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PostPosted: Fri Jun 06, 2008 11:29 am 
Retired Admin/Techinfo Admin
Retired Admin/Techinfo Admin

Joined: Mon May 19, 2008 2:08 pm
Posts: 26008
Location: Space Coast, or at least it used to be
Year and Trim: 03 SLE, 95 SE, 95 TS SE
Author: willwren

One of the most often questions asked in the Forced Induction section of the Forum is how to upgrade a pulley, and what size to use. Common upgrade sizes are simply a case-by-case issue now.

Due to the age of these cars, and other issues that age brings to light, each case needs to be handled one-on-one by posting a new article in the Forced Induction section of the Forum. Some factors that may dictate what size, or even if your car is a good candidate are:

1. Full Tuneup:
This must be done before modifying anything on the car. Lack of a good tuneup can introduce problems that you don't need to deal with later. Avoid having tuning issues by being able to rule out these items ahead of time. Regardless of age, change the fuel filter and PCV valve. These are inexpensive items. Age-related items are plugs, wires, O2 sensor, and air filter. If you don't know how old they are, change them. Ask on the Forum for preferred brands. If your O2, plugs, or wires are older than 50k miles, change them, and also consider cleaning your MAF sensor, TB, and IAC. Techinfo has an article on this. Bottom line? Change it all if you plan to upgrade performance. It's cheap insurance.

2. Fuel pressure:
If you run lean under boost, you may go BOOM. Fuel pumps on the older cars are all getting weak, and fuel pressure regulators may be an issue as well. Before considering a smaller SC pulley you MUST check your fuel pressure. Key on, ignition off, you must have 41-47 psi. At idle, you should have 41 psi minimum, and it should jump to 42-44 psi when you pull the vacuum line off the fuel pressure regulator at idle. If it doesn't meet these specs, your problem is either a fuel filter, fuel pump, or fuel pressure regulator. Posting a new topic in the 92-99 section will help us help you nail down the root cause.

3. Exhaust cracks are common with age:
These are the best flowing GM exhaust manifolds ever produced (91-95 L67), but they all crack with age, and can cause serious problems that will be made worse by a smaller supercharger pulley. The cracks are small, and often hidden by the exhaust heatshields. The best course of action is to simply remove your exhaust manifolds, remove the shields, and carefully inspect for cracks. Have the cracks welded by a good exhaust shop, then have them stitch-weld each runner to the OUTSIDE of the flange. This will allow you to lightly grind away the restrictive OEM weld on the inside of the runner/flange to improve exhaust flow. This must be done by a COMPETENT exhaust expert, to insure the flanges are not warped from the heat of welding. Make sure you use gaskets when you put the manifolds back on the car, even if they came with none from the factory. You may also want to try a high-temp coating at the same time. Standard exhaust paint won't hold up long-term. But there are DIY aftermarket coatings that will help, and will last a long time.
Remember to re-torque your exhaust manifolds 500 miles or so after re-installation. Another option is to get manifolds from a wrecker, and take your time to do this right, then swap them in when they're ready. Keep in mind the 91/92 manifolds are different with regards to the EGR tap than the 93-95. This is important information to know before looking for replacements. Don't forget that a catalytic converter will start to plug with age as well, and a weak or bad O2 sensor can kill a Cat very quickly.

4. Scantool and KR:
You MUST either own a scantool or have one readily available (friend, mechanic, etc) that you can use before upgrading pulleys. You need to know if you have KR (knock retard) with the stock setup. If you have KR, you MUST fix it first. If you don't have any stock, but get more than 1-2 degrees after the pulley change, you either need to fix the problem or go up another tenth of an inch in diameter to kill it. KR will destroy your engine internals over time. Remember that hot and/or humid weather will make KR worse. Zero KR on a 60 degree day means nothing. Make sure your engine is fully heatsoaked before testing.

If you have any questions regarding any of these items, please feel free to post them on the Forum, and link back to this article. These 4 factors MUST be addressed installing a smaller pulley on any 91-95 supercharged GM car. Smaller pulleys are not plug 'n play as some people believe. But with these 4 items taken care of, MOST cars SHOULD be able to do this:

91-93 change from stock 2.55" to a 2.2". SCAN FOR KR AFTERWARDS.

94/95 change from stock 2.85" to a 2.55" 91-93 stock pulley or aftermarket 2.5". SCAN FOR KR AFTERWARDS

Every car is different, and will react to these changes differently. KR is something you must stay on top of constantly if you swap pulleys.

Original Author : Willwren

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