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Cooler Runnings

Slashing the charge-air temps of a Nissan S13 SR20DET

The stockie intercooler fitted to a turbo car is usually fairly average. When you force a few extra psi boost through the standard unit, its heat-exchange and airflow performance are often quite severely reduced. Not surprisingly, therefore, an upgrade aftermarket intercooler is required in all truly serious power-ups. Furthermore, an upgrade intercooler should be an even higher priority for 'grey' Japanese-import vehicles; running an engine designed for 100RON fuel on only 98RON (or less) is a formula for engine-destroying detonation. Keeping a lid on intake air temps is an effective way to combat detonation.

In this story we look into the gains of fitting an aftermarket intercooler on a lightly tuned Nissan S13Turbo...

The Demo Car

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This particular SR20DET 5-speed S13 arrived at the shop equipped with just a HKS pod air filter and a 3-inch turbo-back exhaust system. On the rollers of Dyno chassis  the car produced a reasonably repeatable 138kW at the back wheels.

 

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The 138kW peak power figure was achieved with absolutely no boost mods and with a maximum manifold pressure of 9 psi. Oh, and - on the dyno - we measured the intake air temperature immediately before the throttle and saw a maximum 41.8 degrees Celsius (with an ambient temperature of around 20 degrees Celsius).

 

Fitting the New 'Cooler

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The front-mount intercooler kit being fitted here suits SR20DET powered S13 180SXs and Silvias and is a development from good JDM brand, you receive a Garrett bar-and-plate core with mounts and all necessary plumbing and hoses. The new core measures some 450mm x 305 x 90mm and contains dense offset turbulators for maximum cooling efficiency. Used this core on a full-house CA18DET making 270kW at the wheels, so it's obviously quite capable.

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The first task is to remove all of the factory intercooler pipes found between the standard intercooler and the throttle, plus the pipe that passes through the guard between the turbo and 'cooler. Oh, and don't forget to stuff a rag inside the open pipes - this prevents foreign particles getting inside the engine.Next, the front of the car needs to be jacked up and secured on chassis stands. The guard liner retainers are then removed, which allows access to undo the bolts securing the bumper to the body. Once the bumper bolts and indicator wiring connectors are removed, the entire front bumper assembly can be slid out.

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Now - with much easier frontal access - the standard intercooler, blow-off valve and entry/exit pipe assembly can be removed from the vehicle. As seen here, the factory 180SX intercooler is particularly small, measuring just 170 x 222 x 60mm. Its inlet and outlet fittings have a 47mm internal diameter.

The replacement intercooler gobbles pretty well the entire nose cone cavity. To support the 'cooler's weight, a metal mounting strip is attached to a pair of threaded fittings welded onto the top and bottom of the core - these connect to the vertical support for the bonnet latch and the lower radiator support panel respectively.

Once the big 'cooler is mounted, it's time to hook up the plumbing.

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Interestingly, this kit retains the first section of factory plumbing out of the turbo compressor, but replaces the pipe into the 'cooler and from the 'cooler into the engine. The pipe leading into the 'cooler (and the 'cooler fittings themselves) are normally 54mm ID, but - in this particular kit - they were the standard 47mm diameter. Note that all of the pipes have a rolled lip to prevent hoses popping off under high boost.

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A 35mm ID fitting is welded on the side of the intercooler entry pipe, which allows fitment of either the original or aftermarket blow-off valve. In this instance, the original valve was retained and connected back to the pre-turbo induction pipe using the OE piping. This is widely known as a 'plumb-back' arrangement.

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Inevitably, there is some cutting required to install the kit. First, the radiator shroud needs to have a 100mm square section removed from its top half - this allows clearance for the large diameter pipe into the throttle. Second, the front bumper needs to have some material removed. A slice needs to be taken off the under-tray section, while the central air cooling passage has to be cut back to allow the bumper to fit against the new fat 'cooler.

Total installation time is around half a day.

The Results

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With ambient temperatures virtually the same as the 'before' run, we again fired the 180SX up on the chassis dyno and slipped our temperature probe into hose before the throttle body. The results were particularly interesting - running the same 9 psi boost, intake air temperatures were slashed from a high of 41.8 to just 25 degrees Celsius (which was only slightly above ambient temperature). There was little question the new 'cooler was performing magically.

And did it bring a massive power gain? Well, no, not really...

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Despite its considerably lower intake temperatures, the turbo Nissan gave only a minimal power improvement. As seen in this graph, it picked up a reasonable percentage down low but hardly anything up high - power went from 138 to 142kW (a gain of around 3 percent). We can only surmise that the relatively low boost level on this car minimised the potential for any large gains - there weren't the extreme charge-air temps for the new 'cooler to haul down. Interestingly, Tim tell us he's done similar intercooler conversions in the past and seen only small gains; as he went on, however, it's the potential to allow more boost that makes the process worth while. There's no way you'd want to run more than 15 psi through the standard intercooler, because intake air temperatures would go through the roof. This robs power and can lead to detonation.

So, in summary, we've shown that an upgrade intercooler doesn't always release a huge amount of power - certainly not in the case of a lightly tuned 180SX. Instead, think of this $1000-odd investment as an essential step that allows to you safely increase boost pressure and net the biggest gains.

More Boost?

Installing an aftermarket intercooler often sees higher boost pressure felt in the intake manifold - but not in the case of the 180SX...

On the majority of turbo cars, the wastegate takes its pressure feed from the compressor outlet. In these instances, any airflow restriction on-route to the engine (such as an intercooler) reduces the boost pressure that reaches the intake manifold. Say, for example, the wastegate is set to deliver 15 psi, a restrictive intercooler may allow only 12 psi to make its way to the manifold. Fitting a less restrictive intercooler may see 14 psi reach the manifold.

Some vehicles - such as the demo Nissan 180SX SR20DET - take their wastegate feed directly from the intake manifold. This means the turbo will work to deliver the same manifold pressure, regardless of the amount of flow restriction before the throttle. That's why - in this case - the 180SX saw 9 psi manifold pressure both before and after the new 'cooler went on.

By Michael Knowling
 
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Written by Administrator   
Sunday, 11 January 2009 23:17

  

  

Overview

Unlike many contemporary engine designs which were being constantly up sized (for example, from 2 to 2.2 or 2.4 litres), the engineers stuck with the ‘traditional’ 2-litre swept volume, gained from a bore and stroke each of 86mm. To keep engine mass low, an aluminium block was used. This design used a closed upper deck and a skirt which extended well below the crankshaft center line. The head used compact, pent roof combustion chambers (cross-flow, of course), with the spark plug located in the centre of the combustion chamber.

The Head

 

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The straight intake ports were designed with what Nissan terms an ‘aerodynamic port shape’, that is, a port that decreases in cross-sectional area as the runner/intake port gets closer to the intake valve. The ports were also positioned high in the head, so reducing the angle which the air had to negotiate before entering the combustion chamber. In addition to improving flow, the greater length of the port served to improve torque through giving a longer tuned length to the intake port/intake runner combination. In fact, a combined intake port/runner length of 450mm was used in the SR20DE engine. Compared with a low port design, the high port design improved measured torque by 4 – 7 ft-lb at engine speeds of over 4400 rpm.

 

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A narrow valve angle of 29 degrees was selected – this can be compared with the 45-degree angle of the CA engines.  Over the CA18DE, the SR20DE engine provided a 2.7 per cent improvement in its brake specific fuel consumption at the same torque output (one which corresponded to 60 km/h road speed, presumably in top gear).

The high ports required that the camshafts worked the valves through Y-shaped rocker arms pivoted between the intake ports. The rockers featured reduced contact area with the cam followers and also reduced inertial weight over other designs, so reducing valve train friction.  The cams were chain driven.

The exhaust side of the head was designed last. To reduce exhaust interference effects, the exhaust manifold used a design where cylinders 1 and 4, and 2 and 3 were each combined into a dual manifold – standard practice on most four cylinder engines. The dual part of the exhaust extended as far rearwards as the rear part of the sump.

 

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Nissan engineers very carefully considered the structural options open to them before settling on a DOHC, narrow valve angle head with the valves operated through outer pivoted Y-shaped rockers. Other options considered included:

  • a similar design to the final iteration, except for the use of one rocker per valve and the use of inner pivots for the rocker arms (the negatives were greater mass – and so friction - in the valve train, and a very wide head)
  • direct-operated valves with a wider valve angle (negatives: wide head, couldn't’t use roller rockers, built-in hydraulic lifters would add to masses, valve lift restriction because of bucket size)
  • direct operated valves with a narrow valve angle (negatives: couldn't’t use roller rockers, built-in hydraulic lifters would add to masses, valve lift restriction because of bucket size)

    The Block

     

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    The SR20 engine was developed around the time of the 4.5-litre VH45 V8 engine used in the Infiniti luxury car. Both engines used Low Pressure Die Cast alloy blocks and drew on the experience gained by Nissan with their first alloy block engine, the 1-litre MA series. The technology jump was a large one, although the weight saving of the SR20 block over the CA18/20 iron block was only 9kg. However, as Nissan engineers of the time suggested, “attention was devoted not merely to reduce weight, but to assure functional reliability and to improve NVH [noise, vibration, harshness] characteristics”.

    The block alloy was heat-treated JIS AC2A, a material already used by Nissan in cylinder heads. A closed-deck design was adopted for these reasons:

    • cylinder head gasket seal ability
    • improved NVH characteristics
    • reduced permanent bore distortion

    To test the reduction in NVH of a closed deck, Nissan engineers had a CA20 block cast in aluminium (the CA being an open deck design) and then tested it back-to-back with a prototype closed-deck SR20. In the closed-deck design the greater stiffness of the water jacket wall reduced radiant noise by 2-3dB over the whole engine rev range.

    Other Nissan testing showed that cylinder bore distortion of the cast-in iron liners could reach 0.05mm in an open deck design, causing piston slap noise and oil consumption problems. This permanent distortion was reduced to 0.04mm in the closed deck version.

     

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    A deep skirt block design was adopted to improve power train rigidity – but to give reduced NVH, rather than improved engine strength. To prove this, the engineers tested a modified VG30 3-litre V6 Nisan engine in deep skirt and half skirt block configurations. In deep skirt guise the engine showed a clear increase in frequencies, indicative of a stiffer power train. In addition, the connection to the gearbox was improved by the use of a two-piece oil pan, with the upper half an aluminium casting. This was needed particularly because of the Pulsar GTiR application, where the engineers were concerned with the mass of the four-wheel drive transfer case and differential being mounted on the side of the engine and transmission.

    A cast-in-place dry iron liner was used within the aluminium block. However, unlike many other engines of this construction, the iron liners were ‘buried’ beneath the surface of the block. This was done for two reasons:

    • To improve cylinder head gasket seal ability
    • To improve the life of machining tools (the resulting gain was 5 -10 times)

    The Sound

     

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    Nissan engineers said that they placed great importance on both reducing generated engine noise and also creating “improved sound tone and quality”. To this end, they concentrated on the rigidity of the engine (and of the engine/trans combination, which used 10 connecting bolts) by using a main bearing girdle, the two-piece sump and the closed-deck block. (It’s interesting to consider that it’s quite likely that much of the engine’s legendary durability came about through technologies aimed at improving the quality of the sounds made by the engine....)

    Reliability and Maintenance

    Nissan bucked the trend of going to cam belts by retaining chain drive for the twin cams. The single roller chains used a tensioner applying force through the use both of oil pressure and springs.

    Unusually for the time, platinum tipped plugs were used which were said to not require adjustment or replacement for 100,000km. Also aiding reliability were cylinder head bolts which were tensioned such that they stretched an appropriate amount and a “large size distributor [that allowed] the necessary secondary voltage for up to 7500 rpm” to be available.

    The 16-bit ECU controlled bottom-feed injectors with a high heat resistance and a hot film type airflow meter was fitted. In addition, the engine management system included control of the air/fuel ratio (with learning control from an oxy sensor), knock control and self-learning idle speed control.

    Conclusion

     

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    Nissan spent about 3 years developing the SR series of engines – including the SR20DE, SR20DET, SR20DI, SR18DE and SR18DI.

    Said the engineers: “We believe that the goal of this development, namely a good balance between high performance and fuel economy combined with a pleasant engine sound, has been attained by the design technique of the 4 valve DOHC engine which Nissan has been cultivating over many years, and by the solid reliability built into this car by Nissan’s production technology.”

     

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    The Specs
    Type:Water cooled, 4 cycle in-line 4 cylinder
    Combustion Chamber:Cross flow, pent roof type
    Valve mechanism:DOHC, 4 valves per cylinder, chain drive
    Displacement:1998cc
    Bore x Stroke:86.0 x 86.0mm
    Bore Pitch:97.0mm
    Block Height: 211.3mm
    Compression ratio:9.5:1
    Crankshaft journal diameter:55.0mm
    Crank Pin diameter:48.0mm
    Con rod length:136.3mm
    Valve diameters:In: 34.0mm, Exh: 30.0mm
    Dimensions:685 x 610 x 615mm

    Maximum power:140hp at 6400 rpm (SAE net)
    Maximum torque:132 ft-lb at 4800 rpm (SAE net)
    COURTECY FROM AUTOSPEED
Last Updated on Tuesday, 13 January 2009 15:58