FAQ: Smaller SC pulley? What Size?

i need a part number for a 3.5 inch Tensioner pulley

Hey guys my next door neighbor is big on racing and he loves my 97 sc riviera. He also saw my friend who has a black sc riviera and noticed that the series 1 sc rivs have a smaller pulley. He told me that I could increase the boost if i could get his pulley and put it in the place of my supercharger pulley. Is this true, because I saw another one at the junk yard that I thought about getting. Also if this works how much of a gain could I expect and how do I remove the pulley at the junkyard, the belt is already off of the car but when I turn the bolt of the pulley, the whole pulley turned with it.

Hi,

You cannot mix an M62 pulley with an M90 supercharger, sorry. Your '97 with the Series II 3800 has an M90 supercharger, which has plenty of mods available, including smaller pullies. But do NOT just dump a smaller pulley on and expect wonderous results. You will enjoy it at first, then eventually figure out you are slowly destroying your motor with detonation. There is plenty of information here about how to mod if you want to go for it. Read the FAQs.

The pulley on the M90 is a press-on pulley and requires a specific pulley removal tool to get off, after you remove the vent plug (the big nut). The M62 has a pulley held in place with a bolt and keyway - no puller required.

thanx im glad i read this before attempting

i was wondering when i put my 3.5 pulley on my riv can i reuse my stock size belt it only has a few hundred miles on it and shows no signs of going bad i just wanted to know if i needed a smaller belt or if the tentioner will litterally pick up the slack

You can use the stock belt.

I just changed to a 3.4 SC pulley, kept my stock belt because it was new also and bought a 3.5 tensioner pulley to replace the stock 3.0 pulley.
This combo works perfectly. I bought a Dayco pulley P/N 89006 (IIRC) to replace the the stock size.
I don't know if you'll need to do the same but it can't hurt to have the larger pulley on hand in case you need it. If you don't need it then you can always return it.

Kevin, read page 1 of this thread. Good luck!

I wanna up my boost a little

what is the smallest pulley i can run bone stock?

What is the smallest pulley i can run with colder thermostat and colder plugs?

What do you recommend?

I would not run ANY smaller size pulley with zero supporting mods. Many of our cars, mine included, have a few degrees of KR in stock form even. No pulley drop is recommended, at least until you can scan for KR and confirm you have none to begin with. With no KR and no supporting mods, you can likely go to a 3.6" pulley w/o issue. But being able to scan for KR is very important.

Assume you're referring to your "new" Riviera? Always helps to give us some basic car info when asking for help. You can easily add this info to your default signature.

With just colder plugs and tstat, I'd still not go lower than a 3.6 pulley unless you can confirm you have zero KR.

I didn't dare install a smaller pulley until I had installed Headers, 1.9 rockers, AL 104 plugs, 180* thermostat with PCM programming for the thermostat and fan settings first. Also gutted the airbox.
The plan was to open up the inlet somewhat by gutting the air box and putting in a high flow air filter then open exhaust with headers and high flow Cat, then the 1.9 rockers and new springs to open the valves a little earlier and close a little later. Then scan, tune, install 3.4" pulley and scan, tune some more to eliminate KR. I also put in cleaned and flow matched injectors, new wires, etc.
I did not want to sacrifice a good engine by installing a smaller pulley and increasing boost first without doing all the above.

i know this may sound like a dumb question. where can i find a 3.6" supercharger pulley for my 1996 Riviera?

http://intense-racing.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=IR&Product_Code=IMH-090&Category_Code=BE

96ncriviera wrote:

i know this may sound like a dumb question. where can i find a 3.6" supercharger pulley for my 1996 Riviera?

http://smoothflowpulleys.com/3800_MPS.html

if i replace the stock pulley with a 3.6" pulley, will i need to get a smaller belt?

look at the top of page 8 with a answer from turtleman.
some use a larger tensioner pulley to compensate for the small belt size increase.

You won't need to change the tensioner pulley with a 3.6" SC pulley. Just keep the belt and all other pulleys the same when running the 3.6". See page 1 of this thread.

Your current SC tensioner pulley is a 3.0" pulley.
When i went to a 3.4" sc pulley I changed the tensioner pulley to a 3.5" with stock length belt.
If after you have installed the 3.6" SC pulley you decide you want better belt wrap or are experiencing any belt slippage you can buy a 3.25" tensioner pulley for it. Which should still keep the tensioner in its normal operating range.

Just wondering if anyone had a smaller supercharger pulley for sale ? My car is basically stock so i didnt know how small i could go and be safe not hurting the engine. Let me know ! Thanks

Dont drop pulley sizes until you open up the exhaust a bit and have some way of scanning for knock. You could probably get away with a 3.6" pulley but it's still a risk.

I recommend buying an MPS, Multiple Pulley System, if you are going to start playing with pulley sizes. If you get one of the more popular sets with a 3.6, you can easily find used 3.4s and such out there for future easy bolt-on changes.

But you need to open up the exhaust manifolds a bit and watch out for KR before you start dropping pulley sizes. I couldn't run a 3.4 with no KR until I had 1.9 rockers installed.

I couldn't even run a 3.6 w/o getting several degrees of KR, and that was with typical supporting mods already in place. If you can't scan for KR, DO NOT drop pulley sizes!

Quote :

Dont drop pulley sizes until you open up the exhaust a bit and have some way of scanning for knock. You could probably get away with a 3.6" pulley but it's still a risk.

You can run a slightly smaller SC pulley without opening the exhaust, although a downpipe can help you make more power. Read page 1 of this thread for more info we've collected on this.

A few degrees of knock is not the end of the world. Even stock engines knock from time to time. The engine will hold up. This is why you can run a 3.6" pulley safely. Most can run a 3.5" safely as well, but here is where you need to start scanning for KR.

I agree with Deek, an MPS is the way to go. I also agree with Dave that you never can be 100% with dropping SC pulley sizes. There are always things to watch and maintain. Scanning is very good insurance to have.

AA wrote:

Quote :

Dont drop pulley sizes until you open up the exhaust a bit and have some way of scanning for knock. You could probably get away with a 3.6" pulley but it's still a risk.

You can run a slightly smaller SC pulley without opening the exhaust, although a downpipe can help you make more power. Read page 1 of this thread for more info we've collected on this.

A few degrees of knock is not the end of the world. Even stock engines knock from time to time. The engine will hold up. This is why you can run a 3.6" pulley safely. Most can run a 3.5" safely as well, but here is where you need to start scanning for KR.

I agree with Deek, an MPS is the way to go. I also agree with Dave that you never can be 100% with dropping SC pulley sizes. There are always things to watch and maintain. Scanning is very good insurance to have.

Well if his stock motor is knocking 3* with the 3.8", and he adds another 3* with a 3.6", then he's up to 6* KR which is pretty high IMO. Especially when you figure he's running about 10* of timing at that point and is probably slower than with the 3.8". Although each engine is different so a scanner is essential.

Yes, it's possible for that to happen, but it probably won't. KR depends on a lot of factors other than your SC pulley and level of modification. Fuel, air temperature, terrain, vehicle weight, condition, and maintenance history all come into play. This is why some cars have more KR than others.

If I put a 3.6" pulley on my car with no other mods, and saw 6º KR, I would suspect a serious problem. I had about that much KR running a 3.4" pulley for several thousand miles on a basically stock engine (only mods were t-stat, plugs, and gutted box). I don't suggest anyone do this, but my engine did okay.

I agree scanning is a great idea for 3.5" and smaller, but the 3.6" is supposed to be a safe upgrade. A 3.5" pulley is considered a safe mod for a totally stock GTP or GS, but they are slightly lighter cars.

I've routinely seen 10-12º timing advance at WOT without much, if any KR. I don't detect any loss in performance. I also don't notice much of a performance decrease from moderate amounts of KR - see link:

https://rivperformance.editboard.com/series-ii-scans-tuning-pcm-f5/the-consequence-of-kr-t1548.htm