What size Roots?

Need some sage advice here.
I've been looking at used roots blowers. I was told to use something greater than a 8-71 on a 533 BBF.

10-71 and 12-71 are like "Hens Teeth" in the used market. Seems though picking up a used 14-71 Hi Helix isn't a problem though. My thinking is that with a 14-71, I wouldn't have to spin it as fast keeping intake temps down. I could be wrong though, hence this post. I understand that spinning a bigger pump is going to require more horsepower, but this shouldn't be a issue, right? This would be used on a lake boat hot rod using Kasse SCJ heads with bowl porting.

Also due to the longer case of the 14-71 would it make alignment of the drive pulley better, by reducing the length of the drive snout? Are there any advantages other than getting a little more for my bucks?

or should I bolt up a large case 8-71 and just call it a day..

How much power are you trying to make would be the big question?

jasonf wrote:How much power are you trying to make would be the big question?

Hey Jason,

I'm not looking to rotate the earth, but 700 and upwards. Anything over 800 would make me smile for this motor.
I can see where a 8-71 would generate some heat if spun up and held wide open for a mile or so.
A larger blower like an 14-71 I could keep the rotor speed down and generate less heat over the same distance.
But....

Is a 14-71 over kill? Or could I legacy it in for bigger or larger builds later on. Most folks say that a 8-71 will work, but it is almost at it's performance limits for a BBF?



Ideally I'd like to have a 10-71, but you can pickup a used freshly rebuilt 14-71 all day long for the price of a new 8-71.

I guess what I'm asking, is a 14-71 too big for a 533 sized engine. is this doable with good performance results or for some reason would end up being a bad idea. Could I tune the blower to the engines requirements?

I don't know about the bigger blowers but I have a friend that has built a few 521's with Blower Shop 8-71's and they easily make 900 hspr. These are street motors.

Going through exact same dilemma with very similar engine.
But it is in a car. If I can fit the 1471 I probably will.
From my understanding the size increases toward back of motor.
Unless you get one of those set back blowers.

ovakil wrote:Going through exact same dilemma with very similar engine.
But it is in a car. If I can fit the 1471 I probably will.
From my understanding the size increases toward back of motor.
Unless you get one of those set back blowers.

It's interesting to see another BBF guy with the same thoughts as I.

A lot of the 14-71's come with different openings as well. I've seen some with a small delta at the bottom or with a larger square opening machined at the bottom. Some say the smaller delta will build boost better at lower RPM, while the larger bottom opening will flow more at the top end of the RPM range.

After doing some homework, you are right about the expansion of the blower volume. It's all about the rear of the blower. They extend the case with a bolt on extension and longer rotors. If you do jump at a 14-71 make sure the rotors are one piece and not two spliced together. I was told to be aware of this practice of lengthening the the rotors for a longer case.

A 8-71 is looking better the more I learn about working with a roots setup.

I just picked up a 10/71, BDS. Just noticed the opening on the base is slightly longer than 671.
Will have to machine out manifold a bit.

My Blower Shop 1071 is pretty much maxed out at 56% OD
on my 645ci BBF so I'm looking to upgrade to a 1471. PM or
or email me if you are interested in my 1071. Its a polished
all billet full race unit. Freshly serviced by SSI about 10
passes ago.

Rich
rkracing1@aol.com