Technical Where is a reliable place to buy a roots blower?

Didn't mean to imply that it was a "limit", only that it was designed for a specific volume of air to be moved with each rotation. An 8:71 moves even more air per revolution. The diesel was smaller and turned much slower (1800 rpm?)
If someone is going to turn their engine over 3 times that rpm (1800), they will be turning the blower at a speed much greater than it was originally designed for depending on whether they underdrive or overdrive it. I think with a larger engine, an 8:71 is going to provide a better result with less stress and heat.........that doesn't mean that a 6:71 cannot be made to work well.

As I mentioned earlier, I was looking for a similar result as the OP with appx 5 lbs of boost. I also told BDS that was my goal.

I haven't seen anything that says too low rpms will generate more heat. All roots blowers operate over a wide range of rpms and my understanding is that heat generally becomes more problematic at higher rpms. On a street machine the vast majority of driving will be at a lower rpm and I haven't heard anyone having problems. I guess you could say the same thing when comparing the 4:71 to the 6:71......that the 4:71 would be more efficient than a 6:71 when used on a 350 cube engine.........yet we see 6:71s and even 8:71s installed on 350s and working just fine.

Loose clearance helps prevent the lobes from growing enough when they become hotter that they rub the blower case. Loose clearances also allow more buffeting of the air inside the case which causes temperatures to rise. Its a balancing act to find how much (how little) clearance you need to never rub the case and gain reasonably efficient air management. Lot of old cases out there that are useless because someone figured wrong. I'd rather go with a proven set-up that some experienced pro has developed than to experiment ($$$) and ruin a blower and maybe my engine as well. Someone just wanting the look of a blower and not really much power gain could loosen one up and never have any real problems.

 

Some of your information is correct ,some is not,
A loose set up Does not just mean Actual rotor to rotor clearance or rotor to case clearance.
Tight & Loose ( sealing / air leakage) also applies to stripping used & how many used per lobe, Some On a fresh Stripping set up , Have to mount on a a Table/ext take a 1/2 Breaker Bar to rotate & spray WD while rotating
Then Requires a high horsepower starter To start a engine when installed on engine to turn over,
This is not a Blower to run on street , even a 6-71 set up this tight will generate a lot of high air temp & fruition heat below 3,000 engine RPMs & witch fuel used , & how its enters the case ,,

My first hands on & learning started late teens & learning late 80s from BDS /Littlefield , Then more understanding information with use of data logging,
Under driving a 8-71 blower to much with No strips can increase temps under 3,000
Most here (98%) a 4-71 to 6-71 for street use is all required ,,does Not need to be tricked out ,
Drive set ups, I all ways use 8mm to 14
8mm even on 144s & hair dryer blowers

 

So @bolo_lovain . . . . . Did you get a blower yet?

 

I had a 6-71 off a truck rebuilt 20 years ago by BDS and have never had any issues with it.... They don't rebuild blowers anymore but they still sell new ones....I prefer three lobe rotors....Weiand has discontinued there blowers and parts....

 

I respect your experience and what you are saying, but I think we just see things somewhat differently. There is a wide variation in the engines people install blowers on, and results are going to vary as well. You mentioned the strips that get put on the lobes for sealing. Thats pretty much a "race only option" and the strips have to be replaced regularly without too many races on them. Doubt anyone would use them on the street.

Looking at the blower only. The blower of choice will either be overdriven or underdriven. If you run a large engine, on the street, most people are going to figure maybe 6500 rpms or so as the limit. If a blower is overdriven, it going to be turning an even higher rpm and dealing with centrifugal forces as well as higher friction and belt speed.
The larger blower can be underdriven and belt speed as well as lobe speed are reduced.

On a street driven machine, I would prefer to use the option that provides the wanted power without pushing it to a higher stress limit than needed. Granted, on the street 98% of use won't be at high rpms. So the question then becomes whether the larger blower generates more heat at a lower rpm (underdriven) than the smaller blower at a continuous overdriven rpm.

If you use that logic, would someone building a smaller (350) engine not fare better using a 4:71 and overdriving it instead of a 6:71 and underdriving it? The 6:71 works well on many 350 engines, so it seems logical (IMHO) that when increasing the capacity (450+) of the base engine, going to a larger blower seems logical.

Again, I respect your opinion and your experience but we just have to agree to disagree on that one point.

The OP should realize that experiences and opinions vary on many things on the Hamb, and check further before deciding which choice is best for him.

 

There's plenty guys running stripped blowers on the street, including me



When talking to TBS it wasn't a big deal, also talking to pro mod champ Mike Janis at Jan-Cen, who manufacture their own line of blowers, he said the strips would self clearance if they heated up and got to tight. Again, didn't seemed to worried about it.
My old blower was non stripped but you can see that it still moves air just fine.

 

I agree with your approach, but Swade is right; you can run a stripped blower on the street. They just self clearance in time, but still provide a better seal than a regular clearanced blower. But yeah, a big slower turning blower generates les heat than the other way around. The problem with roots blowers is they heat the crap out of the air. Less spinning=less heat.

 

One of my set ups is a striped Rotors , when fresh
It was tight unable to turn by hand , over the years I use on DD & Strip , Now its a loose set up I can fling spin by hand ,turn a few times & stops ,
DD , temp stays around 130 deg @ 2,500-2,800 engine speed , If I switch to 8-71 & drop pulley to equal same Psi Intake temp ( Manifold temp) is higher @'same cruise Rpms ,,, Not moving air fast enough.' I can play with fuel to cool Now richer mix .
Your DD spends more time @ 1,000-3,000 engine Rpms , Wide Open thats something different on its own ( temps)
Data logging will tell you whats going on /happening , I know data logging does not have a place on HAMB but its a TOOL ,
If you want You can data log your Rod , stretch,force Piston ,Ext End less now !!

 

I had not heard of anyone running strips on street engines and letting them self clearance, but that does seem to make sense. The original idea was to use strips on race engines and change them often. The friction from the strips often made it difficult for an engine to even crank over. I can see that installing strips and letting them self clearance until they were viable for street use could be a good idea. I don't know if they hold up for long term use or continue to wear. I also don't know if they scratch the inner case until worn in.
I used to work at a government repair facility as a machinist. We had some parts that had to be assembled by "lapping" the components to each other. That provided the best possible fit for components. Its essentially the same process with the strips. So I stand corrected about the ability to run strips on street blowers, but I would guess that its not done by most people. Kind of makes me wonder why blower manufacturers don't push adding the strips on all of their blowers. It would seem to be no more difficult to set initial clearance with strips and then if lobes ever expand too much.....they would just wear a little more instead of a lobe ruining a case.
Thanks for the info, always glad to learn something new.

 

I think the little B&M's used strips? I only went that route on a 14-71 because a used 14-71 with strips is so much cheaper than a new 6-71 of any kind, (and yes my engine could handle a 14),and when I told Littlefield what I wanted to use it for, they said, "no problem, send it to us and we'll set it up for your application." When I got it back, it was sorta tight to turn, but not like a fresh drag blower. After a few hundred miles, it turned easily. It makes good boost, but not as aggressive at the hit. I probably have about 800 miles on it so far. I know, not much, but so far, so good.

 

Sounds &" More likely" underdrived to much for that size of blower ,
What is the percentage of drive?
What Fuel?
Cid ?
What method are you using to add Fuel?
Curious to know what your cruise rpm's air temp is
Case & under Rotors ,
Im sure if you where to data log & monitor you have erratic unbalances ,
A blower that big & not enough drive ,
(( Your Stumble/hesitation boost lag))
If Boost Related
I would increase drive speed & use a controlled boot leak ,,

If you want to improve on your combo

 

Can you post the page with 4:71 and 6:71 charts? I noticed that the 8:71 doesn't show anything for less than 14 lbs on a 350 but does show 6 lbs with a 450. Thats at 1:1.
Looks kinda like a transitional level for making a decision.

 

These #s are for Average stockish &stage 1,
Stage 2 -up are more than chart .
These is from pre 2000, average
guidelines, , I think if your someone playing with / using You will end up with more then One set of pulleys
( 8mm pulley , had one of pretty much 43-70 #s )

 

Head flow can also dictate what your boost gauge shows, they could act like a bottleneck, so those charts are good for ballpark starting points but definitely not anything written in stone.
I think I've got a half dozen pulleys and a couple belts, a boost gauge that records highest boost level is definitely a must, if you don't have a fancy data logger.

 

Not sure what makes you think the blower is too big, it's a 489 inch Gen 2 Hemi with a good set of Dart heads.
I'm at 3% Overdrive making about 15 lbs. boost on E85 and a pair of C&S 1100 Dominators. Can't remember the cam duration. but it's only .650" lift. It made 1128 HP at 7800 RPM and is very streetable. When I said it wasn't as aggressive at the hit, what I meant was, not as aggressive as a typical tight stripped big blower. It still will annihilate the tires at 70 on the road. It's not a drag car, it's a Land Speed deal. I'm not looking to hop it up any, it still holds the record in its class. I have some data logging onboard, but not induction temps. The engine is currently out of the car and in pieces because one of my Crower Maximus lifters stopped rolling, and my pan is full of metal. I'm busy with another project at the moment, so the money faucet on the Hemi is currently "off".

 

Just picked up these two today.
671 that looks like it has been ran on a gas engine and a V series 871.

 

You where Vague on the details of your set up, It sounded like On pump 92-94 gas DD & Strip ,
You are able to get away with things because of Fuel type & other factors .
Curious to know intake temp just cruising Highway speed
On E85 , & afr @ cruise, ( 85 not a common fuel on pump where im @, Not to far on 10 gal supply not getting down pass having pick up issues)
I can relate to Lifters , I just pulled a Jesel lifters & valve train engine from Street use fear of failure ,
I can relate to High speeds but in sec's (6:40s -50s 1/4) close to 20years ago ,Not Bonneville or other land speed , I recently stumbled up on a thread here for land speed build ,
""Salt Bitch "" Do not know about classes
I like the engineering and build / fabrication, Im interested and thinking
maybe ?

 

All I can say about flirting with Land Speed Racing is, Good Luck! It's highly addictive....I usta drag race, had a 10 second street Vega in the early 90's. I thought this Bonneville thing is easy, all ya gotta do is go straight and keep your foot in it. Oh, and re-gear. And less converter. And maybe a smaller cam. And maybe figure out some stuff about aerodynamics. And jeez, their rules are cryptic....why all this safety stuff? yeah this will be easy. Yeah.
But don't let that discourage you. There's a place for just about every wheel driven contraption conceivable, I even saw a rubber band powered dragster there. If you get the chance, go to an event.