So Im just sitting here wondering, the history, use and facts about the 4/71 as it pertains to street cars and race cars? Anyone here an expert? I see Ed roths beatnick bandit had one in the late 50s, anyone know of an earlier one/
Well, I'm about as far from being an expert as anyone. But I do have a Cragar 4-71 set-up I'm going to put on my 392 hemi. As far as I have gathered, it seems like it was 4-71's with V belts to the late 50's and then the 6-71's with gilmer belts at the end of the 50's to early 60's and on. So, if you are trying to be more period accurate, that might help dictate which you go for on a project. Obviously, engine size and desired performance levels would dictate as well. The 4-71 I have was marketed for the 392, but likely is a bit undersized for that for a high performance situation and probably more suited for the 354's and 331's. As the 392's, it seems Cragar was switching to the 6-71's with the gilmers to probably provide a better set-up for the bigger motors coming out then. edit: I took this photo at the NHRA museum in Pomona which indicates a 4-71 V-belt set-up for a '57 Chrysler which would be a 392. It was questioned if the 4-71 was good enough for the 392's. So, with this I figured out it must have been or at least will be for what I want it for: At one time, I had grabbed a scan of the Cragar catalog page that showed the 4-71 for the hemis, but don't seem to have it handy now. I'll see if I can dig up and post if wanted. Or maybe you can do a hamb search and find it that way too. edit2: Here is a thread where Squirrel posted the Cragar catalog page and it shows both the 4-71 and a 6-71 options for different motors. The 6-71 option for the Chrysler hemis was an extra $20.30 back in the day. http://www.jalopyjournal.com/forum/showthread.php?t=463202
I'm with ya on this... seems clear that early on, when it came to GMC-style blowers, the 4-71 was the choice for most OHV V8s... but at some point (late-60's?) the 6-71 seems to have taken over, making whole 4-71 setups from Cragar or Weiand candy for nostalgia types as opposed to those looking for the best performance. I get that the 4-71 displacement is good for small motors... 265... 283... but I'm curious why companies offered 4-71 setups for larger motors when the 6-71 seemed more logical and ultimately did make the 4-71 nearly obsolete...? Here's the Weiand 4-71 SBC destined for my RPU -
Blake there was actually a time when they thought that a 4-71 was a good size for most V-8 engines and that the 6-71 was too much blower for anything other than an all out balls to the walls car. Then someone figured out that the 6-71 didn't have to work as hard to accomplish the same purpose. If you notice cam shafts went way wilder in the later '60s also. Look at it this way, I have a 288 duration, .500 lift cam in one of my engines. it was advertised as a long duration race cam, but by the later '60s they were starting to run comparable cams on the street and now it is pretty much a wimpy cam compaired to what is being run. Paul, I am thinking that Barney Navaro is going to be considered the first also. In the late '40s to early '50s Danny Kilcup of Portland was running a 4-71 on the flatty in his daily '40 Coupe but I don't know that he did it prior to Barney.
From what I have been able to gather in 1948 Barney Navarro was the first person to use a GMC series engine in his '27 roadster. It happened to be a 471 as well with own blower drives, intake etc and then in 1949 Tom Beatty used Navarro's design for his own race car. From that info it would seem that the 471 would predate the Italmaccanica,S.Co.T and Pepco blowers as they were available as early as 1950 (info coming from TRJ). Before the GMC blowers hot rodders had pirated blowers from larger luxury cars like Graham and Dueseys. So if that info is correct, then the 4-71 would be the most appropriate blower to use for hot rods. I have seen evidence that those were far more popular then the now desired S.Co.T's and such. I really would like to run one on my flathead in my '33 if I can. I would need to gather a bunch of info as I'm just scratching the surface but they are pretty awesome!!! Also wouldn't mind one on a Chevy 265....
In '55, Zora Arkus-Duntov and GM put a 4-53 blower on a new SBC to see if it could handle more than stock power. It worked great! You have to remember that Jimmy diesels are 2-stroke engines, so the blower has to move twice as much air as it does on a four stroke, cube for cube. Yeah, I know that the blower doesn't make much pressure in the stock application, but it still has to move lots of air.
Not specific to the OP questions, but here is a little blower background The blower model numbers are, number of cylinders (4,6,8,12 & 14), model series of original engine, and displacement per cylinder 53ci, 71ci & 92ci being most common. These were 2 stroke diesel engines and the blowers did not create over-pressure, they provided just enough air to fill the cylinders with fresh air and push out the exhaust. Being a 2 stroke they also did this on every revolution. So a 4v71 moves 4*71ci=284ci of air for each rotation a 8v71 moves double that, 568ci. A 283ci 4 stroke v8 uses 142ci for each rotation, so a 4v71 in theory moves double the air needed, because of low effiency of the blower design and some other factors that is not quite correct once you start generating positive pressure in the intake. Over driving the blower in relation to the engine speed helps, but there are limits there, the original engines redlined the blower at around 4,000 rpm. Once you go larger in displacement you need a larger blower to keep positive pressure at reasonable blower rotation speed.
i love the look, sound of a blower on on a engine. i do not know much more than that is there iis a noobie book on the subject. they cant be all that bad and unpractical if even GM would send some of there granny getter to get a small blower.. you can pick up these blowers for a 140.00..... cool stuff. more air is good. chris.
The 71 blowers on the 4 and 6 inline engines run at 2.1 times the crank speed. The governed engine speeds were generally 2100. Some applications ran them a little faster. But not over 2300. So the blower speeds were 4200 to 4600 in the stock applications. On the 6-71 the air box pressure at 2100 was 5 to 7 psi. These numbers from the engine maint manuals. As far as availability, on the east coast, in the early 50's the 6-71's were used on city buses that were fairly new so used blowers were not very common. They do last a long time and are rebuilt, new bearings and seals, rather than being replaced. The 4-71's were in smaller buses that were being replaced by the the larger buses at this time. So many 4-71's were being scrapped and the blowers available for scrap prices.
OK this is an I gave bad info post. I said Danny Kilcup was running a 4-71 on his flatty and I was wrong. I went back and looked at some pictures and I believe that this is an Italmecca or a S.Co.T. (sp). Annyway I just thought I had better clarify that. By the way for you fellas looking to build a period correct early '50s hot rod you can't find a better example than this car. This is what he was driving when I was born. Anyway sorry for the mis information.
several pretty successful small-block gas class cars used 4.71's with the small Hilborn 2-port right up through the sixties. Moody & Jones, Hrudka Willys are two that come to mind...Of course, the motor in the Willys was pretty small.
Hrudka (also known as Mr Gasket if I recall) was running like E or F gas wasn't he? A rare sedan delivery if my memory serves me.
How wide were the gilmer setups available in the late 50s-early 60s? I'm guessing you would still have a v-belt off the water pump for the generator on a street car?
To a point, and especially on a street car (IMO), it is more efficient to spin a smaller blower a little bit faster than a bigger blower under-driven. If you look at current OEM, most are relatively small blowers running over-driven. Under the "it won't have to work as hard" theory, why not drop a 14-71 on a 4-banger? Because you'd have to turn it so slowly, it would turn faster if the lobes free-wheeled under vacuum! There is a happy medium in here - I think a street-driven engine of 400" would probably do just fine with a 4-71 or a 6-71 if set up correctly. I think most engines under 400 probably should stick with a 4-71 and most larger will probably be happier with a 6-71.
Wow, Good info. So, Im running a 4/71 that is 6% under driven on my 355c.i sbc. It works great. i am also thinking of building a 302 c.i sbc which I will also run astraight driven 4/71 on. My cars are built to be in the early 60s period, so I am doing just fine in my builds and at least the blowers ae spot on for the era of cars I am monkeying with. I love it when I ACCIDENTALLY DO SOMETHING RIGHT.
This is a subject I'm VERY interested in since acquiring my first flathead a week or two ago. I do like the idea of a small performance boost, but I also like the look of it even more. So running a bone stock 1950 8BA (239ci?), would it be best to run a 3/71 over a 4/71? I obviously realize that you'd need to change out the intake manifold, but would running either one of those prevent you from having to swap out things like piston heads, rods, etc?
Just fyi, the blower drive & intake is going to put you in a price range that changing out the pistons and such shouldn't make a difference. A blower is going to make a little more heat as well when it's turning I would think so stock heads might store some of that head when compared to finned aluminum heads. This is all speculation but I;ve seen those 4-71 and 3-71 setups go for as little as $1500 and a company like H&H prices their around $6000 for just the blower/drive and intake. So yeah, have your wallet ready!
If I don't get that High Rise Weiand that I have been eyeing up for the last 4 months then I might look into a blower on a flathead. There's just nothing cool then that.
Yeah, the package deals seem to be pretty steep! I saw a 3-71 on EvilBizzle for sub $300...case, rotors, caps, gears. Who knows if it worked, though. Now I see why folks stick to SBC's.
all depends on what you're trying to get out of the thing. What's your goal? Or, perhaps a better question, just how much pressure can stock parts handle ?, and then go from there. I'm working on a 3-71 setup right now myself, and doing the math on my 238 (.060" over) c.i.d. flathead six mopar, rated at 103 h.p. @ 3600rpm stock, with a goal of 200 h.p. I came up with 20% underdrive. As a street car, it won't likely see 3600 or more rpm, especially knowing what the innards consist of. in addition, the factory static c.r. was specified as 7.1 to 1. Except I live at 6000 ft.altitude. And, my cam has a ridiculously low LDA.
Yeah, I reckon I *do* need to sit down and do the math and figure out all that. I think my general goal would be to have a setup that doesn't tax the parts to the point of failure, so whatever benefit can be gained from those settings, so be it. Can't a guy just like how it looks without having to sink 3k into it? I've seen prices all over the spectrum for used 3-71's....what's fair for a core....."miracle finds" or "buddy giveaways" excluded?
Back in the 50-s a lot of blowers were chain driven. Usually double row ... the gilmer belt was a new innovation in the 60-s. I remember a lot of FED-s ran the Potvin drives. They are always 1-1. As I recall most setups were driven at 1-1 or slightly over driven. 4-71-s worked well on small displacement engines. 6-71-s were used on the giant 392s and stroked Olds power plants. NHRA didnt have fuel classes then. Top Gas was the fastest class.
Norm Grabowski also ran one in the mid 50s, on the stock '52 Caddy in his 'T'. Said it was loaned to him by a friend...(setup looked just like Big Bill Edwards' stuff: His 150 MPH Bonneville 4-71 blown Cad/F100; the '56 T Bird w/ 4-71 blown Cad he did for Clark Gable; also some Studes and Salt roadsters with similar blown Cads) I often wondered if Big Bill was the owner of Norm's 4-71...
Jim, you may find that you get more results when searching if you use the proper nomenclature for a Detroit Diesel, which is the number of cylinders, a dash, then the displacement of the individual cylinder (e.g. 4-71, 6-71). You might be inadvertently sabotaging your search.
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