roots vs. centrifical blower

DarkoStoj · Jan 26, 2006

just curious whats better and why? My plans were to origionally run a 408w in the 68 then give it a healthy shot of nitrous, but I've been debating on running boost on the 408 instead. I want to drive the thing on the street, and it seems like a blower would make more sense, plus I want to run the factory a/c and p/s so that really limits a lot of my options when it comes to boost.

sambandit · Jan 26, 2006

Well, I have one car with a roots and one car with a centrifugal. 2 different animals for sure. The roots is brutal, the second you hit the pedal where the cent. has a but of a lag, but then start to pull real hard up top.

I would say it depends on how much power you plan on making with the blower. If alot of your power is going to be made because of the blower, not the engine, and you need that instant TQ hit, roots by far is the way to go.
On the other hand, if you have a decently built motor, and the blower is just kinda the icing on the cake, a cent. might be the best way to go. Remember too, a cent. takes less power to turn than a roots blower.

washMO66 · Jan 26, 2006

Sambandit is on it, depends on what you do the most and where you want your power. On the street I would say roots, instant torque right there when you need / want it at any RPM, the centr will make lots of HP but with more low RPM lag and will pull harder up top where the roots start to leave off........

In my opinion, roots for the majority street driver, centr for the track........

rbohm · Jan 26, 2006

the roots type and screw type blowers both build boost in a linear fashion. boost pressure in these types blowers in predictable and constant. double the rpm, double the boost.

a centrifugal blower builds boost much like a turbo does, double the rpm square the boost.

the biggest drawback with the centrifugal blower is that the impeller turns up some serious rpm, and you have to becareful not to overspeed the impeller and its bearings. the roots blower builds more heat, reducing efficiency.

DarkoStoj · Jan 26, 2006

sambandit said:
Well, I have one car with a roots and one car with a centrifugal. 2 different animals for sure. The roots is brutal, the second you hit the pedal where the cent. has a but of a lag, but then start to pull real hard up top.

I would say it depends on how much power you plan on making with the blower. If alot of your power is going to be made because of the blower, not the engine, and you need that instant TQ hit, roots by far is the way to go.
On the other hand, if you have a decently built motor, and the blower is just kinda the icing on the cake, a cent. might be the best way to go. Remember too, a cent. takes less power to turn than a roots blower.

the motor is going to be built nicely before I throw the blower on there. Cost really isn't an issue so I want to build it right. I was thinking of a C9 block, with a fully forged 408 stroker bottom end, AFR205cc heads, and maybe a small shot of spray in addition to the blower

C0V3R · Jan 27, 2006

Do you think youll even need a blower with a 408 + AFR heads? I've seen numbers in the 4-600hp range out of similar motors. I would have thought that adding a blower would just make you more likely to split the block.

mtbdoc · Jan 27, 2006

Actually a KB twin screw likely has better efficiency than a centrifugal. And there is a new generation of rotor design that will be even better.

These are NOT roots blowers...call them 'positive displacement' blowers.

I get the same question about how much power do you need. I'll likely add a little nitrous on top of my setup in the 66.

muddslide · Jan 27, 2006

I'm all for the Roots, I just finished mine on my 67. I have a few pics posted under the topic "My 347 powered by a 671". I have owned both a cent. and roots blower. I think there is nothing cooler than a 671 sticking out of your hood.

washMO66 · Jan 27, 2006

muddslide said:
I'm all for the Roots, I just finished mine on my 67. I have a few pics posted under the topic "My 347 powered by a 671". I have owned both a cent. and roots blower. I think there is nothing cooler than a 671 sticking out of your hood.

Was just checking out your sig. If that thing is put together right you going to need a lot more than 26X9 slick to get it down the track.

I had 26X9's on my 66 and it was at the edge of traction launching at 3000RPM running 3:70's with only around 500HP at the crank.

Your going to need a serious tub job......

DarkoStoj · Jan 27, 2006

muddslide said:
I'm all for the Roots, I just finished mine on my 67. I have a few pics posted under the topic "My 347 powered by a 671". I have owned both a cent. and roots blower. I think there is nothing cooler than a 671 sticking out of your hood.

where can you buy 671's or get more info on them? I have been looking around and haven't come across anything

washMO66 · Jan 27, 2006

BDS has been making them since 1969 and pretty much have them perfected.

Do a web search and you will find them......

DarkoStoj · Jan 27, 2006

washMO66 said:
BDS has been making them since 1969 and pretty much have them perfected.

Do a web search and you will find them......

yea, they seem like stout blowers. I wonder if I'm going to be crossing the threshold of just too much power here

180 Out · Jan 27, 2006

Also check out Weiand's web site. To compare the two, Blower Drive Service will set you up with everything you need (for a price of course). Weiand just supplies the raw materials, available through Jeg's, Summit, PAW, etc.

Too much power? Yeah, I think if you start with a decent 302, in the 300 to 350 hp range NA, any blower is going to get you into "too much" power pretty easily. At least the Roots' output is easy to control, by changing the driven pulley.

BlueMonster65 · Jan 27, 2006

Procharger

personally i'm a big fan of the centrifugal blower. its stealthy, more efficient and easier on the engine and of course i'm biased because thats what i put on my car. it really all depends on what you want to do. a cent blower or turbo will require a much more elaborate fuel system than a pos. displacement blower. you'll want to visit www.turbomustangs.com for more info on that. if you want rediculous horsepower that is impossible to control and want to maintain drivability than i'd go with a centrifugal blower or better yet a intercooled turbo with meth kit. if you want tire smoking torque, a large protrusion thru the hood and a car that constantly runs hot then go with a roots blower. the twin screw is nice but not easily set up for a carb.
when i added the cent. blower to my car i barely had any change in gas consumption unless i was under boost then it was astronomical. also i did change to a large becool radiator adapted from a 69 camaro because no matter what blower you use the stock cooling system will not be up to the task. on a 68 at least you can fit a good size radiator in there with out having to "modify" the radiator support.

DarkoStoj · Jan 27, 2006

BlueMonster65 said:
pif you want rediculous horsepower that is impossible to control and want to maintain drivability than i'd go with a centrifugal blower or better yet a intercooled turbo with meth kit. if you want tire smoking torque, a large protrusion thru the hood and a car that constantly runs hot then go with a roots blower.

yea, but I want rediculous horsepower that IS possible to control.

DarkoStoj · Jan 27, 2006

oh and here are some cool graphs I came across that compare boost between centrifical and roots

1st is the centrifical
2nd is roots
3rd is turbo

HHStang · Jan 27, 2006

I have an 800+ D1-X Procharged (centrifuge) Blow thru 460 in my 67. Love not having that metal sticking through my hood....

DarkoStoj · Jan 27, 2006

HHStang said:
I have an 800+ D1-X Procharged (centrifuge) Blow thru 460 in my 67. Love not having that metal sticking through my hood....

ok, now you're the person I want to be talking to. How is the driveability with that much power? Is traction even possible or is it just a joke?

latamud · Jan 28, 2006

HHStang said:
Love not having that metal sticking through my hood....

I agree. I have never used Roots myself. I've had a McCulloch, two Paxtons, and am working on a Vortech now. I have a good friend that put a 6-71 on top of a 408W in a 70 Mach1. After the intake, blower, carbs and scoop, that thing sits higher than the roof line. Streetable? Possibly. It has a mild blind spot. Race gas gets expensive. He started trailering the car, and he lives 10 miles from the track. Its a daily driver turned garage ornament.

I deleted a few opinions that didn't need to be there. I don't want to talk you out of it. As the saying goes, its your car, have fun.

ddonaca351 · Jan 28, 2006

Well I like all 3, but that being said...

if you have never ridden in a roots blown machine making 4-500 lb/ft at like 2500 rpm.... it has to be felt to be belived. That is where the "eye balls sucked out the back of your head" expression came from.

BDS (imho) makes excelent equipment. Modern rotor / case / bearing designs are all new BDS design / made. The old GMC designs of the 60s are no-more. The new BDS pieces have much better efficiency than those of years past. (teflon lined, twisted rotors, etc..) They also make a real nice injection set-up which looks just like an enderli, (al-la flopper) but with good driveability for the street.

A turbo will (imho) make better #s than either of the others, but it involves some added cost for the kit, and the exhaust and intercooler plumbing can be more complicated (not always, but usually).

Just an fyi... neither here nor there, most of the good running (TRUE street) motors that I have seen or read about, getting a 6-8/71 installed go from 5 or 600 to 7 or 800 with only 8-10lbs of boost.

Now thats not to say centrif's or turbos cant make those same numbers, (they usually make much better peak #s) but the roots or twin screw (kenbell) really shines at *street* rpms... 2000-4000.

But then you do have hood clearance to considder... and with it theft issues.

Good luck with whatever you decide.
Dave-

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