I read through 12 pages of search crap and still have no answer.

Tech 2 4" pulley theoretically is 7psi on AP1
SOS 4" pulley theoretically 8 psi AP1.

I had a Tech 2 4" and it hit 7 psi on my AP1


I have an AP2 now and want 7 psi or the most boost without changing inj. I have engine management.

I read here that Tech 2 said 9 psi ?" will be 7 psi on AP2.
SOS says 9 psi 3.8" is going to be 8.5 psi on AP2.

Anyone running 3.8" stock inj or anyone make a 3.9" pulley?

 

http://www.scienceofspeed.com/products/eng...000_SC_pulleys/

 

Thats what I was basing my research off of, but it doesnt add up to what Tech 2 said or what people are posting.

 

what is Tech 2? Comptech?

 

Tech 2 was the original maker of the 7 psi and 9 psi pulleys. The company no longer provides the pulleys.

 

I'd say the SOS chart is fairly accurate. They list 8 psi for a 4" pulley on a AP1, and I am getting 7.5 psi with the aftercooler accounting for a small loss. I wouldn't go any smaller than 4" without injectors.

 

My AP2 w/AC consistently produces 8.5lbs of boost using the 3.6" SOS pulley @ about 8400 rpm.

With the stock CT AP2 pulley (4.2"?) I never saw more than 5.1-5.2 @ 8000 rpm. I believe SOS says +1-1.5lbs per .2 drop in size. So my experience was in line with that bringing about a 1.1 to 1.2 increase in boost per .2" drop in size. Assuming readings are linear.

My blower may be an underachiever, but in my experience, there's no way you'd get 8.5lbs using the 3.8" w/AC.

My best guess would be that 4" would leave you safe but probably below 7psi and 3.8" would be a bit above. Your own experience with the 4" spinning 1000 faster @ 7psi on a AP1 kindof says it all. If you are limited to those 2 sizes, I'd go for the 4". You may leave a small amount of performance on the table but you'd be safe. There are many posts of people running lean with the CT kit and smaller pulleys that have maxed out the FPR and stock injectors ability to supply fuel. If you have the option available, check peak boost with the stock pulley and you'll have your answer within a few .1's what the results will be.

 

https://www.s2ki.com/forums/index.php?showt...0&#entry7474933

Try read this thread if you havent already.


"Tech 2 4" pulley theoretically is 7psi on AP1
SOS 4" pulley theoretically 8 psi AP1."

if the pulley is measured at the same place it does not matter who made it.


Pulley size dosen't correlate to boost necessarly and for that matter boost doesn't necessarly correlate to power.


Too many variables here.
What rpm are you running to?
Are you using the stock bypass valve?
I assume your running a comptech system?

check this out too..
https://www.s2ki.com/forums/index.ph...=313786&st=350

this is a chart that you can see what real world people are using what pulleys, supporting mods, etc to get to what power levels..

so saying you want 7psi isn't really the right question.
What RWHP is what you should be asking.