VR4 too much boost

[Buck-Strickland]

I test drove the VR4 for the first time today. Holy $#@!. The SN2000 with the HO impeller was making 7psi @5600 RPM with a 7”(on the ribs, 7.3OD) crank pulley, and a 4.2” blower pulley(on the ribs, 4.45OD) which means the impeller was spinning 41,440RPM.

Same pulley setup on the VR4 and I have to shut it down at 4,500 rpm. As soon as I floor it I’m at 10psi then by 4500 it’s pegging my boost gauge 12psi+.

Boost is instant, no lag or build up it’s just there. Wow!!! Feels like a Turbo.

I really only wanted to run about 8-10psi by 5600RPM.

Anybody know what the biggest 6 or 8 rib pulley available is? I’m thinking I might need a 5” pulley.

Also, I found out the Procharger P1SC-D1SC pulleys are 0.875 i.d. same as our SN pulley i.d., but the keyways are larger on the Procharger (3/16” to our 1/8”) anybody think the keyway size will be a problem? They seem to make a lot more sizes in the Procharger pulleys.

[JPJP]

You could go to a machine shop and have them cut another keyway on the pulley for your size Key.

[JPJP]

Nice boost by the way..........sounds like you've got a real screamer.

[Buck-Strickland]

Good idea, regarding cutting a new keyway. I had not thought of that.

Yeah, it's scary. I do have the timing retarded 15 degrees (18 Total under boost), so that's killing some power.

It sounds really mean.

Anybody know the best place to get pulleys? I'm going to call PW on Monday.

[JPJP]

http://www.aspracing.com/index-8.html

ASP Racing makes a good product and their pricing is relatively better than some of the bigger pulley manufacturers.

[Michael]

There's no such thing as too much boost!

Congratulations on getting your VR-4 up and running.

[Buck-Strickland]

I emailed them last year and they said they no longer make custom order pulleys. Odd, because I had bought from them before.

[Buck-Strickland]

Thanks Michael.

I don't want to spit a head gasket. Plus, I have 9.5:1 compression, so I think 10+ psi is pushing it.

I may pop on a Procharger pulley just to see if it's an alternative for us SN guys.

[JPJP]

Definitely get a new keyway broached on it and let us know how it turns out.

[Buck-Strickland]

I just discovered that my boost gauge was reading incorrectly. I had a SW gauge that only read to 10psi, and then I swapped it for a new gauge that reads to 20psi. Took the car out for a spin and discovered what I thought was 10psi was only 5psi. Bench tested new gauge, original gauge and a third borrowed gauge. The new and borrowed gauge read 5psi when my original reads 10psi. This would also explain why I have 12psi of fuel pressure (7psi base fuel pressure + Boost of 5psi = 12)

So, last year when I thought I had 7psi with the HO impeller, I only really had 3.5psi. When I swapped to the VR4 I thought I had 10-12psi I really am only making 6psi.

Please take note I am very sorry and embarrassed for the miss information, I did not discover this until a few minutes ago. I had no intention of misleading anyone.

FYI:

HO impeller @ 40k rpm was really about 3.5-4psi (7” crank pulley, 4.2” blower pulley, 5,500 engine RPM)

VR4 impeller @ 36K RPM was/is 6psi (same, but with 4.75” blower pulley) The 11.58 ET I ran earlier in the month was really with only 6psi and 25 degrees of timing. Evidently the 11.78 it ran last year was with 4psi and 30 degrees of timing.

[Michael]

Given the impeller RPM you've stated, 7psi from an HO impeller sounds quite normal. 3.5psi however sounds extremely low. Same goes for the VR-4. 10psi-12psi sounds about right; 6psi sounds really low.

Are you sure this new boost gauge you're using is working properly? Maybe you need more ball pressure?

[Buck-Strickland]

Possible. But I'm at 55in/lbs already. I may play around with ball pressure and impeller shimming. Also, it's trying to fill a 406 with a good size roller cam and RPM heads.

I have some things to look into.

[Joo]

how much overlap does your rollercam have? This could be another reason for those low boost values. just a guess

[Buck-Strickland]

112 Lobe sep for the cam, with duration of 230/236@ 0.050

I'm going to look over the entire setup again. Car went from 12.48ET NA to a 11.78 with the HO impeller. And went 11.58 short shifting the VR4, so it did improve the ET's. I have a couple things to do before the next race. One of which is installing an MSD. Knowing it has less boost means I can change the tune up.

[Michael]

The fact that you're trying to fill a 406 with good-flowing heads may very well be why your boost isn't as high as you once thought (because of the 'faulty' gauge), but it still seems a bit low... especially for the VR-4.

This is going to sound like an odd suggestion, but do you know anyone who's running an SN on a 350 that you might be able to swap with your VR-4? Just to test whether the engine capacity/breathing is what's causing this drop in boost.