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Discussion Starter · #1 ·
Hey guys,

I have an original 1970 Monte Carlo with it's original 350 and the 2 barrel set up. I want to upgrade the intake and carb and put in a GM HEI. I am looking for recommendations for reliability. I want something that is basically plug and play. What are your suggestions? Thanks

Dave
 

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A edelbrock performer and a Quadrajet carb. Doesn`t get any simplier than that not to mention the abundance of factory parts to make it a direct slam dunk swap. I know you didn`t ask about this, but I thought I`d mention make sure you add a 12 Volt source to the HEI, and if the engine has over 50,000 miles on it, I`d replace the timing chain.
 

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Discussion Starter · #3 ·
Hey guys,

I was just over my friends house and he gave me a brand new Speed Demon Barry Grant Carb. He took it out of the box used it for 1 month and then sold the car minus the engine and trans. He owed me some stuff and offered it up.

My question: Should I use it and just buy a manifold? If so what manifold do I buy? Or do I sell it and use it to buy a compatible manifold / carb set-up like DoubleVision suggested. I understand Demon carbs are a pain to tune but it should be ok because my buddy had it on his 350 and it ran great. What options do I have now.

Also because I am swapping from a 2 barrel to a 4 barrel what additional linkage will I need. I want to make this as easy as possible so anything you can give me is appreciated. By the way I have a turbo 400 in the Monte carlo.

Thanks again

Dave
 

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There are two basic carb flange types: squarebore and spreadbore. Squarebore has four equally sized butterflies on the bottom. Spreadbore has small primaries and huge secondaries.

All Qjets are spreadbore
90% of the other brand's offerings are squarebore.

Holley makes a spreadbore to replace factory Qjets, but they aren't common. Intakes are made to accept the type of carb you have. If you get a spreadbore carb, make sure your intake looks like this:



If you get a squarebore carb, make sure the intake looks like this:



If you notice the spreadbore intake has the extra set of bolt holes and you can mount a square carb on it with little or no consequence. However, you can't go the other way... a squarebore intake won't accept a spread carb without an adapter and you'll notice performance/drivability problems.

For that reason, I suggest getting a spreadbore intake designed for either carb. More versatile down the road if you want to change again.
 

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With a stock cam (smooth idle) in your 350 a Speed Demon is probably going to have too rich a fuel curve in it's stock form. Demon carbs are very very very dependent on the type of cam that is in the engine. They also flow about 30 cfm more than they are designated, ie, a 650 is really a 680 and a 750 is really a 780. You would be better off with the Q jet as suggested or a Barry Grant Road Demon is you are running the stock cam. :cool:
 

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Discussion Starter · #8 ·
Demon Update

Hi Guys,

I just found out that I have the Road Demon 625 with electric choke. I hope this spawns more answers. Again, thanks I really appreciate everyone's help.

Dave
 

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Ditto on the stock iron manifold/Q-jet idea. Find a complete setup in a junkyard and buy the whole mess at once. Look for a '67-'72 Chevy product and you might find a non-EGR system. It doesn't get any more "plug-&-play" than that.

If you find such a jewel with an original carb, don't replace it with a parts-store rebuilt unit. The original will most likely be real close to what you need calibration-wise, and rebuilt ones often aren't even close.
 

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If you still have the BG Road Demon 625 I would use that carb with an Edelbrock Performer intake. Later if you can get an older Quadrajet 4 barrel from a bone yard I would send it to Jet Performance and have it rebuilt to their stage 2 specs. I have this setup on my car and get great cold & hot starts, smooth idle, very good drivability & excellent fuel mileage. This setup will be as good as you can get short of EFI. If you can spring for a MSD AL6 box you will round out your upgrade.
 
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