VR4 help PLEASE!

[Dirk Diggler]

Well, I put the correct shims in the VR4 setup and got it running! IT sounds totally SWEET, very mild whistle! Not too much, just right:D But I now have a boost problem. When I hit 6-7psi, the boost starts to climb, then the boost falls to about 5psi. DO i need more toruqe on teh ball drive? I have 54 inch lbs on the pulley with the new shim. I had 44 inch/lbs. What do I need to do to get my VR4 to hold boost above 5psi?

HELP PLEASE

And Thank you in advance! ;)

[speedytang]

Sounds like the belt is slipping. Are you still using a 6-rib setup?

[Dirk Diggler]

Speedytang, Yes, I do have the 6 rib belt, however, the boost comes on and once I hit about 6-7psi, the boost then drops down to 5psi. When my sn was on the stock engine, I had 8.5psi/9psi with no slippage. I did max out the tension on the belt so I don't think the slippage is due to the belt. I think the ball drive needs more pressure. My stock reading with the sn impeller was 44 inch lbs. Craig told me that the sn should have 22 inch lbs of torque and the vr4 should have 44 inch lbs. Now my 22 inch lbs with out the seals equated to 44 inch lbs with the seals/pulley. So I am guessing that the torque with the seals and pulley should be 22 inch lbs more that the stock sn had which was 44, so more like 60-64inch lbs. By adding the one .005shim, my torque on teh pulley went from 44 to 54, so I added another .005 shim and I am at 60inch lbs. Hoping this will cure the problem?

[Dirk Diggler]

Well, I took the supercharger apart again and added another .005 shim. Took her out and now it holds boost better, problem is still there so I think I need to take one of the .005 shims and replace it with the next size up which is .010. The car gets about 8.5 psi max, but the boost still falls to about 5.5-6psi once I get in the upper rpm's. I can tell there is a lot more power, but I"m sure once I get it so when it holds boost up in the upper rpm's it will really fly!

LOVE THE SOUND! Drove by a few camaro's adn stang's and they looked at me like UH-OH,:D Caught the eye or ears of a few ricers too which they did not even look at me cuz they KNEW i would humiliate them:D:D

AND I LOVE THE WHISTLE!

[ProZac]

yeah brother having the same problem with his SN-92 i think its his belt but the belt is tight and tenisor is maxed all the way down tight on it i dunno whats going on with it~

[Dirk Diggler]

The vr4 is a different animal from what i have read. it requires 2x the tension on the ball drive. My tension on the ball drive on my sn2000 was 44inch lbs. with out the seals, it should measure 22 inch lbs, but I measured my tension wiht the seals and from the pulley (44 inch lbs). So I am guessing that I need 66 inch lbs. Now, I'm at about 59 inchlbs. going to try for another shim at .005 more, we will see!

[brian88lx]

awesome :)

i finally get to order mine tomorrow. if i have any assembly questions, i know which two folks to talk to.

[Dirk Diggler]

Well, I added another shim to the charger. Now, my inch lbs from the pulley went from 44 to 54, then to 59, then to 66inchlbs currently. Craig said that the inchlbs on the VR4 were 2x of the sn blower. After 3x, I got the shims correct. Tired of putting the thing on and off the car! But at 59inch lbs, the boost was still not holding. But it did improve with the added shim when I went from 54-59 inch lbs. Will keep you updated on the results.

[Dirk Diggler]

OK, I have a solid 8.5psi. An increase of 1.5-2pis from my sn2000 with the modified impeller. I was expecting more boost? I do feel more power with the vr4 at similar boost levels due to the increased cfm's. Love the sound too! Teh added shims corrected the loss of boost during higher rpm's.

[Dirk Diggler]

OK, I have a solid 8.5psi. An increase of 1.5-2pis from my sn2000 with the modified impeller. I was expecting more boost? I do feel more power with the vr4 at similar boost levels due to the increased cfm's. Love the sound too! Teh added shims corrected the loss of boost during higher rpm's. I was expecting more thougth... more power and boost:( It's still good ;)

[brian88lx]

put a smaller pulley on it ;)

what size pulleys are you using?

[Dirk Diggler]

Well, by the calculations, my impeller speed is 44000 rpm's...so called max of the vr4/sn2000. I know speedytang rev's his up to 60k...... maybe I can put a larger crank pulley on?

[speedytang]

Just for a reference of old postings.
With 7" crank and a 3.75" charger pulley I see 10psi.
With 7" crank and a 3.50" charger pulley I see 14psi.
I do run 8-rib pulleys.
I installed a VR4 for a friend on a 87 Corvette and on the Dyno with a 7" crank and 3.00" charger pulley produced 18psi but he had the boost gauge installed on the supercharger not on a vacuum tree so not sure how much boost was lost in the engine.

[Dirk Diggler]

Speedy,

I have a 6in crank pulleyand a 3.25 s/c pulley. My charger is spining a bit above the max impeller speed...44K giving me 8.5psi. 1.5 -2psi more that my modified sn2000 impeller. I do think I am getting more power. Due to the increased CFM's. And I love the whine! Just right! The procharger being the excellent unit it is,,,,,would drive me nuts with the super loud wine No thanks! But I was expecting much more out of hte vr4. So, should I put the impeller closer to the back side of the charger or closer to the outside of the case by using the shims that go on the back of the output shaft? And or get a smaller s/c pulley? maybe a 3in pulley on the charger?

[speedytang]

I really am shocked that your belt is not slipping with a 3.25" pulley and only a 6 rib because even with my 3.75" it slipped really bad and I went to 8-rib and gained 2psi at the top end. Just remember boost is a direct effect of back pressure so you may be showing 8-8.5psi but your building power of 10psi. I think your ok on the impeller shim to see 8.5psi with only 44k rpm.