Cat Hpipe VS Stock VS OffRoad
 

Well when I changed my car from the stock Hpipe to the offroad I got HUGE Gains. It was one of the very last mods I did, so I figured the stock Hpipe was kinda clogged and thats why it made such a huge difference.

Well I just put on a MAC Hi-Flow Cat H-pipe and my car is wayyy quieter! Which is alright, but I lost tons of power.

I DONT GET IT!??!

Everyone had me convinced I would loose maybe maybe 5hp.

It definatly lost about 30-40 hp on the butt dyno. It doesnt feel alot faster than when I had the stock catalytic H pipe on.

It used to just annihilate the tires going into 2nd gear for 30-40 feet, now it just spins em for about 5-10feet.

Is there any explanation for this?

HELP, I need more HP. Im going to have to do something drastic, the car is not what it used to be.

Skyler

Well I just went and ran my cousins 1968 Mustang.

He traps 100mph at the track and I would always just pull like crazy on him.

Guess what.

WE RAN DEAD EVEN TONIGHT.

Neither one of us could pull either way.

So I've lost 7mph atleast w/ this H-pipe, wtf gives.............

Sky

maybe the MAC "high flow" cats aren't as high flow as they are supposed to be. Why are you changing over to cats? For emissions? I have swapped out a set of high flow cats for my off road before, and it wasn't that bad. I think they are bbk or something. But it did make it a bit quieter. I should be back in cali in about a month or two, I hope to see you at carlsbad when I get back to the states. Later, -Chris

Sky- Long time no talk, hope all is well besides this H-Pipe issue.
We run the MAC High Flow cats on Dads 93 Cobra and they flow pretty good, ran much better and picked up mph over a stock H-pipe, his only had 30K on it. He traps 119 with the blower on it so I say get it to the track and see how it runs, you may need a different tune.

They say the Off Roads are worth 10-15hp depending on the set-up, more in the upper rpms. Why did you put it back on, just for testing or as a precaution, I heard they are cracking down out there.

Take Care,

Rick

Im thinking they are clogged?

I am running dead even with a 100mph trapping car.

The power is gone, it doesnt even burn the tires into 2nd gear anymore.

I don't understand how it could possibly rob that much power, is there a chance they came clogged??

Is MAC ****!?

Skyler

Hey Skyman....

My friend went from off-road to the MAC cat pipe and he did not notice a difference at all.

I myself will be going with a MAC cat pipe. Their pipes are quality pieces for sure.

If you can, get to a dyno, I would like to know.

I know what you need....a supercharger :D

Let us know what happens.

How long has it been on the car? Has the computer had time to adjust? It will give the O2's much different readings now...

Hey Rick! Yea, how are things, man your car keeps gettin faster, mine seems to be getting slower and less and less fun to drive. Man Im about ready to get rid of it.

Its definatly lost a LOT of power, no need to hit a dyno, I know my car well.

I am going to check everything out under the car tomrrow, tune it up and reset the comptuer, after that Im going to get a bassani pipe and see what happens.

Im really frustrated and pissed.

Skyler

Sky-
With a vacuum gauge, there are two easy tests you can run to determine if your exhaust is restricted (cats clogged).

First test:
1) Attach vacuum gauge to manifold vacuum source.
2) Observe vacuum at idle.
3) Snap throttle to WOT and release, while watching the gauge.

The vacuum gauge should drop to almost zero when you hit WOT. When the throttle snaps closed immediately after, the vacuum should read 4" to 6" higher than what it did at idle. It should then settle back at the same reading it was at idle before the WOT snap. This whole exchange should go from idle reading to idle reading in 2-3 seconds, tops. If it takes longer for the gauge to return to the same idle reading, your exhaust is restricted. The longer it takes, the worse the restriction.

Second test:
1) Attach vacuum gauge to manifold vacuum source.
2) Warm up engine.
3) Observe vacuum at idle.
4) Leave engine idling for 10 minutes. Do not touch anything on the car during this time. In fact, go inside and fix some coffee.
5) After 10 minutes, observe the vacuum.

If the vacuum is the same or higher, you don't have any resctrictions. If the vacuum gauge has dropped, you do have a restriction. The more it drops, the greater the restriction. If it drops 1" or more, you have a serious restriction. 2" or more and you might as well have the exhaust welded shut. Keep in mind that a rich exhaust will clog up cats in a hurry.

I noticed a loss when I switched from shorties/off-road to long tube/mac cat pipe. It was the same thing for me, wouldn't pull nearly as hard. I've never tracked my car with the this combo with shorties/off road, only long tubes. I trap 107-108 this way, and I feel that with the offroad it's faster. Must be MAC's quality biting us in the butt again. I'm getting an off-road pipe for the long tubes soon, and then I'll know for sure what the difference is.

Anyone running the BBK or Bassani Cat pipe for long or short tubes?? Wonder if they have similar experience?

Stock h pipe hollowed out?
 

This guy I know just took a stock H and hollowed out the cats by bute force beating and a long metal rod. Makes it at least look like it has cats if someone does stick there head under there, and is a lot cheaper to buy a used H pipe than an OR. Any ideas on how well this thing will perform??? In theory I would say better....

Serious torque loss....
 

Skyler, I have only off-road H, flows, CAI, and 3.55 gears and my car smokes 1st and spins all the way through 2nd. Sounds like the MAC H-pipe took about 30ft/lbs of torque. Just guessing.

Hey Skyman,
I also have just recently put on the Mac High-flow cat h-pipe. My experience very different though. I actually gain a lot of low end and did not notice a difference on the top end. I had a mac off road h-pipe before hand.

GOOD NEWS!

Well I reset my computer by taking the battery off for a half hour and hooking it back up.

THE CAR PULLS LIKE CRAZY AGAIN!

I guess it had to adjust to the new H-pipe.

Pretty interesting huh? Well I am excited now. It is jurking and bucking a little bit in the low rpms.

Im sure I can tune those bugs out though.

Skyler

I was going to say that I had a similar experience with going from my BBK hi-flow h-pipe to an off-road x-pipe. I thought I made a huge mistake since it was so sluggish. Resetting the computer was the trick.

I hope you have your air pump hooked up to those cats. If you don't, they won't work as well and will get clogged in no time.