I've been messing around with a 4/71 supercharger set up for the last few years. It was originally set up to run on my 364 Nailhead in my 1932 Studebaker. The initial project was spurred from the desire for more power but I was on a limited budget and I'm also a bit of a stingy bastard. The blower is a rebuilt and polished 4/71 GMC unit I picked up at the Pomona swap meet for $800. I know that's far from cheap and definitely contradicts my limited budget but I was convinced by a buddy that if i was going to do this blower project then I might as well do it right. (I had a roached out $100 unit at the shop, not worth the time to rebuild) Once I had the blower in my posession in all of its shiny glory, I knew that i needed to make this something cool in order to make this thing work. I'm not sure what the Cragar V-belt drive setups are going for these days but I did see them for sale at GNRS a while back and knew that they were beyond my budget. Anyways, long story short, I made the complete drive set up, pulleys, idler, intake to the 364 Nailhead, initially a 2x2 intake for Carter WGD's and eventually the 2x4 Carter WCFB intake that's on it now. I eventually blew a hole in a piston once I upped the drive ratio of the blower to 1:1 and that's when all of the pieces fell into place. Coincidentally, I came across a 1934 Ford 5 window that I've been accumulating special parts for. One of those special parts is a 345 Desoto Hemi that has a long story, but in short, has been BUILT long before I got my hands on it and was built to handle boost. It never did get that boost because Desoto blower intakes, like the Weiand WD-671 aren't exactly readily available. I now have a ready to run 4/71 blower sitting on the shelf, so the next thing to do was, get an intake.... simple enough? About a month ago, at the Pomona swap, I came across a Hemi intake sitting on the ground and luckily somebody who knew the changes, interchangeability and history of the Chrysler, Dodge and Desoto intakes. What I came across, according to him was a tall deck Dodge, Offenhauser 2x4 intake. Supposedly the plenum, runners and ports were nearly identical to a Desoto dimensionally, but the bolt patterns were way off. He said I could easily re-drill the new bolt pattern on my Desoto heads and it would bolt right up. That wasn't really my intention but hearing that the ports would match was all I needed to know. The intake had a hard life, the flanges were thoroughly pitted from water, it had studs busted off inside, threads stripped out and it had been tossed around in many different parts piles so it was covered in scratches, it was the perfect candidate to cannibalize. I picked it up for a couple hundred bucks and took it home, hoping to see the ports line up as I dropped it into place. To my relief, the ports actually lined up really well however the bolt pattern wasn't too easy to handle, a few holes slightly overlapped, they are really close to the intake ports and also, this is a running 345 Desoto with perfect, worked over heads that I'm a bit reluctant to start drilling even more holes into. The decision was made to completely remove the original intake flanges, exhaust and water cross-flow, bolt pattern stanchions and obviously the 2x4 bolt pattern top. Basically all i got was a plenum and 8 ports. Better than nothing. In the following weeks I gutted the intake to make it work. Ill post more photos of the progress if people are interested in seeing. It included pruning my polished blower, the clean up (cannibalism) of the Offy intake, custom flanges for the new bolt pattern, the blower plate itself, machining custom pulleys.... I was a bit apprehensive about posting this thread as I was kicking off the project because I wasn't totally confident that this was going to be successful. luckily only a few minor disasters occurred and it seems like this thing should do the job intended.
This was done in stages to keep as much original material and structure on the intake as possible to ensure A) I wasnt going to cut too much away initially B) to keep as much structure in it to minimize heat distortion and warping. The first step was to remove the original intake top with the 2x4 pattern so I could see what I had to work with when it comes to the plenum. I took slow passes off with fly cutter, using the base exhaust crossover plenum as the level because they were luckily made parallel from the factory. Yes I did feel a little bad about milling off the Offenhauser logo in the center, but like I said, only a little. If you look closely you can see the vertical divider between the left and right bores of the carb location. This was originally a dual plane intake with a small crossflow window in the very center of the plenum. I was actually relieved that it had the dual plane design because it meant that there was more structure that could likely be tied into the top plate i would later be grafting in to adapt the supercharger. I machined the carb bolt up bases completely flat then took out two rectangular windows to give full access to the plenum. You can see the dual plane divider in its original location and I cleaned up the crossover window a little bit, knowing I will be taking a larger chunk out of later to promote even mixture distribution.
The second photo in my previous post shows where I began cutting away the original flanges/bolt pattern between the intake runners on the intake. I used a band saw to cut out these sections that can be seen sitting to the right of the intake. The center runner is the exhaust crossover port that had a separate plenum below the main intake plenum. It was left in place because it added a lot of structure to the bottom of the intake and would hopefully minimize heat distortion considering I would be doing a significant amount of welding on the top of it. more on that later. As you can see, the opening for the intake plenum is actually pretty good size for the base of a 4/71 and even a 6/71 however there is no accommodation for the wide bolt pattern of a supercharger. A Weiand WC-671 is shown below for reference. Now, I have a perfect, polished, good to go 4/71 supercharger with the standard bolt pattern however you can see how it is wider than the original Desoto intake pattern and my intake does not have the width necessary to make pedestal for this to fit. The opening I've cut for the plenum opening is about 12" long and only about 5" wide. It is possible for me to take a big 1" thick plate, cut it to the supercharger footprint, make access holes and weld it wherever I could to give it structure and make sure it seals but that seemed to be a bit bulky and complicated. A simple solution was to "prune" the case. Like I said before, I started with a perfectly polished case that I had been running for years on my Buick Nailhead but I knew it had to be done and considering it was proven to work great and had been done before, I decided to go for it. Below is a before photo of the blower. The case was fixed down to the table on the mill and I removed as much material as possible with a 3/4" roughing end mill. After that I spent too much time with flap discs, sanding drums, and a bunch of other crap to get it looking close enough to good. As much original shape and material was left in the case as possible to keep it looking old and original as possible. It will likely get polished out a whole lot more when I have the patience for it, or just forget how bad it sucks to do that kind of work.
Now that the footprint of the supercharger is small enough to work on top of the open plenum surface I have available, it was time to make a plate to mate the two together. Luckily the local metal supply has a good supply of 6061 aluminum remnants a a variety of sizes. I found a chunk that was about 1.5" thick, 13" long and 6" wide. It was a bit more than I needed but the price was right. First off, it was cut down to a slightly over sized length and width. This was done simply enough with the fly-cutter on the mill. Next I needed to get the angle correct. These intake come with a 3.5 degree angle to them so that the carbs will sit flat when the engine is set for the correct pinion angle. This posed a bit of a problem being that i needed the entire rotating assembly of both the engine and blower running parallel to each other (obviously). Luckily the 1.5" remnant aluminum material thickness gave me plenty of room to play with when it came to milling the 3.5 degree angle into it. This was also done with the fly cutter by simply fixturing the aluminum block into the vice at a 3.5 degree angle and making passes until I had a footprint big enough to mount the face of the supercharger. Once the angled block was made up, I finally had the opportunity to see everything mocked up on the hemi with the geometry pretty close to where it will all eventually sit. A few general measurements were taken with the hope of using my old blower drive as it was without any length modifications. I made a very general layout on top of the aluminum block showing where I could remove material. It was made about 1/2" undersized in every dimension so I could mess around with final placement however it gave me the ability to remove enough material to make the block weldable. I initially tacked it in place without removing any material and it acted as a giant heat sink. Once I removed as much material, inside and out, as possible it tacked up just fine. Oh I also machined out the original dual plane divider in the intake before hand and matched the footprint of the block so it press fit into place to minimize movement during tacking. I did a quick mockup and everything looked to be good enough so I went about welding the block to the intake. It was stitch welded inside and fully welded outside. I ground everything smooth enough and called it a day.
Looks good! Having your own mill and lathe just takes you to a much higher level of accomplishment doesn't it.
technically it could have been. I opted to keep it in the stock orientation otherwise the intake would have a pretty tall arch at the front end. At the back its pretty well hidden by the distributor
The stock flanges were still on, for the most part. I needed to figure out how much material I could take off in order for it to work with something new. The exhaust cross flow was not necessary anymore so I went about cutting off the bottom plenum and the exhaust ports as well. You can see where I cut away the center exhaust port and have started to remove the bottom plenum. All those years of hot carbon buildup took a pretty serious toll on the aluminum. I intended to weld on this material which now seemed like it could be a major problem considering its sorry state. Instead of potentially running into that issue, I opted to completely cut out the bottom intake material in order to replace it with some new 6061 plate. This also gave me extra access to weld the inside of the intake and do some porting work. Next up were the intake flanges. They we're made up from a 3" wide and 3/8" thick piece of 6061 aluminum flat stock. The bolt pattern was drilled on the mill and I opened up the intake ports just enough to get a visual on my port alignment. The final port to gasket match will take place after final welding and machining. Now that I knew my flanges were going to be 3/8" thick, I could go about machining the original flanges off of the intake. I figured if I took about .300" off then that would give me plenty of material to compensate for any weld distortion with the final machining. The previous photo shows how much material needed to be removed in order to get rid of the nasty carbon saturated aluminum from the exhaust plenum. Luckily I have an Adventurer dual quad intake I used to run on this engine so I used it to make a very down and dirty fixture so I could weld the intake plenum to the flanges with minimum distortion. As much welding as possible was done in the fixture and the final pass on the underside of each port was done slowly to avoid too much heat. With the flanges welded on, its easy to see how close each bolt hole is to the intake runner. This is why all of these hemi intakes have the bolt risers, just for head clearance, so thats up next
Next step was addressing the tight bolt head clearance to the intake ports. This required making 16 2" long 1" OD 6061 aluminum bungs with a 3/8" hole through the center. I started with rod stock, cut them to length, faced both ends, through drilled each, gave them a quick OD cleanup to remove contaminants and to slightly undersize them (about .020). The bottom side where they socket into the intake flanges got a significant chamfer for adequate weld penetration. When I made the intake flanges, the bolt holes were slightly oversized so i could play with the fit and how they were positioned on the head flanges. Because I knew the intake flanges sat at a 20 degree angle and I would likely be taking .125" off of the intake flanges during final machining, I located the flanges away from the crank centerline of the block. This was not done in a very precise manner so there was a little variation in the bolt hole locations, therefore I needed to make another precise fixture to ensure that my final placement and drilling of the intake flange holes was right where it needed to be. I took my old 2x4 steel intake and used it, again, as a fixture for a down and dirty aluminum fixture. Fixtures, to make fixtures.... I then securely fastened the fixture to the new intake and fastened it down to the mill. I ensured that it was perfectly parallel to X so I could run the length of the intake flange with only a singly adjustment to my Y dimension. Each hole was perfectly lined up with the DRO and double checked with a dowel in a 3/8" collet. I then used a 1" OD Hougen hole saw. I actually purchased the 1" hole saw for this project and have used them in the past, I cannot speak highly enough about this tool! After the holes were drilled, the intake was placed on the Hemi. I then placed all of the bungs into the hole locations and bolted them down with a 3/8" bolt. Each one was tightened to ensure that the machined face of the bung was sitting firmly and square to the intake surface on the head. Each bung was tacked in multiple places before being removed from the engine. I then bolted it to my old steel fixture to minimize warping during the initial welding. I eventually needed to remove it from the fixture so I could access every weld. The final weld was done on the bottom of the flange where the bung protrudes through. I set my tig up for high penetration and moved slowly to minimize heat.
Wow! Thant's a lot of nice looking aluminum welding! Where is the pop-off valve going to fit? On the underside?
After the intake had cooled from welding, I then went about making the bottom plate to replace the nasty material I removed from the exhaust crossover. I used some 3/16" 6061 Aluminum plate and simply cut it to the odd shape so it'd fit flush and fill in the hole. I welded this completely and was very relieved that I opted to remove the carbon saturated aluminum, in the two areas that I needed to leave some old, dirty material, it really fought with me. Next up was the pop off valve. I just made up a simple 1/2" thick puck with a 3/8"-16 tapped hole in the center and two half round cutouts on each side, the pop off plate was made out a solid cylinder with a 3/8" hole and a countersink to keep the spring centered and apply even pressure. It might be kind of small but it can be opened up or another can be added to the other side of the intake if necessary. Now that the majority of my welding was taken care of, I could do my first pass on the intake flanges to remove extra weld material and flatten out any distortion. There was definitely some warping with the 3/8" Aluminum flanges but I only ended up taking off about .060 in order to get a consistent, flat pass. There are still a few more steps coming up that require welding so I hoped to take as little material off as possible to give myself plenty of room in the future.
Finally, I could bolt the intake onto my engine and see how it would fit. I have to admit, I was really relieved to feel it fall right into place, completely flat and the holes lined up pretty well considering they were all still at 3/8". I bolted it down and began to figure out where my blower needed to mount fore and aft. I made the drive snout, shaft and pulley on the supercharger a few years back for my 364 Nailhead. The dimensions were completely dependent on the Nailhead so I didnt have much faith in the possibility of it fitting the hemi without modification. To my surprise it was actually REALLY close, if anything a little long. The final measurements could not be determined until I made up a crank pulley to reference off of. A few months back I had machined a new 6" diameter 3 groove pulley to drive my blower at a 1:1 ratio. The pulley was a two piece design that utilized the original steel crank pulley on the nailhead with a spacer to the 3 groove pulley. I removed that spacer, machined a new crank pulley for the hemi out of a 6" diamter, 2" thick cylinder cutoff of aluminum (shown far right). This is probably the 6th pulley I had made so it was pretty straight forward. (ill go in depth with this process later) and machined an adapter/spacer to get what seemed to be the correct spacing forward, about 7/8" to make the blower drive work without modification (seen far left). Once it was bolted to the crank I used a flat, rigid piece of material to mate the two front faces of the pulley from the crank to the blower snout. I was then able to mark my intake blower plate so I could locate the bolt hole locations. Let me backtrack a moment. I did need to do a preliminary surfacing to the blower mount up plate on the intake because it had warped a little from welding. This ensured that the intake flanges and the plate were perfectly parallel and that the blower would be directly parallel to my crank. I had also already drilled and tapped my blower case with 4 1/2"-13 holes. they were done in a perfectly rectangular pattern on the mill, i believe 4.5" wide and 8.5" long but I cant remember for sure. Once I had my fore and aft location, The intake was bolted back onto the mill. Once again I used the 1" Hougen hole saw, which I luckily purchased in a 2" length so it could puncture both top and bottom of the intake plenum. Some 1" OD 1/2" ID bungs were made up to act as the bolt up surface to the blower. They were all made the same length so I could use the same length hardware on each. The hole on the blower flange mount surface got a deep chamfer for weld penetration and the bungs stuck out the bottom enough so they could get a good fillet weld around the perimeter. The blower case was used as the fixture, all 4 bungs were securely bolted into place, the intake was dropped over and clamped against the blower case. I tacked each bung sufficiently and then continued to finish weld them into place.
Man that is one hell of a job. I really like tech threads like this thanks for taking the time to post and keep the progress reports coming please.
Impressive!! You don't need no stinkin CNC! A bridgeport, a good TIG, and LOTS of thought and hours and hours of work gets it done. Looks great!!!
The Jalopy Journal
