My car is currently equipped with a newer (Sub 6k miles on it) stock pre-cat, but a high flow Midpipe and M2 dual exhaust.

As we all know and read, the best route is to eliminate the pre-cat with a straight pipe (DP). Previous owner of my car, however, wanted to keep low-end power at its best and felt a DP took power from the lowend and moved it up top...

My car has no other power mods (Stock intake, stock IC), and I've recently given thought (and am about to buy) to ignoring the power difference and getting a DP.

Will my car's boost creep/spike given I'll have no Pre-Cat, a high flow main cat, and an aftermarket catback?

Seems to me it'd be too *unrestrictive*, however, some suggest that the High Flow isn't a world apart from a stock MP and it'd be silly of me to sell off the High Flow to buy a used stock MP, as I put a DP on my car....

Thoughts? Experiences? I would also think that only having a High Flow cat would make the exhaust smell pretty bad, and I'm looking to keep my car modest. Not a sacrifice of drivability/practicallity for the sake of xxHP..

If anyone has ever had this combo (High Flow Cat, DP, CB...with no other mods) let me know. If I can do that for now, that'd be great. From this point I'd definitely invest in boost control and ECU before upgrading my intake, IC, and boost levels at all.

 

getting rid of the precat is a must. not because of the restriction in flow, but because the precat actually cooks your engine and all the rubber parts near it.

you will definately see boost spikes up to 15 pounds at turbo transition with a DP and hi flo cat.

you need to make the cheap manual boost controller or get a greddy profec b.


EDIT:
you will only get the bad exhaust smell for maybe less than a minute when you first start the car as it warms up.

 

?????? A mid-pipe or a high flow cat which do you have?? A mid pipe is a mid pipe, there is no "high flow mid pipe".
The biggest reason people replace the pre-cat with a down pipe is for reliability. As a matter of fact, you'd be hard pressed to find too many FDs out there still with pre-cats.

There is no such thing as a stock MP.
Intake = air in, exhaust = air out. The system works like any balanced equation, increase air in, increase air out to acheive balance and power. You are trying to open up your exhaust and staying with stock intake, why?

 

I had dp and high flow cat on the stock turbos for 2 years and never saw my boost past 11psi on primary, secondary or transition.

 

boost on primary means nothing trexthe3rd.

it takes one spike over 15 psi at turbo 'transition' where the stock fuel injector duty cycle is overworked and... poof. you can get chipped apex seals.

 

You will likely need a boost controller with a downpipe, hi-flow cat, and cat-back. The stock intake will reduce the boost levels and spiking though. The exhaust smell should be fine after a few seconds, as potatochobit said.

If your boost levels are controlled to 10 psi, there is nothing wrong with running those mods on a stock ecu. You are also not going to notice any loss of power down low, you'll be too busy enjoying how much faster the turbos spool up and your increased throttle response.

 

too bad you didn't post this a month ago. you could have come by and checked out my old car with that setup.

DP will give you more power throughout the rev range. Doing a header on a piston engine can sometimes give you the situation you described - less low-end/mid-range more up top, but the concepts are different on a turbo charged car.

When you do the downpipe, consider getting it jet-hot coated. At the very least wrap it in header wrap. It will help reduce underhood temps.

 

I have a similar setup. Not opening my intake or getting a bigger IC until I have a proper ECU.

I have a lot of fun on the primary turbo, boosting to 15psi on the stock ECU.
BUT I am very careful on secondary boost...staying at or below 10psi, which is normally tough to do, but easy for me since I have a secondary boost issue which remains unsolved.

You asked for experience. Mine says that the stock ECU can deliver 15psi on primary boost. Secondary boost, especially over 10psi is probably too much CFM for the stock ECU to handle.
my $.02

 

Trex: I was under the impression that a Midpipe is a midpipe, period. Whether it's stock (Cat), high flow (aftermarket), or straight piping, it's still a midpipe, the one between the DP and the Catback. Sorry if that made things confusing.

I am not "Trying to open up my exhaust" as much as I am trying to keep my car reliable and healthy. The reason it's as opened up as it is now is because of the previous owner. If it were me I'd have just the DP for reliability reasons, and the M2 Exhaust for looks/sound reasons. When I want more power, I'll consider opening up everything else too, IC, Boost levels, ECU, Fuel, etc.

Thanks potatochobit, rynberg, alberto for your input.

I think I am going to put a DP on and get a stock main Cat and keep my High Flow for when I have the money and time for an ECU and other goodies...

 

You are a fool.

In the FD world, the term "midpipe" is typically reserved for a straight pipe without cats. The terms "hi-flow cat" and "stock cat" are used for those situations. Just to help you avoid confusion in the future...

No reason to do that. Running a hi-flow cat on the stock ecu is perfectly safe, just use a boost controller to lower boost to 10 psi, if necessary.

 

A downpipe, high-flow cat, and cat-back system will be fine, especially with the stock air box. You won't get boost creep. If you get a little boost spiking, you can resolve that with some cheap Holley carb jets, hardware store needle valves, or something more sophisticated (EBC). But try it first and see -- I doubt you will have any major problems.

A midpipe (a pipe with no cat) will be very stinky all the time. A high flow cat might be smelly for a short period on start up but will not stink otherwise (this is VERY different from the always-smelly midpipe).

-Max

 

Which high flow cat would some of you reccomend. rx7store.net now offers one, but I've never heard of anyone using it. Everyone else just use the pettit cat?

 

www.rx7.com makes the best hiflo cat and its a reasonable price.