alright so i have a 99 z completly stock and my buddy has a modded mustang and usually when we race we are even until i hit second and then i usualy get a length on him. so in the last month i had a full 3 inch catback put on with a glasspack so i figured i should get a little more on him but we race last night twice and out of the whole we are even then he gradually pulls on me he gets me by a car in both races and he hasnt changed his car since we raced. what is the problem could it be not enough backpressure but then i don't understand how cutouts would make more pressure cuz it seems like like less restriction

 

The catback should have made it quicker. Something else is wrong.

 

i don't know what the problem is cuz i just did a tune up about 10000 mile ago new plugs and wires. what else could i due. what coule i use to clean my fuel system maybe

 

glasspack? People still buy those?
What kind of muffler?
Do you have a cutout?
on many smaller engines, you want backpressure, on our larger ones, its not so important.. (thats what I have heard/understood)

I am thinking you may have clogged something to drop off your power so much..

 

its actually a resinator but its the samething it depends what u call it. maybe my fuel system is getting clogged or could my cats be getting clogged up who knows

anybody open to any suggestions i hate losing to mustangs

i'd like to try something today cuz i will see him again

 

Driver error? It sounds like you bought a Loudmouth. They typically add 15hp. It should have helped some with torque too since you kept your cats. If they're clogging up, you'll get an SES light for inefficiency. However, there's way too many variables to pinpoint one thing like you're asking. It could be he learned how to drive his car better since the time yall first started racing, your plug wires aren't on tight, your fuel filter's clogged, your air filter's clogged, your MAF is dirty, etc.

 

how long has it been since you have changed your oil and filter...

 

yeah... if you dont feel a difference then something is terribly wrong. the car should feel responsive and more powerful throughout the powerband

 

or else your buddy lied and did something to his car....

something like gears would be easy to hide...and would give him an edge

 

Needing backpressure is a myth. Back pressure = restriction. Velocity is what generally generates low RPM gains, higher flow generates higher RPM gains. The reason why it seems smaller engines need back pressure is because they have no torque. The smaller pipes generated higher velocities and therefore more torque. A free flowing small piped system will make more power than a system of the same size with more back pressure.

If you have a stick muffler (glasspack, chambered etc) they usually neck down inside. So your 3" ID/OD muffler may only have an unrestricted 2.5" flow path internally. If so, you just created a nice bottleneck. Even then, stock exhaust size is 2.75". 3" isn't that much larger. At least half (I'd bet more thant half) of the gains people see on 3" catbacks are due to a more free flowing muffler. So if you choked it with the muffler.....
Poor flow characteristics are why people have experienced lost power with 3" flowmaster catbacks.

If you actually have a loudmouth or a bulllet muffler then its something else.

You just did a tune up, what plugs did you get? What did you gap them to? Did you check/change your wires? Are they all on good? Did you change your fuel filter? etc etc etc.

 

ya i just had the tune up like 10000 miles ago bocsh platnuim 4 plugs 8.5mm msd wires new fuel filter and system flush air filter and it wass good for a while and when i got the exhaust it seemed to get worse but i just put seafoam in the intake and in my gas and so far it seems like it is starting to run a little better oh ya i also checked my plugs and wires and there all fine

 

my buddy has an intake exhaust underdrive pulleys 4:10's and a programer he had that all the first time we raced so anything other than that i think i would notice he even asked me what happened when we got done so i don't know any info would be great

 

What kind of catback did you have put on? A crimp bent exhaust from jonny's muffler shop? A good name brand 3" kit shouldn't have cost you power........A jonny's muffler shop cherry bomb might though.

Let's see, if I was beating a mustang and now I can't, and I know he didn't change anything, I'D TAKE OFF WHATEVER I CHANGED AND PUT IT BACK THE WAY IT WAS! JM $.02

 

10000 miles? that is a lot maybe you should check your filter out... i know it was my problem... i couldnt even do a burnout

then again abq is dusty as a mother

 

2 things here.
As stated 10000 is a while ago as far as fuel filter. It could very well be dirty. All it takes is one dirty tank of gas.

The second thing are the Plat 4 plugs. I've read where they don't do very well with some engines. Here is a good rule of thumb for you. If you're paying over $2/plug, you're wasting your cash.