Here is the compressor map for (V3)Si : http://www.vortechsuperchargers.com/pdf/si_cmap.pdf

Why Vortech rate the V3 Si at 1150cfm and give a +1300cfm on his MAP (at max rating of 52k) ?

As it's seems to be very commom to overspin a vortech, according to his graph, if overspin at 60k (max rating is 52k) shoud be +100Lb/Min, and because of rule 1 Lb/Min = 10 FWHP, can hit 1000FWHP instead of 775HP (vortech rating), right ?

Other rule, 7000rpm and 1bar(14.7psi) of boost give 1.61 lb/min for each 100cc
So, a 383ci(6276cc) give 101.0436lb/min... exactly were the virtual 60k line should finish at 2bar (=1bar of boost) :-)
And according v-2 / v-3 calculator ( http://www.vortechsuperchargers.com/page.php?id=33511 ) a 8 ich damper and a 3 inch pulley give a 67200 at 7000rpm
Going forged, so, i was planning to buy the jeggs 10% overdrive damper (8") and pulley down from 3.4" to 3" but... 67k2 vs 52k is a HUGE overspin ! Go ? No Go ?

FYI : Street car, just drag race 2 weekend a year or so

No. People overspin the race blowers with HD bearings not the base units like Si-trims. I doubt the blower would last long at all, and efficiency/heat/etc goes to hell when spinning it that hard. You can make low 700s spinning a Si hard enough but depending on your goals you maybe better off with a T/Ti/Ysi.

I bought my blower (v3si) from a respected member on here who ran a 3.25" pulley for ~10k miles and I ran it on a 3.5" for another 6k miles before I pulled it to upgrade to a T-trim. It was in excellent condition when I removed it so I wouldn't be afraid to overspin a bit so long as you can keep the belt from slipping.

As you start to overspin you get out of the blower's most efficient operating range. Do you plan to spend a lot of time driving at the top end RPM or do you want boost to come on stronger/quicker?
What HP are you shooting for? You should try to match your HP goal to a blower's efficiency range. Also, what size engine?

3.4" or 3.2" on stock crank pulley is vastly different from 3.0" on a 8" ans vastly different even from a 3.0" on a stock crank pulley.

Plus how do you know it was in excellent shape? Did you open it and look at the bearings and pull it apart to inspect?

@Unreal, lots of S/Si are overspun, realy !
TRIZ Here have use 2.8 pulley (cannot contact him :-( )

@neveret, if you stay at oem max rmp (6200), you were just fine with 3.25 pulley (51.5k for 52k max)
With my 346, i done 2 or 3 runs at 7400 (and 150 others at 7k)

@Silver Bullet C6
I dont plan to be at high rpm all day long, just 2 weekend a year when dragrace (30 runs or so)
I DREAM to hit the 1000FWHP (383 all forged, ported head, 10:5, Ls6 intake, 23x/24x at 63x lift cam, 2" header, E85, agressive tune, 7000rpm
I have already the V3Si... I'm sad to not having Ysi, but when it's buy, it's buy

Just because people over-spin their SI trims doesn't make it the right way to do things. A 3" pulley with an 8" balancer is going to massively over-spin that thing. Besides durability issues, I doubt you'll be in the blower's efficiency range.

When talking power goals, you should stick to rear wheel HP (RWHP). Talking in flywheel horsepower is pretty much useless, unless you actually have the engine out of the car and on an engine dyno. 1000 flywheel HP is 800+ at the wheels through a manual trans. Stepping up to a Ti-trim or even a YSi would probably be needed.

If you bought the V3 SI from A&A, they may take it back for a partial credit against a YSI, but the install on the YSI upgrade is quite involved. I did it, so I know. That said, you're dreaming if you think you'll get 1000 WHP from an SI, especially with that build. You'll blow up your engine in the process. 7000 RPM will get you nothing more than 6-6.2k RPM or so...except a lot more wear and a lot more of a chance to blow it up.

The Si is designed to get about 700RWHP, that's it.

If you dragrace a 1000 RWHP Vette, you'll also need to build your drivetrain, because with good traction, you'll snap the drivetrain in half like a 10 cent pretzel the 1st time out...

That's about as abusive as you can get on a car with 1000 RWHP. You'll do that even with 750 RWHP and no drivetrain upgrade.

He mentioned "1000 FWHP", so unless he converted his C5 to front wheel drive, I think he means at the flywheel. Either way, it's not happening with that blower. With that cam on a 346 motor, he might make peak power up near 7k if everything else in his combo is set up correctly. I made peak power at 6550 with quite a bit smaller cam on a 376ci engine. So it's possible.

And yeah, that drivetrain will have some issues unless it's upgraded. I didn't even drag race and managed to shear off my transmission main shaft at less than 700 whp. Maybe I was just unlucky, but I think you're on borrowed time at anything over 600 rwtq with a stock drivetrain in a regular C5 or C6.

I'm going to machine the shaft coming out of the blower so it is ribbed and just run that as a pulley. Should be 3/4" pulley or so. Shooting for 2000FWHP out of a Ysi.

Even if the blower survives which it won't for long, the temps of air coming out of it is going to be like a flame thrower.

That pretty much sums up this thread....