How Big is TOO Big! --- Carburetor ---

[MarsMonster]

Hi,

I have a 360 in my truck. Just did a compression test and all cylinders checked out to be 120psi. I suspect that this is the lower end of the compression ratio, or stock pistons.

Anyway with my birthday just around the corner I decided to purchase myself and intake manifold and carburetor. I have not installed the parts yet and they are new in the box so that I can return them.

I just wanted to run it past a few of you to see what you think of my purchase before I attempt to install them. I figure if I got the wrong stuff I can always return/exchange them.

Ok, so I bought the Edelbrock RPM Air Gap manifold (7576) and I bought an Edelbrock performer series 4 barrel carburetor (1412).

My question is this; the carburetor that I was talked into buying for the manifold is an 800cfm carburetor. Is that just TOO big for my application?

All I plan on doing with my truck is driving it to the local track and making a few high speed runs. So I am not worried about fuel economy at all.

I am concerned that this carburetor might be TOO big and will cause low speed hesitation, a problem that I am currently trying to resolve.

I suspect that my 360 has a stock cam in it as well, as it idles very smoothly.

Thoughts…

Thanks

DavidH

[cudajimmy]

I sell about 3 Edlebrock carbs a week. Your's is WAYYYYYYYYYYYYYYYY too big. You need a 1405 (manual choke), or 1406 (electric choke). Then if you wanna fine tune it, buy the calibration kit part # 1480. Hell, I had a 1407 (750 cfm) on a 500 h.p. big block!

[MountainMoparRobin]

I have to agree with Jimmy, I have a few thousand in performance parts with the largest cam without having to shim the valves and I run a 750 Edelbrock with 101 jets, for economy and to pass emissions, I will go with bigger jets for performance and faster ET's but 750 is plenty for the 440.

[cowboy]

mars, all the 360 need's is a 600 cfm top's for stock , go exchange that big one for the smaller one , the 800 will just dump a lot of gas in the cylder & flood it out

[JJ]

I agree with the above posts, however......something to think about. Mopar installed 800 cfm Thermoquads on everything from 318 to 440s. Since both the Thermoquad and Eddie carbs are vaccuum secondarys they are only going to use what ever the motor needs. This means the 800 should be able be jetted down and made to work. Mopar muscle had an article a few years back doing just that on a 318 with the new 800cfm Edelbrock AVS replacement(adjustible air door) and got pretty good horsepower and damn good milage. Just food for though. Anyway if your not into the jetting the 600cfm would be a much better choice.

[wideblock]

jj one small over sight, the TQ was a spread bore carb, meaning the front bores were smaller then the back. only the back barrels are vaccume. that eddy is square bore wich dumps a lot moire fuel then the TQ even if the back barrels arent open. im running a 650 eddy on my poly, and its jetted down 3 stages up front, 2 in the back, just to agree with the engine a little bit. still feeds way too much gas. that 800cfm is gonna be way too much.

but something else to consider mars, the air gap manifold is a single plane design, this too, no matter what carb you got, is gonna give you a hesitation off the line. its made for a much higher rpm range then a stock 360 agrees with. the performer/performer rpm would be a better suite for your engine without doing block and head work. your compression sounds right in tune with a bone stocker, most likly factory 2bbl motor. you aint got the cam or the lower end to run the parts you bought. you wont be happy with the results if you use them.

an eddy performer, and a 650 vacume secondary carb is about the biggest youll get any upgrade from without block work and at minimum a cam swap. but id be willing to bet money the 500cfm eddy would make it run stronger

[Hemikuda71]

Sorry Trey, but the RPM Air Gap is a dual-plane manifold. I do think that the 600 CFM would be a better choice with a bone stock motor though.

[Rodger]

Hola

Go to the local Pick & Pull for a factroy 4 bbl intake manifold that will cost about ten bucks. Haul in that carb ya got and tell them your friends say 550 to 600 CFM's are ok for me. Hey who knows. While there you may spy a 4 bbl carb on a Van for twenty bucks.

With this returned cash in hand go get a dual exh at a muffler shop that is not part of a National Chain.

[Jeffc]

I agree 100% with Trey, square bore 800cfm, even jetted down is just too big for a stock 360. The TQ is a differant setup than the square bore carbs and cfm rates to not relate in the same way as a square bore carb.

[JJ]

Guys the Eddie performer series carbs are spread bore, at least all the ones are that I've bought. The old Carters may be a different story as I'm going to have to dig in the parts stash to look but the new ones are spread bore.

[MarsMonster]

Gosh, did I open a can of worms or what?

The manual that came with the carb says this,

"Secondary main system: The secondary main system delivers fuel only when the secondary throttle blades and air valve are open. It ensures that fuel flow delivery varies with air flow.


....


Air flow through the secondary side is controlled by air valves. These valves are located in the secondary bores above the throttle blades. They are balanced against a counter weight and open to admit additional air flow only if there is enough air velocity to allow the proper operation of the secondary metering systems."

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and to clear up a few things.... yes the manifold that I bought is a Dual Plane manifold.

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I have dual exhaust already

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If I am not mistaken the engine originally came with a 4 barrel and it was removed. The person I purchased the truck from gave me the original 360 4 barrel manifold I have it now but it needs to be hot tanked. It is not what I want to run with, but I am hanging onto it. I don't need to pass emmissions with this truck anymore.
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Thank you all for the feedback.

DavidH

[Jeffc]

Like the old AFB carb, all Carter and Eldenbrock's all use the Holley sqaure bore pattern (unlike the early WCFB (Will Carter Four Barrel intro 1952, first 4v carb) which used the early square bore pattern which is smaller than the later Holley square bore pattern).

The TQ is not any of these above, it is it's own family. The Carter TQ, Rochester TQJ, Holley 4165 and 4175 are all "spread bore" carbs; meaning that the primarys are smaller then the secondarys. None of these carbs will
fit the early, or late(Holley), square bore pattern with out mod's since the
secondarys are so large that they will strike the
intake man. holes.

The Eldenbrock Preformer will fit the spread bore pattern because is has the holes to fit the intake studs, but is not a spread bore carb.

Since the above is true, then replacing a 800cfm TQ carb with a 800cfm Eldenbrock Preformer is not a good idea in most cases. This has to do with the way the carbs work and how they are rated in cfm's. All most all applications that came with a 800cfm TQ would be more than happy with a 600cfm to 750cfm Eldenbrock Preformer(depending on engine size and build) and this is because of the primarys size of both carbs. If your primarys are too large you will have to spend time(and money for the spring/rod/jet kit) to down jet your carb to match its use and even then it may not be able to tuned to prefection. Even the Eldenbrock AVS carb (or old Carter AVS) fits the above (though there are some real advantages to the AVS over the AFB in racing and street applications since you can tune the secondary's to open when you want not just when engine vacumm tells them to open).
So, what it really comes down to is time/money spent;
when you could buy across the counter what you needed in the frist place.

If you buy too big of 4v carb you will end up running off the the primarys all the time and the secondarys will hardly ever open, so what is the point of having the secondarys; you might as well run a big 2v carb instead (and live with the poor fuel milage).

Four barrel size formula.....

engine size X max engine rpm / 3456 = need cfm carb

stock truck-- 360 X 4500 / 3456 = 468.75cfm

So a stock 360 should be happy with a 500cfm 4 barrel
carb, though I would think a 600 should work fine
and not be too over carbed.

[JJ]

I love these debaits . Jeff the primarys on these carbs are smaller then the secondarys. I checked both the new 500 cfm I just bought to go on my 273 Dart and a 600 cfm I had in the shed. And yes the 500 cfm will fit on a stock "65 cast iron intake with no adaptor. You just have to make sure it is centered.
I really don't want anyone thinking that I would run a 800 cfm carb on a 360. I just brought that up as something to think about.

[MarsMonster]

Thanks for all the help everyone.

I exchanged my carburetor today. I now have a 600cfm carb Edelbrock 1406. It has an electronic choke. The 800cfm that I had before had a manual choke.

I also picked up a 2 inch riser that fits between the carb and the manifold. I did some measuring and it looks like I will have about 2 inches of clearance now between the hood and the air cleaner when it all goes together.

I mades some 5 inch cones made out of play doh and put them on my existing air cleaner and then shut the hood, they seem to clear ok. Sounded kind of funny but thats what the instructions said to do to measure the clearance.

DavidH

[JimE]

Dave, I assume you have the throttle adapter kit? Seems we had this discussion before. Jim

[MarsMonster]

I bought #1481 Chrysler Throttle Lever Kit for Automatic Transmission.

Is that the one you were talking about?

Thanks for your help!

DavidH

[Jeffc]

I love these debaits . Jeff the primarys on these carbs are smaller then the secondarys. I checked both the new 500 cfm I just bought to go on my 273 Dart and a 600 cfm I had in the shed. And yes the 500 cfm will fit on a stock "65 cast iron intake with no adaptor. You just have to make sure it is centered.
I really don't want anyone thinking that I would run a 800 cfm carb on a 360. I just brought that up as something to think about.

Guess I'm going to go pull one of my 2 600's 1406's and my 1 500 1403 (you could well be right as far as the hole sizes) because the
750 1411 I got on the bench sure tape all the same ...1 9/16".......
However, there were often differant bore sizes pri/2nd (i.e. AFB 9626 625cfm will have
1 7/16"pris and 1 11/16"secds) but they all still the square bore pattern. Why? because they all fit the Holley square bore pattern on the intake.

Spread bore's are way differant> 1 3/8" pri with
2 1/4" 2nds, that is a spread bore carb.......can't put one of those on a sqaure bore intake that had a
AFB/Elde without a riser, or cutting the 2nds real big, and drilling holes
for the studs.

The 1403 and 1406 are the same carb body with venturi's made smaller with a reducer and down jetted on the 1403....

Here are a few AFB carb bores.
3721 575cfm 1 9/16 1 11/16
9400 400cfm 1 7/16 1 7/16
9500 500cfm 1 7/16 1 11/16
9625 625cfm 1 7/16 1 11/16
competition series AFB
CS 4759 625 1 7/16 1 11/16
CS 4760 750 1 11/16 1 11/16

probably got everone pulling out oldcarbs and taking the mic or tape to them now.....

[Jeffc]

I bought #1481 Chrysler Throttle Lever Kit for Automatic Transmission.

Is that the one you were talking about?

Thanks for your help!

DavidH

David,
You will need that kit, you may also find that your kick down arm will need to be extended to fit (with the riser you bought) and you can't do it with the the stock set up... and the one that Elde sells will not work on the truck kickdown linkage, it has the wrong threads and hole size. I have had to make them a few times to use the stock kickdown arm with a highrise intake or spacer.
Let me know if you run into this.... you do not want to go out testing that new setup without the kickdown hooked up and working!!!

[JJ]

Jeffs right on the kickdown linkage. If you don't extend the lever the tranny won't last very long.

[MarsMonster]

Thanks for the tip. Here is what my existing linkage looks like...

I hope this comes through.