86 IROC

iTrader: (14)

After another round of mods, it feels like I have went backwards from a performance standpoint. Last weekend I had the cats deleted, installed 02 SIMMS, an SLP y-pipe, and had a "dyno mouth" built w/ a single 3" bullet muffler. It should have gotten faster in theory, but in reality it feels like a dog and can't seem to get out of its own way.

The car/mods are as follows: 2000 Z28 A4 w/ 2.73's, 34K miles. The earlier mentioned exhaust work, SLP lid, free mods, NGK TR55's gapped @ .052", MAFT, MAF ends.

Bone stock the car seemed to pull a lot harder esp. down low. I'm aggrivated right now and need some help from fellow LS1 owners. Also - that bullet muffler has to go, it sounds like ***! I can't stand it. Any suggestions? I was looking at that twister muffler like is being discussed in another thread. I want something that doesn't sound like it belongs on a redneck truck.

Thanks in advance to all.

4mula1

I'm obviously not the expert around here, but since no one else has chimed in yet I'll go ahead and say that I think your change is actually going to cause you to lose bottom end, just like you've noticed.

I don't know that I would have replaced the stock y-pipe w/out adding headers. I think the resulting loss in back pressure has kind of un-tuned your exhaust. however, I'll bet you did pick up some top-end power though as a trade-off.

I think you might benefit more from a catback system that the y-pipe at this point. Used catbacks can certainly be found if you don't want to shell out $500 or so at the moment.

Anyways, good luck

CamaroSS

iTrader: (2)

Sounds to me like a case of getting the wrong muffler! You should get the long Dynomax Bullit, if that is what you have, then you have different tastes. But I thik Dynomax sounds BADASSSSSS!!!!!!! Other then that, bad move on the Y-pipe, your gonna need to replace it when you get headers. You did lose torque however. You will see a gain in MPH on the E.T. but the E.T. might get lower. Here is the deal; Good Back Pressure= Torque////Good Flow= Horsepower. All I can say is that you should have waited on the Y and saved for duh headers. Horsepower doesn't kick you in the seat, thats the torque. You might be faster, but can't feel it, so it has to be visual (Time Slip) so take her to the track to compare. If you have never been racing then SOL. Sorry.*********Dares Duh Truth*********

SMOKIN01TA

iTrader: (10)

gettnig a good flowing exhaust is going to cause backpressure loss, causeing a bit of throttle hesitation, try getting a ported trottle body from thunderracing, it will give you some of the response back, also your gears are going to kill all low end performance. i drove a automatic with 2.73 and i though something was wrong with it at first because i was used to driving the auto's with 3.42 or better. come to find out it was just really low gears. they rob all of the low end power. if you don't want to change gears for gas mileage, try getting a 2600 or 3200 stall to get some more of the line power

86 IROC

iTrader: (14)

I have the long bullet muffler, 18" body, 23" overall. Sounds worse as it breaks in. It might be better w/ cats, but w/o them it sounds like absolute ****. It really turns me off about the car, can't wait to change the muffler in about a week. About the y-pipe.... bought it used for a good deal, figured it would be much better than my stock one.

I'm getting the feeling that these LS1 cars are just super finicky. I've had lots of different cars in the past and all of them responded well to a freer flowing exhaust.

Amen on the 2.73 gears, they suck for performance - but I love getting 25-26 MPG. However, if I end up switching jobs... a set of 3.73's are in my future.

I had planned on not messing with this car at all since I already have one highly modded car. But, my mental illness with cars has gotten the best of me once again. I shouldn't have messed with it, but there's no turning back now.

Thank you to all who replied. Looks like I may run it this Wed. to see if it fell off any. Previous best w/o most of the mods was a 13.41 @ 104+ Was deadly consistent running mid to high 13.50's @ 103 for the most part.

black_z

iTrader: (4)

I bet your just feeling the loss in low-end. These cars do feel slower than they are due to the very flat torque curve.

onebadz

Get rid of those 2.73s and also get someone with ls1 edit or predator to make sure you are getting no knock retard and that your A/F mixture is correct. Also you should defiantly invest in a higher stall converter. Check out the sponsors---------------->

Good Luck man
WeS

Ravenous T\A

iTrader: (12)

Have you autoTaped it? I noticed U had ported maf ends and a MAFT, maybe a loss due to runnin to lean. Did u know what your A/F was before U played with the MAFT? maybe that has something to do with it. Gears would really help to, 3.23 and 3.42 are great if U like them strong for daily abuse, maybe some runs with the some DR's, i have always heard 3.73 and 4.10 in a 10bolt are weak, but people have had good luck with them.

Vendetta

track times are the only way to tell

As for the muffler, if I had an LS1 I'd definitely go Spintech.

Let us know what ya run! Good luck!

CamaroSS

iTrader: (2)

Hate to break it to ya but the Ported MAF end, and MAF De-screeen are not a good idea on a automatic car. The MAF sensor detects the amount of air coming into the engine, and on an automatic, it also tells the tranny when to shift, and how hard to do so. This is the line pressure, and with the mods you have done, and note I did too, it will effect the shifting performance.

As for exhaust, I am getting Loudmouth, and was going to do the dynomouth, but local exaust wanted way too much to do it, $450. I like loud, and dynomouth, and loudmouth are loud. I think nothing sounds better then as close to open headers as you can get so that is why I like these systems.

Also, the stock Y-pipe flows quite good, and even with the driver side crunch, it is O-K. It is almost 3 inches at 2 7/8 inches, it shouldn't realy need to be replaced until Headers, or super/turbo.

So Dare Ya Go.

pdd

iTrader: (3)

i agree

86 IROC

iTrader: (14)

Well, have heard all the fuss about the MAF ends & such... my car shifts just as firm as it always did. Villian from this board is a co worker of mine, his 2000 A4 formula has ported ends and shifts fine as well. In fact, so well that he's running consistent 13.00's @ 106 on GS-C's. Our mods are similar, I have more exhuast, but less gear.

We verified that it had a definite flat spot as compared to his car the other day on lunch break. Still haven't managed to find someone to A-tap the car for me as of yet. I'll post my results the moment I have it done and/or race the car again.

Thank you again for all the responses. The more the merrier when trying to track down car gremlins.

jaberwaki

bet you have gone fat in your a/f almost sure of it...
get it on the wideband and dyno tuneher in...
bet you find she goes rich right about 2200-3000 rpms....

SSunset 02

Just a little FYI... I am basically stock and I had the SLP MAF in my car and was PISSED because my car was slow at the track - until one day I put the stock MAF back in my car... LOW AND BEHOLD - the car was .4 FASTER with the stock MAF! Just to show you - you never know!

shadowSS

Whoever says you need backpressure for exhaust is a moron.

CamaroSS

iTrader: (2)

Not saying you need it, it is a good amount will make more low end torque, and it will run better from what I have heard.

jRaskell

iTrader: (1)

Backpressure = low end torque, which is easier to feel with the butt dyno.

No Backpressure = high end HP, which you really can't feel with the butt dyno, other then maybe it feels like it pulls the same for a few hundred extra RPMs then it did before.

Nobody was saying you NEED it for anything, just stating how it affects your power curves.

jaberwaki

basically you wanna feel fast keep backpressure
you wanna BE fast open her up

Villain281H

iTrader: (5)

I rode in his car, and I'm not sure if it's the gears or the new exhaust, but it's definately more sluggish than mine. Again, I'm no expert, but I'm not thinking the maf ends are slowing him down. They picked-up my car by over a tenth in the quarter with no loss of bottom end torque/grunt. Hope you get it figured out Brian!

DANSLS1GTO

>Whoever says you need backpressure for exhaust is a moron.

While this is true, you will need to retune if you go from a standard exhaust to a free exhaust.