mid pipe or hi flow cat?
 

which is better?

depends if staying smog legal is important to you. Hi flow gives alittle more torque as well, but Mid pipe gives alot more top end and is better overall. Both are better then stock ;)

High Flow Cat!

Gotta' love the Random cat! 3" in and 3" out, stainless steel. BIG difference over stock. Not to sure how a mid pipe would feel compared, but with an otherwise full exhaust I would probably have to port my wastegate.

Frank

it also depends on how much fuel you have.
if u dont have a fuel pump, or injectors, you may lean out with a straight pipe.

Re: mid pipe or hi flow cat?
 

Do you have a ported wastegate?

Do you have a boost controller?

What ECU do you have?

Are you still running stock twins?

Is your motor ported?

What fuel mods do you have?

Without knowing all of this I would say definitely go with a high flow and stay far, far away from the midpipe.

The cat would also quiet the car down.

removing cat converters on standard cars could hinder performace, because this may adversely effect mixtures, boost levels etc etc. However if other mods such as aftermarket ecu, fuel pump and injectors have been fitted no problems should be experienced. Just be prepared for that stench of rich rotary exhaust fumes!!!!!

It'll hinder performance, all right--removing both cats on an an intake/catback equipped FD leads to uncontrollable boost/lean out situation and a blown motor.

Even with ecu, fuel pump, inj's (all of which I have) I was still creeping to 13psi hot day/15psi cold day *with a ported wastegate!* Imagine what would/could happen with a stock wastegate...

hey goodfella...would adding a good quality external gate fix the boost/lean out problem?

The guys that go single turbo use aftermarket external wastegates, which fixes the boost creep problem. The stock internal WG is inadequate to vent all of the exhaust gases (when you're open exhaust--no cats) away from the turbine.

So, to answer your question--yes, kind of. If you keep the stock twins then you're stuck with the stock WG.

And of course, you can still lean out, although it won't be b/c of excessive boost creep.

lemme know if you have any more questions....

Rich

I was planning on getting a midpipe but my mind has now been changed after reading these posts. To hell with a blown engine. I'm paying $3K for a tranny swap so I definitely don't have the funds for a new motor.

The high flow cat is a good compromise in my opinion. I used to me a midpipe guy, but now love my highflow. Not only that, but I've shot flames twice with the highflow, so it is possible :)

3 grand for a tranny shop? KD charged me about a third of that for my rebuild....are you going from auto to manual?

Rich

I had a clogged cat, so KD installed a mid-pipe. I thought it was too loud, and asked Dave to switch to a high flow cat. He dynoed before and after the change, and found no HP difference. The graph lines were almost identical. The high flow is quieter, but still loud.

Some hi-flo cats flow pretty close to midpipes as stated above but I think most of the pros are with the hi-flo cat.

Hi-Flo cat you definitely get more low and mid-range but overall less peak hp, much quieter, easier to tune and can help solve boost creep and spikes - the only bad thing is if used without the airpump they might go bad in a few years

Midpipe sucks with low-end power but really pulls above 6K rpms, uncontrollable boost, can lean out (especially on cold days) and is hard to tune perfectly, smells like a truck stop in your car, mind-boggling noise

Most drag racers will stay with a midpipe but for street cars, I think the midpipe is overall the better choice.

oops, I mean the hi-flo cat is the better choice

Yep

Goodfellas,
I would be happy also to have a HF cat and hit 368 RWHP.
I would be happy to hit 330 RWHP w/ HF. Must hit 330, must hit 330...

Steve

So which HF cat seems to the one of choice? I mean the one that is similar in flow to the midpipe, gives some low-end, is smog legal and controls boost creep better? Am I asking too much? lol

what about going non-sequential? That would eliminate boost creep.

Without a midpipe, you cant shoot flames

I really dont know much about exhaust systems or dp or mp's. would it be better to just but on a high-flow cat, or a dp, and which one is more cost effective? what are the results of putting a 3 in dp on there?

I run full sequential with a full open exhaust (DP/MP/Cat-back) and have been doing so for about 25K miles with the proper tuning. Do I have boost creep? Yes. When? 5th gear lugging it at 2K rpm and flooring it. How often do most people do that? Never. Sure, you'll have boost creep in 5th running down the back straight at Sebring International, but day to day, if your car is tuned right and you have a competent boost controller, it works just fine. A midpipe will be less expensive than a high flow cat. Your car will be louder however and not meet federal or state emissions. I saw a 40hp gain going from the stock main cat to a midpipe. I've posted dyno graphs on the forum so just do a search :-) If you're looking for a resonated stainless steel midpipe, I just happen to have a Pettit one for sale. Swapping out the twins for a modified T78.

Oh, going non-sequential will not solve boost creep problems. Even if you port the wastegate, you'll get a bit of it under certain circumstances. A way to safeguard the motor in those instances is to simply enrich the fuel maps considerably above a pre-determined boost level. Typically I run .95kg/cm2 on the twins daily in S. Florida (hot). Above that level on my PFC fuel maps, I've maxed out the fuel correction cells to 149's across the board (a percentage increase of the base map injector duty cycles). If I do overboost, it happens quickly and the extra fuel protects the motor.

So...if your car is properly modified then go with a midpipe for the power. I had MANY people, who really had no experience with midpipes, tuning, etc...say that I'd blow my motor within a week.
Michel

Falmes :drool:

http://www.gothamracing.com/catalog/...roducts_id=407

This high flow has stainless steel piping and has a bung for the airpump already welded on. It bolts right up. Can't beat the price, too....it's less than half the price of the one I have on right now. I think it's time for a change :).

i used to think midpipe, but after reading this, i have changed my mind to high flow cat.