unfamiliar territory: 3.0" pulley tuning

So I was sitting there and figured "what the hell?" since I had it sitting in the garage and was running the 3.25" pretty much KR free before the ported SC.
First let me say, the old screws in the MPS did not want to come out. They had been on there about 2 years now. I started it up but the right above the larger tensioner pulley, the belt sounded like it was rubbing a bit. I put a peice of paper between it, and it didnt rip it, so it wasnt touched obviously.
I replaced the idler pulley with a larger 3.5" one I had, and it fixed the problem and gave the belt more clearance.
Only problem now is that my tensioner is even tigher and more off allignment. I suspect its been going out so I should probably replace it anyways. If anything this will put it out of its misery and I'll be forced to buy another.

I saw up to 4.6* KR with about 75% throttle. Not too bad all things considered. I tuned in 1 to 2% more in the upper MAF ranges (7000-11000) and will check the IPW's and KR again to see if the injectors are gonna go static on this pulley.

I changed to ZZP MPS screws. MUCH better than INTENSE's. They won't strip out like the rounded, low-profile types.

I have serious doubts about you being able to run this small without an IC and/or larger injectors.

GOOD LUCK!!!!!!!!!!

I dont' think you'd max out the 42.5's this soon on a Gen 3?

Although it looks like they are on your to do list.

AA wrote:

I changed to ZZP MPS screws. MUCH better than INTENSE's. They won't strip out like the rounded, low-profile types.

I did notice that the screws I got with the Intense MPS strip easily. Happen to know what grade/size they are? They look nice but man they suck. I've swapped pullies probably 4+ times with them and they are still good enough but I definitely dont like the way they feel when I tighten them.

Just order the ZZP replacement screws for $5. You'll thank me.

Or, keep using the INTENSE screws. When you strip one out, I'll send you a free replacement. I have 4 left.

AA wrote:

I have serious doubts about you being able to run this small without an IC and/or larger injectors.

everyone has doubts, which is kinda why Im curious to see just what RIVs can do. I know the riv runs less stock boost than many other series II models so maybe you can run a 3.0 on a riv with less mods.

either way, it wont be long before the injectors go in. Does anyone thing the stock fuel pump is sufficient to runs 42.5lb injectors? I seen a guy running a GTP in 12's on the stock fuel pump. And are W-bodys the only one notorious for the fuel pump wiring problem requring the re-wire kit?

I dont plan on changing pulleys often ( this was the first time ) but will get some ZZP screws whenever I need to order something else from them.

I didn't know about Rivs running less stock boost, and I still don't. We see 6-8 PSI, same as GS & GTP. The only thing that would cause that is the U-bend they have, but when removed, they should have the same as us. I see 10-11 PSI with 3.4", 12-13 PSI with 3.3", and 14-15 PSI with 3.2". On the dyno, I pushed 16 PSI at 6k RPM with only a 3.4".

With basically the same set-up you have, I'm running a 3.3" comfortably. A 3.2" when it's very cool, and 3.4" for the summer months.

The stock fuel pump should be more than sufficient, imo.

Keep in mind that while increasing boost does increase torque, it won't make your car that much faster in a race. Letting the engine breath & raising shift points will do more for your times, imo. Holding 2nd gear to 6kRPM, I ran a 13.9 with the 3.2", but ran 14.0 with 3.4" pulley. I ran a 14.2 with a 3.2" and stock shift points, loosing 2 mph in trap speed.

You are borderline running a 3.0 with any kind of safety without an IC or cam. You need someplace for that air to go.

Lower your shift points, going near 6000 RPM with the 3.0 will be a waste. You'll just boost stack and build up too much heat. But you'll have loads of low-end torque!

Good luck, let us know how it goes! I'm skeptical of anyone running a 3.0 pulley without cam or IC. IMO There just isn't enough airflow through the heads to let all the air out of the intake.

Quote :

Lower your shift points, going near 6000 RPM with the 3.0 will be a waste. You'll just boost stack and build up too much heat. But you'll have loads of low-end torque!

Good point. With that much boost, you can't rev as high safely. You'll make gobs of torque down low, but actually less horsepower. You'll be unable to use each gear as effectively. It'll be like driving a diesel truck!

update:
i took it out the other day since I had to run a quick task just to see how quickly I get KR.
the roads were wet and I couldnt get any traction with even half throttle. the boost builds so quick, I dont know how you could keep traction with a 3.0" pulley even on dry payment. I'd leave burnout marks with 3/4 throttle launches on the 3.25"

I think that if I went WOT, the fueling would be okay in the upper ranges, but it seems that mid/partial throttle creates some KR (about 3.6*) even with fuel trims locking in. Ill keep messing with it. as I experienced the same problem with the 3.25" at first.

One of the biggest differences I've seen in dropping SC pulley size is throttle/boost application. It really comes on fast with just a small decrease in dia. For example, at 40-50% throttle with a 3.4" pulley, you'd get the same amount of response with only 20-30% running a 3.2". Trick is to be able to use the 30%-WOT safely!