I am tapping into the wealth of experience and knowledge here on HAMB on this project I have started. I am adapting an Eaton M112 from a Jaguar v8 to a small block ford. It is carbureted and draw thru as a conventional roots would be. I have a few options for a manifold but this is a rock bottom el cheap o project which focuses on reuse and exploitation of generic parts. I do not want to buy a speedmaster chicom unit and have to modify. My options are any dual quad American manifold with an 1/2 inch plate to adapt the outlet via a plenum. In the used market there is the edelbrock f28 which is still plentiful and about $250. What I don’t like is the independent runner throats at the carb flange. Seems like it would not flow as well as option B. An Edelbrock RPM late model air gap unit set up for afb style spread bore flanges. The oval conjoined throats seem like it would flow far better. Any old offy Is cost prohibitive and very tall and also rare. Two questions that stand out: 1- Would it be beneficial to mill the web on each quad open so that it becomes more like a single plane plenum as you would find in a victor junior or super victor? Leave a smooth floor for mixture to flow? 2- I would need to mill the carburetor compensation angle off and make the deck parallel to crank centerline. The question is for milling setup- would the bottom edges of the head flange be considered parallel enough to centerline to use as a reference? Meaning, slap it on the mill table and fly cut away? I don’t have a manifold to examine to know if the bottom edge of the mating surface is dead flat/uniform and dead parallel with crank. The manifold references the crank via the head flange surface. I feel like there will be enough variation in the casting that I will have to bolt the manifold to two reference fixtures that use the head flange. This would translate the centerline from flange face. Am I overthinking? I just don’t want to screw up a good manifold and still have a belt fly off due to parallel issues. Alternately- I suppose I could create a plenum side wall that opposes the carb pad angle. The box makes the blower pad flat. Then lastly I need to reintroduce the carb angle at the blower but that is a pretty simple 90 degree fabricated elbow the foot print of a carb spacer that can be tipped a few degrees to compensate. I guess another final question. Mating the plenum- there are 8x 5/16 Stud holes in the manifold. I envision those becoming Allen head bolts and having them drilled for a safety wire arrangement all being looped together to prevent any opportunity for an event to occur. A roots blower is new to me and I expect a good amount of torque from belt tension to be yanking on the assembly. Is 8x 5/16 enough to resist the pull or should the 8x be enlarged to say 3/8? Or like I learned from a mechanical engineer on a commercial construction project- just add more! There is plenty or room and “bosses” to install another 6-8x 5/16 around the perimeter. I am leaning toward more! If I don’t hurt the manifold (mill)’then the manifold could go on to live another life if the project ever ends. Do no harm! It seems as though the best path is build plenum to fix angle, use more small fasteners. Is this manifold selection to bastardize a poor candidate? I recall reading a similar choice being discussed here positively. I thank you in advance for your wisdom and thoughts regardless of which way they point. Mike in Memphis
sounds to me like you are indeed overthinking it.... A blower intake wants a big open plenum. It's not very fussy. Roots blowers are held on with 8x7/16 studs, but they are often made of aluminum (if the engine burns alcohol), and at any rate are only torqued to about 10 ft lbs at most. So there's not that much clamping force needed. I don't see a problem with using 8x5/16" studs The bottom surface of the manifold should be sufficient for reference for machining operations. The only thing that cares about it being parallel is the belt, and it's a rubber belt, so perfect alignment might not be as critical as you imagine. have fun! be sure to post pictures as you work on it. (I don't have any experience with the modern blowers, but I have 30 years experience with good old 6-71 on street and strip)
View attachment 6360948 Thanks for the reply and confidence inspiration. I uploaded a picture marked up of the prospective manifold. The manifold pictured is vastly different from the F28. This Air Gap version is more like a blower manifold with super short straight runners but has a convoluted upper section for carbs. It appears I can mill pretty much all of the webs away down to the STEP in the middle of the carbs, in that rectangular pocket. That would seem to give a BIG plenum as you specified, and unify both ends of the plenum. This simplifies my adaptor box. Not sure how deep I can cut into that middle box but it looks like one side has a link passage bewteen carbs. Id have to have a specimen to view in hand. Pics from Edelbrock are not very helpful. The idea is to make a huge rectangle from the center, as I have marked up in the picture. The hopefully mount blower (God willing on snout length) near the middle of the manifold (blower outlet to manifold middle) so that dispersion is relatively equal front to back. The manifold seems to have banks that are linked which could be fully unified. I think I could mill the manifold right down to the floor and pretty much have just runners, one bank being about an inch higher than the other. Passenger lower than the driver side. Might that be sufficient a plenum for the task? I have also attached a bottom view of M112. The outlet is about 4.75 inch wide and thats pretty close to a 4150 width. Since the carb is mounted on the end of the blower (back) I am guessing fuel will favor the rear cylinders more than the forward cylinders. There is only one way around the deal and that is to block off the back inlet and fab a carb adaptor on the top of the blower. It has been done at least twice that I can find reference on an Eaton blower and had marginal impact on function and performance. Still way more blower than the engine can use. I have no experience with a roots blower and dont fully understand the fuel distribution issues that are typical. My mind says its a blender flinging everything violently but that cant be true. Path of least resistance thing kicks in. Running super rich to offset a lean region in the distribution will suck. 2 fouled plugs, 4 perfect and 2 lean would be disheartening (and dangerous) I have attached a prospective end result from someone who has done the rear mount satisfactorily. Alternately I envisioned adding a carb to the top which has the long ribs to be able to use for connectivity. The roof of the blower is thin so welding, etc not wise due to obvious reasons. But using the extra material unique to the Jaguar housing as seen in pic, allow for a top mount flange/plenum, centered over rotors without welding, using those ribs as mounting flange/adpator attachment points. Machined in fasteners and adhesives would allow fairly simple attachment. I would have to machine a seal surface to make a rectangle box to start the plenum. This only solves the carb location issue and does reduce the blower efficiency. Eaton would be less than enthused. But if it helps with distribution of fuel, then that is an option. More important though is the manifold decision. I will absolutely document and distribute here the progress. Blower (s) in transit now.
I just looked at an Early F28 manifold, better pics. If I weld up the heat riser ports it appears it is even more cavernous and as it is not an air gap, the floor can be taken down further in the middle of the manifold. And it is vastly cheaper to be had. Everyone wants to add holleys to it and cant due to spacing.
Don't forget about the distributor clearance needed. Most SBF blower setups are quite tall to accomodate the drive snout.
This engine will be microsquirt for spark.a cam sync will be the distributor hole plug. Yes, it’s a challenge. Blower I am into for $200 and it’s merry new, great JY find from an early wreck. If I go chicom, then Soeedmaster has a SBF 6-71 manifold that has the proverbial part in the upper section. With that removed, I have exactly what I am after, a large opening easily covered with an oring seal and alum plate. Straight shirt runners. If it seals the China walls and mates correct to the heads, it is the cheapest alternative and least invasive. Already parallel with crank. But is Chinesium and I have become so against Chinese parts, as they are mostly junk. I may have no alternative. It has the 8 bosses for blower base as well, very well supporting of blower and simple to adapt. challenge, weird, extraordinary and probably not wisdom —- cheap too. That’s the project.
fuel distribution...when I first started running a 6-71 with two Holleys, with progressive linkage, a guy with a lot of racing experience said I was an idiot, the mixture distribution would be awful, because the fuel would go straight down and the cylinders under the "open" carb would be rich, the others would be lean. But after pulling plugs and looking at them, and finding them all exactly the same, over the course of 30 years of running blowers, I kind of got the idea that he might be wrong. I've never seen distribution issues under a 6-71, neither evidenced by differnet plug appearance, or other issues like pistons getting too hot. They've always been exactly the same, every cylinder. I never burned a piston. But that funky blower that shoots the air/fuel forward, maybe things are weird with them. I think of a roots blower as a blender...it does a pretty good job of mixing things up.
Hence the reason checked in here. With a short runner (2 inch) that has no bends piped straight into a box with a blender on top, I would guess everyone involved has an equal opportunity to draw from the mother ship. I also believe that if luck is on my side, I might be able to “generally” center the outlet over the manifold. I believe I will order the Chinesium speed master, Jegs, free ship, for mock up. Worst case in 10 days it goes back due to port mismatch or bolt hole issues. I’ll eat return shipping for test fitment, that is affordable.
Chinesium high performance alloy manifold in route from Jegs. I feel like this part is going to end poorly.
I'd check the block's china wall to crank bore front and back with a caliper. I'd guess it's pretty darn close. Then, I'd check intake top angle to the intake's front and rear using a straight edge and the calipers again. Hopefully the angle is published. Compare. If you wanted to be really anal, mock up the heads and intake and use straight edge and calipers again to check front and back, crank bore to surface. Nothing but time and some gaskets. With those numbers, you could shim up the intake using the front and back on the mill table, clamp it down and mill your top. Just realize the threaded holes are probably perpendicular to the original top face. If it's say 5 degrees, the adapter could have that built in too, rather than trying to mill the intake. All of that for the non blower intake. If you are feeling like you want to QA the new blower intake, this could be done as-is. Set heads and intake in place and check front and rear height to crank bore. The shaped outlet for the blower is to counteract the flow characteristics of the roots style compressor. They tend to stack the air toward the back. I wouldn't want to run that on the pictured dual quad intake unmodified, but you have already got the chi intake coming. It sounds like with an open plenum, you won't have to mess with that or the bolt angles. Don't forget front to rear belt spacing for the adapter! Best of luck and let us know how it goes. This guy is on the T bucketeers forum. Maybe you could reach out to him there or on the tube. www.youtube.com/user/TheMykkH/videos
Have you considered a mid 80's 5.0 EFI lower intake manifold as your base? It would be easy to fabricate a plenum on top to support the blower and they are a bit taller so that should help give you a bit more distributor clearance. Added bonus, normally super cheap in just about any junk yard.
@Mike Crain are you looking for max efficient out put of the screw Eaton ? I'm sure The screw is going to be more richer on back cylinders more then Roots , With carb , This is Why the screw is more suitable for MFI & EFI , Carb will work But experimenting will be required for a good balance feeding all 8 cylinders.. Any ways If not I would use the 80s 5.0 lower or Old Dual carb Or a single Four intake , Back when I was young no $$ & No internet In late 70s, Family used a single 4 intake for 4 & 6 71s , remembering seeing done in mages in 50s before a-lot of commercial intakes were made, Thinking out side of box ,
Mill the manifold flat on top. Make a plate that matches the bottom of the supercharger. Center it and weld it on.
Following this with interest Mike. Have you seen this from blowby? https://www.jalopyjournal.com/forum/threads/small-displacement-blower.862569/ I'm toying with putting one on a 215 Buick to go in the '33 Ruby.
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