Technical GM 4-71 blower

^^^^ Yes on paper & what is shown will work , the hard part is making Everything square and level, Good on penetration when welding ,
I have a Aluminum flat head intake was going to do the same also .
This is how they do a lot of modern BB Mopar and Ford intakes,
Original aftermarket Cast poured blower intakes mid 60 -70s $$$$

 

My 471

 

My old T with a 4/71 on a cad 331.

 

Mockup of my current 4-71 build

 

OMG! What manifold is that?!

 

^^^^ I would say a 1 off prototype,
Looks to be straight 6 chevy?
Can not make out name on valve cover & only 4 bolts .

 

Valve cover looks like Thickston,,,not sure ?

Tommy

 

It's sure thick with coolness!

 

I am currently running a 471 built by Gary Dyer. And the intake and drive built by his son . 421 CID, have had it up to 16 lbs of boost. Properly built, tuned and in my light weight Model A. Yes I may go to a 871 soon, however this combination, I have , trans , rear gears, tune, has propelled this little coupe to high 8's in the 1/4 mile on alcohol. Go Blown! Have fun!

 

Madmikey is your 4:71 abig lobe rotors or 3 strip Teflon per lob ? Just off top my head I would think on 400cid max boost around 5-6 psi (typical 4:71) gas.
I know Alky will help temp & increase psi , 8 on 421.
A good tight 8:71 on sb if not spinning fast enough can heat up the charge on gas & rob hp / boost out put.
You do have 421 cid
(basically close 427 BB)
I just wonder if 8:71 would Hurt street/drag, would be curious what a Dyno test data would say .

 

It is a manifold from James Larrowe of JJ Inlines on a 235 Chevy stovebolt. He also set me up with the blower, headers, double-keyed crankshaft and a mul***ude of other related goodies. The valve cover is a Thickston repop.

http://www.jjinlines.com/

 

Seen last year at Rodtoberfest in NY:

 

All the cool kids have one.

 

Wow! That's a lot of shine! Amazing!

 

Moonshine!!!

 

Damn RIGHT! Go fast stuff, worked way back in the day, and GUESS what, still works!

 

I may try a 871 . The alcohol makes a hell of a difference on my combination with the party pully on top. Maximum overdrive!

 

Mikey ,
I respect your opinion a lot,,,,but I’m concerned about an 8/71 on a small block .
That is a pretty big ( long ) case on a SBC deck .
I’m concerned you would have to drive the 8/71 at a much lower ratio to keep the boost from lifting the heads,,,,and other components .

I feel a 6/71 would be just about perfect for your combination,,,,and your driving style and use ,,,,and it was designed for use with an engine with 426 cu.in.,,,,,6 x 71 cubes .
A 6/71 overdriven at say 12 -15 %,,or better,,,,,would produce an enormous boost level ,,,,I think .
I’m ***uming your static compression is compatible for this .
You already know more than I do on this,,,,,,and of course I’m commenting without knowing your full combination.

You’ve got a mean machine,,,,,keep it rolling .

Tommy

 

Tommy, the main advantage to running a bigger cased blower is a cooler intake charge. Say , for instance, a 4-71 @ 15 percent O/D, makes 15 lbs. of boost and an 8-71 at 15 percent underdrive makes the same amount of boost... You'll get more horsepower from the underdrive combo, because of the cooler intake charge of the bigger cased blower. Bigger is better when it comes to blowers, for this reason, but not this reason alone. It boil's down to this... The slower you can turn a blower and get the max boost possible, the cooler the intake charge and the more power will be available.

 

Well,,,,,Mikey is running a 421 cid engine on alcohol .
A 4/71 will make approximately 3 pounds at 15% over on that engine
An 8/71 will make approximately 8 pounds at 15% under on it .
That’s ***uming the static comp.ratio is about 8 to 1 .
And boost is not written in stone,,,,,,the cam,,,,the heads,,,,the exhaust all contribute to total boost levels ,,,,,,at best it’s just a guide to reference .

Also,,,,,alcohol is a cooling effect on an engine,,,,,depending on the mixture,,,,,,rich or lean,,,,,it can dramatically change the temps .
I understand the heating from the pressure,,,,,but not the case effect.
The rotors never touch each other or the case,,,unless they are stripped with Teflon or Nylatron,,,,,,then the clearance is very tight and will generate extra heat .

I would still keep it with a 6/71,,,,,for Mikey’s use,,,which is primarily racing,,,,,the rotor speed with increased air flow is important .

Tommy

 

The case is just more cubic inches to disapate heat, and the engine doesn't have to work as hard to make the boost. Soooo... Spin it faster, add more fuel to keep it cool and make more power!

 

Alcohol doesn't care about high compression with a blower.
Alcohol doesn't have a detonation tendency like gas.

 

This was told to me by Gene Mooneyham, You will have to over drive a 4-71 to get enought power to warrent the cost. You can get the same result with an under driven 6-71. Dosen't take Einstine to see which blower will last longer. I listened to Gene.........................................

 

Each stage / upgrade design in that that case size will start creating more heat then then One below it.
You can have serious compe***ion 6-71 with all the up grades/lobe & case design that will out perform a stage 2
8-71 , but that 6-71 will creat more heat on gas street driving .there is ways to drop temp with Meth a gallon will only go so fair , water chiller ,1234 refrigerant witch takes $ most will not spend or can.
You can drop 7-10k just on a case set up .6&8-71.
Thats why Im curious to know about Mikey's 4-71
Thats a lot off Boost Im sure he spinning the 421 7,200-7,500 & the 4-71 is Really spinning the Rs. (30% over)
I would think Mickey does not have a head or exhaust restriction, ( witch will creat more boost) A real tight no leakage 4-71 & a bad A$$ cam grind. On my 32 header are My restriction ,I need a true set of 1-7/8s - 2.00 primaries, Im not cutting up a FoMoCo front fenders & I did not think to drill out dimples marks the stahl pattern on mill before ***embling. (215 stahl optional)
Back in early 90s worked on a 351W the owner was shifting @7,800 on a 144 , the rib belt would start slipping around 6,000rpms boost not consistent ,So I contacted RCD make me some parts ,converted belt to 8MM ""No Slipping !! But ended up with bent & twisted rotors, another blown set up 355 sbc also early 90s with 6-71 spinning 7,500 , change Rod bearing every 3,000 miles & mains every 6,000 miles
every day street driven 32, Die hard Hot Rodder /racer !!!
bearing Technology has changed over the years

 

Well,,,,with alcohol,,,,,,you run a much higher compression ratio,,than gas,,,,,blown alky loves compression.
Usually in the 11-12 ratio range,,,,,that will greatly contribute to the boost levels .
I guess that is why Mikey is running such high boost levels,,,to aid the burning of alcohol.
I figured Mikey had converted to alky from gas ,,,,.,and was running a fairly light compression load ?

I’m sorry I omitted that earlier when I was talking about CR ratios .
I knew Mikey already knew that though ,,,,,lol .
I would love to know the details of his short block build though,,,it must be solid .
The block ,crank and rods must be good pieces!

I’m sorry we’re high jacking poppinjohnnies thread,,,but this is some of the best hot rod talk I’ve read here in a while,,,,,,but that’s just my opinion,,,,lol .

Tommy

 

The one thing that no one mentioned, Unless those cases and rotors have already p***ed inspection don't spend a dime on conversion parts until they are inspected by someone who knows what he is looking at and p***. In the past 40 years I have seen too many guys get their hands on used blowers straight off the diesel truck and then find out that the cases and rotors are shot. I've even had a couple one that I planned on making a dummy out of.

 

I do not want to have the OPs thread high jacked. The blower i have have was built by Gary Dyer and yes I spin the living **** out of it with no issues so far. The combination I have, some people have said will not work. However for some reason that I am not even quite sure of , it does, and beyond my expectations. Some times I guess you just have to roll the dice , experiment and see what happens.

 

Quite honestly, it will cost just as much to set up and aquire components for a 4-71 as for a 6-71 but your results will be far less. If you want not only the looks of a blower but the additional power of a blower, you really need to step up to a 6-71. The 4-71s are fine for most small engines and flatheads, but to get any real power with your 383 you will need to overdrive it . Heat goes up and gas mileage goes down for marginal increase in power. The 4-71 also looks kinda small (in my opinion) on a Chevy. You are going to be using gasoline on the street, not alcohol or methanol, so heat generated by the blower will stay with the intake charge. I'd sell them to some of the flathead guys and keep looking for a 6-71. Put your money into the 6-71 and you know it will work better than the 4-71 when done.

 

When you bring alcohol, it becomes a completely different party.

 

Actually, I think I’ve decided to save it for a future project ‘36 Ford truck w/ a flatty. Planning to leave it crusty and old school.