Flywheel and clutch selection for Spridgets

June's article is a bit earlier than planned but as we are doing a batch of flywheels it seemed like a good time to talk about what makes a good clutch and flywheel combination for a track Spridget.

Clearly the original assembly rated for 75ftlb and 65bhp isn't really suitable so we'll probably be replacing the clutch and flywheel completely. But "Wait" you say, "can't I just lighten the existing flywheel and get an uprated clutch?". Not if you use more than 6500rpm or make more than 85ftlb... Read on to find out why.

There's a few things we thought about when we did our clutch and flywheel package.

  1. Torque rating - Clutches are rated for torque not bhp, with a max torque of <150lbft getting a clutch with sufficient performance for even the best tuned A series isn't so difficult.
  2. Weight - 2 things here really, total package weight (clutch and flywheel) and mass centralisation. There's no point having a lightweight flywheel when all the mass is at the outer edge.
  3. Transmission protection - the gearbox (and diff) (and halfshafts...) are weak links in a performance Spridget. Whilst SCCR boxes and uprated halfshafts increase reliability, they are still a high frequency failure point on many vehicles. There are 2 causes of stress on these components - periodic rotational acceleration and impulse loading.
    Impulse loading is caused when the clutch is engaged or the car regains traction after wheelspin. There is a significant mismatch in speed between the input and output of the system and a single high load is applied.
    In a  theoretical unsprung system this is applied as an instantaneous load at a single point in time. In reality the force is always applied over a period of time, the longer the period is the lower the peak force is and the less chance there is of going over the failure point for the weakest component.
    Periodic rotational acceleration is a force continually applied to all the transmission components. At a constant road speed, the car moves forward linearly, the wheels convert the linear motion to rotational with little or no acceleration as observed at the driveshaft. At the engine end however the action of a piston engine means that the force is applied periodically (ie when it goes 'bang') which tries to accelerate the crankshaft. Now while the average rotational speed is equal (unless the clutch were to slip) the force being applied across the transmission is changing at the same frequency as the engine is firing.
  4. Clearance - When we started racing we bought an off the shelf race clutch and then spent 2 days taking the engine and gearbox in and out while we resolved all the clearance issues and ground sections from the bell housing and turned down bolt heads. Apparently this was Ok because it was a 'race' clutch(!)
  5. Safety - It may surprise you to hear that separate ring gears are not allowed in many forms of racing outside the UK due to their ability to 'float' and fail at high rpm. Also EN8 (which many of the available flywheels are made of) is not used in performance flywheels as it's not considered strong or hard enough compared to Chromoly steel like as AISI 4140.

Our 180mm clutch and flywheel package has been developed by us and is used by many UK racers with great results. The organic plate with sprung center has a softer take up to protect the gearbox. Because its only a 180mm plate, the flywheel can be made lighter and there is greater clearance to the bellhousing. Using Chromoly steel means the wearface of the flywheel is harder and doesn't 'pick up' when used aggressively. It also means the ring gear can be machined directly into the flywheel removing the risk of failure. 

As always, if you are building or upgrading a Spridget for competition or fast road use and want help or advise, please do drop us an email or give us a call.

-Rich & John

245mm (9.6") Midget / Sprite big brake kit - front

Complete kit suitable for race cars and fast road/track vehicles. 4 pot alloy calipers (Wilwood) 245mm solid discs (9.6") Fittings Price INCLUDES VAT The Mamba big brake kit fits under most 13" alloy wheels and steel competition wheels like Weller. A replacement for the caliper and rotor gives a great road upgrade with m1144 pads or consider m1155 or bp20 for track days. For circuit racing we recommend the Hawk DTC30.

£650.00

SOLO 2 + 4k Camera mount bundle

The excellent Solo 2 laptimer and the Mamba Camera Kit together as a bundle. Get predictive laptiming and analysis from the solo live on track then download the video and data and create overlays of time, speed, etc on your video before sharing to Youtube or doing some more driver training. Example: https://youtu.be/JaPou5L9TsE   Perfect for improving your car and your driving without breaking the bank. Includes billet camera mounting kit. The Aim Solo 2 GPS Car Racing Track Day Lap Timer is a completely automatic motorsport laptimer. receives the data from two satellite constellations GPS and Glonass, which is a huge step forward since it is unbelievably faster and more precise than the previous version.The power ON requires only a few seconds and the lap times are calculated with a max 2/100 sec of tolerance. 

£375.00 £410.00

Aim Solo 2 GPS Racing Lap Timer

These are just amazing - predictive lap timing like the F1 guys have plus analysis and logging and G-force. Add a camera and combine the data to provide great video overlays for youtube too.  The Aim Solo 2 GPS Car Racing Track Day Lap Timer is a completely automatic motorsport laptimer. receives the data from two satellite constellations GPS and Glonass, which is a huge step forward since it is unbelievably faster and more precise than the previous version.The power ON requires only a few seconds and the lap times are calculated with a max 2/100 sec of tolerance. 

£354.99

Midget Steel Flywheel Kit - 180mm

The perfect solution for UK racers: 180mm steel clutch cover + bolts 180mm organic, sprung center plate Roller release bearing and billet carrier Lightweight steel flywheel (2.7kg) Saving over 4kg from the standard setup, this package provides a clutch that can cope with any A series race engine torque along with a smooth, progressive take-up that protects the transmission and low rotating mass to help protect the crankshaft. AND it fits in the bell housing without having to grind anything away. ARP crankshaft bolts are +£35.00   Please add £60.00 if you would like us to assemble and balance the assembly.  Note if you have the crank out of the engine we recommend getting your full assembly balanced.

£725.00

Distributor - full race (Red spec) + Electronic ignition

Mamba have teamed up with a main-stream distributor manufacturer to produce a special race-spec A and A+ race distributor. In answer to recent problems with quality from our usual suppliers we felt there was no option but to produce a new high quality product with all the features a club racer needs. Proper race spec rotor arm Electronic ignition  Race advance curve designed for long duration ( >286 degree) cams. Finished with long silicone leads so they don't suffer vibration fatigue We believe this is now the best A series race distributor on the market. Available for A or A+ with either side or straight cap. Please specify your preference in the notes of your order. 

£154.99

3 cylinder pedal box with balance bar & master cylinders

Triple cylinder pedal box fits in standard midget / sprite mounting. Complete with balance bar, cylinders and cover. Clutch cylinder has integral reservoir and brake cylinders use a shared remote reservoir (due to the fitment angle in the car, an integral reservoir is less suitable but we can provide this as an option if required). Update: 2019 version has additional slot for mounting remote bias adjuster cable. Master cylinder sizes: 0.5 (1/2)" .625 (5/8)" .700" .75 (3/4)" Add the required master cylinder sizes in the comment box after confirming your order.

£479.99

Midget to MGB damper conversion kit

Mamba have designed a front suspension upgrade package that replaces the standard radial arm damper units. By using an MGB Shock Absorber the top king-pin mounting point is significantly strengthened, thus improving it's location and providing more consistent geometry. The 'Shock' is mounted on Mamba designed laser cut slider plates, which allow the camber angle to be set to better suit the application, i.e. circuit, sprint or hill climb. Includes plates, all bolts, nuts, trunnion bushes and instructions. MGB dampers are not included. Supplied unpainted so you can colour match to the chassis but let us know if you want them painted (in black) instead.

£159.99

Midget adjustable camber front suspension kit

Laser-cut steel mounting plates and fitting kit. The plates sit between the damper unit and the chassis turret to allow fine suspension adjustment WITHOUT replacing the trunnion.  Set your camber to any value 1.0 - 4.0 degrees. Allows you to dial out any minor inconsistencies. Note: the plates raise the inner pivot centre which gives improved toplink geometry for cars using shorter than standard springs. This results in less bumpsteer and less Camber gain in roll  (ie more grip!) Kit includes: plates, nuts, bolts and instructions. Supplied unpainted so you can colour match to the chassis but let us know if you want them painted (in black) instead. We have full alignment setup in-house and can fit these and setup the camber and toe for you. Call for setup price.

£159.99

1380 Fast road engine for Midget / Sprite / Minor

Reconditioned 1380 in line A series engine: Suit MG Midget/A H Sprite/Minor etc. MG Midget A series thick flange 11 stud block freshly bored 73.5mm (1380cc) New high quality cast pistons Crank uprated to Marina crank with Midget flywheel flange New MET270 billet and drilled fast road camshaft Vernier cam drive with Iwis duplex chain New Metro hi-flow oil pump New no bypass water pump with glass filled impeller Oil galleries tapped & plugged and all new core plugs - block chemically cleaned. Standard "Big Valve" 11 stud head with hard exhaust valve seats EN24 competition head stud set ARP rod bolts MED roller tipped rockers Block decked to give 10.5:1 static compression Lightened Midget flywheel with good clutch & cover & new ring gear Bottom end with clutch & flywheel balanced. Aldon points type vac distributor The price is based on a suitable exchange engine. That means a serviceable in line thick flange 1275 A, A+ Marina or A+ Ital engine, not sleeved and no more than +0.040" bores.If there is no exchange unit available there will be a £650 surcharge. Collection only and payment by BACS before or cash on collection please (no paypal on this one). An invoice will be provided with limited warranty.Any questions please ask .

£3,495.00

Steel flywheels (A-series)

Steel flywheels for high performance Midget & Sprite. 2.7kg (4.5kg less than standard) Featuring integral ring gear for balance, weight and safety.  Chromoly steel  - not cheaper EN8 Available for 180mm or 184mm clutches - please specify in comments when ordering. (+£10.00 if you require bolts and dowels)

£299.99

Steel Race Clutch Cover 180mm

180mm Steel race clutch cover is light and designed to handle torque outputs well in excess of even our long-stroke 1496cc race engines. No pad design Requires a modified or race flywheel. Clutch plates sold separately All our clutches are built to order so allow 4-6 weeks for delivery (call if you need sooner)

£224.99

Road spec 180 clutch cover

A heavier design of the 180mm clutch cover more suitable for spirited road use rather than race. Requires a modified or race flywheel Clutch plates available separately All our clutches are built to order please allow 4-6 weeks for delivery (or call us)

£124.99

Billet Alloy Race Clutch Cover 184mm

Full race, lightweight billet alloy lug-type clutch cover. The lightest cover available for a Midget.  Friction plate available separately. Requires a race-spec flywheel. Clutch covers are made to order. Delivery in 4-6 weeks, please call to check before ordering.

£499.99

JWIS Ultimate Simplex Race Timing Chain - A series 1275

These are proper, JWIS top quality automotive cam drive chains, made in Germany, NOT cheap industrial quality chain as most of the factors offer. It has taken me over a year to get access to this product - and believe me I don't fit cheap timing chains to expensive race engines if I can help it - no point in taking all that time & effort to get everything right to have it go off in 1/2 a season because the timing chain has stretched beyond use or worse still................! If you are running an inferior product on your £4000 engine, you really should think again! Available as Duplex or two types of Simplex (for those wanting the very minimum weight/drag on their cam drive)

£37.50

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    June's article is a bit earlier than planned but as we are doing a batch of flywheels it seemed like a good time to talk about what makes a good clutch and flywheel combination for a track Spridget.

    The A series engine (inline) in a Spridget can be tuned to more than twice its original design specification. Our race engines are making over 140bhp. Getting 130+ from an engine isn't actually that hard if you know how but making it reliably takes a bit more skill.