In this article I will be going over all the details involved in the rear mount turbo on my 1997 Nissan Maxima.
Being the first to put a rear mount turbo on a Maxima I had to figure out a lot of things along the way. This article will answer many questions that I have been asked over the years as well as address myths that are generally mentioned. The article is organized in the same way and order that I addressed the project:
Why a Rear Mount?
One day I was watching an episode on TV where they showed an installation for a rear mount turbo on a Corvette. During the episode I started to day dream about the maxima being turbo charged and how easy it looked on TV. I reached out to a friend who had a turbo and injectors collecting dust in the garage and decided to go for it. I was a full time college student with no job so the budget was minimal and I had no resources other than a DIY mentality; this is why the rear mount was attractive. I was clueless on how turbos worked as I had never been involved or even driven a turbo car before; I started to learning all the aspects of a turbo system
How a turbo system works?
The turbo has three parts, the compressor housing, the turbine housing and the mid section. Both the compressor and turbine have wheels that are connected by a shaft which are held by the mid section. The turbine side connects to the exhaust piping from the engine and as exhaust flows from the engine it makes the turbine wheel spin. The turbine varies in size and dimensions internally and produce a back pressure in the exhaust between it and the engine. The turbine housing also has a variety of flanges with different sizes such as T4, T2 or even a V-band nowadays. This pressure forces the wheel to spin with greater force and velocity. As exhaust flows through the wheel, making it spin, it then exists out of the turbo and out to the atmosphere.
As the compressor wheel spins it pulls in fresh air, compresses the air inside the housing and then exist into piping that is connected to the engines intake manifold. Often the compressed air needs to flow through an intercooler since air becomes hot as it is compressed. The turbine and compressor both have similar designs, an inlet and outlet.
The pressure generated between the turbo and the engine is regulated with a wastegate. Think of the wastegate as a bleed valve that releases pressure in a controlled manner. By controlling the pressure thats flowing into the turbine, you are therefore controlling the pressure being generated by the compressor side that flows into the engine’s intake. The wastegate has a spring inside that keeps a valve closed preventing exhaust pressure from bleeding out. The wastegate’s body is connected to the compressor side of the turbo via a hose, this is usually called the boost/pressure reference. As pressure builds up in the compressor and pressurizes the body of the wastegate, this force pushes against the spring and starts to open the valve.
Wastegate springs vary in size and tension which is what dictates the ultimate boost pressure your turbo system generates. In addition to the spring most systems also have a boost controller. Boost controllers are another form of bleeder valve that regulate how much pressure is begin sent to the wastegate body from the compressor. The less pressure it sees the less force is applied against the spring, therefore keeping the wastegate valve from opening fully to the spring’s force. A simple way to think about it is, when the wastegate valve is fully closed, you generate all the boost the turbo is capable of producing, when the valve is fully open the turbo does not generate any pressure since its all being bled out of the wastegate.
One last piece of a turbo system is the blow off valve. The blow off valve allows for the compressed air to escapes out of the charge piping when the throttle body plate is closed. Without a blow off valve when you close the throttle, the pressure generated will need to go somewhere and therefor will push back out of the compressor wheel. In the long run this can cause damage to the turbo’s bearings and in balance in the shafts spin. So as you build boost, you let off, the air pressure escapes; this is the sound you hear in most turbo cars. Often times there are recirculating valves where the released air is sent back into the inlet of the turbo but I wont get into those details here for simplicity.
Turbo lubrication and cooling
The shaft of the turbo is suspended in the middle by bearings, they can be journal or ball bearing. A journal bearing is when a shaft rotates in a surface that contains oil; the oil keeps the shaft from coming in contact with the surface it sits on. Ball bearing is like a the bearings on a skateboard and requires less oil. There are other technologies such as oilless turbos and different ball bearing materials to but these are the basics and as far as I needed to understand.
When using a journal bearing the volume and pressure of oil applied to the turbo is important and checking with the turbo’s manufacture is always recommended to see what the required volume and pressure is. Ball bearings require less oil so a smaller restrictor is needed than a journal bearing, some journal bearings are said to not require any restrictor but I have never come across this with the VQ; we always need one from my experience.
Another function of the oil is to cool the turbo’s center section; some turbos are also water cooled where they connect to the cooling system of the engine.
The Rear Mount Turbo
Now that we know how a turbo works lets get into the details pertaining to the actual rear mount turbo configuration.
After laying under the car for some times and brainstorming where the turbo should fit best I decided to locate it where the muffler is. I unbolted the muffler and cut off right after the rear beam, then had a local muffler shop weld a T4 flange using the turbo to mock up. Once I was home, I then bolted up the turbo.
The turbo air filter I used was a large 4inch open K&N. I had to hammer in the spare tire well so that the filter could fit however that is not necessary as there are filters that have a much lower profile. I had a few ideas for locating the filter including having it inside the truck, or routing it to the driver side. I tested putting the filter in the trunk while having an additional hole for fresh air to come in. The hole I made for the fresh air to come in was not large enough so with the windows closed when the turbo would go into full boost you could feel the negative pressure in the cabin; not good. At the end I kept the filter like shown in the picture for years and never did I have issues with water. This car was driven daily in Miami where it is raining often.
Oiling the turbo in the back.
I purchased a generic eBay sandwich plate that has 4an ports, added a 4an fitting and then connected a nitrous line (what I had at the time). I routed the line on the passenger side of the bottom of the car using zip ties to hold in place.
On a traditional front mount turbo setup the oil feeds the same way, but the drain or outlet of the oil from the turbo goes back into the engine via gravity; most front mount turbo’s are located above the engines upper oil pan. Since I did not have this possibility I needed to figure out how to get the oil from the turbo back to the engine.
My solution was using a Shurflo 8000 series scavenge pump that is generally used for water, such as in RV’s for sinks or other uses. I decided to use this after having long conversations with someone in the Cavalier Z24 community that was also working on a rear mount turbo. I used an 8an line that connected from the turbo, into the trunk (by the spare tire well) and into the pump. The pump outlet had a 3/8th hose that came out of the trunk by the driver side of the car, over the rear beam and to the front of the car beside the fuel line. At the front of the car the line then came up over the transmission toward the front valve cover and then to the oil cap. I bought a metal oil cap then I drilled, tapped and screwed in a 3/8th barb which is where I connected the hose. I also had a clear glass inline fuel filter without the insides so that I can observe the oil flow for testing and diagnosis.
Oiling was the most challenging part of this project because I had to deal with regulating the flow going to the turbo in coordination with how well the pump removed oil from it. If you feed it too much oil, the pump may not be able to pull it fast enough so then the oil builds up pressure in the mid section and leaks out of the turbine housings. I quickly learned that blue smoke on vehicles usually means that oil is being burnt (white smoke being coolant, black smoke being fuel).
Part solution was using an oil restrictor. These restrictors are sold specifically for turbos but being on a budget I had to work with what I had, and that was using nitrous parts. For the Garrett T04b, I used 4an fitting, cut off the flared part that connects to the hose and put a nitrous jet in its place where I then drilled a 1/16th hole; this gives you an orifice size of 0.063.
This helped stopped the turbo from smoking and i was finally able to drive around with it but there were more complications.
I noticed that when the car was at a stop and then I started her up, smoke would come out again. The reason was that while the car was turned off, the feed line to the turbo continued to drip oil into the turbos mid section and then leaked into the housings. I fixed this by putting a check valve that required 1psi of pressure to allow fluid to pass, with the car off it no longer leaked.
Another issue was that even with the pressure check valve in place it would smoke. The reason for this was because the pump was wired into the ignition. So when you turn off the car, the pump does not have time to pull all the oil collected in the line and turbo; this causes it to leak into the housings. The solution was to leave the pump running on a turbo timer for a few seconds to clear out the line. I used a generic eBay turbo timer for this.
The last problem I had was when doing long highway runs where the engine was at high RPM’s for an extended period of time (for example a 1/4 run) the pump was not able to keep up with the oil delivery. I ended up adding a second pump using a T on the line for pulling from the turbo and another T on the line that went to the front of the car. This was the last step needed to not have any oil issues again. This process was all through discovery by trial and error so doing this again would be very simple.
Turbo Charge Pipe
Initially the turbo charge pipe size used was 2 inches. It was out of steel as it was the quickest and cheapest option available for me. For bends I used heater hoses and worm gear clamps. I routed the pipe from the turbo to a 90 degree turn towards the drive side, then a U bend over the beam and towards the bottom of the gas tank. From the gas tank I ran a straight pipe beside the fuel lines and oil line to under the transmission, then a 90 degree turn up where the blow off valve was placed, then another 90 degree turn that routed towards the intake manifold. This initial setup was without an intercooler and the initial boost pressure I went with was 6psi.
At first, I did not use an intercooler for simplicity. Eventually I purchased a methanol and water injection kit (there will be another article about this) because I quickly started to pick up engine knock. There is this common misconception that by having a turbo mounted in the rear, you no longer need an intercooler; this my friends is completely false. I was able to push the system without an intercooler up to about 10psi with the methanol and water injection. Without the intercooler at 10psi I achieved 299whp and 291wtq, at 6psi it made 250whp and 242wtq.
I routed the charge pipe from the turbo by going under the transmission, then a bend that turned towards the passenger and between the radiator and the front engine mount. Then the pipe continued to near the fog light area where it turned towards the radiator support and through it (after drilling a hole through the support). Then a bend into the intercooler and on the driver side the pipe exited and turned into the support back towards the engine bay. Then the pipe turns upwards with the blow off valve in place behind the fans and then towards the MAF and throttle body.
I then upgraded to an intercooler with the size of 28X5.5X2.5 and the inlet/outlet were 2 inch. My temperatures before the intercooler on average were 130’s F during boost. After the intercooler installation the highest temperature I saw was 111 F. This was on typical Miami summer weather so likely in the low 90s or 80s.
With the intercooler, I at the same 10psi it made 312whp and 301wtq.
Upgrading to 2.5 inch Charge pipe
Over time I felt that the 2 inch charge piping was a limitation, so I purchased an intercooler piping kit from eBay for 2.5 inch diameter. I then pressed them into an oval with 2/4 pieces of wood and a mallet. This was the pipes that went directly under the car between the gas tank and the engine.
The performance gains from upgrading to 2.5 inch was drastic in all aspects. Spool up was faster, the mid and top end of the RPM performance were significantly improved. The 2 inch piping which I believed would have improved spool up due to more velocity was actually a big restriction. I recommend starting off with a 2.5 inch charge pipe from the beginning.
Exhaust Piping and Spool Up
From the engine to the turbo I already had a 2.5 inch y-pipe and a 2.5 inch cat back. One of the most important parts of the whole system as far turbo performance and response goes was to wrap the entire exhaust with header wrap. I wrapped the y-pipe and the cat back; this improved the spool up of the turbo. The next improvement was removing a 22 inch Magnaflow resonator. I found that even though the resonator was completely straight through, it slowed spooled up by a lot. This could be because the resonator could have been functioning as a heat sink absorbing a lot of heat and therefore slowing down the velocity of the exhaust. With the piping wrapped and no resonator the turbo responded just like it would on a front mount, at the time I had no way of logging so I did not record data for this, but it was a significant improvement.
I then had the muffler shop route a straight pipe from the turbo to the factory muffler tip location. This picture below shows another rear mount turbo maxima where the same straight pipe was done.
The next step was to figure out what to do about the sound, it was very loud and being automatic it did not make for a good daily driver like this. I went to the local muffler shop where they put on a bend out of the turbo near the tire, then into a muffler. At first the bend was crushed style but we all know this is not acceptable so eventually I upgraded to a mandrel bent outlet.
I now had a turbo rear mount maxima that was quiet and performed really well. I drove this car for years with this setup and raced it a lot. Here are additional photos showing how one can route the piping on the 4th gen Maxima.
First 1/4 Track Time as a Rear Mount Turbo
With the TO4B turbo, boosting 7.5psi non-intercooled, a 2000-2001 Maxima intake manifold, and an APEXI VAFC2 for tuning the fuel, this is what the car ran in the 1/4 mile.
My previous best time was with the 75 nitrous shot and I ran a 14.2@98mph with a 2.3 60′. The turbo at 7.5psi was putting down more power than the 75shot.
In the next article I will continue to discuss the rear mount. I will write about a different solution for the oil system among more details regarding the rear mount. Thank you for reading and feel free to comment or ask questions that were not covered so far.