Ok, I have a UDP coming in from ZXtunner. I would like to just get the stage 4 engine from you Jayco, but money is a factor and want to get a little more mileage out of my current engine. This write up is rather easy to understand,


but I wanted to ask, has anyone else done this mod and is there any thing in additional that I should know that could be helpful? I also got this.

[url=https://zxtuner.com/displayProductDocument.hg?productId=180&categoryId=17]https://zxtuner.com/displayProductDocum ... egoryId=17[/url]

Any tips would be cool.

edit actualy there are two things in that artilce that I would like collraboration on.
1.“Slide a pipe (I use the top part of my floor jack handle) over the breaker bar or ratchet, then making sure that the bar is positioned against the floor at 7 o’clock position or better.”

2.“Install new udp, tighten bolt to specs.”

What are the specs anyway?

I believe the bolts are tighten to 85-90 ft/lbs. I cant remember what I tightened mine to.

there is a very good sticky over at team zx2 with pics and how too’s its very simple job to do it took me like 15 to 20 min to do i cant remeber what the sticky is under and i cant look it up for you because my damn school blocked the site

Thanks! I’ll go check.


Did you ever get your UDP installed?
When I did mine there were a few things that werent obvious in any write-ups.

I’m gearing up to. I’m waiting until roush sends me a EGT rear disk setup. Figured I’d get a few things ready to go in one shot. What issues did you run into? How’d you get the old UDP off?

Shouldn’t be any issues. The splash guards are just a pain to take off because they have so many damned little bolts and screws on them. Make sure you have something to grind down the plastic cover that fits where the stock pulley does, you’ll need to flatten it out.

Here’s some pictures of the different spots during installation on the UDP


a more precise picture of the guard you have to grind down here…

[url=http://www.boombaprojects.com/images/howto/udp/shielding.JPG]http://www.boombaprojects.com/images/ho ... elding.JPG[/url]

You can see in that picture where i ground down the shielding to make clearance for the belt. A belt sander works wonders or a wheel sander either way, or you can grind it on some rough concrete if needed. Either way it’s self explanitory…

1: Take off wheel
2: Take off splash guards
3: Tighten tensioner to get stock serpentine belt off
4: Use an air gun to take the stock pulley off, or immobilize it and take it off…
5. Take off the plastic shield behind it, grind down the ring so that the belt will clear it
6. Put the sheild on, put the UDP on, tighten it down
7. Put the new belt on using the stock routing diagram (if you have a manual)
8. Reverse the order you took stuff of, splash guards, wheel, etc…

Its pretty simple really. I wrote a write-up on it here and on teamzx2 but can’t remember where they are.


Well for instance to immobilize the stock pully put the car in gear(motor turned off ofcourse) and have someone step on the brakes. Simple and easy but not mentioned in any of the writups for peeps without airtools. If I dont count the discovery process where I worked out immobilizing the pulley mine was done in 20 minutes.

BTW I found the writeups I looked through before I did mine. Enjoy.

Instruction set 1

Installing a Underdrive Pulley:

Tools you`ll need: Floor Jack, 18mm socket and ratchet, 13mm combo or box wrench (The longer with more offset, the better), 8mm & 10mm combination wrench or sockets, Air Impact, breaker, or cheater bar (to put over a ratchet).

  1. Jack the car up and remove the passenger side wheel.

  2. Remove the lower plastic splash guard that covers the fan belt area underneath the car. Bolts take a 10mm wrench.

  3. With a 18mm socket (3/4" 6 point socket will work), remove the center bolt on the crank pulley. An air impact gun works best, but if you dont have one, here is a backyard mechanic way...put the socket on the crank bolt, Slide a pipe (I use the top part of my floor jack handle) over the breaker bar or ratchet, then making sure that the bar is positioned against the floor at 7 oclock position or better. Make sure itll stay there on its own… don`t try to hold it there. Disconnect the coil power plug on the side to keep the motor from running - then, using the starter, crank the car over for a second or two. The bolt should now be on the floor with the ratchet BE CAREFUL!

  4. Put a 13mm wrench on the center bolt of the belt tensioner pulley, and turn the wrench clockwise to relieve the spring tension against the belt.

  5. Remove the belt.

  6. Slide off the pulley.

  7. Remove the plastic lower timing belt cover thats behind the crank pulley. Its 2 bolts, 8mm wrench.

  8. Grind off the raised lip around the crank pulley opening. ) I did this by rubbing the plastic cover against a concrete driveway) If you fail to do this, the cover will interfere with the new belt.

  9. Re-install lower timing cover

  10. Install new udp, tighten bolt to specs.

  11. put on new belt the same way the old one came off, using the belt tensioner as the last pulley to slide the belt onto.

  12. Now go enjoy the power!

Instruction Set 2

Underdrive Pulley

Tools Required Side Notes
Socket Set (8mm, 10mm, 18mm)
13mm open end wrench
Impact Gun with 18mm socket or “persuader” bar
Installation of the pulley went nice and smoothly!

Clicking on pictures will open up larger versions in new windows!

Step 1
Raise and support the the passenger side of the vehicle. Remove the wheel.

If you can’t do this, then it is not advised that you continue.

Step 2
Remove the lower splash shield.

Held on by 7 10mm bolts.

Step 3
Remove the crank pulley.

Use your impact gun with 18mm socket to remove the pulley.
If no gun available, use a ratchet with 18mm socket and large “persuader” bar. Position the ratchet and bar as pictured below.

With the key in the ignition, crank the car over once or twice to break the bolt loose. Come back around to the side of the car and remove the bolt once loosened. Do NOT attempt to have a friend hold the ratchet, and please make sure that nobody is on that side of the car when cranking it over.

Step 4
Remove the pulley and belt.

Use your 13mm wrench to release the belt tension. The tensioner is located directly above the A/C compressor.

Push the wrench towards the rear of the car to release the tension and slip the belt off of any pulley.
Remove the pulley from the crank and belt from the engine bay.

Step 5
Remove the belt guarde and shave it down.

Remove the 2 8mm bolts holding the guard on and remove the guard.

The guard has a small lip on it facing the outside of the car which must be shaved down. I clamped a hacksaw to a table and carefully ran the guard along it until it was shaved smooth. Other methods include Dremels, drills, rubbing it on concrete, and sandpaper.

The final result should be a smooth front of the guard.

Install the newly shaved guard using the 8mm bolts you removed.

Step 6
Install the new pulley and belt

Place the new pulley onto the crank and tighten. You can use the ratchet to tighten it, using a few quick motions once it is snug. You do not need to crank the engine and use a cheater bar.

Place the supplied belt in the same way it came off. Use the supplied belt routing diagram for assistance.
Re-install the splash shield, slap the wheel back on, lower the car, and go cruisin!

The UDP FAQ. *Created by FourDiceS .Ford Racing UDP (100 MM)
.Unorthodox UDP
.ZXTuner (100MM)
.EBAY (100 MM)

New Edge Performance

Q. How does a UDP work?
A. The crank pulley drives the accessories on the car, such as A/C and alternator. The underdrive pulley is smaller and lighter than the stock unit. Because it is smaller and lighter, less energy (horsepower), is used to turn the pulley. The underdrive pulley does not produce horsepower – it simply frees up some horsepower that was being used to drive the stock pulley.

Q. Is it true that underdrive pulley’s are rarely balanced causing a vibration that will cause the crank berings to go bad in the long run?

A. There is some controversy about the pulleys, as they are not equipped with the harmonic balancer that the stock pulley has. We feel the risk of removing the balancer on certain engines is not really a risk. Inline, four-cylinder engines for the most part have short, stiff crankshafts. These do not need a balancer as much, because of their high natural frequency. Engines with long, whip-like cranks, like inline six-cylinders, need balancers to prevent failure, but most four cylinders do fine without them

Q. Will a UDP will affect alternator life?
A. We have no proof of that. Alternator life should be increased, because you are spinning it 30% slower [as well as the other driven components].Since our idle is computer controlled, at the same speed there will be less load, and a smoother idle.

Q. Will a UDP will affect my car idle’s?
A. Only if you have Audio equipment. But if you do, you should also buy the Alternator ODP.

Q. Will I need a new Serpentine Belt?
A. Yes, since the pulley is smaller you need a smaller belt.

Q. What Belt size is needed?
A. 83.5 Inches

Q. What is the belt part number?
A. 835k6, 4060835, 6pk2120

See, this is why this message board rocks.


+1 vote for tommyatomic to put copy/paste this write up in the “How To” section.

Its posted.