FAQ: Smaller SC pulley? What Size?

AA wrote:

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

Right, but if you are upping boost and losing timing just to break about even with performance, then it seems kind of pointless to drop the pulley size anyway. Especially when you consider the unnecessary danger added with the moderate knock. The money would be better spent on the mods needed to support the pulley before dropping sizes.

I have seen STOCK GTPs with 4-5 degrees of KR at WOT, so just because it's stock doesn't mean everything is okey dokey already. That's why a lot of people say 'oh it's probably okay' when for some it may not be. Before and after scanning is important. You need to know what's going on before you start modding.

Some '04-05 GTPs had 4-5º KR, due in part to their hotter timing tables. Series II engines should not be seeing much above 1-2º at most. This is why ZZP only recommends using 3.5" pulleys on stock Series II cars. Also remember these stock cars had the u-bend, whereas we do not.

i got some extra cash and im looking to get a smaller super charger pulley.. this would be the first performance part i would put on my 98 riv i was wondering how small to go without having to change anything drastic.. also wondering with everything stock how many pounds of boost do you think im running and how many would i be running with a diffrent pulley?

Your SC pulley is far from the first performance upgrade you should do. Do some reading around here, there's a guide to the process before you consider a pulley swap.

Plain and simple: The smallest you should go w/o supporting mods done first, would be a 3.6 pulley, which isn't worth the money anyway.

Read here:
https://rivperformance.editboard.com/series-ii-engine-transmission-f4/modding-101-how-to-make-the-car-faster-t23.htm

Alright so I decided to drop from a 3.8 to a 3.5 pulley. I has enough small mods and a scanner, so I will be able to run it safe. I ordered it earlier. So will I notice a pretty noticable difference in throttle response and top end?

SCbuick010 wrote:

Alright so I decided to drop from a 3.8 to a 3.5 pulley. I has enough small mods and a scanner, so I will be able to run it safe. I ordered it earlier. So will I notice a pretty noticable difference in throttle response and top end?

Since you haven't filled out your Signature line yet (hint, hint,) let me combine the questions and comments that are going to pour forth...


-WHAT MODS DO YOU HAS??

-What brand did you buy?

-Is it a modular pulley?

-What octane are you running?

-If your mods are 'healthy' you will see more bottom and mid-range torque...

SCbuick010 wrote:

Alright so I decided to drop from a 3.8 to a 3.5 pulley. I has enough small mods and a scanner, so I will be able to run it safe. I ordered it earlier. So will I notice a pretty noticable difference in throttle response and top end?

A 3.5" pulley is the "safe" route. Really no mods at all are needed besides a CAI. You say you have a scanner.....does this mean a tuner? If it is a tuner, I would go with a 3.4", colder spark plugs, CAI, and a tune......

Abaddon wrote:

SCbuick010 wrote:

Alright so I decided to drop from a 3.8 to a 3.5 pulley. I has enough small mods and a scanner, so I will be able to run it safe. I ordered it earlier. So will I notice a pretty noticable difference in throttle response and top end?

A 3.5" pulley is the "safe" route. Really no mods at all are needed besides a CAI. You say you have a scanner.....does this mean a tuner? If it is a tuner, I would go with a 3.4", colder spark plugs, CAI, and a tune......

Uh, I think the pros here would disagree about blindly going to 3.5"... Personally, I followed their advice about intake, thermostat and exhaust before I went that small, especially with my octane limitations. Not to mention, there are many bad "cold air intakes"...

And generally, just like a cigar is sometimes just a cigar, it's safe to assume that a scanner is just a scanner...

3.5" recommended for totally stock 97-03 GTP/GS
from ZZP....

* 3.4 Cold air intake, cooler thermostat and mild exhaust work (u-bend delete, cat back)
from Intense...mind you Riv's don't have a U-bend to delete.

Abaddon wrote:

3.5" recommended for totally stock 97-03 GTP/GS
from ZZP....

* 3.4 Cold air intake, cooler thermostat and mild exhaust work (u-bend delete, cat back)
from Intense...mind you Riv's don't have a U-bend to delete.

Aaron, do you have any input here?

I didn't go to a 3.4" pulley until I installed 1.9 rockers and exhaust (headers) etc.
That was based on many people saying they couldn't go down to 3.4" without seeing an increase in KR, without doing intake, exhaust and rocker arm mod's.
Need to provide more flow of air in and exhaust out.
Then you can adjust timing and Air/ Fuel ratio as well.

Abaddon wrote:

3.5" recommended for totally stock 97-03 GTP/GS
from ZZP....

* 3.4 Cold air intake, cooler thermostat and mild exhaust work (u-bend delete, cat back)
from Intense...mind you Riv's don't have a U-bend to delete.

Without scanning for KR you are asking for trouble.
But try it and see how long it lasts.

Apparently nobody trusts what the clear pros say
I think I'll trust ZZP and Intense

From my perspective it wasn't a situation of not trusting what the PRO's said it was what I kept reading on this site.
Not knowing any difference, I listened to what these guys had to say about safely increasing the boost on my Riviera,
I know that all 3800's should be the same but I was getting differing opinions on here from these guys experience, so i went with that.
Wasn't trying to break any new ground, just wanted to be safe.

I have nearly the same engine mod's done as rick w and I set mine up with the research I've done here and with the help of chris morales @ Intense racing.Also to coinside with rick's earlier statements you shouldn't go to 3:4 pulley until CAI,rockers and headers at least.Couple that with a rewritten PCM and you will be on the right track then!

crlombardi69 wrote:

I have nearly the same engine mod's done as rick w and I set mine up with the research I've done here and with the help of chris morales @ Intense racing.Also to coinside with rick's earlier statements you shouldn't go to 3:4 pulley until CAI,rockers and headers at least.Couple that with a rewritten PCM and you will be on the right track then!

If this is true, then they shouldn't advertise the latter of the two. It clearly states on their website what mods you need for what pulleys
http://www.3800pro.com/forum/superchargers/29199-required-mods-pulley-sizes.html
This is from their 3800pro forum, which is linked on their website.

I'm not trying to argue with anyone, but I don't think they'd post it if it was going to blow up your car.

Here is ZZP's $.02
http://www.zzperformance.com/grand_prix/products1.php?id=198&catid=111

LOL @ Robo

I don't know about zzp but I put my engine modifications together with Intense directly(not buy what it says in the forum)Also all of the research I've done through other car forums show more mod's than that to run a 3:4 pulley.its true some may get away with less mod's for a while but how about this summer when its 80 deg or more with 100 percent humidty? If you value you're engine like I do you might consider where we are coming from!if you don't believe do your install run the hell out of it and let us know how it works out.I know you'll find that we are just tring to help people avoid internal damage.

norsky86 wrote:

i got some extra cash and im looking to get a smaller super charger pulley.. this would be the first performance part i would put on my 98 riv i was wondering how small to go without having to change anything drastic.. also wondering with everything stock how many pounds of boost do you think im running and how many would i be running with a diffrent pulley?

As 1998_Riv suggested, before you do anything to the car, please read: Modding 101

It's also a good idea to read through our FAQ to answer some common questions on this topic before posting.

SCbuick010 wrote:

Alright so I decided to drop from a 3.8 to a 3.5 pulley. I has enough small mods and a scanner, so I will be able to run it safe. I ordered it earlier. So will I notice a pretty noticable difference in throttle response and top end?

You will notice a difference in throttle response, not so much in top end power.

Eldo wrote:

Abaddon wrote:

3.5" recommended for totally stock 97-03 GTP/GS
from ZZP....

* 3.4 Cold air intake, cooler thermostat and mild exhaust work (u-bend delete, cat back)
from Intense...mind you Riv's don't have a U-bend to delete.

Aaron, do you have any input here?

Yes, as stated on Page 1 of this thread, my opinion (written Jan '07) is:

"Aftermarket SC pulleys are now available in sizes ranging from 3.6" down to around 2". A word of caution: start bigger and work your way down. A 3.6" pulley can be used with little or no issues on a stock Riv, giving up to a 10 HP increase. A 3.5" pulley may give 15-20 HP and is probably fine if you run cooler plugs and t-stat, but scanning is still a good idea. Running the 3.4" size on a stock engine is not a good idea unless you scan and tune the PCM with a tuner or AFC device."

What that means is, there IS NO DEFINITE FORMULA for calculating SC pulley size for every car, only a loose guide for suggesting a range, and if it's my engine, I'd rather side with caution than watch it go "boom", as we've seen with some who've tried to break the rules, or listen to "professionals".

Unlike ZZP, I am not in the business of selling pulleys. My opinion is based on Riviera owners doing pulley swaps and giving feedback based on scans. I'm just providing the info for other Riv owners to read. I have no reason to tell someone they should run this size or that - I'm only supplying information based on actual reports from our membership.

However, if you want to trust a pro's opinion, I would suggest Smoothflow Pulleys, a VERY respectable vendor that specializes in modular pulley systems for the 3800. Here's what they have to say:

"# 3.6 - 3.8: No modifications necessary
# 3.5 Cold air intake, cooler thermostat and mild exhaust work (u-bend delete, cat back)
# 3.4 All the above plus better flowing exhaust(hi-flow/no cat, 3" down pipe) and colder range
plugs (AL104's)"

Abaddon wrote:

Apparently nobody trusts what the clear pros say
I think I'll trust ZZP and Intense

Consider this:

• INTENSE was so unfamiliar with the Riviera's exhaust system, they would not install SLP headers on my car. They had no idea if they'd fit.
• ZZP sold me braided SS brake hoses supposed to fit G-Body. The result was both sides failed at 15K miles (about 6 months use), causing sudden brake system failure.
• INTENSE supplied me with a 3.4" pulley, AL104 plus, and a 160º t-stat and said "this will work fine". Little did they know, the Riviera's PCM is different than W-Body cars, and has no protection against knock (KR) below 158ºF.
• INTENSE returned my car to me with SC belt on the wrong pulley grooves.
• Morad Parts tried to sell me a GTP transmission for my Riviera, even though we know these will not work.

These are just a few of the things the PROS DON'T KNOW about Rivieras, things WE DO KNOW from experience. This is why you should trust ZZP and INTENSE as respectable product vendors, but do not depend on them for accurate information regarding the Riviera, a specialized car they have little experience working with.

AA is right on here.I do use my car as an example, but I could not get the 3.4 pulley to run KR free until I installed 1.9 rockers. I could never get a 3.2 pulley to run KR free.

I am running a high flow cat, SSAC headers and the rest of the exhaust is stock. On my current setup, Gen V blower and VS cam, I am running the 3.2 pulley KR free.

For stock valvetrains I cannot recommend anything smaller than a 3.5. Best to get a MPS system with a 3.5 pulley, scan and if you see KR either go up to a 3.6 or start looking for more airflow. The exhaust is more restrictive than the intake. A "CAI" ... well the STOCK airbox is a fantastic CAI. The most you would need to do is gut the internals of the stock airbox until you are pumping a LOT more air.

Yes AA, you are right, the PCM for the Riv IS different than the GP's. LOL at giving your car back messed up....they sposed to be "the ones" aren't they?! I was just giving info that they suggest.....

Most all of the 3800 vendors do a great job. I have a lot of respect for their knowledge and expertise. I don't wish to make anyone out to be less competent than anyone else. My point is, even with their vast understanding of GTPs and Regals, etc., there are slight differences with Rivieras that make us a unique group with the need for a better understanding that the pros may not be able to provide.

Hello. Being new to Riviera's I don't have any scan/tune equipment for them. I'm hoping after a little digging I will be able to get some of my DSM stuff to work. I currently use TunerPro RT on my laptop, Ostrich 2.0, Jackal, and a PalmPilot Dattalogger.

The question I now have, is based upon experience, what size pulley would you guys recommend knowing ahead of time i have no way of checking for KR?

I will be replacing the plugs with Copper Autolite 104's, the thermostat with a 180 unit, and the intake will be upgraded (not sure yet whether CAI or FWI).

The exhaust will be upgraded as well, I am just not currently sure how much of it, or to what size I'm upgrading.

Given the above info, would I want to go no larger than a 3.4 (therefor keeping stock tension & idler pulleys)?

Or perhaps a 3.3 (3.5 tensioner, stock idler)?

Or even a 3.2 or smaller (tensioner and idler 3.5)?

I'm just not sure, since I have no experience with these cars, what a safe bet is for SC upgrade given the above mods. Obviously none are 100% safe, and I will eventually want to know for sure, but I would venture to say that someone here has enough experience with these motors to know roughly when KR will kick in with above mods. Thanks for your help - Hollywood

I feel that a 3.3 or 3.4 would not be the best decision with the additions that you mentioned. A 3.4 may be safe to get, but I personally would definately scan first before going that low. A 3.5 would be a safer bet right now for you. I just purchased a scanner recently which I felt would be wise to do before a pulley swap. Thankfully, I have 0 KR at all so far after scanning for a few days. Just think of your goals: Do you want to go fast now? Or would you rather go fast a bit later, without potentially sacrificing your engine's safety?

Is a 3.5 enough to be noticeable?