Personal project converting a 1991 Nissan 200sx S13 to a V6 twinturbo

The Nissan 200sx S13 talked about on this page has been in my possession for almost a decade and has become my primary engineering guinea pig. Many other projects on this website converge into this whole project. This 200sx S13 was made in 1991, uses a 1.8 turbocharged engine driving the rear wheels for 165hp. At just 1190kg, it makes an ideal platform for many forms of racing.

Overall improvements 

The S13 will be used as a fast road car with track capabilites, and upgraded allround;
-Custom front & rear suspension with double triangular control arms
-Carbon-ceramic brakes
-Larger VG30DET engine, heavily tuned for over 600hp at the wheels
-Complete weld in roll cage and renewed interior
-Widened bodywork for 300mm more width and 300mm additional wheelbase

The interior is the least crucial and will be performed last. The bodywork is a design in progress, as I haven’t found a good (cheap) CAD program to do this with. I’d love to build the bodywork from carbon fibre and I’m studying the use of it. The car has to be stalled outside my shop and I’m looking for a way to perform bodywork to it in this way.

Engine choice

The original 1.8 liter 4 cylinder CA18DET engine was removed years ago and replaced by the 3.0 liter V6 VG30DET engine. The VG30DET was introduced in 1987 and used till 1995 on various luxurious Nissans. It’s a steel block with aluminium heads, quad cam, short and variable intake manifold and uses a single turbo. The engine was never used in Nissans in Europe nor the United States. However it’s younger sister – the VG30DETT found in the globally sold 300zx (Z32) – has so many similarities finding high performance parts is easy. The VG30DETT was a slight improvement in head design, but I chose the VG30DET mostly since it allows the fitting of a custom variable intake manifold.

Why not a 300zx from the start?

The 300zx Z32 is the ‘big sister’ of the 200sx S13, the cars were in fact developed alongside. The Z32 is 10cm wider and lower, has the VG30DETT from factory and a much stiffer chassis, at a price. The lightest S13 weighs 1180 KG, the lightest Z32 twinturbo 1480 KG. The Z32 gains it’s weight mostly from the stiffer shell, thick doors and heavier trunk lid. Unfortunately, the stronger Z32 chassis not a worthy advantage once a full roll cage is welded in, as the strength of the cage far outweighs that of the base chassis itself. If I’d start with a Z32 twinturbo, the roll cage would add around 50 KG, while I may be able to shave around 80 KG off the rest of the car without making it too uncomfortable. At the same ‘comfort level’, the S13 would gain 50 KG from the cage, and another 80 KG from the VG30 engine and it’s gearbox. However, the weight reduction would be comparable thus in the end the S13 with the same engine and drivetrain would weigh in 200 KG less than a Z32.

In addition, the Z32 engine bay is low and narrow, compromising the mounting locations for the turbochargers and the shape of their manifolds. This also leads to the Z32 having a cramped, hot engine bay, when compared to most other cars which works against performance and longevity of any parts involved. The Z32 does have a lower bonnet and roof line, and likely be more aerodynamic.

Starting

Using a VG30DET oil pan along with an ’empty’ engine I measured the space within the S13’s engine bay. The much stronger gearbox of the VG30 is also wider and taller, but I wanted to avoid cutting & welding the transmission tunnel. I managed to do this, with only a couple of dents to be made to fit the starter engine. This is also as I decided to lower the engine slightly. I decided to use solid engine mounts. VG30’s are quite smooth engines and using an urethane gearbox mount should absorb most vibrations (with a solid gearbox mount the vibrations have nowhere to go which will lead to a broken gearbox casing). The aluminium engine mounts were designed and fabricated by me, but back in the days I had to have them welded. They’re very light and allow more space for the turbo’s. The S13 subframe was modified to fit the VG30DET oil pan, additional reinforcement plates were welded in and aligned with the new aluminium mounts. Eventually the engine will be converted to a dry sump, and when the new front suspension is fitted a different lower arm and steering housing mounting so these parts will over time be replaced.

The S13 has a steel gearbox mount that bridges between the 2 sides of the transmission tunnel. Kept stock for now, it just had to be ‘spaced’ out with a 10mm thick aluminium plate on both mounting sides. The factory rubber mount was replaced by a stiffer urethane mount to avoid to much movement from the transmission side towards the engine mounts.

Rollcage

A complete rollcage may compromise the ‘comfort’ of the car, in fact requiring a helmet to drive, it is the best way to make it safe and reinforce the chassis substantially. The rollcage is made by customcages from the UK, and is of the full weld-in type. It even welds to the front suspension turret, the reinforcement is so great that the car no longer warps when jacking it on one just side.

A video of the ‘raw’ cage shortly after welding. I had to use different welding techniques since the cage was a little ‘loose’ on some bars but very tight on the other. This is not an issue as long as the welds are properly performed. After the installation pictures and a weld test performed by me were sent to Customcages. I received an official certificate allowing the chassis to be run in a couple of racing classes. I won’t use it but it came with the cage free of charge.

Turbo’s

Initially I wanted to install a pair of HKS GT2530 turbo’s that will allow for 600hp at the rear wheels, but there was no way to mount them right next to the engine with a properly shaped exhaust manifold. This is because Garrett uses very large housings, so that they can use the same casting for larger turbo’s and just change the internal profiles. Another popular turbo for this engine is the Mitsubishi (MHI) TD05 16G, but the design is obsolete. Through a friend I acquired a pair of 3K K16 turbo’s coming from a Porsche 996. Although these turbo’s in stock form allow for barely 500hp at the rear wheels, they can be easily fitted with larger compressor wheels and use turbine and compressor housings of smaller outer dimensions, unlike the unnecessary oversized HKS turbo housings. One nice additional feature of these K16 turbo’s is that they lack water cooling, saving a large number of troublesome water lines and hoses.

Installing oversized compressor wheels is common practice within the Porsche community. Tuning specialist install MHI TD05 16G compressor wheels, they have the same 60mm exducer but a 6mm larger inducer over the 40.5mm factory item. With the turbine wheel of these turbo’s being relatively large compared to the compressor wheel, the Porsche engines respond very well to the enlarged compressor wheel and can make around 600hp at the rear wheels with these 16G compressor wheels. I came across 2 Garrett GT2860RS compressor wheels that are of similar size to the 16G wheels, but of a newer, lighter design. As the K16 turbo has a 5,40mm shaft versus the 6,00mm shaft on the GT2860RS, I cut them out to about 9mm and inserted a press in sleeve that was cut to 5,40mm. I had a local specialist with complex CNC machinery measure the compressor housing profile from a GT2860RS, and he cut the K16 compressor housings to that profile. Prior to having the housings cut, I welded new flanges and pipings to the housings so that the housings would not warp after being reprofiled. The turbo’s were balanced by a shop in the UK called http://www.turborebuild.co.uk/

Exhaust manifolds

From factory, the VG30DETT has a pair of so called steel log manifolds that are mounted extremely close to the engine. The space in between them is so small, both turbine housing inlets face directly towards the 5th and 6th cylinder exhaust port. A Japanese company called Pentroof made a nice tubular manifold setup, but the location it puts the turbo’s at does not work in my S13. I wanted to place the inlets for the turbine housings further up front, so that the inlets sit next to the central cylinder on each side. This is made possible due to the shape of the engine mounts I made. In doing so, it’s so much easier to make the manifold runners more equal length.

Starting from scratch, and having more space higher up in the engine bay (the strut towers stand wider apart on the S13 than they do on the 300ZX) I was able to design very efficient exhaust manifolds. I had 2 flanges made in steel, and I purchased high quality 321 stainless steel bends from this company for the runners themselves; <a href=”http://www.skydynamics.com/”>http://www.skydynamics.com/</a>
The piping is very thin at just 1.25mm but the turbo’s will be supported with additional mounts and braces (Porsche uses braces for these turbo’s from factory as well since they ‘hang’ on the manifold). As can be seen, the manifolds are close to even length as I feel the shape and angle of the merge collector and bends is more important when I had to compromise. Once the engine is fully installed I will make heat shields that completely cover the manifolds.

Each turbo is supported by an additional hangar/mount. On the factory Porsche engine this consist of a stainless steel V shaped plate. It bolts to 2 of the 4 thread ends that in turn bolt the turbine housing to the CHRA. The plate then bolts to a hangar fitted to the engine. This way most of the weight of the turbo and exhaust is carried by the hangar. For the driver side I made an aluminium mount that bolts to the engine with 2 M10 bolts. It was a very tight fit but I managed to get proper clearance with the actuator and manifold. The passenger side uses the engine mount as support. But this leaves the hangar somewhat horizontal, so the hangar is not as much supported from above. This will be changed when the engine sees a new subframe and engine mounts, that will allow for more space for a higher hangar location.