Background |
Charles Probst, in his excellent book How to Understand, Service and Modify Ford Fuel Injection & Electronic Engine Control (Cambridge: Robert Bentley, 1993), mentions that the SHO is rev limited at 7300 RPM to avoid over-revving the accessory drive, and that engineers say the engine itself is safe up to 8500 RPM with underdrive pulleys installed. Several manufacturers offer pulley sets to do exactly this. Note that removing the rev limit requires installation of an aftermarket chip. | ||||||
Cost |
Underdrive pulleys are not cheap; expect to pay around $200. They are also very difficult to install. | ||||||
Side Effects |
With underdrive pulleys, your accessories will be driven
approximately 20% slower at all engine speeds. This typically translates
into insufficient alternator output to charge the battery at the normal
engine idle. The air conditioning will also be weak at normal idle speed.
Your headlights will dim at idle speeds as well.
See Alternators 101 for more information on the UDPs and charging. This can be counteracted by raising the idle to 1300 rpm with the chip.
Don Donelson mentions :
In so doing I took off my underdrive pulleys and put them on the new engine. I also bought a new alternator which replaced the 91 factory unit. In attempting to put the UDP on the new alternator I discovered that Ford SLIGHTLY redesigned the housing where the UDP rubbed and would'nt fit as before. I quickly solved the problem w a couple of high quality spacers (washers) ... and so far ... no problem. |
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Auto Specialties |
These are the only pulleys still available for the SHO.
They are available through all of the major SHO performance vendors (SHO
Shop, Scott Performance, CSR). They consist of a 20% smaller crank pulley,
and a larger alternator pulley. This set slows the alternator to 52% of
stock, and it slows the water pump, power steering pump, and air conditioning
compressor to 80% of stock.
These pulleys are available for both the automatic and manual transmission cars. The manual cars take two accessory belts, automatics only one. Thanks for Don McKinnon for the following : It appears Ford changed the alternator during the '93 model year. The change that is important for UDPs is that the pulley width at the shaft hole increased from 7/16" to 5/8". You must make sure you get the right set of pulleys for your model year or you will have problems with belts rubbing. PN 921107 is for the 1989-4/93 3.0l SHO
It appears Ford changed the alternator on the MTX models during the mid-93 model year, then again in 94 while still using some of the mid-93 unit up into 1995. There may not be many built this way, but as luck has it you just never know (I have one of these not so common 93 units on my 95 SHO!!). Joe Scott has also run into this with a 94 SHO in Maryland. If your SHO was purchased used and the Alternator was replaced, who knows what alternator was installed in its place! The pulley Thickness AND Bore at the hub varies from the different years, from .594" to .670" and .450" to .600" respectively. You must make sure you get the right set of pulleys for your model year, or you will have problems with belts rubbing (See Don Dolersons notes,) or the Pulley failing and damaging you pulley shaft (this happened to me), or worst yet, the Alternator itself being damaged. Replacement Alternators for the SHO's run $300 without the Voltage requlator, this is discounted pricing, not your neighborhood dealer. I was quoted by the local dealer for a new unit at $449 w/o the V regulator, or Rebuilt with the V regulator at $440 - OUCH no matter which way you look at it! Before the installation is done on the Alternator, you should measure and compare both pulley's you have just to make sure they are the same. Ideally you should measure the Alternator pulley before you order the pulley set. Now that I have done the pulley removal on the alternator 3 times, I can do the task in 10 minutes! This is an update the PN's for the Pulley sets as told to me by Auto Specialties themselves: Set 921107 (1989-4/93 3.0l MTX SHO): Bore = .594"
Height = .450"
BTW, no changes were made to the Crank pulley during the MTX Model years. |
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Here's a collection of belt part numbers for the Automotive Specialties
pullies :
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Hypertech |
The discontinued Hypertech pulleys were supplied by March. I have heard rumors that Hypertech is offering refunds to customers with their pulleys. See below for details of failures with these pulleys. | ||||||
March |
The discontinued March pulleys had a problem staying together. The outer ring would separate from the center hub. When this happens, you lose all of your accessories and damage the front engine covers. |