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· Registered
107,597 Posts
Discussion Starter · #1 ·
I've got an 83 zx turbo and just discovered that the exhaust has been altered for the worse. It looks stock to the cat (3 inch pipe to it), but the outlet which appears to be 2.5 inch has a very restrictive pipe welded to it. It looks like it's about 1.75 inch pipe to a universal silencer/muffler. Local muffler shops here give me the same crap about how you can't go bigger then stock.
What should I replace this with? Who makes it and what is the diameter and cost.
What was the original diameter and would it work when I raise the boost?
Finally, how can I raise the boost above stock? I want to intercool when I up the output...
Thanks much.

· Registered
107,597 Posts
Discussion Starter · #5 ·
> Well to start of I believe your 83's system
> to be identical to my 81 turbo. The pipe
> coming from the downpipe starts a 3
> but steps down to 2 or 2.5 as it
> nears the catylitic converter. Yes, what the
> muffler shop did by going to the 1.75
> pipe is restricting the flow necessary for
> the turbo to perform. I am going with
> 3 pipe starting from the turbo and
> going all the way to the back. The question
> that I have to ask is what type of money do
> you plan on spending? This is what I
> recommend for the ultimate exhaust
> performance with the stock turbo. Get a
> 3 mandrel bent downpipe with the O2
> sensor adapter welded in. Some muffler shops
> can do this, but they will use a normal
> pinch type bending machine. Check out
> www.racetep.com and see what they will
> charge for the 3 mandrel bent downpipe
> with sensor mount. Than check out
> www.a-1performance.com/index.htm for the
> 3 catylitic converter and 3
> inlet-----6in round muffler. They have some
> unbelievable prices and many muffler shops
> carry their line. Even here in California
> their products have been approved and are
> legal to install. You can read the legal
> jargon on their website. At the extreme most
> the exhaust should cost you $500, but I
> would shoot for $300.

> As for the boost. Get yourself a manual
> boost adjuster. This will allow you to turn
> up the boost to as far as it will go. You
> can get one from Motorsport
> auto(1-800-633-6331) approximately $100. You
> will also need to remove the stock pop off
> valve and either plug the hole up or buy an
> adjustable pop off valve from Motorsport
> auto, another $100.

> Now this will only let you go so far. 8-9lbs
> of boost will be the limit. This is due to
> the possibility of detonation(motor
> meltdown) and stock fuel limitations. To
> pass the 8-9lbs of boost you wil need to
> install an intercooler and a boost dependant
> fuel regulator. This will allow you to get
> 12-15lbs of boost. Anything higher and you
> will need internal motor modifications and a
> larger turbo. Good luck and I hope this
> helps.
Great info, I ordered the motorsports catalogue yesterday, so I hope to see the boost adjust in the book. The good thing about living in Tennessee is that we have no sniff tests or any inspections for that matter--anything goes short of slicks and bumper laws. A few bills on a good flowing exhaust is no biggie since I just graduated and deserve it. The turbo has got to be replaced soon, too. It's just not boosting much at all now.
As far as an intercooler I will probably try to scrounge one from a Volvo, Saab or Toyota.
I don't know if you've ever heard of this one, but my car has a potentiometer wired into the ECU that controls the lean/rich mixture. Turbo cars (stock) suffer a little in power above 4500 RPM. This control allows me to turn the resistance down which produces a richer fuel mixture which , in turn makes more power in the higher RPMs. The local Z-guru now recommends that I replace the pot with a resistor valued at about 250 or 300 Ohms hardwired right in the ECU. This is probably what I will do so that I don't have to take my hands off the wheel when someone wants to go a little.

· Registered
107,597 Posts
Discussion Starter · #8 ·
> You guys are forgetting something about
> opie's car. If the thing has a 1.75
> exhaust, that will kill the performance of
> the engine. The engine should have no
> problem pulling to redline (6400) with all
> of the stock components. I highly recomend
> replacing the exhaust system before you do
> any other mods. Yes, it is true that a
> 3 exhaust from the turbo out is the
> way to go. I am currently working on
> producing a 3 mandrel downpipe for the
> 280ZXT's. However I don't have a car to
> prototype. Anyone willing to lend me their
> car for a day or so could end up with one
> for free. I am in the Fresno, CA. area and
> the Phone# is (559) or (209) 346-4480.
> Fresno Auto Sport Technology.

> I think that the problem you are having is
> due to the small exhaust pipe. This may also
> be causing the turbo to spool slowly and
> reduce boost levels. More flow = more go.

> BTW. the stock system is 2.5 from the
> downpipe back. The stock cast iron downpipe
> starts at about 1.9 at the turbine
> outlet and increases to 2.5. However,
> it is rather restrictive. Go w/the 3
> for great performance. Good luck!!!

> Ian
An upcomer out of his shop put the pot in for the previous or original owner, I don't rememember which, when he tried to make a Z-shop off on his own. The main Z guy likes to keep everything stock and to factory specifications. I can't get much as much info here in Volunteer country on mods as when I lived in Tampa.
The truth is the car did pull better 10 months ago when I bought it. Now on cold mornings (35 degress or lower) the turbo lets out a monotone type of squeal at idle for about 2 minutes or so. I'm sure the turbo is expiring. The smaller downpipe does look like it has a megaphone design to it, slightly. The pipe in between the cat and downpipe is 3 inch.
It's possible that it is aftermarket, but it's 3 inch for sure and 2.5 inch rearward of the cat into crappily welded 1.75 incher.
Question: should I leave the pot wired in or remove it when I up the boost? What do ya think?
The car has 210000 miles on it, but other then the recent low power it runs like cars with 100000 on them. With the mileage in mind I will probably go back with a stock turbo(395.00)turbo timer and harness(125.00) and the oil feed lines(?). Or does a turbo timer come with replacement oil feed lines? Also going with the adjust-a-buse I mean boost. thanks
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