Turbo FAQ

Written by Raagi Pandya   

[0.0] PROLOGUE
So there sits your new 300ZX turbo (new to you at least). The perennial sports car of it's day. A smooth, comfortable high speed touring machine. Beautiful, sleek, and powerful; at first seems insurmountable; but like anything else the shear sense of speed soon dulls. The yearnings for more speed beckons you like a siren, tantalizing you with mustangs, camaros and corvettes that lay just out of reach. You see all the hubbub about twin turbos, and all writhe at the sight of multi and variable valves. Annoying teens in integras, golfs, and even civics are nipping your heels. This is unacceptable. Something must be done.

Ya Ya, my vain attempt at writing prose. So what.

Now to the real stuff. The what, how and why's of series I turbo Z-cars. This covers any and all 84-89 300ZX turbos, what to modify, how to modify, when to modify. Most of this knowledge is based upon first hand experience on what works, and does not work on turbo Z's. You find me harping on some points, and completely ignoring others. There is usually a reason (beside me forgetting :) ). A lot of things out there in the 'performance' world DO NOT WORK. Or more importantly DO NOT WORK AS ADVERTISED.

At this point, I am going to focus on power producing modificationss (engine, turbo etc.), no drivetrain, suspension, wheels, or anything else. Not yet at least :)

The sections will be broken down in order of recommend modifications. Some modification should not be done without the previous ones. Should as in DON'T. Of course you can ignore these warnings, but don't blame me. And don't post a message saying 'Need new motor for a 8X turbo.....". The modifications are usually listed in most expensive to least expensive, you may notice that many times I do not recommend the most expensive parts. BTW --- All prices quoted are approximate, based on my recollection. (So I could [rarely] be wrong :)

Included also are the REALISTIC performance improvements, based on REALITY, not some otherworldly premonition. ALL horsepower numbers will be for REAR WHEEL HORSEPOWER, the only kind that matters: add around 15% for FLYWHEEL horsepower, used only by dumbass people for comparisons and bragging. To give you an example of some inflated/inaccurate claims, one manufacturer claims his exhaust adds 30 horsepower! Maybe on a heavily modified car with a stock exhaust, but a stock car adding an exhaust will NOT give you anywhere near that number. In case you hadn't noticed yet, advertisers don't always represent themselves accurately. For your information (in case you don't have a calculator handy), a stock turbo Z has around 170 rear wheel hp.

The basic premise for modify the early model of the 300Z turbo is BETTER BOOST. Almost all modifications are done to improve, coax and beg for better boost. I say better boost in place of more boost. Idiots talk about more boost. 20psi - 25psi, means nothing by itself. The goal here is not to make high boost levels, but to IMPROVE PERFORMANCE. That said, it must be stated that nothing will be more noticeable, will give you that 'kick-in-the-back feeling' like turning up the boost. But there is a limit. Higher boost begets a host of other factors, factors which are often ignored, understated or just plain forgotten. An automobile power plant is a 'system', where everything is closely coupled. Ignore one step, one section, and improvements will be very difficult to achieve.

First some theory: A stock 300ZX has one of the most basic turbo systems available. It is a single, fixed pitch turbocharger (Garret T-3), with a stock boost of 4-5psi. There is no intercooler or compressor bypass valve, and the wastegate is built into the turbocharger assembly(internal). There is an external pop-off valve (not the same as a bypass valve), which is in the intake manifold. Why is the system so simple? Because it is only made to handle low boost situations. I once had some yahoo go on and on about intercoolers, saying how they are so great, why doesn't the Z have one... nanana... An intercooler is NOT EFFECTIVE below 8 psi, the costs/losses from an intercooler would exceed any possible gains; dumb guy still doesn't understand it. Same for a bypass valve. What this means for us is that there is a lot of room for improvement :)

The functions of these aforementioned pieces will be explained as they become important.

This should ALWAYS be the first step. Yes you can skip this step, but it will not be good for the motor, will not give you the performance you want(expect), and will haunt you later on. A good exhaust system will allow exhaust gases to leave in most efficient fashion. The exhaust on a turbo is as follow: Exhaust manifold/Down-pipe with turbocharger bolted to it, single catalytic converter, center pipe, rear pipe/muffler/tip.

Some units are sold as 'cat back exhaust systems', which usually means it comes with the center pipe. I do not think anyone makes an exhaust system that removes/replaces the stock cat. If it is just a muffler, you will need to get someone to make/bend some pipe for you, which could be annoying.

If you can get away with it, remove your cat, or have it punched out. It is basically a honeycomb structure inside which can be broken up with a broomstick. Of course this is totally illegal in some places, so you didn't hear it from me :), but it does make a difference. Installation of a system should never cost more than $50, at any reputable muffler shop.

I have also heard of some people running their turbo(ONLY) cars without a muffler. This is possible only on turbo cars, due to the inherent quieting nature of a turbocharger. I have no idea if this kills low end torque, but I don't think it would, as most high-flow mufflers have little to no restriction whatsoever. Of course this would be REAL cheap (like...uhh... nothing), but I don't know how legal it is. Of course you should still get some bigger piping.

One quick word about exhaust tips. If there is one thing I cannot stand, it is these ridiculous cars with 5 inch tips welded on to the end of a 2" system. What a bunch of LOSERS, get a freekin' life. There is no point whatsoever to have a tip whose diameter exceeds the exhaust system pipe diameter. Similarly, some these half wits bolt 3.5" - 4" diameter systems to non-turbo cars (i.e. civics), thereby killing any low end torque, and making their cars even SLOWER. Some people do not have a clue, you have my full permission to laugh like hell at them. Retards.

SOME VENDORS:

1. Borla Stainless-Steel Mufflers: ~ $400 for the muffler only

Excellent high quality piece and performance. Load, but not obnoxious, louder than the GReddy, but less than Dynomax. Will not rust, comes with 10 year warranty. Quite expensive. Need to find/ make center pipe.

2. GReddy Exhaust System: ~ $400 US

60mm (2 1/2) pipe with highflow muffler. Louder than the HKS, but not obnoxious. Not much noisier at speed. Does not rust except for welds, where surface rust will form eventually. Good quality but expensive.

3. HKS Exhaust System: ~ $300 US

65mm (2 7/8?) pipe with highflow muffler. Near stock volume inside, low grumble from outside, probably the quietest system available. Not much noisier at speed. Does not rust except for welds, where surface rust will form eventually. Good quality but mildly expensive.

4. Dynomax Muffler: (I think there is a 'system' too) < $100 muffler

Good performance but loudest of the bunch. Some say too loud. Optional stainless steel one costs more but will last longer. Need to find/make pipe. Works as well as all the others, costs less, but only you can tell if it's too loud. They are available at your local speed shop.


RECOMMENDATIONS:
 

[2.0] STAGE II: INTAKE

This step is often overlooked. It SHOULD be the second step. I have heard of bad things happening if this step is skipped. Bad things like having your intake pipe collapse under high boost(intake pipe is made of rubber) because of insufficient flow. It is not expensive, very easy to install, and doesn't take any time.

The intake system is as follows: Intake filter assembly/filter, resonator, intake pipe, mass air sensor, compressor side of the turbo, turbo-to-throttle body pipe, throttle body and intake manifold. Don't worry, all you will need to change at this stage is the filter assembly/filter and resonator. Most filter systems are 'cone' types, which actually replace the entire air filter assembly. They are usually washable and reusable, so they will never need to be replaced, just cleaned.

You can also take off the resonator (changes the sound a bit, but does nothing else). Do not, under any cirsumstances, attempt to cover the holes in the resonator with tape. The tape will be sucked off. If you're lucky it'll get stuck on the air flow meter screen. If not, well, engines don't run on tape.

SOME VENDORS:

1. HKS Powerflow: ~ $250 US

A fancy shamancy intake filter shaped like a funnel, replaces the entire assembly, is cleanable and reusable. A bit of overkill in my opinion. I don't think it's available anymore?

2. K&N Filtercharger (Cone) and all types similar: ~$ 120 US

Simple cone filter. I got mine before it was called the 'Filtercharger' so it was about $70! Easy to install, needs cleaning once a year.

3. Universal K&N cone filter: ~ $60 US

Rich tells how easy it is to install the bare filter and save yourself $100 over the "filtercharger" system, which is the same thing. These are available for $48(shipping included) from Sam Strano


RECOMMENDATIONS:
 

[3.0] STAGE III: BOOST CONTROLLER

[4.0] STAGE IV: INTERCOOLER

Intercooling has been the buzzword for turbo speakers for a decade. The basic job of an intercooler is to reduce the temperature of the inlet air, which is usually quite high due to the compressor. One of the theories of gases states that as pressure rises so does temperature, along with creating higher pressure the turbocharger's compressor also increase the temperature of the inlet air dramatically. Sustained high boost can rocket up the intake charge temperature; stock boost settles at ~110'F, running 12psi jumps that number up to 280'F+!!(Tested at 70'F ambient) High inlet temperatures can cause severe detonation. This is not good! This is why above 8 psi, an intercooler is highly suggested.

There are two main types of intercoolers, air-to-air, and air-to-water. An air-to-air intercooler uses a big, efficient 'air radiator' that cools down the intake charge by using cooler outside air; an air-to-water intercooler uses water in place of air to do the cooling, and cools the water with a radiator. Air-to-air systems tend to be simpler and weigh less, but air-to-water I/C are more efficient, and have a smaller pressure drop. I do not know of anyone who makes a air-to-water I/C for the turbo Z any more, it would have to be a custom job; air-to-air IC's are fairly common.

There are two main factors that are commonly used to explain intercooler performance: I/C efficiency, and pressure drop. Efficiency is a direct equation of how much[well] the inlet temperature is dropped at maximum boost/temperature. Using the above numbers, HKS' intercooler was tested to be 69% efficient(by Turbo Mag back in 1987). This means at 70'F ambient temperature at 12psi, the inlet temp will settle at 135'F, a drop of 147'F. Not bad!!!

Pressure drop is the amount of boost pressure 'lost', due to the intercoolers installation. This is somewhat of a misnomer, however. If for example you have two vehicles, both running 12psi with fixed manual boost controllers and without intercoolers. An intercooler is added to one, the boost pressure of this car is now measured at 10psi, so a pressure drop of 2psi was experienced due to the installation of the I/C and all the associated piping. But this pressure can be regained by setting the intercooled car's boost controller up a bit to 12psi. On a fuzzy logic boost controller, the boost would stay at twelve psi, as the unit will compensate for the pressure loss automatically. What this does mean, however, is that if the turbo in both cars max's out at 15psi, the non-intercooled car could hit the true 15psi, while the intercooled car could only hit 13psi, because of the pressure drop. So why get an I/C? Because of the inlet temperature reduction, it may only be possible to get 13psi with an intercooler; without it the car would severely detonate. It's that simple. It makes the system more reliable; it does not necessarily 'make' a lot more power, it allows the turbo to 'make' more power.

In addition to the actual core, the piping of the intercooler is also very important. Like any piping, it must be mandrel bent (smooth bends, no kinks/ripples), and should minimize the number of bends. The length should also be minimized as much as possible, but remember one foot of bent pipe equates to about 5 feet of straight pipe. It must safely clear all underhood objects (no small feat in a Z), and be relatively easy to remove sections for repair work. The size of the pipe should not exceed 60mm, in fact 50mm is recommended to improve boost response. A stock or even modified turbo will not need more than 50mm. A good system will come with a compressor bypass valve. When the throttle on a turbo car is suddenly closed (from a high boost situation), the pressurized air must go somewhere, without a bypass valve it travels backwards to the compressor and the backpressure might stall the compressor blades. This puts undue stress on the turbo (imaging going from 100,000rpm to zilch in 1 second flat!) and kills the boost response. The compressor bypass valve will allow air to travel in one direction, but when the pressure is reversed, the valve opens and lets the high-pressure air out the valve. Of course this makes a really loud, high pitched scream. It sounds great and scares the hell out of pedestrians and motorist. It also keeps the compressor spinning, allowing the boost to build quicker when the throttle is reopened. This will lower a quarter mile by a good 2/10ths.

Installing a intercooler system can take anywhere from 8-10 hours, but most are not beyond the ability of the average home mechanic and his/her tools.

SOME VENDORS:

1. GReddy Intercooler System: ~ $1500 US

Comes with a large, efficient Air to Air Intercooler, all associated piping (ABS plastic), a very effective compressor bypass valve(racing type). Probably around 75% efficient, with 1psi pressure drop.

2. HKS Intercooler System: ~ $1200 US

Comes with a efficient Air to Air Intercooler, all associated piping (ABS plastic), a compressor bypass valve(standard type). Around 70% efficient, with 1.5psi pressure drop.

3. Spearco Intercooler System: ~$1000 US

Spearco is a dedicated intercooler manufacturing company. Very large, very efficient Air/Air I/C, stainless/steel piping, no bypass valve. Around 80% efficient and less than 1psi pressure drop.

4. A Custom System: ~$300-500 US

This will take some considerable planning but is not too hard to do. First find an intercooler which will fit up front of the condenser from a local boneyard(you will more than likely need to remove the condenser cooling fan to install it), make/buy bend the piping for yourself. Get a good quality bypass valve. Making your own sounds a lot worse than it is, drop a post on the board for more details. Quite a bit cheaper, and you should probably get about 65% efficient with 2psi drop.

RECOMMENDATIONS:
 

Here's where thing start to get a bit murky. You must be very careful with the parts you get, as at this point you are pushing the stock motor/turbo/drivetrain setup. You can very easily go backwards in power, or worse, blow something up. What is usually involved here is some type of aftermarket fuel control. Here are some options:

Modified Fuel Pressure Regualtors:
These are sometimes called 'Rising Rate' pressure regualtors, what they do it increase the fuel incrementally with additional boost. They are usefull, but a bit of a kludge method, you are essentially 'fooling' the stock computer, and your left trying to 'tune' the air/fuel ratio yourself. This additional pressure squirts more fuel per pulse thru the injectors. Of course this does not increase the maximum rate of the stock injectors, they still will max out at about 14 psi. The stock pressure regualtor can be 'modified', simply restricting the amount of fuel that is returned to the fuel tank. However this modification is on ALL the time, meaning the car will run very rich at low boost levels, killing you spark plugs, and actually decreasing you low end hp. Pretty Cheap: ~$200US for a Rising Rate Regualtor.

HKS/GReddy Aftermarket fuel Computers:
Plug in units that retime the fuel delivery curve and the amount of fuel injected by the injectors. These can allow the injectors to flow more fuel, but are still restricted by the physical size of the injectors. To compensate, you can add Additional Injectors under the units control, this can get you to the 15psi stock turbo limit. These are usually thread into intake system. Expensive: $1000+ US for the controller, $200 for the injectors.

JIM WOLF Computer Upgrade:
This firm will exchange your stock ECU (computer) for one that is recalibrated for additional boost/fuel maps. They will also remap the timing curves, maximizing horsepower and reliability. They are also limited by the size of the stock injectors, but they can provide larger, higher flow injector as a replacement for the stock ones. Moderately priced: $500 for initial computer, $100 for a reburn. $400 US for the larger injectors. The Wolf package is by far the most advanced and reliable way to increase boost levels on a turbo Z.

A NOTE ABOUT COMPUTERS & CHIPS:
Any good chip manufacturer will need to know what components you have/do not have on your SPECIFIC car, and where you live (climate, fuel quality). Anyone who offers you a chip without knowing what modifications you have done to your car is a FOOL. These 'dumb' chips can actually slow you down, and may even cause engine damage! When you change components, you should get a new chip reburnt with these new parts taken into account. This is the ONLY way to do this correctly. Chip manufacturer typically used advanced timing as the main way to
show gains in horsepower. If you advance the timing too much on a modified 300ZX turbo, you can very easiliy blow the motor! This must be taken into account.
 

TURBOS:
Increased size turbo can flow more air, changed compressor/turbine blades can increase boost response and still flow more air. Rebuilt ones can be cost effective replacements for worn/dead turbos. There are many, many turbo manufacturers, most are able to get you customized rebuilt turbos or a larger
upgrade. The most popular upgrade is usually a 'hybrid' turbo. This uses the stock turbo's housing(making installation a snap) and modifies/changes the compressor/turbine wheels. The intricacies of different turbo options is way beyond the scope of this FAQ. Contact a reputable vendor and explore your options. This is one way to get those massive power increases (50hp+).

BTW -- alot of people these days are going on and on about twin/two turbo charger systems. These provide good off boost response and good power. However any large, upgraded turbo system for most twin sequential turbo cars (i.e. supra, rx7) will invariably switch to ONE big turbo. Why? It is
mechanically much simpler, will flow much better than any two-turbo system, and is MUCH cheaper. For some cars (TT 300ZX, TT Stealths), underhood layout makes this a non-option, but contrary to popular opinion, two is NOT better than one. So when some moron starts going on an on about how wonderful twin turbos are, point out that all high horsepower cars (you know, the Grand Nationals running in the sevens) have ONE turbo. Only babies who need off-boost response need twin turbos. Of course this is what we have nitrous for :)

PRICE: Ranges from quite moderate ($500US) to outrageous ($2000US) +installation

VENDORS: TEC, Turbo City, Jim Wolf Tech, Stillen, GReddy.

CAMSHAFTS: My recommendation is to stay away from this one. I have yet to hear any good stories about the reliability of aftermarket cams in these turbo cars. I have heard of some breaking, ruining
heads. If you do got for it, get the most reputable kind you can find, based on a NEW billets, not reground from stock ones. Go for a mild cam, nothing too outrageous. The ultimate here is to have a custom cam ground to your head/systems exact flow specifications. (Yeah sure, that sounds real cheap!)

PRICE: Probably $400 US for a good sets. (There are 2 BTW)

VENDORS: Nissan Motorsports, Crane Cams(?), Bullfrog Cams(?)

HEAD/MANIFOLD PORTING, POLISHING, REPLACING PARTS: Once again, from what I am told, not very worthwhile. The only thing I would recommend is port matching, that is matching the intake port to the heads to the exhaust ports to the turbo. When Nissan designed the motor, it used what is called a maximum displacement theory. That is, the motor cannot (should not) be bored, stroked or ported. The motor is designed for a specific size, to keep weight and reciprocating masses down. A good condition stock head should easily handle 350-400 hp. The bottom end is nearly indestructible. For those speed freaks: you can buy large race-only heads from Nissan Motorsports, or custom pistons and valvetrain components, but I'm sure they are real cheap :)

HEAD GASKETS(METAL): This is a highly recommended modification. High boost can obliterate the stock head gasket. A good quality metal gasket will make damage due to light detonation a thing of the past, allowing for some leeway during tuning.

PRICE: $200 US parts +installation (8 hrs??)
VENDORS: HKS, Greddy, FelPro

NITROUS: Probably has the worst reputation of all aftermarket components in history. Credited for destroying thousands of engines. Almost all the problems associated with nitrous can be explained by one sentence: NITROUS DOES NOT BLOW MOTORS, IDIOTS WITH NITROUS BLOW MOTORS.

Taking a stock four cylinder motor and expecting it to handle a 150-200hp nitrous[shot] is ridiculous. Like any other modification, nitrous must be well planned and installed correctly. The danger with nitrous is the fact that it can be relatively cheap, so unfortunately 'cheap' people buy it, cheapout on
installing it professionally, and cut corners where ever they can. This is exactly what kills motors. Many people are unrealistic in there expectations; a 100hp stock motor will not handle a 100hp nitrous shot without some serious internal modifications. However a 250hp motor will easily handle a 50-70hp shot, with very little if any internal modifications. All that is required is to maintain a proper Fuel/Air ratio. In essence nitrous is simply a very dense amount of air, which has 37% more oxygen by volume that standard air. When injected into the cylinder heads with an appropriate amount of fuel, this creates much more power. Nitrous is neither flammable nor volatile, it is however stored under extreme pressure (>1000psi) and is very cold (-127'F). Despite what you may hear, nitrous with turbocharging is a fantastic
combination. The nitrous comes on low, providing the off boost response and improving low end torque. It also spools the turbocharger immediately, and since it is so cold it provides some serious secondary intercooling (like 50-75'F). In addition, advanced computer controlled fuel delivery and timing control make a realistic and professional installation practically bulletproof.

Any addition of nitrous must have an additional amount of fuel to maintain the proper F/A ratio. This can either be done with supplemental injectors, increasing flow of the stock injectors or larger injectors. On a turbo car, most nitrous systems are what is called 'wet' systems; that is additional fuel is injected with the nitrous right into the throttle body or intake pipe, and the positive boost pulls the air into the cylinders. The danger with this system is some vehicles may not have the most optimum chamber distribution, i.e. chamber 1 may get lots of it, camber 6 may be very little.

Fortunately the 300ZX turbo has an excellent distribution pattern, all cylinders get equal amounts of flow. For low HP levels (50-100) this 'wet' method can be used, however for higher HP level (100-150HP) you will NEED larger injectors and probably an upgraded fuel pump; the all-out way of doing nitrous is to have your nitrous direct-injected into your intake manifold/cylinders (direct port injection) with larger injectors providing the fuel. This is only necessary for those really crazy levels(150+HP). Note here that using high boost (12psi+) with full nitrous is a BAD idea, the stock pump cannot feed enough fuel for much over 300 HP. Many good turbo nitrous systems are set up to use full nitrous when boost is below some preset level (7psi) then gradually tapers it off as the car approaches full boost.

BTW -- a 50HP nitrous will feel like a lot more (due to the secondary intercooling and instantaneous turbo spool). And no joke people, it will be an increase of 50 Rear Wheel horsepower.

PRICE: ~ $500 US for a 50-70hp shot. Probably the least expensive way to get 50hp, installation is fairly straight forward, although the system will need some calibration. I recommend having it professionally
installed and calibrated($200US).

VENDORS: NOS, CompuCar, TopGun

[7.0] COMPONENT LIMITS FOR STOCK EQUIPMENT

All this talk of running high boost has gotten me thinking. I placed a call to Jim Wolf Technologies, who has been modify, racing and tuning 300ZX's for over a decade. In fact, many components sold by other retailers (Stillen, Motorsports Auto, Options) are actually manufactured by JWT. I spoke to Clark Steppler, the co-founder about some basic component limits for a turbo Z car. Some of these are real eye openers. I'll start with the most relevant stuff.

MAXIMUM USABLE BOOST[for a the stock T-3 Turbo]: 14.5psi

Anything above that point, the rise in inlet temperature, and backpressure in the exhaust manifold (due to the manifold and turbo, not your exhaust system) gets to catastrophic levels. Without a VERY efficient intercooler and a modified turbine wheel, playing above this point is dangerous. In addition, the increase in actual produced power will be very small, in the neighborhood of a few (~5)hp per POUND of boost. So running 17.5psi will only net you an additional 15hp over the maximum of 14.5.

MAXIMUM FLOW RATE [for the stock injectors]: 14.0 psi (~300 Flywheel HP)

He was very adamant about this, the stock injectors are at 100% DUTY CYCLE AT 14.0psi. At this point your injectors are injecting as much fuel as they possibly can, running very hot in the process. That means above that point, the injectors will not be able to maintain a safe fuel/air ratio. Under some conditions you WILL run lean, and this will blow your head gasket, or possibly damage your motor.

MAXIMUM FLOW RATE [for the stock injectors with a stock computer]: 12.5 psi (~270 Flywheel HP)
Without a change to the stock computer, the limit on the injectors is even lower. Safety margins limit the stock injectors to 12psi (for overheating reasons, actually). So for the many of us with a stock computer, 12.5 psi is the usable limit.

MAXIMUM FLOW RATE [for the stock fuel pump]: 14.0psi (~300 Flywheel HP)
In addition, the fuel pump's flow rate maxes out at 300HP, it cannot provide sufficient fuel for anything over that. At that point, the pump must be augmented with an aftermarket pump, or swapped for a larger pump (a la Twin Turbo)

MAXIMUM CALIBRATION RANGE [for a stock Air flow Meter]: ~350 Flywheel HP.
Above this, the meter cannot give accurate readings.

MAXIMUM FLOW RATE [for a stock throttle body]: ~400 Flywheel HP.
Above this, the body should be modified/enlarged and the TPS sensor recalibrated.
 

All these numbers are fine and dandy, but what does it mean in real life measurements?

Here's an example (my car):