I have a few questions regarding blower speed that’s been on my mine lately.
I know the basics that Crank pulley/Blower pulley * internal step up ratio * Max RPM = Impeller Speed.

Someone on this board built an Excel sheet that calculated blower speed (just a fast way of doing it) and I came up with this. I’ll use my pulley combination for example and list blower speed at certain Motor RPM levels.

D1SC model 7.65 Crank pulley, 3.2 Blower pulley.
2,000---3,000---4,000---5,000---6,000-------Motor RPM
19,603--29,405--39,206--58,809--60,770------Blower RPM

Max rev 6300 = 61,750 out of 62,000

Now let’s try a different combo of pulleys using the same blower model
D1SC model 7.65 Crank pulley, 3.7 blower pulley.
2,000---3,000---4,000---5,000---6,000-------Motor RPM
16,964--25,431--33,908--42,385--50,862------Blower RPM

Max rev 7200 = 61,882 out of 62,000


Notice how much harder the blower is working with the 3.2 combo in the lower RPM’s opposed to the 3.7. As long as belt slippage is not a problem I would think the 3.2 combo would be a lot quicker than the 3.7 combo even though they are both max revving there Blowers?? What do you guys think?? Reason is that I have the first pulley combo on my car with a 383 and I believe even with the centri blower its going to be a TQ monster and I hope for boost to come on early.

Ok now let’s look at the INTERNAL STEP UP RATIO and its effect of blower speed.
Let’s retake the pulley combo.

D1SC model 7.65 Crank pulley, 3.2 Blower pulley.
2,000---3,000---4,000---5,000---6,000-------Motor RPM
19,603--29,405--39,206--58,809--60,770------Blower RPM

Max rev 6300 = 61,750 out of 62,000

F1A model 7.65 Crank pulley, 3.2 Blower pulley.
2,000---3,000---4,000---5,000---5,700---6,000-------Motor RPM
25,819--38,728--51,638--64,547--73,583--OVER reved---Blower RPM

Max rev 5,700 = 73,583 out of 74,000

Ok the D1SC has a internal step up ratio of 4.10 and the F1A has a internal step up ratio of a 5.40, but it seems that the F1A model came on stronger earlier than the D1SC did????? I was under the impression that with the larger Internal step up ratio the boost would be lazier in the lower RPM levels and come on stronger in the upper RPMS??? That doesn’t look like the case here??

Here is a Good question at what Blower speed does a procharger model start making boost?? Around 20,000 RPMS????

 

I highly doubt you can run a 8rib on a f1a with a 3.2 pulley, we have belt issues with a 3.90 (ati bracket).

The impellers are diffrent on the f1 vs the d1 so its sort of a apples to oranges. The efficency map is entirely diffrent. Even though there both spinning 20k or so, the f1a looks like it wants to be spun up top due to the 74k rating.

Your motor might make good torque if you have the cam set up right, but a centri is definatly not known for mega torque, a positive displacement or a turbo is, this is due to the boost during the midrange.

 

I agree with you that a 3.2 would cause crazy slippage on a F1A, but lets put that to the side and just say it could be done. What would be the pros of reving the blower in a smaller RPM range and making the boost come in earlier???


With my particular combo I have the SDCE tensioner with a mild 224/230 duration camshaft with a tighter than normal lobe seperation for a typical blower application. My thought on spinning the blower harder in the lower rpms would equal a better midrange IMO.

 

It will make boost sooner with more rpms, so it should make a gain in tq.

 

I have no idea about this stuff but I think your blower RPM for 5k engine rpm is off by 10k. Not that it matters just adding my pathetic 2¢. GL

John

 

I looked at everything and the math looks correct, not sure what your referring too??