Got the high-flow cat...now, do I put it on?
 

I recently purchased a Pettit high flow cat (used, but in great shape, from another Forum member). I already have a Pettit dp, and Racing Beat dual tip cat-back. I also have a modded airbox that has at least a 50% increase in the intake opening (with ducting to the front of the car). The downpipe and the airbox mod made a HUGE difference in the car's performance, and in cool/cold weather I often hit fuel cut as the boost will go over 11 psi when I get on it really hard.
Adding the RB cat-back just 'helped' that much more, I was once again amazed at the felt difference in power delivery, but also just about freaked out by how fast the boost hits. Keep in mind this is an automatic car, and unless you have driven one I don't know if you really understand the difference in the boosting of these cars over their manual counterparts, it is essentially just one big rush as when you stomp the gas, the boost hits 10 - 11 psi, drops for just a FRACTION of a second to 8 - 9 psi at transition, then it just keeps at max boost until you let off the gas. Since you aren't shifting and thus going thru the boost cycle as in a manual, this is the big difference.
Anyway, what can I expect with the high-flow cat? And how dangerous (as far as potential leaning out) will it be, or would it make that much difference?
I don't have an air/fuel ratio gauge, so I don't know what I am running.
I've got stock NGK plugs, always use 93 octane fuel and add about 4 oz. of Marvel Mystery Oil at every fill up, and I also use a can of Berryman's every other fill up.

I'd welcome all thoughts on this.

As long as you can keep that boost at 10-11 psi you should be safe. You will get quite a bit more flow out of the hi-flo though... So I'd keep a VERY close eye on the boost gauge.. If you see it creep, I'd take it off (or drive like grandma) until you can do something to keep the boost at a safe level.

When it comes to apex seals, better safe than sorry.......that main cat is a huge bottleneck. If you had a totally stock intake I would say go for it.

I just did the same thing as you (airbox, pettit downpipe, hi flow cat, cat back exhaust) but also have a M2 Performance ECU in the car (it came with the used engine I just bought). The guys at M2 specifically say not to put a midpipe on even when using their ECU --- I guess because not enough back pressure and the turbo pressure will build too fast or too much resulting in a lean condition.

I guess you can deduce from that that they would also think a stock ECU would be too dangerous with the open exhaust.

So when I was at Pettit and asked them if the hi flow cat would be a problem, they said no, but to keep an eye on the boost gauge. Sure enough, the boost would rise so quickly and seemded to want to go right past the 12-12.5 boost limit that the M2 ECU is programmed for. When it hit around 12-13 and seemed to want to go right past, I was concerned and would let off the gas. It is possible that it would not have gone any further, also possible it would have gone up another couple lbs and resulted in a lean condition.

I am at the point of deciding whether to get a Profec B to control the boost spikes along with a a/f gauge, or (as the previous engine owner recommends) put the cat back on until you are ready to spend some cash with a PFC (or other programmable ECU) that can specifically program for a hi-flow cat or midpipe. I guess at that point I would probably consider larger injectors and higher flow pump.

When I put the hi-flow cat on, it did make a difference; a bit quicker to hi boost. I am going to keep the "spirited" driving to a minumum until I decide to put the cat back on or upgrade computer/fuel systems. One way to look at it is this: you can buy a computer to limit boost or leave the cat on to limit boost, at least with leaving the cat on there is no added cost and nothing to dial in.

Probably didnt help you one damn bit, but hopefully someone else out there can give some more direction to the both of us.

John

Thanks for the replies so far. I would think that higher boost is fine as long as the car doesn't lean out to the point of detonation. I was thinking that even though the stock injectors might be at a high duty cycle they SHOULD be capable of keeping the a/f ratio correct.

Keep in mind I am wanting to retain the 'hold' function of the auto tranny, so that limits my electronic options....

I have a Pettit Hi-Flow sitting. I have an APEXI, Pettit DP, Pettit Exhaust, M2 Intake. Would the APEXI be good enough for boost control (currently on default map).

Obviously every car is different (and mine is a manual), but my experience with the hi-flow cat installation (with M2 airbox and RB dual) would suggest that you will easily hit the fuel cut (thus approaching dangerous a/f ratio levels) unless you have some method of limiting boost or adding fuel.

Just get a boost controller to keep boost levels at 10 psi. You have been here long enough to know that by now...:)

Yeah, I guess you're right. It is just that there isn't any one particular way to do so that really appeals to me.

The Europeans have some interesting ideas, I've seen some stuff on the Volvo forums that I might try....

Right now it is kind of academic as I am not sure exactly how the air pump fitting from stock to the Pettit is supposed to match up.
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