my idea:

I will leave everything the same as in my sig. except I will go with a smaller blower pulley.I still want to maintain a 12-13# max. boost at my shifts,which I currently do with the 4" pulley and shifting at 6100.

So going with a smaller pulley I will have to lower my shift points but I should be making more power at any given rpm do to more boost.I might not make the same peak power as before though but maybe more overall power.

I know I drop about 2000 rpm's between shifts,so lowering the shift point to much will not be beneficial.
Which leads me to what pulley should I try?
I'm guessing around a 3.7" pulley,also want to avoid bent slip.

Ultimately which set-up would produce a better quarter mile time-

4" shifting at 6100 OR 3.something" shifting at 5xxx something rpm's

 

do you have a dyno graph handy?

 

Naw man,I've never had it on a dyno.I've been thinking about it lately though.

 

Get it dynoed first to see where your torque peak is first, then you can determine your shift points based on a ~2,000rpm drop between gears.

 

will my peak torque location change a lot do to a pulley change?

if it doesn't than I see how this will help me determine which pulley to run because I have the 12-13# max. boost limit

 

IMO your going backwards unless you pulley down a lot more than that. At which time the stock 6-rib stuff gives up. I'd say if your gonna keep the 6-rib stuff, throw a 3.85" on there with a good belt, leave the shift points where they're at and enjoy and extra pound or two of boost with the added benefit of a slightly quicker spool.

In my experience going from a 4" to a 3.70" (on a stock 6-rib) doesn't net enough gain to warrant the loss of the meaty part of the hp curve and rpm by dropping your shifts a significant amount. An 8-rib with serious tensioner might change the situation a little as belt slip would be non-existent with a 3.7".

You have the right idea though. Several guys run their high boost (race fuel) pulleys all the time and just turn the shift points down when crusing on pump fuel. I just think that the limitations of the stock 6-rib belt prevent you from pulleying down enough to make it worth while. I'm assuming that your talking about a shift point drop of at least 750-1000 rpm right?

 

Sharpshooter and I have been tossing around the idea he stated in post 1. We were thinking of shifting at 5800 and pullying down at the same time. You think the 6 rib will slip with a 3.7" pulley? Hmmmm, wonder where I could get an 8 rib setup?

 

I ran a 3.7" 6-rib on a P-1SC for 20k miles, never had a problem with slipage. Used the same Goodyear belt I bought when I built the kit.

Go for it. Your just going to end up taking it back to the origan shift points and enjoying the extra boost.

Then down the road you can use a restrictor plate to drop it back down to where you want it.

Rick

 

if my calculations are correct with an 7.5 inch stock crank pulley using PI(D) the circumference is 23.5619449"

with a 4" procharger pulley using PI(D) the circumference is 12.56637061". so for every turn of the crankshaft the pc pulley turns 1.875 times. multiply by 4 (which I believe the procharger ratio is 4:1 correct me if im wrong) and you have the impeller revolutions per crankshaft revolution.
1 crankshaft revolution/7.5 impeller revolutions x rpm

with a 3.7" pc pulley using PI(D) the circumference is 11.62389282". so for every turn of the crankshaft the pc pulley turns 2.027027027 times. multiply by 4 (which I believe the procharger ratio is 4:1 correct me if im wrong) and you have the impeller revolutions per crankshaft revolution.
1 crankshaft revolution/8.108108108 impeller revolutions x rpm

4" pulley at 6100 rpms x 7.5 = 45,750 impeller revolutions
3.7" pulley at 5850 rpms x 8.108108108 = 47,432.43243 impeller revolutions = slightly more boost quicker spool and less rpms.

correct me if I am wrong but I believe this is correct
but other factors such as torque and horsepower curve over time and peaks come into play also to figure out which is best

 

Your just slightly off. In a perfect world with no belt slip:

Stock balancer, 4.0 pulley, 6000 rpm = 46125 impeller speed (74.4% of max)
Stock balancer, 3.7 pulley, 5850 rpm = 48618 impeller speed (78.4% of max)

On paper this looks awesome, belt slip is not accounted for in a perfect world. However, I didn't realize how slow you guys were actually spinning these things with a 6000 rpm shift point.

My personal experience is with a shift point of 7000 rpm which with a 4.00" pulley brings the impeller speed up to 53813 rpm. No wonder I was encountering belt slip with 3.85" on a stock 6-rib!

That being said, this is something you can try relatively easy for the price of a pulley and belt. Give it a try and let us know how it works. Testing is most of the fun. See if you can get someone to data log it so you can compare boost curves.

Also, as sureshot pointed out....I have the equipment available for anyone to take a D1sc to the limits and beyond. At 7000 rpm I was spinning my D1sc 65912 rpm (106+%) on my 10.46 pass at 4550 lbs.