7in/3.15 or 8in/3.33 how fast?

[musclestang89]

How fast am I spinning the S-trim with those pulley combo?


Right now I have the 7in/3.15 on it, but my 3.33 pulley just came in. And I also have a 8in sitten here. I'm wanting to put the 8in/3.33 pulley combo on there and maker around the same power, but let the boost come in sooner. Also right now I'm seeing around 11-12psi.

Any info?

Thanks, Brandon

[frdfandc]

Here are the numbers (blower speed) for the 3.33 pulley with the 8 inch pulley. It will make around 15-17 psi with good H/I/C combo.

3.33

34,018 4000 rpm
35,719 4200 rpm
37,420 4600 rpm
39,121 4800 rpm
40,822 5000 rpm
42,523 5200 rpm
44,223 5400 rpm
45,924 5600 rpm
47,625 5800 rpm
49,326 6000 rpm
51,027 6200 rpm
55,279 6400 rpm

There isn't a specified impeller speed on the supercharger spreadsheet I'm using for the 3.15 & 7 inch pulley, so here is the 3.00 and 3.33 with the 7 inch crank to give you an idea.


3.00 3.33

32,426 29,213 4000rpm
34,048 30,674 4200 rpm
35,669 32,134 4400 rpm
37,290 33,595 4600 rpm
38,912 35,056 4800 rpm
40,533 36,516 5000 rpm
42,154 37,977 5200 rpm
43,776 39,438 5400 rpm
45,397 40,898 5600 rpm
47,018 42,359 5800 rpm
48,640 43,819 6000 rpm
52,693 47,471 6200 rpm

Personally I would use the 7 inch crank and the 3.15 upper if its on a stock short block

[Hustler]

You can actually change the pulley size values in that spreadsheet to change results in that field. If the 8 inch crank pulley clears everything, you can run a larger blower pulley to get more belt wrap and less slip. To get the same ratio as the 7/3.15 pulley setup you have now you would need a 8/3.60 pulley. As it sits now you will make more boost as stated above with the 8/3.33 pulleys.

7 / 3.15

4,000 30,667
4,200 32,200
4,400 33,733
4,600 35,267
4,800 36,800
5,000 38,333
5,200 39,867
5,400 41,400
5,600 42,933
5,800 44,467
6,000 46,000
6,500 49,833

[5150 LX]

Chris is correct, on the spreadsheet that is available on here you can change nearly any of the variables and get the #'s you are looking for.

[92rohcp]

Would I be spining my Strim too much with a 2.95 blower and 7 crank. I don't race and rarely see the top of the tach.

[Hustler]

Via Vortech's site 50k is the maximum rpm they recommend, of course they must place some buffer in that number so you are probably fine, long as you don't take it past 6500.

RPM 7/2.95
4,000 32,746
4,200 34,383
4,400 36,020
4,600 37,658
4,800 39,295
5,000 40,932
5,200 42,569
5,400 44,207
5,600 45,844
5,800 47,481
6,000 49,119
6,500 53,212

[frdfandc]

NIce, now its time to play with pully sizes.