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Old 09-17-2019, 10:44 PM   #1
Sunnybaba
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Smile any advantages to downdraft carb & header..??

Hi, just bought a 1930 coupe with completely rebuilt stock engine... I am wondering if I bought a downdraft intake manifold, with weber carb.... and bought a cast iron exhaust header... would that really up the horsepower any..? I know it would make it breath better... but would it have better acceleration.? poorer gas mileage.? what are the advantages and disadvantages.... ?? I want to know from those who have done it or know someone who did.... Before I put out The $1,000..... Thanks
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Old 09-17-2019, 11:09 PM   #2
CWPASADENA
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Default Re: any advantages to downdraft carb & header..??

With a completely stock engine, I do not think you would realize much improvement.


If the engine had some upgrades, cam, more compression, bigger intake valves, some port work etc, then you would also want better induction and exhaust systems.


This just my opinion and I am sure others may have other opinions.


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Old 09-18-2019, 04:09 AM   #3
Wick
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Default Re: any advantages to downdraft carb & header..??

High compression head and a good tune up would be my first choice. You will see a difference. Do a plug reading after some miles,and maybe a little larger jet. Check tire pressure and make sure the brakes are not dragging. (This is over looked Alot )

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Old 09-18-2019, 07:24 AM   #4
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Unhappy Re: any advantages to downdraft carb & header..??

I did it, If I started all over again, I would just leave the car original, aggravation can come with change.
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Old 09-18-2019, 07:32 AM   #5
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Default Re: any advantages to downdraft carb & header..??



Yes,more power,cooler running engine with better fuel economy due to more efficient combustion ..not to mention its funner..

the only internal change was a cam,the stock a cam sucks..
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Old 09-18-2019, 07:35 AM   #6
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Default Re: any advantages to downdraft carb & header..??

Quote:
Originally Posted by 1929 View Post
I did it, If I started all over again, I would just leave the car original, aggravation can come with change.
if you flip your throttle arm over your linkage will run smoother..
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Old 09-18-2019, 08:50 AM   #7
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Default Re: any advantages to downdraft carb & header..??

http://www.amuffler.com/articles/DynoTestArticle.pdf


Look at the discussion paragraph on the last page.
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Old 09-18-2019, 10:30 AM   #8
Jim Brierley
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Default Re: any advantages to downdraft carb & header..??

When I bought my tudor many years ago, it had a stock 'C' engine with A manifolds. I ran it at a hill climb in Auburn, CA. to get a "base" time. At a second hill climb 6 months later I had changed to a 6:1 Winfield head, gained a full second in e.t. on the hill. That same day I switched to a downdraft, Stromberg 81, carb, another full second was gained. At the next climb I switched to a 97, slightly larger than an 81, another 3/10 of a second quicker! All was with the stock B cam and A exhaust manifold. A bigger carb and more compression are the 2 quickest and easiest ways to increase power. Fuel mileage is better too as the engine is more efficient. I run three 81's on my speedster and on tour get better mileage than anybody else on the tour! A header may also help a little but not much at touring speeds, racing, yes, and they look cool!
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Old 09-18-2019, 10:48 AM   #9
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Default Re: any advantages to downdraft carb & header..??

Dual 81's, very peppy!
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Old 09-18-2019, 11:06 AM   #10
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Default Re: any advantages to downdraft carb & header..??

Harold Hicks designed the a exhaust manifold a did an outstanding job.I see an engine as an air pump,air in,air out..the header extracts better
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Old 09-18-2019, 07:57 PM   #11
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Default Re: any advantages to downdraft carb & header..??

Thanks for all your advice... and responses.... I will drive it as is, stock and restored to new original condition... and see if I feel a need to improve it's performance But I see that a Brumfield-Finley head, and weber downdraft and free flowing headers would be my first step if I was going that way... we will see... thanks again
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Old 09-18-2019, 11:16 PM   #12
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Default Re: any advantages to downdraft carb & header..??

If you are going to make some changes with the engine itself, consider Cam and Compression. As stated before, the stock Model A cam is not much. The "B" cam is much much better and there are aftermarket cams out there that are also very good.


Compression is also necessary to get some performance.


You may want to keep things simple by changing the cam and adding some compression with a Snyder Head. then try a "B" carb with an opened up A intake or a "B" intake. You would be surprised how much better it will run and still stay simple.


Of course, for a lot more power, go with a downdraft carb, exhaust manifold or header, more compression yet and cam change.


It all depends on how you want to use your Model A.


JMO<


Chris W.
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Old 09-19-2019, 10:38 AM   #13
Jim Brierley
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Default Re: any advantages to downdraft carb & header..??

The carb doesn't have to be a downdraft, just bigger to pass more air. Changing cams is a lot more work, do the carb and compression first, you will be pleases. This coming from a guy the grinds cams.
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Old 09-19-2019, 11:12 AM   #14
Purdy Swoft
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Default Re: any advantages to downdraft carb & header..??

I prefer to run dual model B carbs . Updraft carbs don't flood and overflow like some of the down draft setups . A downdraft setup will flow more gas , it does have gravity on its side . Severe flooding causes dilution of the oil . With a downdraft setup you lose the original choke and GAV adjustment . An exhaust header should help some . I read that the original exhaust manifold is good for an engine that is putting out as much as one hundred horsepower . An exhaust header gets in the way of a dual updraft carb set up . I like to keep mine mostly original and use the type of performance parts that were or could have been used in the day . I like the cool old timey look of dual updrafts .
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Old 09-19-2019, 11:25 AM   #15
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Default Re: any advantages to downdraft carb & header..??

How does the GAV work on dual updrafts? Seems like you'd only have the adjustment on one carb?
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Old 09-19-2019, 12:25 PM   #16
Purdy Swoft
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Default Re: any advantages to downdraft carb & header..??

I only adjust the GAV on the front carb . The GAV on the rear carb remains closed . Being as I'm running model B carburetors I run both GAV settings closed completely after a brief warm up . Model B carbs should be run with the Gav closed instead of one quarter turn open like the Zenith one or two model A carbs . In cold weather the B carbs will hesitate if the GAV isn't opened more . When cold I may need to open the front GAV a full turn or more or it will hesitate until it warms up .
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