S/C power curve

[fastrike1]

I am running a SN 93 on my Dakota w/406ci stroker. I am watching my SN 93 starting to loose boost around 4500 rpm I am running a 7" bottom pulley and a 3.5 top. I am wondering if I am making it boost too early with this pulley combination. Should I try a 3.75 top pulley and let it boost a little latter in the rpm range. I was told that if I am turning the SN too fast that I will be putting too much hot air into my motor and hurting my performance, is this true?
It now boost 6psi, I would love to raise the boost a little, but was told that the best thing would be to upgrade to a larger S/C. Give me some insite to what yall think I can do to better my motor.
Thanks Michael

[blownzoom440]

with that little bit of boost you are not stressing the performance of the blower i wouldn't think.there should be minimal heat to effect performance.can i ask what cam you are using and installed at?

[speedytang]

Well you have been told correct information, to a point.
1st. Your over spinning big time and that is why your boost drops.
Top pulley on a SN93 with a 7" bottom should be no smaller than 3.75"
2nd. Sn93 should not be used for anything larger that 350ci to get 5-6psi in a stock engine.
3rd. You are Super Heating the Intake charge so I am shocked that your not Detonating the engine to death with anything under 93 octane and removing so much timing that you would be just as fast with out the supercharger.
P.S. At your pulley size your over the operating range of the supercharger at 4200 rpm.

[blownzoom440]

thanks speedytang!i was trying to reserch the sn93 to get the flow rate for cu in size with no luck for info.do you have a link for info on that modle?

[pavement pounde]

fastrike1 ,
I think you need to upgrade to a VR4.
I had the same thing like you with my 454.
Measured 7 psi in the tube before the tbi and only 3 psi in the manifold.
However now that I have made the VR4 upgrade I have not tested it yet, probably next week.

[speedytang]

Sn93 Flows about 785 cfm at 5psi - 685cfm at 7psi
VR4 Flows 1476 cfm at 6psi - 1600 cfm at 14psi
As you can see the SN93 starts dropping power because the impeller is not made to produce power over its Rpm limit.

[blownzoom440]

i have a lot to learn!Thanks.

[fastrike1]

Anyone has a VR-4 upgrade I can buy from them?
Looks like I need to upgrade. :teeth:

[pavement pounde]

[link]http://www.paradisewheelsinc.com/[/link] has the upgrade kits for about $600.
A bit pricy but perhaps you can find a busted VR4 for the nessesary parts, that's what I did.