Tuesday, February 28, 2012

Set Up Part 4: Suspension & Handling for the AP2 S2000

The S2000 is blessed with the combination of a stiff chassis with race derived suspension design which makes it a very able candidate for the building of a race track performer. Having come from a coilover equipped 4WD turbocharged sports sedan, I did feel there was some room for improvement in the overall setup as it seemed to me that the shortfalls in the production car were attempting to address both sporty handling while hoping to still provide a modicum of comfort within the production budget of the car. It suffices to say that the final result may not have won many fans on either end of the spectrum. I decided to focus my attention on building handling to optimize it's track ability eschewing the comfort part of the equation as this car would spend much of its time at the track.

The tyres on the stock S2000 are the Bridgestone RE050, which must not be confused with the more grippy Bridgestone RE050A, and come in 215/45/17 front 245/40/17 rear. Feeling that the front lacked turn in and tyre grip, I decided to go for a non-staggered setup with 255/40/17 tyres all around which I have detailed here . The result was vastly improved turn in and grip far above what the stock tyre configuration could achieve. Realizing that tyres are probably the most critical part of the suspension, I went with the choice of the razor sharp feeling Advan Neova AD08 which cost me about 380 SGD per piece. An all round performer, this tyre wears at a very reasonable rate while delivering class leading wet & dry grip even when worn down past the tread markers.

Next up, I focused on the suspension and since my heavy track use over the last few years had pretty much worn out the stock suspension, I decided to replace this with a six month old second hand set of Tein Super Racing Circuit (SRC for short) Master coilovers which I had managed to purchase from a fellow S2000 track buddy. Brands such as KW, JIC, Bilstein and Ohlins had suspension models selling in the 3000 SGD range that I did consider but realized that since the suspension choice would be crucial for my handling on the track, it would be best to go with a suspension that has been proven on the track. I did briefly look at the Ohlins TTX but this quality comes with a very steep price and I rationalized that I would not have much left over to develop the rest of the car should I opt for these.

My choice of the Tein SRC's come with 16kg/mm spring rates front and rear which may seem overly stiff for the street yet damping seems to be relatively compliant which makes it bearable in terms of comfort while managing the bumps of the street pretty well. The recommended ride heights for the Tein SRC are far too low to be running daily on the street so I have had the suspension raised to clear day to day driving with the aim to lower the car as recommended the next time I hit the track. The external canister design of the shocks helps cool the suspension and the short stroke design of the suspension is clearly a track derived design originating from the Tein N1 race coilovers. Although I have not had very long track sessions on this suspension due to unfortunate disruptions in my track schedule, I am confident from the winning track record of s2ki.com competitive trackies that this will be a key component to help me outhandle the competition.

With the non staggered setup that I am running, the alignment I run would correspondingly need to be altered to match. After researching on many settings for camber and toe, I finally settled on a setup with the following numbers:
Front Camber 3.0
Front Toe 0
Caster : Max (usually ~6-6.25)
Rear Camber 3.0
Rear Toe 0'20 per side
These settings are subject to change as I have purchased a LongAcre probe type pyrometer to help determine how well this alignment suits the overall setup of my car. The pyrometer will also put certainty into determining optimum tyre pressures at the track when properly utilized and is thus a crucial investment in sorting out handling. It is rather surprising that little to no people I know actually venture to use a probe type pyrometer to determine and tune optimal alignment/tyre pressure settings which points once again in inherent gaps in the approach in local motorsports with regards to building competitive setups. I have not mentioned any changes to sway bars or stiffening structural bars and the like as it is my opinion that outside of building a full roll cage, the car would not appreciably improve from such fitments. This thought is once again shaped heavily by feedback from s2ki.com amateur racers who openly discuss their winning setups to share with the local community.

I would like to share some thoughts about how my approach to tuning or setting up the car was viewed by "old birds" in the local community as I find a significant gap in the thought process as opposed to search for actual performance when I discussed my setup in the local community. Most make their decision on a brand before even looking into what technology the brand accesses and if that is cost effective to deliver the end result desired. I will not go into length about how many times I faced derision on taking a path atypical from most FR setups (sometimes this derision was backed up by shockingly flawed theory!) but understanding that it is the malaise of the local industry to focus on fiction (hearsay) above fact, I soldiered on resolutely. In short, the typical local build up of a car is a piecemeal bit by bit addition process that is usually disjointed and not particularly focused while relying on potentially outdated theories (often from hearsay) to base the build on.

I hope that the fact that I do specific targeted research to focus my efforts on the current build allows the true potential of the S2000 to be realized with valid fact to back up the principles underpinned. Being heavily influenced by the open ways of the folks on s2ki.com, I look to share my knowledge through the above series of set up pieces and help any S2000 owners on their journey to enhancing the performance above their stock S2000.

Tuesday, February 21, 2012

Set Up Part 3: Braking in the S2000

Consistent and good braking power is of critical importance at the track as it allows you to carry as much speed as possible from the straight, helps you to turn in certain corners, allows you to dictate position when challenging for a corner and helps you allow the car to take a set before the corner entry to be as stable as possible. An optimum combination of pads, fluids, brake lines and discs used in consideration of the conditions the brake system, as a whole, will be exposed to will be necessary to achieve the desired braking. The stock brake system on the S2000 has pads & fluids which are not equipped to take the stress of track racing while the rotors may crack frequently if heat management modifications are not undertaken.

I decided to modify the stock brake system to suit my track use as opposed to replace it with an aftermarket big brake kit due to the massive cost that a brake system would entail which would be in excess of 5500 SGD just for the front set. The other 2 reasons why I chose to stay with the OEM stock caliper setup would be that most aftermarket brake kits only sell brake kits for the front whilst those that sell kits for the rear are either extremely expensive (exceeding 1500 SGD) or sell a kit that deletes the hand brake mechanism & the fact that staying with the OEM calipers allows me to keep the stock brake balance thereby removing an additional variable in troubleshooting brake related issues.

I opted to use quality brake fluid by Motul, currently RBF660, which has high fade resistance together with braided steel brake lines on slotted OEM discs. This setup combined with Ferodo Racing DS2500 brake pads, has proven relatively reliable when coupled with the grip of the stock suspension and Federal 595SS budget tyres while being able to deliver approximately 1G of straight line braking on both of the long braking zone of my local circuit. These results were with the addition of a brake ducting system, as previously discussed here, which helped stave away fluid fade in most part. The choice of the brake pad did give me rather low, although easy to modulate, bite especially when track temps were high although pad fade/degradation would eventually rear its ugly head. 

With recent upgrades to a track focused coilover, high downforce aerodynamics, higher speeds capable on the straights due to an increase in the power of my car and much gripper performance tyres, I have decided to look for high performance pads which are able to give high consistent bite throughout the heat range. I had used Seido-ya N1 500 pads but the compound was extremely heavy on disc wear which is not comparable performance when considering the advances in ceramic brake pad technology which can give good pad/disc wear, flat torque and high bite throughout the heat range. 

Options considered were the Pagid RS19 and Ferodo DS 1.11 as there was a possibility to get these in both front and rear sets as opposed to most major brands which only sell performance pads for the fronts. Having the same front and rear compound is important in my view when your car is of a 50-50 weight balance much like the S2000 so you can maximize the braking potential at both ends of the car. This will help bring out one of the comparative advantages that the S2000 commands in terms of braking.

Monday, February 20, 2012

Set Up Part 2: Aerodynamics of the S2000

Big leaps in aerodynamic improvements on road cars have been made in the span of the recent two decade. Items like the "shark tooth" vortex generator, rear underbody diffusers & specially designed front bumpers aiming to reduce drag have made their appearance on virtually every part of the spectrum of modern road cars. In comparison, the S2000's 1999 design has remained virtually unchanged even until its end in 2009 with the exception of the Type S.

The combination of the boxy shape of the front end, relatively high angle of the front windscreen and the lack of a rear diffuser exposing the rear bumper to collecting underbody air flow culminate to a Cd around 0.34. Certain modern sports cars also have Cd's of around 0.34 but usually incorporate aerodynamic aids to increase downforce at the expense of some drag yet the S2000 has little to none of these and thus generates large amount of lift at higher speeds. It suffices to say that aerodynamics would be one area where the S2000 falls short when compared to the current models of sports cars.

Lowering any car will improve aerodynamics significantly and this would be done by my change of suspension to a high end coil over suspension yet the problem of overall lack of downforce would still need to be addressed with further modifications. I decided that a combination of a front lip or splitter and rear wing would be the first changes needed to be done to add downforce, hopefully without a huge increase in the Cd.

OEM options to increase downforce on the front of the car included the Honda Modulo lip and the Type S (or CR) front splitter but I ruled both of these out as I felt that a splitter extending out from the bumper would be a more effective way to generate downforce. This effectiveness comes from the pressure created on the top of the splitter to push the splitter down and air flow underneath the splitter which helps to suck the splitter down.

 The APR carbon fiber splitter extending about 2.5 inches from the front of my bumper was my choice but decided against mounting the splitter on the bumper which is a typical fitment by most buyers. This is because I have had feedback from folks running on high speed tracks that the additional downforce created could be so high that it could cause huge pressure on the bolts holding the bumper on and in some cases even tear the bumper off. My decision was then to mount the splitter to the chassis with the construction of a splitter frame bolted to the splitter. This had a two fold benefit: 1. To create a frame strong enough to hold the splitter firm during high downforce situations 2. To create a linear increase in downforce transfer to the chassis. The result after fitment was noticeably large amounts of grip which increased with the higher speeds I drove.

The next on the list would be the hunt for a rear wing which my S2000, being a non-Type S version, did not come with from the factory. Various choices abound for the S2000 including even chassis mounted offerings but needing to balance the need for the boot (for carrying of my spare tyre to the track) with best available downforce ability, I chose a Voltex wing for my car. I selected Voltex Type 2 with a 1600mm wingspan over a Voltex Type 3 as my car would fall under the lower power category and the drag from the Type 3 might be excessive compared to the acceleration ability of my car. 

To enhance the downforce capability of the Type 2 wing, I had it mounted the highest available mounting at 275mm to put the wing in the cleanest airflow above the profile of the car. Looking at wind tunnel tests on the S2000 showed me that the high windscreen of the S2000 does necessitate a high mounting for a rear wing to be effective. I also specified a gurney flap (or wickerbill) to be included to be fitted to the wing which would increase downforce without a large increase in drag. The result of the fitment of the wing was a significant improvement in high speed stability to a point that high speed corners that usually made the tail feel light and prone to oversteer now could be taken with more aggression with the large increase in grip delivered by the wing. 

I did not feel a noticeable increase in drag at with the aerodynamic setup and a check of my fuel consumption showed little or no difference in my fuel consumption on day to day highway driving so I am pretty satisfied with the balance of grip and drag offered by this setup. Setting of the wing rake or Angle Of Attack would need more frequent track sessions for me to determine what would be optimum so I will need to wait until later this year to get a bit more feedback. The key point I have learnt with aerodynamic modifications is the need to balance the grip you add to the chassis as too much front or rear grip will result in a significant bias to the car's balance which could lead to a poor handling at speed.

The final part I added to my S2000 to enhance aerodynamics was a Mugen FRP hard top. The soft top of the car flapping in the wind combined with the ribbed profile of the soft top mechanism disrupts the airflow above the car and causes drag which a hard top would reduce. This would increase the Cd and may significantly reduce the effectiveness of a rear wing. The OEM hard top is slightly heavier with a bigger glass rear windscreen but is more expensive to purchase locally and probably slightly less aerodynamic in my view. Being given a good offer for the Mugen FRP hard top, I decided to bite the bullet on the high cost and go for it. To be honest, I am not able to discern the aerodynamic gain of the hard top as I have had some other modifications done at the same time but feedback from various owners who kept everything else the same while changing to a hard top reported improved gas mileage coming from the improvement in aerodynamics.

The final item I am toying with getting to further improve the rear aerodynamics would be the addition of the rear diffuser but as I do not want to run too far off the budget I've set for myself, I am still putting that move on hold for the moment. There is also a concern on streetability as the low ride height of the S2000 (especially since I am on a race derived coilover suspension) might result in damage to the parts after contact with humps. Companies such as Spoon, Downforce and J's Racing do have splitter setups for the S2000 costing slightly more than 1000 SGD.

Sunday, February 19, 2012

Set Up Part 1: Engine power in the AP2 S2000

Coming in at 240bhp from the factory form, the 2.2 litre F22C in the AP2 2000 is already highly tuned with a power to displacement ratio of 109 bhp/litre. This is why many S2000 owners tend to feel that additional modifications to intake, exhaust and header do not give huge increases in output for the amount of money spent. 

An example based on local pricing shows that a combined cost of a combination of possibly the best performing intake, header and exhaust for the S2000 tuned with a Hondata Flashpro may cost upwards of 7500 SGD. This would likely yield gains of around 40hp at best which seems pretty low on the bang to buck scale compared to similar but lower cost setups on the K series VTEC engines. If we, however, look at the absolute power to displacement ratio post modifications, we can see that approximately 280 bhp for a 2.2 litre gives us 127 bhp/litre which is in itself already a high level of tuning for a naturally aspirated engine.

Going further than 280-290 bhp naturally aspirated would require significant work on the engine and consequently cost a fair amount. Estimated costs for an engine rebuild up to a 2.4 litre setup, individual throttle body intake, standalone ECU and required engine headwork would probably exceed 20,000 SGD. To go to these levels of performance at this cost will require a huge commitment on the part of the owner and at this stage, it is probably relevant to consider your long term goals versus the budget allotted for the car's running or upgrades.

In my case, I have decided that the current level of 280-290bhp would be sufficient to run longer term and reliably on the track as I retain stock compression ratios and most of my modifications are simply bolted on with a tune. Although I will not have performance numbers like 12.X quarter miles numbers to boast, my personal view is that the strength of the S2000 has never been in its engine power but rather in the handling potential of the chassis thus spending should correspondingly focus on highlighting its strength in that area.