This Cannot Be Good. (I ain't got a MAIN-CAT!!)
 

So I took all youz guyz advise and removed my pre-cat last night to replace it with a Pettit SS DP this week-end...and then IT HIT ME...the pre-cat was bolted to what seems to be a 3" pipe that connects to the rear pipe that's part of the HKS Draggar II mufler on my 93 FD.

I've been driving the car (just bought it about 2 months ago) with out a Main-Cat. So...my questions are... 1.) What the hell should I do? 2.) What changes am I going to experience when I install the DP? 3.) I was boosting 10-7-10 with the pre-cat, what type of boost change can I anticipate now without a Main-Cat but with the DP installed?

The cars exhaust really wasn't very loud before, but something tells me things are about to change.!!

This really sucks!! Give me some direction guys. THANKS.

Are you saying you had a MP in place of a stock cat? If this is so then opening it up with the DP is going to cause you to boost higher. How much? really depends on your car. then you can start looking at threads on boost control.

Well if you want to call it a mid-pipe. Looks like the previous owner may have taken it to a muf shop and had it rigged that way. The "pipe" is made of steelcause it's rusted all over( no holes yet). This is a pretty long pipe, bout 4' to 5 ' in length. I thought a mip-pipe was kinda short?

So you're saying that a Mid-Pipe replaces the Main-Cat? Excuse my ignorance!!

correct. mid-pipe is a replacement for the main cat. it's just a pipe that's about 4 foot long.

It's going to make your boost creep like a mofo :)

I suggest geting a boost controller or an ECU upgrade.

Is it a Possibility or Probability that my boost will go up? And how much HP will I gain if the bosst pattern only goes up to let say...11-9-11. Current boost pattern is 10-7-10. Thanks.

It doesn't matter how much hp you will gain. You will (probably) have uncontrollable boost creep, and massive spikes on transition. What matters is STAY OFF THE BOOST!

What you need is a cat until you can get your wastegate ported, and get an ecu or boost controller. You're really playing with fire having a full open exhaust on a stock ecu. It was not designed to handle it, and boost spikes or creep = rebuild. (I've been down that road, not a pretty one)

I'd suggest purchasing a hi-flow cat, but even that will give you higher than stock boost. Long story short is you need either a cat, or a boost controller ASAP.

That does suck, but you need to pony up the cash for a high flow cat. Do you still have an air pump? There should be a tube running from under the UIM to where your midpipe is. Hopefully it is still there. You will need to buy a hi-flow cat that has the tube for the air pump like the Bonez cat (from www.rx7.com) or the rx7fashion one (www.rx7fashion.com).

You may also need to purchase a boost controller (home depot or electronic) once you have everything installed but you might be ok with your restrictive stock intake.

Whatever you do, do not run that midpipe on the stock ecu. I suppose you could pick up a used M2 or Pettit ecu instead of buying a hi-flow cat and boost controller for now, if you are really tight for money.

Yea, what I want to know is why would someone put in an mp before the dp... dp=not only performance but cooling also

the previous owner saved you the time and money to get a mp/catback. i do think that you are running some kinda after market pill/boost controller because with a mp/catback, you should be boosting way more then 10-7-10 which is a damn near perfect boost curve. I agree with the others when they say with the pre-cat/dp installation, you should watch out for boost spikes and creep.

You can put in restrictor plate to help prevent boost creep. It's just a plate with a hole that you put somewhere in your exhausts system (e.g. between your MP and CB). It reduces the effective diameter of your exhaust system so your wastegate can do its job properly.

Restrictor plate's dont always work. Ask GoodfellaFD3S

You guys are awesome. Great advise from all !! But "IF" I begin to gain abnormal boost (above 12), I'll just give-up the benjamins for a boost controller. Maybe the GReddy Profec B?

Rynberg: I ran into the tube last night .It's sitting next to the Tranny plugged with a spark plug.

I'm hoping skyrocketing Boost won't be a problem, cause the Pre-Cat seemed to be in pretty good shape (didn't look clogged). SO might be the DP won't really produce much greater flow than the pre-cat.?? Do you believe in miracles??? Thanks to all who took the time to help with their comments. I'll do a write-up shortly after I install the DP in a few days.

If your wastegate is overloaded (i.e. too much exhaust), then a boost controller will not help you. You need to port your wastegate (port = widen the diameter) or install a restrictor plate.

JONSKI: Thanks for the info. I'll consider porting the wastegate if extreme boost becomes a problem. Maybe porting the WG is something I can do?

apart from taking out your dp and turbo's and changing all the necessary gaskets... and then porting the wastgate... sure you can do it yourself... just time consuming... ;)