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Discussion Starter #1 (Edited by Moderator)
Im looking to run a 650 edelbrock but having a hell of a time finding one at a decent used price.

So, in the meantime, **********.......... is it possible to change some rods, jets and springs to get a 750 to run like a 650 or a 600 to run like a 650??????? Im more less referring to edelbrock carbs.

Thanks in advance guys!!!!!!!!!!
 

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Why use the edelbrock copy of the Carter AFB/AVS design?

A carb that is slightly too small will always run better on the street than a carb that is too big. Too big may work at the drags, but not on the street.

You really can't make a carb that is too big for the engine run right. (except see my note below). The booster signal will always be weaker in a carb that is too big for the application. The idle and low-speed torque will be down on power since you can't get the port velocity through the boosters until high RPM. Throttle response will be mush with much too large a carb.

*note* That's the beauty of a carb like the Q-jet. The small primaries give good torque and the spring loaded secondary air door could be adjusted to work on a 305 or a 454. I think the AVS has a secondary air door but I don't know if the tension can be adjusted. A larger vacuum secondary Holley can be made to work on smaller engines by using a high tension secondary vacuum spring.
 

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Discussion Starter #3
the secondaries are adjustable on the eddy..................

I get ya on the too big carb and idle circuit. Makes sense. So i guess im trying to find a 650 carter or somehow try and change some things out on this eddy 600 to get it to run like a 650.

Reason being, the HOLLEY 650 i had on before ran so perfectly for both street and highway but......I prefer the easy changes and rebuild of the Eddy if im on the street/highway and something goes fubar.
 

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Im looking to run a 650 edelbrock but having a hell of a time finding one at a decent used price.

So, in the meantime, if nobody has one for sale.......... is it possible to change some rods, jets and springs to get a 750 to run like a 650 or a 600 to run like a 650??????? Im more less referring to edelbrock carbs.

Thanks in advance guys!!!!!!!!!!
Not really the CFM designations for carburetors are based on the CFM air flow the carb delivers through the venturi/throttle bores at a given pressure depression which is 1.5 inches of mercury for 4 barrels and 3 inches for 2 barrels.

Jet and metering rods control fuel flow which needs to be a ratio roughly between 11 and 15 parts air to each part fuel. The springs control the timing of events, in the case of a Edlebrock/Carter they control the metering rod's cruise and power sizes. The spring is reacting against manifold vacuum that wants to pull the metering rods to the cruise position. As the throttle is opened manifold vacuum decreases toward atmospheric pressure. As the vacuum fades the spring pushes the metering rod piston up richening the mixture into the power circuit. This is good for the Edlebrock/Carter and the Quadra-Jet. The Holley uses a fixed main jet with no metering rod for cruise with a power valve that functions with a spring against manifold vacuum in process functionally similar to Carter and Q-Jet but different in detail design. The power valve is simply a switch in the Holley case there are additional power jets that can be size modified if necessary.

The Holley is generally favored for performance work, it shows better top end power and is easy to modify for specific purposes. The Carter and Q-Jet designs tend toward a little better fuel economy.

In the end the only way to get more air into an engine is with a larger cfm capacity carburetor, then you work on the fuel flow through jet sizing, metering rod sizing and the power valve spring for timing between cruise and power metering. Note that the power valve is sometimes called the economizer valve.

Bogie
 

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I have a Weber in my boat. Same carb. I have been studying it this winter while I build a stroker.
I mis read your first post, so you have a 600?
You can jet and rod that carb up if your engine is a little big for it. I defer to Bogie, but...they do offer tuning stuff.
Read Edelbrock's tuning info. It's right in their webpage for download.
It will give you the recommended tuning kit and how to use it.

Chiphead is kinda right in that the primary venturi's are bigger on the 750 eddy than the ones in the smaller carb. But I'll bet you can jet, rod, and spring it down to get it to behave better.
And to clarify someones remark about the secondary doors, they, like a Qjet, open when there is enough vacuum to pull them open. The throttle blades open below there, but the air doors need engine vac.
The edelbrock secondary jets can be changed, but there isn't any air door adjustment.
On the Carter, Weber, Edelbrock the resistance is provided by a fixed weight on a pivot.
On the Quadrajet there is a spring which can be fine adjusted.

************
 

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Reason being, the HOLLEY 650 i had on before ran so perfectly for both street and highway but......I prefer the easy changes and rebuild of the Eddy if im on the street/highway and something goes fubar.
Didn't think there was anything easier to rebuild than a Holley... and parts are easier to find... what is your engine/vehicle?
 

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Discussion Starter #7
Thanks for the input. But...................just how easy is a HOLLEY D.P. to rebuild and adjust on the road vs. an EDELBROCK.

I can deffinately tell the difference all around between the Holley 650 DP and eddy single feed (i changed jets,rods 2 sizes larger hoping to get more out of it) at low end, cruise and deffinately top end when secondaries kick. The eddy has almost nuthin' in the secondary department considering I have an extended cab lifed truck on 33" tires.

So, according to the zz4 owners man. they accomplished their 400ft lbs and 400hp with a 770 but i will blow my rear end out in 2 seconds with a 770 or a stock 750.

Thus im trying to get that 650 or close to it.
 

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Discussion Starter #8
Awesome, but as i replied to the guy above you........ a 750 stock would blow my rear end off my ext. cab lifted chevy on 33" tires. (I THINK THATS WHY THE GUY SOLD IT TO ME WITH A HOLLEY D.P. 650 ON IT AND..................... I FOUND A RECEIPT FOR A REBUILT CARRIER/RING ON THE REAR LOL LOL!!!!!!!!
 

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Discussion Starter #9 (Edited by Moderator)
I have a Weber in my boat. Same carb. I have been studying it this winter while I build a stroker.
I mis read your first post, so you have a 600?
You can jet and rod that carb up if your engine is a little big for it. I defer to Bogie, but...they do offer tuning stuff.
Read Edelbrock's tuning info. It's right in their webpage for download.
It will give you the recommended tuning kit and how to use it.

Chiphead is kinda right in that the primary venturi's are bigger on the 750 eddy than the ones in the smaller carb. But I'll bet you can jet, rod, and spring it down to get it to behave better.
And to clarify someones remark about the secondary doors, they, like a Qjet, open when there is enough vacuum to pull them open. The throttle blades open below there, but the air doors need engine vac.
The edelbrock secondary jets can be changed, but there isn't any air door adjustment.
On the Carter, Weber, Edelbrock the resistance is provided by a fixed weight on a pivot.
On the Quadrajet there is a spring which can be fine adjusted.







Im trying to buy a 650 now, rebuildable or not, i cant wait for ya! ha ha
 

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Discussion Starter #10
ZZ4 mild cam 6.5 constant fuel flow peak 8 psi. according to GM its a 400ftlb/400hp motor that loves running LEAN! I can tell from the carb change between the Holley 650 dp to my now mod'd Eddy 600 carb. But, the 600 even though i went up with everything and have the stiffest spring doesnt even come close to the performance at all rpm's i got from the Holley DP.

But in comparison how much easier are they to work on then the eddy's?? changing idle circuit stuff etc.?
 

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Going to a 750 or 770 carb. wouldn't do anything... except maybe cost a little low RPMs torque...your engine is satisfied by a 650 carb. and that's all the air it will use, no matter how big a carb. sits on top of it... the Eddy 600 is too small because it's not 600 CFM the way a Holley spreadbore 650 is 650 CFM...
 

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Discussion Starter #12
Going to a 750 or 770 carb. wouldn't do anything... except maybe cost a little low RPMs torque...your engine is satisfied by a 650 carb. and that's all the air it will use, no matter how big a carb. sits on top of it... the Eddy 600 is too small because it's not 600 CFM the way a Holley spreadbore 650 is 650 CFM...

Then if the Eddy 600 isnt a true 600 cfm carb what is it? Also what would an Eddy 650 be then? Now im really confessed between true and untrue CFMs on carbs. Thought they were all "as advertised."
 

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a 750 Holley wont damage the diff in any way. The driver might damage the diff,,,
750 cfm is very easy to tune. I personally prefer the Holley "HP" series.
 

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X2 with Vinnie.

The difference between the 650 and 750 is all top end if both are tuned properly unless you have 4000+ stall and are launching from there. The reason for a bigger carb is to allow for enough air at higher rpm's. At idle and off idle cruising is not affected by a larger cfm carb - pertaining to your comment about a larger carb wrecking your rear. There are several things that will break a small rear like sticky tires, 'highish' stall launches with a properly tuned suspension without any wheel spin. A small rear, like a 7.5" that is setup correctly, will last a long time in a moderate weight car that is a street cruiser.

I'm confident that you've read here alot of recommendations for 750 DP's on 350's and 850's on 383-400 sbc's. Those recommendations are all about getting the most out of the top end. You could put a 600 onto a 454 and it would work just fine with no loss of throttle response at idle or off idle. The issue is that a carb that small on a BB will just be out of capacity before 4500-5000 rpms.

So, if you have a 600 Edelbrock, that it sounds like you like for the tuning capabilities of it, then use it and get the car tuned and running properly. If you think that it's giving up a little too soon on the top (around 6000), then upgrade to a larger carb later. If your car is going to be at the track or dyno rarely, then if I were you I'd put on the 600 and forget about it. And remember that your motor has some more in it on the top side with a bigger carb.

BTW, what is your car and rear?
 

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Awesome, but as i replied to the guy above you........ a 750 stock would blow my rear end off my ext. cab lifted chevy on 33" tires. (I THINK THATS WHY THE GUY SOLD IT TO ME WITH A HOLLEY D.P. 650 ON IT AND..................... I FOUND A RECEIPT FOR A REBUILT CARRIER/RING ON THE REAR LOL LOL!!!!!!!!
Sounds like you think a bigger carb pushes more air through the engine, giving it more power???
 

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I can tell from the carb change between the Holley 650 dp to my now mod'd Eddy 600 carb. But, the 600 even though i went up with everything and have the stiffest spring doesnt even come close to the performance at all rpm's i got from the Holley DP.
That should tell you to put the 650 Holley DP back on. I'm sorry but it does not seem like you know what you are doing, even though you apparently think so. Up with what? Stiffest spring for what? More does not mean better. You need to listen and learn from these guys. Even better yet read and understand some reference like Vizard's book on Holley Tuning. It explains how a carburetor works and engine requirements. Need to know how they work before trying to modify.
 

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Discussion Starter #17
X2 with Vinnie.

The difference between the 650 and 750 is all top end if both are tuned properly unless you have 4000+ stall and are launching from there. The reason for a bigger carb is to allow for enough air at higher rpm's. At idle and off idle cruising is not affected by a larger cfm carb - pertaining to your comment about a larger carb wrecking your rear. There are several things that will break a small rear like sticky tires, 'highish' stall launches with a properly tuned suspension without any wheel spin. A small rear, like a 7.5" that is setup correctly, will last a long time in a moderate weight car that is a street cruiser.

I'm confident that you've read here alot of recommendations for 750 DP's on 350's and 850's on 383-400 sbc's. Those recommendations are all about getting the most out of the top end. You could put a 600 onto a 454 and it would work just fine with no loss of throttle response at idle or off idle. The issue is that a carb that small on a BB will just be out of capacity before 4500-5000 rpms.

So, if you have a 600 Edelbrock, that it sounds like you like for the tuning capabilities of it, then use it and get the car tuned and running properly. If you think that it's giving up a little too soon on the top (around 6000), then upgrade to a larger carb later. If your car is going to be at the track or dyno rarely, then if I were you I'd put on the 600 and forget about it. And remember that your motor has some more in it on the top side with a bigger carb.

BTW, what is your car and rear?


You are kick *** for the info and time you spent typing to me!

The TRUCK is lifted 1991 Chevy 4" on 33" tires and its an extended cab with stock 3.73 gears so i can still drive it on the highway petal to floorboard.

It wont see the track anytime soon if ever, its more for towing and street and offroad. 10.1 comp mild cam good vacuum numbers at all rpm zz4 motor with headers, 3" exhaust, flowmaster muffler.

So you see the issue here, someone put a car motor in a heavy truck (ext. cab) with lift, heavy tires etc.

But...........its actually pretty cool, just trying to get a 750 eddy to flow like a my old Holley 650 DP or my current 600 eddy to flow like the Holley.

It loses that secondary kick at high throttle, rpm, and doesnt wanna give me more acceleration on flat road like the HOLLEY DP. That thing would let me go as fast as i wanted and watch the speedo go! This 600 just taps out at 4k motor is built to withstand 5500.
 

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It loses that secondary kick at high throttle, rpm, and doesnt wanna give me more acceleration on flat road like the HOLLEY DP. That thing would let me go as fast as i wanted and watch the speedo go! This 600 just taps out at 4k motor is built to withstand 5500.
The 650 is a spreadbore with tiny primary throttle bores and enormous secondaries bores... that's why you get such a kick from the secondaries opening on the 650...

The 600 has about same size primaries and secondaries, that's why the 600 doesn't give the same kick when the secondaries open... plus the whole carb. is smaller and flows less maximum air...

Does your ZZ4 have the stock cam?
.
 

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In actual testing of a 700 CFM carb! The less restricted and cooler the air the more a carb can flow in CFM , Most air cleaners restrict air flow significantly. Testing has shown that the average stock air cleaner assembly with a new filter drops the typical 700 CFM carburetor to 480 CFM, Adding a second air inlet snorkel (like early Muscle cars) got it up to 550 CFM. A 14 inch in diameter 2 inch tall open element air cleaner gave 675 CFM, Two of these 2 inch air filters stacked gave the full 700 CFM. Just removing the choke and Milling off the choke housing can add significant CFM. A sealed scoop (sealed to the carbs inlet) out of the hood in the cars air stream can add significant CFM by a ram effect! But all of these mods need to have jet changes !! Also most stock carbs are designed for stock air cleaners and the 600 is designed so as to flow enough CFM that the engine needs with restricted induction and exhaust systems so a larger carb is installed bigger then the stock engines actually need! ! A 600 CFM carb may be installed on an engine that only needs 400 CFM to reach peek performance at max RPM (Because the 600 CFM carb is needed to just reach 400 CFM with the restricted induction and exhaust) !!

Thats why there are different formulas for figuring carb CFM, the more you do to increase engine flow the higher the engines efficiency the more the carb can flow! A 600 CFM carb can flow actually much higher CFM then it is advertised as its maximum !! The reason for this is Carbs are tested at average air temps and an RPM that is picked randomly by manufacturers!

Jester (Chris)
 

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You are kick *** for the info and time you spent typing to me!

The TRUCK is lifted 1991 Chevy 4" on 33" tires and its an extended cab with stock 3.73 gears so i can still drive it on the highway petal to floorboard.

It wont see the track anytime soon if ever, its more for towing and street and offroad. 10.1 comp mild cam good vacuum numbers at all rpm zz4 motor with headers, 3" exhaust, flowmaster muffler.

So you see the issue here, someone put a car motor in a heavy truck (ext. cab) with lift, heavy tires etc.

But...........its actually pretty cool, just trying to get a 750 eddy to flow like a my old Holley 650 DP or my current 600 eddy to flow like the Holley.

It loses that secondary kick at high throttle, rpm, and doesnt wanna give me more acceleration on flat road like the HOLLEY DP. That thing would let me go as fast as i wanted and watch the speedo go! This 600 just taps out at 4k motor is built to withstand 5500.
I just re-read this and I didn't see you mention how much displacement. Assuming a 350, there is no way that it should be giving up at 4000 rpms. I agree completely with Jester, but for it to give up at 4000 due to the air cleaner, then that is one restrictive air filter. I think your 600 has issues. Also, 3.73's with 33" tires is not optimal IMO even with a non overdrive. 33" tires need 4.10's without an overdrive and 4.56's with overdrive AT A MINIMUM.
 
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