driver mod maybe? A ton of time can be lost launching and shifting. I'm guessing 2005hhrauto has hundreds of passes. I bet most go once, pass 5 times and call it a day. You simply can't learn your car on the track in a few passes. It took me 5 passes just to get consistent times within .2s. Bolt-ons are less important than a great tune and driver mod goes a long way.

 

I kind of got used to running 12.4's, after running 12.4's the last 3 times that I was at the track last year, so 12.77 was slow...
13's with a 2.2 would be really cool, alot of the SS guys can't get into the 13's...

 

Your buddy will definitely be in the 12's with slicks...

The lighter wheels/rotors, a saving of 100lbs, only helped for a tenth , in the quarter...
I really had hoped that it would've helped more, but the lighter wheels/rotors, really shine on the street, with crisp handling, & better throttle response.
1. K&N intake system, to remove the intake restriction.
2. Cored the 2nd cat, to remove the exhaust restriction, on our "buggys", & I still run with the 1st stock, factory, cat in place. Keeping the 1st cat, is best for retaining low end torque.
3. TurboTech engine mount, to 'plant' the power.
4. Slicks are a MUST, for wrong-wheel-drive...
5. E47 "tune", good for at least 30HP, & at least 60 ft lb of torque, over straight gasoline.
See post #256 of this "thread", for my best day at the track, last year.

 

Yes, your correct, autos rule, on the quarter mile.
Yes I have a ton of passes down the track...

1. I "Brake-Boost", on the line, at 2,500-3,000RPM, @ 5-10LBs of boost, & slicks.
This lets me "rocket" off the line for a best 60' of 1.78 seconds.
The automatic holds up really well with this, but for how much longer, I don't know...
2. I run the smallest slicks needed for my "buggy", 23.5" diameter, 8" wide, with NO tubes needed. So my 15", 9.5lb wheels, with my 12lb slicks = the best ETs. 22lb vs 50lb, for a stock wheel/tire.
Most guys run a heavy 17" wheel, with a heavy 26" tall slick, with tubes, that will add a ton of weigh, & slow you down...
3. I bring the "Boost" on really quick, more boost = more torque.
4. I "Overboost" the turbo, which creates "Monster" amounts of TORQUE, with the E47 fuel blend.

Our automatic "buggys", can really fly down the track, with the right set-up...
If anyone is using HPTuner, email me, & I'll send you my "tune", maybe it might give you some ideas, to make your "buggy", better for you. I'm just playing-it-forward, as alot of smart guys on HPTuner, have helped me get my "tune", to where I wanted it. There's just so many really crazy tables that need to changed in our "tunes"...
This "tune" will work on any LNF engine, E0-E100, only 2 things need to be changed for the fuel of your choice,
the fuel constant, & ALL the spark tables. This "tune" is a true E47 "tune", only because the fuel constant is set for E47,
& ALL the spark tables are set for E47, as the rest of the "tune" is the same for any fuel...

lindadave83@hotmail.com

 

I would say your biggest benefit would be the wheel & tire selection. You forgot to mention you re-drilled the hubs to a 4 lug. Those size wheels are not available in our 5x115. The smaller the wheel, the more rubber you can fit. More rubber=more traction.