3/71 on 250xflow

L

lyonsy

Well-known member
hey
iam just after some info on a orginal gm 3/71 supercharger.
whould it work well.
how much hp could it produce ie 250/300hp
how much overdrive can they handle reliable.
ive also been told that you have to run carby's or methnol injection to keep the blades lubricated and cool. i cant work out why as when on a desiel they dont have any thing but oil feed to them.
whats a endplate and pully kit worth to buy or easyer to make one.
drift
 
The rotors don't need to be cooled on a diesel when pumping straight air because it is there to scavenge the cylinder of exhaust gases....

....not make lots of boost.


Roots blowers get HOT HOT HOT when working hard (as boost goes up efficency plummets!!).

Also, the clearances are all wrong on facotory built "diesel" blowers (not tight enough) and for street use you need a professional to go through it (figure at least $1000-$1500 AUS)

and also a custom (read: NOBODY makes one!) drive system (another $1000-$1500 AUS!!)
 
That's the thing: Old Jimmy's are often on cars that already have 2-3g spent on them, as they are the HOT ROD thing... not the rust-bucket-turned-performance-machine thing. If you want a cheap blower, shoot for an Eaton. It'll be really small for a 250, but it may work. Keyword: may.

I already called Mooneyham about putting a 3-71 on a 200, and the guy sounded like I just told him that Martians were invading the Earth. These guys probably only worked with people who had 350's and 302's as well as other V8's, but I believe they recently did some 2-71's (!!!!) on Hondas. Why would someone want a blower bigger than even the biggiest Eaton on a 1.5/1.6? I have no clue.

However, consider this: how many people do you know of have an off-center blower sticking through the hood of their car- and can sit on their hood? Imagine being able to attract people's attention with that blower AND the performance it could create. With just 6 pounds of boost, you could net as much as 250hp at 4500RPM. That's more than a stock 5.0 Mustang. While 3g may sound like a lot, the end result may be worth it.

(Can you tell I'm a Jimmy fan?)
 
If you could mount it low along side the engine like the original diesels did you could keep most of it under the hood/bonnet
 
Vertigoomg":2hy6k1fa said:
Why would someone want a blower bigger than even the biggiest Eaton on a 1.5/1.6? I have no clue.
Click to expand...

That's easy: more boost at a lower temperature. And to be different--I would be very impressed if I saw that.
 
hey
ok now iam a bit confussed.
so the gm 2/71 is a bigger blower then say a eaton off 3.8v6 ford?
as i was think that a 3/71 whould be to small for a 250 or border line on it?
next question was there any difference in the side mount and v mount blowers as the guy who has seems to think some had different oil passages?
and what extacly whould be required to make it work on a petrol engine?
as i whould only be looking for a max of 10psi.
as the engine it whould go on whould have a lot of nice goodies in it all ready.
drift
 
The V-mounts (6V-71, 8V-71) were never adapted to gas engines, just the normal *-71's. I can't find any conclusive info on how big the 3- or 4-71's are, but I've heard that a 3-71 is about 125 cu. in volume. I don't know for sure.

The Super Coupes used an Eaton 90, which is 90 cubic inches. Eaton does make bigger blowers, a 120 for sure, but I don't know about bigger ones.

I do know that the 6-71's and 8-71's pumped 411 and 436 in^2 of air respectively (according to Weiand), but the volume is not directly proportional to the number designation.
 
hey
ok that makes it easyer as i can side mount or top mount it as ether is possible.
so what do they do to tighten the tolerance's up if its only machining ill be able to get it dont cheap as.
with draw through set ups can you run normal carby's?
do you have the volume of a 4/71 as ill be able to measure the difference between the 2 and work out how much volume per in or the length of 6/71 as the housing only gets longer not larger.
drift
 
Sorry I don't know the volume. I'd assume that they are 175 in^2 or so but there's no way for me to check. Here's a couple of charts to help extrapolate down though. Looks like a 4-71 will be 13-14".

superchargervolume.jpg


superchargerdimensions.jpg
 
hey
well i found some info on 4/71 from bds and they flow 260cfm with an effiecncey of 55% (info off desktop dyno)
so how much over drive can they take ie how many rpm reliable.
drift
 
That would be more than enough airflow for big hp numbers. The smaller the blower, the more you can overdrive them. That being said, this is twice the size of the blower generally used with a 200. I'd probably run 1:1 or even underdrive it a little or you could get 25 psi backed up in the intake real quick. I don't feel like converting the cfm to lbs/minute to run the math, it's been a long day...
 
OK, here's a rough estimate.
Settings:
  • Bore (in)=3.68
    Stroke (in)=3.91
    RPM=5000
    Ambient Temp (F)=75
    Engine VE=82
    Boost Press (psi)=20
    S/C Efficiency=55
Lbs/min airflow=20
Results:

  • N/A CFM=296
    Air temp after charger (F)=195
    CFM after charger=466
    Total Lbs/min airflow=33
    BHP=358
    BTQ=376

This is very rough, of course. I think the numbers are on low side if anything.
 
Dyers Machine Service used to do 6V71 setups, and other custom setups too. I know it has been 10 years ago, but I talked to Gary Dyer on the phone and he would build just about whatever you wanted. I hope they are still around, because they were an excellent company to deal with.

Darrell
 
Darrel, I think their still around.Also would be nice for mike if he could run into someone who use to work at or knew of someone to contact from HunterPerformance, they use to make the intakes and such for the B&M 144's that Clifford use to sell as a kit.And best of all IIRC they were here in town.
 
Darrel, I think their still around.Also would be nice for mike if he could run into someone who use to work at or knew of someone to contact from HunterPerformance, they use to make the intakes and such for the B&M 144's that Clifford use to sell as a kit.And best of all IIRC they were here in town.
 
hey
ok its just every time ive run the 4/71 or lower blower on the 250 it makes the same power as when its n/a due to droping comp.
which is what has had me woried as while its not real life it does give a guide on what works and what dosent.
but if you could o/d it 2/1 then its not sa bad but not great ether.
drift
 
If you really want to make some power, then consider a turbo

see signature below
 
The GM blowers are not bad on bigger engines.

The smaller blowers have straight rotors and pulse a lot. Even on the blowers that have helix they still don't have much helix and the pulsing is a problem. Look at pics of the GM blowers and then look at pics of an Eaton. Yop will notice that the Eaton has a rotor that is more like a screw. This gives a more even output. (less pulsing)

To reduce (cover up) this problem companies like B&M have used smaller blowers turning at a higher RPM. More pulses but they are smaller less violent pulses.(less heat from pulsing possibly more from RPMs) This pulsing, beats and heats the air and that is a problem.

When these are used on diesel engines, they are primarily used to help scavenge(fresh charge in, burnt charge out) because these engines are two strokes. I don't think they build a lot, if any boost.

I have seen SBC engines with cast cranks break the snout off with 6/71 blowers and 1:1 pulleys. The Ford sixes have larger snouts but they are still cast.

If you have a Detroit blower and you want to play, have fun. But you should try to keep it in perspective. I would think you could make 5psi of boost and not kill the motor but an Eaton at 10psi would be less destructive to your engine. A turbo at 15psi would probably just as easy on parts as a Detroit blower at 5psi.

These are just my opinions.
 
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