6-71 or 8-71?

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07-29-2005, 11:01 PM
Bernesto

6-71 or 8-71?

I am getting ready to make the jump and put a blower on my 454. I have done a great deal of research on selecting which would be best size (6-71 or 8-71) for my application but can't seem to find any definitive answers. The motor is already a torque monster (Edelbrock performer package) built for bottom-end power (idle to 5500) but 470 lb/ft just isn't enough! I understand the advantages of both, i.e.
the 6-71 makes more boost at a lower engine RPM but the 8-71 produces less heat for the same amount of boost (on the same size motor). Does anyone have any real-world experience they can share? Also, I plan on running dual Edelbrock Performer 750's (AFBs) any thoughts on these carbs as opposed to running Holleys? Thanks in advance!
07-30-2005, 03:36 AM
DynoDon

I assume that you already have the compression at a blower friendly level & want to run pump gas. Detonation is going to be your biggest enemy with a blower & keeping the air charge as cool as possible will help avoid detonation. The 8-71 will make about the same boost 10% underdriven as the 6-71 will running straight up on a 454... so, less heat. Lots of folks like the Edelbrock carbs, but the Holley or Demon carbs are (IMO) are best suited for blowers. Other things that help keep the heat down would be aluminum heads, running straight water (no anti-freeze) BIG aluminum radiator & dual electric fans, high flow mechanical water pump, engine oil cooler & keeping the timing advance down. There are several other members here that have quite a bit of blower experience, perhaps they will have a few other suggestions.
07-30-2005, 05:07 AM
deepnhock

If you stuff an 8-71 on there, you won't be able to use a stock location distributor...
Except for looks, why would you want an 8-71?
Sheesh, you hot rodder guys:p
Jeff:toocool:
07-30-2005, 05:22 AM
J. Robinson

Since you guys are on the subject of blowers, may be you can clear up something I have been curious about for years. Can someone tell me what the numbers mean? I know they were originally produced to use on GMC diesels. I've seen them range from 3-71 to 18-71. Obviously, the first number relates somehow to physical size, but how? Why do they all end with 71?
07-30-2005, 05:29 AM
R Pope

GM diesels were rated by number of cylinders and cubic inches per cylinder, a 6-71 had 6 cylinders of 71 cubes each.
07-30-2005, 10:02 AM
DynoDon

Quote:

Originally posted by deepnhock
If you stuff an 8-71 on there, you won't be able to use a stock location distributor...
Except for looks, why would you want an 8-71?
Sheesh, you hot rodder guys:p
Jeff:toocool:

An MSD distributor works fine. The 8-71 just doesn't have to work as hard as the 6-71( less RPM's for the same amount of boost) MORE POWER UHH..UHH..UHH :LOL:
07-30-2005, 10:35 AM
MAW

6-71 vs 8-71

I've had both on my boat motors and can't say I could tell the difference with the same boost levels.

I'm not sure if the 8-71 will produce less heat than the 6-71 at the same boost level. It's the compression of the air that creates the temperature rise and the required horsepower drain from the crank, although there might be a few second order effects like windage and frictional losses involved. You'd probably need a dyno to see these slight differences though.

The Littlefield blower I'm running on my present boat came from a friend who replaced it with a brand new 8-71 from Summit. After $3500 and 2lbs more boost his boat ran the same speed.

If you're running oval port heads on your 454 the 6-71 will produce more flow than your heads can accomodate. You can end up building big boost numbers in the manifold plenum, but not making any additional power.

As stated the first number indicates the number of cylinders, the second the displacement of a single cylinder (and the engine series). Two stroke Detroit Diesels were offered in 53, 71, 92, and (I believe 121) Series. The 53 Series blowers were the basis for the small B&M blowers.

Regards, Mark
08-26-2005, 11:26 PM
van454

Gee some people are greedy!!!
Oh well I guess you can never have too much Horsepower.
09-27-2005, 11:45 AM
Superjim427

would putting a 177 blower with a single 750cfm edelbrock carb on a 427 chevy be dumb or would a 671 be better i was thinking of hiding it under my 6 inch cowl hood
09-27-2005, 02:34 PM
76GMC1500

Quote:

Originally posted by J. Robinson
Since you guys are on the subject of blowers, may be you can clear up something I have been curious about for years. Can someone tell me what the numbers mean? I know they were originally produced to use on GMC diesels. I've seen them range from 3-71 to 18-71. Obviously, the first number relates somehow to physical size, but how? Why do they all end with 71?

But what about blowers like the 14-71? GMC never made a 14 cylinder as far as I'm aware. What about the 92 series, GMC never made a 8-92 blower. It's probably just a 12-71 blower, but why don't they call it an 8-92? For the 16v92, they just bolted 2 8v92 blocks together, made a 16 cylidner crank, and installed everything on one bedplate. That one just used 2 of everything from the 8v92 including the superchargers.
09-27-2005, 04:17 PM
lt1s10

about the carb. i ended up runing the Edelbrocks, because on a hot day the gas in the holly would boil over from the blower heat and with the Edelbrocks i didnt have that problem. i ran holly, Edelbrocks and predators. the predators did better at the drag strip. i used the 6-71, didnt see no need for a 8-71 on the st. had more power than i needed anyway. what ever you do just keep it simple and you'll have more fun.
09-27-2005, 06:26 PM
techinspector1

"But what about blowers like the 14-71?"

The 14-71 as used in Top Fuel and Funny Car is a purpose-built aftermarket design. Here are the spec limits:
Case length max. 22 1/4"
Case width max. 11 1/4"
Rotor length max. 19"
Rotor diameter max. 5.840" including fixed stripping
The case must be one piece with removeable front and rear bearing end plates. Rotor must be contained within one-piece case. Inlet/outlet cavity restricted to max. one inch, measuring from the face of the bearing plate to the back of the cavity.
09-27-2005, 06:44 PM
techinspector1

Quote:

Originally posted by J. Robinson
Since you guys are on the subject of blowers, may be you can clear up something I have been curious about for years. Can someone tell me what the numbers mean? I know they were originally produced to use on GMC diesels. I've seen them range from 3-71 to 18-71. Obviously, the first number relates somehow to physical size, but how? Why do they all end with 71?

Actually, they don't all end with 71. GMC made other motors with blowers.

53.. 2.3.4.V6.V8.V12..
71.. 2.3.4.4Twin.6.6Twin.6Quad.8V.12V.12VTwin.16V.16VTwin
92.. 6V.8V.12V.16V..
110.. 6.6Twin..
149.. 12V.16V..
add to those Turbo .. Turbo intercooled .. Turbo aftercooled .. Turbo intercooled aftercooled ..
those are documented but may be a few others not certain if there was a 171, and there were some V71 Twins and Quads.. inline had High and Low blocks..
there were also V53 and 671 alloy block versions
09-27-2005, 06:57 PM
techinspector1

Re: 6-71 or 8-71?

Quote:

Originally posted by Bernesto
I am getting ready to make the jump and put a blower on my 454. I have done a great deal of research on selecting which would be best size (6-71 or 8-71) for my application but can't seem to find any definitive answers. The motor is already a torque monster (Edelbrock performer package) built for bottom-end power (idle to 5500) but 470 lb/ft just isn't enough! I understand the advantages of both, i.e.
the 6-71 makes more boost at a lower engine RPM but the 8-71 produces less heat for the same amount of boost (on the same size motor). Does anyone have any real-world experience they can share? Also, I plan on running dual Edelbrock Performer 750's (AFBs) any thoughts on these carbs as opposed to running Holleys? Thanks in advance!

I assume you've checked out all the blowers available???.....
http://streetmachinesoftablerock.com...topic.php?t=81