How do You have your s-trims pulleyed? I have a stock crank pulley and a 2.75" blower pulley and I am only pulling 8 psi. I would like to get more around the range of 12-15. How are you high psi s-trim cars pullied?
Scott

 

I ran the 7" crank and 2.75 blower and saw 12 pounds through a 355 with 218/230 cnc heads, etc on no intercooler or aftercooler. I will be upping the cam and putting a 2.50 blower pulley and ATI 3 core intercooler and I am hopin to stay at the 12 rating. I heard that the 7 and 2.50 through a aftercooler could net 15 pounds. Ill get back to you in a month and tell you what boost it made.

 

You don't specify what your setup is, especially in terms of cam and CR/type of bottom end parts. But if you have decent heads you will need to max the S-trim out to see 12-14psi. Assuming your bottom end is up to it, the way to approach this is to consider the max impeller speed fo your blower and pulley it up to this speed at the top of your cam's "sweet spot". Prventing a mismatch between the cam and the blower is one of the primary methods to getting the most out of your blower. A corollary to this it's another argument for using a relatively small cam with a blower. A samll cam will work most efficiently at a relatively low rpm range. By pulleying up the blower to max out at that point, you maximize boost at low and mid range revs, noramlly a weak point of a centrifugal SC.

The setup I was using last year was an example. An S-trim has a specified 50,000rpm max and a 45,000rpm "maximum efficient" impeller speed. The 214/224 cam's sweet spot was in the 5,500-5,700rpm range. I used a 7" crank pulley and a 2.93" blower pulley. This gives the impeller 46,000rpm at 5,600rpm. I shifted at 5,800-5,900 rpm, where the impeller speed was ~48,000rpm. On a 383 with mediocre heads this produced 13-14psi and a ton of midrange boost and power as well as 600rwhp (M6). There was significant boost as low as 2,500rpm (~4psi).

Hope that was helpful.

Rich Krause

 

Thanks Rich, My car is a 357 ci with forged internals 9.3:1 compression, eagle crank, and je pistons. The cam is a 224/236 with 1.6 rr's. The heads are untouched. I have an s-trim with an aftercooler. Where can I get a 7" crank pulley? Everyone I have called says they have to be custom made and it will take up to 6 weeks.
Scott

 

I got mine from Vortech, $$$ but it was in stock. You could go with 6/2.75 for a ratio of 2.18. This would give you 47,000 impeller rpm at 6,300rpm, which should work well for your cam.

Rich Krause

 

What is the stock pulley size that comes with the vortech? Isnt it 6? I have a 2.75 pulley on it now and am only getting about 8 psi at around 5500.
Scott

 

Not sure of the size you have (it's easy to measure though). With 6/2.75 the impeller rpm at 5,500 crank rpm is ~41,000 rpm. With 8lbs at 5,500 you should see the desired boost at 6,300-6,400. If you don't, you need a bigger blower!

BTW: you can spin the blower past 50,000rpm. Many do. From what I have seen on the dyno this is counterproductive. The additional boost is negated by the hotter intake charge and the extra power need to spin the compressor that fast. Little, if any, more hp is produced and the chance of detonation is much higher. Not to mention the possible negative effects of a trashed impeller on your motor.

Rich Krause

 

Rich, well see that is where the problem lies. I dont plan on reving my motor to 6400. Would it be safer on the blower to go with a 7" crank pulley and a bigger blower pulley? say 2.95 or 3.12? B/c I would like to reach around 12 psi at about 6000. What formula are you using for your calculations? Thanks for your help.
Scott

 

You can get the 7inch crank pulley from PerformanceSS.com. Steve is great and he gets it from ASP for a cheaper price then if you get it direct. Vortech does not carry this anymore only the 6.66" and expect at least a 3 - 4 week to get it.

Impeller speed and info try http://www.vortechsuperchargers.com/tech/

before
350 stock, AFR 190s, cam, 1.5rr - 6" and 3.125" saw 10# at 6000rpm 476rwhp

now
396, opened up the heads, 229-242-114 cam, .. 7" and 2.75" see 11# around < 5500rpm
6" and 2.75" saw 6#

cheers

 

Hugh,
Thanks for the reply. How long am I looking at if I get it from performanceSS? What is the stock size crank pulley that comes with the s-trim kits from Vortech?? I need to find this out first. With my stock crank pulley and a 2.75 blower pulley through stock heads and an aftercooler I am getting around 8 psi at 5500.
Thanks
Scott

 

Getting from PSS.com will take about 3-4 weeks for no more than $220. Getting from APS will be about 3 weeks for at least $250. You get the same peice which ever way you go. If you tell Steve that Quang or Hugh sent you and ask for a little off he can drop that a little too.

If you had an older kit like mine, it came with the 6" crank pulley. The newer kit actually comes with the 6.66" crank pulley. The best way to do this is get a string and wrap it around the pulley to get the circumference, where
Circumference(inches) / 3.14 = diameter(inches)

cheers

Hugh

 

Do you know any companies that have these in stock. I need it here by the 10th of April.
Scott

 

You will not be in the best rev range for your cam, but it won't be far off. So, you do need to pulley up.

crank pulley/SC pulley*3.45*crank rpm = impeller RPM

The common Vortech's have a 3.45:1 internal step up.

Rich Krause

 

So Rich, you are saying that the best pulley combo for my setup would be just to keep what I have now. Stock size crank and a 2.75" blower pulley?
Thanks alot
Scott

 

Sorry for any confusion. My recomendation to try 6/2.75" was based on the assumption that you were planning to redline at ~6,400, which IMHO would be a good choice with your cam. But since you plan to shift at ~5,500, you should select pulleys to give the desired impeller rpm at that crank rpm.

A 6.66/2.75 would put the impeller at ~46,000rpm at 5,500 crank rpm, so that's where I'd start with the 5,500red line.

Rich Krause