Roots Blowers Displacement

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Roots Blowers Displacement

Post  511Fox on April 10th 2010, 10:17 am

I know a 6-71 displaces 411 cid & an 8-71 around 436.29.

Hey guys anyone know the Displacement of a 10&12&14-71 Roots Blower Question

Anyone have the old Weiand technical data sheet on this Question

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Re: Roots Blowers Displacement

Post  res0rli9 on April 10th 2010, 3:48 pm

I would like to know this to, ive got a 584 and 614 to put one on affraid

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Re: Roots Blowers Displacement

Post  DaveMcLain on April 15th 2010, 5:18 pm

According to your numbers 25.29cid per size increase above a 671. The big jump is from a 4 to a 6 but then after that every increment is the same amount of size increase. So a 1471 is 4 sizes larger than a 671 so take 4x 25.29 and you get an additional 101.16cid.

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Re: Roots Blowers Displacement

Post  DanH on April 16th 2010, 7:04 pm

I always thought 71 was cubes for 1 cyl. so 4x71 would feeda 264 cid engine & a 10x71 would feed a 710 cid engine

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Re: Roots Blowers Displacement

Post  DaveMcLain on April 16th 2010, 11:59 pm

While 671 stands for 6 cylinders that displace 71 cubic inches the blower is not that size exactly. It doesn't necessarily run at the same speed as the engine which being a 2 cycle would in theory intake and exhaust it's displacement with every rotation of the crankshaft.

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Re: Roots Blowers Displacement

Post  RapidRuss on April 18th 2010, 9:05 pm

Dave I'll admit I'am blower dummy..I have often thought about how the ratio works..But havent had anyone with any knowledge expain in to me.. I was always under the impression...that say a 6-71 Blower would handle an air exchange of 426 ci.. divide that by 2 and thats 213ci for filling and exhaust of the cylinder ? Boy am I learning different from an old drag racers tale...
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Re: Roots Blowers Displacement

Post  RapidRuss on April 18th 2010, 9:21 pm

But then isnt there always the smaller hubs to put on the blower drive to make more boost ? making the smaller blower more efficient ? Thus pumping out more charge per revelution ?
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What I Was Told

Post  511Fox on April 19th 2010, 11:37 am

A source on the other site gave me the following chart.

6-71 is 411
8-71 is 436
10-71 is 469
12-71 is 497
14-71 is 522

A 10-71 looks like a good choice for a street/ strip engine of 472-500+ CID.

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Re: Roots Blowers Displacement

Post  DaveMcLain on April 19th 2010, 12:47 pm

It's probably too big for a street 475 incher. You have to remember that a four cycle engine only pulls in 1/2 of it's displacement per revolution. An 871 just one to one or slightly overdriven would probably be a better choice.

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Re: Roots Blowers Displacement

Post  Frank Kramer on April 19th 2010, 2:49 pm

DanH wrote:I always thought 71 was cubes for 1 cyl. so 4x71 would feeda 264 cid engine & a 10x71 would feed a 710 cid engine

Think that is not correct from what I know about it.

The number 71 is reffering to the 71 series detroit engines that the superchargers were used on. The first number is for the number of cilinders on each engine in these series.

4-71 is a 4 cilinder
6-71 is a 6 cilinder
8-71 is a 8 cilnder
and so on....
each step in size is 1" more rotorlenght

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Re: Roots Blowers Displacement

Post  blown86hallet on April 19th 2010, 3:12 pm

6-71 = 6 x 71 = 426 cui
8-71 = 8 x 71 = 568 cui
and so on.

If you spin the 6-71 up like you were talking to make more boost, you will make way to much heat! Run a larger blower, use the VOLUME it will produce and keep the temps down...
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Re: Roots Blowers Displacement

Post  DanH on April 20th 2010, 4:04 pm

blown86hallet wrote:6-71 = 6 x 71 = 426 cui
8-71 = 8 x 71 = 568 cui
and so on.

If you spin the 6-71 up like you were talking to make more boost, you will make way to much heat! Run a larger blower, use the VOLUME it will produce and keep the temps down...
thats how i thought it worked

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Re: Roots Blowers Displacement

Post  DaveMcLain on April 20th 2010, 4:39 pm

6-71 = 6 x 71 = 426 cui
8-71 = 8 x 71 = 568 cui
Is how it works for the Detroit Diesel ENGINE displacement but it's NOT how it works with the blower displacement. For instance a 1271 is NOT 2X a 671 blower even though it would be engine displacement wise.

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more on blower size

Post  blown473 on May 24th 2010, 9:01 pm

Keep in mind the bigger the blower the more power it eats to turn it, a 871 is plenty for most, a 1071 for the 575 and up motors. Too small a blower and you have to spin it so fast it heats the air, so unless you have a big intercooler (think Lightining/Shelby/Cobra) you must size carefully.

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Re: Roots Blowers Displacement

Post  jones on May 27th 2010, 12:43 pm

DaveMcLain wrote:6-71 = 6 x 71 = 426 cui
8-71 = 8 x 71 = 568 cui
Is how it works for the Detroit Diesel ENGINE displacement but it's NOT how it works with the blower displacement. For instance a 1271 is NOT 2X a 671 blower even though it would be engine displacement wise.

I think Dave is assuming everyone remembers that the old Detroit diesels where 2 strokes not 4 strokes. Ole scream'n demons!

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Re: Roots Blowers Displacement

Post  res0rli9 on May 28th 2010, 1:11 am

jones wrote:
DaveMcLain wrote:6-71 = 6 x 71 = 426 cui
8-71 = 8 x 71 = 568 cui
Is how it works for the Detroit Diesel ENGINE displacement but it's NOT how it works with the blower displacement. For instance a 1271 is NOT 2X a 671 blower even though it would be engine displacement wise.

I think Dave is assuming everyone remembers that the old Detroit diesels where 2 strokes not 4 strokes. Ole scream'n demons!

I remember them days, I worked in the parts department for western branch diesel then, they built and sold Detroit Diesel's.
Dam im an old fart
Sad

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