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I'm currently trying to determine if I should change out my current Holley Ultra HP 750 Carb on my 1968 Chevelle SS for something bigger on my 496 engine. Would welcome any thoughts/suggestions from the group. The car will be used mostly as a weekend fun car and occasional driver to and from work if I need to change things up just for a little fun. Will be driven out in Los Angeles, so you know it will be in traffic more than I would like.

Here's the engine specs:
496 ci big block Chevy
Bore 4.310 inches
4.25” stroke crank
Compression Ratio of 10.50:1
617.5 HP @ 5383 RPM
653 Torque @ 4500 RPM
Forged Mahle 18cc Dome Pistons
Chamber Volume: 116 cc
Cranking Compression: 165 PSI
7562 edelbrock intake
Head Intake Volume: 305 cc
Head Exhaust Volume: 158 cc
Hedders Exhaust primary diameter 1.875" Primary Length: 28"
Hyd Roller Cam and stainless valves
Intake Valve Diameter: 2.25"
Intake Open Pressure: 400 PSI
Intake Lift: 0.521" @288 degrees
Exhaust Lift: 0.540" @294 degrees

For what it's worth, if I go bigger, currently trying to decide between the Holley Ultra XP and HP 850/950. Thanks!
 

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a 750 will be on the small side for higher rpm's
but would be very driveable
you are not considering an EFI set-up like sniper or fitech??
 

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Discussion Starter #3
a 750 will be on the small side for higher rpm's
but would be very driveable
you are not considering an EFI set-up like sniper or fitech??
No, not currently contemplating putting in EFI at this time as it is a little more than I want to spend. Right now looking at if it's worth it to go bigger on the carb.
 

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I got a custom carb from Prosystems for my application , very happy , carb came tuned perfect , just fill out the spec sheet and you ll be in the ball park ... plus cheaper than a holley ultra xp

https://prosystemsracing.com/custom/
 

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I'm currently trying to determine if I should change out my current Holley Ultra HP 750 Carb on my 1968 Chevelle SS for something bigger on my 496 engine. Would welcome any thoughts/suggestions from the group. The car will be used mostly as a weekend fun car and occasional driver to and from work if I need to change things up just for a little fun. Will be driven out in Los Angeles, so you know it will be in traffic more than I would like.

Here's the engine specs:
496 ci big block Chevy
Bore 4.310 inches
4.25” stroke crank
Compression Ratio of 10.50:1
617.5 HP @ 5383 RPM
653 Torque @ 4500 RPM
Forged Mahle 18cc Dome Pistons
Chamber Volume: 116 cc
Cranking Compression: 165 PSI
7562 edelbrock intake
Head Intake Volume: 305 cc
Head Exhaust Volume: 158 cc
Hedders Exhaust primary diameter 1.875" Primary Length: 28"
Hyd Roller Cam and stainless valves
Intake Valve Diameter: 2.25"
Intake Open Pressure: 400 PSI
Intake Lift: 0.521" @288 degrees
Exhaust Lift: 0.540" @294 degrees

For what it's worth, if I go bigger, currently trying to decide between the Holley Ultra XP and HP 850/950. Thanks!
Cam nr’s?

What carb was it dynoed with?
 
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I got a custom carb from Prosystems for my application , very happy , carb came tuned perfect , just fill out the spec sheet and you ll be in the ball park ... plus cheaper than a holley ultra xp

https://prosystemsracing.com/custom/
I went with a pro system on my 489 BB.
10 years ago still working as new. 1000hp version only had to adjust the idle out of the box.
Another option Mark Whitener aka jmarkaudio https://www.chevelles.com/forums/members/48836-jmarkaudio.html
 
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I also called Prosystems. I gave him all the info he wanted. All I had to do was pay for it & set the idle. Best carb I ever had. :thumbsup:
 

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I have a 496 in my Chevelle with a Holley "model 4150" 780 cfm on it. It runs good when the engine is up to it's running temperature but not when cold because it has no choke. I'm planning to get rid of the carb to go efi this year. :yes:

Claude. ;)
 

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Prosystems 1000hp here,no issues and was dyno with my 496.still goin strong
 

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Call or email the guys at AED.
 

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I went with a 950 custom carb by Mark Whitner, “Jmarkaudio” has the QF body his own billet metering blocks etc. it literally went from the box to my engine and has performed flawlessly. Throttle response is insane, my 496 revs like a small block.

If you go Holley ultra HP, I believe Mark Whitner, has mentioned the 850 ultra HP outflowed the 950 ultra and had a much higher signal due to smaller Venturi size? Do a little searching on here and you’ll find the posts by Mark and others.
 

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I'm currently trying to determine if I should change out my current Holley Ultra HP 750 Carb on my 1968 Chevelle SS for something bigger on my 496 engine. Would welcome any thoughts/suggestions from the group. The car will be used mostly as a weekend fun car and occasional driver to and from work if I need to change things up just for a little fun. Will be driven out in Los Angeles, so you know it will be in traffic more than I would like.

Here's the engine specs:
496 ci big block Chevy
Bore 4.310 inches
4.25” stroke crank
Compression Ratio of 10.50:1
617.5 HP @ 5383 RPM
653 Torque @ 4500 RPM
Forged Mahle 18cc Dome Pistons
Chamber Volume: 116 cc
Cranking Compression: 165 PSI
7562 edelbrock intake
Head Intake Volume: 305 cc
Head Exhaust Volume: 158 cc
Hedders Exhaust primary diameter 1.875" Primary Length: 28"
Hyd Roller Cam and stainless valves
Intake Valve Diameter: 2.25"
Intake Open Pressure: 400 PSI
Intake Lift: 0.521" @288 degrees
Exhaust Lift: 0.540" @294 degrees

For what it's worth, if I go bigger, currently trying to decide between the Holley Ultra XP and HP 850/950. Thanks!

You already have an excellent carb, and if your driving consists of <95% WOT settings I think you'll be quite OK with what you have.
 
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If it’s a street car I’d spend some time optimizing it along with your ignition. Your current carb may not be optimal for track use, but that doesn’t seem to be its intended purpose. As mentioned above, 95% of daily usage is at part throttle, you may never feel a difference with a different carb if you dial in your current combination.

Steve R
 

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You already have an excellent carb, and if your driving consists of <95% WOT settings I think you'll be quite OK with what you have.

That is my thinking. A bigger carb will use more gas more then likely and be less responsive for the driving that you do.
 
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If it’s a street car I’d spend some time optimizing it along with your ignition. Your current carb may not be optimal for track use, but that doesn’t seem to be its intended purpose. As mentioned above, 95% of daily usage is at part throttle, you may never feel a difference with a different carb if you dial in your current combination.

Steve R

Exactly!
 
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I think the proper sized carb will work great at both ends. I went from 750hp Holley to the 850HO from AED and picked up performance all around. I’m running it straight out of the box. Tried jetting up and down and ended up leaving it alone. Very responsive.
 
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I got a custom carb from Prosystems for my application , very happy , carb came tuned perfect , just fill out the spec sheet and you ll be in the ball park ... plus cheaper than a holley ultra xp

https://prosystemsracing.com/custom/
I will have to second using Pro systems. I have a 496 with very close to the same specs as yours. I fought with a 950 HP for a year and finally gave up and call pro systems. Patrick will build you that you will like and you get the best support in the industry.
 
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