Mugen Technical Essay - S2000 Concept

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Leider in Englisch



Concept of development for
Mugen S2000 parts
April 2001

Exhaust Manifold Kit
During the development, the performance test on the exhaust manifold by so many different specifications had been conducted and as a result, we were able to obtain many data. Some of them are as follows.



45mm diameter of the primary manifold is better than that of 48mm.



When compared between 4-1 and 4-2-1, 4-2-1 is better in overall. General notion that 4-1 is for the high speed and 4-2-1 is good for the middle speed range is not necessary applicable to F20C.



Exhaust manifold of standard specification was an ideal specification as expected. It is also a collector configuration aimed at the peak power output.



Regrettably, however, since the emphasis is placed on the mass production, the standard parts have the different primary manifold lengths for each cylinder and therefore, the engine performance between 6000 and 9000rpm is not necessary the best.

Actual running test has confirmed the following.



Since there is a brake master cylinder placed near the exhaust manifold, it is indispensable to place a heat insulation material such as heat insulation plate between the cylinder and the manifold. We have actually confirmed that there was overheating phenomenon when the test was run without such a heat insulation.

From the result of the test conducted, we decided the specification for Mugen’s exhaust manifold as follows:



For the primary manifold pipes, a diameter of 45mm has been adopted.



The length from the exhaust port to the collector has been optimized and now have completely equal lengths.



4-2-1 layout has been adopted.



A collector’s configuration which emphasizes the torque performance from 6000 to 8000rpm has been adopted.



For eliminating the overheating problem, an exclusive metal molding has been installed to make new heat insulation plates.



Of course it is adapted to the Japanese regulation; JASMA.



Sports Exhaust System
Performance of the standard silencer is as follow:



As the manufacturer’s genuine parts silencer, it produces a very low exhaust pressure which normally has never been thought before. Our system is compatible to produce both a low exhaust pressure, far less than that of commonly modified mufflers, and a very effective exhaust noise silencing performance. During the test conducted on engine dynamometer, we tried a straight pipe from the catalyzer down and measured an increase of only several horse power output.



Noise level is just about low enough to clear the noise level regulation in Japan (JASMA) after October 1998 while the exhaust sound gives a sports car feeling.



Only the short coming is that it is rather bulky and heavy which significantly interferes with the air flow under the floor.

Objectives for the development of Mugen sports exhaust system.



Lighter weight.



Use of titanium material: Use stainless alloy for the high heat area and titanium material for the lower heat area in order to achieve a balance between the durability and lighter weight.



Optimizing the pipe’s diameter: If the pipe’s diameter is increased excessively, that will result in power decrease. It also produces banging exhaust noises which in turn will require larger silencer as well as inner silencer which can significantly resists the exhaust pressure. The exhaust pipe diameter appropriate for F20C engine is about between 60mm and 70mm and there is no noticeable change in the maximum power output in this range. (At below 6000rpm, there is no torque change seen even when the diameter of the exhaust pipe was changed, due to the effectiveness of the valve timing control on the V-Tec’s low speed range). As a result of our repeated test on the dynamometer, we selected the pipe’s diameter of 60,5mm which is the minimum size requirement, and 45mm for the extension of pipe after the junction manifold. (More than 1/2 of the cross section area of the main pipe after the junction section is not necessary and if the diameter is smaller, the silencer could also be smaller). We took a special care for manufacturing the junction section in order to minimize the energy loss and as a result, the system is smaller and 11kg lighter than the standard system.


Standard System
Mugen System

Weight:
23kg [50.6lbs]
12kg [26.4lbs]




Achieving a good exhaust sound quality for sports cars.
Exhaust noise criteria applied to S2000 after the 1998 regulation is as follow:

Noise Regulation
Before 1998
After 1998
Standard Cars
Mugen Cars

Close to Exhaust:
103db
96db
95db
94db

During Accelleration:
78db
76db
75db
76db



We decided the final specification of the exhaust noise quality on the basis of repeated test results by emphasizing the sound volume and quality at the practical speed range at which it requires the exhaust noise volume most for an open-hood sports car. Even though our exhaust noise level meets the ’98 noise regulation, we did not make any compromise to produce a good sports car sound volume and rigid sound quality as well.



Designing a lower exhaust pressure.
The standard equipment silencer is a silencer of high performance equipped with a return pipe and with a low exhaust pressure resistance. We studied the inner configuration of the silencer and as a result, we were able to further reduce the energy loss after the catalyzer.



Use of stainless steel alloy as sound absorbing material.
Sound absorbing material of stainless steel alloy used for GT-NSX and JTCC Accord was selected in order to assure the durability for the sports driving which tends to increase the heat load.



High quality TIG welding.




Temperatures of Intake Air and Cooling Liquid (Coolant)
F20C engine achieving a high level of performance is a very delicate engine. Even a small factor may hinder the real power of 250ps. Following is our advice for the optimum use of the engine’s real power.

Always induce the cool outside air.

Reason 1:
Since the density of high temperature air is low, it causes to decrease the power output. For an example, if the induction air temperature rises more 3ºC, there will be a loss of 1% power output.

Reason 2:
If the temperature further increases, the engine protection program installed in ECU will activate and limit the engine power output.

Reason 3:
Regrettably, the induction port of the standard air box is laid out in such a way that it sucks hot air in the engine room. Therefore, it always induces hot air heated up to above 20ºC to 30ºC.

Solution:
Install Mugen air box kit which is designed to induce cool outside air.




Maintain the engine coolant at an appropriate temperature range (between 70ºC to 90ºC.)

Reason:
If the coolant temperature were too low, it will not change into HI-VTEC range and if it were too high, the protection program activates and limits the power output.

Solution:
It will be effective to install a radiator with increased capacity and also a bonnet (engine hood) with air outlet duct. For the driving on the racing circuit, remove the front license plate to increase the air flow to the radiator. A radiator cap with high pressure valve is also effective. (Remarks: The water temperature gauge in the combination meter alone is not sufficient to correctly understand the water or coolant temperature. For driving on a racing circuit, we recommend that a highly accurate water temperature gauge be installed.)





Aero Bonnet (Engine Hood)
This is a bonnet with air-outlet for an effective engine cooling. Power bulge for containing Mugen air-box is integrally built. Since prepregnated carbon fiber clothes by precisely controlling the amount of resins used was formed in a pressurized high heat autoclave oven, it is expected to produce a product of high strength, rigidity and heat resistance which is indispensable for manufacturing a light weight product.

We have conducted a number of trial productions and tested their strength. As a result, we were able to reduce the weight of the carbon fiber bonnet to 4.7kg while maintaining the strength equal to that of standard aluminum bonnet.


Standard Hood
Mugen Hood

Weight:
7.35kg [16.17lbs]
4.7kg [10.34lbs]




Cold Air Box Kit
(An air induction system to induce as much cool air as possible)

At Mugen, air box for S2000 cars has been developed for almost a year and half. Many different types of air boxes have been repeatedly tested and the specification was finally decided as a result. Since the development has been carried out for the people who give the first priority to the power performance, there are some unresolved roughness remained for such an area as intake air noise. (It may cause some irritation to ears). Therefore, for those who prefer to have quiet open air driving, we do not recommend the use of this product.

Performance of standard air box and filter.
High performance filter with a only slight loss of pressure is adopted.

As a result of measuring the filter’s performance without air box, we found that there was only few horse power (2 to 3 PS) of output loss due to the pressure loss. Overall power loss with the air box was only about 5PS at the top end (in comparison with that of naked racing funnel).


It is regrettable to comment that the standard air box installed in a car induces heated air passing through the radiator into the engine.

(Remark)
As a result of the measurement of the induction air temperature of a car running on the racing circuit and high speed freeways, it was found that heated air which was about 15ºC to 30ºC higher than the ambient air temperature was induced into the engine room.

(Remark)
The density of air becomes about 1% thinner as the temperature rises for about 3ºC and it directly relates to the power down. Inducing heated air of 30ºC will also cause the power down of about 10%.

(Remark)
When the high temperature air is induced over the limit, the engine protection program activates and enter into the power save mode.



Performance of Mugen air box and filter.



Complete reduction of intake air resistance.

Since it exceeds even the high performance of a standard filter, the following elements have been adopted.

Adopted a large diameter aluminum funnel of a racing type.


Adopted a racing filter of low pressure loss type.


Adopted an air box design of smooth configuration made of carbon fiber.

Induction of cold air:
It is designed to induct outside air from behind the license plate in order to directly induct the outside air to the air box. There will also be a useful effect from the ram pressure air flow which directly hits the induction mouth of the air box if the license plate were removed during the sports running.

Caution:
When installing the air box, a portion of the supporting frame underneath the standard bonnet is needed to be cut off. This will require a professional work and therefore please take it to the professional metal working shop. (In case of Mugen aero-bonnet, this work is not required).

Caution:
When raining, install the attached rain protection plate.

Caution:
Do not run through the deep standing water. Splashed water will get into the engine cylinders which will cause the water lock and eventually the engine trouble. During storm and hard rain, there will be deep pool of waters formed on the road surface and therefore the driving under such a condition should be discouraged and avoided as much as possible.



Suspension Tuning (for Racing Circuit)
Parts development for S2000’s suspension is currently being conducted for sports driving on the racing circuit. We are accumulating the knowledge about the suspension through the basic experiment on the test course and tests conducted on the actual racing circuit.

Characteristic of standard cars.



Steering response is very good.



The car requires a severe slide (drift) control by the driver.

Since the car’s response during the slide is delayed one step behind the driver’s input, it is not possible to make the sensitive control.

Since the car’s response is delayed one step behind the input from steering and accelerator, the car may ended up in zigzag running or spin unless the driver predict the car’s movement early and make responsive control accordingly.



When the slide (drift) becomes apparent, the car’s rear end may abruptly thrown out to the opposite direction and the driver may not be able to control it unless he or she is an expert driver.



Even though the ride is rather hard, the car’s positional change is significant.



Since LSD of the standard equipment is very effective, the street type radial tire has sufficient performance to run on the racing circuit.



Since this same LSD is very effective, it requires the driver to be cautious of accelerator operation on the wet surface. S02 standard tires installed on S2000 has such a characteristic that its slight under steer on the dry surface changes to over steer on the wet surface. Therefore, the driver should give a special caution to the driving on the wet surface.




Mugen recommended S2000 suspension set-up.

Spring and damper (especially undamping side) were set rather hard, the ground clearance was lowered and the car’s positional changes was restricted as much as possible. As a result, when the car is sliding, the car’s response to the driver’s control became faster and the sensitive control also became possible. Further, with the new suspension arrangement, it is now possible to use a wider range of tires from S02 standard tire to S tire which is designed for the sports driving.

Basing on the separately listed specification chart, we recommend that a suspension set up appropriate for your particular needs be used for the improved driving.



Important points for S2000 suspension tuning.



Tire.
Selection of tire is one of the important works.

Standard S02 tire and S2000 are the perfect matching. Without doubt, the performance is also the first class quality and it gives a reliable performance for either the new tires and slightly worn tires (on dry surface). We strongly recommend S02 tire especially for the sports driving.

If you wish to use “S Tires” for the exclusive sports driving, we recommend BS540S (Fr215/45-17, Rr.235/40-17).



Balance between the front and rear ground clearances.
The car’s behavior could be changed by adjusting and changing the front and rear ground clearances for a 10mm interval. It is possible to have over steer characteristic if the front end is lowered and under steer characteristic if the rear end is lowered. For S2000, the ground clearance adjustment is a very effective approach for changing or improving the handling. When tuning the springs and dampers, make sure to measure the ground clearance (in millimeter unit) of the front, rear, left and right before installing and assembling the parts. And after the installation, the ground clearance should be readjusted to the original position. Otherwise, any behavioral change which may be caused by the ground clearance change will interfere with your correct assessment of the result of tuning.



Front and rear toe alignment.
The front and rear toe alignment, along with the ground clearance adjustment, is a very effective method to change the car’s handling characteristic. For an example, the standard toe-in angle of a base car is 6mm. However, if the angle were adjusted to 6mm, 8mm and 10mm, the rear end behavior will become more stable by taking foot off the accelerator as the car enters a turning corner. As a general tendency, when the toe-in is increased, it tends to become under steer and when decreased, it tends to become over steer. For those having a hard time with under steer on the mini-circuit or gymkhana, downward adjustment from 6mm to 4mm and to 2mm may be very effective.



Front and rear springs.
Spring rate of the standard car and Mugen recommendation is as follows.


Standard Car
Mugen Recommendation

Front
3.9kg/mm
7kg/mm

Rear
5.2kg/mm
11kg/mm


For S2000, it will be difficult to significantly change the handling characteristic by changing the spring rate only. It will be necessary to make overall adjustment with tire, ground clearance, toe angle, camber angle, etc. Even though the vertical (grounding) load of each of the 4 wheels is same, we believe that it will be necessary to install soft spring for the front and hard spring for the rear in order to neutralize the turning characteristic since the front has narrow tires and the rear has wide tires. Even when the spring rate was increased, we believe that this balance should be maintained.

Damping force of dampers.
Mugen’s sports type damper is tuned to be soft for very slow speed range and hard for the mid and high speed ranges. The damping force of this damper can be infinitely adjusted for a wide range by turning a needle at the top point of the piston rod. Generally, the needle should be fully tightened and turn back 2 or 3 times for the normal correct range. When entering a sharp tight corner, it will be effective to adjust the front harder and the rear softer. Conversely, when the rear’s following performance is important to improve the stability during a high speed cornering, we recommend to adjust the rear harder.



Camber angle.
Try to adjust the angle for 15 degree at a time. It should be noted that the front camber must not have too much angle.

If a driver is troubled with the drift control or spin during the sports driving, we recommend to adjust the ground clearance and toe angle of the rear wheel toward a slight under steer. You will find that the car is clearly easier to control.

Uii das kann man bei GT3 auf der PS2 machen? Wußte ich garnicht. Muß mir wohl doch oder übel mal so ein Teil holen damit ich meinen S auch mal vorm Fernseher im Bett liegend fahren kann