FAQ: Selecting Proper Supercharger Pulley & Belt Size (Series I)

I'm running stock idler on a 2.4" pulley, though I have a shorter belt. I've run as low as 2.55" on stock idler and stock belt, so if your belt is new, you will be fine.

Thanks, Karma...I'm ordering the pulley and a new belt today. YEE HAW

Make sure you scan frequently, especially on hot days, if you don't have a lot of supporting mods to go along with the pulley drop. Due to the fact that it is WOT that you want to scan at its often easier to have a passenger watch the scanner for you while you drive. If you have KR after the pulley drop you will need to do further upgrades to get rid of it. If you do not you will never take full advantage of the swap and may damage your engine or reduce its life. For those of you who wish a mostly stock appearance a custom tuned chip MAY be all that's needed with such a small drop in pulley size to reduce any KR. Companies like sinister performance offer such a product, and another member seems to have had a good experience with them, but I can't personally vouch for them. For those with the skill, porting stock exhaust manifolds (they don't make headers for the series 1, $$$ custom jobs only) will reduce KR and will also leave a stock appearance.

Good advice in previous post, and for those trying to fight KR, the design of your intake can help. A FWI design offers the coolest intake air temperature (IAT), which lowers heat in the cylinders. It's not an intercooler, but does the same thing to a lesser extent. You don't need the biggest cone filter, nor the largest intake tube, as these will increase air flow into the engine. Although it seems counter-intuitive, feeding too much air to the intake with an existing KR condition might increase boost and make things worse. Think: cool air good, more air bad. Whatever you do, stay away from the "short ram" cone right on the throttle body, as it does both things incorrectly (hotter air, and more of it), pushing any existing KR to a higher level.

thanks Aaron i was looking to build an air intake this weekend.. that is some helpful advice..So maybe a smaller cone filter and 3' inch tube will work just fine for a FWI????

I wouldn't go much smaller than the OEM intake tube diameter. I think 3.25-3.5" is a good size (3" might work, but without scanning MAF we don't really know). A cone with at least the same surface area as the OEM flat panel will work fine. OEM measures 7.5" x 10.5" = ~78 sq in of filter. A 5.5-6" diameter cone or cyl about 5-5.5" long would be enough to flow a bit more air than stock, but not too much.

Would a sinister tune be able to reduce the KR from dropping pulley sizes?

this is just a thought but from i read here on this site you need to do some proper mods first before pulley drop. Greg look up some info here, sinister can help but safety first..

I have read plenty of info on modding before dropping pulley sizes on this site and on the bonneville site. I'm not going to try to drop down to a 2.5 pulley with a completely stock engine. I am trying to be smart and gather information on KR reducing mods before i just spend money. I drive my riviera everyday so i need to make sure it is reliable. I want to get a 3 in down pipe, make a CAI, a 2.7 or 2.6 supercharger pulley and sinister tune that will tune for the extra air going in(smaller pulley and CAI) and the extra air going out( 3 in down pipe) and have my fans set for 180*. I don't understand why i always get crap about searching the site, when i do go through and search and read threads all of the time. I ask questions when i don't understand something, I thought that was the point of a car forum. It's not like i sit on here and brag about 300 hp or 12 second 1/4 mile times or anything. I'm simply trying to learn more about my car and maybe raise questions that others will find interest in.

Well dude it sounds like your on the right track. I wasnt trying to give you crap bro, just trying to help from what i read. I think Robo may have a better insight on sinister since he has through it and has two i think. Dont forget to swap out the plugs to the autolights 104, and if your fuel pump is oridge you may want to look into changing to also.

Alright. My 95 Sc is stock at the moment but I'm going to be adding a 4" fwi, new plugs (iridium al104s maybe?), and a 180*tstat.
1) With these mods could I drop to a 2.7 without much worry of Kr?
2) What about 2.6?
3) 2.5?
4) mostly curious as to what I need to do to accomplish the extra drops safely. My local shop can scan for Kr but I myself cannot. Magnaflow has that cat/downpipe for increased flow so I guess that could help? My riv is my daily driver and I don't want to sacrifice durability/reliability

The FWI is a good breathing mod, and it's cooler air. But since it's pre-blower, it can create more KR, especially with a pulley drop. I saw 1 PSI increase in boost when I installed my FWI. Just something to be aware of.

Depends on who you ask, but most 3800 modder folks will stay away from iridium/platinum plugs for a couple reasons: #1 They have a very fine tip electrode that tends to focus heat. This is can create a source for pre-ignition or spark knock, compared to a cooler running copper plug where the electrode emits a wider spark from multiple points. Reason #2: why would you want a plug that lasts forever? Plugs are an informative indicator of a cylinder's condition, and should be checked at least once per year if you're going to be suping up the engine.

Links: GM, Chrysler, Ford

Could you drop to a 2.7? 2.6? 2.5? Think of it this way...

You're in the weight room on the bench, and there are 3 sets of weights for you to try. You have no idea how much they weigh, but one is "heavy", one is "really heavy", and one is "even heavier". Your spotter is basically serving the same function as using a scan tool for your engine. Without him, you might get crushed. So... do you want to start with "heavy", or "really heavy"?

The downpipe mod is your best bet. It's guaranteed to fight KR, while building power. But to know how much it will help, you need to scan.

Very good analogy there. I'll definitely be playing the build-up game with this. One thing at a time and playing smart is a good idea anyway. Sometimes my mind likes to run away with things haha
As usual, thanks for the quick and very helpful response. And thanks again to everyone for keeping this community active and strong. Without it I'd surely have become a lot more frustrated with my riv than I am. So much great info!

So I can change the pulley without any PCM mods? I figured maybe it would need more fuel. Unless it monitors boost for all that.

ratnfested wrote:

So I can change the pulley without any PCM mods? I figured maybe it would need more fuel. Unless it monitors boost for all that.

You can go down as far as a 3.5" pulley without any modifications really. Colder plugs, a 180* T-stat, and a CAI are recommended, but no PCM modifications are required. The PCM controls fuel all on its own. It isn't until you get into the 3.4" and smaller pulleys that you need to modify the tune.

Tuning is always recommended though....

^^^ This is a Series I SC application.

ratnfested: please read through this thread, Page 1.

ok thanks I did read through most all of this. I was looking for mention of octane. What octane do most run who use the 2.5" pulley? I can get 93 with 10% ethanol or 91 non eth which is what I run now. I am thinking the ethanol would be better as a deterrent from detonation/knocking. I have to ask my race car buddy but I think it burns less violently that gasoline. I have a Chevelle with a 540 Dart motor in it and its got high compression and does well on 93 with ethanol. I just have to be careful of the moisture dangers in the older car since its from the 70s.
Thanks

AA wrote:

^^^ This is a Series I SC application.ratnfested: please read through this thread, Page 1.

I'm stupid

Ignore me please....

A 2.5" pulley on a Series 1 is not uncommon with just basic mods, such as a plugs and thermostat as AA mentioned. The intake will help get cooler air in there of course, and the downpipe will be a big deal for the Series 1.

Take a look at my signature for my Lesabre and it lists everything Ive done to prepare for a 2.5" pulley, but i was being very precautious. I could likely do a 2.4" without any issue, but every engine is different.

What octane fuel do you run?

2.5" or 3.5" pulley?

The PCM will compensate for a smaller pulley because the air still goes through a Mass Airflow Sensor, which helps the PCM decide how much fuel to give it, among other operating parameters. You can reach a point where you want to richen the fuel mixture sooner, adjust timing and things of that nature, but for just a smaller pulley you will most likely be okay on the stock computer with a few basic mods.

I only run 93 in my 95 and a 2.5" pulley. With minor mods, similar to Z-Type's Lesabre, Ive never had any issues with knock during normal driving. My car is also not yet tuned and the car adapted fine to the 2.5" on the stock tune.

Just realized these are Series I.