LS1 C5 going from no cats & muffler to cats and stock muffler, does it need a retune?
10-04-2013, 02:51 PM
#1
Teching In
Thread Starter
Join Date: Nov 2012
Posts: 2
Likes: 0
Received 0 Likes
on
0 Posts
LS1 C5 going from no cats & muffler to cats and stock muffler, does it need a retune? Hi, I hope I'm asking this in the right place here.
I got a C5 coupe with the LS1, no motorwork just bolt-ons. Blackwing intake, Kooks 1-3/4 long tubes with 3 inch X-pipe & mids until the axle back where it goes back down to 2.5 inches for stock-style exhausts. I had B&B Bullet axle-back mufflers previously.
Here's a pic for reference.
Well now that the car is seeing daily driver duty, I want to tame the exhaust noise and I need to get cats back on to avoid state inspection issues.
I had the car tuned by a reputable vette shop here in NJ years ago, but at the time I had the above mods.
So my question is will I need a retune going from no cats and virtual straight pipes, to hi-flow cats and adding back the stock muffler system? My exhaust will be going from very free flowing to a lot more restrictive, so I'm not sure how much of an effect that will have on the dyno tune it has in place.
I do have my own HP Tuners Pro kit now to check things out myself, but the car isn't wired up for a wideband. That's something I'm planning on doing in the next couple of weeks, I'm just not sure if I should be driving the car until then or if it should be OK to drive with these changes.
I got a C5 coupe with the LS1, no motorwork just bolt-ons. Blackwing intake, Kooks 1-3/4 long tubes with 3 inch X-pipe & mids until the axle back where it goes back down to 2.5 inches for stock-style exhausts. I had B&B Bullet axle-back mufflers previously.
Here's a pic for reference.
Well now that the car is seeing daily driver duty, I want to tame the exhaust noise and I need to get cats back on to avoid state inspection issues.
I had the car tuned by a reputable vette shop here in NJ years ago, but at the time I had the above mods.
So my question is will I need a retune going from no cats and virtual straight pipes, to hi-flow cats and adding back the stock muffler system? My exhaust will be going from very free flowing to a lot more restrictive, so I'm not sure how much of an effect that will have on the dyno tune it has in place.
I do have my own HP Tuners Pro kit now to check things out myself, but the car isn't wired up for a wideband. That's something I'm planning on doing in the next couple of weeks, I'm just not sure if I should be driving the car until then or if it should be OK to drive with these changes.
10-04-2013, 08:45 PM
#2
Teching In
Join Date: Sep 2013
Location: Straya
Posts: 43
Likes: 0
Received 0 Likes
on
0 Posts
If it's tuned with the maf you should be ok. The increased backpressure will reduce airflow through the motor but the maf will see this. If it's tuned speed density it will probably get richer at full throttle - no harm done really.
The stock mufflers probably flow quite well, as do most high-flow cats, so you might not see much difference at all. I'd drive it, do some logging with HPT and watch for knock retard and make sure your fuel trims aren't too far out of line. +/- 5% is what you want.
The stock mufflers probably flow quite well, as do most high-flow cats, so you might not see much difference at all. I'd drive it, do some logging with HPT and watch for knock retard and make sure your fuel trims aren't too far out of line. +/- 5% is what you want.
10-04-2013, 10:46 PM
#3
Teching In
Thread Starter
Join Date: Nov 2012
Posts: 2
Likes: 0
Received 0 Likes
on
0 Posts
If it's tuned with the maf you should be ok. The increased backpressure will reduce airflow through the motor but the maf will see this. If it's tuned speed density it will probably get richer at full throttle - no harm done really.
The stock mufflers probably flow quite well, as do most high-flow cats, so you might not see much difference at all. I'd drive it, do some logging with HPT and watch for knock retard and make sure your fuel trims aren't too far out of line. +/- 5% is what you want.
The stock mufflers probably flow quite well, as do most high-flow cats, so you might not see much difference at all. I'd drive it, do some logging with HPT and watch for knock retard and make sure your fuel trims aren't too far out of line. +/- 5% is what you want.
That's pretty much what I figured but since I'm new to tuning I figured it would be better to ask. I was successful in tuning my other vehicle's turbo setup, so after I get my WB in I figure I'll dial in the tune it has to better suit the changes. Shouldn't be too difficult given it's just a bolt-on car.
The tune that's on the car right now was done years ago, I don't remember when probably 4-5 years ago maybe more. Not sure if it was done HPT or LS1edit, I'm hoping HPT so that I can just read the existing tune instead of starting from scratch.