Lose The Rear Cats, Lose Torque.

[back_in_black]

Regarding emmissions .... I put cats on the car this past FALL - passed emissions 1st shot. AND I GAINED HP AND TORQUE. My exhaust was just TOO big and I was losing some power obviously. My NA numbers went from 307/308 to 315/316 -this is from scott's thread

 

[KronicRacer]

i agree with that it shifts the power band.

bottom line in a non forced induction car the main concern is making sure the piping is not to big and if it is combat it with a gear set.well. do the old 5.0 trick and slap on the 3.75 or 4.10/30 gearset. that will remedy that power drop real quick.

 

[wms004]

Just bought an 03 gt. Looks like the previous owner cut out the back cats. She seems to lag through first then really kick it in second. A friend told me the the loss of rear cats is what is causing the sluggish #1 gear performance. Any truth to this?

The first 2 "cats" you still have are preheaters, so technically your car doesn't have cats right now. Switch to a catted x pipe and I think it will feel better all around

WAde

 

[Boestang]

I can understand both sides of this torque argument/debate. My question is this, y would you want to break the rear wheels loose on the launch anyway. The longer you can keep your wheels planted the better your launch is or am i wrong? I would rather have my powerband kick in in the upper rpms then the lower to keep from a sideways kick during take off. On the other hand on the 98 cobra i had, I installed a bbk h-pipe w/cats and i noticed an in crease in power. I did notice a bit of a flat spot in my lower rpms but i did not have a tune up on the car either.
On my 03 GT i have noticed that my low end seems slugish on 1st and 2nd but i thought it just may be the clutch is slipping or giveing. I just rolled over 19000 miles and i know it has prob been some hard miles depending on the prev owners driveing style. I myself have been lookn at x-pipes with cats thinking it might help the slugish feeling the car has. Who the hell knows one mans drink is another mans poison.

 

[sgarlic]

Well, regardless of how much traction a person desires at the track, the ability to smoke the tires on the street is something every Mustang owners is entitled to (except the V6 owners,) anyway.. like I said in an earlier post of this thread, when I did my midpipe swap, I literally lost the ability to smoke the tires unless I pop the clutch, or I'm above like 3k. Before, I could mash the gas at 1500 rpm and smoke them.. I'm used to it now, but having the torque shift on you is deceiving.

 

[tonys5.0]

I have a '04 gt 5 speed. i purchased the car with 10,000 miles on it and I've always been burdened with the sluggish 1st gear. In normal driving situations when I leave the red light cars are either walking away from me or i got some yo/yo riding my bumper. Once I'm shifting out of second into third I'm ok. I'm used to an '89 5.0 foxbody with a loooong first gear. That made me happy

For what it's worth, I changed out my stock h with cats to an o/r mac prochamber last week and I feel no difference in 1st gear than before. It's still sluggish. I thought that it would at least improve with my predator tune.

With the o/r prochamber, I'm happy with the aggressive sound! Before I hated the muffled growl. Upper rpm's are a huge improvement however the car seems to drop off further than before when shifting into 5th at top speed.

 

[djtech]

kitty catty

I have an offroad X pipe 2.5 inch. Based on the "backpressure" idea, I should either buy catalytic converters and install them, or reduce the diameter of my pipe for more power. Since I am a cheapskate, I guess I should buy a 2 inch exhaust to get more torque?

This concept makes no sense to me. Sure, I can understand exhaust flow and proper sizing of exhaust pipe but I do not understand how having something in my exhaust impeding the flow can increase power. Yes, different setups will yield different results but I can not come up with a situation where placing cats in the exhaust would benefit power production.

Catalytic converters are for emissions, not power. Your configuration may benefit from this restriction, but mine does not.

 

[mogs01gt]

Just bought an 03 gt. Looks like the previous owner cut out the back cats. She seems to lag through first then really kick it in second. A friend told me the the loss of rear cats is what is causing the sluggish #1 gear performance. Any truth to this?

nah, that is a load of BS. If they removed the rear two cats, your SES light should be on unless their is a chip installed or some MILs.

 

[big blue]

before I put on the O/R Prochamber. I could also break the tires loose just by stomping the gas from a rolling start. Now it's all power at 2500+ rpm. That is the magic number because at that rpm the car comes alive, it's acctually scary that I can be cruising along and push it to 2500+ hard and the tires will break and the car fishtails.

I also had a 2.3L mustang and put a SVO exhaust on it just to see what kind of power gains I could have . There was a major need for back pressure in that car because what power it did have was gone in daily driving. It is all about efficiency. The car is more efficiently making power in lower RPM range with 2.25 pipe and cat's, but after a set # of higher RPM's they are a major restriction.

 

[hognutz]

this thread cracks me up. from what I understand no cats have been removed. what had been removed are the resonators.

cats are up front I do belive and the resonators are down stream if memory serves correct.

these threads always kill me. If cats are such a good torque producing item why not put more in the system to increase torque. ha ha.

given the same tubing diameter you will never have a better preforming car becasue of cats. that is the stupidest thing I have ever heard. when designing and exhuast you set you torque curve by the diamter of the tubing mainly not buy putting restriction in the exhaust. think about what you are actually saying.

now one could argue going up to 2.5 from 2.25 could shift the torque curve up. I had the opposite effect on my x-pipe. I had noticably less traction from a roll than stock even with the 2.5 tubing.

 

[mogs01gt]

this thread cracks me up. from what I understand no cats have been removed. what had been removed are the resonators.

cats are up front I do belive and the resonators are down stream if memory serves correct.

these threads always kill me. If cats are such a good torque producing item why not put more in the system to increase torque. ha ha.

given the same tubing diameter you will never have a better preforming car becasue of cats. that is the stupidest thing I have ever heard. when designing and exhuast you set you torque curve by the diamter of the tubing mainly not buy putting restriction in the exhaust. think about what you are actually saying.

now one could argue going up to 2.5 from 2.25 could shift the torque curve up. I had the opposite effect on my x-pipe. I had noticably less traction from a roll than stock even with the 2.5 tubing.

no newer mustangs have 2 sets of cats. Some Older ones had 3 sets though.

 

[white-04]

How about this....we've seen data on how mufflers have made more hp than open pipes. Why can't the same be true for high flow cats?

I agree, if it is between the stock cats and an O/R pipe, I'm taking the O/R pipe. But a well made hi-flow cat could concievably outlflow a straight pipe. I haven't seen any data on it, but I wouldn't be surprised given what they have done with mufflers. I'm not saying a lot of hp, but 1 or 2 hp more wouldn't surprise me.

 

[ponysarepretty]

You do know that power is a fucntion of torque and to say you are losing torque is to say you are losing power, you are losing torque low rpm and gaining it in high rpm.

 

[djtech]

Where can I read more about exhaust restriction creating more low end power?

Just think, back before catalytic converters were installed on cars how much power they were losing! That must be why the 60's cars had no torque.

before I put on the O/R Prochamber. I could also break the tires loose just by stomping the gas from a rolling start. Now it's all power at 2500+ rpm. That is the magic number because at that rpm the car comes alive, it's acctually scary that I can be cruising along and push it to 2500+ hard and the tires will break and the car fishtails.

I also had a 2.3L mustang and put a SVO exhaust on it just to see what kind of power gains I could have . There was a major need for back pressure in that car because what power it did have was gone in daily driving. It is all about efficiency. The car is more efficiently making power in lower RPM range with 2.25 pipe and cat's, but after a set # of higher RPM's they are a major restriction.

 

[mogs01gt]

Where can I read more about exhaust restriction creating more low end power?

Just think, back before catalytic converters were installed on cars how much power they were losing! That must be why the 60's cars had no torque.

No you are thinking the wrong way. You do not gain power by creating restriction. What happens is, when you remove the cats or get a larger mid-pipe without cats, you flow more creating more power but it moves your power band up slightly. Now when you put the stock stuff back on with cats, you loose that added power and it moves your power band back down so you feel it sooner.

YOU LOOSE POWER, you dont gain it with adding restriction.

 

[back_in_black]

I agree, some restriction aides in low end torque, but it will take it away in the higher rpm's.

 

[hognutz]

no newer mustangs have 2 sets of cats. Some Older ones had 3 sets though.

I think you are mistaken. I think they have 2 cats and two resonators. I used to think they were all cats as well but someone informed me I was wrong.

 

[hognutz]

How about this....we've seen data on how mufflers have made more hp than open pipes. Why can't the same be true for high flow cats?

I agree, if it is between the stock cats and an O/R pipe, I'm taking the O/R pipe. But a well made hi-flow cat could concievably outlflow a straight pipe. I haven't seen any data on it, but I wouldn't be surprised given what they have done with mufflers. I'm not saying a lot of hp, but 1 or 2 hp more wouldn't surprise me.

I have seen this as well but it was usually on very expensive exhaust systems with hight dollar mufflers. not POS factory cats/resonators. most of the time on the tests I have seen though It was open header vs exhuast not full exhuast with just tubing and no mufflers.

adding restriction may turn the torque curve down lower in the band but it will decrease overall power. I mean you could put a 2" exhaust on the car to give it better power down low but it would not perform as well overall.

 

[mogs01gt]

I think you are mistaken. I think they have 2 cats and two resonators. I used to think they were all cats as well but someone informed me I was wrong.

Nope, 4 cats on must mustangs and I think the Cali models had 6. If it was a resonator, then there wouldnt be a reason for the rear to o2 sensors .

 

[djtech]

Well I disagree with your generalizations. I was being sarcastic in my last post because of all the people here who believe catalytic converters will give you power.

See my other posts on the thread and you'll see how I think these changes make a difference.

No you are thinking the wrong way. You do not gain power by creating restriction. What happens is, when you remove the cats or get a larger mid-pipe without cats, you flow more creating more power but it moves your power band up slightly. Now when you put the stock stuff back on with cats, you loose that added power and it moves your power band back down so you feel it sooner.

YOU LOOSE POWER, you dont gain it with adding restriction.