Primary cat delete power gains

I want to go totally catless, but I've heard mixed reviews on power gains. Are there any good links of power with/without primary cats on a stock tune.

 

Currently I have LOC and secondary deletes on a 6.2 car.

 

*I don't care about my environmental footprint*

 

Nick

Ive got the same,but on a 09 lp640 the way you are now,Im thinking of a set of high flow cats i think its the step between,and im in MA it would never pass without any cats.Doing away with them would not give any notice in HP.

I replaced my primary cats with pipes from SP on my 03, the car feels stronger. I have passed NY inspection four times with no problems.

 

Call SP you will not regret it.

 

 

 

 

PMB - they probably just hooked up your car to the computer like they do in AZ so as long as you do not have any lights coming on it would read as ok. No cats will make it louder for primary but I honestly did not feel a power gain or weight savings. That car will be extremely loud FYI. If you want your car even more obnouxisly loud then take the primary cats out otherwise your wasting your money if you are seeking HP/torque gains.

PMB - they probably just hooked up your car to the computer like they do in AZ so as long as you do not have any lights coming on it would read as ok. No cats will make it louder for primary but I honestly did not feel a power gain or weight savings. That car will be extremely loud FYI. If you want your car even more obnouxisly loud then take the primary cats out otherwise your wasting your money if you are seeking HP/torque gains.

 

 

Mine seems to pull a little stronger, however, I have not had it on dyno.

I have a question: how can you tell what cats you have? When i purchased my '03, it came with a Larini exhaust. Is there a way to tell if i have high flow cats?

I'll see if i can dig up some old dyno graphs of the 6.2 with stock/aftermarket exhaust + primary cat deletes.

That would be awesome Will, thanks!

 

Nick

Generally speaking the engineers who design exhaust systems do so in a manor that gives you the best BHP they can. It is called scavenging. Tuning an exhaust is Far More Difficult than tuning the intake. Even going to random straight exhaust pipes will not give you as much BHP as a properly "tuned" exhaust system. I would bet that most if not all "bolt on" modification result in less performance for cars.

 

aehaas

Generally speaking the engineers who design exhaust systems do so in a manor that gives you the best BHP they can. It is called scavenging. Tuning an exhaust is Far More Difficult than tuning the intake. Even going to random straight exhaust pipes will not give you as much BHP as a properly "tuned" exhaust system. I would bet that most if not all "bolt on" modification result in less performance for cars.

 

aehaas

 

Sort of agree.... Engineers design the exhaust systems to make the best BHP they can with all cats in place. More power with bolt on if all other areas are tuned at the same time such as timing and fuel mixture. Quite a bit more.

I replaced my primary cats with pipes from SP on my 03, the car feels stronger. I have passed NY inspection four times with no problems.

 

Call SP you will not regret it.

 

Do you still have the oxygen sensors + thermal sensors hooked up/plugged in? Any issue w/ the CEL (Check Engine Light)?

From the pictures, it looks like SP has spacers for the narrow-band, after cat, o2 sensors. Which pull the sensor out of the exhaust flow, to basically subject it to the same amount of exhaust particles as if there was a cat. If it doesn't come with them, use spark plug spacers to back the narrowband o2 out of the flow path.

 

Nick

Generally speaking the engineers who design exhaust systems do so in a manor that gives you the best BHP they can. It is called scavenging. Tuning an exhaust is Far More Difficult than tuning the intake. Even going to random straight exhaust pipes will not give you as much BHP as a properly "tuned" exhaust system. I would bet that most if not all "bolt on" modification result in less performance for cars.

 

aehaas

Factory engineers have to factor in other aspects to exhausts than mere power gains, such as emissions compliance in many different locations; noise levels for all types of buyers; cost to mass produce; heat control; and many of these compliance create backpressure that may allow for more low-end torque, but it does leave room for better flow.

 

Aftermarket exhaust builders are aiming for power. So they don't have to comply with emissions (aside from the use of a high-flow cat); worry about noise levels, and since many aftermarket exhaust systems don't have sound suppression, aftermarket exhausts weigh less than stock; cost difference with aftermarket units is between the use of stainless steel, mild steel, and titanium; therefore taking advantage of an exhaust design with better exhaust flow for the specific reason of making more power without having to cater to the other aspects that the factory has to worry about.

 

For example, here is the OEM downpipe of a Subaru WRX STi vs. an aftermarket downpipe. Notice how the OEM unit uses a flat flange to block the exhaust flow from the wastegate, where the aftermarket unit has a divorced tube for a more smooth exhaust flow from the wastegate. Also, note the diameter of the primary exhaust pipe has gone up in size. A WRX STi will pick up 30whp from a different downpipe.

 

 

or for a better example, here is a friend's '12 GTR:

 

stock:

 

HKS Kansai Service Titanium Exhaust:

 

 

stock:

 

HKS Kansai Service Titanium Exhaust:

 

 

Nick

Reason you are not feeling any gains after removing primary cats is most likely you have not had the car tuned. Stock ECU's are not tuned for no cats. Get an Evoms tune and I bet it will be significant. Plus, they can tune your car to keep the cel light off.

I straight piped my old Murci, had no cats, RWD, and a proper tune and made 525.1 RWHP. Have yet to see any other 6.2L come close.

Good to know. Thanks!

booty dyno says there is more power.

 

Nick

Factory engineers have to factor in other aspects to exhausts than mere power gains, such as emissions compliance in many different locations; noise levels for all types of buyers; cost to mass produce; heat control; and many of these compliance create backpressure that may allow for more low-end torque, but it does leave room for better flow.

 

Aftermarket exhaust builders are aiming for power. So they don't have to comply with emissions (aside from the use of a high-flow cat); worry about noise levels, and since many aftermarket exhaust systems don't have sound suppression, aftermarket exhausts weigh less than stock; cost difference with aftermarket units is between the use of stainless steel, mild steel, and titanium; therefore taking advantage of an exhaust design with better exhaust flow for the specific reason of making more power without having to cater to the other aspects that the factory has to worry about.

 

For example, here is the OEM downpipe of a Subaru WRX STi vs. an aftermarket downpipe. Notice how the OEM unit uses a flat flange to block the exhaust flow from the wastegate, where the aftermarket unit has a divorced tube for a more smooth exhaust flow from the wastegate. Also, note the diameter of the primary exhaust pipe has gone up in size. A WRX STi will pick up 30whp from a different downpipe.

 

 

or for a better example, here is a friend's '12 GTR:

 

stock:

 

HKS Kansai Service Titanium Exhaust:

 

 

stock:

 

HKS Kansai Service Titanium Exhaust:

 

 

Nick

Comparing exhaust changes on a turbo car to a naturally aspirated car are apples and oranges. Turbo cars benefit from higher flow, NA engines still require a certain degree of back pressure for optimal performance.

Are you stating that there is not enough back pressure in the aftermarket systems for the Murcielago, or just stating in general that n/a engine's need backpressure?

 

Nick

 

Even replacing a cat with just a straight pipe is not simple. If that new pipe is just 1/8 inch wider or narrower it will change the tuning. If it was put in and resulted in 1/4 inch longer or shorter overall length of the pipe the tuning is changed.

 

Most people modify the exhaust because they want a louder sound. If there was 20 more BHP they wound not notice it anyway. Louder may be caused by the exiting of multiple pressure ways at the same time. This can only mean they were stacked somewhere in the exhaust and Increased back pressure.

 

Also, a dyno reading of more peak BHP does not mean anything. You need the better part of the curve to be higher at more RPM ranges. The only real test is road testing as a 0-60 or 1/4 mile run. Making modifications and then tracking each one is time consuming and not possible most of the time. And I doubt these aftermarket companies have dynos anyway.

 

Most “seat of the pants” gains in BHP are a result of intake tuning for low RPM gains, rather than exhaust tuning. Few sell intake improvements as there is no increase in exhaust sounds to “prove” the added power.

 

And who volunteers their car to be chained to a dyno machine and then tracked a few dozen times for this research? It would mar and tear up the car quite a bit.

 

aehaas

SP and Fabspeed both have dynos.

 

Dyno has virtually zero wear on a car, there's not even enough load put on the driveline to get an exact tune. Hence the reason that many people do a baseline tune on a dyno, then go road-tune the car.

 

20bhp is noticeable.

 

My car pulls significantly harder through the midrange. When the secondary cams kick in (upper power band) the power delivery is MUCH more powerful than it was with the cats. Low range of the powerband. . . I do not do pulls from 1,000 rpm (or anything below 5k); so there could be a low rpm power loss (or no gain or mild gain) and I wouldn't notice it because it's not an area that I frequently use aside from city driving.

 

I will have to line up with another Murci to see the exact differences though.

 

Nick

From the pictures, it looks like SP has spacers for the narrow-band, after cat, o2 sensors. Which pull the sensor out of the exhaust flow, to basically subject it to the same amount of exhaust particles as if there was a cat. If it doesn't come with them, use spark plug spacers to back the narrowband o2 out of the flow path.

 

Nick

Nick, can you send me more info regarding these freaking spacers. Who supplies them?

You shoot flames now?

Nick, can you send me more info regarding these freaking spacers. Who supplies them?

They came with the SP kit, so SP is the best place to contact for these specific spacers. Otherwise some google brings up many options.

 

You shoot flames now?

It sounds like it, but my mirrors haven't lit up at night.

 

Nick