usa1racing

Planning on building a carbureted boost motor wiht eihter a roots blower or a centrifgual blower. What are the pro's and con's of each? Hood clearance, emissions, are not issues. Difference in power numbers and cost are. Relative to cost and complexity, what setup makes more power? Any other ideas would be greatly appreciated.

B4Ctom1

why not a turbo?

usa1racing

too complicated, too quiet, too much custom fab work, takes up too much engine bay room, I'm assuming, costs more?

B4Ctom1

sorry I was just kidding and knew I would be coming back to give you a more serious answer. if you can work out the hood clearance issues, I would highly recommend the simplicity and low costs for carburated cars to go centrifugal. you could probably buy the cowl hood with the saved money.

usa1racing

I like the thought of stuffing it all under a small cowl hood, but then there's always the look of an 8-71 sticking through the hood. This will be a hot street/strip motor that I will probably only drive on the weekends, and i'm aiming for the 10 second range and probably about 650 flywheel horsepower. Oh, this has all got to be on a 10 inch tire because I don't want to cut the car. It's in excellent shape, no rust at all (came from Florida). Anyway, I plan to run a 4 speed, or will a T56 hold up to this? Does all of this sound possible? I hope all these specifics will garner some informed opinions. B4C, thanks for your help. Anyone else want to add anythign?

usa1racing

Oh, this all has to run on pump gas

B4Ctom1

I figured on something larger than the 142-144 more like the 174

usa1racing

Looked at the smaller roots-style superchargers. Wasn't really impressed with them. If I do go with a roots blower, I'm going with at least 6-71. If you're gonna go, go big, right? What brands of centrifugal superchargers does everyone recommend? Dollar for dollar, what's going to give me the best all around power for the intended use?

Apeiron

You mean roots, don't you?

B4Ctom1

yes sorry

unknown_host

iTrader: (1)

A centrigugal carb setup may not even require you to get a different hood. www.procharger.com the D1SC would be good, intercooling and several other factors make centrifugal superior to roots...

RoadRacer

Centrifugal blowers are FAR more efficient than roots-type. They may not "look" as cool sticking up through the hood, but if you plan on driving it on the street at all and want to make decent power on pump gas, then forget the roots.

Just my experience . . . have fun!

Damon

Neither the 142 or the 174 will get you to 650 HP. I can tell you from personal expereince that the little 142 is done at about 500 HP so I would estimate the 174 would be finised somewhere around 600. They just can't move enough air even when spun to their maximum safe RPM with overdrive pulleys.

You'll need to look at a 71-series blower or a hefty centrifugal setup for that kinda HP.

A roots blower has the advantage of making max boost from the instant the pedal hits the carpet and it's easier to tune a carb for this since the carb never sees boost. You WILL have carbs sticking through the hood or a BIG bubble in the hood to clear everything. With a big cam the idle can get kinda unstable, too.

A centrifugal is easier to package under the hood and is more efficient. It's a b1tch to tune a carb for a blow-through setup, however, and max boost isn't achieved until near redline.

demonkey36

i'm not really what you'd call "well-educated" in the world of blowers. what do the numbers in 6-71, 8-71, 10-71, etc. mean?

demonkey36

never mind....i found out!

Kingtal0n

I dont consider myself an expert but I will add a few things, but first lets do some math:

6-71 stands for 6 cylinders, 71 cubic inches each. That means 1 revolution of a 6-71 blower technicaly pushes / produces 426 Cubes of air. if you consider that a small block chevy 350 can only eat (350 \ 2) 175 cubes of air in 1 revolution, 426 cubes of air is ALOT more than it would like, and you have pressure / boost / torque as the result. Typically, a 6-71 blower can produce WAY more boost than you will ever even use on a small block 350, and if you DO use that much boost, it WONT be on pump gas!

Now take a STREETABLE / PUMP GAS version of the 6-71. Typically this means a 12% underdrive, with 8-10 PSI of boost on a well-flowing setup, this should produce between 550-650 horsepower. thats IF and only IF you have matched cam / heads / pistons etc.. for this combination. Adding a 6-71 to a stock 220 Horsepower 350 will not yield 550 horsepower. Adding a 6-71 to a well built 420 horsepower small block chevy 350 will bring your power up about 150-200 horse.

if you consider that the 6-71 can make so much more boost than the engine would even think of using, you can also consider the fact your wasting a ton of space up there on top of the engine. By using a SMALLER blower more TONED down to the level of a 350~~ chevy, you can save yourself space and produce the same amount of boost. More math:
6-71 With 12% underdrive: (6*71=426*12%=51.. 426-51=<b>375</b> cubes) thats forcing 375 cubes of air into an area that only desires 175, so we are produceing 275 cubes of etra air making 8-10 PSI of boost.
Now take a Smaller blower, the 177 Weiand. Its typically over-driven about 120% as opposed to the 6-71 underdriven 12% for small block chevys. (177 * 120%= 212 + 177 = <b>389</b>)
thats 389 Cubes of air, when compared to the 6-71's 375, you can see the <b>177 Weiand actually out-produces the 6-71</b> on a street driven Small block chevy 350 with pump gas.
nd you have to remember a few more <b>facts</b> that work for a smaller blower, with its way-overdriven setup there is less time for air to leak back out under boost. the 6-71 at lower rpms gives ample opportunity for leakage, especially after a few thousand miles of use. And to top it all off, a 177 weiand will fit underneath a 2" cowl hood on a camaro if a 2.6" X 14 dropbase air cleaner is used, and before you say "thats not big enough" I will add that if you add a K&N Extreme Lid to the top, you have a perfect induction setup for a blower, that no one can see or hear until its too late.
see a few more pics at: Http://www.geocities.com/kingtaling

83 Crossfire TA

iTrader: (2)

Yea, I’ll agree with that, mostly. The problem is that you run into 2 inefficiencies:
- it takes more power to spin a blower faster, especially as you start getting near the design limits of the blower
- your pumping losses get greater resulting in less efficiency for the same airflow, meaning much more heat. Less air density and more prone to detonation.

Both of these will kill the power produced at the crank for the same boost, so effectively you’ll have to spin it proportionately a little faster to make the same power.

Lastly, I’ve said it before, power produced is up to the mass of the air (with the correct amount of fuel added) that is forced into the engine. Total mass of air will roughly follow the power produced, so it doesn’t make that big a difference how you get the air in the engine, but the amount that you get in it.

B4Ctom1

that is a perfect examle of what I'm talkin about

usa1racing

I've been reading and it sounds like it's harder to tune a blow through carb system than a roots system, as you guys have stated. I don't want to convert to EFI (TPI) because of the greater expense. With all this in mind, am I taking a step in the right direction toward 10 second timeslips?

usa1racing

King Talon, jsut curious, what size blower are you stepping up to?

Bobalos

an under-driven blower moving X amount of air will out perform an overdriven blower moving the same amount of air EVERY day. if there is a question regarding which blower to use, pick the bigger one. this is assuming that they are both sized right (or close) for the desired amount of HP. of course a 14-71 is not the right choice for a 350 on pump gas, but a 6-71 is not a bad choice.

I would start with How much HP you trying to make? there are a bunch of good 144 kits out there that make a good amount of HP, & can be used as semi daily drivers.

to answer your initial question, "what makes more HP", the answer is a VERY big motor with LOTS of blower on it. Wanna make a great motor, get an essentially stock 454, pick the right blower cam & put a 6-71 or 8-71 on it & spend too much money on carbs & you dont have to do much dialing in, they come that way.

BW

Kingtal0n

<b>- it takes more power to spin a blower faster, especially as you start getting near the design limits of the blower
- your pumping losses get greater resulting in less efficiency for the same airflow, meaning much more heat. Less air density and more prone to detonation.
</b>
I want to point out that a 144 blower spun 120% overdriven will absorb about <b>40-50</b> horsepower from the engine at 6000 RPMS, as opposed to a 6-71 12% underdriven will absorb <b>over 90</b> horsepower from the engine at 6000 RPMS. it does take more power to spin a blower faster, but the bigger the blower, the more power it takes!

As for pumping losses, a bigger blower has MUCH HIGHER pumping losses due to its size! its easier for air to squeeze out of .1" gap that runs over 12" long and the rotors are spinning slower than the engine! a used 177 blower will always outflow a used 6-71 as far as <b>Efficiency</b> is concerned.

You can go either way, But this is how I would decide if it was ME:
Is the car going to be driven more than 3000 Miles / year
Is the car a "daily Driver" I use the word looselly
Is the car supposed to run on pump gas
Is the car engine under 427 Cubic Inches
Is the car expected to use only 1 carbeurator and get decent fuel economy
Is the car expected to "behave" itself in a street environment
Is the cars target horsepower goal 450-580~ horsepower

If you answered YES to these questions ( I feel like a TV commercial advertisement)
Then a 6-71 is probably not for you!
Now some people will swear by a bigger blower. To each, their own.

I am stepping up to a weiand 177 or a holley 250. I will probably go for the weiand however, simply because it can perform as well on my engine as the 250 would and it will clear my small cowl hood, which means no one will see the blower, and it wont get stolen. Anything around here that looks good will get stolen / vandalized. I live in south Miami and I dont like it. This is the reason I chose a crappy looking thirdgen for my street rod.

I will NOT be putting the blower on UNTIL I change my water pump, radiator, and I get Holley's Commander 950 Throttle body injection setup. I DO WANT fuel economy with this thing. And I will have it.

usa1racing

Responding to the questions:

Is the car going to be driven more than 3000 Miles / year?

No. Probably only driven on weekends and short trips, no more than 1/2 hour most likely.

Is the car a "daily Driver" I use the word looselly

No. Probably only on weekends and occasionally otherwise.

Is the car supposed to run on pump gas?

Absolutely. I can get 93 or 94 around here. Want it to run on pump gas on the street and the strip. Will add octane booster on the strip only if it is absolutely necessary, but would prefer not to.

Is the car engine under 427 Cubic Inches ?

As of right now, yes. Eiether 350 or 383. This leads me into another question. Can the 6-71 or the mini blower housings be used on small blocks or big blocks by changing the manifold, and not the entire setup?

Is the car expected to use only 1 carbeurator and get decent fuel economy?

1 or 2 carbs.... doesn't matter. I would probably lean towards two carbs if the blower was able to be used on a big block. Fuel economy is not really a concern considering the amount of road time the car would see

Is the car expected to "behave" itself in a street environment ?

Yes. However, behind the motor will be a manual tranny no matter what car it's in, so that should eliminate idle surging problems. Any other street behaivoir problems, inform me please.

Is the cars target horsepower goal 450-580~ horsepower?

The horsepower goal is at least 550 horsepower, preferrably more, especially if the blower can be used on a big block.

I should mention that low-speed performance is not as important as drag strip performance. Any more info you guys can provide would be great.

B4Ctom1

Im telling you the 172-177 series are the shiz-nit, from what I have witnessed, even on cobbled together rides

Speediedoug

I know which one I picked

Kingtal0n

<b>
As of right now, yes. Eiether 350 or 383. This leads me into another question. Can the 6-71 or the mini blower housings be used on small blocks or big blocks by changing the manifold, and not the entire setup?

Yes. However, behind the motor will be a manual tranny no matter what car it's in, so that should eliminate idle surging problems. Any other street behaivoir problems, inform me please.
</b>

The 6-71 sounds like the right choice for you. The benefits of a huge supercharger sticking through the hood destroy the need/want for fuel economy / driveability.

The blowers can be swapped from big to small blocks by chaging the intake manifold. A Manual transmission will compliment a 6-71 perfectly, in almost every aspect EXCEPT the fact it better be BUILT or it will be in peices after 1 run down the strip. Especially if you plan on hooking off the line... let the parts fly!

A 6-71 will also provide you with almost as many boost levels as you can think of, for your small block on the street maybe you would run 12% underdrive, but when you got to the strip a simple pulley swap and your 4% underdriven blower becomes a boost monster, then of course you could put in the race fuel to keep your timing. A timing retard box is a must. MSD makes a 6AL-BTM I would recommend.

and THEN if you put a BIG BLOCK under the blower you can simply do a pulley swap and bring the boost up to where you want it. The 6-71 has un-matched combinations for street / strip wherever you want / need them. Also remember you can use 1 OR 2 carbs with a 6-71, although nothing can compare to a 2 carb setup. a single carb will simply not flow the requirments of a 6-71 under high rpm boost.

Camshaft selection is also more picky, since your looking for strip performance not street performance and you have unlimited stall speed (manual tranny) I would go with a radical cam maybe 3000-6500 RPM to maximize the blowers power producing flow, of course your fuel economy will absolutelly SUCK @$$ but the car will fly. a high rear gear 3.90 / 4.54 will also help the cam put its power down to the ground. A very, very, very sticky rigid race clutch will be required to put all 600 Ft. Lbs of torque to the ground under a drag launch, any roots blower is going to absolutelly KICK YOU in the **** off the line, especially if you hook. It all comes back to the traction...

If you want cam / head / engine / boost / etc.. recommendations feel free to email me. Remember I do NOT know it ALL and all of my information is an OPINION of me, but I like to beleive im fairly knowledgeable about what Im talking about. B4Ctom is ALSO a very knowledgable thirdgen member.
Feel free to email me, I can talk about this $#IT all day.
Kingtal0n@aol.com
use a big subject "HEY THIRDGEN BLOWER" or somthing, I get alot of junk email and tend to delete anything that doesnt catch my eye.

tyty49

I know that this post is way old but if NE1 is around I have a couple questions:

I read the articale on 500 hp with 21 mpg. That got me really intrested in building a blown motor. However instead of using a roots supercharger and a Holly 950 TBI set-up could I use a Super Ram setup with a centrifugal supercharger asnd make more horse power approx 600?? Or would you suggest to keep with the roots type?

Thanks for the help I really don't know much about supercharging.

Oh yea I also got 1 more question:
Is NOS safe with a supercharger- Yes I used the search button but didn't find a straight yes or no answer.

Kingtal0n

With a centirfugal intercooled and a super-ram (or any mutli-point EFI setup) you can make WAY more power than any roots/throttle body combo.

Easilly 650-800 horsepower on pump gas with an ATI intercooled 12 PSI setup and the right blower motor combo is possible. easilly.

its just ALOT more money. probably about $6000 more than the roots/TB setup. I chose roots/TB setup simply because it was $6000 cheaper....

a centrifugal/multiP setup would make more power, get better fuel economy, and be more drivable on the street.

and yes, NOS is perfectly safe and fun to use with any supercharger, provided you enrich the mixture enough and retard the timing and take other such precautions....

dans82bird

LMAO! you crack me up!

turbo:
a little more complicated (i'll give ya that)
quiet? ever heard those LOUD **** BOV's on those ***** cars?
too much room? uh if you say so

if you want simplicity go with a roots blower
if you want power go with a turbo

Kingtal0n

Dan, <b>if you want simplicity go with a roots blower
if you want power go with a turbo</b>

DOnt confuse people more. a blower adds power too. lots of power. a turbo is just more efficient, but ALOT less cost effective.

$1399 for a small blower VS $4000 for an intercooled small block turbo setup. PLUS Efi setup.

dans82bird

efficiency = power
think about it...

and intercooled turbo can push lots more boost than a roots blower without detonation or something... i donno i gotta go to work... another freekin graveyard... later

daverr

iTrader: (1)

ok instead of a roots howabout a more efficient whipple superchargers,screw superchargers etc.these types of superchargers are rather simple to install AND can be intercooled like a centrifugal.and yes u could intercool a roots,screw,vane,whipple charger.take a look under the hood of a thunderbird SC notice the intercooled eaton roots supercharged.

dave

ramair'df-body

What about the amount of tuning that will be needed when you have an efi setup. For reliabilty efi is the way to go, but for the price of efi to make all amounts of horsepower you can take your carbed motor and keep a spare carb in the trunk. There's not much else to go wrong. I was into going fuel injection until I found out that I would need a bunch of computer software. Don't forget about the amount of time that will need to be put in in order to get the efi system just right. If you have the time and money then thats cool.

dans82bird

HAHA! You better become a holley tuning g.o.d. :lala:

JAYDUBB

Damn, is that an 8-71?

83 Crossfire TA

iTrader: (2)

Yes, efficiency=power, but that lack of efficiency could always be compensated for until you reach the ragged edge, and I don’t know of many (any?) of us that are there. Run more boost, better intercooler… and don’t worry about efficiency.

dans82bird

well you can't really intercool a roots type blower... though you can with a whipple/eaton style.

Dewey316

YES YOU CAN.

dans82bird

hah! that's cool... never seen that before!

tyty49

I bet those are way cost effective

Just my .02

Dewey316

i have no idea how well they work, and they cost some big coin (about 2k for a 6-71 version). all i was doing was pointing out that they DO exist.

dans82bird

but still, it's going to be MORE than a turbo and still not as efficient my point over rules

Randel '86

The twin screw type superchargers in my mind are probably the best of both worlds. Because they have the ablity to produce the low-end boost and torque numbers a small block really needs (about 95% as good as a roots does, sometimes better) and keeps right up with the centrifugal in the higher end, does not quite match it, but close.
But you asked about the roots, and centrifugal.


Help me out here guys, cause I dunno, but I am going to throw out 650 rw-ft-lbs of torque and 650 rw-hp in order to achieve your desired 10 second 1/4 mile.

So basically what you need to know is how much boost your going to need to get those numbers. I guess he is talking about a gen-1 small block?

First you must find out what your required pressure ratio is. Pressure ratio is the amount of increase in the final pressure going into the engine. 14.7 psi is considered normal atmospheric pressure at sea level, so you simply add your boost to it, 5 psi would be 19.7 absolute.

Your pressure ratio is PR=(14.7+boost psi)/14.7

Now you can determine the required PR to achieve your desired engine power increase.

PR=desired horsepower/existing horsepower

You want 650/650, and I am going to say maybe stock you have 300/300 out of that small block.

so 650/300=PR

PR=2.16

So you need to be pumping in about 116% more air than stock. But unfornutely more is actually needed. As superchargers are not perfectly volumetricly efficient.

First off you will have air density problems.

Second abiatic losses in the supercharger and belts. Drive power efficienty is usually about 90%.

So to estimate your real power.

Absolute temperature=ambient temp+460

your engine, will have around an 88% Ev, and that should be reasonable for ballpark figures.

Roots= 55% volumetric efficiency
Centrifugal=70% volumetric efficiency

Volume Ev ratio= supercharger Ev/engine Ev

Density ratio=original absolute temperature/final absolute temp

power=orginal power x new pressure ratio x density ratio x volumeric efficiencies ratio x drive power efficiency

300 x 2.16 x 0.67 x 1.05 x .9=410.8 rw-hp

that really sucks, as you will soon see.

Power is limited by knock, and knock is limited by heat. Now on pump gas, you are looking at around a maximum absolute heat of 1100 degrees farenheight. A roots has a Ev(volumetric efficiency) of around 50-55%, which can be improved at your local machine shop, but is usually what your looking at right out of the box. A centrifugal has something more like 75-80% Ev. The goal is to first figure out how much 1 psi of boost is going to cost you in terms of temperature gain. On any given day that is about 18.5 degrees for the roots and 13.6 degrees for the centrifugal.

Heat is also generated by the compression ratio of an engine.

charger gain=(PR^0.28-1) x Tabs

Tabs= ambient temp on the absolute scale. (90 degrees would be 550, which is what I'll use).

Compression gain= CR^0.28 x Tabs

But to find the temperture after both sqeezes have been performed you need to account that the compression ratio raises the absolute temperature coming out of the charger, not the outside air.

temperature= CR^.028 x charger output temp

All other things equal a roots could run 2 psi, centrifugal and' screw could run 3 psi, under normal conditions. This really blows.

Adding a intercooler or timing retarding is the only way.

Using an 85% intercooler, you could than run about 10 psi roots and 13 centrifugal and screw. Intercooling would provide the same temperature gain at 40 psi, that normally would occur at 8 psi, you can see the point made.

I can already tell you that 10-13 psi will require bottom half engine strenghthing, or your crank is headed for the deep south son. Most books say much over 50% power gain from supercharging is the line between stock and modified supercharged engines.

my biggest suggestion is that you start out with an already powerful engine, or your gonna be dropping some serious cash.


you'd need to be in the 30-40 psi range, which is just ridiculous

Damon

Yikes! We just dug up a post from almost 2 years ago!

Randel '86

you saying I copied someone else's post?

83 Crossfire TA

iTrader: (2)

You want low end get a fast spooling turbo. Otherwise any positive displacement (roots, screw…) will work.

About 475-490hp at the wheels for a mid 10 in a 3600# f-body. About 600 at the crank.

To be honest, I couldn't make heads or tails of the rest of your post, mostly because VE has nothing to do with power output, just how fast you have to spin the thing to move the air. Adiabatic efficiency tells you how much you loose to heating the air.

I'm assuming that for the rest of your post you're starting with about 300hp at the wheels. That works out to about a 1.63:1 density ratio to get to 490hp. From there you just need the adiabatic efficiency of the compressor to figure out how much boost you need. Assuming about 65% adiabatic efficiency that works out to be about 19psig boost or about 11psig with a 70% efficient intercooler…

Damon

No, I'm just saying this thread started almost 2 years ago and somehow came back to life.

Randel '86

my bad Damon