Hey yall,
In my little town there is a old detroit diesel 4-71 with transmission sitting on the side of the road for sale. It said its from a crane and ran fine when pulled. And to make an offer.
My thought is the blower might be worth something. Would my Silverado 1500 even be able to carry it all to the recycling center after I pull the supercharger off?
Is it worth the effort?
Honestly, most people don't even bother with actual -71 series blowers off a Detroit anymore. Too much work is required to make them run as a supercharger on a gasoline engine. The bearings aren't up to snuff for the higher rotational speed, the clearances aren't tight enough to make them generate boost, etc. With companies like BDS making brand-new cases with the bearings and rotors ready to go, its the better route to go. And the 4-71 was never particularly popular anyways, mostly limited to running on stuff like Ford flatheads or 283 Chevys or 303 Olds Rockets. You might find some old guy over on H.A.M.B. who would go nuts for an original 4-71, but for 99% of people, it won't even be on their radar.
It's worth more to someone that needs it for their old tractor than it is for any performance benefits from the blower
I didnt realize the blower needs to be upgrade to use as a performance part. Since I have nothing to put a blower onto, I will skip this thing, especially since its probably really heavy as its connected to an engine and trans.
In reply to RossD :
Yeah. The blower was just that, a blower, on a Detroit two-stroke. It moved fresh air into the intake charge and helped with exhaust scavenging. It did not really generate any sort of pressure per se, so the rotor clearances are pretty large and the front and rear plate will also tend to bow under pressure. And despite sounding like they turn 5 million RPMs, a 2-stroke Detroit diesel runs much lower speeds than a gas motor, so the bearings weren't designed to see gas engine speeds. Back in the day, guys scavenged them because, well, nobody made brand new ones designed to be used as a supercharger on a fuel dragster. And the 4-71 is a bit of an oddball. In fact, I don't think there are many 4-71 blower manifolds even produced. I almost recall reading that even for an SBC Chevy, you have to go used for a 4-71 blower manifold, or use a 6-71 manifold with an adapter plate.
In reply to RossD :
I'd be more tempted just to drop that engine in a rat rod for the sounds. Nothing screams like a Detroit.
Whatever scrap is going for nowadays.
I would look cool on my mailbox...
I guarantee there's a traditional hotrodder looking to build a period correct rod looking for one. Buy it for pennies and throw it on the H A.M.B. classifieds
A running 4-71 with trans is worth something to a diesel guy. It'd be fun in diesel-rod.
I think one of the bigger things is to machine the inside of the case to accept seals to keep the gasoline out of the bearings in a carbureted application. Or something like that.
Sure would look neat hanging on the garage wall, though.
buzzboy said:A running 4-71 with trans is worth something to a diesel guy. It'd be fun in diesel-rod.
Same here - I was thinking it might be better to just put the entire engine and transmission in something interesting. It's probably too big for anything short of a medium-duty truck - not that this should stop you if you want a 4-71 powered T bucket.
Streetwiseguy said:I think one of the bigger things is to machine the inside of the case to accept seals to keep the gasoline out of the bearings in a carbureted application. Or something like that.
Sure would look neat hanging on the garage wall, though.
There's something also about having to change the timing gears to ones with lower helix angle. The blower on a Detroit was more of a kind of air diode than anything else, so it never made "boost pressure". Run it at higher speeds and under actual loads as a supercharger, and the stock gears would put a lot of end loads on the bearings.
They can be made to work, but there are better options out there for the cost of modifying a 4-71 Jimmy. 6-71s have more presence, and the mini B&M and centrifugals are better choices for boost.
That said, they were used quite a bit BITD. I have this Weiand 6 carb setup from when my dad was still racing with Corvette based short blocks in his drag car. I have a Jimmy, and will need to machine the lip off the bottom, cobble up a blower drive (planning to run multiple V belts) and make my own log manifold to adapt it to a 291 DeSoto that will likely end up in the '29 Model A pickup that I got from my uncle. Boost will be 3-5lb, which will be just fine, as the setup will be more for nostalgia than speed. It will be injected because I really don't want to tune 6 carbs. Just need to source a set of matching carb cores for it...
In reply to RossD :
Hi did the blower sell? I'm in England and looking for a 4-71 .. I have a friend who ships regularly from New Jersey .. I would be interested if still available
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