1 blower, 2 blowers. Let's Compaire.

[PSE SVT]

Nice write-up. Only thing I'm confused about is the blower RPM and associated low flow you're limiting the calculations to; especially giving the twin blower arrangement an extra 4K RPM to work with. The twin screws are typically spun much harder than 11K without crossing the max threshold outlined by the manufacturer. KB and Whipple typically limit their twin screws to a conservative 18,000RPM. Many folks run them into the lower 20s with no issue. The biggest flow restriction for the large (2.8L/3.4L) PD blowers is getting an inlet large enough. The new KB Mammoth and the 3.4L revised inlet look to finally address the problem. Of course, they come at a cost. These PD blowers put out much more than 1200CFM when spun within their efficiency.

The 3.4L is getting ready to crack the 8s@150+ in an SRA/auto Cobra. That's blower-only, with no spray. Hard to argue with simplicity that works.

There is nothing bad about running a single 3.4 or a 2.8. The numbers I posted indicate that Lysholm has set a maximum RPM for the 3.3 because the blower becomes very inefficient at RPM's about 11K. Also, just because a bearing has a rating of 18K means nothing. The 18K rating is only in a perfect environment. Angular load and heat will drop any bearing rating to its knees. The gears in a twin screw are helical style, so that means during acceleration and deceleration they are continuously trying to pull apart, putting a tremendous load and heat on the bearings. To prevent this, a match set of dual angular contact bearings are required at $325 per set. Because of this great cost, these bearings are not used. So when you do take you’re 3.4 to 18K and it blows up or fries the gears, do you really think that you will be able to return it for a refund, or get it replaced for free? Sure it will work, but only for a short time. I have piles of over spun blowers to prove it.
The max RPM limit for the 1.6 Lysholm is posted at 15K. Yes, you can spin it at 18, but it’s life can be shortened and the adiabatic efficiency goes South. The twin superchargers will supply a tremendous amount of air keeping the adiabatic efficiency in a reasonable 61-64%

Would I ever do this again? NO! This was a dream that I have had that I couldn’t get out of my head. I knew I was capable of engineering it, so I just did it. I checked the numbers and if twins were worse I would not have done it. I was going to compound a turbo feeding into the 2.2 that I had, but why would the owner of a supercharger company, be messing around with a turbo. I ran twins for the cool factor.

 

[04MystiCobra]

So how much is it?

 

[WDW MKR]

The twin screws haven't shown to blow up after a short time at 18K blower rpm. Many have run for thousands of miles with the pulleys ratios needed for such blower speed. That blower speed is only seen at the upper end of the rev range in each gear. Dustin at whipple stands behind his products and certainly wouldn't walk away from a customer that ran the blower at the speed deemed ok by him. Same goes for KB.

There are land speed records set with these blowers running WOT in that range for miles at a time. There are road course cars running blower speeds much higher than the referenced 11K. Regardless, you have an awesome setup and i'm glad you shared the details with us. It's quite an accomplishment and you obviously know what you're doing.