Replacing CAT with test pipe

There is no benefit OTHER than not having to replace a cat every 10-20 years!. I replaced the cat on my 328 with a pipe ONLY because the slow-down light system no longer worked and since the slow-down light "computer" is not available, I didn't want to have the possibility of an overheating cat/fire caused by a fueling problem with no warning system.

There is no difference in power at all unless the cat is rotted out/clogged. I couldn't tell any difference in the sound between a hyper flow Cat and the test pipe. I installed a HF cat shortly after buying the car, assuming the oem Cat was probably in need of replacement...turns out that the HF was a waste of money and the oem CAT was fine. But then, a few months later the Slow down system quit working and since there is no replacement for the SD computer, I bought the straight pipe and sold the HF Cat to a site member.

Obviously, if you have to meet emissions, you probably will need the Cat but since you don't, it's not an issue. I didn't have to meet them here in MD since the car was registered as a classic. FWIW, I would prefer having the cat but NOT without the slow down system working. IOW, WITH a working Slow Down system, I would have kept the cat as opposed to using a straight pipe.

 

Removing the cat should free up a few ponies and make it a little louder. Like the Euro cars...I removed the cat when I had my US spec '89...

 

It won't "free up" any ponies. There are tons of Dyno tests showing that. With modern cats - after those of the 70s' - there is no performance advantage to removing them. John Lingenfleter did a test of cats/no cats on a 700+ HP engine and the difference was less than 7HP and that, as he explained, could have just as easily been the error in the Dyno. If one ASSUMES that the 7HP was real, then, you could get maybe 1.5 on a 3x8. It would make a difference of about the the same as whether the driver weighs 160 lbs or 180 lbs.

 

Incorrect. Cats block flow, flow is power. I gained a few ponies on the dyno when I had my 328, 6 if I recall at the wheels, same day, same dyno, same correction factor. Also made it a tad louder. Anybody who says modern cats make the same power as no cats is wrong, I don't care who you are. Yes, sometimes (usually actually) new tuning will need to be done to realize all the gains. On my '11 GT500 I gained nearly 19 horsepower at the wheels after adding a cat delete H pipe. Bottom line, even the best cat is more restrictive then no cat. Don't let anyone tell you otherwise, heck just look inside of one, simple physics can tell you an open pipe will flow better then one full of material.

 

You added a crossover and removed the cat? That's a totally different thing than just removing a cat. Crossovers have been known for years to increase power and there are tons of tests available showing that. We added crossovers to car exhausts years ago for exactly that purpose. Most modern performance engines have crossover exhaust systems - they make more power and are quieter than a straight though dual system.

If you are saying you changed the exhaust in some way AND made other changes thus resulting in more power, that's a different thing to me than saying that removing a cat added HP. I have done a ton of Dyno tests with mufflers/cats. Most of the time there is no difference at all. Sometime the "performance' part reduces power over the oem part.

I personally was involved with Dyno tests for a company that makes performance mufflers where their performance muffler made less HP in a Dyno test than a new oem muffler. The performance muffler was a very famous bright red muffler that you could look straight through - very loud and "obviously" more powerful...but the only thing thing they WERE, was loud.

I readily admit I have never tested a 3x8 on the Dyno at all so I have no idea what removing a cat will do but my experience tells me that it will do nothing as far as power ASSUMING the cat in question is in like-new condition. Comparing a clapped out cat to a straight pipe is, of course, totally invalid. Any such test must compare new components.

 

On the 328 all I did was remove the cat. Was in perfect working order. Still gained a few ponies...on the GT500 I just swapped H pipes, one had cats, one didn't...19 hp gain at the wheels. Of course the more power a car makes the bigger the gains, but to think any cat makes the same power as an empty pipe is 100% incorrect. Plus then you compare a straight through muffler (assume a Cherry Bomb, which is junk) which will lose hp and tq by nature if not retuned to a discussion about cats? If that car is question was retuned for the lack of a muffler it would have gained power too. Even with that junk LOL. I have been using tuning software like HP Tuners for years and have been racing for over 15 years, and have seen first hand the benefits of cat deletes...I would put up any amount of money that any engine when tested and properly tuned after a cat delete will pick up power. I even have first had experience on back to back tests on a C5 Corvette at Kooks headers facility to confirm this.

 

A test pipe will make it sound much more "throaty".

One downside is the CO has to be dead on or you will get an eyeburning exhaust. If the O2 sensor is on, that should help.

I drove with a test pipe for about half a decade. I finally went with a Hyperflow. No difference in anything except the sound. The HF made it a tad quieter.

 

I guess what this really comes down to is simple - install a new cat and then a new test pipe on a 3x8. Put the car on the dynO with each of those AND NO OTHER changes. See what the Dyno says. I'm saying it will show no change that is beyond the standard error in any Dyno. I'll be glad for someone to prove that wrong by doing that test on a 3x8 and posting the dyno results here. And please, no inertial dynos.. REAL dynos, please!

My point re the muffler test was simply to point out that looking at a muffler OR a cat does not tell you anything about "restriction" or how how it will react with a particular engine. The muffler that I mentioned appears to most people to be totally unrestricted, and therefore "better" because it's essentially a piece of pipe that you can roll a 2" ball through from one end to the other. So it MUST let that poor engine breathe better! But that totally "unobstructed" muffler is a power loser on most cars we tested.

Here's an interesting observation re "performance" cats.
I replaced an oem 328 Cat with a performance cat back in '09. I did that simply because I figured the original cat might have been clapped out by then. Turns out it wasn't but that's not the point. The oem cat could actually flow more air than the Hyperflow cat...as tested on a flow bench. However, both cats could flow more air than the engine could generate for exhaust so the fact that one could flow more than the other was of no value as far as the engine was concerned.

 

Re-read my posts. That is what was done on both of my cars. Dyno, pull cat/s, recalibrate, dyno. Both showed gains as I said...a good Dynojet doesn't have anywhere near the "errors" you think either, and if you use corrected numbers with the proper SAE smoothing there will be no errors when doing pulls that close to one another.

Because you in most cases you can not simply remove a restriction without re-tuning for the extra flow. If proper procedures were done it would have most likely showed a gain. Case in point would be a cold air induction kit on most new cars. If you just pull of the stock airbox and add the aftermarket set up (with more flow, just like a cat delete) you will gain nothing, maybe even lose a little. But if you tune it for that extra air, gains will be had.

Must have been a poor quality cat then. Good aftermarket cats like the Magnaflow bullets flow much better then OEM, but nothing beats a test pipe. Another advantage of deleted the cats, especially on the 328 is lower operating temps. The Euro (cat-less) cars run cooler and do not even have the cooling vent in the rear bumper.

 

My test pipe certainly made the sound more throaty and much better pitch at high RPM as in 5K and up. It also has a small HP gain of around 2 ponies, but still, a gain is a gain.

 

My cats are gone and I have an ANSA exhaust. Let me tell ya brothers something about that power gain... I still can't beat an Accord V6

 

new Hyperflow Cat vs oem Ferrari Cat.

I'm not aware of any serious tuning/engine builders who use an inertia Dyno. However, they are fun at the Saturday Harley Davidson get-togethers. .

To say that John Lingenfleter didn't know what he was talking about re the cat/no-cat power thing is pretty heavy duty stuff. I'm pretty comfortable with my background in performance engine building/testing, having built several class-winning race motors and a lot of performance engines. But I wouldn't care to argue a point with someone who is (was, in his case) literally a legend in the competition/performance engine field. And no, I don't even like Chevys.

However, maybe we are not that far apart...

There are two questions in essence being discussed, not one.
The common question here regularly is, "will removing a cat and adding a straight pipe increase performance," Most people who are interested are just doing THAT - removing the cat/installing the straight pipe, that's it. MY answer to the question is "no,"

If the question is, "If I remove the cat and install a straight pipe AND make other mods [ usually fueling] will it increase power?" My answer to that is "Maybe."

Also worth noting the fueling mods might have increased power anyway because the fueling mods that usually accompany the cat removal could have been made with the cat but aren't because they will affect emissions testing. This was the point Lingenfelter made - that tuning can accomplish essentially the same power with either cats or not - at least up to power levels that none of our cars here will ever remotely approach.

 

How much hp increase is needed before we can actually notice it? That is the magic number. Anything below that is a 100% waste of time and money.

Why buy a test pipe, jack the car up and put it one if you can't tell any difference? If you like the sound, it my be worth it, otherwise.....

 

Generally, it is a fairly common view that on a car the weight/HP of our cars, 30HP is is considered the point where you can reliably feel a difference in power. That is, the difference is consistently noticeable by the way the car reacts...NOT how it sounds.

Obviously, you could tell much less on a Dyno or as a trap speed at a drag strip but nobody can feel the difference between two cars that have a a few MPH or tenth of seconds between them in the 1/4.

 

The question should be how much more Tq is needed and where

Hp is work over time so what one is looking for is more Tq in a given period of time. How much till it's noticeable? vehicle weight and MOI play a factor in that and more importantly where in the rpm range that Tq increase is located. And then you have sensitivity to dv/dt, some can feel it some can not, it really comes down to how sensitive your butt and head are to such things.

 

I went with test pipes.

My cats were so clogged when pointed at the sun all I saw was the Black Hole of Uranus.

I am old school. I love the smell of rubber, grease and gas. I love the headache REAL engines bring. I don't care.

If ones nose is that sensitive, leave Ferrari and drive a electric.

 

Not true for everyone. I can feel as little as 15 hp or so. I can tell when my cars are even slightly off. But I have been doing sanctioned drag racing for many years. A good driver can feel a car that is a few tenths quicker in the 1/4 as well, being that 2-3 tenths can be a 25 or more difference in power, or a big difference in gearing or stall speed if you have an auto.

 

+1

There is a big difference between the old pellet style cats of the 70's to the more modern honeycomb design. Just a change in replacing a good working cat will probably provide very little change in hp/tq.

 

I recently drove a friends 89 with a cat and my 88 without a cat. I felt more power without the cat. Butt dyno.

 

the wire is the thermal couple that reports temps via a resistance signal to the cat 'ecu' blocks that trigger the slow down light. it's a simple trigger circuit in reality that is triggered when the thermal couple senses high temps. So any new cat would need the port for the thermal couple, same type of circuit found on water heaters, gas heating units etc.. If you put in test pipes you can also provide a port for the thermal couple too, as exhaust gas will not get hot enough to trigger the light there is no harm in doing so, also keeps the sensor from dangling around.

 

FWIW, the Hyperflow straight pipe has a bung for the thermocouple. OTOH, the HF is a mighty expensive piece for just a section of pipe with a couple of fittings.

Your oem Cat is probably fine but you can do what I did and replace it first and THEN determine that it's OK!

If I had it to do over, I'd just go to a muffler shop and get them to make up a test pipe. Also, a reminder, I installed a straight pipe ONLY because the slow down light wasn't working. Of course, the test pipe does save a few pounds over the oem cat.

 

Just my view, but have noticed with many cars that removing cats improves temperature mgmt. Engine runs a little cooler.

 

Not on the QV's

I had the typical temp issues the entire time I drove without my cat.

4 years with the factory cat, about 6 with no cat and the rest of the time with a Hyperfolw - all the same. No change.