Well, I wanted 9# of boost and the shop got the #8 boost kit sent with the 4.25 pulley. They installed the SVO 30lb injectors (it was still running lean with 24lb) and dynoed it again. The max boost on the sheet was 5.6lbs and 273 rwhp. I drove it from the shop to my house (40 miles) and noticed after the trip that the pulley had some belt dust in it and could be turned more about 1/2 way. So I tried to adjust the tension and the pulley is fully seated at the top of the groove on the plate and the top adjuster bolt is all the way down. I was thinking of calling ATI to get the 4.00 or 3.70 with the appropriate belt to raise the boost and power. Would I have to get the car dynoed again to get the correct Air/Fuel ratio setup with the pulley change? Or should I just get a new 8 ribbed belt for the 4.25? I understand just because it says 8# of boost doesn't mean I'll get it but........5.6??

 

Jeff,

I've always taken a specific "boost rating" blower manufacturers publish with a grain of salt. Boost is dependant on so many variables. When ATI says the 4.25" blower pulley is an "8 pound pulley", that is true for a STOCK 350 and at a specific rpm (I don't know the value). Your intake system has been opened up quite a bit from stock. Just this fact means you'll get less boost because of less restrictions. Approximately 2 pound less of boost sounds within reason to me. Question: You must have an awfully accurate boost gauge to know your system produces 5.6 pounds. I'm lucky if I can guess within a 1/2 pound!!

When I initially installed my D1SC, I started with a 4.00" pulley. It got me 8 pounds of boost @ 5,200 rpm. I then went with a 3.70" pulley, which yielded 10 pounds at the same rpm's. I'm currently using a 3.45" pulley and seeing 13-14 pounds @ 6,000 rpm. I would suggest you step down in pulley sizes one at a time. And yes, you'll have to get dynoed each time because at any given rpm, you'll be producing more boost -- it's not just at the top end. Currently, I have a spare 4.00" and 3.70" pulleys (with belts) that I'd like to sell but your system uses the 8-rib belt. Mine is one of the first D1SC third gen kits to be sold and mine has the 12-rib.

I'm planning on making a couple of changes in the near future. One is going to either a 3.25" or 3.10" pulley. I want to produce as much boost as I can with this blower. The second change is to custom fabricate the fourth gen twin high-flow intercooler setup and dumping my three-core. Because I live in an extremely hot climate, this change can be considered a necessity -- the three-core severely restricts air to the radiator and I'm having some cooling issues (or lack thereof) in temps over 100 degrees. The twin system mounts the IC's in the front corners and will not hinder airflow to the radiator.

 

yeah, I'm going through the same thing right now. 9# kit on my 305 and only seeing about 5.5-6#'s of boost. My dealer said they rate the kits at 6000 rpm on a stock 350. He also said that he thinks we could warranty exchange the bigger pulley for a smaller one at no charge. That might be something to look into.

Matt

 

do they have different crank pullies or should I make my own? what is your current crank pulley dia. so I can figure max impeller RPM on mine?(switching to 12 rib and smaller "more boost" pulleys soon)

 

ATI only makes 1 size crank pulley for third gen's. It is 7.65 inches. To figure impeller speed:

crank pulley dia. / blower pulley dia. * step up ratio * rpm

Step up for P series is 3.05
Step up for D series is 4.44
Step up for SC series is 4.1
Step up for F series is 5.0

I can't seem to find the max impeller rpm's, but they should be on ATI's web site. Hope this helps.

 

Tom,

My 12-rib crank pulley is 8.00" in diameter. I believe the 8-rib is slightly smaller. 92Z has the correct formula. The D1SC step-up ratio is 4.10 to 1. Based on these numbers and the following given blower pulley, impeller rpm at 6,000 engine rpm (my car's shift point) is:

4.25" = 46,306 rpm
4.00" = 49,200 rpm
3.70" = 53,189 rpm
3.45" = 57,043 rpm
3.25" = 60,554 rpm
3.10" = 63,484 rpm

These are the available 12-rib blower pullies. My D1SC has a redline of 65,000 rpm.

Willie

 

Thanks Willie, I got the peak 5.6 boost number from the dyno sheet. I'm going to email ATI and see if they'll do a warranty exchange for the 4.00 pulley and belt like Matt suggested. Then I'll take it back to the shop to do the install and get it dynoed again. Thanks for the help!!

 

Willie; Just curious, are you measuring the shoulders or the actual ribs? I believe ATI goes off the ribs for pulley sizes (crank and blower pullies). You may not be getting the blower rpm that you think, since a larger crank pulley size will spin the blower faster. Not to be ****, just curious (that even sounds funny).

 

Willie I have not seen the twin hi flows your talking about. But I have twin coolers from my ATI vette kit I was planning on using myself. Have not figured out the mounting and piping yet, but almost anything is better than the stock 3 core position. My coolers are single core units, not sure about the ones your talking about.

 

here's a pic of the twin intercooler setup on a 4 gen f-body



later
larry

 

Thanks! Right click