Rear Chassis

Motor Mounts

There are many motor mounts available aftermarket. They accomplish two things. Aluminum dissipates heat much better than plastic. Motor runs cooler meaning lower resistance in the winding making it go faster and have longer life. Also, aftermarket motor mounts allow you to adjust the distance between the pinion and spur gear. Properly adjusted gear is very quiet just like how the car is when is new. Proper adjustment also lengthens the life of the gear. Most of the popular motor mounts are made by either PN or Atomic.

Motor mounts fall into three major category. RM, MM and HM.

RM is motor behind the axel. This put the most weight on the rear wheel for traction. This configuration is popular with some racers in Europe where racers like to slide into corners. Very few racers use it in the US. For very short 86mm wheelbase cars like the 934, RM is your only option.

HM is for next larger size 90mm cars like many hatch backs, ie Mini Cooper, VW Beetle. Hatch back bodies ends right after the rear wheel, so there is no room for a RM motor mount. Otherwise, the motor will hang outside of the body. HM put the motor on top of the rear axel. This is a little top heavy, but there are some race where only hatch backs are allowed. Recently, PN made a hybird HM mount that combine the shortness of HM with low CG of MM. The motor is placed in front of the axel in a mid motor configuration. This make for a lower motor position, so the car handles more like a mid motor configuration. When used with short Ferraris like the F40, it is possible it could be more competitive than the standard mid motor mounts in certain tight tracks.

MM is the most popular motor mount. MM is divided into two sizes. It comes in either 94mm or 98mm. The first generatiion 98mm MM mount replace the plastic MM mount from Kyosho.down on the very bottom of the chassis for very low CG. The other size MM mount is the 94mm size. Coming stock on Kyosho cars, all 94mm bodies use their plastic rear motor mount. PN and Atomic made a mid motor mount that fit the space of the 94mm body. The compromise is that the motor sits higher than a 98mm motor mount because of lack of space. The new second generation motor mount from PN actually lowers the motor to as low as the first generation 98mm mount. The improvement on handling is dramatic.

Advantage of 94mm MM mount is quick handling and good acceleration traction. Advantage of 98mm motor mount is stability at the expense of traction and quick handling. Reflex Racing has a 96mm H-plate that adjust the motor mount to an in between 96mm position for best of both worlds. I personally don't like wheels that are not centered on the wheel well.



Stock Length (98mm) Mid Motor Mounts

These are stock replacement mid motor motor mounts.

Atomic AR281 98mm V6

3 position adjustable axel height. The motor is tilted about 60 deg for lower CG. Not as low as PN can get at lowest setting, but per Atomic, higher CG is better for carpet. Rear diffuser suppose to help with aerodynamic.

PN Racing LCG V3

Motor lay flat on the bottom of the mount. Lowest CG location of any 98mm mounts for fast cornering. Fits MR2061 disk dampers. 4 Adjust ment positions for axel height. Mount stress analyzed with finite element analysis for minimum weight.

3 Racing MZII-005

A motor mount that does not require drilling of motor. As usual for 3Racing, a good deal for $20. Motor is about the same position as stock.

3 Racing KZ01

Motor mount that incorporates the H plate into it. Top plate has hole for damper. Does not require drilled motor. Adjustable chassis height. Similar motor height as Atomic motor mount, but not as low as PN.

Atomic AR240 LCG LM Motor Mount

This is actually not a 98mm motor mount, but a 102mm motor mount for the Le Mans series cars. It will not work with 98mm bodies. This mount is made wider to work with LM differential that is 4mm longer than the normal MR015/MR020 diff. Normal diff will not fit in this mount. Motor lay flat on the bottom of the mount for low motor CG location that is as low as the PN mount. 3 position adjustable axel height.

R246 MM Mount

Kyosho's (R246) motor mount.Is designed to hold a stock motor without drilled holes.Same configuration as stock motor mount, but in aluminum to dissipate heat. CG about same height as Atomic. Not as low as can be on the PN mount.



Shortened (94mm) Mid Motor Mounts

94mm mid motor mounts are shorter than the stock 98mm motor mounts. This means the H-plate would have to be moved back a notch to keep the same wheelbase. Or you can use the rear motor H-plate which is 4mm longer, and use the same notch. Using the longer H-plate will give you a softer suspension. This means more traction in back and less in front to reduce oversteer. If you use the MM H-plate, and adjust it to the shortest of 3 position, the chassis wheelbase will be 94mm short rather than 98mm. This opens up a lot of bodies possibilities. The down side is to make the motor mount as short as possible, the motor is tilted at 60degrees, and slightly higher, so the CG is higher than the stock 98mm motor mounts. 94mm wheelbase cars will have sharper handling, but less stable than 98mm cars.

If you can only get one motor mount, 94mm mount is the one to get. You can adjust the H-plate to fit 98mm bodies if necessary, and still retain a relativly low CG.

Atomic AR271 94mm Version 6 Mount

3 position adjustable axel height. Damper mount is mid mounted so height is not adjustable. There is no real advantage to a mid mounted damper mount IMHO. Makes it harder to take out the motor. Rear diffuser included. Higher motor location than PN LCG, but per Atomic, is better for carpet.

Atomic AR266

This version of Atomic mount has adpter plates to use with stock motor that has no drilled motor. Higher CG than PN.

PN Racing ML LCG

This is the most competitive 94mm motor mount. You will see almost all racers use it for 94mm. Forward tilt motor configuration gives a CG location for the motor is lower than the typical 94mm mount for good handling in corners. Motor position is about as low as the typical 1st generation 98mm motor mount. Adjustable 4 position axel height. This is the motor mount to get if you can only have one. You then can adjust the chassis to fit 98mm bodies.



Stock Length (86mm) Rear Motor Mounts

These are stock replacement rear motor mounts.


Normal stock replacement RM mount.

PN Racing RM -1044M

Rear motor mount that is 1 gram less than stock. All the benifit of aluminum motor mount without the weight. The middle tap that looks like a damper post but does nothing can be cut off to save some more weight.


This Kyosho optional motor mount falls into the why bother category. This is the exact same design as the stock motor mount, meaning use of shims to adjust pinion mesh. Besides being hard to find, you loose half the reason for using modified motor mount, which is to be able to adjust pinion mesh.

3Racing KZ06

Incorporates H plate into the motor mount. Do not require drilled motor. Adjustable wheel height. Good deal at $14.

R246 RM

Designed to work with stock motor without drilled motor hole. Carbon fiber top and bottom plate.



Longer (90mm) Rear Motor Mounts

These are rear motor mounts that are 4mm longer than stock. The main reason for using the longer mount is so the damer plate can be mounted low behind the battery/radio compartment below the top deck of the chassis. Some super car bodies like Lamborghini LP400 or the Cobra have low profile, and normal height of the disk damper are too high for it. This will solve that. Also with the longer mount, with the H-plate adjusted to the longest of the 3 positions, the chassis will be 98mm rather than 94mm long. You would be able to use a longer body in RM configuration. Longer bodies are more stable. This along with RM configuration which tends to understeer when you accelerate means a easier to drive car.


RM motor mount 90mm mount. Is 4 mm shorter than stock. Gives more room for disk damper AR33. Disk damper sits lower in the chassis behind the battery box. This allows you to use RML body style where the car has low profile.




High Motor Mounts

Stock replacement high motor mounts

PN 90mm Motor Mount

The PN 90mm motor mount is different than the Atomic AR-083 in that the motor is in front of the diff rather than on top of the diff. PN is first to come up wit this design.The result is that the motor is lower in the chassis than the Atomic mount for better handling. With the PN 90mm mount, performance is close to the 94mm mount in terms of handling. Is not as good as the 94mm mount because the motor is higher than the 94mm mount, but is close.


High motor mount. The motor sits on top of the axel. Minimum chassis wheel base is 90mm. The motor sitting on top of the axel shortens the overall chassis length. Less over hang weight behind the axel. More weight is concentrated in the center of the car for better handling. The compromise is that there is higher CG. Easier to flip over. High motor mount is also required for short cars like the Mini Cooper or Toyota Vitz.


This is similar to PN 90mm where motor mounts in front of the rear axel. PN has lower profile damper plate design than atomic for low profile bodies.







Rear Dampers

Mid motor dampers


Standard Atomic mid motor damper for 98mm chassis. Use optional length plates for other chassis length.

AR-15 fiberglass plate 98mm

AR15SB graphite plate 98mm

AR147 Ti plate 98mm

AR131 graphite plate 94mm

AR133 Ti plate 94mm

Optional different length plates:

AR63-94mm chassis

AR64-102mm chassis

AR65-106mm chassis

PN Racing MR2061

For use with PN MR9498 94mm motor mount. Has 2 adjustment hole to adjust for 94mm and 98mm chassis. Using stock length (98mm) motor mount, this would only adjust to 98mm chassis. Presumably, this can be used in RM motor mount as well with 86mm chassis.

(With the MM H plate in middle position the shortened 94mm motor mount would give you a 98mm chassis as claimed. The damper post would be in the same location as a 86mm RM chassis. Therefore, this should work with 86mm RM chassis like the Porsche 934 / 935 and Lancia Stratos.)

3Racing KZ04

Disk damper from 3Racing. Good deal at $13. Adjustable for all chassis length (86-106mm). Works for both RM and MM chassis. Very versatile



Rear motor dampers

PN Racing MR2039

Side damper for RM application. This should fit 90-94mm RM chassis. Should also fit a 98mm RM chassis with lengthened motor mount like the Atomic AR067. Don't believe this will work with 86mm chassis. There is hardly any room between the motor mount and rear bulkhead on 86mm chassis.

Side damper place spring far out on the side for greater moment arm to resist against chassis roll. This allow for high roll sitffness even when using soft spring because of the greater moment arm. With softer springs, there would not be excessive vertical stiffness. Is good for RM chassis since they tend to oversteer. Higher roll stiffness in the rear brings handling more to neutral or maybe oversteer.

Atomic AR-033 Damper

Must use AR067 motor mount which is 4mm shorter than stock. Note the damper disk sits below the top deck of the radio box. Disadvantage is the moment arm is shorter from the pivot point which is the H plate to the damper disk. This gives less effective damping. However, it allows you to use a disk damper in low profile bodies that otherwise would not fit, or would require cutting. Can only fit 90mm wheelbase bodies.

Atomic AR-069 Disk Plate System Version 2

AR149 Same, but in Ti

This is a unique disk damper system that also incorporates 3 springs. Two are for roll and one for vertical movement. This allows for ultimate adjustability in setting roll stiffness and vertical stiffness. Also must use AR067 motor mount. Probably can only be used on 90mm chassis.

Kyosho MZW216

This disk damper use graphite for both damping disk and plate. There is extra friction for more effective damping.

3Racing MZII-006

Side damper from 3Racing. Good deal at $15. Assume is for 90-94mm chassis. May work for 86mm chassis.

3Racing KZ04

Disk damper from 3Racing. Good deal at $13. Adjustable for all chassis length (86-106mm). Works for both RM and MM chassis.

PN Racing MR2061

MR2060 for fiberglass version

For use with PN MR9498 94mm motor mount. Has 2 adjustment hole to adjust for 94mm and 98mm chassis. Using stock length (98mm) motor mount, this would only adjust to 98mm chassis. Should be able to be used in RM motor mount as well with 86mm chassis.

(With the MM H plate in middle position the shortened 94mm motor mount would give you a 98mm chassis as claimed. The damper post would be in the same location as a 86mm RM chassis. Therefore, this should work with 86mm RM chassis like the Porsche 934 / 935 and Lancia Stratos.)






Drilling Motor

Many aftermarket motor mount requires two threaded holes in the motor case. See link above for step by step direction.


H-plate usually comes in 3 different widths for 3 different stiffness. Mid motor is shorter than Rear motor H-plates by 4mm, which is the distance of one adjustment notch on the chassis. For example, you can use a mid motor H-plate instead of a rear motor H-plate if you move the chassis length adjustment by one notch. The reason for doing that is so you can have a stiffer H-plate.

H-plates stiffness are usually not symetrical. For one reason or another, it tends to twist one direction easier than the other. The result is car tends to spin out easier turning one way than the another. Use shims under the H-plate to solve that. Use a thin washer like the stainless shims sold by PNracing (low cost) or Kyosho MZW215 (expensive) setting spacer. For a car that tends to spin out or steer more going left than right, place a shim between the h-plate and the motor mount on the righ side of the motor. If you have to use more than 2 shims, then take the shims out and instead, place one shim between the h-plate and the chassis on the left hand side. Shim on the chassis has greater effect than shim on the motor because of the distance between the screws is less on the chassis. The best H-plates are made by Kyosho followed closely by PN racing.


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