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Suggestions for carb/intake combination mild rebuild
Hey guys,

I get not rid of the thought that my current setup of my rebuild in my restoration is not the optimum in perfomance as it could be...

Currently I have rebuilt the original 2-bolt-block, original crank, original rods, '70 heads with porting and milling, stainless one-piece valves, 3-piece springs etc. with a 274XE CompCams Xtreme Energy cam which have similar Boss-cam-specs as 274/286 duration etc. Topped it by a Offenhauser 360 degree Even-Flow single plane intake and a 4300A Autolite 600 cfm.

Before rebuilt with a unknown cam I had 281 netto horsepower on the dyno with all the worn out hardware and gaskets, piston rings etc.

But now I think it could be better than that. The cam had a rpm-width of 2.000-6.000, the current intake from 1.800 to 6.000-8.800, depending on carb.

So my question is, would this be a good combination or should I change the carb for a 750 cfm Holley for example? Or is that to big and I have to go better with a 670 or 650? Or should I forget the manifold and go for a dual plane?

I have some other parts too:

an original 73 spreadbore cast manifold with an original 73 spreadbore 4300D carb

a '70 squarebore 4V cast manifold

Since I am a bit on a budget what are your suggestions?

Hold the current setup but go for a bigger carb?

Take the 600 Autolite and the 70 cast iron intake and install it?

Take the 73 spreadbore parts and throw them on the Block?

Or should I forget that all and should buy different parts as a Edelbrock Performer or Air Gap? Or should nothing go over a blue thunder?

Remind please that I have the ram air for clearance. And I want something like in the Boss-range performance, a car, that could easily rev, but not over the top. Should say with 330 HP and a good strong rpm-width to 6.000 I would be satisfied, no need to go up to 400 with that mild built.

Hope to hear some suggestions out of personal experiences and would be happy with!

Thank you very much!

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Never drive faster than your guardian angel can fly Angel
You didn't say what cubic inches, 2V or 4V or comp ratio but based on the cam you are using a dual plane intake and 650/670 carby would do well
RPM Air Gap is a good dual plane intake but not sure of clearance problems with the ram air especially if you use a 1 inch spacer between carb/manifold
If you're going for a stroker engine then a 750/770 carb is ideal
Using what you have might work fine but will depend on your combination and engine specs
Perhaps post your specs and other more experienced members will chime in

sorry, I did forget that whistling 

It is a 351C 4V with a 4-speed and 3.55 gears. Tires and rims will be 215/70R14.

Compression ratio I do not know - it is a 72/73 standard 2-bolt block with a milled 4M crankshaft, factory rods and some clean and even pistons. The heads are not the '73 ones, instead there are 1970 closed chamber 4V quench heads, ported and milled for better flow.

Headers wise I have Hooker Competition Headers 6915HKR, 2,5" pipes and Flowmaster American Thunder Mufflers.


Never drive faster than your guardian angel can fly Angel

I am with OzCoupe72. I would save your old equipment and get the Air-Gap dual plane and a new Holley . I would recommend the FiTech 600, but, i know you mentioned your budget plays a big roll. No spacers though for Ram Air clearance.

According to Summit Racing Carburetor CFM, 6500 RPM , 362 Cubes, Street 578.2 CFM and race is 748.93 CFM.

Interesting as Mr. Spock would say!

mustang7173 Thankyouyellow

"Courage is being scared to death but saddling up anyway" -- John Wayne
Thank you for your rating thumb 

I have often read (mostly between the lines) that an upgrade from a good stock cast iron to a classic Edelbrock Performer 351C 4V nothing gains than fuel mileage and wheight. That isn't that much for the money I think for an occasional just for fun driving car...

But then I read that the Ede RPM Air gap is a different kind of intake - alone for the rpm-range which is said from 1.500 - 6.500. So I assume that there are more advantages than wheight and mileage, right? Any personal experiences?

According to you words I would have no clearance issues with that intake and ram air if getting off of any spacer?

Would it be a proper way to take this RPM Air gap intake and combining it with a 670 cfm Holley street avenger according to the upgraded 274XE cam (2.000 - 6.000 rpm range)? Thinking of hat a 750 cfm would be too much...


Never drive faster than your guardian angel can fly Angel
The most important question is if there would be clearance issues with ram air. That makes also a decision point... If I can't use the RPM Air Gap with ram air on a 4V I have only few choices I think... But before I would buy a standard Performer for almost no gain am I better with a stock cast iron, especially the 1970 4V squarebore? For how much rpm are they good? Or would it be better by all means than any of the intakes I have?

Questions over questions... whistling

Thank you for help!


Never drive faster than your guardian angel can fly Angel
Found some threads here which let assume that there a clearance issues with a RPM Air Gap and ram air so if confirmed this intake is unfortunately not the one I can bolt on...

So my other questions are still standing.

Thanks Wink


Never drive faster than your guardian angel can fly Angel
Then the dual plane maybe the path to go with.

mustang7173 Thankyouyellow

"Courage is being scared to death but saddling up anyway" -- John Wayne
I currently have the RPM Air-Gap on my car, and you for sure will NOT be able to use Ram-Air. That said, it does pull strong, BUT I think the port mismatch leaves a little to be desired. I have a Pro-Systems 780 XP carb and it works REALLY good!!! I tried a standard 750 and 850 DP carb and actually lost power. I am going to try a Blue Thunder intake this year, which is a glorified stock Boss intake because I think it will out perform the Air-Gap. I might lose a little on the bottom end, but there is plenty to spare, I just think it will pull harder through the RPM range with proper port match. But as I have said before, I think Cleveland heads are very special, especially the CC version, and for them to run their best you have to use what was made for them. I am by no means an expert, just giving my 2-cents. I have heard many times that the stock square bore intake works very well with iron 4v CC heads, out of what you have I would try that with a 750. Then you can have your Ram-Air and an intake that is capable of moving the air/fuel that a good Holley can deliver. Good luck!!
Thanks for your suggestion, I think that too. What I read out of many articles is for normal abuse and a dual plane the Blue Thunder and a Holley is the measure of all things!

So that could be the more expensive but also ultimate solution for my needs. According to a few threads here the Blue Thunder would also clear the ram air quite good if not used a spacer, only a gasket.

Then I think a budget solution would be taking the '70 squarebore and go with a Holley first thumb This would allow me a little spacer too...

But with the size: wouldn't a 750 cfm be too big for that setup? I thought more in a 650-680 cfm dimension, for example a 650 Double Pumper (4777)... Or what are your personal experiences/preferences with such setups?


Never drive faster than your guardian angel can fly Angel
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