What is the best performance upgrade for 2003 C5 convertible Automatic that I can still take to my local Chevy dealer for service?

 

Supercharger.

 

3.42 or 3.73 rear gears.

 

supercharger/cam/headers/cat back.

If you're looking for an entry level type upgrade, do headers+catback exhaust, maybe an intake and definitely a tune.

On the rear... 3.73? please.. 4.11s!!!!

 

If you have the 2.73 gears, I would ditch those immediately. 3.42 gears or 3.73. I have the 3.73 gears. If you plan on a supercharger, you might like the 3.15 gears, if you have that option on your car. Otherwise, don’t do 3.73 gears with a supercharger, you probably won’t get traction until 3rd gear.

 

Chief, true performance modifications and using a GM service department normally don’t go together.
If you have the 2:73 final drive; a stealership service department could recalibrate to 3:15 but if you go 3:42/3:73 > the service department will give you the car back and tell you they aren’t able to work on the car.
If you add a supercharger most factory GM service departments will not even take an appointment
By using a dealership service provider you handcuff yourself to just a few modifications. As in exhaust, intake, possibly a removable tune unless you have a remarkable relationship with the service provider
Good Luck

 

Guess it also depends what the goal is… something like improved acceleration and/or higher top speed, or are you chasing lap times, in which case you may also want to be looking at other things to improve the handling and braking as being worthy.

 

Good recommendation, but other items depends on the tech expertise of the dealer.

 

Your best move is to speak with the dealer you like and see what they are comfortable with. Dealerships I worked for in the past (not GM) would work on anything that was still used on the street for service work but we did not do custom fab work unless it was really basic.

 

As mentioned, gearing. The difference between 2.73 and 3.15 is eye opening, a different car off the line and around town. 2.73 to 3.42 or lower would really wake it up!

 

Thank you all for your suggestions.

 

Agree with your point on the super charger, but not necessarily on the gears -- I had 4.11s, headers ,cat back, and a tune as my only mods for years, and never had an issue with dealerships doing warranty work in NY or CT. Though, it's a good point to be wary, as some dealerships interpretation of what voids a warranty and what doesn't may vary wildly.

I'll take your point one step further -- all of our cars are out of warranty now, so to the OP, *why* would you *want* to take it to the GM service center? Even back in the day most of us went to GM service centers because we were under warranty .. but today, most of the guys in GM service centers have never worked on a c5, the newest c5 is almost 20 years old. Find a good, local mechanic and develop a relationship. I found a guy in my area that used to do all sorts of mods to c5s back in the day... when I gave him my c5 two years ago to do the super charger and a cam, it was like riding a bike for him, he knew exactly what to do. I have him do all the maintenance I don't want to do. I wouldn't let a GM service center within a mile of my car.

 

If he has an automatic, wouldn't the gears give him terrible gas mileage for highway driving since the engine will be at a higher RPM in top gear (and he only has 4 gears)?

Not sure if the OP cares, just something to consider.

 

it would give you worse gas milage regardless of whether you have an auto or 6spd, but not sure anyone buys a c5 becuase of fuel efficiency :-)
OP is asking about modifications -- pretty much any mod that adds power will have a detrimental effect on gas milage.

 

Headers, CAI, X-Pipe/CatBack with a solid tune will be your best entry-level upgrades.

 

^^^^^^^THIS 110%^^^^^^^ I'll say this to you, OP; I lucked out that my 2000C5 A4 vert came with the G92/3.15 diff. With boltons and tune, a C5 is pretty potent. I got high 12s with stock exhaust manifolds. If you do as suggested, and I think JGM2 was spot on. If I had started with the 2.73, I'd have shot right past the 3.15, and gone to at least a commonly available C5 Z06 3.42 gear. I'd probably go to a 3.73 or 4.10. I personally favor a 3.73. I'll tell you this-I had a seat of the pants, educated guess tune, and it really helped, more than I ever thought possible with stock internals. With a 3.73, an LS6 intake, dyno tune, UD balancer, and a Blackwing or Vararam, you'll be at least mid 12s if you're a decent driver. My .02. If you want more detail on what my package consisted of, PM me. Best of luck......

 

Oh, Totally agree with you about gearing and N.A. mods by the way. It's just that Chief mentioned in his opening post, he wants to remain to use GM Service Dept. So; unless he stays with 2:73/3:15 all the ECU settings will probably become service warnings a GM service Dept can't adjust or overide strictly using a stearlership service dept. An aftermarket tune could easily deal with this but that requires an independent shop/tuner that a GM shop might not care to share the service responsibilities with
Problem with Chief's mandate is severely limiting uses of most options. Unless; you DIY or use an Indy shop that are qualified and have history using and preparing a C5 A4 setup they "can" reset the ECU shift points/ MPH settings, electric fan settings, timing, fuel maps etc that "possibly" a GM service center that don't have narrow minded policy about performance options could be accommodating enough to work with


The idea of a higher gearing used in conjunction with certain performance upgrades has positive potentials although this is about Chief's perspective and I respect his choice so makes sense Chief should probably call around to GM service Dept's in his area and use local Corvette groups on Social Media, the CF's local regional section to ask for members reviews of the best ones that might work with him to use appropriate mods.

Good Luck Chief

 

Thanks guys, you've all given me a lot to digest. I'll see if I can find a shop close by and dig their brain a little before I make a final decision. I'm not looking for a lot of horse power, just enough to be respectable. I'm a retired Marine living in Jacksonville NC. As we say in the Marine Corps, Semper Fi! Thank you.all.

 

I’m not going to lie, you can spend 2-$5000 for a few decent upgrades. It’s money well spent if you enjoy it.
Let us know what you decide on and how you feel about it after

My father was Army and I have the utmost respect for the people in the military.
Thank you for your services

 

Everyone has an opinion for themselves. The real question is just what do you really want to accomplish and then we can try to match the proper mod to your expectation.

What kind of gain would you like to see and then how are you going to use the car. Finally is there a budget.

There are a number of options and you need to be aware of the good, bad and the cost of each and how it relates to the use of the car.