PSI with 6" crank and 3" pulley

[Orion_134]

I have an sn-92 with a 3.75 pulley on it and need more boost after I installed the intercooler...went from 9 to 5...It has a 6" crank pulley, unchangeable, and I want to put a 3" pulley I have on it. Will I be exceeding the 36k rpm limit? Also, how much shorter should my belt be for .75 inch pulley swap?

Jesse

[speedytang]

You could gain 2psi if you could keep belt slip from happening which will be really hard with a 3" pulley. You was exceeding the 36k rpm with the 6" and 3.75" pulley and if you only have a 6-rib your just going to smoke the belt or put so much pressure on the crank you could destroy the blower bearing or the front of the crank. I would suggest a 7" crank and a 3.5" charger pulley to get you boost back and keep the engine rpms under 6000 rpm and don't exceed 5000 rpm for any real length of time. Do you have a dipstick cooler also? You really need one and you better get a 255lph fuel pump or your FMU will not keep up. You do have a FMU...right?

[Orion_134]

To clear up a few issues, read my signature. It is an 01 ranger with a returnless fuel system. The crank pulley is unchangeable because the harmonic balancer and the pulley are a single unit and the aftermarket has yet to produce one that doesn't explode. I only go above 5k at the track, and that is only to 6k at most because of rev limiter, but I shift between 55 and 58k rpms, but I drive on the street under 5k. I have a belt tensioner on the supercharger bracket that brings the belt to where it is almost touching itself, covering 80% or so of the pulley, so I hope I won't see any slip. I need to get the boost back up to where it was when it was tuned, it was tuned before the intercooler and I lost around 3-4 psi.

Any advice?
Jesse

[speedytang]

No place did I see Ranger listed but I figured it was not a Mustang because of the horsepower numbers.Your pump still is not large enough and I did read your signature and the pulley size your thinking off is not the solution because you will be 10k rpm at least over the SN-92 operating range. All you can do is try it with the smaller pulley. If you want to have the unit live the cooler unit for the supercharger will help probably more than that intercooler does.

[Orion_134]

Sorry about the confusion. I tried the smaller pulley...wheeeeeeee!...but I don't have anything onboard for a/f, so I took it off after 2 runs. IIRC, I think I read that you said that a 7" crank and 3.5" sc pulley won't overrev. Mine is 6" and 3", am I confused, that's a total of 1/2" more pulley than the first combo? I agree about the cooler, but it's pretty expensive, and I think I am switching over to Vortech soon.

Jesse

No place did I see Ranger listed but I figured it was not a Mustang because of the horsepower numbers.Your pump still is not large enough and I did read your signature and the pulley size your thinking off is not the solution because you will be 10k rpm at least over the SN-92 operating range. All you can do is try it with the smaller pulley. If you want to have the unit live the cooler unit for the supercharger will help probably more than that intercooler does.

[speedytang]

It will still be overrevving the difference is no belt slip for a lot of combinations because the location of the idler on a stock setup, but you said your setup has a full belt to pulley contact so since you can not replace the 6" your pulleys you are as good as your going to get. What boost did you see with those small pulleys?

[Orion_134]

Before the intercooler, I saw 8-10 psi (can't remember) with the 3.75. After the intercooler it was 5 psi with the 3.75 and 10 with the 3" before the belt slipped ~4500. I didn't get a chance to break in the new belt so it slipped and I am going to take it back and get one .5" shorter and fully break it in and let you know how much more boost I get in the upper rpms

Jesse

It will still be overrevving the difference is no belt slip for a lot of combinations because the location of the idler on a stock setup, but you said your setup has a full belt to pulley contact so since you can not replace the 6" your pulleys you are as good as your going to get. What boost did you see with those small pulleys?