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Discussion Starter · #1 ·
I've read a lot about blown BB's on the search. But I'll beat this dead horse somemore..:D I already have a T-ram on a 327 (67 Malibu) and a hole in the hood and the wow factor now. Over the winter I want to put a BB in with a blower and more yes more show than anything. What is the setup for you guys that have this now and what would you change? What are the big differences with the Roots/BDS/others ect? Cam, Stall setup? if any?
 

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6-71
get a cam to match
you are laying the easy ground work.. you want to have fun.. be seen and that is indeed where it is at for a blower.
Once you start thinking performance.....and hp #'s you will spend mad money.
Enjoy a nice simple set up. AND keep it SIMPLE. It can be done with a blower.
 

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Thanks, Yep I want to keep it simple. What is underdrive/overdrive? Percentage boost to go with?

Underdrive/overdrive and also 1:1 all relate to the blower drive ratio. Simply stated, if the blower turns faster than engine rpms, it is overdriven; if it turns less than engine rpms, it is underdriven; if it turns the same as engine rpms, it is a 1:1 ratio.

Overdriven makes more boost and more heat.
Underdriven makes less boost and less heat, typically recommended for street blowers.
1:1 is inbetween.

This is the most common reason to go as big as you can afford when it comes to roots blowers. For example, if you have two blowers on identical engines making the same boost but one blower is a 6-71 and the other is a 10-71, the 10-71 will create less heat because it is spinning at lower rpms when compared to the 6-71.
 

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If you're going to do it you might as well do it right. The cost won't be much different, either way it's expensive. Judging from the original post, you need to do a little research and reading before you drop a dime on any parts. The other option is to buy an engine already done, but you will still need to tune it.

The very best first purchase I can suggest is to buy the book called "Street Supercharging" by S/A Designs. This will give you a better understanding of exactly what's going on and a foundation to build on. You will still have questions, but the basics will be covered )like blower types, drive ratios, compression, cams, pistons, etc...)

By the way a BDS blower is a "roots" blower. All the lobed rotor blowers are roots blowers (142, 172, 174,192, 250, 4-71, 6-71, 8-71, 10-71, etc..).
 

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An 8-71 is the best chioce for a street bound SB. or BB. you will gain more hp. from 17% under to 17 over, than you will at any other setting.

When we first started racing with the 540, we set the blower @ 17 under. The car ran 4.90's with a 4.56 gear in the 1/8th. After breaking the gearset and a few planitaries, we went to a 4.10 gear and the car picked up to 4.80's. Still with the 8, set @ 17 under. The 1st. time we set it up @ 17 over the car went into the 4.60's. It never went faster than a 4.40 with the 8-71, spinning it 47 over, and 3.89 gears.
The next step was a 14-71, then a 14-71 retro, and a 14-71 High Helix, in which (the rotors have twist, kinda like a screw) and all the air escapes through a hole in the back of the blower about the size of your fist. All the other blowers have two holes that travel the entire length of the case,along the intake.
That's what it took to run 4.0'[email protected] 180mph.
To make a long story, short, an 8-71 is the best choice for a roots type supercharger.
Make sure you order it with 8mm. pulleys, too. Because, you will be very limited with the 1/2" pitch set up. You can turn an 8mm. set up, up or down 57%, and the belt is stronger, too.
 

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There's two ways to go about building a blown motor. Just like B-Man said, you can keep it simple, by building a mild BB, with a underdriven 6-71, and cruz it around, and have fun with it (which will still make good power). Or you can spend 10K plus on something, with a 10-71, dual dominators and all the good parts. But I'll tell you one thing that will happen for sure. Once you stick that blower on that BB you'll be hooked. There's nothing like the sound of a roots blower coming down the street. My first blown BBC was a 468, 6-71 with 2 850's. Now it's a 496,10-71, with 2 1050's. which ever way you go, There's nothing cooler, than a blower sticking out of the hood of a chevelle...:thumbsup:

here's mine


 

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Here's a blown 489 I did for a customer's 68 Elky.






And here's what it did: 9.2 lbs boost, 33* timing, 853.6hp, 730.5 lbs/ft @ 5000 with a 50/50 mix of 110 and 91.
With straight 91 oct., 28* timing, 6.5 lbs boost, it made 789.5hp 6400rpm, 686.5 lbs/ft @ 5000. Probably would have made right at 800 by 6500rpm.

489/8-71, Canfield 310's as cast, BDS w/ a pair of AED 850's and a Straub HR blower grind. Power still going up considerably.:thumbsup:

 

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building a 489 w6-71 and 8.5 cr wow factor is there. the other cost u have to look at is going to be blower carbs, linkage fuel lines and the bottom end to handle the extra power. the blower price is just the start
 

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I've read a lot about blown BB's on the search. But I'll beat this dead horse somemore..:D I already have a T-ram on a 327 (67 Malibu) and a hole in the hood and the wow factor now. Over the winter I want to put a BB in with a blower and more yes more show than anything. What is the setup for you guys that have this now and what would you change? What are the big differences with the Roots/BDS/others ect? Cam, Stall setup? if any?
Dave.I have found that roots type blowers do a better job of pushing vs pulling.They flat out hate carb restriction and require a ton of potential carb cfm vs a n/a combo.Valve timing events differ also..the blower does a nice job of packing the cylinders full and is less dependent on the exhaust scavenging/overlap effect brought on by lumpy cams with tight lsa,s.
Here is where i am going for your consideration..at idle speed..you will have a cam that suits your needs and a low static compression engine with a large by huge plenum area and dual 4bbl.s miles away from the backside of your intake valve.Roots blowers offer up insta torque..but still require a stall convertor that falls inline with cams @ .050" and carbs that can transition quickly to the main ckt.Get this wrong..and you will open the pop off valve with any type of throttle input at low speed with a daily driver and street gears with a tight convertor.
 

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Discussion Starter · #12 ·
Thanks guys! lots to digest there! I ordered a DVD on blowers and setup of blowers. Yeah if I could find one already set up would be nice and go from there. I dont know, Maybe a 454 with a pair of 600's on a T-ram. Be cheaper for sure. Know a guy that had one on a 427. Gobbs of power even on the low end. But thanks for the info and Matattack68 holy crap! Nice!!
 
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