# 1984 300ZX-T boost control method



## blakeZX (Apr 29, 2005)

Hello-

I recently acquired a 1984 300ZX-T 5spd Coupe, and I'm pretty sure it's using the stock Nissan wastegate (which runs 6.7 PSI of boost). I'm going to be putting in a manual boost controller soon, which I am making myself from a guide located at this site. Now, my baby's already got an APEXi N1 exhaust and a K&N Filtercharger intake, so I'm ready to alter stock boost to push more power. But I recently discovered that my car's boost used to be controlled electronically by an APEXi AVC-R Boost Controller (which costs a few hundred bucks, at least). Here is a picture of the unit that used to electronically manage the boost level; in a normal AVC-R install, this goes to the main control unit inside the cockpit.

APEXi Unit

Now I have two questions:

1-Since the vacuum tubing hooked up to the APEXi unit still seems to be hooked up to the manifold and wastegate, do I just need to undo the clamps and put my M.B.C. in between those two lines? That would render the APEXi unit completely useless, so I would probably just strip it out and toss it.

2-Has anybody found it *highly* beneficial to run their boost through the electronic controllers (such as APEXi AVC-R, Greddy Profec-B, etc.)? I actually considered getting my hands on a used AVC-R, since I've already got the lines routed to a good spot in my engine bay. I've never actually talked to an owner of an E.B.C., but I've seen many many people that run the AVC-R in their cars.

Any feedback appreciated.

Thanks,


:givebeer: :givebeer: :givebeer:


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## asleepz (Feb 24, 2004)

The thing about EBC are that they don't boost spike (go over the set limit for a short period of time during spool up) like some manual controllers. If you can find a used unit, I'd probably go that way.. If not, find the instructions to the unit and see how it was hooked up. You don't want to take off on the first drive and the turbo try to spool up 30PSI or so.


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## Zen31ZR (Mar 24, 2004)

I liked the Profec-B when I had one. Not the spec-2, but the older unit. Holds rock solid boost to 25 psi, and now shouldn't be hard to find fairly cheap since the Spec-2 is out. The AVC-R is ok, but requires dyno tuning to be truely effective. It's also a pretty invasive system since it actually goes into the ECUs wiring harness. I don't like those kind of boost controllers, personally. I'd pick a Profec-B Spec-1 before anything else.


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## back2vinyl (May 22, 2008)

Looking at the homemade boost controller shown on the link in the first post, I have concerns about how it will function. Since it is basically a spring loaded ball valve, I think it will need a constant flow of air past the valve to function properly, which is not how the system works.

Based on a visual inspection of my 87 Turbo, it looks like the wastegate is controlled by an actuating rod connected to a spring loaded diaphragm which responds to manifold pressure. So, there isn't really any flow through the line leading from the manifold to the diaphragm. If the spring valve did open and allow boost to activate the waste gate, it would close when manifold pressure dropped and the wastegate would be stuck open until the pressure leaked back out of the system.

It seems like a good way to raise the wastegate activation pressure would be to either replace the spring in the boost controller diaphragm, or maybe add some shims so that it under tension at rest. Has anyone tried this?


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## Spongerider (Nov 18, 2002)

blakeZX said:


> Hello-
> 
> I recently acquired a 1984 300ZX-T 5spd Coupe, and I'm pretty sure it's using the stock Nissan wastegate (which runs 6.7 PSI of boost). I'm going to be putting in a manual boost controller soon, which I am making myself from a guide located at this site. Now, my baby's already got an APEXi N1 exhaust and a K&N Filtercharger intake, so I'm ready to alter stock boost to push more power. But I recently discovered that my car's boost used to be controlled electronically by an APEXi AVC-R Boost Controller (which costs a few hundred bucks, at least). Here is a picture of the unit that used to electronically manage the boost level; in a normal AVC-R install, this goes to the main control unit inside the cockpit.
> 
> ...


Before you do any boost controller you need to to a few things first.

1) Make your engine is healthy.
2) Upgrade your IC to a larger IC.
3) Do research on how much boost you can safely run on 91 octane for the Z31.

I have seen *A LOT of DUMB Dumbs* get Boost Happy and blow their engine in less then a week. I'm not saying you are but it can happen fairly easily.

The AVC- r is a great unit and can be used by a amateur or you can tweak it out like a Pro. I've had this unit for several years and it has not given me any problems. Blitz, HKS, Greddy, & Apexi make great products it's just how many bells and whistles you want. As for a manual you'll have to adjust it daily depending on weather (temp and humidity) if you want consistent boost.


Answer to your 2 questions,

1) You would slice the vacuum tube going from the wastgate to the intake track. I would advise you look at the Apexi-usa web site for instruction not only for vacuum diagram but wiring as well. 

2) A while back at a dyno day, I had a chance to compare 2 identical z32 one being a manual and the other EBC at the same PSI. What showed on the dyno sheets was a quicker boost response and not a wavering hp line from the manual BC. 

Again it behoves you to to the 3 thing I stated above before proceeding to a BC.


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## blakeZX (Apr 29, 2005)

Holy thread resurrection, batman!

Well, this was posted like 3 years ago. Since then, my 84T sat for a year and a half, then I re-did the interior, and treated all of the rust, but I haven't altered the engine at all yet, or ran any more than stock boost through it.

I'll be rebuilding it soon with Z32TT rods, BRC pistons, a GT35R turbo, Nismo 555cc injectors (designed for the Z31, ultra-rare, NLA), a custom turbo relocation manifold, ported heads, and a Spearco vertical-flow IC. Probably going to be tuning it with Nistune or an SDS unit. I've also picked up a genuine 88SS VLSD/axles and some suspension goodies for it as well. Just waiting til I get my new DD (05 WRX) so I can take it off the road for a while and get the motor out.

Anyways, in the past few years I've learned a LOT more about how turbocharged engines (especially the VG30ET) should be treated, specifically in maintaining proper A/F ratios and keeping charge air temperatures down to avoid detonation.

That being said, I have found the answers to my questions and I will be regulating boost through either the wastegate spring or with an EBC...I'd rather spend the money on a quality unit than trust that DIY crap, especially on a build as pricey as this one.

But thanks for your replies, and the useful info.

-Blake


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## jtz31ae (Sep 7, 2007)

+1 for the Apexi AVCR


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