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Detritus Maximus
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Discussion Starter · #1 ·
So I got to thinking about all this custom header talk and got to wondering about a custom tubular intake manifold to replace the stock Opel intake manifold. Something with equal length runners and better flow and still have a stock carb flange pattern. More plenum volume, maybe?

I can't help but think that this might be a very effective piece in conjunction with a 38 or 40 DGAS, maybe better than a single sidedraft.

Any thoughts or opinions from the more knowledgeable or experienced?
 

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Old Opeler
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Snap!

Dave and I have brain-stormed about this too!
One of the ideas we tossed about was using the ends of the runners from a stock manifold and joining them with a bit of 2" ali tube. This would allow the construction of either a downdraft or single sidedraft intake manifold .......
Wees' bin thinkin' ;)
 

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Banned
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3,842 Posts
I've gotten as far as removing intakes and finding the Ali wire. I'm still leaning toward SSD with that manifold.
 

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Super Moderator
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The hard part is getting the flow equal. Not the airflow so much as the wet flow. If the air flow equally but the fuel does not get distributed equally in the airstream, then you can smoke a cylinder in a heartbeat.

I once tweaked a stock downdraft intake radically for my friend's racecar, and while I spent 14 hours cutting/welding/flow testing the intake, I spent another 5 hours getting the fuel distribution flow decent. That's just one intake, and that's assuming you have the equipment to test it! Then on to the dyno with individual EGT probes and slowly creep up on the rpms and throttle loading until you're sure the air/fuel to each cylinder is within safe limits. If you run #2 cylinder lean you're almost guaranteed to crack the head or break a pie-shaped piece of the exhaust valve right off!

FWIW, this is one of the biggest issues with most brands of SSD intake manifolds, the distribution is horrible. In order to make the leanest cylinder safe the richest cylinder will end up being too rich!

Bob
 

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Senior Contributor
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Why is the wet flow not a concern when we do the radical porting and bottom flow piece in a stock intake?
 

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Old Opeler
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It Is!

markandson said:
Why is the wet flow not a concern when we do the radical porting and bottom flow piece in a stock intake?
It is! But Webers downdrafts are usually run "rich" - for power - and this masks the issue. Ever heard of anyone swapping on a Weber for economy ?? :)
Also LOTS of effort and flow testing from Bob have pretty much established how to port a standard intake manifold. ;)

The idea with an ali tube and the original intake manifold ends was to use "turbulence" at the somewhat abrupt corners and transitions to keep the air/fuel mix "stirred up" on the way to the ports - a "street" rather than peak power "race" manifold. The provision of water heating has also been considered ..... We has bin thinkin' - quite a lot.... there are not enough Steinmetz SSD manifolds out there for ALL of us!
 

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Detritus Maximus
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Discussion Starter · #7 ·
Isn't the wet flow partly related to the size of the plenum below the carb? If the plenum was bigger and the carb was a DGAS (synchronized two barrel), would this not help with balancing between cylinders? I've read about the issues of progressive carbs and maintaining the rich/lean balance between cylinders (and why you can't use the Pinto carb with the primary and secondary barrals switched), but it seems to me (first sign that I'm about to get in trouble...) that a synchronized two barrel and symetrical carb action (synchronized versus progressive) that it would help reduce the wet flow problem. Notice I said reduce and not eliminate.



Or maybe we should just cut the front portions of the stock manifold off of two manifolds and convert the rear sections (with carb flanges) to a pair of intakes for twin DGAV's or DGAS's. Two seperate manifolds, both curving to the front of the car. This way, we keep the stock Opel intake runners and still get dual carbs....could be cheaper than sourcing a pair of sidedrafts and the requisite manifolds.

Which, by the way, I could use some for a pair of 40 DCOEs I have. I have a 'hotrod' Manta I wish to drag out of storage and the motor (high compression pistons (but don't know how high...), Chevy valves, and supposedly a Torquer type cam from C+R (specs also unkown) has 8 miles on it.The previous owner had the work done and never finished the rest of the car (some rust, but not a whole lot) or tuning it. He had a single 40 sidedraft on it. I'm thinking this motor may need twins. If I get it running it may be for sale in the spring. Got a few goodies to go with it, perfect dash, front airdam (nice one, not a duckbill spoiler), German sport seats (Scheel, I think), and the wheels off my GT (see gallery). Don't know what carb set-up, might not even sell the carbs with the car, but if I sell it it will be running and driveable, just supply your own carbs.
 
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