Converting a updraft manifold to downdraft (Page 1 of 2)
Posted: 12/9/2019 2:07:54 PM EDT
| I thought I would post this to show some of the work i do , manifold is a 29 stutz 2 bbl updraft man. The customer wants a downdraft stromberg carb on it so I'll post some pics of my method I've used on a lot of homemade manifold conversions, don't know if anybody's interested but here goes |
For people that want to know why, the updraft zenith is not known for performance, the customer wants a stromberg 48 over my objection but they are always right more on that later it will probably wind up with a stromberg 250 cfm later or bigger, the motor is a 29 stutz 6 cyl. About 250 cubic inch
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The stromberg 48 is a good carb as it flows a little more than the 97. About 180 CFMversus 140cfm , so later I may try one of the new 97 carbs they are making that flow 250 cfm, the best option would be a downdraft stromberg from the early 30s as they can flow up to 325 cfm 
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Originally Posted By AZBADBOY:
That's going to be some nasty casting to weld on. Does the plenum box part for water? I know nothing about said motor. I've done lots of intake stuff but on modern big horsepower turbo cars. |
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Originally Posted By Stutzmech:
Most carbs I use one of these to get airflow synced then go to jettinghttps://www.AR15.Com/media/mediaFiles/498772/image-1189290.jpg Originally Posted By Stutzmech:
Originally Posted By Hillbilly69:
On those mulitiples, how do you sync them? By ear? Vacuum gauge? Both?  |
I won't be wronged. I won't be insulted. I won't be laid a-hand on. I don't do these things to other people, and I require the same from them
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Originally Posted By Hillbilly69: 10-4 |
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Originally Posted By Stutzmech:
You can use the whistle but not accurate, also a temp gauge on flange for idle but with su,s or any single carb on a multi carb setup I've found the uni-syn to work best, go for idle first and then 2000 or 3000 rpm and the color on spark plugs or air/fuel meter I lent it to my old boss to use on his Jag, and never got it back. Hey! They still make them! Gunson Color Tuner It was a nice way to double-check the mixture distribution. |
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Originally Posted By Lost-Drive-In:
Back when I was into British cars with side drafts I used that same synchronizer and a gunson color tune. Even a backyard hack could get those motors singing. |
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Nice work!
Now, on to the disparaging comments... My dad had E-types. 3 of them. The moment I saw the word "Stromberg" I felt a movement in the force. I think it was the same movement I felt while pushing all 3 Jag's around the the warehouse and towing them off the side of the road during 40 years of dicking around with Stomberg carbs. I stayed away from English cars for 2 reasons, Lucas electric - the prince of darkness, and Stromberg carbs. However, customers get what they want, and your work looks awesome. But... why? |
"A man can never have too much red wine, too many books, or too much ammunition" - Rudyard Kipling
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Originally Posted By xanadu:
Nice work! Now, on to the disparaging comments... My dad had E-types. 3 of them. The moment I saw the word "Stromberg" I felt a movement in the force. I think it was the same movement I felt while pushing all 3 Jag's around the the warehouse and towing them off the side of the road during 40 years of dicking around with Stomberg carbs. I stayed away from English cars for 2 reasons, Lucas electric - the prince of darkness, and Stromberg carbs. However, customers get what they want, and your work looks awesome. But... why?  The why is performance while still keeping in the era of the car, the orig zenith 2 bbl updraft is an ok carb but not a performer... No accelerator pump, poor atomization of fuel and flows about 200 cfm, the stromberg I want him to use is the new one that puts out 250 cfm ,or better yet the earlier stromberg that flows 350 cfm, the later strombergs used in English cars were not very good
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| This is the messy part that people never see, when done all the seams will be smooth and have nice lines with no welds showing, normally the beads would be left showing but this has to look like it was cast this way so it does not matter how the beads look as they will be ground away, all that matters is that it's a full penetration weld, interesting thing about most aluminum welding is you leave the beads for additional strength, a lot of aluminum welding does not penetrate very deep unless you know what your doing, so sometimes a very nice looking bead conceals very little penetration, you need to look at back side to see this |
Here's a pic of the bottom of manifold with the former top that will be welded and blended in, got to shrink the back side a little to get a good line, this is the last pc to go on ,for all the people that will question how I deal with warping I'll address that later 
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For people that go to guys to get custom stuff done you can see why it gets expensive, it takes a lot of time to do this kind of stuff, a lot of hand work and figuring out, I envy the CNC guys that once its programmed you just let the machine cut it, but that kind of takes the fun out of one-off pcs.......edit this is sure different than GD, no wise ass's
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Originally Posted By chase237:
I have to ask, is this an old hand me down modification you learned form an old timer? Or something that originated out of some sort of bench racing session? Or is it an old hot rodder mod and I've just never paid any attention to it? I'm fascinated. |
| . This is for a 29 stutz that I'm rebuilding engine for, common for classic car people to modify the car for a little better performance usually done with available parts from the era and using some of the techniques so it looks like it was done then, you would be surprised how many orig classic cars have had work done to them, if done properly you can't tell |
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Originally Posted By Stutzmech: . This is for a 29 stutz that I'm rebuilding engine for, common for classic car people to modify the car for a little better performance usually done with available parts from the era and using some of the techniques so it looks like it was done then, you would be surprised how many orig classic cars have had work done to them, if done properly you can't tell |
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Originally Posted By brian4wd: I was wondering why you didn’t fabricate a complete new manifold but I doubt that would be considered a period correct modification.  
And an exhaust 
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Converting a updraft manifold to downdraft (Page 1 of 2)
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