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

Question: If I go w/ a smaller pulley and I have no way of scanning...how do I know how much KR I have? Could I end up with the car running slower because of increased KR with the new pulley or will I see definate gains from the new pulley? Please help!

I had incredible gains with a 3.4 on the series 2 with no scanning. If you go with a reasonably sized pulley and the supporting mods, you will see a very nice gain. You just won't be able to squeeze every last hundredth out ouf your car without knowing KR.

quote: "If I go w/ a smaller pulley and I have no way of scanning...how do I know how much KR I have?"

You don't. It's that simple. There's going to be some risk.. how much depends on how small you go with the pulley. It also depends on what your baseline KR is. Every car is a little different. You may have KR now, scanning is the only way to know.

A 3.4" pulley is a 10.5% size reduction from stock. I did the same thing as Jason with only a gutted box, 160º stat and 104 plugs. I was knocking in the 6º range at times, and didn't even know. Sure, I saw a big increase, but it was bigger once I tuned out the KR.

For Series I, the 2.5" size would be a 12.3% reduction. Your blower might respond differently than a Series II, but still it's something to consider. Imo, running the 2.5" will give improvement, but it will also give you added KR for sure. Not enough to blow your engine, but enough that you won't see some of the gain to pulley has to offer. Stepping down to smaller sizes could give enough KR that you could get slower than stock.

Another thing to consider is, say you get the 2.5" and everything is fine. How will you know? How do you know when you can move down to a 2.4", 2.3", etc.? Without a scanner, you won't know. You'd be guessing at best.

Alright my riviera has around 195k miles on it. I just rebuilt the engine and cleaned out the tranny and replaced a few valves. I talked with a mechanic about putting on a slightly smaller pulley and he said i should. He told me that it puts a lot of strain on the whole car and that it is hard on the tranny. From what i got out of the conversation he said that lets say im going around 30mph and i punch it, he said that the tranny would lag a little due to the increased speed of the supercharger or something and that the tranny would take a beating from trying to catch up with the engine. Is this true?
Also he said that if i put a 180 degree thermastat on that i would get a lot less fuel economy and that my engine might be dog out sometimes. Could someone elaberate on that too if possible?

A 180* tstat will be fine. I didn't notice ANY drop in fuel economy at all. I don't know what he meant by the engine might dog out but the engine will be fine. It will help the engine out more as it will allow it to run cooler.

There were some problems with people using the 160* tstat because the knock sensor doesn't come on until around 157* or somewhere in there and that could be dangerous.

Welcome to the board.

It all depends on who you talk to. If your mechanic is concerned strictly with reliability (many are), he is not going to agree with any enhancements that add power (strain) to the engine/transmission. A lot of people firmly believe that GM did the best possible job designing each and every part of every car they build, and changing anything at all will throw off that delicate "balance". That's fine. They can keep driving their Buicks exactly the way GM intended.

But some have wondered, "What can I do to get more of the car?", "How can I do it reliably?". and "What are the costs/risks involved in experimenting?". It's this kind of curiosity that drives our site to try different things and share the results, so you can decide for yourself if it is a level of risk worth taking for the reward received. Every car and driver is different, but some things are consistent. It's sort of like investing.

Having said that, a drop in SC pulley size does this: it builds boost (and torque) sooner than a stock (larger) SC pulley would. Because of this, your boost at WOT will be more with a smaller pulley than with a stock one. So let's say with a stock SC pulley you're driving in 2nd gear, at 2000 rpm, and you push the throttle 20%. For the sake of discussion, let's assume your supercharger makes 1 PSI of boost when you do this. At 50% throttle, we'll say you make 2 PSI of boost; at 100% or WOT, it's 6 PSI.

Now, if you change the SC pulley to a smaller dia. and drive under the same conditions, you might get boost numbers like this: 3 PSI at 20%, 4 PSI at 50%, and 8 PSI at WOT. These are theoretical figures, but close to what you can expect to see. The result of dropping the pulley size in this example would show a horsepower gain in the form of improved throttle response (torque). In effect, what you are doing is moving your engine's torque curve into the lower RPMs. This would mean when you push the throttle 20%, it will accelerate much like a stock car does at 50%. Make sense?

So how does this extra torque destroy your transmission? It doesn't, really. There is increased load delivered to the tranny, but a healthy one should take the extra power... up to a point. As far as "lag", that happens regardless of the power you are making, and it's up to you the driver to treat the tranny with respect. Everyone's hit the gas at the wrong time before and felt a sharp jerk, even on a stock engine. This doesn't change when you add power, but if you do it all the time, of course you increase the risk of failure. The trick is to drive your car the right way. Be easy on power delivery, don't stab the throttle at the wrong time, and the transmission should last a long time.

It's true, a 180º deg t-stat will give you worse fuel economy. But to say it gives you a "lot" worse... that's just not true. When my car was stock, I drove a few hundred miles on the freeway and saw 31 mpg. A couple years later, after many mods including a 180º t-stat, I took another trip and got the same 31 mpg. What does that say? To me, it indicates I may have lost a few mpg from the t-stat, but I also gained some back from more efficient intake, rocker, and exhaust parts. We're talking about a couple mpg here at most.

I think what you should consider is, your car has 195k. That's a lot of miles, so some stuff is going to break. Adding power will make things break sooner than later, but it doesn't mean you shouldn't do it. You could have a lot of fun with the new engine, especially if you help it perform better. I started modding when mine had 35k; now I have over 135k. Original engine, trans, stock exhaust after the cat converter. Everything still works inside and out, I drive the car every day. I race it a couple times per year. Maintenance plays a part too. If you take care of the engine, it shouldn't mind putting out a few extra horses once in a while.

any one ever ran a 2.4" SC pulley on there series 1. will it be ok to run with stock internals and what not, im doing intake and exhaust if i get it. would it be save to run,. but my questions are as fallows

#1, Is it save to run on my car

#2, Will it give a noticeable gain

#3, What other parts do i need

#4, what kind of puller for the pulley

#5, will my engine blow up

#6, what kinda boost would that put out

#7, should i get a boost gauge

please help a fellow river owner with that, my car is a 95 series 1, and im looking at a pulley boys

#1 - Only way to know is to scan for KR.

#2 - Yes, if you have good result with #1.

#3 - A scanner, cooler plugs, cooler T-stat, possibly exhaust, intake or more depending on result with #1.

#4 - 3-jaw pulley puller.

#5 - If result of #1 is good: No. If result of #1 is bad, or if you skip #1, possibly.

#6 - Need a scanner or boost gauge to know.

#7 - Up to you. I've never run a boost gauge, but lots of folks like to have one.

what is KR, if you could get on AIM so we can chat

https://rivperformance.editboard.com/series-ii-faq-f19/what-is-engine-knock-what-is-kr-t28.htm

(sorry, no access to AIM right now)

Running a 2.4" SC pulley on your engine means a decrease of 16% from the stock 2.85" diameter.

On our Series II engines, that would be the equivalent of running a 3.2" SC pulley in place of our stock 3.8". I need all the mods in my sig to run that size, and I can only do it under about 55F. Boost levels have seen 15 PSI running this pulley.

Some have seen significant levels of KR just dropping pulley size by 5%. This is why I'm suggesting you scan your car before taking such a big step.

http://www.seriesoneperformance.com/induction.html
http://www.pulleyboys.com/gms1p.html

this is saying a 2.5 will work fine but what would .1 do would,can it really be that much of a difference

.1" is significant in your case. I wouldn't even run the 2.5" without scanning if it were my car.

what kind of scanner, my school has a gennisis 2 scanner, i dont know if that would work. but

http://www.seriesoneperformance.com

They have one that will work with your car.

ok im think i will just go with 2.5 or 2.6. just to be safe BTW im doing cam and roller rockers pretty much the whole valve train as a early Christmas present from my mom

Any scanner that can do the OBD 1.5 your car is equipped with. I ran a 2.4 pulley on my old series one with the following

CAI
Full tune-up
NGK TR-55 (gapped to .055 They must be copper)
CAT and RES delete (res was deleted when I bought thee car)

I had 1 degree of Knock retard from 0-90 MPH

You need a scanner that can scan 94-95 gm cars. Slang term for it is OBD 1.5

Also check your fuel pressure and make sure it is up to spec. Your car is 12 years old you don't want your car to go lean from lack of fuel.

that shouldnt be a problem, were doing a high flow pump and injectors, , i want to make my car quick enought to smoke the gay little slomaros and rustangs in my area

what is your full tune up

BTW thanks for the help

Air filter
fuel filter
plugs and wires
oil change
three new ignition coils
sea foam
clean MAF sensor
Tranny flush

You will need to program your PCM for the new injectors if no they will not fire right and may not allow the fuel to fully atomize.

Bigger injectors not needed, imo. Series I has the 36 pounders, right?

ok then i wont order them. are taylor wires ok

Yes. Stock wires are also fine, but not as pretty.

palermocorey90 wrote:

ok im think i will just go with 2.5 or 2.6. just to be safe BTW im doing cam and roller rockers pretty much the whole valve train as a early Christmas present from my mom

uhhhhh i wouldnt get CAM AND ROCKERS................ its one or the other.

what kind of plus should i go with, i have decided to go with 2.5" pulley

quote: "uhhhhh i wouldnt get CAM AND ROCKERS................ its one or the other."

He can run roller rockers, as long as they don't have extreme lift ratios. I think some cams can be used with 1.7:1 rollers, depends on the grind. Probably not much to gain with the 1.7s, though.

Plugs should be 2 ranges cooler than stock. I use Autolite 104s.

ok, what kinda time could i run with them mods