difference between a 6-71 supercharger, and a 8-71 supercharger?

[1972roadrunner]

hey all...just kicking around the idea of a supercharger, or tunnel ram....wish my wallet was fatter than it is...

ok, i have seen 6-71 and 8-71 blowers....whats the difference? i also couldn't believe the price of an intercooler either...

the tunnel ram i was lookin at was either an Offenhauser (argh! pricey...) or a Weiand... the Offenhauser has different tops for it, so you can switch from single to dual carbs w/out taking the whole thing off...and the Weiand doesn't, BUT, the Weiand is LOTS cheaper...

keep in mind, i'm just kicking the idea around, not beating it to a bloody pulp....yet....

[nwf_snake]

I am no expert, but it seems that I read about 100 years ago that a 6-71 came off a six cylinder engine, and an 8-71 came off and eight cylinder engine. What kind or type of engine I can't remember, but the assumption was that the 8-71 was bigger and should be used on higher displacement engines.

I am sure this is not exactly what you wanted to know, but is at least a start until someone knowledgeable answers!

[1972roadrunner]

hmm...possible, but the 6-71 is avail. for my motor, with an upgrade to an 8-71... your probably right, it's probably a bigger blower

[72Challenger]

nwf_snake got it right. The original designation came from GM's deisel engines. The first number (4,6,8,etc) is the number of cylinders, 71 is the cid of each cylinder. So a 6-71 was sized for a 426 cubic inch engine (hmmm, REALLY like that number for some reason...). But since they were deisels, the RPM was much lower. So to get airflow to a similar size gas engine, you need a larger size, or to run it with overdrive pulleys. Also, huge blowers like 14-71 and the like were never made by GM, but are available by the aftermarket. They use the same numbering designation to identify equivalent flow capabilities.

[1972roadrunner]

alright...cool thanx to both of you. so a 6-71 is plenty for my 340? or would it be better to go with the upgrade? (if we choose a supercharger)

[72Challenger]

It depends on how much boost you want to make. It is better to use the larger unit rather than overdrive pulleys, as the faster a Roots-type blower spins the more heat it generates. But too big and you'll make too much boost. Then you're either blowing it off with a release valve, or blowing your engine.

[Tarrbabe]

If they weren't so expensive, more people would have then and that is the problem. When you spend that much money, you need the input from the real experts, the ones that make them. Street is different from racing and to survive on the street they have to be built differently. Whatever the experts tell you, you should take to heart.
I would think the larger unit would build and hold more heat and that would be bad.
Theres a guy with a 71-72 RR that lives somewhere around here and I see him on weekends of car shows. Never met him but saw him get on it at the stop sign here at the house. He isn't affraid to mash it and it is sweet. I beleive he has the 6-71 on a 440.

[John Kunkel]

All of the 71 series Detroits are inline motors except the 8-71 which is a V-8.
The 6-71 blower bolts on the side of the original motor and has a flat mounting flange, the 8-71 sits in the valley of the V-8 and the original case is V shaped at the bottom and attaches with angled bolts. The 8-71 isn't usable on cars unless the case is changed to the aftermarket flat flange case.
From the introduction page of the 6-71 service manual: "At 2000 rpm the blower will deliver 1000 cfm of air". I don't know if you can extrapolate those numbers but...............

[1972roadrunner]

i'm confused... http://www.blowerdriveservice.com/CG...iption_id=1166

this is why i asked... there is an option to upgrade to an 871... heres the link:
http://www.blowerdriveservice.com/CG...t_number=C7008

its only $180 more...

its $200 more to polish the blower only, not the intake...

[1972roadrunner]

hmm...dad called...said if we went with a supercharger, or a tunnel ram, the ram would be first cuz we can use the same pistons... we're afraid my c/r will be too high for a supercharger... thats ok though... dual quads w/velosity stacks looks pretty sweet!

thanx for all the help...i could probably use the info in the future for another motor (if or when i get another MoPaR)....who knows, i'll probably keep this car for ever, and ever, and ever, and ever, and ever, and ever, and ever, and ever, and ever, and ever, and ever, and ever, and ever, and ever, and ever, and ever, and ever, and ever, and ever, and ever, and ever, and ever, and ever, and ever, and ever, and ever, and ever, and ever, and ever, and ever, and ever, and ever!!!!!!!!!

[dirty dan]

Your dad is right blowers require 7.5 to8.5 comp: for gasoline. and they like lots of food . for big block at least 2 -750cfm. I don`t know how much you would have to down size for a small . The 71 series engines came as inline and v`s . The inlines were used more in trucks and industrale applications. The V`s were used mostly in marine applications. If you are thinking of getting one off these blowers from the boneyard ,forget it. the bearrings won`t hold up. they weren`t designed for such high rpm. should you decide to perchuse a blower go with the 871 if you run a small engine you can under drive it to suit your aplication. wich would reduce rpm ,save on wear and tear as well as lower the heat levle . If you have an old 78 or so anti smog enhanced engine. Get a set of 60 th`s thick head gaskets or perhaps some copper ones for it. install the blower set up and strap yourself in Tight. You will be suprised. But they really like to drink alchole by the gallon. becuase of many resons. But if you run this fule it is easy to add about 3-5% of nitro meth; and Oh NO don`t do that on cast pistons! Besides I forgot this is a street aplication. sorry no need for flames from the pipes.

[1972roadrunner]

thanx dirty dan...i have forged pistons so i'm not worried about that...

[rainydazes]

i have started lots of research on blowers, supercharger, nitrous oxide. if you what to learn alot get a book called supercharging,turbocharging& nitrous oxide perfommance handbook by powerpro series. It's very helpful. I'm only halfway done reading it.

[1972roadrunner]

where can i get it? sounds like i could use it w/my NOS etc...

[rainydazes]

i bought mine at waldon book at the mall automotive section
it's written by Earl Davis & Diane Perkins-Davis

[1972roadrunner]

gee...must be nice to live in a big city and actually HAVE a mall... i'll search around on the net. i'm gonna go take my oil pan off... yes, i know its 1 in the morn, but its the best time to work on my car cuz i don't have anything else to do (not tired yet) and its actually cool in the garage...

[rainydazes]

go to WWW.AUTOMOTIVEBOOKS.COM they should have it

[1972roadrunner]

cool thanx... i can't find my "pickle" bar!! now i have to use a big screwdriver to take my steering arms apart...