20b Intake Manifold Questions
12-12-2003, 03:34 PM
#12
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Three carbs would be ideal. I do have access to a dellorto 48 DHLA, but Racer X said it needs a vacuum signal to work correctly. I guess that means it wouldn't work very well on a 20B feeding all three rotors?
I noticed something common with most of the V8 manifolds. Due to their reletively short height, the AF mixture coming down from the carb hits the bottom of the plenum and then gets sucked horizontally to whichever valve is open. The highrise manifolds are a little taller, and the tunnel ram manifolds are the tallest. Maybe I could do some sort of tunnel ram feeding into six runners?
I noticed something common with most of the V8 manifolds. Due to their reletively short height, the AF mixture coming down from the carb hits the bottom of the plenum and then gets sucked horizontally to whichever valve is open. The highrise manifolds are a little taller, and the tunnel ram manifolds are the tallest. Maybe I could do some sort of tunnel ram feeding into six runners?
12-12-2003, 03:41 PM
#13
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Hey Mike, would the engine suffer horribly if I were to use the secondary ports only? I need to speed up the process here because I want to get the engine running before my friend goes into the millitary. He leaves in Feb. This manifold thing is taking a long time.
I'm still going to try to get the car running with a 13B first. No sense accidentaly overheating the 20B if the cooling system isn't good enough.
I'm still going to try to get the car running with a 13B first. No sense accidentaly overheating the 20B if the cooling system isn't good enough.
12-13-2003, 02:19 AM
#14
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I think I figured it out (again).
The plenum will have three runners coming out of it. Each runner will go to a secondary port. Somewhere along each runner, a smaller diameter tube will draw a smaller amount of the incoming AF mixture into that rotor's primary port.
I'm sure you all have seen Ito's semi peripheral port intake manifold. His primary runners are shared between the the peripheral ports and the primary ports. I'll do something like this with my primary port runners feeding off the larger secondary runners. My theory is the primaries are small and won't be able to suck as much as the secondaries, so why give them an equal presence in the plenum? They shouldn't do any harm if joined at the hip of the secondary runners, right?
Am I finally on to something that will work?
The plenum will have three runners coming out of it. Each runner will go to a secondary port. Somewhere along each runner, a smaller diameter tube will draw a smaller amount of the incoming AF mixture into that rotor's primary port.
I'm sure you all have seen Ito's semi peripheral port intake manifold. His primary runners are shared between the the peripheral ports and the primary ports. I'll do something like this with my primary port runners feeding off the larger secondary runners. My theory is the primaries are small and won't be able to suck as much as the secondaries, so why give them an equal presence in the plenum? They shouldn't do any harm if joined at the hip of the secondary runners, right?
Am I finally on to something that will work?
12-13-2003, 04:33 AM
#15
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I'm not sure about the size or shape of the plenum, so I just drew a rectangle under the carb flange. Notice the somewhat horizontal outlet of the three runners? Perhaps this is the missing link? I'd been previously trying to have three or six holes directly below the carb. Now there are three to one side. It's the same idea, which seems to work, with V8 manifolds. I even noticed that the Edelbrock Performer manifolds are like this. I got a reman 1407 Edelbrock 'Performer' carb (9907), so I think I'll go for it.
Should the plenum be larger? Should the bottom tilt toward the runners?
I didn't include a top view because it wouldn't have shown much. The middle pipe is as equal in length to the front and rear as possible (in my imagination at least ).
Should the plenum be larger? Should the bottom tilt toward the runners?
I didn't include a top view because it wouldn't have shown much. The middle pipe is as equal in length to the front and rear as possible (in my imagination at least
12-13-2003, 05:20 AM
#16
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Do you need a Upper Intake manifold for a 20B to modify? If so I have a extra one. also if you dont need to worry about turbo clearance because your going NA I'd be looking for a old slant six type manifold to hack up, then cut the lower manifold off just after the runners and then build new runners to connect the two. You need to make sure you keep the runners as close to the same length and I would recoment making them as short as possible to help lower tork and increase HP since you already have plenty of tork with the 20B...
12-13-2003, 06:02 AM
#17
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If I had an upper manifold, it would be useful if it can work with a side draft carb attached where the throttle body would normally go.
Yes I'm going carb NA for now.
Do you think it would work ok to simply attach a weber DCOE or even a dellorto 48 DHLA to the upper 20B manifold? Do you think it would flow correctly into all six ports? Or do you think the middle rotor would be rich? It's been a while since I looked inside an upper manifold.
If this idea will work, I'd consider it over my previous ideas. I'd also have the lower manifold shortened like you did.
Man, I hope it will work. It would save me tons of time. That dellorto of mine is just sitting there right now just waiting...
I think I sold my upper manifold with all chrome nuts and bolts for $75 to rotaspec down in NZ. Or was it $45? What kind of price are you asking? I think I sold my throttle body for $75?
Yes I'm going carb NA for now.
Do you think it would work ok to simply attach a weber DCOE or even a dellorto 48 DHLA to the upper 20B manifold? Do you think it would flow correctly into all six ports? Or do you think the middle rotor would be rich? It's been a while since I looked inside an upper manifold.
If this idea will work, I'd consider it over my previous ideas. I'd also have the lower manifold shortened like you did.
Man, I hope it will work. It would save me tons of time. That dellorto of mine is just sitting there right now just waiting...
I think I sold my upper manifold with all chrome nuts and bolts for $75 to rotaspec down in NZ. Or was it $45? What kind of price are you asking? I think I sold my throttle body for $75?
12-13-2003, 06:33 AM
#18
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If you want the 20B manifold I'll sell it for $130 shipped if you live in the USA. I've already pulled most of the steel vaccume hose nipple inserst and welded the holes shut with a mig. I also have a extra lower intake manifold I'll add for anouther $100 if your looking for one to chop up and expirement with..
12-13-2003, 06:36 AM
#19
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also, the 20B mani is divided down the middle in to 2 sections with the top 3 runners being the secondarys and the bottom 3 being the primarys. If you don't have to run a carb for fuel I'd recomend running a FD throttle body and the stock 550cc injectors and you should have plenty of fuel for the NA engine.
