Anyone try this? I know it should change the power curb to a lower RPM peak. Anything else I should know about? Anyone try this?

 

It will spin your blower faster making more boost. It's basically the same as going with a smaller blower pulley assuming you keep the same blower pulley when you go larger on the crank. This being said, make sure your not gonna over spin the blower.

Ken R.

 

Well, I have the smallest blower pulley already. I am maxing out the impellor speed now, but it isn't until 6500 RPM. Any idea of what I will be maxing out the impellor speed at if I go with the underdrive pulley?

 

What size pullys do you have? give us the size for your current crank and blower pully and I or someone on this board can tell you what combination will work best for you. Jeff

 

The blower pulley is the smallest one ATI offers. I think it's either 4, or 4.25 in size. As for the crank pulley, it is the one that the D1 kit came with. I also have the ATI super dampner if it makes any difference.

 

ASP makes custom Blower Pulley's, I have a 3.2 Blower pulley myself.

 

What was the boost difference from the smallest ATI offers (4 or 4.25 I can't remember) to your 3.2?

 

ATI makes small blower pulleys for the D1SC. I believe the smallest they make is 3.4" in 12 rib. Maybe it depends if you're talking 8 rib vs 12 rib setup. An approximation on boost vs pulley size for the head unit... every .1" reduction in pulley size ~ 1lb of boost. So, 4.0" to 3.4" should add at least 6 lbs of boost.

BTW, I believe the biggest crank pulley they (ATI) makes for the D1SC is 7.65". Next size down is 7.0" What do you have?

 

Found my exact pulley sizes. My blower pulley is a 3.40 pulley, and the crank pulley is a 7.65 pulley. I had been told that I could change the crank pulley to a 8.5 one, but need to know the new RPM at which the impellor will be maxed at. Currently, it is maxed at 6500 RPM.

BTW, I am running an 8 rib setup if that makes any difference.

 

Max impeller speed for a D1SC is 62,000 rpm. So,
Crank pulley/blower pulley X 4.10 X Engine RPM = Impeller speed.
4.10 is the step-up ratio of a D!SC s/c. You'd want a 12 rib only to reduce the chance of belt slippage. Also, if you go to the larger crank pulley, I'd check your clearance. The 7.65" crank pulley is pretty big but then again I've got a 12 rib.

 

I've got a tensioner on it, so I'm not really worried about slippage. I'm just concerned with what the new RPM will be that the impellor will be maxed out at.

Anyone have a figure for me??

 

Crank pulley / blower pulley X step up ratio X max engine RPM = Impeller RPM 7.62 / 3.4 x 4.10 x 6500 = 59727 D1SC max rpm 62000

You are a little short of maxing the blower but I wouldn't change anything.

 

Not sure I completly follow the math here. I was told my current setup maxes out my D1SC at 6500 RPM (crank pulley 7.65, blower pulley 3.4).

Now, if I were to change the crank pulley to a 8.5 one instead of the 7.65 one that is currently on, then it would change the power curb to reach max boost at a lower RPM, which should equate to maxing the impellor speed as well at a lower RPM (should it not?, correct me if I am wrong here).

Doing the math with the new pulley, I got a number of 66625 compared to your calculation of 59727 with my current setup. Where did you get the D1SC max RPM at 62000?

If you could explain a little more, I am a little confused I guess. Thanks.

 

62k is what procharger rates the D1SC at. You were probably told that because it may be the pully combo that comes closest to maxing your blower.

8.5 is a huge change you will max out your blower at 6k. I'm not sure you can fit a crank pully that large anyway. My advice would be to upgrade to an f1 if you realy want more boost or look to make your system more effecient in other areas.

 

ATI rates their D1SC for 62,000 rpm max impeller speed. You can overspin the blower but the chance of failure increases. With a 8.5 crank pulley, you'll max out at about 6048 engine rpm. You'll have to go to a bigger s/c pulley to be able to run your engine higher without overspinning the blower.