I was searching for possible causes for my boost loss. I've got a pfc and when I run 14.5 boost I get a good boost pattern until maybe 5500/6000 rpm when it starts to drop off down to maybe 10psi. I dyno'd about 300rwhp and you could see the power levels off at 6-8k instead of continuing to climb. No problems running 10psi.

Assume the PFC is working correctly, there are no leaks, and stock turbos(only about 30k on em)/manifold are in good shape.

One thing I found is a collapsed filter/intake hose could choke off boost. I don't have a pic handy but I have the pettit intake and my filters are kind of fubar. They got kind of bent when I installed em and have worsened each time I need to remove/replace. Could that do it? Or maybe the boost control solenoid?

And say I do find the problem and the car holds boost to redline. Now my problem is S.Kan tuned the car to run with this condition on sunoco 94. I'm worried that if the car holds boost it'll lean out too much. Maybe an octane booster as a safeguard?
thanks

 

any cats?

smashed fiters aren't too good for flow...but I don't think they'll account for a 4psi drop, but considering the twins air path, maybe it is bad enough to choke them at high rpms.

if the car is only tuned for 10psi at redline, there is no way octane booster will save you at 14psi.

 

Got a dp and I bought the car with an N-tech hiflo 5 years ago. Might have the previous owner's receipt for that to see when he put it in... Average life of a hiflo? Would replacing a clogged cat necessitate a retune? I would think not but to be safe...

You can see my problem. I can't test to see if I got the problem fixed but I won't know until I test it. Only thing I can think of is to get it tested with a tuner who can add the appropriate fuel *in case* I fixed it. But its a waste of money if I didn't get it.

 

I invested in a WB just before x-mas and can't believe I didn't spend that money years ago...since then, I've now got an EGT too. Zeitronix controller can monitor and log EGT also, to me...those on a modified rotary are priceless.

 

You are running 14.5psi w/ 94 Sunoco and you only made 300RWHP? Are you running the stock IC? Also, a slight taper is somewhat normal, but not one that is less by 4.5psi. Are you using the PFC to control boost?

Also, most ocatane boosters are worthless. Their claim of "raises ocatane by 5 points" is really just .5 octane boost. Toluene is a better solution (http://www.elektro.com/~audi/audi/toluene.html).

 

WaLieN, yes on 300rwhp @14.5psi on 94O. And its a streetport that pulls about 17in of vacuum @750rpm. Plugs were a bit fouled but thats it. I had the old coolcharge2 IC then, now asp large. Thanks for the octane booster tip, never used the stuff but trying to think up a solution.

Heard back from the original owner who said it may be a hiflo or it may be the ORIGINAL stock cat. 90+k on it. Time to find some comparison pics and crawl under there. Unfortunately if it is stock and I replace it with a hiflo that will most definitely require a retune, correct? Whatever is in there has had me passing emissions here in PA.

dubulup, i don't even have a datalogit yet

For the record, relevant mods are:
1200cc sec inj., supra fuel pump, power fc
pettit intake, asp large ic, dp, some cat, rb catback
KD rotary streetport + rebuilt stock turbos, both 30k miles

 

stock cat is HUGE heavy and ugly...can't mistake that.

anytime you change air flow characteristics it is a good idea to re check A:F's. Steve tunes pretty conservative (11.1:1 or so), unless you ask otherwise (at least what I read). So, if you are tuned for 10psi at redline, a new hiflo cat will lean you out some...maybe get you closer to 11.5 or so (its a hard call, because where you max torque is...is the real crucial area...not just redline). Just try to keep boost under control and around 10psi. With your mods you should see 300rwhp at 10psi.

 

At 14.5psi the vacuum check valve could be getting blowby that empties the vacuum reservoir.

The first thing to do is check that cat, like the others mentioned.

The second thing I'd do it hook up my boost gauge to the vacuum chamber and make sure it's got plenty of vacuum available (15"+) during all times that you're boosting. Or, without hooking up anything, get the car to lose boost, let off throttle for a split second, and punch it again - if the let-off results in the boost coming back, that suggests the vacuum was leaking out.

Another possibility is the solenoids leaking or getting overwhelmed by the 14.5psi pressure, but that would only affect the turbo control solenoid and prevent a transition at 4500, but no effect above that.

Dave

 

I would definitely wager on the cat being a problem.

 

If I recall the 10psi tune turned about 275rwhp.

The transition is pretty good right at 4500 -quick and it gets right back up to 14.5psi before it starts to drop.

Thanks a ton everyone, the next time I post I'll add a pic of the cat. If its stock I won't need any more advice

 

A restriction in the intake trac could easily cause the boost to drop off at high RPM I'd fix that first.

 

I think this rules out the cat. If I remember what the stocker looks like this piping is wayyy too big for stock, looks like same 3in as dp and catback. A confirm is always nice though.

Cat:


Cat, different angle:


Cat, er heat shield:


cat/rb exhaust:


cat/dp:




So if thats not it, how about a look at my sad filters:
top view:


front view:


Thanks again for having a look.

 

You've got a highflow cat, no doubt about it.

Unfortunately, the ordinary aftermarket cat will collapse due to the extra high exhaust temps of an FD. So unbolt that thing, take it down, shake it and see if it's loose inside or crap falls out.

With the air pump removed, it may shorten the life as well - but that all depends on tuning. Afterburn in the cat can really cook it.

Dave

 

I've always run the airpump and the cat should be an ntech. It has passed PA inspection every year. Waiting to confirm the mileage on it but I suspect its about 30k.

 

I figured you didn't have an airpump since I it looked like the air injection pipe wasn't hooked up to the cat.

Those filters are pretty cruddy. If they're producing enough restriction, the elbow to the primary turbo can sometimes collapse.

Dave

 

You know I belatedly thought that too. duh! I never asked if the last owner hooked up the air pump, just assumed so.

But is it possible to get emissions down enough to pass without the airpump and precat? I didn't think the cat would get heated up enough to work right.

If that hasn't been hooked up for the past 5 years the cat has to be toast and could be problem solved. I just jacked the car up enough for pics, I've gotta get under there and see if the airpump got hooked in somewhere else for whatever reason. thanks dgeesaman

 

In my county, emissions on a pre-96 car are visual inspection only. If it is a sniffer test, then a good tune may work, but I know very little about that subject.

And most of the mechanics who look at an FD have a hard time finding the dipstick. So I wouldn't take that for much value.

Dave

 

We have visual and sniffer in the philly burbs. Most mechs don't know to look for the precat though. Its passed on both a kd rotary tune and kan's, never a failure though the HCs are always at the limit.

Anyway, the airpump connects to the cat via a hardpipe right? Just to help me track it down. I was reading maxcooper's site and his ntech looks just like mine and he does mention getting the airpump welded in there.

http://www.maxcooper.com/rx7/parts_info/cat/index.htm