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Discussion Starter #1
I'm thinking ahead to replacing my 1850 Holley 600cfm with a Demon carb. I'm just not sure which one I need to go with, the Road Demon jr, Road Demon, or Speed Demon. What are the differences in the 3?

I also think I need something in the 500-600 cfm range based on my engine mods and C4 transmission.

'65 289 block
.040 over with flat top pistons
.010/.010 under crank
.204/.214 dur. / .448/.470 lift cam

'65 289 iron heads
stock springs and rockers
triple cut valves
shaved (not sure of the amount but just enough to ensure flat surface)
headers


Opinions?
 

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What are your plans for the car? Any spirited track events or just plain daily/weekend driver.
I think you have the CFM in the ballpark at 500-600. I think the speed demon is overkill, but not sure on the other 2. Either of those or comparable in a holley series.
 

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I recently replaced a 625 cfm electric choke Road Demon in my kids' '65 fb (unmodified C code 289 long block) with a 500 cfm electric choke Edelbrock Performer, and it was the single best mod I've done to this car. And I've done a bunch.

The Demon just could not achieve a proper A/F mixture at idle. Start up required 2 to 3 restarts every time, and this is in the summertime. I shudder to think about winter. Gross overrich smoke at every stop light. Bad fuel economy.

One VMF'er with similar problems told me that Demon sent him some kind of idle mixture add-on kit that almost solved the problem but not quite. He said he was about to give up too.

I'd seriously advise you to avoid the Road Demon. I's just too much carb for a 289. This makes the even bigger Speed Demon out of the question.

The Demon Jr., I don't know about. After my bad experience with the Road Demon I wasn't about to take a chance.

The Edelbrock (PN 1403) worked great right out of the box. All I had to do was turn the fast idle screw down (way down), fiddle with the idle mixture screws and the curb idle, and it was perfect. My daughter and I hopped in and took a 6000 mile road trip to celebrate. Day long cruises at 75 mph. Driving from sea level to 11,000 feet, up the Sierra Nevada from the west and up the Rockies from the east. Starts every time, one little bump from the starter (a little more cranking needed when hot).

Others have reported real good results with their Autolite 4200's. I defy you to find anyone who's happy with a Road Demon on a mild 289.

7
 

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Discussion Starter #5
What are your plans for the car? Any spirited track events or just plain daily/weekend driver.
I think you have the CFM in the ballpark at 500-600. I think the speed demon is overkill, but not sure on the other 2. Either of those or comparable in a holley series.
Daily driver/occasional open track

I had a Holley previously and got tired of having to fiddle with it everytime I started the car. It would be running fine but when you turned the car off and went to start it the next day it would barely run. Maybe I didn't know what I was doing (likely) but it was very annoying.
 

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Many people report "problems" with Demon carbs. Others tune them and have no issues. Some throw them on out of the box and they're good to go.

Your symtoms with the Holley sound like a tuning/rebuild situation.

For the mods you have and what you intend for the car, you might consider a Edelbrock 600cfm. My experience has been they tune easy and hold the tune.

If down the road you decide to build a higher performance mill and you want the most hp out of it, I'd say then consider a Demon or Holley style carb.
 

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Demon Carbs do not work well for stock type to mild engines, Unless you stick to the smaller 525cfm carb. They flow more than rated, which is great for a built engine. For a monster engine it is really GREAT. I have 4 of the carbs 1 650 750 and 850 speed demon and one 625 road Demon. Even on a dead stock 351W in my sons truck, the 625 was to much.
 

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Agree with others, carb swap is waste of money in your case, unless of course your Holley is warped or something. You have got the best universal carb already. Vacuum secondary 600 Holley can be tuned easily from stock to more than mild performance. If you want to jet it right, you should go to place, where they use lambda censor and/maybe exhaust temp censor. Then you can jet the main jets to leanest possible, for example I am down to 61 main jets but I do have strong DUI distributor to burn that lean mixture. Then I STRONGLY recommend to invest in quick change vacuum unit top. Then you can tailor the vacuum spring to lightest without bogging for best performance and when economy is needed, put a black spring and the secondaries won't open as easily.
 
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