NOOB question
 

Ok, so I bought my FD a few months ago and I just got my trust airinx today.
The previous owner had the stock turbos professionally rebuilt about 3000 miles ago (2000 before i bought it) and did the precat delete with a full 3" exhuast, the only problem with this is he left the stock muffler on (cheap as) and got a crappy ceramic catalytic converter.
My question is if I run a straight pipe through by deleting the cat and muffler and put my trust airinx on before I get a pfc will I start to run too lean and risk blowing the seals?
It's the original motor with 84xxx miles on it and no rebuild other than the turbos. And at the moment the compression is 105, 105, 105 on the front and 100, 100, 100, on the back, +/- 5 psi all around.

I've seen and read damn near everything and nothing is black and white one way or the other. I know about the three mod rule, but at the same time I also read a full exhaust can cause you to run lean by itself.

It's best to assume the answer is yes, it would be bad. You haven't specified what ecu/fuel mods are in place, so you have to assume it's stock.

The 3 mod rule is outdated. The best way is to follow the boost. Install a boost gauge, get the car running 10psi, then as you change/add mods make adjustments to keep the boost at 10psi or whatever boost the car is capable of supporting. For a stock ECU and injectors, I wouldn't let the boost get over 11psi. Preferably 10psi.

So if you find out the car is running 10psi on a stock fuel/ecu, and you want to delete the cat and change muffler, do them one at a time and do a boost test in between. If you're set up for 10psi you have a little cushion to go one mod at a time.

Dave

yeah, stock fuel, that'll come at the end of the summer, what about the greddy airinx with 3 in exhuast but the same cat and stock muffler? but thanks for the tip about following the boost, and with this setup I might put 1000 miles on it before i get a pfc and walboro pump, is that too long?

The stock ECU is fine for stock boost levels (10psi). I would be very hesitant about trying to do anything which will raise you up to, or above, 11psi.

As long as you can maintain stock boost levels, the stock ECU and fuel system are perfectly safe. Just be wary of creep and spiking.

IMO, you have a better than fair chance of boost CREEP with a downpipe, mid-pipe and straight pipe w/no muffler.
Your intake is another issue. In a couple of months we could start seeing pretty big temp swings here, and what you can get away with at 85 F. (in the afternoon) may be different at say...55 F. (in the morning or evening). Without a boost controller I think it's possible to see some SPIKE. Do you have any other INTAKE mods?

No, unless you consider rebuilt turbos an intake mod.
So let me get this straight, w/ DP MP and a cat and muffler, it's a little less than fair chance of seeing boost creep?
and would it be a better investment to get a boost controller and gauge now to controll the boost with my other mods? or should I save my money and get an a'pexi PFC in five weeks when I have the money?

Don't confuse boost SPIKE with boost CREEP. While both can lead to lean conditions, they're not the same.
Boost SPIKE is associated with INTAKE mods. It can usually be kept in check with a boost controller, either manual or electric. Can't say for sure, but IMHO, your Greddy intake by itself shouldn't be an issue for SPIKE. But later on if you added say, a big free flowing IC or even an Efini 'Y' pipe, it would be a bigger concern. Bigger yet with cooler temps when air is denser as I mentioned above.
Boost CREEP is a result of too much EXAUST flow overwhelming your wastegate. Your proposed DP, MIDPIPE and straight-pipe with no muffler would likely put you there. And a boost controller doesn't help with that. Generally the only cure for CREEP is to port the wastegate (which is a bit of a PITA since it's internal) or add sufficient back-pressure back into the exhaust.
Good luck either way. Hope to see your car sometime yet this summer.

ok, well if i don't have to worry about spike then I won't as the intake is my only mod at the moment, i'll get a gauge and check it out.
but from what you're saying i shouldn't have to worry about creep either because I still have the cat and muffler?
Is this correct?
Come down to Lincoln on Fridays and especially saturdays and cruise O St. you'll see me sooner or later