I have a V2 SQ trim on my car with a 6" crank and 3.125" blower pullies - what amount of boost should I be seeing?

Stock cubic inches btw - I also have a custom hard intake pipe. If more information is needed please ask - i'm trying to learn how all of this works.

 

Just to add to this:

When I dyno'd the car I had the stock 48mm TB and a 2 1/4" y pipe (not sure if that matters) and saw a spike of 8lbs and a consistent 7lbs after the spike. Does this sound correct?

I've since added a 52mm BBK TB and will address the exhaust issue. Also, had ignition issues at the time of the dyno - would this have affected the boost numbers?

Will the amount of boost go up with the addition of the 52mm, fixed exhaust and fixed ignition woes?

 

There's a lot of factors involved, including the motors NA efficiency. If you know your engines flowrate (CFM) at a particular RPM, this will help.

Pressure ratio = (ambient pressure + boost pressure)/ambient pressure---->

Boost (gauge) pressure = (pressure ratio x ambient pressure) - ambient pressure

Assuming your at sea level, the ambient pressure = 14.7 psi

Looking at the efficiency island on vortech's website, and calculating your impeller speed as 41,472 rpm from your pulleys, the pressure ratio is approx. 1.85 at 50 lbs/min flowrate, therefore the calculated boost pressure:

Boost = (1.85x14.7)-14.7 = 12.5 lbs

The higher up in altitude you go, this value will decrease.

Other equations of interest:

CFM = CID/1728 x RPM/2 x V.E.
1 lb/min = cfm boosted x .07 (80deg @ sea level) = approx. 10 horsepower
CFM boosted = CFM unboosted x pressure ratio

Ed

 

Wow

So, if I were at sea level I should be seeing approx 11.76# of boost - correct?

Elevation here in Akron is 1050ft

 

I did the calc wrong, it's 12.5 lbs, not 11.76.

At 1000 ft altitude, the 14.7 becomes approx. 14.3, so the calculation of boost then becomes 12 psi, you lose about 1/2 of a pound.

But, all those calcs have a lot of assumptions and are based mainly on cid, volumetric efficiency, rpm, barometer, and temperature. You will see more boost on a cold day and make more power because the air is denser. Go higher up and the air is thinner and you will see less boost because the inlet pressure (barometer of the air) to the compressor is lower to begin with. That is why you will make the most power at or below sea level. Put on a good flowing heads and exhaust and you will see less boost, but more power due to the increased volumetric efficiency of the engine.

In addition, vortech compiled that efficiency chart during certain weather conditions which affected the test data. Those values are listed next to the chart.

How much boost are you seeing on the gauge?

 

I saw a spike much like a big stall torque spike of 8lbs then immediately settled into 7lbs for the rest of the pull - I don't have a guage but the dyno shop was able to monitor boost with their laptop.

Maybe the 48mm throttlebody or the restrictive exhaust could be causing it to lose boost? I also had ignition issues at the time of the pulls. Perhaps it was the way I originally had the plumbing? There were some leaks and I had the MAF up top then.

I took the car right to the dyno after installing the blower - my first FI car so for the last 4 months of last year I learned quite a bit about the physical parts of the blower and fixed errors that I made during the install. I had a lot of small issues to work out so maybe it losing boost from one of them.

Is there a way to tell if the belt is slipping?

It will go on the dyno when it's back together again, now that the problems have been taken care of, i'll also install a boost gauge to monitor boost while driving.

That's a lost of boost if the calculations are correct - I'll be sure to install a methanol kit as soon as possible. And start thinking about an intercooler.

 

What would happen if the belt was too small/tight? Would this have an effect on boost? I know it would eat my bearings (at least).

 

If the belt slips, you would have a situation where you would see like 7-8 pounds at 4000 rpm and from 4000-6000 rpm, the boost would not rise anymore. What rpm did you see 7 lbs? Boost is dependent on rpm.

And, your not supposed to overrev the blower per it's specs according to vortech, but some guys do it anyway.

 

I believe it was from 3500 on up to 6300 when I shut down.

 

I hit it on the dyno at 3500 - it hits 8#'s then drops to 7#'s and holds the entire run. Does this sound like slippage or is it possible that i'm having a tensior/belt issue?