FAQ: Smaller SC pulley? What Size?

Your goin to blow it up!!!

Carlos, i would really listen to the advice these guys have been telling you. They are speaking from there own experience in blowing there own cars up and learning what not to do. Just a few small mods will do wonders for your new pulley. If you dont want to any mods then just dont push the car to hard, if you drive normal you should be fine. but really whats the fun in that? I would hate to see you lose a really nice car when you can stop it from blowing up. this is just our opinion and you can do what ever you like, we're just trying to help..

Sure, you might be fine driving long trips on flat ground, but when you push the gas to the floor or go through the mountains, that's when you'll get a problem.

I just ordered a 3.5 pulley and was wondering what size belt i would need to get for it, its a 96 series II sc, Thanks

You can use your stock belt. See page one of this thread for different options.

I just spent over an hour and about $250 worth of belts and pulleys (not including the s/c pulleys) to figure this out so It's probably worth sharing lol. It's info I needed anyway

I'm running a full size 2.25" intercooler and a smoothflow belt wrap and found the best belt to use for the riv since our tensioner and whatnot is a little bit different than the w-body's. The goal was to have one belt that can run anything from ~3.4" all the way down to a 2.55" supercharger pulley, using a couple idler/tensioner pulley sizes as necessary. Something to note is the smoothflow belt wrap kit needs to be shimmed up from the blower a little to work on the riv's setup primarily to open up the pinch gap of the belt. I tried a few different heights from 1/4" to 1" but found 1/2" higher to be ideal (high enough to keep clearance enough but not excessive (negating the affect of the belt wrap) for all the pulley combinations and have good clearance for the #6 plug wire to coil). With that, the magic belt size was 73.3" (Gates part# K080733)


I test fitted all the combinations I could have a use for and took measurements of the resulting clearance in the pinch area and tensioner position. The belt wrap has a 3" smooth pulley on it fyi.

The area I measured clearance at is where I'm pointing to in the above picture - where the belt comes close to touching its self.

All the following combinations are good:

2.55" s/c pulley, 3.0" tensioner, 3.5" idler : 1/4" clearance; tensioner good
2.70" s/c pulley, 3.0" tensioner, 3.5" idler : 7/16" clearance; tensioner good
2.80" s/c pulley, 3.0" tensioner, 3.5" idler : 9/16" clearance; tensioner tight
2.70" s/c pulley, 3.0" tensioner, 3.0" idler : 3/16" clearance; tensioner good
2.80" s/c pulley, 3.0" tensioner, 3.0" idler : 1/4" clearance; tensioner good
3.00" s/c pulley, 3.0" tensioner, 3.0" idler : 1/2" clearance; tensioner good
3.20" s/c pulley, 3.0" tensioner, 3.5" idler : N/A (remove belt wrap); tensioner good
3.3+" s/c pulley, 3.0" tensioner, 3.0" idler : N/A (remove belt wrap) untested

Hey everyone,

im thinking of getting a hogan down pipe an i was wondering what you guys think a safe SC pulley size is for my riv.


mods on the car already

short ram intake
cat back exhaust
3.5" SC pulley
180* stat
9mm wire set

Without some valve lift increase, 3.5 is a good place to be. 1.9 rockers or a cam would be next on your list. Until then you can increase performance quite a bit by tuning your WOT timing.

What are you using to tune?

i havent tuned it yet im on a budget so its kind of one thing at a time for me.

but what are good options to tune?

HP Tuners is the most common place to get started for 3800s. There is an older tuner out there called DHP PowerTunr but they are not made anymore, software is a pain for it.

If you want to do any more than you have now, you will really need to tune. Also you will really need to increase engine airflow (valve lift/duration) somehow.

thanks

When I replace my stock SC pully with a 3.6, do i also need to replace the belt with a smaller size? Or is there some way that i can just adjust it to tighten it up without having to replace anything else?

no need to put in a different belt. the tensioner will take up the slack.

Alright thanks man. I was hoping i wouldnt have too

go into the search bar and look up what others have done to their series 2 rides. lotsa good info

I have a 97 with 144,000 miles. I have very limited money to spend on this I'm going to buy the mps bu t I'm not sure if I should go with 3.5 or 3.6? I can't afford a scanner yet but I'm.going to buy a 180 t stat and spark plugs. I don't want to spend a hundred bucks and get a 3.6 if I won't feel a difference but I don't want to mess up my engine, which is a better decision?

If you "can't afford a scanner" you can't afford a smaller pulley. Unless you can find someone locally who can help you scan your car, don't do it.

If you can't find someone near you on this forum with a scanner, look around for local 3800 clubs. They are everywhere. clubgp.com is a national forum of Pontiac Grand Prix owners, lots of 3800 SC love there. Use that site as a resource to find your local people, but otherwise watch out, that site in the past was loaded with as much useless info as useful info. Someone will be able to help you scan.

Even for just a 3.6?

Yes. The scanner saves you money by letting you not mod "blind."(Saves potential engine damage. Some engines have knock stock.) It also saves you tons of money and headaches down the road when something goes wrong with the engine and you need to troubleshoot. I cannot stress how useful it is when "something" is wrong, being able to just plug in your handy scanner and see what all the sensors are doing, what codes may be present, etc... The scanner WILL save you time and money in the future. Take it from those of us who heave tried it the hard way first, start with a scanner. (The scanner can also be used on other cars, friends, family, future cars, etc. A very good investment.)

Kk thanks. I guess that means ive gotta save a little longer, what scanner do you recommend?

Jake, there's a certain level of risk in anything you do to an engine, albeit our 3800 V-6 reduces that risk - it's one stout motor. Still, there are some things that can make a difference; some are out of our control. There are so many factors that come into play, even the way you drive it.

Agree with Karma that some 3800 SC have KR stock, although these tend to be the 260 HP Gen V Pontiacs more than ours.

We can say that the majority of SC 3800s will have no trouble supporting a 3.6" pulley with minimal risk, but you won't know for sure until you scan. Also, one person can drive a car with 3.6" pulley for years without trouble, and someone else can get behind the wheel and have significant KR. The driver's style, the weather, even the fuel in different regions of the country can make a difference.

So if you want to be 100% certain the mod is safe, you must scan. If you want a low risk mod that will probably be okay in most cases, put on the 3.6" and drive it. Even if you get some knock, the engine is tough, and likely won't do any harm. Or, there is a small chance you could blow it up (I have never seen or heard of a 3800 SC engine being destroyed by a 3.6" pulley, but it's possible).

In 2003, I drove my car for 40K miles with a 3.4" SC, AL104 plugs, K&N panel, and 160º t-stat, that's it. The engine seemed fine. Later I found there was actually some considerable KR happening at times, but it did not harm the engine, because I was only abusing it a small part of the time. Most of those miles were gentle highway miles. Nowadays, we would never advise a 3.4" pulley with such minimal supporting mods, because we know how dangerous this is. Even so, I got away with it, and that engine accumulated 246k miles over the next 8 years, running the 3.4" pulley the entire time, but with the addition of several knock-reducing mods of course!

My advice: if you are planning to do only the 3.6" and be done with modding, just buy the pulley, AL104 plugs, and 180º t-stat. Have fun. But if you want to do more in the future, perhaps do some exhaust work and work your way down to a 3.4", might as well get the scan tool up front. Knowledge is power.

Alright, I appreciate the advice

anopther question, when i bought this car the supercharger puller was loose so i had to have it replaced. is it possible that i dont need a pulley puller to change pulleys now? how can i tell if they used modular or press on or whatever?

It is unlikely you already have the modular pulley system. If the pulley has 5 screws holding it on, it's MPS. Otherwise, it's pressed-on. You will need a puller, or have it done by someone who has the tools.

yesterday i gutted my air box( no money for fwi yet) took the red thing out and the grey baffle thing i just cut the end off of it so it could breath more, and today i took i old piece of tin siding i had from my garage, measured and cut to try to isolate the fender well from engine bay more, going to get 180 temp stat and already ordered 3.5 sc pulley, this aint to small is it??? before putting it on I'm going to do the fwi and temp stat first.