been wanting to build a blown motor for awhile now 4-71 and 6-71 cores don't seem as plentiful as they once were... Any chance of getting some tips from you guys on what to look for when I do see one at a swap meet like all the variables ... What makes a really good one, what makes a decent useable so-so one ,for just street use and what makes it boarder line junk and what is just s**** and unusaeable? Thanks all for any imput
Look up Hansen Superchargers/Blower service in Long Beach. Richard Hansen used to work closely with Joe Reath (Reath Automotive) and had hundreds of good to great 671 cores. (some 471s, too... I heard he's still doing them on a limited basis) He supplied me with a great deal for my Reath engine way back when... Good hunting.
The biggest issue are a scored case and/or rotors from injesting debris and from badly worn bearings but the mounting surfaces can also get warped requiring machining. It's always best to get the complete drive system that fits your application otherwise a good swap meet deal could get real expensive if you had to buy new drive components.
If...you don't want to spend a hand full of money "fixing" your cheap/inexpensive blower, just buy fresh/new. Will save many head aches in the long run in 99.99% of cases. Mike
Never trust what the swap meet seller is telling you-- Don Garlits never went 5 seconds with a 4/71 back in 1965 with it
Haven't seen any " new 4-71" cases on the market and I would like my stuff to look " old" or be old blower shop , BDS, wieand , or b&m cnc'd on the side of the case really isn't going to cut it , thanks for the input though
Yes , I get it ... I have a couple someday builds I would like to do ... A flathead and maybe a big Chevy
I think he means you might be better off getting a rebuilt 4-71 blower from a blower guy, than trying your luck at the swap meet. But if you can find a "straight off the diesel" blower that is still grimy and looks good, it would be worth buying it if the price is reasonable.
Oh ok.. I see ....there was a guy at the reunion that had 4 blowers " rebuilt by a buddy who used to work for BDS " didn't know to trust the story or what really to look for to be honest.. Which is kinda what prompted this post...I didn't see major scoring on rotors that's about all I knew to look at
That's the problem....if it was done right, it'll be fine. But you don't know for sure, so you take it to a blower guy, and it's not done quite the way he would do it, so you have to pay to get it gone through again. So try to only spend your money once.
what ever you buy will be junk soon if you don't sand the manifold flat after its torqued into place. every manifold deck is warped when its installed. this distortion goes right to the blower case.
Check with a reputable close by rebuilder ask if they have one they could build for you and ask what a core is worth then that would set the price for a swap meet used one.
There was a "straight off the diesel" 4-71 I saw at the last Goodguys Pleasanton for $400 or best offer. I thought about it but I didn't as I've already got a pair of 6-71s waiting for projects. I got my last greasy 6-71 with no case scoring for $300. Still needs to be converted and pinned but I'll get a round tuit.
I have always read the terms "converted" and "pinned" what does this involve also I have seen the back plate switched for a aftermarket unit which seems like a common practice?
pins go through the rotors to attach them firmly to the shafts. The rear bearing plate is pretty weak and the aftermarket ones are stronger, plus they don't need a separate cover plate. Converting from diesel to gasoline mostly has to do with setting up the clearances, etc. so it will live in a hot rod. A virgin case also needs the lip machined off the "base".
Ok, thanks , can you explain the clearancing? I'm ***uming turning the diameter of the rotors to allow for mor heat expansion?
No diameter change, rotor height adjusted in case and ends reamed for oversized pins. Rotor to rotor clearances set by "timing" gears and ends of case and rotors also trimmed to clean up and set gaps.
No machining, just rotor to rotor and rotor to case clearance using long feeler gauges. Pinning the rotors is as simple as drilling holes and pressing pins through the rotor and shaft. Back in the day on unstripped rotors guys would drop the rotors down tighter to the bottom of the case to gain pressure. Also you can have steel rings pressed on the front bearing plate to help strengthen that area instead on buying a aftermarket plate. You'll need a rear aftermarket plate . Like squirrel said there is a big flange on one side of the base that you must cut off for clearance. The gear mesh is set with shims and once you have that number it's better to machine the back of the gear down and eliminate shims on the opposite gear if that make sense. It's not super simple to do but once you dig in, it's not that complicated.
Some good basic advice given by landseaandair, squirrel and DDDenny. If you want to bone up on how to build a blower, get yourself a copy of Pat Ganahl's book, "A DIY Guide to Street Supercharging". Amazon has some. There's so much more to building a blower properly than can be explained in a forum thread.
You can easily get a converted GMC blower from the guys who do blowers, like Hampton and others. They have cores, know how, experience and a reputation. You pay your money and get a good product. That's the easiest way because we don't learn a damn thing doing anything that way . It's not the cheapest because you're paying for the education and experience they have acquired - Instead of paying for your education about blowers and investment of time and the accociated risks of screwing it up. Converting one isn't a black art, but the first one probably won't be cheaper or easier because of the learning curve you'll need to travel.
I would also advise to just buy from a reputable blower shop. I will also add that I bought complete 471 and 671 set ups from Dyers. They were great to deal with on both. The 471 ended up costing basically the same if not a bit more than the 671 because the intakes are hard to come by usually. I found a NOS Weiand but paid dearly for it.
The case needs to be annodized that helps with the clearance. When on the Diesel these blowers do not build boost so you want to close your clearances a little to build boost
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