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Bellhousing vs Adaptor Plate
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Site last updated on 15/08/08

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Why use an RJES Bellhousing instead of an Adaptor Plate / Flywheel kit?

  
Despite the advantages of a bellhousing being obvious to a lot of people, there does seem to be some mis-information out there about the relative merits of each solution to the problem of joining a Subaru engine to a VW transaxle. This page is intended to briefly explain the pros and cons of each. Much more detailed info is contained on this site. The ‘Bellhousing FAQ’ page is a good start if you’re interested in the detail.

 

Q1: Clutch Availability?

Q2: Clutch Cost?

Q3: Known Adaptor Plate Problems?

Q4: Clutch Size?

Q5: Engineering Quality?

Q6: Installation Neatness?

Q7: Why adaptor plates been around so long, but not bellhousings?

Q8: Do adaptor plates have any advantages?

Q9: Bellhousing vs Adaptor Plate Cost

 

 

 

Q1: Clutch Availability?
A1: Adaptor plates usually depend on the aftermarket heavy duty 200mm VW clutches, for which you have to go to a specialist supplier. RJES bellhousing kits need no heavy duty clutch parts (as long as your engine is standard), as they use the clutch Subaru intended for it. These are readily available anywhere.

Q2: Clutch Cost?
A2:This seems to be a reason for using an adaptor plate kits which crops up more regularly than others. It’s origins seem to be distributors of adaptor plate kits (strange, that), but they are not necessarily true, as the following typical UK prices show:

    Adaptor Plate Clutch Parts Prices:
       HD VW 200mm pressure plate   120
       Clutch disc                   25
       Release Bearing              15 
       Total                       160

    RJES Bellhousing Clutch Parts Prices - ‘push to release’ Subaru N/A clutch:
       3 piece clutch kit              125 - often (new, OEM) on eBay @ 90
       Clutch Disc                   35
       Total                       160 maximum

    RJES Bellhousing Clutch Parts Prices - 225mm ‘pull to release’ Subaru turbo clutch:
       3 piece clutch kit            150 - OEM, new, grahamgooderacing.com
       Clutch Disc                35
       Total                     185 maximum

   Don’t forget that you can sell on the clutch disc which you don’t need in the 3 piece Subaru clutch kit needed with an RJES bellhousing kit too, reclaiming some of it’s cost, and that you won’t need a Subaru clutch kit at all if you are lucky and your donor Subaru has a recent clutch.

Q3: Known Adaptor Plate Problems?
A3:
There are two known problems with adaptor plate type Subaru conversions. These are burned out starter motors, and broken adaptor plate bolts. These are both regular discussion topics on the subaruvanagon Yahoo group. The starter motor problem is without doubt due to a fundamental design problem with the adaptor plate kits. See Bell Housing FAQ’s for more details. The cause of the broken bolt problem is far more controversial, and is very likely to be caused by increased load on the join in a VW compared to the engine in it’s original application. It is likely that some VW engine mounting designs make this problem occurring.
   Solving these problems was one of the objectives behind the development of the RJES conversion bellhousing.

Q4: Clutch Size?
A4: The majority of adaptor plate kits use a 200mm VW clutch, as originally designed for a 60 bhp VW engine. Aftermarket heavy duty clutches are available which bolt straight on, and will handle considerably more power. They achieve the extra capacity by increasing the clamping force, which is directly proportional to clutch pedal effort. Therefore you will have a very heavy pedal, especially with the heavier duty clutches. If you look at factory fitted clutches on production engines of 130 bhp and above, you will find that they are almost exclusively bigger than 200mm. This is because the diameter increase increases the torque capacity with no increase in pedal effort. It also increases the life of the clutch by increasing the available friction face area available.
   Some adaptor plate kits are available to use a VW 228mm clutch. However these were only ever designed to handle a maximum of 112 bhp, and no heavy duty upgrades are available. Their suitability depends on how hard you intend to drive your conversion.
   Making use of the clutch designed for the engine was one of the objectives behind the development of the RJES conversion bellhousing.

Q5: Engineering Quality?
A5: When was the last time you saw a production car - even a low volume one such as a TVR which used an adaptor plate and fabricated flywheel? This kind of technology is used by production manufacturers, but only ever at the prototype stage. For production they will always engineer a proper solution.

Q6: Installation Neatness?
A6: If you take pride in the quality of your projects, you probably like them to look as anything which is is actually a conversion to look as ‘factory fitted’ as possible? An adaptor plate between the engine and transaxle instantly says ‘conversion’ to anyone looking who knows their stuff.

Q7: Why adaptor plates been around so long, but not bellhousings?
A7: It’s all down to engineering development cost and effort. An adaptor plate kit is a ‘minimum effort to get the job done’ solution to a problem, involving only relatively simple processes such as machining and welding. Almost no specialist tooling and fixturing is needed, and the design effort is minimal.
   A bellhousing is the correct solution in terms of quality of engineering, involving more specialised knowledge and processes to design and manufacture, such as casting, pattern making, and heat treatment. Considerable tooling and fixturing are needed.

Q9: Bellhousing vs Adaptor Plate Cost
A9: An RJES bellhousing kit costs less in the UK than an adaptor plate kit with a fabricated flywheel. Beating the (rather high) UK cost of adaptor plate kits with a better product was
one of the main objectives behind the development of the RJES conversion bellhousing. Enough said!
 

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 Inventors of the Subaru - VW conversion bell housing using Subaru flywheel, clutch and starter

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