3.75 pulley too much ??

[Nutzy19]

I have a stock SN89 setup on my Mustang and I ordered the 3.75 pulley from ASP. Now I believe my crank is 6 in. and my stock s/c pulley is 4.25 in. I did the math and if I shift at 5600 Ill be close to the S/C redline of 39k. Is this setup trouble from the start?? Will I make more than 4.5 psi ? Will I definitely have to upgrade my fuelpump for this new pulley? Will the FMU still be adquate, and finally will I need a bypass?

Sorry for all the Q's but thats what this " FORUM " is for ... the exchange of knowledge. I wouldnt want to be " running my mouth" (you know who you are). Thanks to all those that HELP.

[speedytang]

If the fuel pump has not been replaced get a 190 or 255lph. You will be fine at 5-6psi with the FMU if you replace the pump. You just don't want to be lean at WOT because your injectors will be forced with 100psi of fuel pressure at 5psi boost. I would not worry about the 39k rpm. Paxton even re-rated the 'SN' to 42.5krpm and the only change was the 3-lip rear seal because at higher rpms the rubber seal was tearing. The VR4 has more pressure on the ball drive but it was still rated the same rpms. I will let you do the math. I run 15psi on a VR4 with a 3.5" and 7"crank at 6800rpm. I have been doing this on all my VR4 units for 14 years and really no failures other than that rear seal, till I replaced it 4 years ago with the new design. I am going to rebuild the ball drive this year when I do my winter teardown. Missed shifts is what I have seen do the most damage.

[Dirk Diggler]

You will be fine with that set up. I spun my sn2000 with the 3.25 s/c and a 6.5 crank @ 5800

[Nutzy19]

Now Im thinking of going with a 3.5 in pulley... HELP ME DECIDE PLEASE!!!!

[Dirk Diggler]

do you have an oil cooler? If so, I have my 3.25 I'll sell ya. Like I said, i was getting 8.5-9psi out of my unit. 6.5 x 5800 x 4.4 /3.25 = 51000. As long as you have the oil cooler, you be OK. with the 3.25, given you have the 6 in dia pulley, your impeller speed would be about 45K. You'll be fine @ that rpm.

[speedytang]

I really don't see a problem. If you don't see a increase in boost then go to a bigger pulley so at least your not over working the blower and you can get a cooler air charge.

[Nutzy19]

nah.. no cooler yet...

[Dirk Diggler]

definatley get a cooler. I bet you could make one a lot cheaper than what paradise sells their unit's for. A small tranny radiator kit @ summit, pump and some rubber hose...OH the dip stick, crap, I did not think of that. HMMMM, Maybe you can just get that from Paradise? I think it's 150 bones? not sure, but it helps a lot in keeping hte internals cool.